ताजे फल और सब्जियों की परिपक्वता और गुणवत्ता पहलुओं की विवेचना
Fruits and vegetables, being a rich source of essential nutrients, are generally important in our diet for their high content of fibers, vitamins and minerals. However, they contain a very high percentage of their fresh weight as water and consequently exhibit relatively high metabolic activity which continues post harvest and makes most fruits highly perishable commodities.
It is this perishability and inherent short shelf life that presents greatest problem for the successful transportation and marketing of fresh fruits. The principles dictating at which stage of maturity a fruit or vegetable should be harvested are crucial to its subsequent storage and marketable life and quality.
It is that stage of development, which ensures proper ripening. Maturity of fruit and vegetable can be defined as two type namely physiological maturity (The stage of development when a plant part will continue development even if detached; mature fruits) and horticultural maturity (The stage of development when a plant part possesses the necessary characteristics for use by consumers).
The stages of maturity for a fruit consists of immature, color turn, ripe, overripe and senescence and for vegetables are immature, mature and over-mature.
Maturation is indicative of the fruit being ready for harvest. At this point, the edible part of the fruit or vegetable is fully developed in size, although it may not be ready for immediate consumption.
Ripening follows or overlaps maturation, rendering the produce edible, as indicated by taste. Senescence is the last stage, characterized by natural degradation of the fruit or vegetable, as in loss of texture, flavour, etc. (senescence ends at the death of the tissue of the fruit).
The maturity indices are important for the consideration of sensory and nutritional quality, use (Fresh market or Processed), adequate shelf life, facilitate marketing standards and productivity.
1. Some typical harvesting indices of fruits and vegetables:
This factor is commonly applied to fruits, since skin color changes as fruit ripens or matures. Some fruits exhibit no perceptible color change during maturation, depending on the type of fruit or vegetable. Assessment of harvest maturity by skin color depends on the judgment of the harvester, but color charts are available for cultivars, such as apples, tomatoes, peaches, chilli peppers and ber etc.
The shape of fruit can change during maturation and can be used as a characteristic to determine harvest maturity. For instance, a banana becomes more rounded in cross-sections and less angular as it develops on the plant. Mangoes also change shape during maturation. As the mango matures on the tree the relationship between the shoulders of the fruit and the point at which the stalk is attached may change. The shoulders of immature mangoes slope away from the fruit stalk; however, on more mature mangoes the shoulders become level with the point of attachment, and with even more maturity the shoulders may be raised above this point.
Changes in the size of a crop while growing are frequently used to determine the time of harvest. For bananas, the width of individual fingers can be used to determine harvest maturity. Usually a finger is placed midway along the bunch and its maximum width is measured with callipers; this is referred to as the calliper grade.
Most fruits synthesize volatile chemicals as they ripen. Such chemicals give fruit its characteristic odour and can be used to determine whether it is ripe or not. These doors may only be detectable by humans when a fruit is completely ripe, and therefore has limited use in commercial situations.
Leaf quality often determines when fruits and vegetables should be harvested. In root crops, the condition of the leaves can likewise indicate the condition of the crop below ground. For example, if potatoes are to be stored, then the optimum harvest time is soon after the leaves and stems have died. If harvested earlier, the skins will be less resistant to harvesting and handling damage and more prone to storage diseases.
As part of the natural development of a fruit an abscission layer is formed in the pedicel. For example, in cantaloupe melons, harvesting before the abscission layer is fully developed results in inferior flavoured fruit, compared to those left on the vine for the full period.
A fruit may change in texture during maturation, especially during ripening when it may become rapidly softer. Excessive loss of moisture may also affect the texture of crops. These textural changes are detected by touch, and the harvester may simply be able to gently squeeze the fruit and judge whether the crop can be harvested.
Today sophisticated devices have been developed to measure texture in fruits and vegetables, for example, texture analyzers and pressure testers; they are currently available for fruits and vegetables in various forms. A force is applied to the surface of the fruit, allowing the probe of the penetrometer or texturometer to penetrate the fruit flesh, which then gives a reading on firmness.
The juice content of many fruits increases as the fruit matures on the tree. To measure the juice content of a fruit, a representative sample of fruit is taken and then the juice extracted in a standard and specified manner. The juice volume is related to the original mass of juice, which is proportional to its maturity.
