fruits & vegetables

FRUITS & VEGETABLES

S U P TA S A R KA R

H H M / 2 0 1 3 / 1 0

M . S C F N - 1 S T Y R

CONTENT:1. STRUCTURE & COMPOSITION

OF CELL TISSUE

2. CHEMICAL COMPOSITION OF PLANT MATERIAL

3. FRUITS

4. VEGETABLES

5. CASE STUDIES:

I. Retention of nutrients in green leafy vegetables on dehydration

II. Evaporative cooling system for storage of fruits & vegetables- a review

STRUCTURE & COMPOSITION OF CELL TISSUE

Fruits & vegetables are composed of both simple & complex cells

Simple tissue: -Dermal tissue -Parenchyma tissue Complex tissue: -Vascular tissue (Xylem & Phloem) -Collenchyma tissue & -Sclerenchyma supporting tissue

COMPONENTS OF PARENCHYMA CELL

CHEMICAL COMPOSITION OF PLANT MATERIAL

1.Carbohydrate: (Simple & complex form)-Complex carbohydrate:• Starch(α-1,4)• Cellulose(β-1,4)• Hemicellulose• Pectic substances2. Protein (<1%)3. Fat (About 5%)

4. Vitamins5. Minerals6. Water (80-90%)7. Phytochemicals8. Pigments -Chlorophyll (green pigment)-Carotenoids (yellow, red or orange)-Anthocyanin (red, blue or purple)-Anthoxanthin (white) Flavonoids

9. Flavour compounds:• Allium• Brassica• Organic acids (Citric acid, malic acid or tartaric

acid)

Sulphur containing

A plant’s turgor pressure is the pressure

that water-filled vacuoles exert on the

cytoplasm & the partially elastic cell

wall.

TURGOR PRESSURE

FRUITS

FRUITS

• A fruit is a part of a flowering plant that derives from

specific tissues of the flower, one or more ovaries, and in

some cases accessory tissues.

• Fruits are the means by which these plants

disseminate seeds. 

CLASSIFICATION

1. Berries2. Citrus fruits

3. Drupes4. Grapes5. Melons6. Pomes

7. Tropical & subtropical fruits

COMPOSITION & NUTRITIVE VALUE

Fruits are very poor source of protein & fat. (Exception: Avocado)

Contain high amount of moisture

Good source of fibre

Not very good sources of calories (Exception: Banana)

Higher percentage of sugar

Generally poor source of iron (Exception is

watermelon, Seethaphul)

Mangoes are excellent source of carotenes.

Oranges are fairly good source of carotene.

Citrus fruits are good source of vitamin C.

If fruits are bruised, peeled, cooked or exposed to air, alkali or copper large amounts of vitamin may be oxidised.

Apples give fibre to the diet.

Pigments

Fruits contain different pigments:

1. Chlorophyll2. Carotenoids3. Anthocyanins4. Anthoxanthins

Anthocyanins Enzymes like anthocyanase catalase

reactions that result in the loss of colour of anthocyanins.

In addition to heat & oxygen various metallic ions can cause undesirable change in colour.

The metal iron precipitates anthocyanin. This reaction may cause ‘pin-holing’ of cans.

Effect of canning or preserving: Colour deteriorate on storage.

Effect of sulphur dioxide: Antimicrobial preservative Potassium metabisulphite at high concentrations 1 – 1.5% causes total irreversible bleaching.

Fruits: 70 to 90% water Found in the vacuoles Soluble substances: sugar, salts,

organic acids & water soluble pigments.

Water

• The framework of fruit is made of cellulose

• Forms the wall of plant cell• Pectic substances are also found in cell

walls & between cells.• Act as cementing substance.

• Pectic substances: protopectin, pectinic acid, pectic acid.

CELLULOSE & PECTIC SUBSTANCES

• Change in solubility is influenced by heat.• Acid make structures more firm.• Alkaline disintegrate the fibre.

Volatile compounds: Esters, aldehydes, acids, alcohols, ketones & ethers.

Sugars, tannins, acids & mineral salts also affect the flavour of fruits.

Flavour constituents

Comprised of catechins, leuco-anthocyanins & hydroxy acids.

They are present in the tissues of those woody plants while absent in herbaceous plants.

Tannins affect the colour & flavour

High amount: skin & seeds

Polyphenols or Tannins

EFFECTS OF POLYPHENOLS ON FRUIT QUALITY:

• Undesirable astringency in some fruits & desirable astringency in ciders & wines.

