The effects of different concentrations (0%–20%) of soybean oil or lard added to pomfret surimi gel on its physicochemical properties and protein structure were studied. The addition of 8% lard or soybean oil significantly increased the whiteness, water-holding capacity (WHC), gel strength, storage modulus (G’) and sensory evaluation of surimi. When the addition level was higher than 8%, the strength, WHC, and G’ decreased. Surimi gel with 8% lard was better than that with the same concentration of soybean oil. The results of scanning electron microscopy (SEM) showed that lipids not only filled the void between protein molecules, but also formed an interfacial protein film on the surface, which combined with the protein matrix through protein filaments. It was shown that there was an interaction between lipids, the interfacial protein membrane and proteins in surimi gels. Raman spectra showed that the addition of lipids decreased the relative content of α-helix, and the first increases and then decreases of β-sheet. The addition of soybean oil also significantly increased the relative content of random coils, while the change in random coils of lard was not as significant as that of the soybean oil treatment group. Both soybean oil and lard led to the exposure of hydrophobic groups on the side chain of proteins in surimi gels. These results suggest that the addition of oil changes protein structure and microenvironment in surimi, which in turn affects the physicochemical properties of surimi gels. The surimi gel with 8% lard has better properties.

The purpose of this study was to optimize the extraction process of citronella essential oil using ultrasonic-assisted steam distillation and to evaluate its effect on keeping the freshness of gold pomfret. The optimization was carried out using single factor and orthogonal array design experiments. The effect of citronella essential oil emulsion on keeping the freshness of gold pomfret was evaluated by measuring its thiobarbituric acid reactive substances (TBARS) value, total volatile basic nitrogen (TVB-N) content and freshness quality index (K value). The optimal extraction conditions were as follows: solid-to-solvent ratio 1:25 (g/mL), ultrasonic time 30 min and ultrasonic power 260 W. Under these conditions, the average yield of citronella essential oil was 6.77%. Citronella essential oil emulsion reduced the TBARS value, TVB-N content and K value of gold pomfret during storage. Citronella essential oil can keep the freshness of gold pomfret.