Effects of Heat Treatment on the Quality of the Onion Juices Prepared with Sulfur-applied Onions
2014
Choi, B.G., Kangwon National University, Chuncheon, Republic of Korea | Surh, J.H., Kangwon National University, Chuncheon, Republic of Korea
Onion juices were prepared by various heat treatments (at 105-120oC for 4.5-5.5 h), from the onions cultivated with increasing numbers of sulfur applications (once for Sulfur-1, four times for Sulfur-4). As heat treatment intensity increased, the onion juices darkened (p0.001), which adversely affected the sensory preference. In addition, increasing the heating temperature significantly increased the organic acid content of onion juices (p0.001), and therefore, decreased pH (p0.001). Heat intensity did not affect the thiosulfinate content of onion juices, suggesting that the rate of decomposition of thiosulfinate into low-molecular weight sulfur derivatives is similar over the temperature range of 105-120¡�. Total flavonoids were higher in onion juices derived from Sulfur-4 than in Sulfur-1 onions, and increased with heat treatment intensity (p0.001). These results indicated that heat-facilitated conversion of bound forms of flavonoids to their free forms increases the extractability of flavonoids from onions.
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