Changes in water-holding capacity of halibut muscle during cold storage

Abstract

A useful tool for describing quality in muscle foods post mortem is to measure the water-holding capacity (WHC) of muscle. Two storage experiments were carried out to study the changes of WHC in halibut muscle during chilled storage for 15 and 18 days, respectively. To investigate the effect of normal spoilage bacteria on WHC, the storage experiments were performed both in the presence and absence of bacteria. Bacterial growth was inhibited by soaking the muscle in 3 mM NaN 3 prior to storage . A centrifugal technique was used to measure WHC. Under normal conditions, the liquid loss (LL) initially increased followed by a decrease after approximately 8 days. When bacterial growth was inhibited, no such reduction in LL was observed before day 18. Under normal storage conditions, no increase in muscle pH due to bacterial growth that could explain the improved WHC, was detected. The expelled water was analysed in order to investigate the mechanisms behind the changing WHC during storage. In both experiments, the total amount of protein lost from the muscle tissue correlated to the amount of LL. Hydroxyproline could only be observed in the LL from muscle heated to 50°C and no significant changes were observed during storage. This indicates that extensive solubilisation of collagen did not occur during the storage period. Hexuronic acid was detected in the LL but no time-dependent increase could be observed. In the normal samples, the amount of hexuronic acid in the LL actually appeared to decrease in the last part of the storage period. Gelatinolytic activities in the muscle tissue during storage were investigated by gelatine zymography. The results showed that samples with spoilage bacteria present had higher gelatinolytic activities. The increased proteolytic activities are likely to result in more degradation of proteins including core protein of proteoglycans, which then contribute to the increased WHC.