Original article
The effect of long-term frozen storage on the quality of frozen and
thawed mashed potatoes with added cryoprotectant mixtures
Cristina Fernández & Wenceslao Canet, M. Dolores Alvarez*
Department of Plant Foods Science and Technology, Instituto del Frío-CSIC, José Antonio de Novais nº 10, E28040 Madrid, Spain
Running title
Frozen storage effect on quality of mashed potatoes C. Fernández et al.
*Correspondent: Fax: +34 91 549 36 27;
e-mail: mayoyes@if.csic.es
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Summary Cryoprotectant mixtures were added to frozen/thawed (F/T) mashed potatoes in
the form of amidated low-methoxyl (ALM) pectin and xanthan gum (XG), kappa-carrageenan
(κ-C) and XG, and sodium caseinate (SC) and XG, and the effect of frozen storage was
examined. F/T mashed potatoes without added biopolymers had higher storage modulus G'
after freezing and frozen storage, associated with sponge formation due to amylose
retrogradation. Oscillatory measurements indicated weakening of the structure of mashed
potatoes without biopolymers and with added κ-C/XG and SC/XG mixtures at the end of
storage due to ice recrystallization, whereas the structure of samples with added ALM/XG
mixtures was reinforced by increasing time in storage. Mashed potatoes with added mixtures
exhibited water-holding capacity for one year. Samples with added κ-C/XG mixtures were
more structured, although when both κ-C/XG and SC/XG mixtures were included in mashed
potato, very acceptable sensory quality was maintained in usual frozen storage conditions.
Keywords Potato puree, freeze-thaw stability, frozen food storage, overall acceptability,
cryoprotectant mixtures, quality, water-holding capacity.
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Introduction
Starch is one of the most important functional food biopolymers and is added as a functional
ingredient to many products such as sauces, puddings, confectionery and a variety of low-fat
products; also mashed potatoes as prepared in this study contain native potato starch. In food
processing, gelatinization and pasting of starch granules occur during heating process along
with shear leading to changes in starch granules and viscosity. On cooling, retrogradation is
induced by reassociation of starch molecules, causing gel formation or increased viscosity
(Hermansson & Svegmark, 1996).
Previous studies showed that mashed potato made from Kennebec potatoes should be
quick-frozen and microwave-thawed to obtain a product quite similar to freshly made mashed
potato (Alvarez et al., 2005). In corn starch pastes, higher freezing rates also preserved
textural characteristics and produced less exudate (Ferrero et al., 1993, 1994). The rapid
transition from the melt to the glassy state prevents nucleation and propagation of amylose
and amylopectin crystals. Amylose retrogradation is commonly associated with rheological
changes in the system; amylopectin retrogradation can usually be measured by differential
scanning calorimetry (Ferrero & Zaritzky, 2000). However, increasing time in frozen storage
produces a firmer texture in mashed potato (Alvarez et al., 2005). During distribution and
storage, starch pastes may undergo transformation of starch biopolymer molecules: namely,
chain aggregation and recrystallization. Moreover, it is difficult to keep frozen food products
constantly in an optimum frozen state when they undergo repeated freeze–thaw cycles during
the supply chain, which leads to changes in syneresis and related rheological properties (Lee
et al., 2002).
Incorporation of an appropriate amount of hydrocolloids may improve or maintain
desirable textural properties and stability of most starch-based products during prolonged
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storage (Downey 2002, 2003). Five different hydrocolloids and two dairy proteins were added
at five concentrations to fresh and frozen/thawed mashed potatoes to investigate ways of
improving the effects of freezing and thawing (Alvarez et al., 2008a, 2008b; Fernández et al.,
2008). Dairy proteins affected the taste and odour and were judged unacceptable in the
sensory analysis, while samples containing 0.5 and 1.5 g kg–1 added xanthan gum (XG) were
preferred organoleptically due to the creamy mouthfeel they produced. In addition, the
product yielded by adding XG was softer than the control without added cryoprotectants in
F/T samples, and it was therefore suggested that XG might be suitable for use as an additive
to mitigate the thickening effect caused by long-term frozen storage (Alvarez et al., 2008b).
Knowledge of the mechanics of protein-polysaccharide systems is also important in order
to develop desirable properties in food products (Hemar et al., 2001). The purposes of the
present study were therefore (a) to investigate the effect of adding mixtures of: (1) Amidated
low-methoxyl (ALM) pectin and xanthan gum (XG); (2) Kappa-carrageenan (κ-C) and XG;
and (3) Sodium caseinate (SC) and XG on the quality of F/T mashed potatoes in order to
determine how the presence of gelling (pectin and carrageenan) and non-gelling (xanthan)
hydrocolloids and proteins (sodium caseinate) and a non-gelling hydrocolloid (xanthan)
modifies instrumental parameters and sensory attributes of processed mashed potatoes; and
(b) to determine the freeze-thaw stability of these systems in order to be able to control and
maintain the quality of mashed potatoes during long-term frozen storage.
Material and methods
Test material
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Data presented in this report were obtained using potato tubers (Solanum tuberosum, L., cv.
Kennebec) (cv Kennebec) from Aguilar de Campoo (Burgos, Spain). The material was stored
in a chamber at 4±1°C and 85% relative humidity during two days to the maximum before
processing (Nourian et al., 2003).
Cryoprotectant mixtures
Amidated low-methoxyl (ALM) pectin (GENU pectin type LM-104 A; pectin was methylated
to a degree of 27%, and in addition a further 20% of the residues was amidated (DA = 20%)),
kappa-carrageenan (κ-C) (GENULACTA carrageenan type LP-60), and xanthan gum (XG)
(Keltrol F [E]) were donated by Premium Ingredients, S.L. (Girona, Spain). Sodium caseinate
(SC) EM-6 was supplied by Manuel Riesgo, S.A. (Madrid, Spain). Following range finding
experiments (Alvarez et al., 2008a, 2008b; Fernández et al., 2008), the level of each
biopolymer to be used in mixtures was fixed at 1.5 g kg-1. Notations used to refer to each of
the samples were: C, F/T mashed potatoes without added biopolymers; ALM1.5/XG1.5, κC1.5/XG1.5, and SC1.5/XG1.5, F/T mashed potatoes with 1.5 g kg-1 added ALM pectin, κ-C
or SC, respectively and 1.5 g kg-1 added XG.
Preparation of mashed potatoes
Tubers were manually washed, peeled and diced. Mashed potatoes were prepared in 650-g
batches from 607.7 g kg-1 of potatoes (total starch content, 736 ± 26 g kg-1 dry basis, amylose
content, 256 ± 21 g kg-1 of starch), 230.8 g kg-1 of semi-skimmed in-bottle sterilized milk (fat
content, 15.5 g kg-1), 153.8 g kg-1 of water, and 7.7 g kg-1 of salt (NaCl) using a TM 21
thermal mixer (Vorwerk España, M.S.L., S.C., Madrid, Spain). Mixtures of cryoprotectants
5
were added at this point; the appropriate amount (1.5 g kg-1) of ALM pectin and XG, κ-C and
XG and SC and XG was added to the rest of ingredients in form of a dry powder. The
ingredients were cooked for 25 min at 100 °C (blade speed: 100 rpm), as described elsewhere
(Alvarez et al., 2005; Fernández et al., 2006). The mash was immediately ground for 40 s
(blade speed: 2000 rpm). The product was immediately homogenized through a stainless steel
sieve (diameter 1.5 mm). Following preparation, mashed potato sample was immediately
packed in 300×200 mm2 rectangular polyethylene plastic, sealed under light vacuum (−0.05
MPa) on a Multivac packing machine (Sepp Haggenmüller KG, Wolfertschwenden,
Germany), and frozen and thawed according to procedures indicated below.
Freezing and thawing procedures
Mashed potato was frozen by forced convection with liquid nitrogen vapour in an Instron
programmable chamber (model 3119-05, −70 °C/+250 °C) at −60 °C until their thermal
centres reached −24 °C. Air and product temperatures were monitored by T-type
thermocouples (NiCr/NiAl; −200 to +1000 °C) using the MMS3000™ Multi Measurement
System™ (Mod. T4, Commtest Instruments, Christchurch, New Zealand). After freezing,
samples were placed in a domestic freezer for storage at −24 °C. For microwave thawing
process, frozen mashed samples were unpacked and then thawed in a Samsung M1712N
microwave oven (Samsung Electronics S.A., Madrid, Spain). Samples were irradiated for 20
min with an output power rating of 600 W, as described previously (Fernández et al., 2006;
Alvarez et al., 2008a, 2008b).
Long-term frozen storage
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Mashed potato was prepared and frozen, stored at −24 °C for 0 (1 day), 3, 6, 9 and 12 months
and thawed by microwave as described above. Each testing date was replicated twice for each
type of mashed potato.
