Effects of sorbic acid and potassium sorbate on the quality of vacuum-packed, smoked skipjack tuna (Katsuwonus pelanus)

A study was conducted to determine the shelf life of skipjack tuna treated in a two-stage smoking process, then vacuum-packed and stored under normal refrigeration temperature. The study specifically aimed to measure the effects of pH levels 3.00, 4.50 and 6.00 in the soaking solution applied before the first smoking and those of 0.50%, 2.50% and 5.00% of K sorbate in the dipping solution applied before the sceond final smoking. Biochemical and micro-biological tests were employed to detect quality changes during 3 weeks of storage at refrigeration temperature (4 deg C). Trimethylamine (TMA-N), total volatile bases (TVB-N), thiobarbituric acid (TBA) and pH were determined, and bacterial, yeast and mold counts were made. Sensory evaluation by a taste panel was used to assess the acceptability of the stored product. The biochemical and microbiological indicators significantly increased, except pH, under 3 weeks of storage. The low rate of increase might be related to the very minimal presence of spoilage microorganisms responsible for protein degradation which produces volatile substances. Decreasing the pH of soaking solution significantly decreased bacterial count while increasing 12 sorbate concentration inhibited the growth of yeasts and molds. The odor of samples soaked at pH 3.00 was more stable, while at pH 4.50 and 6.00, the acceptability tended to decrease close to the average limit during storage. Increased concentration of K sorbate with prior soaking at pH 4.50 reduced the taste acceptability significantly. The golden brown skin and brown meat of the samples did not change significantly throughout the storage period. In the same way, the texture of smoked fish was not affected by any treatment and did not change during storage period. After the 21-day storage all treated samples were still acceptable in terms of general acceptance, odor and flavor. This was an improvement of about 5 times the shelf-life of 4-5 days currently achieved under traditional smoking