Harvest and Postharvest Technology PDF

HARVEST AND POSTHARVEST TECHNOLOGY TERMS ▪ Postproduction – Handling of products from harvest technology until these reaches the final consumer. ▪ Postharvest handling – Specific term used for the movement of commodities and operations through which a commodity undergoes from harvest to posse...

HARVEST AND POSTHARVEST TECHNOLOGY TERMS ▪ Postproduction – Handling of products from harvest technology until these reaches the final consumer. ▪ Postharvest handling – Specific term used for the movement of commodities and operations through which a commodity undergoes from harvest to possession of the final consumer ▪ Postharvest life – Duration of usability of the commodity ▪ Perishables – Food crops whose food value is maintained over a short period of time after harvest. ▪ Durables – food crops which can be maintained as food over a long period of time. ▪ Loss – decrease in quantity and quality of crops/products for human consumption TERMS ▪ Respiration – Biological process by which organic materials are broken down to simpler forms accompanied by the release of energy and heat. ▪ Relative Humidity – ratio of water vapor pressure in the air to the saturation vapor pressure at the same time temperature ▪ Ambient – ordinary room conditions of temperature and relative humidity ▪ Climacteric Fruits – those that can be ripen after being picked, produce much more ethylene than non-climacteric fruits. (e.g. Apple, Banana, mango, papaya, pear, apricot, peach, plum, avocado, cantaloupe etc.) ▪ Non-climacteric Fruits – which cannot ripen once removed from the plant (e.g. Citrus fruits such as grapefruit and lemon, berries such as raspberry, strawberry and cherry, pineapple, melon)  COMPARISON BETWEEN PERISHABLES AND DURABLES Perishables (Fruit, Vegetables, Flower, Durables Root Crops) (Cereals, Oilseeds) 1. High moisture content (75-95%) Low moisture content (10-20%) 2. Large units size (5g-5kg) Small unit size (16 weeks Nuts, dried fruits Principles of Harvesting Harvest should be completed during the coolest time of the day, which is usually in the early morning, and produce should be kept shaded in the field. The produce has to be handled gently Crops destined for storage should be as free as possible from skin breaks, bruises, spots, rots, decay, and other deterioration. Bruises and other mechanical damage not only affect appearance, but provide entrance to decay organisms as well. PACKING LINE POSTHARVEST HANDLING Is crucial in preventing further losses of produce due to deterioration and in preserving its quality. Primary processing ▪ Postharvest handling that will market the product suitable for consumers or to prepare it for further processing Secondary processing ▪ Postharvest handling that results in a product that cannot be subjected for another change – include food processing in food crops and industrial in non-food crops Transport Storage Marketing Customer POST-HARVEST STORAGE Produce (fruits, vegetables etc.) are marketable as long as they maintain their quality to a level that is acceptable by consumers. Thus, post-harvest storage technologies are aimed at maintaining the quality of vegetables a s long as possible. IMPACT OF TEMPERATURE ON POST-HARVEST LIFE OF PRODUCE Temperature is the single most important factor in maintaining quality after harvest. Refrigerated storage retards the following elements of deterioration in perishable crops: ▪ Aging due to ripening, softening, and textural and color changes; ▪ Undesirable metabolic changes and respiratory heat production; ▪ Moisture loss and the resultant wilting; ▪ Spoilage due to invasion by bacteria, fungi and yeasts; ▪ Undesirable growth, such as sprouting of potatoes  FRUITS AND VEGETABLES AS PERISHABLE PRODUCTS Key processes during the Post-harvest Life ❑ Respiration ❑ Transpiration ❑ Ethylene production ❑ Maturity process  IMPACT OF STORAGE TEMPERATURE ON RESPIRATION RATE One of the most important functions of refrigeration is to control the crop’s respiration rate. Respiration generates heat as sugars, fats, and proteins in the cells of the crop are oxidized. The loss of these stored food reserves through respiration means decreased food value, loss of flavor, loss of salable weight, and more rapid deterioration. The respiration rate of a product strongly determines its transit and postharvest life. The higher the storage temperature, the higher the respiration rate will be.  