Roch-Chui Yu

Changes in some components of soymilk during fermentation with bifidobacteria

Abstract Bifidobacterium longum B6 and B. infantis CCRC 14633 were grown in soymilk for a period of 48 h. During various fermentation periods, changes in the contents of crude protein, sugars, B-vitamins, acetic and lactic acids in soymilk were examined. Crude protein and titratable acidity were increased during fermentation. Soymilk fermented with B. infantis had higher titratabale acidity than that fermented with B. longum. The degree of protein hydrolysis, thiamin and riboflavin contents were increased while niacin content was decreased in soymilk fermented with either B. infantis or B. longum. Acetic and lactic acid contents were increased while the molar ratio of acetic and lactic was decreased during fermentation. Stachyose, raffinose and sucrose contents were decreased, with stachyose showing the largest magnitude of reduction. On the other hand, contents of fructose and glucose plus galactose contents were increased during fermentation.

Kinetics of direct fermentation of agricultural commodities to L(+)-lactic acid by Rhizopus oryzae

SummaryThe kinetics of fermenting barley, cassava, corn, oats, and rice directly to L(+) lactic acid byRhizopus oryzae NRRL 395 were determined. The rates of carbohydrate consumption and L(+) lactic acid production were found to be influenced by the type of substrate, the substrate concentration, the fermentation temperature, and the presence of a neutralizing agent.

Increased acid tolerance of Escherichia coli O157:H7 as affected by acid adaptation time and conditions of acid challenge

Three strains of Escherichia coli O157:H7, ATCC 43889, 43895 and 933 were subjected to acid adaptation in Tryptic Soy Broth (pH 5.0) for 1, 2, 3, 4 and 6 h. Acid tolerance of the adapted cells was determined in subsequent acid challenge at pH 3.0, 4.0 and 5.0 (acidified with HCl) and in the presence of lactic, acetic or propionic acid. It was found that acid adaptation increased acid tolerance of the E. coli O157:H7 strains tested and was dependent on strain, acid adaptation time and pH of the challenge. Among the acid adaptation times tested, 4 h of adaptation enabled the test organism, regardless of strains, to exhibit the most pronounced acid adaptation response which was most marked at pH 3.0, followed by pH 4.0 and 5.0. The extent of increased acid tolerance varied with the strains of E. coli O157:H7 and challenge of organic acid. The 4-h acid-adapted cells of ATCC 43889 and 933 showed an increase in acid tolerance in the presence of lactic, acetic and propionic acids. An increase in tolerance was also noted with ATCC 43895 in the presence of acetic and lactic acid, but not in the presence of propionic acid.

Antiproliferative and anticytotoxic effects of cell fractions and exopolysaccharides from Lactobacillus casei 01.

Cell fractions including heat-treated cells, crude cell walls, intracellular extracts and exopolysaccharides (EPSs) obtained from Lactobacillus casei 01 were first studied for their effects on the proliferation of human intestinal epithelial cells, intestine 407 and the human colon cancer cell, HT-29. Their effects on the cytotoxicity of 4-nitroquinoline 1-oxide (4-NQO) against intestine 407 were further investigated. The results revealed that EPS exhibited the highest antiproliferation activity on HT-29 cells while the viability of intestine 407 cells was not affected by EPS at a concentration of 5-50μg/mL. It was also noted that all the cell fractions and EPS from L. casei 01 reduced the cytotoxicity of 4-NQO against intestine 407 with EPS showing the highest anticytotoxic activity. Additionally, it was found that EPS might exert blocking and bioanticytotoxic effects by both adjusting the function of intestine 407 and repairing the 4-NQO-damaged cells, thus reducing cytotoxicity of 4-NQO.

Purification and characterization of a glucoamylase from Rhizopus oryzae

Glucoamylase (EC 3.2.1.3) of Rhizopus oryzae NRRL 395 was purified approximately sevenfold by sequential ammonium sulfate fractionation, Biogel P-100 gel filtration, Q-Sepharose anion exchange and S-Sepharose cation exchange. The pH and temperature optima were 4·8 and 60°C, respectively. Enzyme was stable at temperatures up to 40°C and pH values between 3 and 8. The molecular weight was 67 000 daltons as determined by sodium dodecylsulfate-polyacrylamide gel electrophoresis, and the pI was 8·7 as determined by chromatofocusing. The Km for amylopectin and soluble starch were 0·98 and 1·34 mg/ml, respectively. The Vmax for amylopectin and soluble starch were 782 and 136 μmoles of glucose produced per mg of protein per min, respectively. The enzyme activity was inhibited by Hg2+, Pb2+ and Cd2+, but not by EDTA.

Beneficial preventive effects of gastric mucosal lesion for soy-skim milk fermented by lactic acid bacteria.

