Enzymatic modification of oat protein concentrate for increased fibrillation during high-moisture extrusion cooking
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Kemian tekniikan korkeakoulu |
Master's thesis
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CHEM3022
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en
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79 + 10
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Abstract
This thesis was done at VTT Technical Research Centre of Finland Ltd as a part of the OatHow project funded by Business Finland. The aim of this thesis was to increase fibrillation between oat proteins during high-moisture extrusion cooking by enzymatic modification of oat protein concentrate (OPC). Protein concentrates do not typically fibrillate well due to their low protein content and the presence of other components e.g. starch. Enzymatic modification of oat proteins and hydrolysis of starch may lead to improved fibrillation due to the creation of a stronger protein network. Three commercial enzymes were used to modify the OPC. Transglutaminase (WM enzyme) was used to cross-link oat proteins, a mix of transglutaminase and protein-glutaminase (SYG enzyme) was used to cross-link as well as deamidate oat proteins, and α-amylase (BAN enzyme) was used to hydrolyse the starch from the OPC. Different treatment conditions were tested e.g. preheating, temperature, enzyme dosage, and incubation time. Protein solubility, viscosity, particle size distribution, and SDS-PAGE were analysed from the modified OPC. The modified OPC samples were extruded in a high-moisture extrusion cooker and tensile strength as well as free thiol groups were analysed from the extrudates. The results showed that both protein-modifying enzymes (WM and SYG) were able to induce the cross-linking reaction in the oat proteins. The highest cross-linking reaction was observed in the BAN+WM sample, where the starch had been hydrolysed. The samples treated with SYG had increased protein solubility, and decreased particle sizes. Viscosity was increased in the preheated SYG 5 U and the preheated BAN+SYG 5 U samples. The WM modified samples had a slight decrease in protein solubility and decreased particle sizes, although less than in the SYG treated samples. In addition, WM had no effect on the viscosity when compared to the control. When the samples were studied in the extrusion, two extrudates (SYG 0.5 U and WM 0.5 U) showed indications of fibrillation when compared to the extruded reference sample. All the non-preheated extrudates showed a rigid structure probably due to the formation of more disulphide bonds during the extrusion, while fewer disulphide bonds were formed in the preheated extrudates. The preheated SYG 5 U sample had the strongest structure according to the tensile strength results, probably since the proteins gelatinized in the elevated temperatures and formed a strong protein network. The viscosity result also supported this hypothesis. The BAN treated extrudates had a brittle structure, probably due to the strong hydrolysis of starch. Overall, this thesis provided new information about the functional properties of the modified oat proteins and the high-moisture extrusion cooking of the oat proteins. It was observed that a stronger protein network can be formed by enzymatic modification, however, a clear fibrillated structure was not observed. In the future, higher protein content OPC, partial hydrolysis of starch, and larger variety of the extrusion parameters could be tested to increase the fibrillation of the OPC.Description
Supervisor
Deska, JanThesis advisor
Nisov, AnniNordlund, Emilia