Pre-Storage Treatments. Next. Introduction. Pre storage treatments are the treatments given to a commodity (fruits and vegetables in present context) generally after harvesting to reduce postharvest losses, enhance storage life and retain quality.
Introduction Pre storage treatments are the treatments given to a commodity (fruits and vegetables in present context) generally after harvesting to reduce postharvest losses, enhance storage life and retain quality. Some of the important pre storage treatments are : Cleaning, Washing, Sorting, Grading, Waxing, Packing, Pre cooling, Curing, Desapping, Chemical treatments, Irradiation, Vapour heat treatment
1. Cleaning This is a treatment given to remove adhering dust, dirt, extraneous matter, pathogenic load etc. from the surface of a commodity. Cleaning basically sanitizes the produce and avoid entry of undesirable contents to enter the packaging and storage line. Cleaning is a broader term and includes, dusting, washing etc. Methods of cleaning i. Dry method (Dusting etc.) ii. Wet method (Washing)
i. Dusting This method is mainly used to remove the adhering soil, etc from commodity i.e. potato, root vegetables, carrot, radish etc. Dusting helps to shed undesirable load (weight) of the commodity and thus reduce transportation cost. It also removes pathogenic microorganisms present in the soil from the surface of the vegetables. ii. Washing This method is used in most fruits and vegetables. Washing is done at the pack house through automated washing system fitted with overhead sprayers and smooth rotating brushes to clean and wash the fruits. Washing with clean water mixed with a neutral detergent such as Teapol, Sandovit or Indtron at 0.1% (1 ml / litre of water) is effective. The process of cleaning and washing will take 3-5 minutes. The temperature of water should be at room temperature (270C).
2. Sorting and Grading This may be done manually or by using a machine. Fruits are graded on the basis of their colour, size and weight and sorted for freeness from damage/ diseases. At the sorting and grading table, trained workers wearing gloves sort out the oversized and undersized fruits, immature/scarred/blemished fruits, diseased/insect damaged fruits and as well as fruits with sap injury (in mango) under the supervision of quality supervisor. The segregated fruits in the grader machine kept in plastic crates are removed at the end each working shift from the process area and are distinctly labeled for disposal.
3. Waxing / Coating It is the process of applying wax on the surface of commodity by spraying, dip or immersion, brushing, fogging or foaming. Some fruits develop natural fruit wax on their surface at the time of maturity. i.e. plum, apple, citrus, grapes etc. This has its role in reducing water loss fro the commodity and thus reducing shriveling and weight loss. While handling care is taken to touch the fruits as minimum as possible to retain as much of the natural wax (also called bloom) on the fruit. Types of waxes: Paraffin wax, carnauba wax, bee wax etc Examples of some commercial formulations: Tal-Prolong, Semper Fresh for apple, Frutox, Waxol, Nipro fruit wax for apple, and citrus, Ban seel for banana, Nu-coat flo for citrus, Brilloshine L for apples, avocado, melons
Advantages of waxing: • Improve appearance of fruit • Reduce moisture loss by 30-50% and retards wilting/ shriveling • Heals minor injuries • Protects fruits from minor infections • Provides modified atmosphere and increase shelf life • Acts a carrier for various chemicals etc
4. Pre-cooling • It is the prompt cooling of the commodity immediately after harvest (generally within 24 hrs of harvest), to its safe storage temperature , which aims at removal of field heat. • Rate of cooling depends on • Initial product temperature • Rate of flow of cooling media around the commodity • Temperature difference between produce and cooling media • Thermal conductivity of produce • There are different cooling methods followed for different commodities. Some fungicides may be mixed in water during hydro-cooling to reduce decay incidence Weight loss during forced air cooling can be reduced by maintaining high (95%) relative humidity in the pre-cooling chamber
5. Chemical treatment • Various chemicals are applied to fruits and vegetables in order to control postharvest diseases and pest infestations. • Methods of application of chemicals • Dipping: The commodity is immersed in water containing appropriate concentration of chemical which is toxic to the pathogen. However, the concentration of chemical should not be toxic to the fruit/ vegetable and should not endanger public health. For improving the efficacy of the dip treatment and better surface coating some wetting agents may also be added. The effectiveness of the fungicidal solution may also be enhanced by hearting the water in which the fruit is being dipped. 500 ppm of benomyl in water at 50-55 min, for 2 to 15 min is effective for controlling anthracnose in mango without damaging the fruit.
