Hung-Der Jang

To determine the optimization of aging time for improved antioxidant activity and bacteriostatic capacity of garlic during its aging, garlic produced in Yunlin region, Taiwan, was employed as the test material in an analysis of the allicin content, total phenol content, antioxidant activity, and bacteriostatic capacity of fresh and aged garlic extracts. Allicin content of the aging garlic decreased to a minor level, whereas total phenol content increased to 16.96 mg gallic acid equivalent (GAE)/mL after 35 days of the aging process. The results of antioxidant testing demonstrated favorable positive correlations among IC₅₀ of DPPH scavenging capacity, Trolox equivalent antioxidant activity, and superoxide dismutase activity for both the fresh and aged garlic extracts. The analytical results showed that aging of garlic at 70 °C and 85% relative humidity for 40 days substantially increased the quantity of phenolics, DPPH scavenging capacity, Trolox equivalent antioxidant activity, and superoxide dismutase activity and enhanced the antioxidant activity. The extracts exhibited higher bacteriostatic capacity against Gram-positive bacteria such as Bacillus subtilis and Staphylococcus aureus than against Gram-negative bacteria such as Escherichia coli and Pseudomonas aeruginosa. In conclusion, black garlic aged under the optimum conditions exhibited favorable antioxidant activity and bacteriostatic ability.

High initial glucose concentrations may inhibit glucose utilization and decrease ethanol fermentation efficiency. To minimize substrate inhibition, the effects of feeding yeast with different glucose concentrations on the ethanol production by batch and fed-batch cultures in a 5-L fermentor were investigated. When a batch culture system with Saccharomyces cerevisiae was used for ethanol fermentation with glucose concentrations ranging 10–260 g/L, as a result, 0.2–7.0 g/L biomass and 5.1–115.0 g/L ethanol were obtained. However, substrate inhibition was observed with the initial glucose concentrations greater than 200 g/L in the fermentative media. When a fed-batch culture system (an initial glucose concentration of 180 g/L and total glucose concentration of 260 g/L) was performed, the maximum ethanol concentrations and ethanol yield were significantly higher than those of the batch cultures. The cell biomass, maximum ethanol concentration, and ethanol yields for the fed-batch fermentation cultures were 8.3 g/L, 130.1 g/L and 51% (100% of the theoretical value), respectively. The results indicated that high ethanol concentration and ethanol yield could be achieved by the fed-batch cultures with total glucose concentrations up to 260 g/L.