Composition of Fruits, Vegetables and Flowers

    Cell components their function relevant to postharvest management

    Components

    Functions

    Cell wall

    Primary wall

    Includes cellulose (9-25%) hemicelluloses (25-50%) pectin substances and protein (10%). It stretches plastically during cell growth & allows the free passage of water minerals dissolves in water

    Sec. wall

    Cellulose (45%), hemicelluloses (30%) and lignin (22-28%). Provide structural support to the plants

    Middle lamella

    A layer of pectin substances forms the middle lamella and acts to bind adjacent cell together

    Protoplast (Content of cell with out cell wall)

    Cytoplasm : (Cytoplasm + nucleolus =Protoplasm)

    PLASTIDS


    Chloroplast

    Chloroplast contains 50% protein and 50-55% lipids and small amount of nucleic acids. These are found in green cells.

    Chromoplast

    These are developed from mature chloroplasts after degradation of chlorophyll ands responsible for yellow – red pigmentation in the fruits.

    Leucoplasts & Amyloplasts

    Leucoplasts are colour less plastids and contain protein. In the later stages leucoplasts are known as amyloplasts

    Vacuoles

    These are reservoir of cell and occupies about 80-90% of the cell volume. It contains various inorganic ions, sugars, amino acids, organics acids, gums, mucilages, tannins, flavonoids, phenolics, pigments and others nitrogenous compounds

    Nucleus


    Ergastic substances

    Crystal like calcium oxalate, tannins, fats. CHO and proteins are stored in various components of the cell.

    Bio chemical constituents which plays an important role in determining the composition and quality of F & V are as follows.
    1. Water
    Most of the fruits and vegetables contain 70-80% moisture while some vegetables like leafy vegetables and melons contain almost 92-95% moisture. The tubers crops like cassava, yam and corms contain less moisture ( around 50%) and are more starchy. Moisture plays an important role in fruits and vegetables because many of the nutrients exist in soluble state in them. The higher moisture content makes the fruits, vegetables and flowers perishable as it is easily vulnerable to attack by microorganisms. Further moisture is lost during the biological activity of these commodities which deteriorates its quality in terms of freshness. Therefore, retention of the moisture or prevention of loss of moisture is one of the important considerations in planning a storage technique or strategy for extension of shelf life. The actual water content is dependent on the availability of water to the tissue at the time of harvest. Water content of produce will vary during the day if there are fluctuations in temperature. For most produce, it is desirable to harvest when the maximum possible water content is present as these results in a crisp texture.
    Examples of moisture content of some of fruits and vegetables
    • 95% - cucumber, lettuce, melons
    • >80% - many F&V
    • 50% - starch tubers and seeds like –yam, cassava and corn
    2. Carbohydrates
    Carbohyrates are the major constituent after water, which account for 2-40% in tissues with lowest found in cucurbits and highest found in cassava. They occur mainly as starches and structural polysaccharides like pectins, celluloses, hemicelluloses. In many of the fruits and some vegetables the starches and few other polysaccharides undergo conversion into simple sugars like sucrose, glucose and fructose during ripening. These are responsible for sweetness. Small quantities of carbohydrates also occur as organic acids which are responsible for sourness or acidity. The major organic acids found in fruits and vegetable are citric, malic, tartaric, oxalic and pyruvic. Small quantities of bi- and tri- carboxylic acids also are present. In fruits and vegetables carbohydrates contribute mainly for its calorific value.
    Examples of carbohydrates content in some of fruits and vegetables
      • Most abundant group after water, accounts for 2 - 40 g 100-1 g
      • Low in cucumber and high in cassava (20g 100-1 g)
      • In fruits and vegetables carbohydrates contribute mainly for its calorific value.
    Sugars constitutes major carbohydrates in fruits particularly after ripining
    A) Sugars – Many tropical and sub-tropical fruits contain highest level of sugars. Glucose and fructose are the major sugars in all fruits and often present in similar level, while sucrose is only present in about 2/3rd of the produce. It helps in imparting colour, flavour, appearance and texture to the fruits. Flavour is fundamentally the balance between sugar and acids ratios. Sugar is the primary substrate for respiration and energy.
    The glycaemic index (GI) of F & V varies from 22(cherries) -97(parsnip).
    Potato and sweet potato – 55 - 60
    Bread- 70
    B) Fiber – cellulose, hemicelluloses, lignin and pectic substances
    3. Protein
    Fruits and vegetables are not an important source of proteins. Though some vegetables like brassica group contains 3-5% of proteins and legumes (5g), majority of fruits and vegetables contain not more than 1-2%. These proteins are present mainly as enzymes.