Methods of application of chemicals (-cont-) • ii. Cascade application: Commodity is passed below a shower of shower of diluted chemical. • Electrostatic sprays: Applying the chemical as a spray but producing very fine particles and then charging them in an electrostatic sprayer so that they readily stick to the commodity underneath them. The fine droplets of chemical solution have same charge and thus they repel each other and are attracted towards earth during field sprays. • Dusting: Active chemical is diluted with an inert powder i.e. talc for uniform application and reduced wastage. • Fumigation: Sulphur dioxide fumes are sued for controlling postharvest diseases in grapes. • Chemical pads: Paper pads impregnated chemical are used for wrapping the fruits and vegetables and control postharvest diseases.
6. Curing It is technique where the commodity is left in the field itself in a heap under shade for few days. It is an effective operation to reduce water loss during storage from hardy vegetables viz., onion, garlic, sweet potato etc. In case of onion curing is a drying process intended to dry off the necks and 2-3 outer scales of the bulbs to prevent the loss of moisture and the attack by decay during storage. The outermost layer, which may be contaminated with soil, usually falls away easily on curing. The dry under-layer should have an attractive appearance. Onions are cured generally when they have lost 3 to 5% of their weight. Generally, are dried in the field by stacking in a warm, covered area with good ventilation. However, in cool and moist climates, onions are cured with artificial heat blown through a duct at 30oC. Onions can also be cured by tying the tops of the bulbs in bunches and hanging them on a horizontal support of pole, wire etc. pole in a well-ventilated and shaded place. Curing in shade improves bulb colour.
The essential conditions during curing are: • Heat (~ 30oC) • Good ventilation • Low humidity
7. Irradiation • Irradiation is a treatment given to various fruits and vegetables to control different postharvest diseases and disorders. Fruits are exposed to various doses of electromagnetic radiations for small durations (few sec to few min.) of time under highly controlled conditions. The unit for measuring radiation dose is Gy or rads. It is very effective treatment but in many of the cases, the technology of irradiation finds a limited commercial application due to the following reasons • either some cheaper and more effective alternatives are available • the irradiation treatment leaves undesirable effect on the produce and cause abnormal ripening.
8. Vapour heat treatment This was developed to control infections of fruit flies in fruits. The treatment consists of stacking the fruits in boxes in a room which is heated and humidified by injection of steam. The temperature and exposure time may be adjusted depending upon the stage at which the fly is to be killed i.e. egg, larvae, pupa or adult. The most difficult stage to control by VHT is larval stage as the insect goes further into the fruit and away from the surface thus requiring high temperatures for short time. Generally the treatment of citrus, papaya, mango or pineapples may be given at 43o C in saturated air for 8 hrs followed by maintaining the temperature for further 6 hrs.
8. Desapping Desapping of mango fruits is carried out in processing area by trained workers under the supervision of processing supervisor. Desapping is done by holding the mango fruits upside down while cutting the stalk of fruits. The stalks of mango fruits are cut very carefully to 0.5 to 1.0 cm by trained workers by using a scissor with sharp long nose to avoid causing skin injury. For exports, the pedicel of the fruits is cut approximately at a length of 1 cm from the fruit with the help of sharp scissors and fruits are kept up side down in special knitted pallets, for two hours so that the latex flows out from the fruit completely. Care should be taken that the latex drop does not fall on the fruit.
Let us sum up • Pre storage treatments are the treatments given to a commodity (fruits and vegetables in present context) generally after harvesting to reduce postharvest losses, enhance storage life and retain quality. • Cleaning removes adhering dust, dirt, extraneous matter, pathogenic load etc. from the surface of a commodity. Dusting, washing etc. are methods of cleaning. • Fruits are graded on the basis of their colour, size and weight and sorted for freeness from damage/ diseases. Waxing is the process of applying wax on the surface of commodity by spraying, dip or immersion, brushing, fogging or foaming. • Pre-cooling is the prompt cooling of the commodity immediately after harvest (generally within 24 hrs of harvest), to its safe storage temperature , which aims at removal of field heat. • Chemicals are applied by spraying, dusting, dipping etc. for reducing disease incidence during storage. Irradiation is application of radiation under controlled conditions. For reducing incidence of disease or disorders.