Protein hydrolysates were produced from shrimp waste mainly comprising head and shell of Penaeus monodon by enzymatic hydrolysis for 90 min using four microbial proteases (Alcalase, Neutrase, Protamex, Flavourzyme) where PR(%) and DH (%) of respective enzymes were compared to select best of the lot. Alcalase, which showed the best result, was used to optimize hydrolysis conditions for shrimp waste hydrolysis by response surface methodology using a central composite design. A model equation was proposed to determine effects of temperature, pH, enzyme/substrate ratio and time on DH where optimum values found to be 59.37°C, 8.25, 1.84% and 84.42 min. for maximum degree of hydrolysis 33.13% respectively. The model showed a good fit in experimental data because 92.13% of the variability within the range of values studied could be explained by it. The protein hydrolysate obtained contained high protein content (72.3%) and amino acid (529.93 mg/gm) of which essential amino acid and flavour amino acid were was 54.67-55.93% and 39.27-38.32% respectively. Protein efficiency ratio (PER) (2.99) and chemical score (1.05) of hydrolysate was suitable enough to recommend as a functional food additive.

Protein hydrolysates prepared by hydrolysis of shrimp waste (Penaeus monodon and Penaeus indicus) for 90 min. using Alcalase enzyme following pH-stat method. Antioxidative activities of SWPH were assessed determining FRAP, ABTS and DPPH radical scavenging activities, which increased linearly with increasing concentration of protein hydrolysate upto 5 mg/ml maintaining good correlation. SWPH showed high stability over wide ranges of pH (2-11) and temperature (up to 100°C for 150 min), in which the activity of more than 80% was retained. Protein hydrolysate solution with a concentration of 5 mg/ml significantly lowered TBA values of Croaker fish fillet and maintained yellowishness of skin colour compared to untreated control sample during 10 days of refrigerated storage at 4°C. SWPH also restricted the increase of PV and FFA values in Croaker fish fillet within acceptable limit.

Effect of chitosan on physicochemical attributes of croaker fish surimi during storage at −20±2°C for 180 days was evaluated. The quality of croaker surimi added with 1% (w/w) chitosan was examined in terms of muscle protein, thaw drip, gel strength and Ca 2+ ATPase activity comparing with those surimi samples added with 4% sucrose and 4% sorbitol. Surimi without any cryoprotectant was treated as control. Chitosan showed cryoprotective effect similar to commercial cryoprotectants as both of them minimized the negative effects of frozen storage on physico-chemical attributes of myofibrillar proteins. The residual Ca 2+ ATPase activity and gel strength of surimi with chitosan were higher than those of control throughout the storage period. Ca 2+ ATPase activity and gel strength had high positive correlation. It is concluded that chitosan was effective in preservation of croaker muscle protein native structure during 6 months of frozen storage and is comparable to other commercial cryoprotectants.

Effect of sodium lactate as cryostabilizer on physico-chemical attributes of croaker (Johnius gangeticus) fish muscle protein was studied during freezing and frozen (-20 ± 2°C) storage for 3 months. Minced meat was mixed with 4% sucrose, 4% sorbitol, and 0.3% sodium tri poly phosphate (STPP) (T1), minced meat was mixed with 6% (w/v) sodium lactate and 0.3% STPP (T2) and control (C) was without any additive. The decreasing rate of Ca(2+) ATPase activity, thaw drip, water holding capacity and relative viscosity in T1 and T2 samples from that of C was significantly lower, indicating higher protective effect of additives. In case of cryoprotectant treated samples, the degradation of myosin heavy chain was much lower than that of C which prevents the aggregation and subsequent insolubilization of myosin during frozen storage. The sodium lactate prevented Ca(2+)ATPase activity more than that of sucrose/sorbitol during isothermal storage at -20 ± 2°C for 3 months. This inferred that sodium lactate can effectively be used as an alternative cryostabilizer to sucrose/sorbitol for stabilization of croaker muscle protein native structure.