Post harvest management and value addition of onion
- 1. Dr. R. T. Patil Director, Central Institute of Post Harvest Engineering and Technology, Ludhiana Post Harvest Management and Value Addition of Onion
- 2. Introduction • The annual average world production is at around 72 million metric tones. • China is the leading producer and the other major onion producing countries are India, United States, United Arab Republic, the Netherlands, Japan, Brazil, Bulgaria, Spain, and Italy. • In the international trade, these countries play an important role in exporting the onions contributing 74.6% of the total export (FAO 2008).
- 3. Characteristics • Onion is a short term crop with less pay-back period. • Onion is highly perishable and therefore high post harvest losses occur during transportation and storage. • Onion are also grown in large quantity in developed countries and they have better quality and longer storage life
- 4. Production & Utilisation • Onion (Allium cepa) is an important export- oriented crop of our country. • Both immature and mature bulbs are used as vegetable and condiment. • The cultivation of onion is done at different times throughout the year in different parts of the country. • The crop comes to the market three times in a year Rainy Kharif 20%, Late little rainy Kharif 20% and Rabi 60% (April-May)
- 5. Nutritional and Medicinal Importance • Onions (Allium cepa L.) are grown as vegetable as well as spice. • They are highly valued for their flavour and for their nutritional value in supplying minor constituents such as minerals and trace elements. • It contains vitamin B and a trace of vitamin C and also traces of iron and calcium. • The outstanding characteristic of onion is its pungency, which is due to a volatile oil known as allyl-propyl disulphide.
- 6. Medicinal Effects • Onion can lower blood lipids and prevent hardening of arteries. • It contains selenium that can induce the human body to release large amounts of glutathione which lowers the occurrence of cancer. • Onion flavonoids have antidiabetic, antiaging, and bacterial-inhibition effects. • Presence of several sulphur compounds makes it antiseptic. Onion paste is reported to be effective for external applications in case of insect bites. • Onion is said to possess stimulant, diuretic and expectorant properties and hence useful in flatulence and dysentery. • High amounts of sulphur in onions make them particularly effective in regenerating hair follicles and stimulating hair regrowth
- 7. Pre-harvest Operations • The post-harvest technology combined with pre-harvest factors determine the shelf-life. • Restriction on use of excessive and delayed nitrogen application (not exceeding 100 kg/ha under normal fertility condition and application of N in 2-3 splits within 60 days of transplanting), use of ammonium sulphate instead of urea for top dressing, more use of organic manures to fulfill nutritional requirement, use of vermicompost, neem cake etc. have also showed encouraging results. • Similarly last irrigation given 10-15 days before harvesting reduces microbial losses in stored onions compared to withholding of irrigation before five days.
- 8. Pre-harvest Sprays • Pre-harvest pesticides sprays of 0.02% streptocyclin and 0.1% carbendazim ten days before harvesting. • Application of thiophanate methyl @ 0.1% + streptocyclin or klorocin @ 0.2% + ekalux @ 0.25% immediately after neck cut and combined with field and shade curing is promising under North Indian conditions • Use of maleic hydrazide @ 2000-3000 ppm 75 days after planting for kharif onions and @ 2500 ppm combined with 0.1% carbendazim spray 10 days before harvesting in rabi onions gives better post harvest storage.
- 9. Harvesting • Stage of harvesting also determines the shelf-life of onions • Storage losses at optimum maturity are normally lower than those harvested before the tops collapse. • Harvesting one week after 50% neckfall and field curing by windrow method for 3- 5 days till foliage turn yellow is recommended.
- 10. Curing • Single most important post-harvest treatment required for the long storage . • Curing is a drying process intended to dry off the necks and outer scale leaves of the bulbs to prevent the loss of moisture and the attack by decay during storage. • The essentials for curing are heat and good ventilation, preferably with low humidity. • Shade curing for 10 days is optimum to eliminate the chances of microbial infection in storage. • Curing of kharif onions in sun or solar dryer with foliage and storage with dried foliage is better • Curing in perforated crates with forced air circulation is recommended for rabi onions. • Bulbs cured artificially for 16-20 h were ready for market or further storage compared to 8 – 10 days (240 h) in traditional sun curing (Centre of AICRP on Post Harvest Technology). • Artificially cured bulbs could be stored at ambient conditions for 30 days with a maximum weight loss of about 10.5%
- 11. Grading • The outer dry scales usually rub off during the grading process, giving the onions a better appearance for market. • It has been experienced that if storage is arranged after proper sorting and grading losses in storage are reduced. • For local market the onions are graded based on their size. – Extra large onion (>6 cm dia.) – Medium (4-6 cm dia.) – Small (2-4 cm dia.)
- 12. Irradiation to Improve Shelf- life • Exposure of onion bulbs after harvesting with 60-90 Gy inhibit their sprouting regardless of crop season, environmental condition and type of storage. • However, to reduce the microbial and other losses, combined use of irradiation with improved storage and providing the irradiation facilities at production level may be considered.
- 13. Characteristics of Good Onion • be reasonably uniform in shape, size colour and pungency of the variety /type • be mature, solid in feel, reasonably firm with tough clinging skins. • be throughout cured and dried. • be free from dust and other foreign material. • be free from defective, diseased, decayed and damaged bulbs caused by seed stems, tops, moisture, dry sun scald burn, sprouting, mechanical or other injuries and staining. • be free from moulds, soft rot and insect attack. • % of seed stem or bolted bulbs shall not exceed 20% in Nasik kharif onions.
