Physicochemical components and flavor properties of acid rice soup (rice-acid) fermented with Lactobacillus paracasei and/or Kluyveromyces marxianus

This study aims to improve the acid and aroma production of rice-acid, shorten its fermentation time and improve its quality. Three groups of rice-acid samples (L-group, Y-group and H-group) were respectively inoculated with Lactobacillus paracasei (L. paracasei), Kluyveromyces marxianus (K. marxianus) and a mixture of the two species. During the fermentation process, L-lactic acid significantly increased (P < 0.05) and its content was the highest in H-group (25.54 ± 2.84 g/kg). The quantity of L. paracasei in L-group ((8.22 ± 0.58) log CFU/mL) was close to that in H-group ((8.23 ± 0.70) log CFU/mL) after 96-h fermentation. The antioxidant capacity of rice-acid under the condition of mixed inoculation was higher than that under the condition of single inoculation. The differences in the content of gamma-aminobutyric acid among three experimental groups were not significant, but the color differences were significant. In addition, the heatmap of the odor activity value (OAV) of 37 fermentation compounds exhibited significant differences and 26 compounds with OAVs greater than 1 showed the significant contribution to flavor formation in three fermentation groups. Potential flavor compounds of OAV included ethyl acetate, propanoic acid-ethyl ester, isobutyl acetate, ethanol, 3-methyl-1-butanol, 2-ethyl-1-hexanol, 2-methyl-ethyl-propanoic acid ester, 1-hexanol, nonanoic acid, 3-methyl-butanal, 2-methyl-butanal, 2-methyl-propanal, and 2,3-butanedione. H-group had the best flavor characteristics and quality. In this study, the simultaneous fermentation of L. paracasei and K. marxianus was applied in the production of rice-acid for the first time, thus providing new insights into non-dairy products.