Enzyme activities and volatile flavor compound compositions of tiger nut paste prepared using different fungal starter strains

Abstract

Abstract In order to clarify effects of different fungal strains on fermented tiger nut paste enzyme activities and volatile flavor compounds composition, koji enzyme activities and volatile flavor substances of six tiger nut paste preparations (S1–S6) were compared. The results revealed that koji enzyme activities of S4, S5 and S6 were significantly higher than corresponding activities of S1, S2 and S3. Among them, S4 exhibited the highest enzyme activity levels for cellulase, xylanase, acid protease, glucosidase, and amylase. GC-MS analysis of the six paste preparations detected 43 volatile components, including 17 aldehydes, 8 alkenes, 4 heterocyclics, 2 ketones, 2 phenols and 7 other types of compounds. Notably, S4 had the most volatile compounds (28), including 5 volatile compounds which were not detected in the other tiger nut pastes. Results of principal component analysis and partial least squares discriminant analysis (PLS-DA) revealed differences in levels of 17 volatile flavor substances among the six tiger nut paste preparations. Notably, PLS-DA results achieved more significant separation and stronger clustering trends when used to discriminate among volatile flavor substances of paste preparations fermented using single-strain starters (S1, S2, S3) versus double-strain starters (S4, S5, S6) consisting of Aspergillus oryzae, Aspergillus niger and/or Mucor. The tiger nut paste (S4) prepared by mixed fermentation of A. oryzae and A. niger had a unique flavor, producing the highest enzyme activity and a wider variety of volatile flavor compounds. Therefore, the production of tiger nut paste through compound strain koji fermentation was a feasible strategy.