Oil content and dry matter percentage:
Oil content can be used to determine the maturity of fruits, such as avocados. According to the Agricultural Code in California, avocados at the time of harvest and at any time thereafter shall not contain in weight less than 8% oil per avocado, excluding skin and seed (Mexican or Guatemalan race cultivars). Thus, the oil content of an avocado is related to moisture content.
In climacteric fruits, carbohydrates accumulate during maturation in the form of starch. As the fruit ripens, starch is broken down into sugar. In non-climacteric fruits, sugar tends to accumulate during maturation.
A quick method to measure the amount of sugar present in fruits is with a brix hydrometer or a refractometer.
Measurement of starch content is a reliable technique used to determine maturity in pear cultivars. The method involves cutting the fruit in two and dipping the cut pieces into a solution containing 4% potassium iodide and 1% iodine. The cut surfaces stain to a blue-black color in places where starch is present.
Starch converts into sugar as harvest time approaches. Harvest begins when the samples show that 65-70% of the cut surfaces have turned blue-black.
n many fruits, the acidity changes during maturation and ripening, and in the case of citrus and other fruits, acidity reduces progressively as the fruit matures on the tree.
As fruit mature, their specific gravity increases, this parameter is rarely used in practice to determine when to harvest a crop but it could be where it is possible to develop a suitable sampling technique. To do this the fruit or vegetable is placed in a tank of water; those that float will be less mature that those that sink.
To give greater flexibility to the test and make it more precise, a salt or sugar solution can be used in place of water.
For perennial fruit crops grown in seasonal climate which are more or less uniform from year to year, calendar date for harvest is a reliable guide to commercial maturity.
Light transmission properties can be used to measure the degree of maturity of fruits. These methods are based on the chlorophyll content of the fruit, which is reduced during maturation.
The fruit is exposed to a bright light, which is then switched off so that the fruit is in total darkness. Next, a sensor measures the amount of light emitted from the fruit, which is proportional to its chlorophyll content and thus its maturity.
2. Fruits and vegetables Quality traits for human consumption
It is the degree of excellence, is a combination of many attributes that give each commodity value in terms of human food.
Consumers judge quality of fresh fruits and vegetables on the basis of appearance and firmness at the time of initial purchase. Subsequent purchases depend upon the consumer’s satisfaction in terms of flavor (eating) quality of the product.
Consumers are also concerned about the nutritional quality and safety of fresh fruits and vegetables.
Quality attributes of fresh fruits and vegetables can be classified into three classes according to the occurrence of product characteristics when they are encountered or consumed:
- Feel (Touch) - Manual evaluation of firmness and texture, May be accompanied by mechanical texture analysis.
- Defects - Visual evaluation of absence of defects or deterioration of colour, May be accompanied by mechanical methods (e.g. ultrasound).
- Appearance (Sight) - Visual evaluation of size, shape, gloss and colour, May be accompanied by visual guides and colorimeters .
- Odour - Mostly qualitative and subjective evaluation by smelling, May be accompanied by technical methods (e.g. gas chromatography).
- Taste - Oral tasting (sweetness, bitterness, sourness and saltiness), Technical quantification of taste compounds (e.g. chromatography).
- Texture - Includes tenderness, firmness, crispness, crunchiness, chewness, fibrousness, which are measured by applying force to the produce; additionally, textural characteristics are evaluated as “mouthfeel”.
- Wholesomeness - Wholesomeness is difficult to measure objectively, it can be described as “freshness” “produce integrity”, it also has a ‘sanitary’ component meaning how clean hygienic the product is.
- Nutritive value - Nutritive value is measured by the content of nutrients such as fat, carbohydrates, protein as well as essential vitamins, minerals and other substances that influences human well-being.
- Food safety - safety can be measured via the examination of food items with regard to their pathogenic microbial load, content of chemical contaminants or presence of physical foreign matter in the produce.
Yogender Singh1*, Praduman Yadav2 and K. Prasad1
1Department of Food Engineering and Technology, S.L.I.E.T., Longowal-148106, Punjab, India
2Directorate of Oilseeds Research, Hyderabad-500030, Andra Pradesh, India