Lijun Yin

Effects of sources of carbon and nitrogen on production of α-glucosidase inhibitor by a newly isolated strain of Bacillus subtilis B2

This study examined production of α-glucosidase inhibitors by Bacillus subtilis B2 in Luria-Bertani (LB) fermentation with okara, soy powder, starch or pectin as additional source of carbon and nitrogen. All the fermentation broths of B. subtilis B2 exhibited gradual increase in α-glucosidase inhibitory activity during the fermentation process with or without supplemented source of carbon or nitrogen. Addition of okara into the LB medium greatly enhanced the strength (nearly twice as much of that without okara supplement) of α-glucosidase inhibitory activity of fermentation broth. The α-glucosidase inhibitory activity of B. subtilis B2 fermentation broth was positively correlated (p<0.05) with the bacterial populations grown in LB medium containing okara. Glucose and sucrose were not detected in LB medium during the entire fermentation process and were both reduced drastically in media containing okara, soy powder, starch or pectin after 6days of fermentation. The fermented LB medium containing okara by B. subtilis B2 possessed very strong α-glucosidase inhibitory activity and contained little glucose and sucrose, suggesting that fermentation of B. subtilis B2 in LB added with okara might be considered as a strategy for preparing functional foods for diabetic patients.

Effects of Fermentation Temperature on the Content and Composition of Isoflavones and β-Glucosidase Activity in Sufu

Sufu is a popular fermented tofu product in China. The low quality of sufu produced in the hot summer is a big problem in sufu manufacture, so we prepared sufu at two different temperatures, 26 °C as normal and 32 °C as high temperature, and the effects of temperature on isoflavones and β-glucosidase activity were investigated. Fermentation temperature did not cause significant differences in the recovery of isoflavones, but resulted in a different redistribution of isoflavone isomers in sufu. Sufu fermented at 26 °C was richer in isoflavone aglycones than at 32 °C; the enrichment of isoflavone aglycones might have the advantage of enhancing the physiological function. No 6″-O-malonyl-glucosides were detected in sufu fermented at 26 °C, whereas some 6″-O-malonyl-glucosides were found at 32 °C. A fermentation temperature of 26 °C benefited the β-glucosidase production by fungi, which contributed to valid conversion from β-glucosides to aglycones. It was also found that β-glucosidase converted β-glucosides more effectively than 6″-O-malonyl-glucosides and 6″-O-acetyl-glucosides into aglycones.

Isolation of cathepsin B from the muscle of silver carp (Hypophthalmichthys molitrix) and comparison of cathepsins B and L actions on surimi gel softening.

Cathepsin B from silver carp muscle was purified to 263-fold by acid treatment, ammonium sulfate fractionation, followed by a series of chromatographic separations. The molecular mass of the purified enzyme was 29kDa as determined by SDS-PAGE and immunoblotting. The purified enzyme was activated by dithiothreitol and cysteine while it was substantially inhibited by E-64, suggesting the purified enzyme belongs to the cysteine proteinase family. Optimal pH and temperature were 5.5 and 35°C, respectively. The enzyme catalyzed the hydrolysis of Z-Arg-Arg-MCA with a parameter of Km (90μM) and Kcat (20.3s(-1)), but hardly hydrolyzed Arg-MCA. Analysis of surimi gel strength and microstructure showed that cathepsins B and L were capable of destroying the network structure of silver carp surimi gels, consequently causing gel softening. Cathepsin L might play an important role in the modori effect.

Peroxidase-mediated conjugation of corn fiber gum and bovine serum albumin to improve emulsifying properties.

The emulsifying properties of corn fiber gum (CFG), a naturally occurring polysaccharide-protein complex, was improved by kinetically controlled formation of hetero-covalent linkages with bovine serum albumin (BSA), using horseradish peroxidase (HRP). The formation of hetero-crosslinked CFG-BSA conjugates was confirmed using ultraviolet-visible and Fourier-transform infrared analyses. The optimum CFG-BSA conjugates were prepared at a CFG:BSA weight ratio of 10:1, and peroxidase:BSA weight ratio of 1:4000. Selected CFG-BSA conjugates were used to prepare oil-in-water emulsions; the emulsifying properties were better than those of emulsions stabilized with only CFG or BSA. Measurements of mean droplet sizes and zeta potentials showed that CFG-BSA-conjugate-stabilized emulsions were less susceptible to environmental stresses, such as pH changes, high K ionic strengths, and freeze-thaw treatments than CFG- or BSA-stabilized emulsions. These conjugates have potential applications as novel emulsifiers in food industry.

Effect of magnesium salt concentration in water-in-oil emulsions on the physical properties and microstructure of tofu

The aim of this research was to prepare water-in-oil (W/O) emulsions encapsulating different concentrations of magnesium chloride (MgCl2) and to investigate the effect of W/O emulsions on the physical properties and microstructure of tofu. The results showed that the stability of W/O emulsions improved as the concentrations of polyglycerol polyricinoleate (PGPR) and MgCl2 increased. Dynamic viscoelastic measurements indicated that gelation time decreased with increasing MgCl2 concentration in W/O emulsions, suggesting a more rapid reaction between magnesium ions and protein molecules. As the concentration of MgCl2 in W/O emulsions increased, the yield and water content of tofu decreased, while the protein and crude fat contents and hardness values increased. At a concentration of 2.0M MgCl2 in W/O emulsion, the WHC and microstructure of the tofu samples were optimal. The variations in the physical properties of tofu were attributed to the concentration of magnesium ions and the coagulation rate.

