Heat Induced Changes in Thiol Groups in Squid Proteins

Abstract

Changes in the thiol groups were determined in the mantle meat of the squid (Illex argentinus) after heating at 98°C for 45 min. The contents of ‐SH groups in the raw mince was about 90 μmoles/g protein and after heating decreased by about 30%. The total contents of ‐SH groups after reduction of disulfide bridges by NaBH4 was 120 μmoles/g protein in the raw sample and did not change significantly in the cooked meat. After 45 min of cooking the mince contained about 18 times more dimethylamine and only twice as much free formaldehyde as the raw samples. The correlation coefficients between free ‐SH groups contents and the solubility, degree of thermal coagulation of proteins as well as the water holding capacity of the meat were +0.936, ‐0.947, and +0.880, respectively.

Changes in fatty acids, sterols, pigments, lipid classes, and heavy metals of cooked or dried meals, compared to fresh marine by-products

“…Protein values even increased in scallop viscera after drying, an effect commonly reported in mollusks as a result of loss of moisture (Stanley and Hultin, 1982). Cooking or drying squid viscera did not produce protein drop, which could be a result of low protein solubility as reported in freezed and chilled stored squid mantle (Gómez-Guillén et al, 2003), a result of high proteolytic activity and increased disulfide bonds (Synowiecki and Sikorski, 1988), but also by compounds from lipid oxidation that react with proteins (Thanonkaew et al, 2006), as evidenced by a low but significant negative correlation between MDA and protein levels (r = −0.41; p < 0.05). Raw squid viscera had high levels of diacylglycerides (DAG) and free fatty acids (FFA) that indicate hydrolysis, probably as a result of handling during fishing and/or freeze-storing, as TAG are reduced enzymatically by lipases that can be active during frozen storage (Aubourg, 2001).…”

Thermal stability of myofibrillar protein from Indian major carps

“…The values of SH groups of actomyosin from catla were significantly different from those of rohu ( p < 0.001) and mrigal ( p < 0.01) and the values for mrigal were also significantly different from those of rohu ( p < 0.001). In comparison, harp seal muscle,34 Pacific mackerel and Alaska Pollock,35 squid36 and beet37 had sulphhydryl contents of 63, 76, 70, 79 and 88 µmol g −1 protein, respectively. It was also reported in rainbow trout that in the undenatured protein only 90% of the total SH groups were reactive towards DTNB and the remaining 10% were masked in the actomyosin molecule 35, 30.…”

Heat-induced changes in sulfhydryl groups of harp seal muscle proteins

“…The sulfhydryl content of manually separated seal meat was about 63 µ /g of protein (Table I), as compared with beef longissimus dorsi (Hamm and Hofmann, 1965), Pacific mackerel, Alaska pollock (Opstvedt et al, 1984), squid (Synowiecki and Sikorski, 1988), and mechanically separated chicken meat (Shahidi and Onadenalore, un-published data) containing 88, 72, 70, 79, and 58 µ of SH/g of protein, respectively. Mechanical separation did not influence the amount of free SH groups present in the samples (Table I).…”

“…During thermal processing of meat, disulfide cross-linking of protein molecules due to oxidation of sulfhydryl groups may occur. This has been demonstrated by heat processing of fish (Opstvedt et al, 1984), meat (Hamm and Hofmann, 1965), and squid (Synowiecki and Sikorski, 1988). Changes in sulfhydryl and disulfide groups in muscle proteins and possible formation of H2S are also important for both the taste and texture of canned meat products (Hamm and Hofmann, 1965).…”