Factors relating to the development
of a pink discolouration defect in
commercial cheese – a review
D.F.M. Daly l, 2, P.L.H. McSweeney2, J.J. Sheehanl
lTeagasc
Food Research Centre, Moorepark, Fermoy, Co. Cork,
2 School of Food and Nutritional Sciences, University College Cork
Presentation Overview
 Manifestation of pink discolouration defect in cheese
 Review of theories and hypotheses from international
research undertaken to date
 Research themes
 Different cheese-types
 +/- Annatto
 Conclusions
 Future research requirements
Cheese Grading
 Appearance, texture and flavour
 Sporadic inconsistencies in cheese
appearance may result in
a downgrading of cheese
 Potential market loss
Pink discolouration defect
 Problem across the globe
 Occurring in many different cheese-types
 Producers affected to varying degrees
Occurrence within cheese
Pink
10mm
discolouration
wide border
Pink
blotches within
Discolouration
first of
noticeable
running inside
at surface
cheese
observed
at ~block
1 month
cheese
andpost
block
block
penetrating
15 mm from
into
manufacture
discolouarion along
external
block ~ 20mm
surface
apparent curd junction
Previous research
 Pink discolourations have been reported in a range of ripened
cheese varieties
 Italian-types
 Swiss-types
 Cheddar-types
 Mould-ripened cheeses
 Producers have reported losses due to pink discolouration
 Extent of the problem hasn’t been quantified

2 to 5% of Cheddar and Colby in supermarkets in US
(Dairy Field, 1999, Food Product Design 2000)
 Little consensus exists as to what exactly the pink
discolouration is and what are its underlying causes
 Defect arises intermittently with use of same starter cultures for
production. Why ?
Cheese with/without colourants
 Cheeses such as Cheddar and other territorial-type
cheeses often are coloured to give an orange to red colour
 Other cheeses do not have added colour
 Main colouring agent used in Annatto
 This review will consider separately development of a
pinking defect in cheeses with
 With added annatto
 Without added annatto
Cheddar type: with added annatto
 The principle pigment in annatto is cis-
bixin, a carotenoid
 Also present, as minor constituents, are trans-
bixin, cis-norbixin and trans-norbixin
 Annatto (in solution) can range from
reddish/orange to yellow depending on
the oxidation/reduction potential and pH
(Barnicoat, 1937; Tharp and Young, 2003)
 Annatto, as a carotenoid, is sensitive to oxidation in
foods (Smith et al., 2006)
 This oxidation is exacerbated by the presence of light
and heat.
Cheddar type: with added annatto
 Interaction between CO2 and
high-intensity light leads to the
oxidation of the bixin and a change
in cheese colour (Colchin et al., 2001)
 Major factors that were associated with this discolouration were
High intensity fluorescent lighting in display cases
 pH levels in cheese of 5.4 or more
CO2
Oxidation
the bixin
 Presence of oxygen
in theof
packaging

 Suggestion: producing Cheddar and Colby cheese within a pH range of
4.8-5.1 and use of packaging material such as foil laminate film to block
light and oxygen (Food Product Design, 2000, Dairy Field, 1999).
Cheddar type: with added annatto
 The effects of light type, temperature and pH were evaluated on
stability of annatto colorants in cheese (Hong et al., 1995 a)
 Pink discolouration intensity is dependent on the ratio of red and
yellow components remaining in the sample

As cheese pH values reduced from 5.4 to 4.8:

b* values (yellowness) were reduced at a faster rate compared to a* (redness)
values resulting in an formation of a pink colour at the cheese surface
 Proper packaging films (Low oxygen transmission rate) are critical to
reduce lipid oxidation and pink discoloration effectively in annatto
coloured cheeses, aluminium foil laminate provided greatest stability
for cheese colour. (Hong et al., 1995 b)
O2
Other Factors with annatto ?
 Gouda (Discolouration at surface)
 Interactions between nitrates (added to prevent late
blowing) and annatto in plastic surface coating
 Possibility
 Presence of bacteria with a high nitrate reducing capacity
= higher nitrite in the rind
 Together with annatto and an increase in pH lead to pink
discolouration (Pelaez & Northolt, 1988)
 Processed cheese
 Pink discolouration in processed cheese is associated with:




