Investigating qualitative parameters and antioxidant activity of phenolic compounds extracted from canola meal using solid-state fermentation by Aspergillus niger

Canola meal was solid-stately fermented (SSF) by Aspergillus niger CBS 120.49 to increase its total phenolic content (TPC) and 1,1-Diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity. In order to obtain this purpose, 90 subfractions of canola meal were fermented at different moistures content (MC) of 40, 50, and 60% and different temperatures of 25, 30, and 35 ºC, followed by extraction within 5 days. Results showed that subfractions with 40% MC at of 30 ºC and 35 ºC with growth of 2982 and 2988 mg/100g had the most TPC in day 5. Moreover, SSF samples with 40% MC and at 35 ºC showed the highest (86.7%) DPPH radical scavenging activity. HPLC analysis showed that some free phenolic acids of SSF-treated samples increased approximately by 4-10 folds as compared to unfermented samples. A significant increase about 120-133 ppm in syringic acid content was found in fermented samples at MC of 40% and temperatures of 30-35 ºC compared to its trace amount in unfermented samples, which is probably due to bioconversion of sinapic acid.  It turned out that, a large amount of insoluble phenolic compound of canola meal, treated by Aspergillus niger at 5 day SSF, would be released in the form of free acids significantly compared with unfermented sample.