Byung-Yong Ahn

Statistical Optimization of Ultraviolet Irradiate Conditions for Vitamin D2 Synthesis in Oyster Mushrooms (Pleurotus ostreatus) Using Response Surface Methodology

Response surface methodology (RSM) was used to determine the optimum vitamin D2 synthesis conditions in oyster mushrooms (Pleurotus ostreatus). Ultraviolet B (UV-B) was selected as the most efficient irradiation source for the preliminary experiment, in addition to the levels of three independent variables, which included ambient temperature (25–45°C), exposure time (40–120 min), and irradiation intensity (0.6–1.2 W/m2). The statistical analysis indicated that, for the range which was studied, irradiation intensity was the most critical factor that affected vitamin D2 synthesis in oyster mushrooms. Under optimal conditions (ambient temperature of 28.16°C, UV-B intensity of 1.14 W/m2, and exposure time of 94.28 min), the experimental vitamin D2 content of 239.67 µg/g (dry weight) was in very good agreement with the predicted value of 245.49 µg/g, which verified the practicability of this strategy. Compared to fresh mushrooms, the lyophilized mushroom powder can synthesize remarkably higher level of vitamin D2 (498.10 µg/g) within much shorter UV-B exposure time (10 min), and thus should receive attention from the food processing industry.

Isolation and Identification of Bacillus amyloliquefaciens BY01 with High Productivity of Menaquinone for Cheonggukjang Production

To develop a cheonggukjang with high content of menaquinone (MK), bacterial strains were isolated from good quality cheonggukjang, and MK productivities of isolated strains were determined by high-performance liquid chromatography. After sensory evaluation and MK determination, a potential probiotics, BY01, with acceptable sensory quality and high productivity of MK was isolated. Fermentation under aerobic condition produced more MK than that obtained under anaerobic condition, and the synthesized MK mainly remained in the form of endocellular deposit. To identify species of strain BY01, biochemical tests and gyrase B gene (gyrB) sequence analysis were carried out, and strain BY01 was identified as Bacillus amyloliquefaciens. The content of MK in cheonggukjang fermented with B. amyloliquefaciens BY01 reached 7.54 μg/g, 2-fold higher than that of commercial cheonggukjang products. This is the first report on the isolation of B. amyloliquefaciens as a superior MK producer in cheonggukjang fermentation.

Isolation and characterization of an antimicrobial substance from Bacillus subtilis BY08 antagonistic to Bacillus cereus and Listeria monocytogenes

A wild-type bacteria producing an antimicrobial substance was isolated from Korean traditional fermented soybean paste, and identified as Bacillus subtilis. The antimicrobial substance purified by TLC, tentatively named UV254-B, displayed a specific antimicrobial activity against pathogenic Bacillus cereus and Listeria monocytogenes, without inhibiting the growth of soybean-fermenting Bacillus species. The antimicrobial substance was susceptible to proteinase K and lipase but resistant to esterase. Antimicrobial activity was observed over a wide range of pH from 3 to 11, with the maximum activity at pH 9, and thermal stability up to 80°C. The minimum inhibitory concentration of the antimicrobial substance was found to be 64 μg/mL for B. cereus and 128 μg/mL for L. monocytogenes. This antimicrobial substance has a putative molecular weight either at 1,133.6 or 1,700.5, which differs from that of other antimicrobial substances described for B. subtilis such as iturin, surfactin, fengycin, and subtilisin.

Effect of crude microbial enzyme pretreatment on the liberation of biological compounds and antioxidant activity of red ginseng extract

To improve the quality of red ginseng extract, the effects of crude microbial enzyme pretreatment on the liberation of biological compounds and the antioxidant activity of the extract were studied. The total ginsenoside contents in red ginseng extract pretreated with and without crude microbial enzyme were 199 and 186μg/mL, respectively. More specifically, ginsenosides with the protopanaxadiol type of aglycone moieties showed significant increases (about 10%), while the protopanaxatriol type ginsenosides were hardly changed. Ginsenosides are thermally unstable, as they may degrade during thermal extraction above 70°C, and protopanaxatriol type ginsenosides are more susceptible than protopanaxadiol type. The contents of soluble solid, reducing sugars, polyphenolic compounds, and recovery of the enzymatic-pretreated group were increased 17, 51, 10, and 17%, respectively, compared with control. Additionally, the enzymatic-pretreated red ginseng extract showed significantly higher antioxidant activity and free radical scavenging ability than control.