Effects of microwave irradiation on the distribution of sinapic acid and its derivatives in rapeseed and the antioxidant evaluation

The purpose of the study was to observed the effect of microwave irradiation on the distribution of sinapic acid and its derivatives in hull, endosperm, cotyledon and entire rapeseed. Meanwhile, total phenolic conetent, DPPH and FRAP scavenging capacity of rapeseed were evaluated. Eight main sinapic acid derivatives including sinapine (SP), sinapoyl-glucoside (SG), quercetin-sinapoyl-di-hexosepentose (QSDG), sinapic acid (SA), sinapoyl-malic acid (SM), disinapoyl gentiobioside (DSGG), sinapoylcholine thiocyanate-glucoside (SPTG) and canolol were confirmed in rapeseed by using UPLC-QTOF-MS/MS. After microwave irradiation, canolol in hull, cotyledon, endosperm and whole rapeseed increased by 11.1, 90.0,49.8 and 67.4 mg/100 g, respectively. SP in cotyledon, endosperm and whole rapeseed decreased by 15.9%, 29.1% and 22.1%, respectively. No direct connection was found between canolol formation and sinapine pyrolysis. SG, SA, SM, DSGG and SPTG in endosperm, cotyledon and entire rapeseed decreased significantly except for QSDG. There was no significant different in total phenolic content, DPPH and FRAP scavenging capacity before or after microwave. SP and SA exhibited similar DPPH and FRAP scavenging capacity which were stronger than others. These results indicated microwave irradiation affects the distribution of sinapic acid and its derivatives and contributes to the formation of canolol in rapeseed.