Microwave heating process of moderate-minced surimi based on multiphase porous media model.

Moderately processed surimi products exhibit better nutrient retention and enhanced gels, and the great potential of microwaves application and changes in the way of chopping meat has been reported by previous research. In this study, a systematic analysis of the novel surimi product was made to explore the heat and mass transfer characteristics. A porous media model combining electromagnetic heat and hygroscopic expansion was developed to evaluate this process, and its accuracy has been verified experimentally. It was found that the dielectric characterization of multiphase mixture system has great influence on the results, the complex refractive index mixture equation was used due to its lowest root-mean-square error value. In addition, the effect of moderate processing on microwave heating was examined in terms of porosity changes. However, nonuniform temperature distributions were found in the higher porous samples, especially when the porosity is greater than 0.81. Moreover, the developed model was coupled with the evaluation for gel properties and the results showed the significant effect of moderate crushing on the gel quality during the microwave heating process.

Effects of exogenous lipids on gelling properties of silver carp surimi gel subjected to microwave heating.

Lipids are important components of surimi products because they enhance the whiteness and flavor of food. The effects of three common types of exogenous lipids on the gel properties of surimi subjected to two different heating methods were investigated in this work, using frozen silver carp (Hypophthalmichthys molitrix) surimi as the raw material. The surimi gels were prepared by two-stage water bath heating or single-stage water bath heating followed by microwave heating. We found that the quality of surimi gels was in the order of lard > chicken fat/soybean oil, which may be associated with polyunsaturated fatty acid content. The surimi gel strength was reduced with an increase in the amount of lipid added. Microwave heating significantly increased the gel strength of surimi containing exogenous lipids when compared to conventional heating. Surimi gels prepared by microwave heating showed more denser protein network microstructures by scanning electron microscopy (SEM), suggesting aggregation of protein molecules. The findings of this study provide a theoretical basis for using microwave heating to generate surimi gels with exogenous lipids.

Inhibitory effect of microwave heating on cathepsin l-induced degradation of myofibrillar protein gel.

This work was aimed to compare the effect of microwave (MW) heating on the cathepsin L (Cat L)-induced degradation of myofibrillar protein (MP) gels with that of water bath (WB) heating. First, Cat L from silver carp was purified and determined to be 45 kDa. The gel strength of the MW-heated MP gels were significantly higher than those of the WB-heated when Cat L was added (P < 0.05). The gel electrophoresis pattern and scanning electron microscopy analysis indicated that MW heating inhibited the Cat l-induced hydrolysis of MP gels. In addition, the number of sulfhydryl groups and surface hydrophobicity of MW-heated gels were lower than those of WB-heated gels when Cat L was added. These results indicated that MW heating could effectively weaken the degradation of Cat L on MP gels by manipulating disulfide bonds and hydrophobic amino acids, resulting in good gel properties and a compact protein network.

Influence of fried food and oil type on the distribution of polar compounds in discarded oil during restaurant deep frying.

Deterioration of frying oil greatly affects the nutrition of fried foods. In this study, influence of fried food and oil type on the distribution of polar compounds in oils at total polar compound (TPC) of 24%, 25% and 27% was evaluated. Both food and oil significantly affected the composition of frying oil (P < 0.01) and the effect of oil was relatively more significant than that of food. Five groups of polar compounds were presented: triglyceride oligomer (TGO), triglyceride dimer (TGD), oxidized triglyceride monomer (oxTGM), diglyceride (DG) and free fatty acid (FFA). TGD and DG had the highest contents, up to 6.9%-7.5% and 8.1%-8.9% respectively, while FFA had the lowest content with 1.4%-1.7%. The compound of the greatest concern in frying oil, oxTGM, varied from 4.6% to 4.8%, when TPC reached 24%-27%. Data will be expected to provide the evidence for toxicological evaluation of fried oils and foods in restaurants.