MECHANICAL DAMAGE DURING POSTHARVEST CHAIN ▪ the temperature - affects the degree of response/severity of mechanical damage. ▪ Compromise natural barriers -increasing water loses and pathogenic infections. Impact Respiration Ethylene Time  TEMPERATURE EFFECTS ON RESPIRATION RATE 30ºC At temperatures above the optimum, the rate of deterioration 20ºC increases 2 to 3 fold for every 10ºC rise in temperature. 10ºC High temperature-increases the transpiration rate. Time ❑ Respiration Factors affecting the Respiration Rates: External: ▪ Mechanical damage and product’s sanitary condition ▪ Temperature ▪ Atmosphere composition (< Oxygen and CO2 < respiration; > ethylene > respiration). ▪ Physical barriers (waxes, plastic films, etc.) ❑ Transpiration ▪ Loss of water of water, as vapor, from the product’s area exposed to the air, throughout the cuticle, lenticels, stomates, etc. it depends on: Internal Factors: ▪ Species and variety ▪ Type of tissue ▪ Integrity and sanitary product condition ❑ Transpiration External Factors: ▪ Relative Humidity ( transpiration). ▪ Temperature (> temperature > Transpiration) ▪ Air movement (increase the transpiration rate). ▪ Altitude (higher altitude < transpiration). ▪ Physical barriers (avoid air contact with the product-reduce transpiration rate). ❑ Ethylene production ▪ Climacteric fruits are sensitive to ethylene-produce larger quantities of ethylene in association with their ripening – (auto catalysis). ▪ Non climacteric fruits produce very small quantities of ethylene. At high concentration produce degreening and increase the metabolism. ▪ Leafy vegetables are highly sensitive to Ethylene (withering and yellowing)  RELATIVE HUMIDITY RANGES ❑ FRUITS : 85-95% ❑ DRY PRODUCTS : Onion and Pumpkin 70-75% ❑ ROOT VEGETABLES : Carrot, Radish 95-100% PRE-COOLING Pre-cooling is the first step in good temperature management. The field heat of a freshly harvested crop (heat the product holds from the sun and ambient temperature) is usually high, and should be removed as quickly as possible before shipping, processing, or storage. Most refrigerated storage rooms have neither the refrigeration capacity nor the air movement needed for rapid cooling. therefore, pre-cooling is generally a separate operation requiring special equipment and /or rooms. IMPORTANCE OF PRE-COOLING FOR DIFFERENT VEGETABLE SPECIES Rapid pre-cooling to the product’s lowest safe temperature is most critical for crops with inherently high respiration rates. These include artichokes, brussels sprouts, cut flowers, green onions, snap beans, asparagus, broccoli, strawberries, and sweet corn. Vegetables with low respiration rates include garlic, onions, potatoes (mature), and sweet potatoes. MOST COMMON METHODS OF PRE-COOLING 1.) Room cooling ▪ Produce is placed in an insulated room equipped with refrigeration units. ▪ This method can be used with most commodities, but is slow compared with other options. ▪ A room used only to store previously cooled produce requires a relatively small refrigeration unit. ▪ However, if is used to cool produce, a larger unit is needed. ▪ Containers should be stacked so that cold air can move around them, and constructed so that it can move through them. 2.) Forced-air cooling ▪ Fans are used in conjunction with a cooling room to pull cool air through packages of produce. ▪ Although the cooling rate depends on the air temperature and the rate of air flow, this method is usually 75-90% faster than room cooling. MOST COMMON METHODS OF PRE-COOLING 2.) Forced-air cooling ▪ Fans should be equipped with a thermostat that automatically shuts them off as soon as the desired product temperature is reached. 