Pediococcus pentosaceus JS35 improved flavor, metabolic profile of fermentation supernatant of mulberry leaf powder and increased its antioxidant capacity

Abstract

Pediococcus pentosaceus JS35 was used to improve flavor, metabolic profile and antioxidant activity of mulberry leaf powder. Gas chromatography ion mobility spectrometry (GC-IMS) analysis revealed that fermentation increased the contents of floral and fruity flavor compounds such as dihydrolinalool and 2-phenylethanol, while decreased the grassy, pungent odor compounds. Non-targeted metabolomics analysis showed that Pediococcus pentosaceus JS35 altered the metabolic profile of mulberry leaf, especially increased the content of flavonoids metabolites such as kaempferol, quercetin and daidzein. Compared with the unfermented sample, the fermented supernatant had higher antioxidant capacity in vitro and in Caenorhabditis elegans. Furthermore, the fermented supernatant supplementation significantly prolonged the lifespan of Caenorhabditis elegans. In conclusion, fermentation by Pediococcus pentosaceus JS35 improved the flavor and active compounds of mulberry leaf, and the fermented product had effective antioxidant capacity. This study will provide ideas for the application of Pediococcus pentosaceus JS35 and the processing of mulberry leaf into functional foods or food ingredient.

Keywords: Pediococcus pentosaceus; antioxidant capacity; flavor; metabolic profiles; mulberry leaf.

Figure 1

Effect of lactic acid bacteria fermentation on chemical composition of mulberry leaf powder. (A) Changes of pH and TTA during fermentation. (B) GABA content. (C) Total phenolics content. (D) Total flavonoids content. The letters a, b indicated significant differences in content of GABA, total phenolics and total favonoids contents (p < 0.05).

Figure 2

Sensory evaluation and GC-IMS observation of the supernatant before and after fermentation. (A) Sensory characteristics analysis radar map. (B) Euclidean distance diagram of nearest neighbor algorithm for different samples. (C) Two-dimensional difference plot. (D) Peak intensities of various volatile compounds. (E) Gallery plots indicating the variations of VOCs relative content. Panels (C,E) red and blue colors underline over- and under-expressed components in both.

Figure 3

Effects of non-volatile compounds in fermentation supernatant before and after fermentation. (A) PCA score plot of CK, FS and QC samples in positive ion mode. (B) PCA score plot of CK, FS and QC samples in negative ion mode. (C) Volcano diagram of metabolites in positive ion mode. (D) Volcano diagram of metabolites in negative ion mode.

Figure 4

Analysis of differentially expressed metabolites in fermentation supernatant before and after fermentation. (A) Classification of differential metabolites. (B) Cluster analysis of the top 30 differential metabolites. (C) Bubble diagram of the metabolic pathway enrichment.

Figure 5

Effect of FS on antioxidant capacity. (A) The DPPH radical scavenging capacity. (B) Hydroxyl radical scavenging capacity. (C) The reducing ability. Results are expressed as the mean ± standard deviation (n = 3).

Figure 6

Effects of FS on biochemical indicators of C. elegans. (A) Total antioxidant capacity. (B) Malondialdehyde content. Results are expressed as the mean ± standard deviation. Means with different letters in figure were significantly different at p < 0.05.

Figure 7

Effects of FS on basic physiological indicators of C. elegans. (A) Survival curves. (B) Head swing. (C) Total oviposition amount. Results are expressed as the mean ± standard deviation (A, n = 90; B, n = 30; C, n = 10). Means with different letters in figure were significantly different at p < 0.05.