LOW-COST GREENHOUSE TECHNOLOGY FOR DRYING ONION (ALLIUM CEPA L.) SLICES

Abstract

The performance of the greenhouse solar heat collector was highly dependent on the solar radiation, ambient temperature and relative humidity. Increase in air temperature inside greenhouse varied from 0.7 to 19.0C, and relative humidity inside greenhouse varied from -16 to 25.7% by air exchange at a flow rate of 6.1 m3/s. The average midday thermal efficiency was around 20.82%. The cured red onion (Allium cepa L.) bulbs were cleaned, outer layer was peeled and trimmed manually, and washed in water to remove dirt and infection. Edible bulb of onion was sliced into 3-mm thick slices by using manual stainless steel slicer. The onion slices were pretreated with sodium chloride, and potassium metabisulphite, for 5 min in three concentration levels (0.25, 0.50 and 0.75%) and drained onion slices were spread in thin layers in trays before keeping them in greenhouse for drying. Onion slices were dried in 19 sunshine hours. Preservatives used as pretreatment in 3-mm sliced onion were found to be significantly different (probability, P < 0.05) from each other. It was found that 0.50% potassium metabisulphite was best.