Microscopic elastic structure mapping of frozen tuna (Thunnus orientalis) via scanning haptic microscopy

Abstract

The mechanical properties of fish are closely related to texture and are generally evaluated by macroscopic tests. During freezing storage, however, mechanical damage, such as the growth of ice crystals, occurs at the microscopic level. In this study, scanning haptic microscopy (SHM) measurements were performed on refrigerated and freeze–thaw tuna fillets to observe the microscopic elastic modulus distribution in food samples. In elastic images of the refrigerated samples, areas of hard myotome membrane and soft muscle were clearly discernible. For the muscle area, the elastic modulus of the freeze–thaw sample was significantly higher than that of the refrigerated sample, which was consistent with macroscopic indentation results. In contrast, there were no significant differences in the elastic modulus due to freezing in the myotome area. Thus, we propose that SHM imaging is useful for the evaluation of microscopic mechanical damage.