The nature of off-flavor occurring in stored satsuma mandarin (
Citrus unshiu Marc.) fruits was investigated with reference to the accumulation of ethanol and volatile sulfur compounds in the fruits.
The fruits were stored at 1°C, 6°C, ambient temperature (10°C±2°C) and 20°C, respectively. Part of them were transferred every one month to the elevated temperature at 20°C with and without hermetical packaging in polyethylene bags (0.03mm thick.).
In juice extracted from the fruits stored at above 6°C, ethanol concentration showed a little change during 2 months and a considerable increase after 3 months, while it decreased in the fruits at 1°C. When the fruits were packaged and transferred to elevated temperature, the ethanol concentration increased rapidly. The behavior of ethanol, however, did not coincide with the occurrence of off-flavor or off-odor.
The volatile sulfur compounds were analyzed with gases taken from cavities of fruits as well as head-space of containers in which juice was sealed, using gaschromatography equipped with flame photometric detector. A single peak was found on the chromatogram, and it was identified as DMS (dimethyl sulfide).
The DMS in cavity accumulated notably in fruit stored at 20°C after a month, and it decreased as the storage temperature lowered. When storage was extended by 2-3 months, the DMS concentration decreased in the fruits stored at 20°C and ambient temperature, while it continued to increase at 6°C. When the stored fruits were transferred to elevated temperature, the DMS concentration increased rapidly regardless of with or without packaging. In the fruits stored at 1°C, however, the increase of DMS was suppressed and the effect became conspicuous when storage was extended by 3 months.
It seems that DMS accumulated over a some level in fruit, about 0.5 ppm, is responsible for off-odor felt as fruit is peeled, but not for off-flavor felt as fruit is eaten.
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