Response Surface Modeling for the Enrichment of Gamma‐Aminobutyric Acid with a Minimum Content of Citrinin in Monascus‐Fermented Rice

Abstract

g-Aminobutyric Acid (GABA) is a secondary metabolite produced in Monascus-fermented food. The mycotoxin (citrinin), another major secondary metabolite, is neurotoxic to humans and thus it diminishes the social acceptability of Monascus-Fermented Rice (MFR). The study was aimed to enrich GABA content and to reduce citrinin level in MFR. Plackett-Burman experimental design and response surface methodology was used to optimize a fermentation medium for a high amount of GABA production with less amount of citrinin by Monascus purpureus Microbial Type Culture Collection and Gene Bank (MTCC) 369 under solid state fermentation (SSF). Statistically optimized nutrient parameters for MFR were lactose 0.054 g/g, alanine 2 mg/g, malt extract 37.4 mg/g, and ZnSO 4 0.3 mg/g. The yield of GABA and citrinin in optimized conditions were found to be 24 ± 0.27 mg/g and 3.3 ± 0.19 µg/g, respectively. The optimized medium parameters can be used and explored to produce high amount of GABA with low citrinin in MFR.

Screening of gamma-aminobutyric acid-producing lactic acid bacteria and its application in Monascus-fermented rice production

“…In comparison, the content of GABA in MFR (29.9 mg/g) prepared in this study was slightly higher than that of a previous study, in which a GABA content of 24 mg/g was produced by M. purpureus MTCC 369 (Khan et al, 2019), but the monacolin K content in MFR (2.22 mg/g) was lower than that reported 19.81 mg/g by Zhang et al (2018) and 12.9 mg/g by Lu et al (2013). However, the monacolin K content in MFR could be improved by prolonging the first-stage of fermentation with M. anka 20-2, and a higher GABA yield can also be achieved by extending the second-stage of the bioconversion process with L. plantarum 8014.…”

“…Production of bioactive MFR by microbial consortia. M. anka 20-2 was activated three times in 250 mL shake flasks containing 50 mL malt extract medium, inoculated with 2.5 mL of the spore suspension (1×10 5 spores/mL), and incubated at 28°C for 48 h prior to use as a starter culture for preparation of MFR (Khan et al, 2019). Then 2 mL of starter culture with 1×10 6 spores/mL was fermented in 250 mL shake flasks containing 40 mL fermentation medium for 7 d on a shaker at 28°C, 200 rpm.…”

“…are capable of producing both ingredients, monacolin K and GABA, previous studies primarily focused on enhancing either monacolin K or GABA content in MFR. The highest yield of monacolin K and GABA has reached 19.81 mg per gram of MFR fermented by Monascus ruber (Zhang et al, 2018), and 24 mg/g in solid-state fermentation of rice by M. purpureus MTCC 369 (Khan et al, 2019), respectively. However, the fermentation methods that simultaneously increase the content of both bioactive ingredients have not been reported.…”

Enrichment of dimerumic acid in Monascus‐fermented rice and its in vivo antioxidant activity

“…All the fungal cultures used in the study were cultured on potato dextrose agar (PDA) medium at 30 • C for 7 days and then kept at 4 • C. At every 30 days interval, these fungal strains were subcultured (Khan et al, 2019). Except for DMA production under stress condition, all the…”

“…For solid-state fermentation, 20 g of presoaked substrate was transferred to a 250 mL conical flask, to which 40 mL of iron restricted water containing different nutrients were added. The pH of the fermented medium was adjusted to 6.0 with 0.1 M HCl or NaOH and autoclaved for 20 min at 121 • C. Further, it was cooled and inoculated with 5 mL of 2-day-old seed cultures (15%, v/v spore suspension in sterile water having 5.7 × 10 3 spores/mL) of respective fungal strain, which then incubated for 14 days at 30 • C and 70% relative humidity (Khan et al, 2019).…”