Value-added Onion Powder Production from Rejected Onions from San Pa Tong Onion Grower's Co-operatives Limited Mae Wang District, Chiang Mai Province

Abstract

The onion (Super Rex) studied was grown in  Mae Wang district, Chiang Mai Province. The onion bulb  was  approximately 7 – 9 cm in diameter  with brown dry outer shell, fresh weight of 282.78 ± 38.95 g per  bulb  and moisture content of 92.56% and total solid of 7.44%. The thickness of 1 cm of both ends of the onion bulbs were trimmed. Then bulbs were cut in halves, then lengthwise in slices of  2 – 5  mm, thickness after the removal of the core. The onion slices were dried at  60 °C  for 6 hours. The dried sliced onion had the moisture content  of 4.53 ± 0.07% with water activity of 0.304  ± 0.001. The dried sliced onion were finely ground to powder. The properties of onion powder included  moisture content of 5.28 ± 0.00%, color: L* 90.9 ± 0.1, a* -5.1 ± 0.6 and b* +22.4 ± 0.6, water activity 0.305 ± 0.012, flavonoid and phenolic contents of 10.59 ± 0.59 mg quercetin/g and   4.37 ± 0.14 mg GAE/g, respectively.The onion powder had total sugar of  737.93 ± 12.92 mg/g, its ability to dissolve in cold water was 27.7 ± 1.2% and in hot water 32.0 ± 1.7%. The onion powder was packed in foil bags and stored for 80 days at  4 ± 1 °C. The results showed  water activity increased from 0.305 ±  0.012 to 0.340 ± 0.032, flavonoid decreased from 10.95 ± 0.59 to 8.79 ± 0.32 mg quercetin/g. The onion powder storedat ambient temperature of 26 ± 1 °C for 80 days turned more yellowish than onion powder that stored at 4 ± 1 °C. The actual cost of onion powder is 268.88 baht per 80 g.