Studies on thermal deffusivity [i.e. diffusivity] and conductivity of fresh and dry fish

Thermal diffusivity (α) and conductivity (K) of fresh and dry cured fish at different moisture levels were investigated by a calorimeter (regular regime) method and transient line source technique. Thermal conductivity has a linear correlation with packing density and percentage water content. K values calculated from formula method and line source technique are comparable.

Freeze drying of fishery products: Part IV - Biochemical changes occurring in prawn muscle during freezing, freeze drying and prolonged storage of the freeze dried product

The changes occurring in water and salt extractable protein and non-protein fractions in prawn muscle of different species during freezing, freeze drying and subsequent prolonged storage have been studied. There is no denaturation of water extractable proteins, whereas salt extractable proteins were rendered insoluble to the extent of 21% due to freeze drying. The freeze dried products remained in good edible condition for 32 months of storage up to which storage characteristics were followed.

Shrimp extract from prawn waste

A method has been described for the preparation of protein extract from prawn waste. The process consists of extracting the protein from minced fresh prawn head and shell waste by treatment with mild alkali and neutralisation and concentration of the filtrate into a semisolid consistency. The yield of the final product is about 20% of the weight of fresh prawn waste.

Studies on smoke curing of tropical fishes

Fresh mackerel (Rastrelliger kanagurta), catfish (Tachisurus dussumeri) and sole (Cynoglossus dubis) were gutted, cleaned, washed, brined, and smoked. Though it contributes to the quality of the smoked products, salt does not appear to prevent bacterial growth or spoilage at low concentration. In heavily salted products, salt is found to have a definite preservative action. Smoking lasted roughly 5 hrs for mackerel and 4 hrs for sole. Increasing the smoking time gave the product an unpleasant taste. Fish were then sun-dried to 20% moisture. The fish had been prepared in three groups, (1) turmeric-treated, (2) propionate-treated and control. Turmeric treated samples had a very attractive appearance, especially sole. The course of spoilage, as measured by following changes in total volatile nitrogen content, is tabulated. All controls were spoiled within 3 months; the others remained in good condition for 6 months. Turmeric is considered to be an ideal preservative.

Bacterial flora of fresh and iced Indian mackerel (Rastrelliger kanagurta) and its response to chlortetracycline (CTC) treatment

Quantitative and qualitative studies on the bacterial flora of fresh Indian mackerel (Rastrelliger kanagurta) have been made. The total native flora as well as 5 ppm CTC insensitive flora of the fish showed variations with season. About 90% of the fresh fish flora was sensitive to 5 ppm CTC. The natural flora of the fresh fish consisted of Vibrios, Pseudomonas, Achromobacter, Flavobacterium, Corynebacteria, Micrococci, Bacillus and yeasts. In the CTC insensitive flora, Vibrios predominated followed by yeasts. The selection of bacterial genera during storage of the fish in ice and in 5 ppm CTC incorporated ice has also been investigated. At the time of spoilage, Pseudomonas was found to be the dominant flora of the fish stored in both types of ice.

A biochemical test for the distinction of fresh fish from frozen and thawed fish

It is observed that the freezing and thawing of fish leads to increase in the total activity of aspartate aminotransferase (AAT) in tissue fluid due to the release of the bound form of mitochondrial enzyme. Electrophoresis of the tissue fluid of fresh unfrozen fish shows only a single fast-moving band of AAT in the anodic region whereas frozen and thawed fish shows an additional slow-moving band corresponding to mitochondrial AAT in the cathodic region. The method can be adopted to distinguish fresh fish from frozen and thawed fish.