(2 Hours)
Faculty of Food Science and Biotechnology
Universiti Putra Malaysia (UPM)
 Minimally or light processing refers to:
of fruits and vegetables
 Demand for minimally processed (MP) fruits
and vegetables has increased due to
busy life style
increased purchasing power
health conscious trends
 Consumers are increasingly demanding
with a fresh-like quality
containing only natural
fruits and
 Europe (France & UK) markets for MP fruits and
vegetable grow explosively in the start of the 1990’s.
 USA - market share of fresh-cut produce accounts
for 25% of all produce sales in the retail market.
Minimally processing of raw fruits and
vegetables has two (2) purposes:
 It is important to keep the produce fresh, yet
supply it in a convenient form without losing its
nutritional quality.
 The product should have a shelf life sufficient
to make its distribution feasible to its intended
 In an ideal case, minimal processing can be
seen as “invisible” processing
 the microbiological, sensory and nutritional
shelf life of MP fruits or vegetables should be
at least 4 - 7 days but preferably even longer up
to 21 days depending on the market
 loss of ascorbic acid and carotenes is the main
limiting factor of nutritional quality.
 MP fruits and vegetables are products that
contain live tissues or those that have been only
slightly modified from the fresh-condition and
are fresh-like in character.
 The tissues do not exhibit the same
physiological responses as the normal (raw)
untreated live plant tissues.
 Respiration greatly increased in MP fruits and
Figure 1: Diagrams of intact and processed (cut) fruit or vegetable cell.
(From CTIFL, France.)
 Intact cell is expected to be more resistant to oxidative
browning and entrance of bacteria compared to the cut
cell (MP).
Figure 2: Diagram of product in package and product with surface modification such
as from peeling or slicing. (From CTIFL, France.)
A - shows intact vegetable product in a package.
B - shows condition of some cut surface cells within the majority of intact interior cell.
 The presence of cut surface complicate the modeling of
gas exchange in polymeric package
Reasons for quality changes in MP produce
 MP produce deteriorates because of :
* physiological ageing
which may result in
* biochemical changes
degradation of the colour,
* microbial spoilage
texture, flavour of the
 During peeling and grating operations,
* many cells are ruptured
* intracellular products such as oxidizing enzymes are
 Main spoilage characteristics indicating loss of
quality include:
* development of soft rots
* mould growth
* fermentation
* browning
* production of off-odours
 To minimize physiological decay, both quality
of raw materials and manufacturing processes
must be optimized.
1. Physiological and Biochemical
 Most important enzyme with regard to MP fruits and
vegetables is
polyphenol oxidase (PPO)
which causes
 Enzymatic browning requires the present of four
different components:
- oxygen
- oxidizing enzyme
- copper
- a suitable substrate
 To prevent browning, at least one of these components
must be removed from the system.
 Another important enzyme which catalyzes
peroxidation reactions
formation of numerous bad smelling aldehydes
and ketones
Ethylene production
 Minimal processing increases ethylene (C2H4)
 C2H4 involves in the biosynthesis of enzymes
involved in fruit maturation
partially responsible for softening of sliced
Respiration activity
 Respiration activity of MP produce will increase
1.2 - 7 fold or even more depending on
* type of produce
* cutting grade
* temperature
 If packaging condition are anaerobic
leads to anaerobic respiration
formation of ethanol, aldehydes and ketones
2. Microbiological Changes
 Minimal processing damages tissues of produce
resulting in leakage of cellular fluids containing
nutrients and intercellular enzymes
creates a favourable environment
for microbial growth
 Minimal processing (peeling, cutting and shredding)
expose surface of produce
* to air
* possible contamination with bacteria, yeast and
Factors Affecting the Microbial Stability
and Quality of MP Vegetable Salads
 Intrinsic factors
 Processing factors
 Extrinsic factors
 Implicit factors
Intrinsic Factors
 pH
- varies depending on type of vegetables used.
 Nutrient availability
- mixed salads contain wider variety of nutrients
than single pack of vegetables.
 Biological structure
 Other factors
- Antimicrobial effects of vegetables
Eg antilisterial effect of carrots.
Processing Factors
 Washing
 at harvesting may contaminate produce with
water borne microorganism.
 At the processing plant should reduce the
microbial load
 Temperature
 blanching reduce/destroy vegetative microbial
 low temperature (0-5 C) during preparation and
storage limits growth of microorganisms.
Processing Factors …… continues
 Other processes
processing operations such as chopping, shredding,
slicing may contaminate the MP produce
assembly of salads may result in contamination from
process workers, work surfaces
use of low pH dressings lowers pH
use of packaging to act as O2 and water barriers and to
prevent microbial contamination.
Table 1: Effect of unit operations of commercial processing lines on
aerobic microbial plate counts from various vegetables
(Source Garg et. al (1990)
Extrinsic Factors
 Temperature
* temperature fluctuations during transport and
 Modified atmosphere packaging
* modified atmosphere packaging influences
survival of microorganisms during storage
 Benefits of MA cannot be explained solely by a
reduction in total microbial number.
 There are other influencing factors such as:
 packaging material used
 relative humidity during storage
 type of produce
 type and number of microorganisms present
 Combination of low temperature storage and
MA packaging has been recommended to
enhance quality and to extend shelf life of MP
Implicit Factors
 Competition between predominant microbial
E.g lactic acid bacteria and pseudomonads
 Antagonistic relationships between microbial
 Synergism between microbial group
To be continued … ...