Study on Protein Structures of Eight Mung Bean Varieties and Freeze-Thaw Stability of Protein-Stabilized Emulsions.

In order to evaluate the freeze-thaw stability of mung bean protein isolate (MPI)-stabilized emulsions and its relationship with protein structure, proteins of eight mung bean varieties were compared. The results revealed that MPIs prepared from all eight varieties were mainly composed of five subunit bands, with albumin and globulin content ranges of 188.4-310.3 and 301.1-492.7 mg/g total protein, respectively. Protein structural analysis revealed that random coil structure (32.34-33.51%) accounted for greater than 30% of MPI secondary structure. Meanwhile, analysis of protein properties revealed emulsifying activity index (EAI), emulsifying stability index (ESI) and flexibility value ranges of 6.735-8.598 m2/g, 20.13-34.25% and 0.125-0.182, respectively. Measurements of freeze-thaw stability of MPI emulsions demonstrated that exposures of emulsions to multiple freeze-thaw cycles resulted in significantly different emulsion creaming index, oiling-off, particle size and zeta potential values for the various emulsions. Moreover, the stabilities of all eight protein emulsions decreased with each freeze-thaw cycle, as demonstrated using optical micrographs. The correlation analysis method was used to study the correlation between the original structures, emulsifying properties of proteins and the freeze-thaw stability of MPI emulsions. Correlation analysis results revealed significant relationships between albumin content, subunit bands with a molecular weight of 26.9 kDa and emulsifying properties were significantly related to the freeze-thaw stability of MPI emulsion. Thus, by determining these indicator values, we can predict the freeze-thaw stability of MPI-stabilized emulsions.

Effects of treatment methods on the formation of resistant starch in purple sweet potato.

In order to determine the mechanisms underlying resistant starch formation, three treatments were used to prepare resistant starch from purple sweet potato. The resistant starch yield, amylose content, chain length distribution, thermal properties, and crystal structure were determined, and the results were compared with those of unmodified starch. Autoclaving, pullulanase, and pullulanase-autoclaving treatments significantly increased the resistant starch yield, amylose content, shorter amylopectin branch content, and gelatinisation temperatures of native purple sweet potato starch. Resistant starch prepared via pullulanase-autoclaving combination treatment exhibited the highest gelatinisation enthalpy value and the greatest degree of overall thermal stability. X-ray diffraction patterns and Fourier-transform infrared spectra analysis demonstrated that all three treatments transformed the starch crystalline structure from C-type to B-type, and no new groups were generated during the modification process; all the processes were only physical modifications.

Inhibition Kinetics and Mechanism of Glutathione and Quercetin on Acrylamide in the Low-Moisture Maillard Systems.

ABSTRACT: The inhibition kinetics of glutathione (GSH) and quercetin on acrylamide (AA) formation in the low-moisture Maillard systems were investigated at 180°C. The inhibition rates in an equal-molar asparagine-glucose (Asn-Glc) system were higher than those in an asparagine-fructose (Asn-Fru) system, and the maximum inhibition rates for AA were 57.75% with 10-2 mol L-1 GSH and 51.38% with 10-1 mol L-1 quercetin. The Logistic-Index dynamic model and two consecutive simplified first-order kinetic models were well fitted to the changes of AA in the Asn-Glc system. The kinetics results suggested that the predominant inhibition effect of GSH on AA could be attributed to the competitive reaction between GSH and Asn for the consumption of Glc. The kinetic results and high-pressure liquid chromatography-tandem mass spectrometry analysis of the inhibitory effect of quercetin on AA indicated that quercetin might mitigate AA through the binding reaction of quercetin decomposition products and Maillard intermediate products. These experimental results provide theoretical data that may be useful to control the formation of AA during food thermal processing.

Effect of Oil Oxidation on Acrylamide Formation in Oil-Rich Model Systems Without the Participation of Reducing Sugars.

ABSTRACT: Oil oxidation in an oil-rich system was used to investigate the effect on acrylamide formation. Three kinds of common oil, soybean oil, olive oil, and palm oil, were preheated at different temperatures (120, 150, 180, and 210°C) for different times (0, 5, 10, 15, and 20 h). The oil-rich model systems were composed of pretreated oil and asparagine. Acid value, peroxide value, p-anisidine value, and carbonyl group value were used to monitor the degree of lipid oxidation in the model system. Our results showed that the content of acrylamide increased with oil preheat time and temperature. The highest yield of acrylamide in soybean oil was 0.26 ± 0.012 µg/mL after 20 h of incubation at 210°C. Oil oxidation indices correlated significantly with the content of acrylamide. The peroxide value could provide more information for references about acrylamide formation in soybean and olive oil systems.