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

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