Doctoral Degrees (Chemical Engineering)
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Browsing Doctoral Degrees (Chemical Engineering) by Author "Chiodza, Godknows Kudzai"
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- ItemThe impact of processing conditions on enzymatic protein hydrolysis performance from sardine (Sardina pilchardus) by-products using Alcalase 2.4L, and the influence on final spray dried hydrolysate powder properties(Stellenbosch : Stellenbosch University, 2023-12) Chiodza, Godknows Kudzai; Goosen, Neill Jurgens; Stellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering. Process Engineering.ENGLISH ABSTRACT: Sardine processing by-products are a valuable resource that is currently underutilised. Currently, they are being processed into low value fish meal, which is used as animal feed, despite their being food-grade material suitable for human consumptiom Enzymatic hydrolysis is one of the best methods for producing value-added products as it produces protein hydrolysates with bioactive, functional and physico-chemical properties. However, despite more than 60 years of research and development, some important information relevant to the chemical engineering discipline remain lacking. This study was aimed at determining the impact of processing conditions at different stages of enzymatic hydrolysis of sardine by-products using Alcalase to produce spray dried hydrolysates. This was achieved by (i) investigating the effect of mixing speed, solids concentration and enzyme dosage on dry solids yield and protein recovery, and emulsion formation during enzymatic hydrolysis of sardine processing by-products, (ii) determining the effect of solids concentration and emulsion formation on molecular weight distribution of protein hydrolysates, (iii) investigating the effect of mixing speed and solids concentration on the viscosity and mixing regime of material during enzymatic hydrolysis, (iv) establishing the role played by processing conditions (degree of hydrolysis (OH), maltodextrin addition and inlet air temperature) on powder recovery during spray drying, and handling and storage properties of the spray dried protein hydrolysates. A complex relationship was observed between variables, where the effect of one variable was dependent on the levels of the other processing variables. Low solids concentration at low mixing speed and high enzyme dosage were required to maximise protein recovery in the aqueous phase while minimising protein loss to emulsion and sludge. Simultaneously increasing solids concentration and mixing speed did not attenuate protein loss to emulsion. The peptides in the emulsion phase are of bw value, as they are removed from the hydrolysate that is finally dried. Their recovery requires additional processing, which adds to process complexity and cost At high solids concentration, energy consumption in the first 10 minutes of hydrolysis was significantly higher than in the last 10 minutes (hydrolysis time = 60 min). The reduction in energy consumption was due to liquefaction of solids. Although viscosity was expected to decrease due to liquefaction of solids and reduction in molecular weight of proteins, it increased in the first 10 minutes of hydrolysis and remained high thereafter. This was most likely due to gel formation caused by agglomeration of proteins when their concentration in solution increases, or emulsion formation, or both. It is shown that processing conditions affected powder recovery during spray drying, and handling and storage properties. DH had the strongest influence on powder recovery, with high DH resulting in bw powder recovery. The hygroscopic nature of protein hydrolysates caused a significant amount to stick to the chamber walls. This material can be recovered easily by using appropriate mechanisms or modifications to the drying equipment, increasing powder recoveries to over 80%. The protein hydrolysates at high DH had higher water affinity and addition of maltodextrin had little effect on their moisture adsorption capacity.