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  • Currie Choi posted an update 1 day, 10 hours ago

    The low thermal stability of the sweet-tasting proteins limited their applications in food industry. Improve their thermal stability is the key to developing their applications in food processing. In the present study, saturation mutagenesis was performed on 4 sweet-tasting proteins, brazzein (988 mutations), curculin (2109 mutations), monellin (1824 mutations) and thaumatin (3933 mutations), using structural calculations in order to find more thermal stable mutations. The obtained results indicated that our calculated ΔΔG value (ΔΔG 0 destabilizing) was a good predictor for predicting changes in thermal stability caused by mutations. Moreover, mutating the negatively charged residues to the other non-negatively charged amino acids was an efficient way to improve the thermal stability of the investigated sweet-tasting proteins. In addition, some promising mutations sites were identified for improving thermal stability using mutagenesis. This study provides useful information for future protein engineering to improve the thermal stability of the sweet-tasting proteins.Sodium benzoate (SBA) is a widely-used additive for preventing food spoilage and deterioration and extending the shelf life. However, the concentration of SBA must be controlled under safe regulations to avoid damaging human health. Accordingly, this study proposes a microfluidic colorimetric analysis (MCA) system composing of a wax-printed paper-microchip and a self-made smart analysis equipment for the concentration detection of SBA in common foods and beverages. In the presented method, the distilled SBA sample is mixed with NaOH to obtain a nitro compound and the compound is then dripped onto the reaction area of the paper-microchip, which is embedded with two layers of reagents (namely acetophenone and acetone). The paper-microchip is heated at 120 °C for 20 min to cause a colorimetric reaction and the reaction image is then obtained through a CMOS (complementary metal oxide semiconductor) device and transmitted to a cell-phone over a WiFi connection. Finally, use the self-developed RGB analysis software installed on the cell-phone to obtain the SBA concentration. A calibration curve is constructed using SBA samples with known concentrations ranging from 50 ppm (0.35 mM) to 5000 ppm (35 mM). It is shown that the R + G + B value (Y) of the reaction image and SBA concentration (X) are related via Y = -0.034 X +737.40, with a determination coefficient of R2 = 0.9970. By measuring the SBA concentration of 15 commercially available food and beverage products, the actual feasibility of the current MCA system can be demonstrated. The results show that the difference from the measurement results obtained using the macroscale HPLC method does not exceed 6.0%. Overall, the current system provides a reliable and low-cost technique for quantifying the SBA concentration in food and drink products.The effects of selenium (Se) addition methods on antioxidant activity and flavor properties of fermented Pleurotus eryngii (P. eryngii) using Lactobacillus plantarum (L. plantarum) inoculated and natural fermentation were investigated. After fermentation, the Se-enrichment rates in fruiting bodies of Se-added fermented P. eryngii were all more than 50%. Se addition, especially in the form of Se-enriched L. plantarum inoculation, had a significantly positive effect on total phenolic content and DPPH radical scavenging activity. Non-volatiles analysis revealed that the highest ration of lactic acid to acetic acid and the highest umami intensity were observed in P. eryngii fermented by inoculating Se-enriched L. plantarum (Lp-Se). Principal components analysis and cluster analysis of volatiles clearly separated Se-treated and plain experiments, which mainly due to dissimilarities in alcohols, aldehydes and ketones. Additionally, Lp-Se obtained the highest alcohols, especially 1-octen-3-ol with mushroom flavor. In short, Se-enriched L. plantarum inoculation could produce high-quality fermented P. eryngii.Fresh green peas require blanching to terminate enzymatic reaction induced quality deterioration before frozen storage. Radio frequency (RF) heating is a novel way of dry blanching for fruits and vegetables with high processing efficiency. AZ 628 concentration In this study, blanching effects of RF heating on relative activities of lipoxygenase (LOX) and peroxidase (POD), physiochemical properties as well as cellular morphology changes of green peas were investigated. Results showed relative activities of pea LOX and POD reduced to 0.90 ± 0.78% and 1.10 ± 0.71%, respectively at 85 °C by RF heating with an electrode gap 105 mm. Weight loss, color, texture and electrolyte leakage of peas changed significantly with increasing temperature (60-85 °C). Ascorbic acid, chlorophyll and mineral contents had different loss after RF processing and long term heating at 115 mm exacerbated the loss of nutrients. Microstructure features showed the deconstruction of pea cell well and starch granule gelatinization.In this work, we report the synthesis of a mesoporous molecularly imprinted polymer on the surface of silica nanoparticles (core@mMIP) to be applied as adsorbent in microextraction by packed sorbent (MEPS) for selective determination of pesticides in apple juice. The core@mMIP was properly characterized, showing good adhesion of the polymer to the silica core. The best extraction conditions were 200 µL of ultrapure water as washing solvent, 150 µL of acetonitrile as eluent, 100 µL of sample at pH 2.5, five draw-eject cycles and 8 mg of adsorbent. Thereby, recoveries of 96.12 ± 1.05%, 76.88 ± 6.18% and 76.18 ± 5.57% were obtained for pyriproxyfen (PPX), deltamethrin (DTM) and etofenprox (ETF), respectively. After validation, the method presented linearity in the range of 0.02-10 µg mL-1 (r > 0.99), limit of detection of 0.005 µg mL-1, satisfactory selectivity, and proper precision and accuracy. The method was successfully applied real samples of processed and fresh apple juice.This study explored the effect of three different enzyme deactivation treatments 4 °C slow cold deactivation (RDPH-(4 °C)), -18 °C rapid cold deactivation (RDPH-(-18 °C)) and 100 °C water bath (RDPH-(100 °C)), compared to that without enzyme deactivation (RDPH-(control)) on the structural and functional properties of rice dreg protein hydrolysates (RDPHs). The RDPHs from the different enzyme deactivation methods led to significant differences in the degree of hydrolysis, surface hydrophobicity, average particle size, intrinsic fluorescence and emulsion stability. FTIR analysis revealed that the strength of RDPH-(100 °C) spectrum peaks decreased significantly. All samples showed high solubility (>85%) and potent antioxidant capacity DPPH (~90%), ABTS (~99%), and reducing power (0.86-1.03). Among the hydrolysates evaluated, the RDPH-(100 °C) led to the lowest reducing power and hydroxyl radical scavenging activity. Results reported here will be instrumental for the development of rice protein-based products and in the optimization and scale up of manufacturing process.

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