Factors affecting γ-linolenic acid content in fermented glutinous rice brewed by Rhizopus sp.

Abstract

Fermented glutinous rice is a popular oriental food brewed by Rhizopus sp. in China. Although Rhizopus sp. Q303 can produce γ-linolenic acid (GLA), GLA content in fermented glutinous rice brewed by Xiaoqu of Rhizopus sp. Q303 greatly varied in terms of brewing temperature, from zero to 1.4±1.1% in total fatty acids, and less than that in mycelia of Rhizopus sp. Q303. This means apart from brewing temperature some other factors must be affecting GLA content in fermented glutinous rice. Further studies showed that fermented glutinous rice inoculated with spores of Rhizopus sp. Q303 contained about double the GLA than those with mycelia (4.3±1.6% compared to 2.2±0.9%). The optimal amount of inoculum was 4.90×10 6 spores/100 g cooked rice. The higher GLA content in the fermented glutinous rice was obtained when using spores as an inoculum from fresh culture before inoculation than that from culture preserved for 8 months in a refrigerator (4.3±1.6% compared to 1.4±0.7%). The optimal temperature for brewing was about 26°C. When the brewing temperature was 11°C, GLA content was no longer detected in fermented glutinous rice. GLA content plateaued between 36 and 60 h during brewing of fermented glutinous rice. Under optimal brewing conditions, GLA content in fermented glutinous rice was over 3 times that of the traditional Xiaoqu brewing process.