Agriculture for Engineers 4 (3+1)

Lesson 45. Post Harvest Practices

45.1.1 Respiration:

Fresh fruits and vegetables differ basically, not only from all other commodities, but from other perishable foods, as they are alive and carry on many life process characteristic of living things, even after harvest respiration is the most important of this process. In respiration the metabolites are broke down by oxidation and quality and the life of fruits and vegetable deteriorate. The respiration rate is good index of rate of living. Fruits and vegetables that respire fast give us the greatest handling problems as they are the most perishable. Some vegetables in order of ascending respiration rates are (1) potato, (2) cabbage, (3) peas. Fruits in order are (1) apple, (2) citrus, (3) banana, (4) peaches, (5) strawberry. Other bio-chemical changes occurring in the fruits and vegetable may cause their aging and deterioration.

45.1.2 Loss of moisture:

Loss of moisture with consequent wilting and shriveling of produce is perhaps the most obvious way in which freshness is lost. When one realizes that most fruits and vegetable are compost of from 80 to 95% shrivel so readily. The relative humidity in the intercellular spaces of most plant tissue is continuously near 100% or saturated. produce will loss moisture to the surrounding air almost any time the humidity of the air is less than saturated and thereby deteriorate. 

45.1.3 Harvesting condition:

Harvesting fruits and vegetables when they are not in prime condition of maturity is another cause for deterioration in quality. Fruits and vegetables should be harvested at their optimum stage of maturity.

45.1.4 Handling:

Rough and careless harvesting and post harvest operation causing cuts, bruises and other damages is another important cause of deterioration. Fruits and vegetables are to be handling very carefully. It is said that they should be handled just like handling a new born baby and not like ‘hardware’. Physically damages have a major effect on quality and they provide entry to have a micro-organism causing deterioration and decay.

45.1.5 Post harvest diseases:

Deterioration due to decay is the greatest source of spoilage of fruits and vegetables. After harvest all fruits and vegetables covered with countless micro-organism, bacteria and mould spores. Some of which can cause decay under certain condition when added any sort of skin injury provides entry to these micro-organism causing decay into the fruits and vegetables, When these commodities are exposed to warm temperatures. Especially under humid condition, infection usually increases.

45.1.6 Pre-harvested factors: Length of storage, respiration, chemical composition, external appearance, anatomical structures, decay, taste quality and other post harvest behaviour and characteristics partly reflect certain pre harvest condition to which produce is exposed apart from variety and maturity. These pre-harvest condition may be grouped into, (a) environmental and (b) cultural factors

(a) Environmental: Temperature, relative humidity of the atmosphere, light ,soil texture, wind, elevation, and rainfall.

(b) Cultural: Mineral nutrition, soil management, pruning, thinning, chemical sprays, rootstock, density of planting, weeding, irrigation and drainage etc. These factors affect the attainment of maximum quality at the time of harvest. It is impossible, however to determined the relative contribution of each quality. Since the above factors are multifarious, some are controllable and some are not.

45.2 MATURITY STANDARD (HARVEST INDEX)

The quality of fruit and vegetables cannot be improved, but it can preserve after harvest, Good quality is obtained when harvesting is done at the proper stage of maturity. Immature fruits when harvested will give poor quality and no or erratic ripening. Similarly, Vegetables harvested early may give poor quality or poor yield. Immature tomatoes are more sensitive to physical damage, shrivelling, and decay. Delayed harvesting of fruits and vegetables reduce their quality increase their suitability to decay and hence low market value. In some cases for distance market, they are picked at mature but unripe stage thus difficulty arises in assessing the optimum maturity level for different fruits and vegetables. Maturity standard or the harvest index means standard or the fruit and vegetables if harvested should give optimum quality and yield. Often harvest indices become arbitrary and subjective. Hence the approach should be to combine several methods of assessing maturity.

(a) Visual methods: Skin colour, size, persistence of style, fullness of fruits etc.

(b) Physical means: Case of separation or abscission length, specific gravity, flavor.

(c) Chemical analysis: Solids, acids, solid to acid ratio, sugar, starch content.

(d) Computation: Days from bloom, heat units.

(e) Physiological method: Various physiological methods are described below:

1. Curing: - Under high temperature and humidity outer tissues developed wound periderm which acts an effective barrier against infection and water loss.          e.g. potato, onion and garlic. Potatoes are held at 18’C for 2 days and then at 7-10’C for 12 days at 90% R.H.

2. Degreening:- Process of decomposing green pigment in fruits usually by applying ethylene or other similar metabolic inducers to give a fruit its characteristic colour as preferred by consumers.

• It is applicable to banana, mango, citrus and tomato.
• The best degrening temperature is 27’C.
• Higher temperature delay degreening.
• Relative humidity should be 85-90% e.g.ethylene kerosene.
• Higher humidity cause condensation and slower degreening.
• Lower humidity cause shriveling and peel breakdown.

3. Precooling:- Precooling is a means of removing the field heat, It slows down respiration of produce, minimizes susceptibility to attack of micro-organism, reduces water loss.

4. Washing and drying:-

• This is done to improve their appearance prevent wilting and remove micro-  organism.
• Fungicides or bacteria are used in washing water.

5. Sorting and grading:-

• Immature disorder and badly bruised fruits and vegetables are sorted out.
• Grading is based on size, weight, colour and shape.

6. Waxing:-

Natural waxy layer of fruit and vegetables is properly removed by washing. Waxing means an extra discontinuous layer of wax applied artificially with sufficient thickness and consistency to prevent anaerobic condition within the fruit provides necessary protection against decay of organisms.

• It improves appearance of fruits and make more acceptable.
• It increases storage life at ambient temperatures.

Suitable fungicides should be added in wax emulsion to prevent micro-organisms.