In this study, Lactobacillus paracasei subsp. paracasei NTU101 and Lactobacillus plantarum NTU 102 were used as starter to ferment soy-skim milk, and the optimal mixing ratio was evaluated. The influence of lactic acid bacteria (LAB)-fermented soy-skim milk on mucosal integrity in a gastric mucosal lesion rat model was also investigated. After 24 h, cell densities of L. paracasei subsp. paracasei NTU 101 and L. plantarum NTU 102 fermented in 75% soy milk and 25% milk (optimal condition) were 1.2 × 10(9) and 2.5 × 10(9) CFU/mL. After 180 days at 4 °C, the cell densities of the freeze-dried powders of the fermented soy-skim milks were 1 × 10(9) CFU/g; slight variations in pH and acidity were observed. Pylorus ligation with acidified ethanol treatment was used as the gastric lesion animal model. LAB-fermented soy-skim milk reduced the gastric lesion index and the lipid peroxides (LPO) of gastric mucosa and serum. Administration of the fermented soy-skim milk enhanced superoxide dismutase (SOD) activity and prostaglandin E(2) (PGE(2)) synthesis. Therefore, LAB-fermented soy-skim milk at 10(9) CFU/day protects against gastric injury.

Enrichment of two isoflavone aglycones in black soymilk by using spent coffee grounds as an immobiliser for β-glucosidase.

Spent coffee grounds, discarded as environmental pollutants, were adopted as enzyme immobilisation solid carriers instead of commercialised solid supports to establish an economical catalytic system. β-Glucosidase was covalently immobilised onto spent coffee grounds for the conversion of isoflavone glycosides into their aglycones in black soymilk. Optimum conditions were determined to be 40°C and pH 6 using 4-nitrophenyl β-D-glucuronide as an indicator. Operational reusability was confirmed for more than 30 batch reactions and the storage stability was capable of sustaining its highest catalytic activity for 20 days. The kinetic parameters including rate constant (K), time (τ(50)) in which 50% of isoflavone deglycosylation was reached, and time (τ(complete)) required to achieve complete isoflavone deglycosylation, were 0.16±0.02 min(-1), 4.54±0.32 min, 60 min for daidzin and 0.16±0.02 min(-1), 2.28±0.11 min, 60 min for genistin, respectively. The total aglycone content in black soymilk was enriched by 67.14±0.60% in the enzymatic treatment of 60 min duration.

Some biochemical and physical changes during the preparation of the enzyme-ripening sufu, a fermented product of soybean curd.

In this study, sufu, a fermented product of soybean curd, was prepared by ripening the salted tofu in the mash of Aspergillus oryzae -fermented rice-soybean koji possessing various hydrolytic enzymes for 16 days. It was found that protease, alpha-amylase, beta-amylase, and lipase activities observed in the koji granules reduced most pronouncedly during the initial 4 or 8 days of ripening. Meanwhile, an increase in the activity of the various enzymes was noted in the ripening infusion and tofu cubes. During the ripening period, the content of total nitrogen, pH, and hardness of sufu decreased, while the titratable acidity, protein dissolution ratio, content of free fatty acid, and free amino acid increased with glutamic acid, showing the largest magnitude of increase at the end of the 16 day ripening period. Additionally, the color of tofu cubes changed from pale yellow to yellowish brown at the end of the ripening period.

Purification and Some Properties of Glutaminase fromActinomucor taiwanensis, Starter of Sufu

Glutaminase of Actinomucor taiwanensiswas purified approximately 96-fold with a yield of 18%, by sequential fractionation with ammonium sul-phate, anion exchange with DEAE-Sepharose CL-6B and gel filtration with Sephacryl S-200. The pH and temperature optima of purified glutaminase were 8·0 and 45°C, respectively. Glutaminase was stable at a temperature up to 35°C and at pH values of 6·0–8·0. The molecular weight was 80000 as determined from SDS-PAGE. The enzyme activity was markedly inhibited by HgCl2. In the presence of 100 g litre−1 NaCl, the enzyme activity was inhibited 50%.

Purification and characterization of NAD-dependent lactate dehydrogenase from Rhizopus oryzae

Abstract NAD-dependent lactate dehydrogenase (EC 1.1.1.27) of Rhizopus oryzae NRRL 395 was purified 175-fold with a yield of 63% by ammonium sulfate fractionation and Polybuffer exchanger 94 chromatofocusing. The purified enzyme had a specific activity of > 15 units per mg protein, and its sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) pattern showed only one protein band. As estimated by gel filtration, the molecular weight of the native enzyme was 131 000 daltons, and as determined by SDS-PAGE, that of a subunit was 36 000 daltons. The purified enzyme was stable at room temperature. The optimal pH was about 7·5 and the isoelectric point (pI), as determined by chromatofocusing, was about 5·2. The K m values for NADH, pyruvate, and 2-oxobutyrate were 1·48, 6·40, and 54·4 × 10 −4 M, respectively. Activity was inhibited by Cd 2+ , Fe 2+ , Hg 2+ , Pb 2+ and Zn 2+ , but not by EDTA.