Studies on Off-flavor Formed during Heat Processing of Satsuma Mandarin Juices (II)

Hydrogen sulfide and dimethyl sulfide (DMS) have been investigated as to the off-flavor produced by heating Satsuma mandarin juice. Both compounds increased remarkably with heating of the juice and amounted to approximately 300 ppb and 560 ppb, respectively, at 100°C in 8 hours. Hydrogen sulfide viras detected in all eight varieties of citrus juices, while DMS was detected in Satsuma mandarin and Valencia juices and not detected in others. DMS from Valencia was much less as compared with Satsuma mandarin. pH, heating temperature and the cationic fraction were examined as factors on DMS production from Satsuma mandarin juice. The amount of DMS increased with an increase in pH and heating temperature. DMS was not produced by heating Satsuma mandarin juice free from the cationic fraction. However, DMS was produced by heating the cationic fraction alone. It is apparent that the precursor of DMS occurs in the cationic fraction. In amino acid analysis of several varieties of citrus juices proline was commonly the major amino acid. Sulfur-containing amino acids such as cysteine and methionine little changed in Satsuma mandarin juices before and after heating.