Studies on thermal processing of tuna-A comparative study in tin and tin-free steel cans

Tin-free steel can is an ideal alternative to open top sanitary tin cans (OTS) for thermal processing of little tuna ( Ethynnus affinis ) in curry used as filling media. Effect of heat penetration on physical, biochemical and sensory characteristics of canned tuna product were studied. The chemical analysis of raw tuna fish showed a protein content of 24.20% and a lipid content of 1.37%.Comparatively, tuna used in the present study is more suitable for canning due to the presence of more protein and less fat in its flesh. Precooking is an important step in general canning process as it serves to reduce moisture content along with inhibiting enzymatic reaction, decreasing microbial load and cleansing the meat. The protein content of precooked tuna was 2.92% more than raw tuna due to relative concentration of moisture content decreases due to precooking. The percentage of yield of light meat and dark meat was 36.58% and 10.18% from whole cooked tuna and the same for dark and white meat was 28.40%. Tuna in curry packed in two metal containers subjected to thermal processing at 115°C for 70 minutes. The F0 (slowest heating point) values for canned tuna in curry packed in TFS and Tin cans obtained were 10.13 and 10.23 minutes and cook values were 145.5 minutes and 153.6 minutes respectively. During the storage period, the total volatile base nitrogen, trimethyleamine nitrogen, free fatty acid values were found to increase, while thiobarbituric acid value decreased and pH was slightly acidic. There was no significant difference (p<0.05) in appearance, colour, odour, taste, flavour, texture, overall quality of the raw tuna and final products. However, both canned products were acceptable even after storage of 5 months at ambient temperature and also, the product remained commercially sterile. It was concluded that according to quality of the product and heat penetration studies, tin-free steel container can be used as alternative to the open top sanitary tin cans for canning tuna meat.