Heating of samples
After thawing, all samples were brought up to 55 °C by placing them in a Hetofrig CB60VS
(Heto Lab Equipment A/S, Birkerød, Denmark) water-bath, where water and product
temperatures were monitored by T-type thermocouples as described elsewhere (Fernández et
al., 2006, 2008; Alvarez et al., 2008a, 2008b). The selected sample testing temperature was
55 °C, as results from different analyses showed that this is the preferred temperature for
consumption of mashed potato (Canet et al., 2005).
Oscillatory and steady rheological measurements
A Bohlin CVR 50 controlled stress rheometer (Bohlin Instruments Ltd, Gloucestershire, UK)
was used to conduct small amplitude oscillatory shear experiments and steady shear using a
plate-plate sensor system with a 2 mm gap (PP40, 40 mm) and a solvent trap to minimize
moisture loss during tests. Samples were allowed to relax for 5 min before rheological
measurements were made (Fernández et al., 2006). Temperature control at 55 °C was
achieved with a Peltier Plate system (-40 to +180 °C; Bohlin Instruments Ltd,
Gloucestershire, UK). Linear viscoelastic domain for each sample was determined from stress
sweeps at 1 rad s-1. Next, three frequency sweeps were carried out over the range 0.1-100 rad
s-1 at very small strains, mostly below 10-3. The dynamic rheological parameters used to
evaluate viscoelastic properties of mashed potatoes were the phase angle ( ), the storage
7
modulus (G’) and the loss modulus (G”) at 1 rad s-1. A power-law type relationship was
verified for dynamic rheological data; linear regressions of ln (G’) and ln (G”) versus ln () were
carried out and the magnitudes of slope and intercepts were computed as described in previous
works (Alvarez et al., 2007).
In order to describe the variation in rheological properties of mashed potato under steady
shear, data obtained from increasing shear rate measurements were fitted to the well-known
power law model (Rao, 1999). All the rheological measurements in each experimental
combination were carried out in duplicate.
Instrumental objective texture measurements
Texture profile analysis (TPA) tests were carried out with a TA.HDi Texture Analyser (Stable
Micro Systems Ltd, Godalming, UK) using a 250 N load cell. During tests, mashed potato
samples were maintained at 55 °C by means of a Temperature Controlled Peltier Cabinet
(XT/PC) coupled to a separate heat exchanger and proportional-integral-derivative (PID)
control unit. For TPA tests, a flat 35-mm diameter aluminium plunger (SMS P/35) was used
to move within a 60-mm diameter stainless steel cylinder containing 50  1 g of sample. The
experimental conditions were: deformation rate (180 mm min-1), compression level (33.3%),
with a rest period of 5 s between cycles (Alvarez et al., 2005). There were four replicates for
each experimental unit. Program software (Texture Expert for Windows, version 1.0; Stable
Micro Systems, Surrey, England, UK) automatically calculates the textural parameters from
the curve generated by such a test, as follows: consistency, CON (N), adhesiveness, ADH (N
s), springiness, SPR (dimensionless), cohesiveness, COH (dimensionless) and gumminess,
GUM (N).
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Other quality parameters
Colour measurements
The colour of the mashed potatoes in the pots was measured using a HunterLab model D25
(Reston, VA, USA) colour difference meter fitted with a 5 cm diameter aperture, and results
were expressed in accordance with the CIELAB system with reference to illuminant D65 and
a visual angle of 10°. Parameters determined were L*, a* and b*, recommended by the
International Commission on Illumination (CIE 1978), although colour was also expressed as
L*/b*, i.e., the white/yellow ratio (O'Leary et al., 2000). The total colour difference (∆E*)
between F/T control (C) and F/T mashed potatoes with added cryoprotectant mixtures was
calculated as described elsewhere (Baixauli et al., 2002).
Drip Loss
Drip loss (DL) was measured by centrifugal force. The centrifuge tubes containing the sample
(approximately 10 g of mashed potato) were centrifuged at 6000 rpm (15000×g) for 30 min in
a Sorvall®, RC-5B apparatus (Global Medical Instrumentation, Inc, Minnesota, USA). DL
was expressed as the percentage of liquid separated per total weight of sample in the
centrifuge tube (Eliasson & Kim, 1992).
Total Soluble Solids Content
Total soluble solids (TSS) content g/100 g (w/w) as measured by the refractive index was
determined with an Atago (Itabashi-ku, Tokyo, Japan) dbx-30 refractometer.
Determination of pH
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The pH of the F/T mashed potatoes was measured with a Schott CG pH meter (Model 842;
Schott-Geräte GmbH, Mainz, Germany). Measurements of all the quality parameters were
performed in quadruplicate and the results averaged.
Sensory analysis
Sensory TPA was done by a four-member panel trained specifically in sensory analysis of
mashed potato (Alvarez et al., 2005). Each sample was tested twice and average scores
calculated, so that each sample was tested eight times in all. The Texture Profile system (UNE
87025, 1996) was modified to evaluate frozen mashed vegetables (Canet et al., 2005). Scores
for sensory attributes were based on a 10-point descriptive intensity scale converted to a 1–10
numerical scale for statistical analysis, with 1 = not detectable and 10 = extremely intense.
Profile attributes are classified in four groups as described in a previous work (Fernández et
al., 2006). Description of the sensory attributes evaluated by the trained panel during the
texture profile analysis can be found elsewhere (Alvarez et al., 2008a). Mashed potato
samples were also subjected to an overall acceptability (OA) test based on all sensory
attributes (texture, colour, taste), on a 10-point hedonic scale (10 = like extremely, 1 = dislike
extremely).
Statistical analysis
For analysis of the effect of cryoprotectant mixtures and long-term frozen storage on the
quality parameters studied, results were subjected to multifactor analysis of variance (two
way-ANOVA) using STATGRAPHICS (version 5.0, STSC Inc., Rockville, MD, USA) for
one control and three cryoprotectant mixtures (C, ALM1.5/XG1.5, κ-C 1.5/XG1.5,
10
SC1.5/XG1.5) and five test dates (0, 3, 6, 9, 12 months). Cryoprotectant mixtures and times
were compared using the least significant difference test (LSD, 99% for instrumental
parameters and 95% sensory attributes). Where interaction was significant, long-term results
were analysed for each mixture type using one-way analysis of variance on five test dates, and
times were compared using LSD test as indicated above.
Results and discussion
Oscillatory and steady rheological measurements
Addition of cryoprotectant mixtures to mashed potatoes significantly affected all the
rheological parameters (P < 0.01, Table 1). In general terms, addition of binary biopolymer
mixtures increased phase angle (δ), magnitudes of the slopes n’ and n”, and steady-shear
rheological properties (n and K) with respect to the control (C). Nevertheless, G’ values were
significantly lower in all the samples with added mixtures than in C mashed potatoes. Higher
magnitudes of storage modulus (G’) in starch pastes submitted to freezing and abusive frozen
storage conditions were associated with the formation of an elastic, opaque structure due to
amylose retrogradation (Ferrero & Zaritzky, 2000). Mashed potatoes with added κC1.5/XG1.5 mixture presented greater viscosity (G”) than C control, indicating a more
viscous nature. XG, which was present in all the added mixtures, does not form gels and
therefore its presence has a greater impact on the viscous response than on the elastic response
(Rodríguez-Hernández & Tecante 1999). The fact that the lowest δ values were found in F/T
samples without added biopolymers could be ascribed to the presence of XG in all the other
systems, where it would affect G” more because of its thickening properties. In all the
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systems, the slopes of viscous modulus G” exhibited more solid characteristics (lower values
of the slopes) than those of the elastic component G’.
In food systems like mashed potatoes containing disintegrated starch granules, rheological
properties are governed by the continuous phase, especially by the formation of networks of
solubilized and highly entangled macromolecules released from the granules (Hermansson &
Svegmark, 1996). Oscillatory measurements showed that the addition of cryoprotectant
mixtures to mashed potatoes weakened the gel structure of the products as compared to F/T
control. Probably, freezing of C mashed potatoes produced high local starch concentrations
and allowed chain crystallization of both amylose and amylopectin to occur (Ferrero et al.,
1993). Certainly, a spongy structure was observed in thawed samples which had been frozen
and stored without cryoprotectants. In starch pastes submitted to slow freezing and frozen
storage, hydrocolloids prevent the formation of a sponge-like structure and the production of
exudates due to amylose retrogradation (Ferrero & Zaritzky, 2000; Lee et al., 2002; Mali et
al., 2003). Specifically, it has been stated that in starch pastes with added XG, amylose-XG
interaction competes with amylose-amylopectin aggregation, reducing the probability of
amylose retrogradation or retarding it. It is possible that the amylose chains leached during
cooking and cooling were readily exposed to the XG present in the added biopolymers
mixtures, and the amylose would compete in the chain association between XG molecules and
other amylose chains. Slade and Levine (1987) suggested that the stabilizing properties of XG
might be products of its ability to undergo molecular entanglement within the frozen
concentrated matrix.