• Brown discolouration due to oxidation .

• Undesirable dark coloured complexes with iron due to sequestering action in canned food.

• Leucoanthocyanins cause development of pink to pinkish brown colour.

Bitterness in fruits:

-Limoninoids(triterpenes) &

-flavanone glycosides (flavonoids)

The precursor of limonin in intact citrus tissue combine with acidic pH of fruit

The principal bitter tasting flavonoid compound: naringin

Post harvest changes & Storage

All synthesis of organic compounds halts after harvest but numerous physiological changes continue during storage.

Bulbs, roots, tubers & seeds become relatively dormant during storage whereas fleshy tissues undergo ripening after maturation & then continue to senescence.

Certain biochemical activities occur.

• Respiration rate varies with stage of maturity.

• Based on the rate of respiration prior to senescence fruits are classified as: Climacteric & Non-climacteric fruits.

• Non-climacteric fruits are best when ripened before harvesting.

CLIMACTERIC FRUITS NON- CLIMACTERIC FRUITS

AppleApricotBanana

PlumPapayaMangoTomato

Jackfruit

CherryCitrus fruits

FigsGrapesMelons

PineappleStrawberry

Classification of climacteric & non-climacteric fruits:

• Cell wall components undergo changes after harvest due to various enzymes

• Pectin degrade due to pectinesterases & polygalacturonases.

• Other enzymes: cellulase & hemicellulases.

RIPENING OF FRUITS

• It is genetically programmed highly coordinated physiological process

• Changes occur due to enzymes: lipase, pectic enzymes, invertase, chlorophyllase & peroxidase

• Breakdown of chlorophyll( colour changes from green -> yellow or orange red)

• Softening of flesh ( protopectin -> pectin, & in over ripe fruits: pectin ->pectic acid)

• There is decrese in acidity, increase in sugar, increase in volatile substances & increase in essential oil

• The optimum temperature is about 20°C & relative humidity about 90-95%

Each fruit must be stored at its own optimum temperature

Proper air circulation must be ensured

Commercial storage: Low temperature close to 0°C & relative humidity about 85% is preferred

Home refrigerator: Ventilated covered containers

Strong flavoured fruits can be stored in tight containers.

STORAGE:

ENZYMATIC BROWNINGNormally the natural enzymatic

compounds present in intact tissue do not come in contact with the enzyme phenol oxidases present in some tissues

Phenol oxidase enzyme act on polyphenols, oxidising them to orthoquinones

Orthoquinones rapidly polimerise to form brown pigments.

The optimum pH is between 5 to 7

Schematic diagram of enzymatic browning:

Cut fruit containing catechins, tyrosine, chlorogenic acid , mono &

dihydroxy phenol

DOPA (Dihydroxy Phenyl Alanine)

Orthoquinones

Melanins

polyphenolase

polyphenolase

polymerised

O2

O2

Prevention of enzymatic browning:

• Either by inactivating the enzyme or cutting off the oxygen:

• Temperature

• Change in pH

• Use of antioxidants

• Prevention of contact with oxygen

NON-ENZYMATIC BROWNING

• Ascorbic acid is responsible for browning

• Mixture of ascorbic acid & amino acid develop browning more rapidly.

VEGETABLES

Vegetables are plants or parts of plants.

Botanical classification of vegetables:

CLASSIFICATION:

GROUP EXAMPLES

Roots Carrot, beet root, radish turnip, colocasia

Tubers Potatoes, sweet potato , tapioca

Bulb Garlic, onion, shallots

Leaves Cabbage, lettuce, spinach

Flowers Plantain flower, cauliflower, neem flower, brocoli

Contd….

GROUPS EXAMPLE

Fruits Tomatoes, brinjal, lady’s finger, pumpkin, bottle gourd

Legumes (pods & seeds)

Peas , beans, bengal gram tender, red gram tender

Stems Plantain stem, amaranth stem, celery stem

Fungi Mushroom

Algae Spirulina

…Contd.

