Microstructure of suwari and kamaboko sardine surimi gels

Abstract

In a previous work it was suggested that the texture of kamaboko (set and cooked) gels made from sardine surimi under varying setting conditions was predetermined by the specific matrix forming in each suwari (set) gel. This paper describes the microstructure of the networks formed in suwari and kamaboko gels set at 25, 35 and 40 °C for 30 or 60 min as examined by scanning electron microscopy (SEM). Cooking conditions for kamaboko gels were fixed at 90 °C for 30 min; other preparation conditions were invariable. At low magnification (≤ x 500) the gel matrixes were compact, with practically no differences among lots. At higher magnification (x20 000), the suwari gel matrixes formed at low temperature consisted of globules. At higher temperatures the globules joined up to form fibrillar structures (fibres) and zones of disordered globule aggregation (coagula); at longer setting times, lateral bonding of the fibres became apparent. Kamaboko gels produced from unstructured globular matrixes exhibited only a few fibrillar zones and large areas of coagula. Where there was already an incipient fibrous formation, these developed into individual fibres or bundles of fibres that correlated with the best texture characteristics. Suwari gels with extensive lateral bonded fibres gave rise to kamaboko gels with a highly compact appearance under SEM; this correlated with a decline in texture values. These different structures suggest that the protein-protein bonds in the suwari networks have different levels of stability to heat, and these levels determine whether or not the proteins can subsequently be reorganised when the kamaboko gel forms.