Moreover, significant differences were found between mashed potatoes with added binary
mixtures, regardless of all containing XG (Table 1). Samples with added κ-C1.5/XG1.5
mixture exhibited stronger elastic and viscous characteristics than mashed potatoes with
added ALM1.5/XG1.5 and SC1.5/XG1.5 mixtures (in that order). Therefore, samples with
12
added κ-C and XG were more structured, confirming previous findings for mashed potatoes
with added κ-C and other biopolymers alone (Fernández et al., 2008). Mashed potatoes as
prepared here are themselves combined systems of native potato starch/denatured milk
protein/water/salt plus the added biopolymer mixture. Also, mashed potatoes contain either
sugars, supplied mainly by the potato and the milk, or Ca ions, supplied principally by the
added milk, and complex interactions influence properties of these products.
In a few cases, synergistic gelation occurs when two hydrocolloids are combined. κ- and icarrageenans are considered the most suitable hydrocolloids for commercial dairy products
because of their ability to combine into double helices and to interact with casein to form
network structures (Tárrega et al., 2006). A carrageenan–casein network cannot be expected
to form in mashed potatoes containing denatured milk protein. Therefore, the fact that the
increase in the structure’s rigidity produced by addition of κ-C1.5/XG1.5 mixture was higher
could be ascribed to their ability to combine into double helices, and to interactions between
the anionic sulphated polysaccharide and denatured milk proteins present in mashed potatoes.
A stronger synergistic effect was observed in κ-C/denatured soy protein systems associated
with greater incompatibility because of thermal denaturation of the protein (Baeza et al.,
2002). Then again, it has been found that addition of starches accelerates gelation of κ-C,
possibly due to coupling effects between κ-C and soluble starch molecules (Faria-Tischer et
al., 2006). The positive effect on rheological properties associated with κ-C1.5/XG1.5
mixtures could also be caused by the presence of potato starch, resulting in a decisive
synergistic effect and helping to enhance intermolecular binding. Nevertheless, it has been
reported that the addition of salt exerts a considerable influence on the gelation of
carrageenans (DeFreitas et al., 1997). In the case of κ-C, alkaline ions bind to the helix of the
hydrocolloid, thus partially neutralizing the sulphate groups. This causes aggregation of the
double helixes, increasing gel rigidity.
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In turn, low-methoxyl pectins usually form gels in the presence of Ca2+ ions over a wider
range of pH values, with or without sugar (Axelos & Thibault, 1991), although XG reduces
the reaction of low ester pectin to calcium. This fact could at least partially account for the
intermediate oscillatory parameter values obtained for mashed potatoes with added
ALM1.5/XG1.5 mixtures. In this study, the strengthening of the mashed potato gel network
associated with addition of ALM pectin and XG mixtures was less than expected. Another
reason for this could be competition between potato starch, ALM pectin and XG for the added
salt, the available water and the calcium. It is likely that a large proportion of ions could be
trapped by potato starch and XG, leaving insufficient numbers to promote junction zones in
ALM pectin. The high degree of substitution in ALM pectin may also cause steric hindrance
of the pectin strands, rendering the gel structure more flexible and thus limiting the possibility
of long Ca2+-mediated assemblies (Löfgren et al., 2006). Results suggest that there is a
repulsive effect or incompatibility between ALM pectin and XG when added to mashed
potatoes at low concentrations.
Phase separation in biopolymer mixtures, such as protein-polysaccharide mixtures, is
commonly observed and could be due to different mechanisms such as association between
biopolymers, for example when they carry opposite charges, or to thermodynamic
incompatibility (Syrbe et al., 1998). Adding 10 g kg–1 SC to F/T mashed potatoes significantly
debilitates the consistency of the product, which has been ascribed to phase separation
(Alvarez et al., 2008a). Although SC solutions and XG solutions have been extensively
studied, the behaviour of SC/XG mixtures is largely unknown. Nash et al. (2002) found that
there is no interaction between XG and SC at low concentrations, implying that there is no
phase separation between these two biopolymers at XG concentrations below 0.5 wt.%. In
SC/XG mixtures, no phase separation was observed for samples with 0.1 wt.% xanthan,
although at higher XG concentrations (0.5 and 1 wt.%), micrographs showed that mixtures
14
were not homogeneous (Hemar et al., 2001). As casein and xanthan molecules have an
overall negative charge at neutral pH, net repulsive interactions between them may produce
thermodynamic incompatibility. In this study, mashed potatoes with 0.15% (based on total
mashed potatoes weight) added SC and 0.15% added XG presented no visible phase
separation. The fact that the viscoelastic properties determined in these systems were the
lowest of all could be due either to thermodynamic incompatibility between the three
negatively charged biopolymers or simply to insufficient presence of SC to promote
gelification of potato starch.
The lowest flow behaviour index (n) value, which indicates the extent of shear-thinning
behaviour as it deviates from 1, was found in C samples as mentioned above (Table 1). Their
more intense shear-thinning behaviour could be due to high concentrations of a high
molecular weight substance (potato starch) in the liquid phase not competing with other
biopolymers. The n values increased significantly when cryoprotectant mixtures were added
to mashed potatoes, although the highest n values occurred in samples with added
ALM1.5/XG1.5 and SC1.5/XG1.5 mixtures, confirming that the addition of κ-C and XG
mixtures result in a more solid character. In turn, consistency index (K) was higher in mashed
potatoes with added κ-C1.5/XG1.5 mixtures, although addition of ALM1.5/XG1.5 and
SC1.5/XG1.5 mixtures also resulted in higher K values than in C samples (in that order). This
increase of K suggests that F/T potato starch granules become more resistant to mechanical
shearing in the presence of biopolymer mixtures. Rojas et al. (1999) suggested that there was
an interaction between starch and XG that raised shear stability significantly. This result
evidences that the structure responsible for the yield stress is reinforced when cryoprotectant
combinations are added to mashed potatoes. Akhtar et al. (2006) observed that XG gives very
high apparent viscosities at low shear rates, and yield stress behaviour at very low
15
concentrations. K is the shear stress at a shear rate of 1.0 s-1, and therefore the results are
consistent with the findings in the literature.
Furthermore, time in frozen storage significantly affected all rheological measurements (P
< 0.01, Table 1). Table 2 shows the effect of testing data on each group of mashed potatoes
separately. In samples with added ALM1.5/XG1.5 and κ-C1.5/XG1.5 mixtures, there were
non-significant differences in δ values at 0 and 12 months, whereas in C mashed potatoes and
sample with added XG mixed with SC, δ values were significantly higher at 12 months than
at 0 months. G’ and G” values were lower at final storage time than at the beginning in
mashed potatoes with added κ-C1.5/XG1.5 mixtures. Note that in samples with added κC1.5/XG1.5 and SC1.5/XG1.5 mixtures n’ values were higher at 12 months, indicating that
the frequency dependence of G’ was greater at 12 than at 0 months, and in C samples, G” was
also more frequency-dependent at the end of the storage period. A priori, these results indicate
a weakening of the structure of mashed potatoes without biopolymers and with added κC1.5/XG1.5 and SC1.5/XG1.5 mixtures after one year in frozen storage. In addition, in
mashed potatoes with SC1.5/XG1.5 mixtures, G” values were significantly higher at 3, 6, 9
and 12 months than at 0 months, indicating greater viscosity as a consequence of frozen
storage, and moreover these systems had lower n” values. In samples with added
ALM1.5/XG1.5 mixtures, n’ values were lower at 9 and 12 months than at 0, 3, and 6 months,
showing that G’ was less frequency-dependent at the end of the storage period. The latter
suggests that the structure of mashed potatoes with added ALM1.5/XG1.5 mixtures was
reinforced by increasing time in frozen storage.
In C samples, on the other hand, n values were significantly higher at 12 months than at 0
months, whereas in samples with added κ-C1.5/XG1.5 and SC1.5/XG1.5 mixtures, n values
were lowest after 12 months. Finally, in C samples and in samples with added SC1.5/XG1.5
mixtures, K values were significantly higher at the end of storage than at the beginning,
16
whereas in samples with added ALM1.5/XG1.5 and κ-C1.5/XG1.5 mixtures, long-term
frozen storage had the opposite effect on the consistency indexes, evidencing that the
structure responsible for yield stress is more fragile at the end of the storage period. Nongelling hydrocolloids (e.g. XG) inhibit the formation of elongated ice crystals in frozen
desserts, preventing growth in crystal size at low temperatures in abusive storage with
temperature fluctuations (Fernández et al. 2007). In contrast, Ferrero et al. (1994) reported
that addition of XG to corn starch pastes minimized amylose retrogradation but did not limit
ice recrystallization or amylopectin retrogradation.
