biochem changes in fruits and veggies
TRANSCRIPT
BRINDA RAJENDRAN
Biochemical changes in fruits and vegetables during post harvest storage and preservation
Vegetables are composed of
Water content – 80 to 90%
Nitrogen content – 1 to 5% - Proteins, enzymes, amino acids,
amines (vegetable bases)
Carbohydrates – 3 to 10% - glucose, fructose, sucrose, starch,
pectin, cellulose sugar alcohols
Crude fiber – 1%
Phenolic compounds – delphidin, pelargonidin, cyanogeinc
glycosides, organosulfur compounds, sinapic acid, lycopene
How do fruits differentiate them from vegetables
Nitrogen containing compounds (0.1-1.5%) - free amino acids
Carbohydrates - Fructose, glucose and sucrose ; sugar alcohols
(sorbitol), Polysaccharides (cellulose, hemicellulose, pentosans,
pectins)
Lipids – tirglycerides, glyco & phospholipids, waxes
Phenolic compounds – Carotenoids, terpenes , pigments - flavor &
aroma
Alkaloids , vitamins, minerals
What happens on harvesting?
Breakdown of Chlorophyll Starch hydrolysis Organic acid catabolism Inactivation of phenolic
compounds Hydrolysis of pectin Breakdown of biological
membranes Cell wall softening
Synthesis of carotenoids and anthocyanins
Synthesis of flavor volatiles Synthesis of lignin Inter conversion of sugars Preservation of selective
membranes Protein synthesis Gene transcription Ethylene biosynthesis pathway
Degradative events Synthetic events
Primary post harvest events include
Enzymes
Genetic Expression
Respiration
Coordination and control of hormones
•Interconnected ; one may induce other in different directions•Genetic expression – enzymes •Enzymes – hormones•Hormones – inducers for genetic expression
Respiration ratesRespiration rate
Fruits and vegetables
Very low Nuts, dates
Low Apple, citrus, garlic, onions, potatoes (mature), Sweet potatoes
Moderate Apricots, Cabbages, carrots, figs (fresh), lettuce, nectarines, peaches, banana, peach, pears, peppers, plums, potatoes (immature), tomatoes
High Strawberry, blackberry, raspberry, lima bean, avocado
Very high Artichoke, snap bean, Brussels sprouts
Extremely High Asparagus, broccoli, mushrooms, peas, sweet corn
CLIMATRIC NON-CLIMACTRIC
Temperate fruit Apple, Pear, Peach, Apricot,Plum
Cherry, Grape, Strawberry
‘Vegetable’ fruit Melon, Tomato, Watermelon
Cucumber
Common tropical fruit
Avocado, Banana, Mango, Papaya, Fig, Guava, Passion fruit, Persimmon
Orange, Grapefruit, Lemon, Lime, Olive, Pineapple, Litchi
Less common tropical fruit
Cherimoya, Soursop, Breadfruit, Jackfruit, Mamey apple, Sapote
Cashew apple, Java plumOther Eugenia sp
Response to ripening hormone - Ethylene
S-Adenosyl 1-aminocyclopropanemethionine 1-carboxylic acid Ethyle
ne ACC oxidase ACC synthase
Quality components of edible fresh fruits & vegetables
Flavor – Sweetness; Sourness; Astringency; Bitterness;
Aroma; Off-flavors
Appearance – Size, Shape, Color, gloss, water loss
Texture – Firmness; hard/softness; grittiness, mealiness;
Succulence, juiciness; Tough & fibrous
Nutrition – Energy, protein, vitamins, fiber
Safety – Naturally occurring toxins, environmental
contaminants, mycotoxins, contamination
Color
Chlorophyll, carotenoids, anthocyanins and others
Ethylene can promote degradation of chlorophyll
But ethylene promotes Chl synthesis in dark and
anthocyanins in red cabbage when exposed to
light
1. Chlorophyll structure –
Mg atom replaced by H atom – dark green
to olive green – frozen peas and spinach
2. Hydrolysis of chlorphyll
Chlorophyllase – Chl to chlorophyllide + phytol
followed by repalcement of Mg atom to form
pheophorbide
Brining of cucumbers
3. Bleaching – lipoxygenase, catalase, peroxidase
Degradation of Fatty acids and Redox reaction in
presence of O2
Carotenoids
Color change from green to red – loss of Chl and
unmasking of other colors like
carotenoinds, anthocyanins
Carotenoids are susceptible to
Lipoxygenase - bleaching effect
Non enzymatic oxidation – dehydrated vegetable,
cooking
Anthocyanins
Anthocyanins – water soluble- berries, apple,
grapes, red cabbage, radish
Unstable during canning, bottling and other thermal
activities
Complex formation – phenolics, nucleic acids,
sugars, amino acids, metallic ions – preserves
color.
Textural changes
Cell wall – Cellulose, pectin, hemicellulose, lignin
Ripening – softening
Propectin, an insoluble pectin gets reduced
Soluble pectins – polygalacturonic acid polymers rise
Pectin esterase (demtehylation), polygalacturonase
(depolymerization; FLAVR SAVR tomato)
Cellulase – strawberries, avocadoes
B-galactosidase – during ripening - hydrolysis of galactans
to galactose - apples, strawberries, tomatoes
Flavor and taste
Aroma
short chain unsaturated (volatile) aldehydes
esters, lactones, terpenes, sulfur
Amino acids, fatty acids
Taste
Sugars and organic acids – sweet and sour
Phenolic compounds, tannins – choking, gritty
In short
THANK YOU
FOR BEING PATIENT