3.) Hydro cooling ▪ Hydro-cooling: Dumping produce into cold water, or running cold water over produce, is an efficient way to remove heat, and can serve as a means of cleaning at the same time. ▪ In addition, hydro-cooling reduces water loss and wilting. Use of a disinfectant in the water is recommended to reduce the spread of diseases. ▪ Hydro-cooling is not appropriate for berries, potatoes to be stored, sweet potatoes, bulb onions, garlic, or other commodities that cannot tolerate wetting. MOST COMMON METHODS OF PRE-COOLING 4.) Top or Liquid Icing ▪ Icing is particularly effective on dense products and palletized packages that are difficult to cool with forced air. ▪ In top icing, crushed ice is added to the container over the top of the produce by hand or machine. ▪ For liquid icing, a slurry of water and ice is injected into produce packages through vents or handholds without removing the packages from pallets and opening their tops. ▪ Icing methods work well with high-respiration commodities such as sweet corn and broccoli. 5.) Vacuum cooling ▪ Produce is enclosed in a chamber in which a vacuum is created. ▪ As the vacuum pressure increases, water within the plant evaporates and removes heat from the tissues. MOST COMMON METHODS OF PRE-COOLING 5.) Vacuum cooling ▪ This system works best for leafy crops, such as lettuce, which have a high surface-to-volume ratio. ▪ To reduce water loss, water is sometimes sprayed on the produce prior to placing it in the chamber. ▪ The primary drawback to vacuum cooling is the cost of the vacuum chamber system. CHILLING INJURY ▪ Many vegetables and fruits store best at temperatures just above freezing, while others are injured by low temperatures and will store best at 13 to 170C. ▪ Both time and temperature are involved in chilling injury. ▪ Damage may occur in a short time if temperatures are considerably below the danger threshold, while some crops can withstand temperatures a few degrees into the danger zone for a longer time. Occurrence of chilling injury ▪ Vegetables susceptible to chilling injury may look sound when removed from low temperature storage. CHILLING INJURY Occurrence of chilling injury ▪ However, after a few days of warmer temperatures, chilling symptoms become evident: Pitting or other skin blemishes Internal discoloration, Failure to ripen PREVENTING MOISTURE LOSS While temperature is the primary concern in the storage of vegetables and other perishables, relative humidity is also important. The RH of the storage unit directly influences water loss in produce. Water loss can severely degrade quality resulting in a wilt appearance of the produce. Water loss means salable weight loss and reduced profit. Most fruit and vegetable crops retain better quality at high relative humidity (80 to 95%), but at this humidity, disease growth is encouraged.  ADJUSTMENT OF RELATIVE HUMIDITY IN STORAGE ROOMS OF VEGETABLES The cool temperatures in storage rooms help to reduce disease growth, but sanitation and other preventive methods are also required. Maintaining high relative humidity in storage is complicated by the fact that refrigeration removes moisture. Humidification devices such as spinning disc aspirators may be used. OTHER ASPECTS RELATED TO POSTHARVEST STORAGE OF VEGETABLES / PERISHABLES Sanitation: Important to avoid infections by pathogens Ethylene: A plant hormone that accelerates the ripening process thereby reducing postharvest life. Modified atmosphere (MA): Reduction of O2 and increase of CO2 concentration in the storage room Controlled atmosphere (CA): Controlled modification of O2 (reduction) and CO2 (increase) concentrations in the storage room MODIFIED ATMOSPHERES Use of MA during packing is highly increasing. Usually designed to maintain 2% - 5% of O2 and 8% - 12% of CO2, extend shelf life of fresh-cut fruits and vegetables.  COMMERCIAL USE CA is used for transporting and storage of apples, pears, less used in kiwifruits, avocados, nuts, dry fruits and persimmon. MA- for long distance transport is used in mangoes, apples, bananas, avocados, plums ,strawberries, blackberries, peaches, figs, nectarines. Classification of horticultural crops according to their controlled atmosphere storage potential at optimum temperatures and relative humidifies Range of storage Commodity duration (months) More than 12 Almond, Brazil nut, cashew, filbert, macadamia, pecan, pistachio, walnut, dried fruits and vegetables 6-12 Some cultivars of apples and European pears 3-6 Cabbage, Chinese cabbage, kiwifruit, persimmon, pomegranate, some cultivars of Asian pears 1-3 Avocado, banana, cherry, grape (no SO2), mango, olive, onion (sweet cultivars), some cultivars of nectarine, peach and plum, tomato (mature-green)