During long-term frozen storage, ice recrystallization and sublimation takes place (Canet
& Alvarez, 2006). The former is characterized by an increase in the relative frequencies of the
larger ice crystals at the expense of the smaller ones, causing softening and significant loss of
textural quality. Therefore, as has been reported for various different starch pastes, rheological
changes in mashed potatoes during storage must have been due mainly to ice recrystallization,
which caused softening of mashed potatoes without added cryoprotectants and with added κC1.5/XG1.5 and SC1.5/XG1.5 mixtures. In mashed potatoes with added ALM1.5/XG1.5
mixtures, oscillatory measurements detected an increase in rigidity at the end of storage,
which could be related to either amylopectin retrogradation (Ferrero et al., 1993) or ice
sublimation simultaneously with recrystallization, resulting in overall structure reinforcement.
In any event the present results need to be correlated with other physical techniques before
amylopectin retrogradation can be clearly associated with rheological changes.
Objective texture measurements
Cryoprotectant mixtures and time in frozen storage significantly affected the objective texture
properties (P < 0.01, Table 3). Consistency (CON) values were lower in F/T mashed potatoes
17
with added SC1.5/XG1.5 mixtures than in the rest, but adhesiveness (ADH), springiness
(SPR), cohesiveness (COH) and gumminess (GUM) values were all lowest in the C samples,
possibly due to phase separation between starch and solvent (syneresis), producing a slimy
consistency. In this system, moisture was readily separated from the matrix causing texture
damage and drip loss, as shown below. However, addition of XG mixed with ALM pectin, κC or SC was a significant factor in preventing some negative textural effects caused by
freezing and long-term frozen storage. In general terms, ADH values were significantly
higher at 6 and 9 months than at 0, 3 and 12 months, whereas COH and GUM values were
significantly lower at 9 and 12 months than at 3 months. Table 4 shows textural parameters
for each test date and mixture type. In samples without and with added cryoprotectant
mixtures, there were non-significant differences in CON and GUM at 0 and 12 months. In
mashed potatoes with added biopolymers, ADH values were significantly lower at the end
than at the beginning of storage indicating loss of adhesiveness, possibly due to crystal
growth produced by ice recrystallization due to inevitable minor temperature fluctuations
occurring during long-term frozen storage.
In C, ALM1.5/XG1.5 and κ-C1.5/XG1.5 mashed potatoes SPR values were highest after
12 months. However, in C samples the COH value was highest after 12 months, while in
ALM1.5/XG1.5 and SC1.5/XG1.5 samples the COH value was lowest after 12 months in
frozen storage. In C samples, molecular mobility possibly induced coarsening of the structure
with increasing time in frozen storage due to significant ice sublimation. Results indicate that
the presence of XG in the binary mixtures prevented increase of gel firmness in frozen stored
mashed potatoes (Alvarez et al., 2005). Note that in all the mashed potatoes, there were some
significant differences between textural parameters measured at intermediate test dates,
possible related to inevitable physical changes (sublimation and recrystallization) occurring
during long-term frozen storage.
18
Other quality parameters
Cryoprotectant mixture type and time in frozen storage had a significant effect (P < 0.01) on
colour (a*, L*/b*, ∆E*), drip loss (DS), TSS content, and pH of mashed potatoes (Table 5).
Addition of ALM1.5/XG1.5 mixtures increased a* values, as compared to C samples, i.e.
caused loss of greenness. Conversely, a* values decreased significantly when κ-C1.5/XG1.5
mixtures were added, indicating increase of greenness, whereas parameter a* was unaffected
by addition of SC1.5/XG1.5 combination. In F/T samples, a* colour attribute was also
increased by adding 5–8 g kg-1 ALM pectin, 3–8 g kg-1 κ-C, 1.5–8 g kg-1 XG, or 2.5–10 g kg-1
SC separately (Fernández et al., 2008). L*/b* values were significantly lower at 3, 6, 9 and 12
months than at 0 months, indicating darkening with increasing time in frozen storage. Also,
∆E* values were higher in mashed potatoes after 6, 9 and 12 months, confirming that with
increasing time in storage the product became darker than processed product without storage.
This was true of every group of added cryoprotectant mixtures (Table 6). Instant mashed
potato samples that had been frozen had lower white/yellow ratios (O’leary et al., 2000),
although authors reported that changes in colour over a period of 32 weeks in frozen storage
were small in practical terms.
Frozen vegetables undergo colour alterations during storage, brought about by changes in
natural pigments, chlorophylls, anthocyanins and carotenoids or by enzymatic browning (Canet
& Alvarez, 2006). Such enzymatic browning could not be expected to occur in frozen stored
mashed potatoes, partly because the potatoes were cooked for a long time at a high temperature
during the preparation process, which would cause thermal inactivation of enzymatic systems
responsible for off odours and flavours and changes in colour during frozen storage. On the other
hand, cultivated potatoes contain varying amounts of anthocyanins and carotenoids in their
19
tuber skin and flesh, although blanching also protects anthocyanins and carotenoids from
oxidation by lipoxygenase and by peroxides derived from polyunsaturated fatty acids. However,
ice sublimation at the surface can occur during storage in improperly packaged food, leading to
dehydration, so that the water thus extracted accumulates inside the packaging in the form of
frost (Canet & Alvarez, 2006). Despite the use of non-oxygen-permeable packaging, temperature
fluctuations may have caused ice sublimation, causing the colour of the products to darken
during frozen storage. In spite of these significant colour changes, differences should not be of
great importance, considering that were not detected by the panellists.
In mashed potatoes, addition of ALM1.5/XG1.5, κ-C1.5/XG1.5 and SC1.5/XG1.5
mixtures reduced DL from almost 15 to 0.00% (Table 5); this result shows that the gel
structure in C mashed potatoes was seriously affected by freezing and thawing processes.
Increased water-holding capacity is especially desirable in microwaving to hinder rapid water
loss and render the product less tough, and this has been shown to occur with the
incorporation to mashed potatoes of ALM pectin, κ-C, XG and SC alone (Alvarez et al.,
2008b). DL decrease in XG-added mashed potatoes is in valid agreement with many literature
findings. At a concentration of 0.5/100 g in suspension, XG has been shown to be more
effective than guar gum in reducing exudate production during refrigerated storage of yam
starch pastes (Mali et al., 2003). In sweet potato starch gel with added XG, the reduction of
syneresis has been reported to be more pronounced at low concentration (Lee et al., 2002). In
this study, DL values revealed that addition of biopolymer mixtures was effective in
stabilizing mashed potatoes against freezing, frozen storage and thawing processes. The
course of gelation is controlled by water availability, although the latter depends not only on
the ability of particular gums to hold water molecules but also on their conformational
changes and inhibition of gelation resulting from interactions between gums and starch
granules (Baranowska et al., 2008). Table 5 shows the effect of test data on DL for C control
20
only, since in the products with added mixtures DL was 0.00% at all the tested times. In C
products, DL percentages were significantly lower at 9 and 12 months. However, this could
equally have been due to dehydration by sublimation occurring during frozen storage as
mentioned above.
As Table 5 shows, TSS content was slightly lower in the C samples, whereas the highest
TSS contents were recorded in samples with added κ-C1.5/XG1.5 and ALM1.5/XG1.5
mixtures. This is logical, since two polysaccharides were being added to mashed potatoes in
these cases. TSS content tended to increase with time in frozen storage, mainly in C control
and in samples with added SC/XG mixtures (Table 6). Also, it has been found that TSS values
in natural mashed potatoes increased constantly at each test date over a period of one year
(Alvarez et al., 2005). With increasing time in frozen storage, there was more fluid loss and
hence increasing TSS content in the mashed potatoes, due either to greater breakdown in the
cell structure produced by ice recrystallization or to ice sublimation.
Adding cryoprotectant mixtures to mashed potatoes significantly reduced the pH of the
samples as compared to C control (Table 5). Lowest pH values were recorded in the samples
with added κ-C and XG mixtures, although in all cases the pH was very close to the usual pH
(6) of a well-washed native starch sample (Rasper, 1980). The pH values showed no clear
trend of behaviour with increasing time in storage, but varied depending on the type of
mixture added (Table 6). In C control, pH values were significantly lower after 9 and 12
months, whereas in samples with added SC1.5/XG1.5 mixtures, pH values were lower after 3
and 6 months, and in the sample with added κ-C1.5/XG1.5 mixtures pH values were lower
after 3 and 12 months in frozen storage. On the other hand, in samples with added ALM/XG
mixtures, pH values were significantly lower after 6 months than at 0 months and
significantly higher after 9 and 12 months. Precipitation of the acid phosphates of potassium
and sodium and potassium citrate has been posited as the cause of the final increase of pH in
21
different frozen vegetables during storage (Canet & Alvarez, 2006). Severe acidic conditions
have been found to reduce the viscosity of yam and tapioca starch (Mali et al., 2003).
