To establish the effect of barrel temperature, screw speed, total moisture and fish flour content on the expansion ratio and bulk density of the fish based extrudates, response surface methodology was adopted in this study. The experiments were optimized using five-levels, four factors central composite design. Analysis of Variance was carried to study the effects of main factors and interaction effects of various factors and regression analysis was carried out to explain the variability. The fitting was done to a second order model with the coded variables for each response. The response surface plots were developed as a function of two independent variables while keeping the other two independent variables at optimal values. Based on the ANOVA, the fitted model confirmed the model fitness for both the dependent variables. Organoleptically highest score was obtained with the combination of temperature-110 0 C, screw speed-480 rpm, moisture-18 % and fish flour-20 %.

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Textural changes as well as protein degradation during frozen storage of Nile tilapia (Oreochromis niloticus) at −18C for 150 days were studied. Salt-soluble protein and protein solubility decreased significantly during the frozen storage period. Sodium dodecyl sulfate polyacrylamide gel electrophoresis was performed, and no visible changes in myosin heavy chain were observed up to 90th day of frozen storage period; however, the thickness of band was found to decrease thereafter. A new lighter band with molecular weight of 29 kDa was found on 120th and 150th day of sampling period. Actin was found more resistant to proteolysis. Texture profile analysis revealed that hardness 1, hardness 2, gumminess and chewiness gradually decreased up to 120th day, but showed an increase thereafter. Although sensory attributes decreased with the progress of frozen storage period, the fish was in acceptable condition on 150th day. Gradual toughening of muscle was recorded by the sensory panelists. PRACTICAL APPLICATIONThe popularity of tilapia is gaining importance for the development of different value-added fish products as well as for canning purposes. Therefore, it is important from the part of fish processor to know the changes of protein and texture profile during frozen storage. Although there was protein degradation and changes in texture profile during the study period of 150 days, the fish was in acceptable condition. , etc.) are significantly different (P < 0.05) with respect to period of storage.STUDY OF TILAPIA DURING FROZEN STORAGE K. SUBBAIAH ET AL.

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Like Southeast Asian countries fermented fish is a well known strategy of food preservation in the Northeast region of India. Shidals are mostly preferred salt-free fermented fish product amongst all. Chemical and microbial composition, antioxidative potential, fatty acid profile and proteins profile in gel electrophoresis of shidals were studied. pH and total titratable acidity (TTA) have been found as 5.86 ± 0.11, 0.115 ± 0.01 and 6.62 ± 0.07, 0.092 ± 0.01 in punti and phasa shidal respectively. DPPH · radical scavenging activity of punti and phasa shidal was determined as 80.15 ± 5.67 and 68.30 ± 3.22 respectively. Presence of eicosapentaenoic, docosahexaenoic, arachidonic, linolenic and linoleic acid indicate the nutritional significance of shidal. However, the result showed that punti shidal was rich in omega-3 but poor in omega-6 fatty acid, whereas, reverse was observed in respect of phasa shidal. Poly acrylamide gel electrophoretic study of protein revealed disappearance of myosin head chain (MHC) in the dry puntius fish (raw material of shidal). Proteins or peptides with low molecular weight between 45 and 29 kDa and between 45 and 66 kDa were noticed in both the shidals and indicative of intensive protein degradation during fermentation. Therefore, fermented fish product, shidal could be used as a potential source of nutrients and natural antioxidants.

Ngari and hentaak are the two most preferred traditional salt-free fermented fish products of North-Eastern (NE) states of India. Chemical and microbial composition, antioxidative potential, fatty acid profile and electrophoretic pattern of protein in ngari and hentaak were studied. pH and total titratable acidity (TTA) of the products justified their stability at ambient temperature. Both ngari and hentaak showed higher contents of calcium (362.79 ± 26.89, 472.11 ± 62.7); sodium (199.66 ± 24.92, 94.0 ± 12.78); potassium (58.20 ± 7.36, 75.74 ± 6.62) and magnesium (16.056 ± 3.89, 21.125 ± 3.78) respectively. Iron, copper and zinc were found in lesser amount. DPPH · radical scavenging activity was close to 87 % in both the products and the ferric chloride reducing power assay was dose dependent in both the products. Both omega-3 and omega-6 fatty acids were found in ngari; whereas, only omega-3 fatty acids were observed in hentaak. Linoleic acid (11.68 %) and arachidonic acid (0.65 %) were the n-6 PUFA in ngari; while, in hentaak, it was only arachidonic acid (8.54 %). Apart from essential fatty acids, essential amino acids were also found in considerable quantity in both the products. Micrococcus sp. and Staphylococcus sp. were found to be the dominant bacterial genus in both the products; while Ngari also had lactic acid bacteria group. The nutritional properties afforded by these products justify their preference by the population.

Expanded products with fish flour, rice and corn flour was prepared using a twin‐screw extruder with varying temperature, screw speed, total moisture and fish flour content to establish their effect on the expansion ratio, bulk density, porosity and water solubility index of the extrudates adopting response surface methodology. The experiments were optimized using five‐level, four‐factor central composite design. Analysis of variance was carried to study the effects of main factors and interaction effects of various factors and multiple regression analysis was carried out to explain the variability. Sensory acceptability study was conducted to select best products. The expanded materials obtained at 100–110C with feed material containing 15–20% fish flour and 14–18% moisture had the best properties. The study showed that expanded products produced using rice, corn and fish flour under conditions that induced the maximum expansion had the best acceptability. Practical Applications In the recent time, extruded products are gaining wide popularity. Most of the extruded snacks are cereal‐based and thus have less protein content and are limited in some essential amino acids. The incorporation of protein‐rich fish mince or fish flour would increase the nutritive value of such products. Fish mince or fish flour blended with rice/corn flour can be coextruded to obtain a nutritious snack without compromising the quality of the final product. Fish, which lacks good market in fresh condition, can be easily utilized for this purpose either by mincing or making fish flour. This study primarily aimed at preparing extruded snack‐like products using rice and corn flour with added flour from freshwater fish. Response surface methodology was applied to investigate the different process conditions on the physicochemical and sensory qualities of the final products.