Retardation of quality loss and extension of shelf life of prepackaged hard clam heating by a novel microwave-assisted induction heating (MAIH) during refrigerated storage

Abstract

Microwave-assisted induction heating (MAIH) is an emerging thermal processing technology that combines microwave and induction heating to provide rapid and even heating of food. A research found that the optimum MAIH cooking temperature for hard clams was 130 °C for 110 s or 90 °C for 130 s. The purpose of this work was to investigate whether MAIH could delay or not the loss of quality and prolong the shelf life of clams. Fresh clams were heated via MAIH to 130 °C for 110 s and to 90 °C for 130 s, respectively, and compared to the traditional boiling method of 90 °C for 150 s. Cooked clams were stored at 4 °C for 30 days to determine changes in microbiological quality and physicochemical properties. The results showed the undetectable aerobic plate count (APC) and psychrotrophic bacteria count (PBC) in the samples when heated via MAIH for the first 20 days of storage; thereafter, the counts increased gradually. By the end of the storage period, the final counts were approximately 4.0 log CFU/g. The initial APC and PBC in the sample heated with boiled water were at approximately 3.20 log CFU/g, which then increased over time to reach 7.66 log CFU/g and 8.06 log CFU/g, respectively, by the end of the storage period. After 30 days of storage, the total volatile basic nitrogen (TVBN) in the MAIH-treated samples was significantly lower than that in the water-boiled samples, by less than 36 mg/100 g. In terms of color, the lightness (L*) and whiteness (W) of all samples decreased gradually, while the redness (a*) and yellowness (b*) increased. In terms of texture, the MAIH-treated samples retained greater hardness, cohesiveness, and chewiness than the water-boiled samples (p < 0.05). Based on the above findings, compared to the traditional heating method of water boiling, the treatment of clam samples with MAIH retarded the degradation of texture, and inhibited the increase of TVBN and the growth of microorganisms during refrigerated storage. Thus, MAIH processing can prolong the storage life of the heat-treated clams from 10 days (when treated with boiling water) to 30 days at 4 °C.