However, differences in pH values of mashed potatoes found here, although significant, are
probably too small to affect gelatinization and viscoelastic behaviour of samples containing
potato starch, which is highly stable to heat treatment at pH close to 6.
Sensory analysis
Cryoprotectant mixture type and time in frozen storage significantly (P < 0.05) affected
profile attributes and overall acceptability (OA) of the products. The effect of time in frozen
storage was only not significant in the cases of moisture perceived at the time of putting the
sample in the mouth and of palate coating. Results of multifactor analysis of variance for
sensory attributes have been omitted for the sake of brevity. However, overall acceptability
(OA) of the products increased significantly as compared to C samples after the three binary
mixtures were added (Table 5). Note as scores for OA were higher in κ-C1.5/XG1.5 and
SC1.5/XG1.5 samples (in that order), as well as at the end of storage period.
Granularity and moisture perceived before putting the sample in the mouth decreased
significantly with respect to C samples with the addition of cryoprotectant mixtures (Table 7);
again this indicated a negative effect of processing in mashed potatoes made without
cryoprotectants. When mashed potatoes are frozen, potato starch-rich regions are created in
the matrix, where water remains partially unfrozen. High solid concentration in these regions
facilitates the association of starch chains to form thick filaments, whereas water molecules
coagulate into ice crystals forming a separate phase (Lee et al., 2002). Upon microwave
thawing, ice transforms to bulk phase water, which can be readily released from the polymeric
network, leaving the starch gel sponge-like, and consequently panellists perceived
22
considerable granularity and observable moisture in this system. There were no differences in
the scores for granularity between κ-C1.5/XG1.5 and SC1.5/XG1.5 samples, for which the
scores were lowest. DL and related physical property changes induced by freezing and frozen
storage were reduced at the end of the storage period, and scores for granularity were
significantly lower at the end than at the beginning of storage in C and ALM1.5/XG1.5
samples. However, in mashed potatoes with κ-C1.5/XG1.5 and SC1.5/XG1.5 mixtures,
panellists found no differences in the granularity of the samples at 0 and 12 months in frozen
storage, revealing superior freeze-thawing stability. In C samples, moisture perceived visually
increased linearly with increasing time in frozen storage, possibly due to additional damage
caused in the structure by ice recrystallization, whereas adding biopolymer mixtures rendered
moisture practically constant for one year, again reflecting better stabilization of frozen
products.
C samples scored significantly lower for stickiness, denseness, homogeneity and firmness,
and higher for moisture perceived at the time of placing the sample in the mouth (Table 7),
whereas of these attributes, stickiness, denseness, and firmness were scored highest in F/T
samples with added κ-C and XG mixtures. Also, objective instrumental ADH, SPR, COH and
GUM values were lowest in the samples without added mixtures. In mashed potatoes with
added cryoprotectants, panellists found no differences in the stickiness of the samples at 0 and
12 months in frozen storage, whereas they perceived greater stickiness in the C samples after
9 months. Samples with added ALM1.5/XG1.5 and SC1.5/XG1.5 mixtures also scored
significantly higher for denseness at the end than at the beginning of storage. Panellists found
that all the samples with added mixtures were equally homogeneous, whereas C samples
scored significantly lower for homogeneity. Although scores for homogeneity were very
similar at each test date, it was also significantly affected by time in frozen storage. However,
this was attributed to the low standard deviations accompanying the mean values of
23
homogeneity, which was a consequence of the good agreement of the panellists to assign
similar scores on a given attribute. Also, moisture perceived at this stage decreased
significantly with respect to C samples with the addition of cryoprotectant mixtures; panellists
found the C and ALM1.5/XG1.5 samples significantly more and less moist at 3, 6, 9 and 12
months in frozen storage than at 0 months. Remarkably, the firmness scores were
significantly higher at 9 and 12 months than at 0 months, and the same trend persisted in all
the mashed potato types. The panellists probably detected minor but increasing dehydration
caused by ice sublimation with increasing time in frozen storage.
Scores for cohesiveness and adhesiveness perceived at the time of preparing the sample
for swallowing were lowest in the C samples, and highest in the κ-C1.5/XG1.5 samples
(Table 7), corroborating results from objective texture measurements. In contrast, the highest
scores for fibrousness were recorded for C product, reflecting the formation of thick filaments
as indicated above, whereas adding cryoprotectant mixtures rendered fibrousness significantly
less appreciable. In C samples, adhesiveness and fibrousness tended to increase and decrease
respectively with increasing time in frozen storage. Also, panellists perceived greater
cohesiveness and adhesiveness in samples with added ALM1.5/XG1.5 mixtures after 12
months in storage. In κ-C1.5/XG1.5 samples, fibrousness was significantly higher at 12
months, although again this was the result of close agreement and reproducibility among
panellists on this attribute. Note however that all the scores at each test date are on the same
point of the scale. In SC1.5/XG1.5 samples, panellists perceived greater cohesiveness with
increasing time in frozen storage but did not perceive significantly greater adhesiveness.
Finally, mashed potatoes with added biopolymers scored higher for ease of swallowing
and palate coating, and once again lower for fibrousness than the control (Table 8). However,
the panellists found that samples without added biopolymers were less fibrous with increasing
time in frozen storage; possibly other parallel negative changes made more gentled the
24
spongy structure. The length of time in frozen storage did not significantly affect the scores
for this group of sensory attributes in the samples with added cryoprotectant mixtures,
confirming once more that addition of biopolymer mixtures confers freeze-thaw stability on
mashed potatoes. According to OA scores, panellists preferred F/T mashed potatoes with
added κ-C1.5/XG1.5 mixtures but found that these samples were equally acceptable at 0, 3, 6,
9 and 12 months of frozen storage. Also, the panellists found that samples with added
SC1.5/XG1.5 mixtures were equally acceptable at 0, 9 and 12 months of frozen storage,
whereas in ALM1.5/XG1.5 samples, the OA was higher after 12 months than at 0, 3, 6, and 9
months.
In a previous work on both fresh and F/T mashed potatoes, panellists scored the samples
with 0.5 and 1.5 g kg−1 added XG alone significantly higher for OA than the fresh control,
highlighting the creaminess of the samples with added gum and the gum’s potential to
improve the sensory quality of mashed potatoes subjected to processing (Alvarez et al.,
2008b). Furthermore, XG addition maintained the smoothness characteristic of unfrozen corn
starch and wheat flour pastes and prevented amylose retrogradation (Ferrero et al., 1993).
Certainly, the positive effect produced on the sensory quality of processed mashed potatoes
by the addition of XG was improved when the gum was mixed mainly with k-C and SC, and
this was detected by the panellists. Results for OA in this study showed that F/T mashed
potatoes with 1.5 g kg−1 added XG mixed either with k-C or SC at the same concentration
were mainly preferred for sensory purposes because of their creamy mouthfeel, although a
comparison of results showed that SC1.5/XG1.5 samples also presented a softer mouthfeel.
However, panellists found that samples with ALM pectin/XG mixtures produced a poor
mouthfeel, possibly reflecting incompatibility between these polysaccharides. Creaminess is
related to a pleasant sensation on eating of food products and is often difficult to characterize,
but it is probably related in some way to their rheological properties. Perception of thickness
25
and creaminess increases with increasing viscosity of the continuous phase. The apparent
viscosity at a shear rate of 50 s-1 has been found to have a significant effect on perception of
thickness and creaminess (Fernández et al., 2008). However, shear rates lower than 10 s-1 are
more representative of those found during swallowing of fluids by human subjects (Akhtar et
al., 2006), and in this study creaminess perception also appeared to be enhanced by a higher
consistency index, K.
Conclusions
ALM1.5/XG1.5, κ-C1.5/XG1.5 and SC1.5/XG1.5 mixtures were effective in stabilizing
mashed potatoes against freezing, long-term frozen storage and thawing treatments, as
amylose retrogradation and syneresis were prevented. Mashed potatoes with added mixtures
exhibiting water-holding capacity at all the tested times, whereas the rheological and textural
properties did not remain constant during the same period, providing that they do not measure
only polysaccharides-water interactions. More possible intermolecular interactions (between
different hydrocolloids and protein), and ice recrystallization and sublimation by physical
modifications could increase the values of the rheological and textural properties after one
year in frozen storage, although the hardening detected by the panellist at final storage time
was not considered adverse. Samples containing cryoprotectant mixtures did not develop a
spongy appearance, which is ascribed to the presence of XG. It was possible to develop a
hierarchy on the preference of cryoprotectant mixtures in mashed potatoes: κ-C1.5/XG1.5 >
SC1.5/XG1.5 > ALM1.5/XG1.5. These results have important implications for the production
of frozen/thawed mashed potatoes with improved sensory quality and freeze-thaw stability.
