Optimisation of enzymatic hydrolysis of monkfish heads for preparing protein hydrolysates as animal feed ingredient

Greyling, Nanette (2017-03)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

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.

AFRIKAANS OPSOMMING: Die visspesie Lophius vomerinus kom voor tussen die kus van Namibië tot en met KwaZulu-Natal in Suid Afrika en die vleis in die stert van die vis word gebruik vir menslike voedseltoepassings. Die kop van die vis maak die grootste deel van die afvalprodukte uit, maar word tans weggegooi. Daar is 'n toenemende aanvraag vir vee- en pluimvee gebasseerde proteïen, en as gevolg daarvan het die dierevoerindustrie nuwe bronne van proteïene nodig om die aanvraag te kan voorsien. In hierdie studie word die potensiaal van die Lophius vomerinus se kop, om te dien as 'n proteïenryke visverwerkingsafvalproduk wat verwerk kan word vir dierevoer, ondersoek. Die viskop word ook gekarakteriseer in terme van die algemene samestelling, vetsuurprofiel, aminosuurprofiel en die mineraalinhoud. Addisionele doelwitte van hierdie studie was (i) die optimering van die ensiem hidroliese reaksie van die roumateriaal deur die reaksietemperatuur en pH te varieer, en twee proteolitiese ensieme naamlik alcalase en bromelain te gebruik, (ii) om die pK waarde van die alcalase/viskop en bromelain/viskop kombinasies te bepaal, sodat dit gebruik kan word in die vergelyking om die mate tot waartoe die viskop gehidroliseer is, soos uiteengesit in die pH-stat metode, te bereken, en (iii) om die hidrolisaatproduk te evalueer vir potensiële toepassings as funksionele kosbestanddeel en dierevoerbestanddeel. Daar is bevind dat die rou viskop 'n goeie bron van addisionele proteïene en noodsaaklike vetsure is en sal dien as goeie dierevoerbestanddeel. Resultate het ook daarop gedui dat daar heelwat proteïene verryk met noodsaaklike aminosure in die viskop is. 'n Groot porsie van die vet in die viskop het bestaan uit die waardevolle onversadigde vetsure, DHA en EPA. Hoë vlakke van kalsium is in die viskop gevind, en die toksiese elemente wat opgemerk is, se vlakke was alles onder die maksimum toelaatbare waardes vir voedseltoepassings. Daar is vir elke ensiem/substraat kombinasie wat geëvalueer is in hierdie studie 'n stel optimale ensiem hidroliese parameters gevind. Die ensiem wat gebruik is tydens hidroliese het 'n beduidende invloed op die optimale reaksietemperatuur en pH gehad. Die waarde van die optimale pH vir hidroliese met bromelain was beperk tot 'n alkaliese of neutrale pH, omdat die pH-stat metode slegs toepaslik is onder hierdie spesifieke pH toestande. Die pK waarde vir die alcalase/viskop kombinasie kon suksesvol bepaal word, maar dit was nie die geval vir die bromelain/viskop sisteem nie, moontlik weens die inhibisie van die ensiem as katalis, of die reaksie-pH wat nie toepaslik was vir die spesifieke ensiem/viskop kombinasie nie. In hierdie studie is die funksionele eienskappe van beide die vis proteïen hidrolisaat (VPH) vloeistof en sediment getoets omdat die studie gebasseer is op die opgradering van visafvalprodukte, en die sediment 'n groot porsie van die hidrolisaatproduk opgemaak het. Goeie waardes vir antioksidatiewe aktiwiteit is waargeneem vir beide die sediment en VPH, sowel as goeie emulsiestabiliteit, en vetabsorpsie waardes. Die waardes van die funksionele eienskappe van die sediment was laer as die van die VPH vloeistof, en in beide gevalle het die ensiem wat gebruik is tydens hidroliese 'n beduidende invloed op die funksionele eienskappe gehad. Hierdie studie het tot die gevolgtrekking gelei dat ensiem hidroliese van die Lophius vomerinus viskop 'n hidrolisaatproduk wat ryk in proteïene is, kan lewer, en dat die produk geskik is om te gebruik as dierevoerbestanddeel. Die resultate wat uit die studie gelewer is, kan 'n bydra lewer tot die optimale verbruiking van hulpbronne in die visverwerkingsindustrie sowel as die dierevoerindustrie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101043
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