Effects of “nine steaming nine sun-drying” on proximate composition, oil properties and volatile compounds of black sesame seeds

•The effect of traditional processing technique “nine steaming nine sun-drying” on black sesame seeds (BSS) was evaluated.•The effect of processing on proximate composition, oil properties and volatile compounds and were determined.•SPME-GCMS analysis showed that the main volatile compounds in BSS were aldehydes, hydrocarbons and alcohols.•Based on the PCA results, processed BSS after third cycle were perceived as possessing similar quality variables. Black sesame seeds (BSS) were processed by nine cycles of steaming and sun-drying, and the chemistry of their resulting products studied. That is, the shell color and structure, proximate composition, oil properties and volatile compounds of raw BSS were determined and compared with processed BSS. Various levels of shell color change and structure damage were observed. The proximate composition also differed, whereas the relative proportion of fatty acids and oil properties were unchanged. SPME-GCMS analysis revealed that aldehydes, hydrocarbons and alcohols were the main volatile compounds. And compared with raw BSS, four volatile substances were newly detected in the processed BSS. Principal component analysis (PCA) displayed the overall difference between samples and showed that repeated steaming and sun-drying process had a significant impact on the chemical composition of BSS.