Acknowledgement
26
The authors wish to thank the Spanish Ministry of Science and Innovation for its financial
support (AGL2007-62851) and Premium Ingredients, SL for the donation of ingredients.
27
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32
Table 1 Effect of cryoprotectant mixtures and long-term frozen storage on rheological measurements for F/T mashed potatoes
G’
G”
n’
n"
n
K

(Pa)
(Pa)
(Pa sn)
(°)
Main effects
A: cryoprotectant mixture*
9.400.73 a
5558.1343.6 a
911.2099.00 a
0.10160.0049 a
0.06160.0197 a
0.14450.0113 a
131.9512.66 a
C1
11.760.56 b
4322.8506.6 b
903.22125.09 a
0.13080.0047 b
0.09700.0111 b
0.18940.0057 b
171.2918.34 b
ALM1.5/XG1.5
11.990.79 b
4859.1545.7 c
1046.13165.53 b
0.13000.0055 b
0.08420.0095 c
0.17510.0047 c
181.7115.72 c
κ-C1.5/XG1.5
11.780.94 b
3948.2423.9 d
829.15115.35 c
0.12880.0056 b
0.09630.0076 b
0.18880.0099 b
165.6529.99 d
SC1.5/XG1.5
0.37
113.4
50.01
0.0022
0.0053
0.0033
3.88
LSD (99%)
B: long-term in frozen storage (months)**
10.791.21 a
4579.0793.7 a
869.31123.26 a
0.12110.0113 a
0.08610.0234 a
0.17690.0242 a
152.7932.16 a
0
11.241.68 b
4797.7508.4 b
949.88141.88 b
0.12730.0145 b
0.07520.0257 b
0.17420.0106 a, b
169.5033.78 b
3
11.291.03 b
4417.3797.7 c
872.43111.58 a
0.12020.0140 a
0.08930.0149 a
0.17130.0237 b
148.1911.34 c
6
11.351.21 b
5211.0715.5 d
1031.06186.42 c
0.12080.0112 a
0.08610.0141 a
0.17420.0215 a, b
172.5322.17 b
9
11.471.23 b
4355.4617.1 c
889.44108.76 a
0.12470.0137 c
0.08730.0104 a
0.17570.0165 a
170.2522.09 b
12
0.42
126.8
55.91
0.0024
0.0059
0.0037
4.34
LSD (99%)
1F/T mashed potatoes made without added biopolymers.
*Mean values (n = 40) ± SD. ** Mean values (n = 32) ± SD.
Different letters in the same column indicate significant differences P < 0.01 for cryoprotectant mixture and time storage, respectively.
LSD, least significant difference.
33
Table 2 Rheological measurements for F/T mashed potatoes made with different added cryoprotectant mixtures for 0, 3, 6, 9 and 12 months in frozen
storage, and control
Test date (month)

(°)
C1-mashed potatoes
0
8.800.07 a
3
8.881.08 a, b
6
9.650.40 b, c
9
9.800.27 c
12
9.850.45 c
LSD (99%)
0.83
ALM1.5/XG1.5-mashed potatoes
0
11.750.34 a, b
3
12.380.30 c
6
11.900.12 b, c
9
11.530.33 a, b
12
11.250.74 a
LSD (99%)
0.61
κ-C1.5/XG1.5-mashed potatoes
0
11.230.37 a
3
12.080.65 b, c
6
11.750.57 a, b
9
12.880.80 c
12
12.000.42 a, b
LSD (99%)
0.85
SC1.5/XG1.5-mashed potatoes
0
11.400.39 a
3
11.651.38 a
6
11.850.44 a, b
9
11.200.48 a
12
12.780.69 b
LSD (99%)
1.12
G’
(Pa)
G”
(Pa)
n’
n"
n
K
(Pa sn)
5442.5128.5 a, b
5405.0219.3 a, b
5577.284.6 b
6133.051.6 c
5233.0206.0 a
222.6
879.5517.43 a
834.23115.23 a
925.0357.83 a, b
1004.90108.41 b
912.3066.51 a, b
118.49
0.10350.0039 a
0.10290.0043 a
0.09660.0022 a
0.10280.0065 a
0.10250.0025 a
0.0074
0.04800.0049 a
0.03560.0039 a
0.06640.0102 b
0.08030.0155 b
0.07780.0076 b
0.0166
0.13650.0008 a
0.16000.0087 c
0.13500.0050 a
0.13930.0001 a, b
0.15180.0081 b, c
0.0139
122.002.90 a
114.256.05 a
137.551.15 b
145.850.45 b
140.107.20 b
10.67
4372.596.5 a
4752.5188.7 b
3418.7188.1 c
4668.2195.5 b
4402.2185.5 a
254.7
897.8338.03 a
1025.5049.62 b
720.3046.01 c
954.1032.97 a, b
918.38140.93 a
106.95
0.13360.0025 a
0.13600.0003 a
0.13230.0018 a
0.12440.0016 b
0.12560.0025 b
0.0041
0.10790.0060 a
0.08280.0013 c
0.10230.0010 a, b
0.09610.0122 b, c
0.09700.0111 a, b
0.0128
0.19430.0009 a
0.18620.0004 b
0.18000.0000 c
0.19290.0005 a
0.19380.0027 a
0.0031
177.053.95 a
197.900.10 b
140.950.75 c
169.700.90 d
170.850.75 d
4.51
5106.256.6 a
4923.0127.4 a
4587.7141.1 b
5627.5119.5 c
4051.2229.6 d
212.4
1014.3344.00 b, c
1076.5390.14 b
949.6383.16 c, d
1309.7555.46 a
880.4393.49 d
110.50
0.12500.0008 a
0.13760.0040 b
0.12620.0004 a
0.12990.0000 a
0.13380.0008 b
0.0045
0.09130.0048 a
0.07790.0057 b, c
0.09170.0039 a
0.07470.0065 c
0.08730.0080 a, b
0.0102
0.18100.0047 a
0.17830.0012 a, b
0.17000.0000 c
0.17420.0025 b, c
0.17230.0014 b, c
0.0060
191.703. 50 a
174.452.35 b
166.550.65 d
207.302.20 c
168.551.65 d
5.46
3394.7148.8 a
4110.5274.1 b
4085.529.6 b
4415.2203.0 b
3735.2379.7 a
346.8
685.5536.96 a
863.28118.40 b
894.7871.11 b
855.4889.34 b
846.65104.95 b
129.32
0.12220.0017 a
0.13250.0008 c
0.12570.0015 a, b
0.12700.0018 b
0.13670.0036 d
0.0036
0.09710.0057 a
0.10470.0071 a
0.09680.0023 a
0.09570.0072 a
0.08690.0027 b
0.0090
0.19590.0001 a, b
0.17240.0033 d
0.20000.0000 a
0.19060.0008 b, c
0.18500.0041 c
0.0057
120.400. 00 a
191.4012.60 b
147.703.00 d
167.251.65 c
201.502.70 d
14.35
1F/T
mashed potatoes made without added biopolymers.
Values are means ± standard deviation. n = 8; mean values within a column and cryoprotectant mixture marked by different letters are significantly
different at P < 0.01. LSD, least significant difference.
34
Table 3 Effect of cryoprotectant mixtures and long-term frozen storage on textural and penetration parameters for
F/T mashed potatoes
CON
ADH
SPR
COH
GUM
(N)
(N s)
(N)
Main effects
A: cryoprotectant mixture*
C1
2.230.11 a
-4.110.67 a 0.940.03 a
0.740.04 a
1.650.12 a
ALM1.5/XG1.5
2.230.12 a
-4.830.69 b 0.960.01 c
0.920.05 b
2.060.16 c
κ-C1.5/XG1.5
2.240.12 a
-4.940.66 b 0.960.01 b, c 0.860.04 c
1.920.09 b
SC1.5/XG1.5
2.110.13 b
-4.420.85 c 0.950.01 b
0.900.05 d
1.900.13 b
LSD (99%)
0.06
0.24
0.01
0.02
0.06
B: long-term in frozen storage (months)**
0
2.190.15 a
-4.670.73 a 0.940.04 a
0.870.09 a, b
1.890.18 a, b
3
2.190.08 a
-4.670.69 a 0.950.01 a, b 0.890.11 a
1.940.22 a
6
2.270.06 b
-4.940.34 b 0.950.01 a, b 0.840.08 c
1.900.18 a, b
9
2.160.16 a
-5.020.60 b 0.950.01 a, b 0.850.07 b, c
1.850.25 b
12
2.200.14 a
-3.580.57 c 0.960.01 b
0.840.05 c
1.850.12 b
LSD (99%)
0.06
0.27
0.01
0.02
0.07
1F/T mashed potatoes made without added biopolymers.