Classification based on nutrition:

1. Green leafy vegetables2. Roots & tubers3. Other vegetables

Most of the pigments occur in plastids

Some of the water soluble pigments are dissolved in the vacuoles

The chief pigments: -Fat soluble -Water soluble

PIGMENTS

WATER INSOLUBLE PIGMENTS

CHLOROPHYLL• Present in chloroplasts

• 2 chlorophylls: -Chlorophyll-a: Intense blue green -Chlorophyll-b: Dull Yellow green

• Occurs in the ratio: 3a:1b

CAROTENOIDS

• Groups of yellow, orange, red & fat soluble pigments

• They are present as α-carotene, β-carotene, γ-carotene, xanthophyll & cryptoxanthin

• β-carotene is valuable in the synthesis of vitamin A

WATER SOLUBLE PIGMENTS

• Flavonoids: -Anthocyanin: Red to purple -Anthoxanthins: Colourless or white

ANTHOCYANIN:• In the vacuoles• Anthocyanidins are anthocyanins without sugar in

their structure• They are pelargonidin(red), cyanidin(reddish

blue), delphinidin(blue).

ANTHOXANTHINS

Anthoxanthins

Flavones

Rutinol

Flavonols

Kaempferol

Flavonones

Naringin

Flavanols

Catechins

Gallocatechins

Leuco-anthocyanin

s

Leuco-cyanidins

ORGANIC ACIDSFormic, Succinic, Citric, Acetic, Malic, Fumaric,

Tartaric & Benzoic acid

The concentration is lower in vegetables than fruits

Tomatoes & vegetables with concentration of acid have pH 4 - 4.6

Most vegetables have pH of about 5 – 5.6

ENZYMES

• Composed of protein

• Destroyed by heat & chemicals

• 2 types of enzymes: -Hydrolytic enzymes -Oxido Reductases

Example: Papain, Anthocyanase, Peroxidases, Phenolases, Glycosidases

FLAVOUR COMPOUNDS

• The natural flavours of vegetables are due to mixture of aldehydes, alcohol, ketones, organic acids& sulphur compounds

• Astringent taste is due to phenolic compounds & tannins.

• Strong flavour due to sulphur containing compounds as in Allium & Cruciferae vegetables

Flavour components in sulphur containing vegetables

Vegetables Precursor Reaction with treatment Final volatile compound

Garlic Alliin S-2-propenyl (allyl) cysteine sulphoxide

Cutting/ crushing results in allicin formation.This undergoes non-enzymatic decomposition to disulphide & thiosulphinate

Disulphide further decomposes to a complex mixture of mono-sulphide & tri-sulphide –characteristic flavour

Onion S-1-propenyl cysteine sulphoxide

Cutting/ crushing results in formation of sulphenic acids which is unstable & undergoes rearrangement

Thiopropanal-S-oxide-lachry matory factor

Brassica family- cabbage, cauliflower

S-methyl-cysteine sulphoxide & thioglucosides

Cooking Dimethyl sulphides & isothiocyanates- give off-flavour

CHANGES DURING COOKING

1. Water content2. Carbohydrates

(Cellulose & pectic substances)

3. Protein

LOSS OF NUTRIENTS DURING COOKING

• Mechanical losses• Solvent action of water• Oxidation & chemical

decomposition

1.CHLOROPHYLL

Effect of putting in hot water

Effect of prolonged cooking & acid

Effect of canning Effect of sodium

bicarbonate Effect of freezing Effect of copper Effect of calcium salt

EFFECT OF COOKING ON PIGMENTS

Effect of heat & oxidation Effect of cooking in fat

2.CAROTENOIDS

FLAVONOIDS

1.ANTHOCYANINS:

Effect of pH Effect of metal Effect of method of

cooking Effect of tap water Effect of pickling

2. BETALAINS Effect of pH

3.ANTHOXANTHINS Effect of pH Effect of metal Effect of cooking on sulphur containing

vegetables Bitter compounds in vegetables

STORAGE OF VEGETABLES

Loss of moisture

Flavour gets impaired because of enzyme action & conversion of sugar to starch

Mature vegetables deteriorate less in storage than immature vegetables

STORAGE: In covered containers or plastic bags in refrigerator

FACTORS AFFECTING STORAGE LIFE

• Loss of water

• Respiration

• Microbial spoilage

FUNGI

MUSHROOM:• Umbrella shaped with

a central stalk & a cap called pileus.

• Devoid of chlorophyll• Low calorie• Rich in protein• Less fat

ALGAE

SPIRULINA:• Nutrient dense

food• Rich in protein,

B-carotene & γ-linolenic acid

• Better than 1 soya protein, egg protein or milk protein.