    4. Lipids
    Lipids are not more than 1% in majority of fruits and vegetables except some like avocado(20%) and olive(15%). In most of them it is present as protective cuticle layer on surface. However, nuts contain considerable amount of fats. Generally low fat levels seen in fruits and vegetables make it more healthy foods to combat heart related diseases and disorders like hyperlipidaemia.

    5. Minerals
    Fruits and vegetables are good sources of minerals. Minerals are essential for growth and development of body right from birth to old age. Calcium is present in several fruits as calcium pectate in cell walls. Calcium appears to be linked to control of enzyme activities, respiration and ethylene production. Some fruits like bananas are rich in potassium.

    6. Vitamins
    Generally F&V are rich vitamins but their quantity is varied among them. Fat-soluble vitamins A, D, E and K and water-soluble vitamins C and B group are found in F&V. These are needed for growth, normal function of the body.
    Table: Vitamins and their sources

    Vitamin A

    Leafy vegetables, radish tops, mango, papaya, carrots etc.

    Thiamine (B1)

    Fresh peas & beans, cabbage, bael, pomegranate, jamum, etc.

    Riboflavin(B2)

    Banana, litchi, papaya, radish top, pineapple, cowpea etc.

    Niacin(B3)

    Banana, strawberry, peach, cherry, green vegetables etc.

    Vitamin C

    Anola, guava, citrus fruits, cashew apple, leafy vegetables, green chilli, drumstick etc.

    Vitamin D

    Cabbage, carrot

    Pyridoxine (B6)

    Vegetables

    Folic acid (B9)

    Fresh GLV, lady’s finger, cluster beans

    Cyanocobalamin(B12)

    Yeast, fermented foods.

    7. Pigments
    The attractive colour of the many fruit is due to sugar derivates of anthocynidins. At the time of ripening, loss of chlorophyll and accompanied by synthesis of anthocyanins or carotenoids which present in vacuole and chloroplast respectively.
      • Anthocyanins – gives colour from red to blue
      • Carotenoids - are synthesized in green tissue eg. beta-carotene and lycopene
    8. Phenolics and antioxidants
    Major class of plant compounds, it comprising of anthocyanins, leucoanthocyanins, anthoxanthins, hydroxybenzoic acids, glycosides, sugar esters of quinic and shikimic acids, esters of hydroxycinnamic acids and coumarin derivatives
    The phenols are impotent in determining the colour and flavour of the fruit. Phenols are by products of the metabolism of the amino acids and contribute the sensory qualities of the fruits (colour, astringency, bitterness and aroma) and play the vital role in the resistance to attack of pathogen and stress. It is known for its antioxidant activities.

    9. Organic acids – imparts taste and flavour.
    The major acids are malic (apple), citric(citrus), tartaric(grape), quinic, succinic and shikimic acids
    Organic acids plays important role in - photosynthesis and respiration
    • Synthesis of phenolic compounds, lipids and volatiles aroma

    10. Volatiles (Flavour) compounds
    Important in producing characteristic flavor and aroma (mol.wt <250 possess volatile nature)
    Concentration – 10 mg 100-1g
    Compounds are – esters, alcohols, acids, aldehydes and ketones.
    Ethanol is common to all F&V, where as others are specific.
    Esters present in ripe fruits
    Sulphur in Brassica sp. and tomato

    11. Texture - Texture is governed by structural polysaccharides.

Last modified: Sunday, 3 June 2012, 8:48 PM