*Mean values (n = 40) ± SD. ** Mean values (n = 32) ± SD.
Different letters in the same column indicate significant differences P < 0.01 for cryoprotectant mixture and
time storage, respectively.
LSD, least significant difference.
35
Table 4 Instrumental objective texture measurements for F/T mashed potatoes made with different added cryoprotectant
mixtures for 0, 3, 6, 9 and 12 months in frozen storage, and control
Test date (month)
CON
ADH
SPR
COH
GUM
(N)
(N s)
(N)
C1-mashed potatoes
0
2.290.09 a
-4.010.59 a, b
0.910.06 a
0.730.03 a
1.670.03 a, b
3
2.180.07 a, b
-3.580.37 b
0.940.02 a, b
0.730.03 a
1.590.05 a
6
2.280.05 a
-4.680.30 a
0.940.01 a, b
0.710.00 a
1.620.03 a, b
9
2.130.10 b
-4.610.65 a
0.940.01 a, b
0.760.05 a, b
1.620.17 a, b
12
2.260.12 a
-3.690.47 b
0.960.01 b
0.780.03 b
1.770.16 b
LSD (99%)
0.13
0.72
0.04
0.05
0.16
ALM1.5/XG1.5-mashed potatoes
0
2.220.09 a
-4.970.27 a
0.960.00 a, b
0.940.03 a, b
2.090.08 a, b
3
2.170.03 a
-4.960.33 a
0.960.00 a, b
0.970.04 a
2.110.09 b
6
2.250.09 a, b
-4.880.30 a
0.960.01 a
0.910.04 b, c
2.050.11 a, b
9
2.370.13 b
-5.630.27 b
0.970.01 b, c
0.910.05 b, c
2.160.25 b
12
2.170.09 a
-3.690.27 c
0.970.00 c
0.870.02 c
1.900.07 a
LSD (99%)
0.14
0.42
0.01
0.06
0.20
κ-C1.5/XG1.5-mashed potatoes
0
2.270.12 a, b
-5.480.46 a
0.950.00 a
0.870.03 a, b
1.970.05 a, b
3
2.230.13 a, b
-5.020.25 a
0.950.01 a, b
0.910.04 b
2.010.04 b
6
2.260.03 a, b
-5.250.28 a
0.960.00 b
0.850.03 a
1.930.08 a, b
9
2.130.07 a
-5.030.46 a
0.960.00 a, b
0.850.03 a
1.810.07 c
12
2.300.13 b
-3.930.46 b
0.970.00 c
0.830.03 a
1.900.07 b, c
LSD (99%)
0.15
0.58
0.01
0.05
0.10
SC1.5/XG1.5-mashed potatoes
0
1.980.07 a
-4.220.59 a
0.950.02 a
0.930.02 a, b
1.840.12 a
3
2.170.01 b
-5.110.37 b
0.960.00 a
0.950.06 a
2.060.05 b
6
2.290.02 c
-4.970.30 b
0.960.00 a
0.860.02 c
1.970.03 b
9
2.030.10 a
-4.820.65 b
0.950.01 a
0.890.04 b, c
1.800.03 a
12
2.060.10 a
-2.990.47 c
0.950.02 a
0.860.02 c
1.830.12 a
LSD (99%)
0.10
0.51
0.01
0.05
0.12
1F/T mashed potatoes made without added biopolymers.
Values are means ± standard deviation. n = 8; mean values within a column and cryoprotectant mixture marked
by different letters are significantly different at P < 0.01. LSD, least significant difference.
36
Table 5 Effect of cryoprotectant mixtures and long-term frozen storage on colour measurements, other quality parameters and overall acceptability (OA)
for F/T mashed potatoes
a*
L*/b*
DL
TSS
pH
OA
E*
(%)
(g/100 g (w/w))
Main effects
A: cryoprotectant mixture*
C1
-3.580.04 a
7.370.62 a, b
1.411.50 a
14.972.27 a
14.431.16 a
6.180.02 a
4.751.24 a
ALM1.5/XG1.5
-3.430.14 b
7.420.66 a
1.731.18 b
0.000.00 b
14.611.00 a, b
6.160.02 b
6.960.56 b
κ-C1.5/XG1.5
-3.620.05 c
7.430.61 a
1.191.08 c
0.000.00 b
15.211.40 b
6.140.02 c
8.730.22 c
SC1.5/XG1.5
-3.570.07 a
7.290.58 b
1.181.05 c
0.000.00 b
14.562.00 a
6.160.03 b
8.250.55 d
LSD (99%)
0.02
0.10
0.08
0.13
0.61
0.01
0.07
B: long-term in frozen storage (months)**
0
-3.540.11 a, b
7.960.27 a
0.460.33 a
16.591.04 a
13.700.94 a
6.170.02 a
6.982.21 a
3
-3.560.09 a
7.740.22 b
0.240.11 b
15.840.90 a
14.101.44 a, b
6.160.03 b
6.511.71 b
6
-3.470.14 c
7.840.28 b
0.570.53 c
17.732.32 a
14.740.87 b, c
6.150.03 b
6.981.76 a
9
-3.640.05 d
6.710.14 c
2.930.53 d
12.510.73 b
15.321.61 c, d
6.170.02 a
7.631.13 c
12
-3.530.08 b
6.640.14 c
2.690.25 e
12.200.27 b
15.641.12 d
6.160.02 b
7.761.05 d
LSD (99%)
0.02
0.11
0.09
3.02
0.68
0.01
0.07
1F/T mashed potatoes made without added biopolymers.
*Mean values (n = 40) ± SD. ** Mean values (n = 32) ± SD.
Different letters in the same column indicate significant differences P < 0.01 for cryoprotectant mixture and time in storage, respectively. Mean
values for OA marked by different letters are significantly different at P < 0.05. LSD, least significant difference.
37
Table 6 Quality parameters for F/T mashed potatoes made with different added cryoprotectant mixtures for 0, 3, 6, 9
and 12 months in frozen storage, and control
Test date (month)
a*
L*/b*
TSS
pH
E*
(g/100 g (w/w))
C1-mashed potatoes
0
-3.520.02 a
7.710.25 a
0.000.00 a
13.130.82 a
6.200.01 a
3
-3.590.01 b
7.690.11 a
0.300.13 b
13.930.82 a, b 6.200.01 a
6
-3.600.01 b
8.110.16 c
0.290.13 b
14.530.86 a-c 6.200.01 a
9
-3.600.03 b
6.660.22 b
3.400.21 c
15.470.84 c
6.150.01 b
12
-3.590.03 b
6.680.12 b
3.050.12 d
15.070.74 b, c 6.170.00 b
LSD (99%)
0.03
0.26
0.20
1.44
0.02
ALM1.5/XG1.5-mashed potatoes
0
-3.390.03 a
8.120.22 a
0.820.11 a
13.970.82 a
6.150.01 a
3
-3.420.01 a
8.030.05 a
0.290.05 b
15.430.78 b
6.160.00 a
6
-3.240.03 b
7.670.05 b
1.420.26 c
15.070.82 a, b 6.130.01 b
9
-3.680.02 c
6.720.09 c
3.460.06 d
14.000.83 a, b 6.190.01 c
12
-3.420.03 a
6.590.10 c
2.670.10 e
14.570.86 a, b 6.180.00 c
LSD (99%)
0.04
0.17
0.20
1.45
0.02
κ-C1.5/XG1.5-mashed potatoes
0
-3.610.02 a
7.960.07 a
0.370.13 a, b
14.300.82 a
6.160.01 a
3
-3.620.05 a
7.720.23 b
0.200.14 a
14.730.86 a
6.130.01 b, c
6
-3.550.02 b
8.020.27 a
0.390.12 b
15.070.82 a
6.150.01 a, b
9
-3.680.02 c
6.640.09 c
2.520.14 c
16.700.82 b
6.160.01 a
12
-3.630.02 a
6.800.05 c
2.480.12 c
15.230.86 a, b 6.120.00 c
LSD (99%)
0.04
0.24
0.19
1.47
0.02
SC1.5/XG1.5-mashed potatoes
0
-3.660.06 a
8.040.27 a
0.640.19 a
13.400.82 a, b 6.180.01 a
3
-3.600.02 a
7.530.05 b
0.200.04 b
12.300.94 a
6.140.01 b
6
-3.510.02 b
7.580.16 b
0.160.09 b
14.300.70 b, c 6.130.01 b
9
-3.600.02 b
6.820.04 c
2.320.08 c
15.100.82 c
6.190.01 a
12
-3.510.02 c
6.490.08 d
2.560.10 d
17.700.82 d
6.170.01 a
LSD (99%)
0.05
0.22
0.16
1.45
0.02
1F/T mashed potatoes made without added biopolymers.
