Optimization and Quality Evaluation of Rape Bee Pollen Jiaosu Fermentation by Candida apicola LGL-2

Using rape bee pollen as raw material, the Candida apicola LGL-2 selected from honey was used to investigate the effect of fermentation factors including fermentation time, fermentation temperature, inoculum amount and substrate content on the total phenolic content of rape bee pollen jiaosu. The fermentation process of rape bee pollen jiaosu was optimized by response surface methodology (RSM) using total phenolic content as the response variable. Based on these conditions, the phenolic compounds, volatile aroma components and antioxidant activities of rape bee pollen and jiaosu were further compared. The results showed that the optimal conditions for rape bee pollen jiaosu by Candida apicola LGL-2 were fermentation time 48 h, fermentation temperature 30 ℃, inoculum amount 20% and substrate content 30%, and the total phenolic content of rape bee pollen jiaosu was 11.48 mg GAE/g after fermentation. Phenolic compounds including gallic acid, p-coumaric acid, rutin, ellagic acid and quercetin were detected in rape bee pollen and jiaosu by high performance liquid chromatography (HPLC), and the contents of all the phenolic compounds above were increased after the fermentation by Candida apicola LGL-2. The volatile aroma compounds of rape bee pollen and jiaosu were analyzed by headspace solid-phase microextraction and gas chromatography-mass spectrometry (HS-SPME-GC-MS) combined with the relative odor activity value (ROAV). Twenty-six volatile aroma compounds were detected, 7 of which were identified as key aroma components of rape bee pollen jiaosu, and the contents of some alcohols and esters were enhanced to bring excellent flavor to jiaosu. Compared with rape bee pollen, rape bee pollen jiaosu exhibited stronger antioxidant activities as determined by DPPH·, ABTS⁺· and FRAP assay. These results indicated that fermentation by Candida apicola LGL-2 could effectively improve the phenolic content, flavor and antioxidant power of rape bee pollen.