Browsing by Author "Greyling, Nanette"
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- ItemOptimisation of enzymatic hydrolysis of monkfish heads for preparing protein hydrolysates as animal feed ingredient(Stellenbosch : Stellenbosch University, 2017-03) Greyling, Nanette; Goosen, N. J.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.ENGLISH SUMMARY: The monkfish Lophius vomerinus is found between the coasts of Namibia and KwaZulu-Natal in Southern Africa, and the fillet is used for human consumption. The head is the largest byproduct from the monkfish catch and is currently discarded. Due to increasing demand on animal derived protein, the animal feed industry requires additional sources of protein-rich raw materials to meet the industry needs. In this study, the potential of the head of the monkfish Lophius vomerinus as protein-rich raw material was evaluated. Characterisation of the raw material was conducted, and included a proximate analysis, fatty acid profile, amino acid profile and mineral content analyses. Further aims in this study were to (i) optimise the enzymatic hydrolysis of monkfish head by varying reaction temperature and pH, and using two proteolytic enzymes: alcalase and bromelain, (ii) determine the pK value of the alcalase/monkfish and bromelain/monkfish systems, to use in the equation for the degree of hydrolysis (DH), as described in the pH-stat technique, and (iii) to evaluate the hydrolysate products for functional food application and as animal feed ingredient. The characterisation data showed that an average amount of 8.19 % (wet basis) protein was found per raw monkfish head, and 43.77 % of the protein was found to be made of essential amino acids. More than 31% of the fat in the monkfish head contained valuable long chain polyunsaturated fatty acids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). The mineral content showed a large quantity of calcium, and quantities of the toxic elements, Hg, Cd and Pb, present, were well below the maximum allowable values for food applications. Optimal enzymatic hydrolysis conditions were found for each enzyme/substrate combination used in this investigation. The values of the optimal reaction temperature and pH were significantly influenced by the enzyme used for hydrolysis. The pH range investigated in this study for the bromelain/monkfish system was limited to neutral and alkaline reaction conditions by the pH-stat method used to determine the DH. The value of pK was successfully determined for alcalase/monkfish system. However, the results from the pK investigation for the bromelain/monkfish system showed possible catalyst inhibition of the enzyme, or pH conditions non-conducive to the enzyme/substrate combination used in this study. The pK of the bromelain/monkfish system could not be determined and the literature value for general fish species protein was used subsequently. The functional properties of the sediment and fish protein hydrolysate (FPH) liquid were both tested in this study, as the focus was on valorising the byproducts and the sediment formed a large proportion of the hydrolysate product. The sediment and FPH showed good antioxidant activity, emulsion stability and fat absorption capacity. The values of the functional properties of the sediment were lower than those observed for FPH, and the enzyme used affected the functional food properties significantly. The study concludes that the enzymatic hydrolysis of monkfish heads can provide a protein rich FPH and hydrolysis sediment product, suitable for use as animal feed ingredient. The results can contribute to improved resource utilisation in the fisheries and animal feed industry.