Investigation of enzymatic hydrolsis, solubilization, enzyme inactivation kinetic and functional properties of sesame cake protein

The breakdown of a protein to constituent amino acids is a natural process. Protein hydrolysis can be achieved by a number of chemical processes, in acidic and basic conditions and most importantly by enzymes for example proteases. The more soluble and easily digestible products can be obtained by the break down the proteins to peptides; and some functional properties such as flavour, viscosity, emulsifying and foaming are also affected. Although, the plant proteins are cheap and superabound, the use of these proteins in food industry is limited because of their low functional performances. However, the functional properties of plant proteins can improve by enzymatic modifications; and then these products can be considered as foodstuff in the food industry.The sub-product of the oil extraction process is sesame cake, which has 40 % protein content. The main use of sesame cake is animal feed. The low water solubility of sesame cake limits its use for human food products, but it can be increased by modification. In the present work, a comprehensive study on the hydrolysis of sesame cake prtotein was performed to improve its utilization in food products.In the present study, first of all a general survey of enzymatic hydrolysis and solubilization of sesame cake protein was performed with five commercial enzyme preparations (Alcalase, Neutrase, Flavourzyme, Protamex and PTN) in order to choose appropriate enzyme; and Alcalase gave the highest performance among the other enzymes used. Then, the calibration of pH-stat was performed; and the pK values of the sesame cake protein hydrolysates were determined as 6.88, 6.65 and 6.42 for the temperatures of 40°C, 50°C and 600C respectively. For optimization of the process parameters, hydrolysis reactions were performed at different substrate concentrations (10-30 g protein/L), enzyme concentrations (0.20-0.40 % v/v), pH values (6.5-9) and temperatures (45-650C); and the degree of hydrolysis, solubility of sesame cake protein and residual enzyme activity were investigated depending on the processing time. The optimum process conditions for hydrolysis and solubilization were obtained as 15 g/L substrate concentration, 0.30 % v/v enzyme concentration, 50 °C and pH 8.5. Under these conditions, the values of degree of hydrolysis and solubilization were found as 26.3 % and 82.1 % respectively; and enzyme lost its activity by approximately 56 % at the end of 120 min processing time.The effect of hydrolysis products and pretreatments applied to substrate; such as termal treatment, microwave irridation, and sonic treatment; on hydrolysis were also investigated. Modeling studies were performed to determine the kinetics of hydrolysis, solubilization and enzyme inactivation. The Michelis Menten kinetics was exmined with initial rate assays, and the kinetic parameters, Km and Vmax were estimated as 41.17 g/L and 9.24 meqv/L.min. The effects of temperature and pH on Michelis Menten parameters were also examined. The type of inhibition for Alcalase determined as uncompetitive; and the inhibition constant Ki was estimated as 38.24 % (hydrolysate/substrate mixture).The functional properties (water holding capacity, oil holding capacity, foaming and emulsion properties) were investigated. It was found that the functional properties of sesame cake protein hydrolysates could be modified by enzymatic hydrolysis. The results suggested that the functional characteristics of sesame cake protein hydrolysates make them good substrates to be used in food industry as a natural additive for many industrial food applications; and also for cosmetic and personal care products. So, the by-product sesame cake can be processed into a value-added product.