Dynamic changes in primary and secondary metabolites of monascal brown rice through γ-aminobutyric acid microcapsule supplementation and untargeted metabolomic analysis

Abstract This study aimed to study the effect of modification of monascal brown rice (MBR) solid-state fermentation through supplementation of γ-aminobutyric acid (GABA) microcapsules from the emulsification/internal gelation technique on dynamic changes in primary and secondary metabolites during 25-day fermentation to conduct metabolomic analysis. During MBR fermentation, the d50 values of GABA microcapsules increased due to their swelling during the MBR fermentation. The lowest encapsulation efficiency (EE%) and highest cumulative release (CR%) of GABA microcapsules found after 25 days of the fermentation were 40.18% and 89.13%, respectively. It was an interesting point that supplementation of microencapsulated GABA into MBR substrate could expand the stationary phase (days 10–20 of the fermentation) of the Monascus purpureus growth curve compared to the control (days 10–15 of the fermentation). During the stationary phase, the concentrations of alanine, phenylalanine, arginine, tyrosine, and tryptophan in MBR fermentation with GABA microcapsule supplementation rose by more than 1.2-fold relative to the control, whereas linolenic acid, linoleic acid, and oleic acid demonstrated increases of over 1.24, 1.31, and 1.42-fold, respectively. Following a 25-day fermentation period, the maximum concentration of GABA detected in the MBR supplemented with GABA microcapsules was 1,267.13 mg/kg, in comparison to the control. Considering hierarchical clustering analysis and variable importance in projection, the primary metabolites MBR from GABA microcapsule supplementation positively correlated with days 10 and 15 of the fermentation but days 20 and 25 of the fermentation for the secondary metabolites. The significant metabolic pathways based on the primary and secondary metabolites of MBR from GABA microcapsule supplementation were as follows: (a) starch and sucrose metabolism; (b) neomycin, kanamycin, and gentamicin biosynthesis; (c) biosynthesis of unsaturated fatty acids; (d) phenylalanine, tyrosine, and tryptophan biosynthesis; (e) arginine and proline metabolism; (f) citrate cycle (TCA cycle); (g) fructose and mannose metabolism; and (h) pyruvate metabolism.