- 14. Graders for Onion • The drudgery of human labour involved for grading of onion has been reduced by hand operated as well as motorized onion grader developed by NRCOG, PUNE. • The cost of grading with machine is around Rs. 26/t as compared to Rs. 80/t in hand grading. • The precision of grading achieved by grader is 98% as against 50% in hand grading.
- 15. Packaging • For safe handling, 40 kg open mesh jute bags having 200-300 g weight should be used in domestic market. • For export, common big onions are packed in 5-25 kg size open mesh jute bags. Bangalore Rose and multiplier onions are packed for export in 14-15 kg wooden baskets. • Nylon net bags, when used for packing have resulted in less storage loss because of good ventilation.
- 16. Handling • Bulbs intended for storage must be free from cuts and handled with extreme care. • Onions should not be dropped on to non-resilient surface from more than 6 feet height. • If onions are to be stacked after packing in store or trucks, the better height is 2-2.5 metres.
- 17. Storage • Onions should not be stored unless adequately dried either in the field or by artificial means. • It is necessary to dry the neck tissue and outer scales until they rustle when handled otherwise the bulbs will rot in storage. • Sprouting in onion is controlled by temperature. The temperature between 10-25°C increases sprouting. • Rooting is influenced by relative humidity (RH). More the relative humidity more is rooting. • Weight loss is more when temperature is above 35°C. • Under ambient conditions the onions are stored at a temperature of 30-35OC with RH of 65-70%. • In cold storage, temperature is maintained at 0-2°C while the RH is kept at 60-75%. • Onions are stored in these sheds by spreading them on dry and damp proof floor or racks. Periodical turning of bulbs or removal of rotten, damaged and sprouted bulbs should be done. • Well-ventilated improved storage structures with racks or tiers having two or three layers of bulbs would be desirable for proper storage.
- 18. Good Storage Practices • Construction of storage godown should on raised platform • Use of appropriate roofing material to prevent built up of high temperature inside. • Increased centre height and more slope is better for air circulation and preventing humid microclimate inside godown. • Bottom ventilation for free and faster air circulation to avoid formation of hot and humid pockets between the onion layers. • Avoid direct sunlight on onion bulbs to reduce sunscald, fading of colour and quality deterioration. • Restriction on width of each stack to 60-70 cm for cool humid weather, 75-90 cm for mild and humid weather and 90-120 cm for mild and dry weather conditions • Restriction of stacking height to 100 cm for small and multiplier onion and hot weather and 120 cm for mild weather and for big onion to avoid pressure bruising. • Cubicles should be made instead of continuous stack leaving sufficient space for ventilation from all the sides. • One cubic meter area of store accommodates about 750 kg onions.
- 20. Dehydration / Drying of onions• The desirable traits for dehydration are white colored flesh, full globe to tall global shape of bulbs with 5 to 6 cm in diameter, solids content around 15%; • After removing the tops, roots and outer skin onions are washed thoroughly and then cut into slices 3-6 mm thick with a rotating slicer or bread slicing machines. • After cutting onion slices are carefully washed. Blanching is not practiced, as the onion loses its flavor. • The slices are dehydrated in a tray, cabinet, tunnel type or conveyor belt type drier. The onions are dried when the ratio of prepared raw material to drier product is about 9:1 (moisture content about 5%). • Dehydrated onion has a storage life of about 12 months. • Care is taken during dehydration to insure minimal powder production because of its low value. • Screening, grinding and packaging operations are carried out in special dehumidified rooms (Below 30% RH ) because of hygroscopic nature of the dried onions. • A batch of 50Kg sliced onion takes about 8-9 hours drying time in tray drier and 16-18 sunshine hours in greenhouse drying. The onions are then milled into sliced, large chopped, chopped, ground, granulated and powdered onions.
- 21. Value Added Products • Onion salt is prepared by mixing 19 to 20% onion powder with 78% free flowing pulverized refined table salt and 1to 2% anti caking agent which prevents water absorption, caking, etc. • Onion juice is also gaining popularity. It has fresh characteristic flavour of onion because it is not subjected to high temperature at which thiosulphates (primary products associated with onion flavour) dissociate resulting in cooked onion flavour. • Natural dye-The pink colored peel in the onion is also an excellent natural dye. It gives fast colour on cotton, silk and woolen fabrics. • Onion pickle-Peeling, Blanching for 5 minutes, Filling blanched onions in a jar, Addition of salt, Standing for 24- 48 hours, Draining off water, Addition of vinegar and spices and Storage
- 22. Poly house solar dryer for onion
- 23. CIPHET Process of Mechanical Dewatering and Drying • In drying main expense is the energy used to reduce moisture content of onion. • As a rule of thumb, for each 1% reduction in feed moisture, the dryer energy input can be reduced by up to 4% (Bureau of Energy Efficiency, India 2004). • Process-The onions were washed, peeled and mechanically dewatered prior to drying with centrifugal juicer. • Effect of dewatering on energy consumed and quality parameters like pyruvic acid content, ascorbic acid content, sugar content, rehydration ratio, non enzymatic browning and color change were evaluated. • Partial mechanical dewatering resulted in as high as 60.98 % less consumption in energy than conventional method besides getting high value products i.e. onion juice and onion powder. • The optimum combinations are 60% dewatering and 60-70 C temperatures. • Onion juice was concentrated to 75% solids for increasing its shelf life. • Storage studies of onion powder showed that there has been no significant loss in quality even after 2 months storage at room temperature.