Changes in microbial population during fermentation of tropical freshwater fish viscera

Comparative efficiency of native and non-native starter culture in the production of bio-silage using composite waste from fish and vegetables

The efficiency of native and non-native starter cultures in the production of bio-silage using composite waste from fish and vegetables was studied. An ensilage experiment was conducted in a natural way (without starter culture) of composite waste (fish to vegetable at 80 to 20%) to isolate the native fermentative microflora. An Enterococcus faecalis strain isolated from the natural ensilage of composite waste showed higher efficiency over other commercial LAB strains generally used for ensilation. A total of 60 isolates were screened and characterized biochemically from ensilaged composite waste. Among them, 12 proteolytic and lipolytic positive isolates were identified as Enterococcus faecalis, based on a BLAST search of the 16S rRNA gene sequences. Subsequently, composite bio-silage was prepared by inoculating starter cultures with three (3) treatments T1 (native-Enterococcus faecalis), T2 (non-native-Lactobacillus acidophilus), T3 (a mixture of E. faecalis and L. acidophilus) and compared with control (composite bio-silage without starter culture). The highest non-protein nitrogen (0.78 ± 0.01 mg of N /100 g) and degree of hydrolysis (70.00 ± 0.06% of protein/100 g) was seen in the T3 sample, and the lowest (0.67 ± 0.02 mg of N/100 g and 50.40 ± 0.04% of protein/100 g) was seen in the control. At the end of ensilation, the pH fell (5.95-3.88) in conjunction with the formation of lactic acid (0.23-2.05 g of lactic acid/100 g), and the lactic acid bacteria count nearly doubled (log 5.60-10.60). The lipid peroxidation products PV (0.11-0.41 milli equivalent of oxygen/kg of fat) and TBARs (1.64-6.95 mg of malonaldehyde/kg of silage) were changed within a reasonable range in the following pattern Control > T2 > T3 > T1, which led to oxidatively stable products. The findings revealed that native starter culture E. faecalis, which can be employed as a single or in combination with non-native L. acidophilus, performed better in the bio-ensilation process. Additionally, the finished composite bio-silage can be used as a novel, protein-carbohydrate rich feed component to help manage wastes from both sectors.

Stabilizing smoked salmon (Oncorhynchus gorbuscha) tissue after extraction of oil

Alaska salmon oils are rich in n-3 polyunsaturated fatty acids and are highly valued by the food and pharmaceutical industries. However, the tissue that remains after oil extraction does not have an established market. Discarded pink salmon (Oncorhynchus gorbuscha) tissues were preserved using a combination of smoke-processing and acidification with lactic acid bacteria (LAB). All samples were analyzed for moisture, protein, ash, and lipid contents. Bacterial cell counts, pH, and lactic acid concentrations were recorded as a measure of LAB viability. Neither raw nor smoked salmon were free from spoilage during 60 d of storage. Only fermented samples successfully stabilized below pH 4.7, while retaining lactic acid concentrations over 15 g/L during storage. When smoked, fermented salmon head tissues were dried, the pH of the resulting high-protein "cracker" was significantly lower than when crackers were prepared only from the smoked (but not fermented) salmon material. Both cracker varieties retained valuable polyunsaturated fatty acids. This research suggests that salmon-head tissues discarded after oil extraction represent a good source of protein and high-value fatty acids in a shelf-stable form.

PRACTICAL APPLICATION

Alaska salmon oils are rich in n-3 polyunsaturated fatty acids and are highly valued by the food and pharmaceutical industries. However, the tissue that remains after oil extraction does not have an established market. Material produced from salmon tissue discarded after oil extraction may represent a valuable resource for preparing high-protein crackers and other fish-based food products. In addition to providing a unique smoke-flavoring, the smoked, fermented fish material may also impart antioxidant factors thereby extending the shelf life of the product.