Off-flavor of Stored Satsuma Mandarin (Citrus unshiu Marc.) Fruit

Abstract

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.