Abstract
Browning of onion juice by heating was investigated. Raising of the temperature and pH (range: pH 3-8) enhanced the browning reaction. Addition of Fe3+ and Cu2+ to the onion juice enhanced the browning reaction, whereas Mn2+ and Zn2+ retarded it. Several components assumed to be involved in the browning reaction of onion juice were determined. Total free sugar, total free amino acid, and ascorbic acid contents were decreased, whereas reducing sugar, reductone, and 3-deoxyglucosone contents were increased in the course of heating. These results suggest that the heat-induced browning reaction of onion juice is not ascribable to an enzymic reaction, but to a nonenzymic reaction, i. e. degradation of sugars and/or reaction between sugars and amino acids.
