High pressure processing of fresh tuna fish and its effects on shelf life

Tuna is highly perishable and has been implicated in histamine poisoning because of high histidine levels in the muscle. There is high demand for fresh tuna fillet and steaks for Japanese type foods, and as a grilled item in restaurants. Demand for fresh, additive-free and safe seafood products has stimulated efforts to discover novel methods to prolong the shelf life of fresh products with minimum loss of quality. High pressure processing was investigated for its effects on quality and useful shelf life of fresh tuna. Fresh tuna was subjected to various pressure treatments (220 MPa, 200 MPa, 150 MPa), holding times (30 min, 15 min) and temperature (below 20°C). The pressure treated and control (untreated) samples were analyzed for initial physicochemical properties and subsequent changes during chilled storage. Color parameters (L*, a* and b* values), texture, drip loss, pH, sensory attributes, endoprotease activity, TBA, TVB and histamine levels were all evaluated.; All the pressure-treated samples lost their glossiness, and their redness decreased with pressure and holding time. Pressure treatment increased yellowness of the samples, and the 'b' values increased throughout storage. High pressure processing above 150 MPa resulted in firmer muscles with higher springiness. High pressure also resulted in increased drip loss for all pressure treated samples. However during chilled storage increase in drip loss was significantly faster in untreated samples than in pressure treated samples. Proteolytic activity did not change significantly during storage, unlike the TVB levels that increased during storage. Pressure treatments at 220 MPa/30 or 15 min, and 200 MPa/30 min reduced TVB values the most. None of applied pressure conditions induced major changes in initial pH values. Also no consistent pattern was observed for TBA levels, although the levels were low and indicative of high quality products. Histamine formation was inhibited by pressure treatment at 220 MPa/30 min while other pressure levels appeared to enhance histamine formation. There was no relationship between sensory attributes and histamine content.; A pressure level of 220 MPa/30 min was optimal in controlling proteolysis, texture degradation, as well as histamine and TVB formation, without promoting lipid oxidation in tuna. It also achieved a 9-day shelf life extension of the product.