Frontiers in Marine Science (Jun 2014)
Optimization of a chemical method for skinning of sardines (<i>Sardina pilchardus</i>) during canning processing
Abstract
Most of sardine (Sardina pilchardus) catches is used for canning purposes. The most common product presentation is a beheaded sardine with skin and bones packed in a tin can. Canned sardines can also be presented skinless and boneless. For this last type of product, after beheading and evisceration, sardines are placed in trays, cooked and then skinned by hand, one by one, and placed in the tins, a process involving high labour costs. The aim of this work was to develop a chemical process for peeling raw sardines and its subsequent application in a canning industry processing line just after the beheading and evisceration step and before cooking. Potassium hydroxide treatments (pellets a.r. 85% KOH) were applied at concentrations of 2, 3 and 4% (v/v, distilled water). Frozen sardines were beheaded and eviscerated after thawing and immersed in the different potassium hydroxide solutions at 93ºC (pH respectively 13, 13 and 13.02) for 3 min and further washed with distilled water at 100°C. In this first set of experiments, fat sardines were used (average of 9.86% of fat, w/w). The best performance, with respect to skin removal, was achieved with the 2% potassium hydroxide immersion (pH 13). With this treatment the skin was totally removed after immersion. With the other tested concentrations portions of skin were always visible and in some cases changes in texture with breakdown of muscle structure and changes of colour occurred. It was decided to perform a second set of experiments using the 2% KOH treatment, but this time applied to low fat sardines (average of 4.77% of fat, w/w), following the same subsequent procedures. The results showed that the lower fat sardines are more prone to surface changes of colour and major muscle breaks than fat sardines after the potassium hydroxide treatment. In the canning industry for this type of product (skinless and boneless) only fat sardines are used to assure the total removal of skin. This treatment of 2% KOH can also be applied to fat sardines in the currently processing line just after the beheading/evisceration step. Sardines, then, can follow the cooking step already placed in the tins, as done with the common product (beheaded sardine with skin and bones), making the process less time consuming.
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