Enzyme activity in HPP

1. ENZYMES ACTIVITY IN HPP

2. • Enzymes are biocatalysts that are essential in the
physiology and metabolism of plants.
• However, most enzymes remain active
postharvest.
• Although this may be desired in cases where
ripening takes place during postharvest storage.
• It may also lead to detrimental changes in quality
attributes such as color, flavor, texture, and
nutritional value

3. • Polyphenol oxidase (PPO),
• chlorophyllase,
• peroxidase (POD),
• lipoxygenase (LOX), and
• lipase may be responsible for color and flavor changes.
• Pectinases, cellulase, and hemicellulase may cause
textural degradation.
• Thiaminase and oxidative enzymes such as ascorbic
acid oxidase, PPO, and POD may cause loss of
nutritional value

4. ENZYME ACTIVITY
• . On the other hand, enzymes are used as
catalysts or processing aids in many food-
processing applications, usually to hydrolyze
complex or large moieties into simpler
molecules.
• There is also a growing interest to mimic
nature in using enzymes to synthesize and
transform molecules and improve the nut

5. • The key enzyme responsible for a specific
quality loss may vary from one product to
another.
• The key enzyme in the development of off-
flavor in green peas, green beans, and corn.
• While cystinelyase is the key enzyme
responsible for the development of off-flavor
in broccoli (with some contribution from
lipase) and cauliflower

6. • The main enzymes responsible for quality
degradation may also be of microbial origin.
• For instance, the continued softening of apricots
that is sometimes observed in canned apricot
products.
• The main enzymes responsible for quality
degradation may also be of microbial origin.
• For instance, the continued softening of apricots
that is sometimes observed in canned apricot
products

7. Enzymes Related to Texture and
Consistency
• Texture is an important quality attribute of food
products.
• The structural integrity and texture of fruits and
vegetables can be attributed mainly to the
primary cell wall, the middle lamella, and the
turgor generated within cells by osmosis.
• Depending on the product, special compounds
within the cell (e.g., starch), overall structure and
shape of separate cells, and the structure and
shape of tissues like the presence.

8. • The basic structure of the primary cell wall
consists of a cellulose–hemicellulose network,
which is chemically inert with pectin polymers
interwoven with this net.
• The network of these three polysaccharides
forms the basis for the cohesive force inside the
cell.
• Pectin, as the main constituent of the middle
lamella, cements cell walls and gives firmness and
elasticity to tissues

9. Enzymes Related to Off-Flavor
Development
• Flavor is another important quality parameter
that determines the suitability of a food
product for consumption.
• It is usually difficult to characterize the critical
combination of compounds that contribute to
the characteristic flavor and aroma of food
products and identify the enzymes responsible
for the biosynthesis of flavor compounds and
off-flavor development

10. • Enzymes can cause off-flavor development in foods
especially during storage.
• Vegetables such as green beans, green peas, corn,
broccoli, and cauliflower develop off-flavor during
frozen storage if they are not properly blanched.
• Enzymes can cause off-flavor development in foods
especially during storage.
• Vegetables such as green beans, green peas, corn,
broccoli, and cauliflower develop off-flavor during
frozen storage if they are not properly blanched

11. • This was proposed to be due to calcium
abstraction from the enzyme that increases
the exposure of lipids to the haem group in
the denatured enzyme

12. Enzymes Responsible for Changes in
Nutritional Quality
• Relatively little information is available on the
enzymes that affect the nutritional quality of
horticultural products except on those that
are involved in other quality degrade

13. • Phenols including anthocyanins that are
important phytochemicals.
• Enzymatic browning caused by these enzymes
also results in the decrease of the available
lysine content of proteins.
• Ascorbic acid oxidase causes degradation of
ascorbic acid in vegetables such as squash.

14. • Thiaminase causes the degradation of thiamine
that is an essential co-factor in amino acid
metabolism.
• Riboflavin hydrolase causes degradation of
riboflavin. However, it is only found in some
microorganisms.
• Myrosinase enhances the nutritional quality of
Brassica vegetables as it converts glucosinolates
into the biologically active forms such as
thiocynates and isothiocynates

15. • Ascorbic acid oxidase catalyzes the
transformation of ascorbic acid into
dehydroascorbic acid, which has the same
physiological efficiency as ascorbic acid.

16. The Effects of High Pressure on
Enzymes
• The application of pressure above 300 MPa can
cause irreversible protein denaturation at room
temperature, while lower pressure results in
largely reversible changes in protein structure.
• A lowering of the denaturation pressure both as
the temperature is increased and decreased.
• Enzymes are special type of proteins whose
biological activity arises from an active site
brought about by the three-dimensional
configuration of the molecule.

17. • Denaturation of the enzyme with the
accompanying conformational changes can
alter the functionality of the enzyme resulting
in increase or loss of biological activity and
changes in substrate specificity.
• Loss of activity may occur without significant
change in the conformation of the enzyme

18. Protein Changes
• It has long been known that proteins show changes in
their native structure under high pressure similar to
the changes occurring at high temperatures.
• The structure of a protein is stabilized by a sensitive
balance of disulfide bonds and various non-covalent
forces such as hydrogen bonds and hydrophobic,
electrostatic, and van der Waals interactions.
• Upon heating, all these forces are weakened,
particularly due to molecular fluctuations, and the
protein molecule denatures or unfolds

19. • The amino acid residues that form the active
center of an enzyme are brought together only in
the native structure of the molecule and
unfolding results in disassembling of this domain
and thus loss of enzyme activity.
• The mechanism of pressure-induced enzyme
inactivation is different to that of heat
inactivation.
• Contrary to thermal inactivation, pressure
inactivation near room temperature is usually not
accompanied by changes in covalent bonding.