Characteristics of Onion under Different Process Pretreatments and Different Drying Conditions

Abstract

Introduction: Onion (Allium cepa) is an important spice crop often grown outdoors in temperate climates as an annual crop because of its adaptability to varying weather conditions. It is an underground vegetable which varies in size colour, firmness and strength of flavour. Onion is often called "poor man's orange" because it is a good source of vitamins, particularly Vitamin A and C. It is also a rich source of minerals such as iron, thiamine, niacin and manganese contents. Onion is said to be very useful against heart diseases and many bacterial species including bacillus subtilis, salmoneva, and E. coli. This vegetable crop is highly perishable in its natural state after harvest resulting in huge postharvest losses during storage, transportation and marketing in the production season and extreme scarcity in the off-season which can be checked by drying. Material and methods: The main materials used were 192 samples of pre-treatment and 10 samples of untreated (control) fresh onion. Others equipments used were temperature controlled dryer, sensitive weighing balance, water baths (Shell Lab Model and HH-W420, XMTD-204 Model), thermo-hygrometer, desiccators, desiccants, stop watch, onion slicer, stainless tray, foil wrap, conical flask, measuring cylinder, NaCl and distil water. Agarry and AOAC methods were used for quantitative analysis and nutritional analysis respectively. Statistical analysis of all data obtained was done. Results: Results showed that drying rate, water loss, solid gain, vitamin C, manganese and iron contents varied with different levels of OSC, OPD and OST at p≤0.05. However, drying rate, water loss, solid gain and all the quality parameters were influenced by all the process parameters. Where; OSC=Osmotic solution concentration OST=Osmotic solution temperature OPD=Osmotic process duration Conclusion: Osmotic dehydration pretreatments had significant effect on process outputs (drying rate, water loss, solid gain, vitamin C, manganese and iron contents of onion).