CASE STUDIES:

Study conducted by Sheetal Gupta, B.S.Gowri, A.Jyothi Lakshmi, Jamuna Prakash

Journal of Food Science & Technology September- October 2013 Vol 50, Issue 5 PP 918-925

1. RETENTION OF NUTRIENTS IN GREEN LEAFY VEGETABLES ON

DEHYDRATION

To investigate the influence of dehydration on nutrient composition of Amaranthus gangeticus, Chenopodium album(bathua), Centella asiatica (centella), Amaranth tricolor(tampala) & Trigonella foenum graecum(fenugreek)

OBJECTIVE

The GLV were were steam blanched for 5 min & dried in an oven at 60°C for 10-12hrs.

The fresh & dehydrated samples were analysed for selected proximate constituents, vitamins, minerals, antinutrients & dialyzable minerals

STUDY METHODOLOGY

Dehydration seems to have little effect on the proximate constituents, vitamins, minerals, antinutrient content of the GLV

Among the vitamins, retention of ascorbic acid was 1-14%, thiamin 22-71%, total carotene 49-73% & β-carotene 20-69% of their initial content.

FINDINGS

Dialyzable iron & calcium in the fresh vegetables ranged between 0.21-3.5mg & 15.36-81.33 mg/100g respectively which reduced to 0.05-0.53mg & 6.94-58.15mg/100g on dehydration.

Proximate principles were least affected Calcium & total iron content decreased slightly Dialysability of minerals decreased significantly Among the vitamins, ascorbic acid, total & B-

carotene were lost significantly while thiamine was retained moderately

Changes in the antinutritional factor was not significant.

CONCLUSION

CASE STUDY 2

EVAPORATIVE COOLING SYSTEM FOR STORAGE OF FRUITS & VEGETABLES

- A review

Study conducted by: Amrat lal Basediya, D.V.K.Samuel, Vimala Beera

Journal of Food Science & TechnologyMay- June 2013Vol.50, Issue 3PP 429-442

EVAPORATIVE COOLING SYSTEM

Evaporative cooling is a well-known system to be an efficient & economical means for reducing the temperature & increasing the relative humidity in an enclosure & this this effect has been extensively tried for increasing the shelf life of horticultural produce in some tropical & subtropical countries.

PRINCIPLE OF EVAPORATIVE COOLING

The wet-bulb temperature as compared to air’s dry-bulb temperature, is a measure of potential for evaporative cooling.

The greater the difference in the temperature, the greater is the cooling effect.

METHOD OF EVAPORATIVE COOLING

Direct cooling systemIndirect evaporative coolingTwo stage system

Evaporative cooling system for short duration:

(Scientific storage system)

ZERO ENERGY COOLING SYSTEM:

Developed at IARI, New Delhi

By Roy & Khurdiya (1986)

Based on the principle of evaporative cooling

ADVANTAGE OF EVAPORATIVE COOLED

STORAGE Most suitable for rural application

Size can be fitted to the need

Better marketablity

Retain nutritive value

Environment friendly

Reduce energy use by 70%

Extends shelf life (Reduces surrounding air temperature & increases moisture content)

Less expensive & easy to install, operate & maintain.

DISADVANTAGE:

Requires a constant water supply to wet pad

Space required outside home

Water high in mineral leave mineral deposit

High humidity decreases the cooling capability

No dehumidification

CONCLUSION

Approximately 23-35% of horticultural produce goes waste due to improper post harvest operation & storage

Evaporative cooling system is well suited where temperature is high, humidity low, water can be spared & air movement available

Zero energy cool chamber could be used for short duration storage in hilly regions.

CONCLUSION

TEXT BOOKS:

1. Vaclavik,V.A., Christian,E.W., Essentials of Food Science, Third Edition, Springer.

2. Srilaksmi, Food Science, Third Edition, 2003, New Age International Publisher, New

Delhi.

REFERENCE

JOURNALS

1. Gupta,S., Gowri,B.S., Lakshmi,A.J., Prakash,J., 2013, Retention of nutrients in green leafy vegetables on dehydration, Journal of Food Science & Technology, Vol.50(5), PP 918-925

2. Basediya,A.L., Samuel,D.V.K., Beera,V., 2013, Evaporative Cooling System for Storage of fruits & vegetables, Journal of Food Science & Technology, Vol.50(3), PP 429-442