A Study On Enzymatic Protein Recovery From Skin Of Freshwater Fish And Its Functionality

Considerable amounts of protein rich by-products from seafood processing plants are discarded without any attempt to carry out recovery. The preference in many western countries for bone free fillets necessitates removal of flesh from fish and a substantial amount of original weight is considered a waste of which the skin is inclusive. It would be of great interest to put these by-products which are high in protein to use in human foods instead of use in fish meals for animal feed. Through the development of enzyme technologies for protein recovery and modification, production of a broad spectrum of food ingredients and industrial products is possible.Protein hydrolysate was produced from grass carp skin using an endo-peptidase Alcalase. Hydrolysis conditions were optimized by using a response surface methodology (RSM). A model equation was proposed with regard to effects of temperature (T), pH, enzyme/substrate ratio (%v/w of minced skin protein) (E/S) and time (t) on degree of hydrolysis (DH). The optimum values for temperature, pH, enzyme/substrate ratio and time were found to be 59.74°C, 8.25, 1.70% and 83.83 minutes respectively. Regression coefficients indicated that all linear forms temperature, pH, time and E/S ratio plus one quadratic form t2 and one crossproduct interaction T·t were significant (α=0.05). The model showed a good fit in experimental data since 90.7% of the variability within the range of values studied could be explained by it. The freeze dried hydrolysate contained high protein content (90.8%). The hydrolysate produced was highly water-soluble with good water holding, oil binding and emulsifying properties. Thus production of a hydrolysate with desired functional properties is possible from grass carp skin using Alcalase.Protein hydrolysates from grass carp skin were obtained by enzymatic hydrolysis at varying DH using Alcalase. Hydrolysis was performed using the pH-stat method. The hydrolysis reaction was terminated by heating the mixture to 95°C for 15 minutes. At 5.02%, 10.4%, and 14.9% degree of hydrolysis (DH), the hydrolysates were analyzed for functional properties. The protein hydrolysates had desirable essential amino acid profiles. Results demonstrated that the hydrolysates had better oil holding and emulsifying capacity at low DH. The water holding capacity increased with increased hydrolysis. Enzymatic modification was responsible for the changes in protein functionality. These results suggest that grass carp fish skin hydrolysates could find potential use as functional food ingredients as emulsifiers and binder agents. The influence of using Alcalase on the biochemical and functional properties of the hydrolysis products from different freshwater fish species skin (Nile perch, Grass carp and Nile tilapia) was studied. Reaction conditions were controlled at pH 8.25, 60°C and enzyme was added on basis of standard activity units at an enzyme to substrate ratio of 1.7% (v/wt skin protein). The reaction was allowed to proceed for 85 minutes and enzyme inactivated by heat. The soluble protein fractions were recovered and lyophilized. All freeze-dried fish skin hydrolysates powders had a light yellow colour and contained up to 90% protein. Nitrogen solubility varied from 95.93 to 98.72% and was not significantly different at 5% probability level. The water and oil holding capacities of the skin hydrolysates were good in the range of 2.8 to 3.2 mL/g and 3.4 to 3.8 mL/g respectively. Emulsification capacity varied from 11.3 to 21 mL/0.5 g with Nile perch skin hydrolysate having the highest score while Nile tilapia skin hydrolysate was the lowest. Grass carp skin hydrolysate was not able to form stable foam unlike the Nile perch and Nile tilapia skin hydrolysate. Alcalase treated freshwater fish skin exhibits satisfactory functional properties hence may play an important role as an ingredient in the food and pharmaceutical industry.Macroporous adsorption resin (MAR) DA 201-C was used to desalt different freshwater fish skin protein hydrolysates (FSPHs). The FSPHs were obtained by hydrolysis of fish skin using Alcalase in a batch reactor a 60°C and pH 8.25. The ash was removed by adsorbing FSPHs onto MAR. Desorption was achieved by washing with alcohol at different concentrations. Ash content of the FSPHs was reduced from 4.69-5.57% to 1.07-2.48% range. The protein content was enriched from 89.07-90.82% to 94.89-96.38% range. MAR has good hydrolysate recoveries. The use of MAR showed promising results in decolourization and fishy flavour reduction. Nile tilapia and Nile perch skin protein hydrolysates were moderately bitter compared to Grass carp skin protein hydrolysates. The bitter taste in FSPHs was reduced to slightly detectable levels by our sensor panel. The hydrolysates had relatively low molecular weight. The process of applying MAR to desalt and debitter FSPHs is feasible.The freshwater fish skin based hydrolysate powders can hence be commercially incorporated into foods for human consumption. This makes them potential competitors with dairy based and plant based protein hydrolysates currently being used.