te Li

Influence of high pressure on conformational changes of soybean glycinin

Abstract Influence of high pressure on conformational changes of soybean glycinin was studied by means of sulphydryl groups detection, spectrofluorimetry, ultraviolet difference spectra, circular dichroism, differential scanning calorimetry and electrophoresis. The results indicated that glycinin were dissociated into subunits and the conformation of these subunits had been changed after high pressure processing. More sulphydryl groups as well as hydrophobic regions and amino acid residues which had ultraviolet absorbance had been found significantly after high pressure processing (≥300 MPa). DSC analysis results demonstrated that glycinin had been denatured completely after processed at 400 MPa for 10 min. The CD analysis indicated that some of the ordered structures of α-helix and β-structure were destroyed and converted to random coil after processed at 500 MPa for 10 min.

Roles of hydroxyl radicals in electrolyzed oxidizing water (EOW) for the inactivation of Escherichia coli

The food industry has recognized electrolyzed oxidizing water (EOW) as a promising alternative decontamination technique. However, there is not a consensus about the sanitizing mechanism of EOW. In this study, we evaluated the disinfection efficacy of different types of EOW on Escherichia coli. Based on the hypothesis of hydroxyl radicals existing in EOW, in the present study, the hydroxyl radicals existed in slightly acidic electrolyzed water (SAEW) and acidic electrolyzed water (AEW) diluted to different levels were detected quantitatively. An ultraviolet (UV) spectrophotometer was used to scan EOW with different pH values. Accounting for the results of UV scanning to EOW with different pH value and the disinfection efficacy of different types of EOW, it can be concluded that considering the lower chlorine concentration of EOW compared with traditional chlorine disinfectants, the existing form of chlorine compounds rather than the hydroxyl radicals played important role in the disinfection efficacy of EOW.

Determination of starch gelatinization temperature by ohmic heating

Abstract A method for measuring starch gelatinization temperature ( T ), determined from a change in electrical conductivity ( σ ), was developed. Suspensions of native starches with different starch/water mass ratios and pre-gelatinized starches were prepared, and ohmically heated with agitation to 90 °C using 100 V by AC power at 50 Hz, and a voltage gradient of 10 V/cm. The results showed that σ of native starch suspensions was linear with temperature ( R 2 >0.999) except for the gelatinization range, but the linear relationship was always present for the pre-gelatinized starch–water system. It was seen that the shape of d σ /d T versus T curve was essentially similar to the endothermic peak on a DSC thermogram, and the gelatinization temperature could be conveniently determined from this curve. Thus, the segment profile on this curve was called the “block peak”. The reason for the decrease in σ of native starch suspensions in the gelatinization range was probably that the area for motion of the charged particles was reduced by the swelling of starch granules during gelatinization.

Cloning and expression of a Paecilomyces thermophila xylanase gene in E. coli and characterization of the recombinant xylanase

A cDNA library of Paecilomyces thermophila was constructed, and the gene encoding xylanase (designated Pt xynA) was isolated from the library. Pt xynA consisted of 681 bp, and the translated protein encoded 226 amino acids. This is the first functional gene cloned from P. thermophila. The gene was successfully expressed in Escherichia coli BL21 and the recombinant xylanase (XynA) was purified to homogeneity by Ni-NTA and Sephadex G50. XynA showed an optimum activity at 75 degrees C and pH 7.0. Its residual activity was more than 60% after being treated at 85 degrees C for 30 min. K(m) values of XynA for birchwood xylan, beechwood xylan and oat-spelt xylan were 4.4, 3.6 and 9.7 mg ml(-1), respectively. The enzyme has an endohydrolytic mode of action and can hydrolyse xylotriose to xylobiose through transglycosylation. These results indicate the XynA is a thermostable enzyme and has great potential in various industries.

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.

