English abstract
Traditionally, shark meat is dried in the sun in many regions of Oman. This often leads to a product of low quality. In this study different drying methods (i.e sun drying, convection air drying, osmo-sun drying and osmo-air drying) were used to dry shark meats. Drying kinetics, microbial determinations and quality parameters (i.e rehydrability, color and fatty acid composition) were determined. Sun dried samples and osmo-air dried samples had the highest and the lowest water content, 35.4% and 27.1% (dry basis), respectively. The protein content of dried shark samples ranged from 61.4% for sun dried samples to 67.8% for osmo-air dried samples and the fat content between 0.8% and 1.0% with no significant effect of either drying method or application of osmotic treatment. The water content of brine salted shark meat was higher than dry salted shark meat, but decreased more rapidly to a lower value during drying than dry salted shark meat. Equilibrium moisture content increased non-linearly with increasing water activity. Desorption isotherms showed that equilibrium moisture content was lower for air dried samples compared to sun dried samples at a given water activity. It was observed that in all cases osmotic treatment prior to sun or air drying gave lower equilibrium moisture contents at the same water activity. These trends were more pronounced in the water activity region above 0.2. Air dried samples showed significantly lower total aerobic bacterial counts compared to sun dried samples. Staphylococci counts from commercial samples were significantly higher than other dried shark samples and had significantly higher aerobic bacterial counts. Osmotic treatment of shark meat samples prior to drying significantly lowered the aerobic bacterial count and Staphylococci counts. Molds grew on all samples during storage at room temperature. Identification of molds showed that Aspergillus species were predominant in the osmo-sun dried, the commercial dried and the sun dried shark meat (more than 90%, 83% and 74% of moulds count respectively). Penicillium were the only species in air-dried samples. Color was affected by the drying method. Air-dried samples had higher 5* values (yellowness) than all other samples. The (redness) of shark meat dried by different methods was significantly lower than that of fresh meat samples, suggesting more extensive degradation of fish proteins that contribute to the color of fish. There was no effect of drying methods on the content of total saturated fatty acids of the dried shark samples. Osmo-sun dried samples were significantly lower in their total saturated fatty acid content than osmo-air dried shark samples. Sun dried shark samples contained significantly higher amounts of monounsaturated fatty acids compared to air dried samples. Significant differences were shown in the rehydration ratios among the drying methods, with significantly higher rehydration values for air dried and osmo-air dried samples.
