Biochemical and nutritional changes in fish proteins during drying

Abstract

Biochemical and nutritional changes in the muscle proteins of a lean marine fish Nempiterus japonicus during drying at 50, 60 and 70°C were investigated. Solubility of proteins in water, 0.6 M NaCI, 1.5 M urea, 8 M urea and 10 g litre-* sodium dodecyl sulphate (SDS) decreased as drying progressed at all three temperatures; most of the decrease occurring in the initial 4 h of drying. SDS-polyacrylamide gel electrophoresis of 1.5 M urea, 8 M urea and SDS extracts showed that higher molecular weight (MW) protein fractions were more sensitive to drying and disappeared much earlier from electropherograms than the lower MW protein fractions. Residual solubility of proteins near the pH range of 4-6 was found to increase during drying, but solubility at acid and alkaline pH was adversely affected. Decrease of solubility by drying was more affected at acid pH, especially at higher temperatures than at alkaline pH. Sulphydryl groups registered a regular and sharp decrease with drying except at 5WC, where initially an increase was observed. Apart from disulphide and hydrophobic bonds, free amino groups also appear to be involved in denaturation reactions during drying. Pepsin digestibility of fish muscle decreased slightly during drying but a clear relationship with drying temperature was not evident. Highly significant differences in proteins between protein efficiency ratio (PER), net protein utilisation (NPU) and biological value were observed between the drying temperatures. The PER and NPU of fish dried at 60°C were significantly higher than those dried at 50 or 70°C.

Moisture Migration and Bulk Nutrients Interaction in a Drying Food Systems: A Review

“…The retention of the nutritional value of food products is dependent mainly on the freshness of the raw material and optimal control of associated drying conditions [37]. The heat effects involve in drying affect the protein components in foods especially the thiosulphide groups [38]. Its causes changes in the solubility of proteins, hydrophobic bond break has been attributed greatly to denaturation during drying compared with hydrogen and ionic bonding, which rarely contribute any effect [38].…”

Near infrared reflectance spectroscopy in the prediction of chemical characteristics of minced raw fish

“…This parameter is a measure of nitrogen degradation during storage and protein breakdown in raw fish (Borquez & Speek 1994; Borquez et al . 1994; Raghunath et al . 1995) and is used to determine the quality (freshness) of the raw fish, previous to its entry into the fishmeal factory.…”

“…An acceptable calibration for TVN was observed. This parameter is a measure of nitrogen degradation during storage and protein breakdown in raw ®sh (Borquez & Speek 1994;Raghunath et al 1995) and is used to determine the quality (freshness) of the raw ®sh, previous to its entry into the ®shmeal factory. The results found in this work showed that NIRS could be used to assess this parameter under industrial conditions satisfactorily.…”

“…This variability arises from dierent ®sh species, ®sh processing systems and seasonal variations. Recent studies have shown that deteriorative changes in proteins and lipids occur also during the storage of ®sh (Borquez & Speek 1994;Raghunath et al 1995), increasing variability. Fish quality has traditionally been evaluated through sensory assessments (Freeman & Hearnsberger 1994).…”

Repeated use of oil for frying fish. Effects of feeding the fried fish to rats

“…The use of same oil repeatedly for frying led to marginal but insignificant decrease in digestibility (Table 3). Heating of fish whether by cooking or drying brings about decreases in in-vitro digestibility [14,15], owing to denaturation of proteins. Thus, heating of fish during frying as well as its interaction with the frying oil would be expected to decrease its digestibility as observed here.…”