Isolation, characterization and identification of lactic acid bacteria and yeasts from sour Mifen, a traditional fermented rice noodle from China

Aims:  Considering the effect of natural fermentation on the textural improvement of fermented rice noodles in China and South Asia, and given the lack of reports concerning microbial populations and structure in the fermentation process, this study aims to determine the number of viable micro‐organisms and identify the species isolated from the local factories, and to assess their potential use as a starter culture from their enzymatic profiles.

Electrohydrodynamic (EHD) Drying Characteristic of Okara Cake

Abstract Drying of okara cake was investigated in an oven at 105°C with or without the electrohydrodynamic (EHD) technique. The okara cakes (77 g in weight and 81.57% ± 0.14%wb initial moisture) were put in Petri dishes of 93 mm in internal diameter and 18 mm in depth. One sample was exposed to a high electric field (HEF) established with needle and plate electrodes and the other was treated as control. During drying, the voltage was applied at −20 ± 0.1 kV, number of electrodes in point electrodes were 1 and 3, and the electrode gap was 35, 50, and 65 mm. Varying the number of needles in the point electrodes and the electrode gap in HEF drying, the initial drying rate was found to be 1.7–3.2 times higher than the control sample at the same time. The results indicated that the range of the drying rate ratio changed with the moisture content was one to two during drying process. The results also suggested that the drying kinetics of okara cake treated both with and without an electric field were better fitted with Pages model than the Fickian diffusion model. Moreover, the falling rate period could be divided into two parts. When the ratio of moisture content was equal to e−e (= 0.066), the falling rate period changed from the first stage into the second stage. The drying time under HEF condition reduced by 15% to 40% compared to control measured at the final moisture content of 10% wb. The HEF energy efficiency ratio changed with the moisture content was always more than 1 except for a short period before the end of drying. It indicated that the heat energy should be transported to the okara cake exposed to the HEF more than to the control from the oven.

Purification and Identification of 1-Deoxynojirimycin (DNJ) in Okara Fermented by Bacillus subtilis B2 from Chinese Traditional Food (Meitaoza)

This study was to purify an alpha-glucosidase inhibitor from okara (soy pulp) fermented by Bacillus subtilis B2 and to identify its chemical structure. Membrane dialysis, active charcoal, CM-Sepharose chromatography, and preparative thin-layer chromatography (TLC) were used in the purification, while positive mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectrometry were used in the identification. The MS and NMR data showed that the purified alpha-glucosidase inhibitor was 1-deoxynojirimycin (DNJ) with a molecular weight of 163 Da. This is the first time that DNJ was isolated from foods fermented with Bacillus species. Okara fermentation with B. subtilis B2 might be used to produce a food-derived DNJ product as a functional food for diabetic patients.

The Effects of Vital Wheat Gluten and Transglutaminase on the Thermomechanical and Dynamic Rheological Properties of Buckwheat Dough

The improvement of the processing properties of gluten-free cereals is a challenging issue for cereal technologists. Vital wheat gluten (VWG), transglutaminase (TGase), or combinations of the two have been successfully used to improve the processing properties of food materials. In this study, a Mixolab system and a rheometer were used to investigate the effects of TGase on the thermomechanical and dynamic rheological properties of buckwheat flour dough (BF dough) and a buckwheat flour dough containing 15% VWG (BF-VWG dough). The results indicated that the addition of 1.0% TGase decreased the water absorption and significantly increased the stability, storage modulus (G′), and complex modulus (|G*|) of the BF dough. The presence of 15% VWG had a synergistic effect, enhancing the effectiveness of the TGase in improving the thermomechanical and dynamic rheological properties of the BF-VWG dough. Quantification of the free amino groups showed that the amino groups were more effectively bonded in the BF-VWG dough than in the BF dough when the TGase level exceeded 1.0%. Confocal laser scanning microscopy (CLSM) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis confirmed that the TGase promoted the formation of protein complexes. These data indicate that the combination of VWG and TGase can be used to improve the properties of buckwheat flour for buckwheat-based food production.

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.