Effect of drying temprature, varieties and storage period on Physicochemical quality, functional properties and sensory Acceptability of dried onion powder

Abstract

In Ethiopia, onion is one of the most important vegetables produced mainly as a source of cash income and for flavoring the local stew ‘wot’. The excess production of onion results in a glut in the market and reduction in onion prices. Moreover, marketing of fresh onion during the harvesting season is a great problem because of its shorter postharvest shelf life as well as lack of appropriate processing and preservation techniques, its postharvest lose is significant. Therefore, this study was initiated to investigate the impact of temperature and storage period on quality and storage stability of different oven dried onion varieties. Three different onion varieties were procured from Zeway (Sweet carolin, Bombay red and Qellafo) and subjected to five levels of drying temperature (50, 60, 70, 80 and 90o C) in CRD. For quality evaluation, physical and functional parameter (colour, rehydration ratio, shrinkage ratio, bulk density and water activity), chemical parameter (total soluble solid, titratable acidity, pH, vitamin C, pyruvic acid, moisture, ash and fiber) and sensory quality were analysed. The result indicated that the values of total colour change and functional prosperities increased with increment of drying temperature. Chemical quality such as vitamin C and pyruvic acid were highly degraded at high oven drying temperature. Qellafo onion variety dried at 50o C had higher vitamin C, pyruvic acid and fiber. From sensory quality, the maximum average of overall acceptability was recorded from Qellafo onion variety dried at 50o C followed by Bombay Red onion variety. Storage stability study of onion powder was performed for a period up to 90 days. For this purpose, based on analyzed physicochemical and sensory quality; three temperatures were selected (50, 60 and 70o C). The results showed that total color change, water activity, moisture content, titratable acidity and total plate count increased with increasing of storage period; whereas, vitamin C and pyruvic acid decreased during storage period. Generally the best quality of onion powder obtained at 50o C though microbial loads were higher after storage. In general, the present finding showed that the best quality of onion powder was obtained from Qellafo onion variety dried at 50o C. Furthermore, the best microbial quality of onion powder was obtained at 70o C. Therefore, further research should be done using different packaging materials and storage condition to give conclusive recommendation about quality profile of the studied onion varieties under different drying temperature along with best shelf life.