Monacolin K and yellow pigment, produced by Monascus sp., have each been proven to be beneficial compounds as antihypercholesterolemic and anti-inflammation agents, respectively. However, citrinin, a human toxic substance, was also synthesized in this fungus. In this research, solidstate fermentation of M. purpureus TISTR 3541 was optimized by statistical methodology to obtain a high production of monacolin K and yellow pigment along with a low level of citrinin. Fractional factorial design was applied in this study to identify the significant factors. Among the 13 variables, five parameters (i.e., glycerol, methionine, sodium nitrate, cultivation time, and temperature) influencing monacolin K, yellow pigment, and citrinin production were identified. A central composite design was further employed to investigate the optimum level of these five factors. The maximum production of monacolin K and yellow pigment of 5,900 mg/kg and 1,700 units/g, respectively, and the minimum citrinin concentration of 0.26 mg/kg were achieved in the medium containing 2% glycerol, 0.14% methionine, and 0.01% sodium nitrate at 25°C for 16 days of cultivation. The yields of monacolin K and yellow pigment were about 3 and 1.5 times higher than the basal medium, respectively, whereas citrinin was dramatically reduced by 36 times.
The thermal kinetics of changes of –aminobutyric acid (GABA) and antioxidant activity (DPPH assay) in germinated red jasmine rice milk (GRJM) at heating temperatures of 80, 90, 100 and 121C using Arrhenius, Eyring–Polanyi and Ball models was examined in this study. Under isothermal conditions, the increasing of heating temperature from 80C to 121C resulted in the decreasing of GABA. However, DPPH radical scavenging activity increased under temperature range of 80–100C, but decreased at 121C. The highest residue of GABA was 94% after heating at 80C for 30 min, while the highest increasing of DPPH radical scavenging activity was 230% at 90C for 30 min. Thermal degradation of GABA followed a second–order reaction kinetic, while the increasing of antioxidant activity (80–100C) followed a first–order kinetic as well as the degradation of antioxidant activity (121C). The heating temperature dependence of rate constant for degradation of GABA and increasing of antioxidant activity were described by Arrhenius, Eyring–Polanyi and Ball models. Following the Arrhenius law, activation energies were 59.62 kJ/mol and 30.31 kJ/mol, respectively for degradation of GABA (80–121C) and increasing of antioxidant activity in GRJM (80–100C). Arrhenius, Eyring–Polanyi and Ball models could be used to predict accurately GABA content and antioxidant activity in GRJM during isothermal heat treatment.
In the present work, rice pasta by-product (RPBP) was used as a raw material for the production of Monascus vinegar. Alcoholic fermentation using RPBP and red yeast rice koji were carried out, and the fermentative characteristics based on the yeast strains (Saccharomyces cerevisiae TISTR 5169, TISTR 5196, and TISTR 5197) were investigated. The compositional changes and functional properties of Monascus vinegar were examined. S. cerevisiae TISTR 5169 produced a higher yield of alcohol in a shorter time as compared to other strains, in which 10% alcohol was observed after four days of fermentation. Descriptive sensory evaluation showed that Monascus wine fermented by S. cerevisiae TISTR 5169 (W5169) showed the highest result of intensity in cereal, fruit, and alcohol aroma. Therefore, W5169 was selected for subsequent acetous fermentation. During fermentation for 39 days, the titratable acidity (acetic acid) increased, associated with the decrease in alcohol contents and pH values. Acetification increased total phenolic content in accordance with an increase of antioxidant activity. Moreover, Monascus vinegar contained functional ingredients including Monascus pigments; yellow (0.17 OD unit/mL), orange (0.08 OD unit/mL), red (0.06 OD unit/mL), monacolin K (0.0141 ppm), and total phenolic content (71.70 µg GAE/mL). Monascus vinegar exhibited potential for antioxidant activity (58.8%) and xanthine oxidase inhibitory activity (73.7%), and in particular, was without the mycotoxin citrinin.
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