Effects of sodium carbonate and potassium carbonate on colloidal properties and molecular characteristics of konjac glucomannan hydrogels.

When konjac glucomannan (KGM) molecules are deacetylated under alkaline conditions, the aqueous KGM solution is transformed into a thermally stable gel. In this study, series of Na2CO3-induced and K2CO3-induced KGM hydrogels were prepared by deacetylation using different concentrations (0.1, 0.2, 0.3, and 0.4 M) of alkali. The hydrogels were characterized using texture profile analysis, scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy, X-ray diffraction, and rheological property analysis. The data showed that KGM hydrogel formation was facilitated at all the alkali concentrations used. The mechanisms of Na2CO3-induced and K2CO3-induced KGM hydrogels formation differed slightly. The hardness, springiness, chewiness, gumminess, and storage modulus G' of the Na2CO3-induced KGM hydrogels initially increased and then decreased with increasing alkali concentration. However, the values of the corresponding properties of the K2CO3-induced KGM hydrogels increased with increasing alkali concentration. All the data were consistent with the structures observed using SEM. The 0.3 M Na2CO3-induced KGM hydrogel had the highest hardness and storage modulus G', a well-proportioned network structure, and a dense architecture; 0.3 M Na2CO3 was therefore the most suitable modifier for inducing KGM hydrogel formation.

Effects of konjac glucomannan on heat-induced changes of wheat gluten structure.

Effects of konjac glucomannan on the structure of wheat gluten were investigated at variable temperatures in this study. Dynamic oscillatory rheology study showed that konjac glucomannan conferred stiffness on gluten with a higher tan δ data at 25°C and 55°C, but this parameter was lower at 75°C and 95°C. Konjac glucomannan decreased the content of thiol equivalent groups and increased the α-helix/ß-sheet content ratio, respectively. The thicker layer of gluten protein with 5% konjac glucomannan was observed by scanning electron microscopy. This study revealed that konjac glucomannan could alter the conformations of gluten proteins upon heating via non-covalent interactions and physical entanglements. It is likely that konjac glucomannan promotes protein aggregation by strengthening hydrophobic interaction at 25°C and 55°C, and alleviates heat-induced denaturation by decreasing the flexibility of polypeptide chain at higher 75°C and 95°C.

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.

Effects of corn fiber gum (CFG) on the pasting and thermal behaviors of maize starch.

Corn fiber gum (CFG) was a novel arabinoxylan hydrocolloid and recent researches showed its considerable potential in food processing. In this study, the interactions of maize starch and CFG were studied. Maize starch/CFG blend gels were prepared from maize starch suspension mixing with 0.1%, 0.25%, 0.5%, 1.0% (w/w) CFG. The pasting and thermal properties, rheological properties, microstructure, leached amylose and swelling power characteristics were evaluated. Compared with the reference, CFG addition lowered peak viscosity and breakdown of the composite system, but increased final viscosity in RVA measurement. The swelling power and the amount of leached amylose of maize starch gels were reduced as the addition concentration of CFG increased. The thermal characteristics of maize starch/CFG mixtures varied insignificantly as determined in DSC heating process. Rheological parameters, such as storage modulus (G') and loss modulus (G"), of the maize starches were observed to increase when CFG was present, supporting the hypothesis that the interaction between CFG and amylose could happen in the composite system. Confocal laser scanning microscopy (CLSM) confirmed changes in gels microstructure as starch components tended to be inhibited from leaching out of the granules when CFG was added, and the morphology of starch granule was more compact when CFG was added.

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 a small amount of sodium carbonate on konjac glucomannan-induced changes in wheat starch gel.

Wheat starch gels were produced with konjac glucomannan (KGM) and low concentrations of Na2CO3 (0.1-0.2 wt% of starch) using a rapid viscosity analyzer (RVA). The gelling properties of wheat starch in varying ratios of KGM and Na2CO3 were characterized by differential scanning calorimetry (DSC), rheometry and confocal laser scanning microscopy (CLSM). A small amount of Na2CO3 resulted in gels with increased elasticity whereas structural ordering during retrogradation was insignificantly affected. Comparison of CLSM images of composite gels revealed that Na2CO3 at 0.2 wt% of starch allowed the formation of fiber-like extensions around scattered swollen granules by KGM and amylose interaction, making swollen granules disperse within the micro phase, which was not typical in CLSM images of gels in the absence of Na2CO3. Dynamic storage modulus and dynamic power law exponent were substantially higher than those observed for the same concentration of KGM in the presence of Na2CO3, supporting the hypothesis that Na2CO3 could promote strong interchain associations between KGM and starch components.

In vivo anti-fatigue activity of sufu with fortification of isoflavones.

BACKGROUND: Sufu is a traditional Chinese fermented soybean food. Isoflavones are abundant in soybean and products incorporated with isoflavones exert many health benefits. The aim of this study was to investigate anti-fatigue effect of sufu fortified with isoflavones. MATERIALS AND METHODS: In vivo anti-fatigue activity of sufu with fortification of isoflavones (IF) was investigated in this study via exhaustive swimming test using ICR mice and determination of biochemical parameters. Factors relating to fatigue, including hepatic glycogen, blood lactic acid (BLA), blood urea nitrogen (BUN) were determined. The isoflavone composition in the IF sufu was also determined to explore the anti-fatigue activity of isoflavones. RESULTS: During fermentation, isoflavone glucosides were converted into aglycones and both sufu with and without fortification of IF prolonged the exhaustive swimming time of ICR mice. Intake of sufu also increased the hepatic glycogen content, while it decreased the levels of both the blood lactic acid (BLA) and blood urea nitrogen (BUN) content. A dose-response relationship was observed in both exhaustive swimming and BLA clearance test, with medium dose (1%) fortification of IF revealing the highest activity. CONCLUSION: IF sufu could possess high anti-fatigue activity.

Konjac glucomannan-induced changes in thiol/disulphide exchange and gluten conformation upon dough mixing.

Effects of konjac glucomannan (KGM) on the changes in gluten upon dough mixing were investigated in this study. Wheat flour was blended with KGM and processed into dough. Farinographic analysis showed that KGM caused a significant increase in water absorption and dough development time to reach maximum consistency. Comparison of electrophoretic protein profile from control dough and KGM-dough revealed that protein fractions were similar in molecular size distribution, but the lability of glutenin aggregates slightly differed. Addition of KGM to gluten induced negative effects on exchange between sulfhydryl groups and disulphide bonds. Fourier transform-Raman spectroscopy indicated that secondary structure of gluten proteins was differentially modified related with water absorption of flours before dough formation. This study reveals that when KGM is added to the dough, conformational behaviours of gluten proteins are changed and the hydroxyl groups of KGM might be involved in the interaction by forming strong intermolecular hydrogen bonding system.

Effects of fermentation temperature on the content and composition of isoflavones and beta-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 degrees C as normal and 32 degrees C as high temperature, and the effects of temperature on isoflavones and beta-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 degrees C was richer in isoflavone aglycones than at 32 degrees 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 degrees C, whereas some 6''-O-malonyl-glucosides were found at 32 degrees C. A fermentation temperature of 26 degrees C benefited the beta-glucosidase production by fungi, which contributed to valid conversion from beta-glucosides to aglycones. It was also found that beta-glucosidase converted beta-glucosides more effectively than 6''-O-malonyl-glucosides and 6''-O-acetyl-glucosides into aglycones.