Nutritional Quality Evaluation of Stored Onion (<i>Allium cepa</i> L.) Powder in Transparent and Amber Coloured Jars

Abstract

This study investigated the proximate compositions, microbial counts and total polyphenols content of onion powder stored at ambient temperature for six months in transparent and amber coloured jars. Standard methods of Association of Analytical Chemists (AOAC), American Public Health Association (APHA) were used to evaluate the proximate composition and microbial count of the powder while the Folin-Ciocalteu method was used to assess total polyphenols during and after storage. There were significant (p < 0.05) differences in the total polyphenol (TP) contents and proximate composition of onion powder stored in amber and transparent jars. Total polyphenol contents of the onion powder decreased from an initial value of 14.60±1.08 mg/g GAE to a final value of 5.92±0.76 mg/g GAE in the amber coloured jar after storage while a final value of 1.64± 0.78 (mg/g) GAE was evaluated after storage in the transparent jar. From proximate compositions, only crude protein, fibre and moisture contents increased during and after storage in both storage jars. There was more retention of proximate parameters in the content of amber storage jar during and after storage. Microbial colony counts in onion powder in the amber jars were fewer than in the transparent jars during and after storage. To minimize wastage of onion during glut season, onion should be made into powder form and better stored in amber coloured material for better retention of nutritional qualities prior to use at home or industry.