No abstract

Summary Endogenous proteases are responsible for gel weakening of fish muscle protein. We investigated inhibitory effect of four selected protease inhibitors: soya bean trypsin inhibitor, leupeptin, E64 and EDTA, to identify the protease groups responsible for gel degradation in both unwashed and washed rohu (Labeo rohita) gel. The protease inhibitory activity was determined by percentage inhibition and SDS‐PAGE pattern. Leupeptin and E64 showed a strong inhibition on the autolysis of unwashed gel, and myosin heavy chain (MHC) band was recovered by the addition of them. The results suggested that cysteine protease was the major endogenous protease involved in the autolysis. In the case of the washed gel, leupeptin and soya bean trypsin inhibitor were shown to have a strong inhibitory effect. Also, the addition of these inhibitors increased the intensity of the MHC band. The results implied that serine protease played an important role in the degradation of the gel network.

The gel-forming ability of rohu (Labeo rohita) mince with and without egg white powder (EW) was investigated. Gel from washed mince (washed gel) was prepared under two setting conditions: kamaboko (40˚C) and modori (60˚C). The gel-forming ability of kamaboko and modori gels was improved by the addition of EW at 2%. The autolytic inhibition of kamaboko gel was obtained in gel added with 2% EW, and 1% EW of modori gel. No marked change was observed in the TCA-soluble peptide content of either gel with the addition of EW above 1%. No effect on the whiteness of both gels was shown after the addition of EW. The addition of EW exhibited smaller cavities and a more compact fibrous network in microstructure.

The gel-forming ability of rohu (Labeo rohita) was investigated. Unwashed and washed gel was prepared under different setting conditions including kamaboko gel (40 o C, 30 min) and modori gel (60 and 65 o C for washed and unwashed gel, respectively, 30 min), then both gels were heated at 90 o C for 20 min. The gel-forming ability was investigated using the folding test, gel strength, and waterholding capacity expressed by the expressible water content. The addition of whey protein concentrate (WPC) at 3% improved the folding test, gel strength, and water-holding capacity of unwashed modori gel. The addition of (WPC) at 2% increased the gel strength of unwashed kamaboko gel and improved the water-holding capacity. The increases in gel strength of both washed gels were found with WPC at 1%. The water-holding capacity of washed modori gel was improved at this concentration, while the addition of WPC did not affect the water-holding capacity of the washed kamaboko gel. Although WPC improved the modori gel, the increases were not as high as those for the kamaboko gel either unwashed or washed. Determinations of whiteness showed that the addition of WPC affected the whiteness of unwashed gel, while not affecting the washed gel.