Values are means ± standard deviation. n = 8; mean values within a column and cryoprotectant mixture marked
by different letters are significantly different at P < 0.01. LSD, least significant difference.
38
Table 7 Sensory attributes perceived before and at the time of putting the sample in the mouth, and at the time of preparing the sample for swallowing, for F/T mashed
potatoes made with different added cryoprotectant mixtures for 0, 3, 6, 9 and 12 months in frozen storage, and control
Test date (month)
Perceived before putting the
sample in the mouth
Granularity
Moisture
C1-mashed potatoes
0
6.330.50 b
3
6.101.04 b, c
6
7.630.71 a
9
6.000.79 b, c
12
5.251.02 c
LSD (95%)
0.91
ALM1.5/XG1.5-mashed potatoes
0
3.480.68 a
3
2.480.78 b
6
3.780.71 a
9
3.600.74 a
12
2.400.79 b
LSD (95%)
0.80
κ-C1.5/XG1.5-mashed potatoes
0
2.080.75 a, b
3
2.330.68 a
6
2.400.64 a
9
1.580.36 b
12
2.000.68 a, b
LSD (95%)
0.70
SC1.5/XG1.5-mashed potatoes
0
2.400.64 a-c
3
2.680.78 a
6
2.600.67 a, b
9
1.900.57 b, c
12
1.850.68 c
LSD (95%)
0.73
Perceived at the time of putting the sample in the mouth
Stickiness
Denseness
Homogeneity
Moisture
Firmness
Perceived at the time of preparing the sample for
swallowing
Cohesiveness Adhesiveness
Fibrousness
2.780.76 a
3.150.68 a
4.730.79 b
5.400.78 b, c
5.730.68 c
0.80
7.050.64 b
5.700.78 a
7.600.82 b
8.850.72 c
8.580.60 c
0.78
6.600.71 a, b
6.000.67 b, c
5.730.68 c
6.750.68 a
6.930.69 a
0.74
7.950.75 a
8.850.11 b
9.600.14 c
7.601.01 a
7.380.78 a
0.72
3.500.72 a
4.630.78 b
5.300.74 b, c
4.950.75 b, c
5.630.71 c
0.80
5.600.75 a
5.400.71 a
5.400.72 a
7.150.79 b
7.201.02 b
0.80
6.450.68 a, b
5.800.64 b, c
4.180.76 d
5.150.64 c
6.700.92 a
0.80
4.250.80 a
3.700.67 a
4.230.76 a
5.650.78 b
6.300.92 b
0.86
7.230.79 a
6.950.81 a, b
6.180.65 b
3.000.67 c
4.030.90 d
0.84
3.480.65 a, b
2.750.75 a
3.951.18 b
3.730.82 b
3.480.76 a, b
0.92
9.030.60 a
8.980.68 a
6.830.72 b
8.000.65 c
8.830.47 a
0.70
6.430.65 a
7.530.60 c
7.300.64 b, c
6.700.62 a, b
7.200.71 b, c
0.70
9.500.32 a
9.400.07 a
9.400.07 a
9.180.13 b
9.100.22 b
0.21
5.330.83 a
3.780.75 b
4.230.82 b
3.650.78 b
3.480.81 b
0.87
5.830.64 a
5.430.62 a
5.550.74 a
7.850.68 b
8.050.81 b
0.76
6.250.73 a, b
6.930.78 b, c
5.980.82 a
6.980.71 b, c
7.380.71 c
0.81
5.450.78 a
5.500.60 a
5.630.64 a
6.950.74 b
6.580.81 b
0.78
1.530.37 a
1.350.25 a
2.700.74 b
3.450.81 c
1.630.47 a
0.62
2.930.75 a
3.350.80 a
4.630.78 b
3.030.78 a
3.630.75 a
0.84
9.130.61 a
8.230.57 b
9.180.71 a
9.050.43 a
8.600.60 a, b
0.64
7.400.74 a, b
7.150.78 a
7.380.59 a, b
7.830.78 a, b
8.100.80 b
0.81
9.500.14 a
9.150.11 c
9.400.14 a, b
9.300.19 b, c
9.430.19 a, b
0.17
3.830.68 a, b
4.130.85 a, b
4.600.72 b
4.000.67 a, b
3.700.74 a
0.80
7.150.90 b
5.830.68 a
6.980.71 b
8.250.78 c
8.180.58 c
0.80
7.750.78 a
6.430.57 b
7.950.81 a
8.550.78 a
8.080.82 a
0.82
7.780.78 a
5.050.68 b
5.550.81 b
7.230.63 a
7.950.64 a
0.77
1.280.18 a
1.330.25 a
1.330.34 a
1.330.29 a
1.750.50 b
0.34
3.850.75 a, b
3.080.68 b, c
2.980.69 c
4.330.71 a
3.350.74 b, c
0.78
7.600.65 b
7.430.75 a, b
8.950.64 c
6.780.64 a
8.050.71 b
0.74
5.650.60 a
7.250.69 b, c
8.330.80 d
6.530.60 b
7.950.72 c, d
0.75
9.530.11 a
9.280.11 c
9.400.23 a-c
9.450.05 a, b
9.350.15 b, c
0.16
5.600.68 a
3.580.68 b, c
2.950.64 c
5.030.64 a
4.180.89 b
0.77
5.580.81 a
6.600.67 b
7.200.54 b, c
7.450.57 c
7.500.72 c
0.73
5.850.65 a
6.700.74 b
7.400.93 b, c
7.480.64 b, c
7.880.71 c
0.81
5.650.67 a
5.800.72 a
5.950.78 a
5.430.69 a
5.700.71 a
0.78
1.430.33 a
1.680.50 a
3.330.65 b
1.700.58 a
1.780.54 a
0.57
1F/T
mashed potatoes made without added biopolymers.
Values are means ± standard deviation. n = 8; mean values within a column and cryoprotectant mixture marked by different letters are significantly different at
P < 0.05. LSD, least significant difference.
39
Table 8 Sensory attributes perceived during the final and residual phases of mastication and overall acceptability for
F/T mashed potatoes made with different cryoprotectant mixtures for 0, 3, 6, 9 and 12 months in frozen storage, and control
Perceived during the final and
Test date (month)
residual phases of mastication
Overall
acceptability
Ease of swallowing Palate coating
Fibrousness
C1-mashed potatoes
0
6.250.76 a
3.330.77 a
7.850.75 a
3.380.78 a
3
6.250.76 a
3.400.71 a
7.700.67 a
3.700.72 a, b
6
5.800.85 a
3.900.67 a
6.130.76 b
4.250.59 b
9
4.180.68 b
3.380.78 a
4.150.75 c
6.430.75 c
12
7.650.81 c
3.550.80 a
3.700.81 c
6.000.65 c
LSD (95%)
0.84
0.81
0.81
0.76
ALM1.5/XG1.5-mashed potatoes
0
9.130.72 a
7.200.57 a
1.400.32 a
7.000.75 a
3
9.050.15 a
7.030.69 a
1.550.39 a, b
6.400.72 a
6
9.200.67 a
7.080.69 a
2.030.78 b
6.800.67 a
9
9.280.67 a
6.880.78 a
3.800.72 c
6.600.75 a
12
9.080.55 a
6.950.81 a
1.530.40 a, b
7.980.64 b
LSD (95%)
0.64
0.77
0.60
0.77
κ-C1.5/XG1.5-mashed potatoes
0
9.180.59 a
7.900.74 a, b
1.380.26 a
8.830.82 a
3
9.230.57 a
7.750.68 a, b
1.350.34 a
8.530.78 a
6
9.400.60 a
8.430.75 a
1.480.36 a
9.000.67 a
9
9.150.68 a
7.380.75 b
1.300.25 a
8.700.72 a
12
9.200.70 a
7.380.71 b
1.230.23 a
8.600.89 a
LSD (95%)
0.68
0.79
0.32
0.85
SC1.5/XG1.5-mashed potatoes
0
9.280.76 a, b
7.830.61 a, b
1.530.39 a
8.700.66 a
3
8.700.74 a
7.580.64 a, b
1.750.53 a
7.430.76 c
6
9.180.11 a, b
7.980.85 a
3.330.68 b
7.850.81 b, c
9
9.400.60 b
7.180.76 b
1.480.35 a
8.800.65 a
12
8.800.72 a, b
7.500.78 a, b
1.330.25 a
8.480.72 a, b
LSD (95%)
0.69
0.80
0.50
0.78
1F/T mashed potatoes made without added biopolymers.
Values are means ± standard deviation. n = 8; mean values within a column and cryoprotectant mixture marked
by different letters are significantly different at P < 0.05. LSD, least significant difference.
40