Changes in Angiotensin I-Converting Enzyme Inhibitory Activities During the Ripening of Douchi (a Chinese Traditional Soybean Product) Fermented by Various Starter Cultures

Angiotensin I-converting enzyme (ACE) inhibitory activities of commercial douchi were determined, and salt-fermented samples were found exhibiting higher activities than dandouchi. Douchi was prepared in laboratory scale by pure culture fermentation. Results showed that ACE inhibitory activity in bacteria-type douchi decreased during maturation, while it increased in fungi-type douchi, with the highest activity observed in Aspergillus oryzae fermented douchi after ripening for 30 days. These suggested that the type of starters affected significantly the generation of ACE inhibitors during douchi ripening. Sensory evaluation showed that A. oryzae produced more organoleptically acceptable douchi than other cultures used in this study.

Peroxidase-mediated formation of corn fiber gum-bovine serum albumin conjugates: Molecular and structural characterization

Corn fiber gum (CFG) was previously conjugated with bovine serum albumin (BSA) via peroxidase treatment to improve its emulsifying properties. The current study was undertaken to evaluate the molecular characteristics of CFG-BSA conjugates prepared at different CFG/BSA weight ratios of 10:1, 4:1, 1:1, and 1:4. After the peroxidase treatment, CFG-BSA mixtures at weight ratios of 10:1 and 4:1 showed an increase in molecular weight from 200 and 193kDa to 218 and 223kDa respectively. But for CFG-BSA mixtures at weight ratio of 1:4, their molecular weight decreased. Peroxidase treated CFG-BSA mixtures had a more compact but rougher surface morphology as compared with the untreated as revealed by scanning electron microscopy. At lower CFG to BSA weight ratio (1:4), particles of CFG-BSA conjugates appeared to be elongated while at higher CFG to BSA weight ratio (10:1), they were approximately spherical in transmission electron micrographs.

Characterization and functionalities study of hemicellulose and cellulose components isolated from sorghum bran, bagasse and biomass

This study was undertaken to isolate and characterize three carbohydrate-rich fractions: Hemicellulose A (Hemi. A), Hemicellulose B (Hemi. B) and cellulose-rich residue (CRF) from sorghum bran (SBR), sorghum bagasse (SBA) and sorghum biomass (SBI). The monosaccharide composition of the Hemi. A and Hemi. B fractions was determined, indicating that SBR has a highly branched structure. The analysis of insoluble dietary fiber (IDF), soluble dietary fiber (SDF) and total dietary fiber (TDF) showed that TDF and IDF contents in original sorghum materials were in the following order: SBA˃SBI˃SBR. CRF from SBA was rich in IDF. Hemi. B fractions were completely soluble in water and so they were rich in SDF. CRFs from all sorghum sources show high water holding capacity (22.76 to 35.27g water/g CRF). The emulsion stability study showed that the Hemi. B from all sorghum sources had a better emulsion stability than the well-studied corn fiber gum (CFG).

Application of Electrolyzed Water to Improve Angiotensin I-Converting Enzyme Inhibitory Activities of Fermented Soybeans Started with Bacillus Subtilis B1

Angiotensin I-converting enzyme (ACE) inhibitory activities of soybeans fermented by Bacillus subtilis B1 with pretreatment of soaking in electrolyzed oxidizing (EO) water, electrolyzed reduced (ER) water, chemically modified acidic and alkaline solutions as well as conventional tap water were investigated. Using electrolyzed water improved significantly (p < 0.05) the ACE inhibitory activities of fermented soybeans as compared with using tap water. The highest ACE inhibitory activity was recorded as an IC50 value of 0.065 mg/mL in the sample, which had been pretreated by soaking in ER water prior to fermentation. The ACE inhibitory activity increased to and tended to keep at a higher level during fermentation of EO water-soaked soybeans. However, there was no evident advantage of chemically modified acidic and alkaline solutions over tap water. Results suggested that electrolyzed water possessed potent ability to improve the ACE inhibitory activity of fermented soybeans, which might be through providing an appropriate microenvironment for the hydrolytic actions of microorganism to generate ACE inhibitors. In addition, this work also suggested a potential ability of electrolyzed water to be applied into the production of functional foods.

Impact of the release rate of magnesium ions in multiple emulsions (water-in-oil-in-water) containing BSA on the resulting physical properties and microstructure of soy protein gel

The objective of present study was to prepare multiple water-in-oil-in-water (W/O/W) emulsions that exhibit different release rates of magnesium ions; and assess their utility as coagulants in improving tofu quality. W/O/W emulsions containing bovine serum albumin (BSA) and magnesium chloride (MgCl2) were developed for controlled release applications. An increasing BSA concentration led to an increase in viscosity and droplet size of W/O/W double emulsions, as well as a decreased release rate of encapsulated Mg2+ from emulsions. The gelation process of soy protein was simulated by conducting dynamic viscoelastic measurements. The rate constant (k) and saturated storage modulus (Gsat) values of soy protein gel decreased as BSA concentration increased, suggesting that BSA could slow the release of magnesium ions from double emulsions. Confocal laser scanning microscopy (CLSM) results showed that increased concentration of BSA created a more homogeneous microstructure of soy protein gels with smaller pores within the gel network structure.