Investigating the impact of ultrasound-assisted cellulase pretreatment on the nutrients, phytic acid, and phenolics bioaccessibility in sprouted brown rice

Abstract

This study aimed to elucidate the impact of ultrasound-assisted cellulase (UC) pretreatment on nutrients, phytic acid, and the bioavailability of phenolics during brown rice sprouting. It sought to unveil the underlying mechanisms by quantifying the activity of key enzymes implicated in these processes. The sprouted brown rice (SBR) surface structure was harmed by the UC pretreatment, which also increased the amount of γ-oryzanol and antioxidant activity in the SBR. Concurrently, the UC pretreatment boosted the activity of phytase, glutamate decarboxylase, succinate semialdehyde dehydrogenase, Gamma-aminobutyric acid (GABA) transaminase, chalcone isomerase, and phenylalanine ammonia lyase, thereby decreasing the phytic acid content and increasing the GABA, flavonoid, and phenolic content in SBR. In addition, UC-pretreated SBR showed increased phenolic release and bioaccessibility during in vitro digestion when compared to the treated group. These findings might offer theoretical direction for using SBR to maximize value.

Keywords: Nutrient composition; Phenolic bioaccessibility; Phytic acid; Sprouted brown rice; Ultrasound-assisted cellulase.

Graphical abstract

Fig. 1

Microstructure of UC treated brown rice and untreated brown rice during sprouting. A-E: Microstructure of untreated brown rice at 0, 12, 24,36, 48 h during sprouting. F-J: Microstructure of UC treated brown rice at 0, 12, 24,36, 48 h during sprouting.

Fig. 2

The GABA content and key enzyme activity in SBR with and without UC pretreatment for different sprouting hours. A: GABA, B: Glutamate decarboxylase, C: GABA transaminase, D: Succinate semialdehyde dehydrogenase. UC: SBR with UC pretreatment, CG: Control group, SBR without UC pretreatment. p < 0.05 (*), p < 0.01 (**) and p < 0.001 (***) were considered statistically significant, highly significant, and extremely significant between UC and CG at the same sprouting time, respectively. Different letters at the top of the columns indicate significant differences (p < 0.05). DW: dry basis weight.

Fig. 3

The phytic acid and γ-oryzanol content, and phytase activity in SBR with and without UC pretreatment for different sprouting hours. A: Phytic acid, B: Phytic acid, C-G: Cycloartenyl ferulate, 24-methylenecycloartanyl ferulate, Campesterylferulate, Sitosteryl ferulate, Total γ-oryzanol. UC: SBR with UC pretreatment, CG: Control group, SBR without UC pretreatment. p < 0.05 (*), p < 0.01 (**) and p < 0.001 (***) were considered statistically significant, highly significant, and extremely significant between UC and CG at the same sprouting time, respectively. Different letters at the top of the columns indicate significant differences (p < 0.05). DW: dry basis weight.

Fig. 4

The phenolic and flavonoid content, and key enzyme activity in SBR with and without UC pretreatment for different sprouting hours. A-C: Free, bound, and total phenolic, D: Phenylalanine ammonia lyase, E-G: Free, bound, and total flavonoid, H: Chalcone isomerase. UC: SBR with UC pretreatment, CG: Control group, SBR without UC pretreatment. p < 0.05 (*), p < 0.01 (**) and p < 0.001 (***) were considered statistically significant, highly significant, and extremely significant between UC and CG at the same sprouting time, respectively. Different letters at the top of the columns indicate significant differences (p < 0.05). DW: dry basis weight.

Fig. 5

The amount of release of phenolic and bioaccessibility of SBR during in vitro digestion. A: Release of phenolic in untreated SBR, B: Release of phenolic in SBR with UC pretreatment, C: Bioaccessibility of phenolic in gastric digestion, D: Bioaccessibility of phenols in intestinal digestion. UC: SBR with UC pretreatment, CG: Control group, SBR without UC pretreatment. p < 0.05 (*), p < 0.01 (**) and p < 0.001 (***) were considered statistically significant, highly significant, and extremely significant between UC and CG at the same sprouting time, respectively. Different letters at the top of the columns indicate significant differences (p < 0.05). DW: dry basis weight.