Annatto containing high levels of norbixin
High heat treatment during processing
Use of aged cheese (proteolysis)
Use of certain emulsifying salts (phosphates)
Cheddar type: with added annatto
 Pink material from defective Cheddar cheese consisted of
norbixin (pink coloured) associated with phospholipid
(preventing resolubilisation of norbixin), β-casein and three
unidentified peptide components (Govindarajan and Morris, 1973)
 Model studies indicated that localised decreased pH (due to
hydrogen sulfide production) resulted in a microfine precipitation
of norbixin
 No further research reported on this mechanism within cheese to
date
Cheese with added annatto: Summary of Factors
 Fluorescent lighting
 Interaction between CO2 and high intensity light
 Oxidation of bixin
  Temperature due to bright lights?
 Packaging
 Oxygen transmission rates
 Lipid oxidation
 Foil laminate
 pH: Conflicting reports:
 pH > 5.4, fluorescent lighting & presence of O2 in packaging
 Decreased pH: Microfine precipitation of norbixin: phospholipid
preventing resolubilisation of norbixin
 As pH decreased from 5.4 to 4.8:  Pinking
 Presence of O2 and redox potential
Cheeses without annatto
 Have considered cheeses with annatto
 Factors associated with pinking in non anatto
coloured cheeses
 Some factors may overlap with cheeses with added
annatto
 However, as no annatto present- what leads to a colour
change ?
Previous research-Italian varieties
 (Romano and Mozzarella)
 Certain strains of lactobacilli associated with pink defect
 While other strains never associated with appearance of
discolouration
 Cheese produced from cultures associated with the discoloration
had a higher oxidation-reduction potential (Shannon and Olson, 1969 a)
 Development pink discolouration was enhanced by penetration of
oxygen and increased curing temp (Shannon and Olson, 1969 a)
 Screening test developed to predict cultures tendency to produce
pink discolouration (Shannon and Olson, 1969 b)
 Milk-calcium carbonate medium (incubation for 10 day at 37 °C)
Cultures have tendency to
produce pink discolouration
Previous research-Italian varieties
 In Mozzarella cheese it was postulated that all rod cultures
may have the means to impart the characteristic defect to
some degree (MSc thesis: Betzold, 2004)
 That study used the screening method by Shannon and
Olson to screen cultures for Mozzarella manufacture
 Low correlation between predictive assay and presence of
absence of pinking in Mozzarella cheese
 Suggested : higher rod : coccus ratio may potentially
result in a greater chance of the defect occurring?
Italian and Swiss varieties
 Grana cheese (Bottazzi et al., 2000).
 A pink discolouration intense ring under the cheese rind

Associated with the biochemical behaviour of a specific
Lactobacillus helveticus used as starter culture
 Cheese produced from this strain (prone to pinking) higher
levels of soluble nitrogen, increased free amino acid levels
 Correlation between proteolytic activity and pinking?
 Swiss-type varieties
 Suggestion (Eye formation- aside - Park et al., 1967)

Possibility that propionic acid bacteria strain may be a factor
in pinking: strain specific
Cheddar-type: non-coloured
 Proposed that Maillard reactions may be involved in the
formation of pinking
 Proposed: At least three factors are required for pinking to occur in
Cheddar-type cheese (Martley and Michel, 2001)



Galactose must be present during ripening
Low molecular weight nitrogen compounds (proteolysis)
Establishment of a required critical oxygen level within the cheese
 Pinkish zone surrounding plug hole cavity
Cheddar-type: without annatto
 Proposed that Maillard reactions may be involved in the
formation of pinking
 Generally Maillard reactions require higher temperatures
than those encountered in cheese ripening




Interesting conference poster: Paramita and Broome, 2008
Hypothesised: Pink discolouration could be due presence of
intermediate compounds of maillard reaction such as α-dicarbonyl
compounds (glyoxal, methylglyoxal and diacetyl) in low
temperature browning
Demonstrated formation of coloured compounds in UHT milk
system at 25oC
Questions still remain:


Source and stability of sufficient quantities in cheese ?
Unproven in cheese system
Mould-ripened cheeses
 Enzymatic oxidation of tyrosine to
melanins by tyrosinase
 (Review of phenolic compounds- O'Connell and Fox, 2001)
 Reaction dependant on:




pH, moisture content,
Oxygen
Free fatty acid
Free amino acid levels (tyrosine)
 Presence of tyrosinase in cheese may be
due to
 Contaminating microbes such as
Pseudomonads, primary starters
(Lactobacillus delbrueckii subsp. bulgaricus and
other Lb. delbrueckii subsp.)
 Pigment-producing yeasts and moulds
associated
with browning of camembert cheese.
(Carreira et al., 1998; Carreira et al., 2002)
Hypotheses proposed from previous research on
pink discolourations in cheese
Coloured
Compound
Future- Key areas for focus
 Very complex- more likely a set
of conditions than 1 factor
 Key issues Oxygen content and redox potential
 Influence of microbial diversity

Presence of other microflora (NSLAB)
 Altered growth profiles of starter bacteria

Particularly rod:coccus ratio

Differing metabolic activity

Influence of altered microstructure

Presence of coloured compounds

e.g. Carotenoids, Tyrosinase products- identification
Pinking
defect
Flow Cell Cytometry
Control
Defect
Dot plots of fluorescence of cells harvested from cheese samples
Difference in patterns of bacterial cell viability and
metabolic state between Control and Defect cheese
Thank You
Acknowledgements
 Martin Wilkinson & Dara Hickey University of Limerick for flow cell
cytometry analysis
 This project is joint funded through the Irish Co-operative
Organization Society Ltd.