De invloed van hittebehandeling op de extraheerbaarheid van haverconstituenten en de colloïdale toestand en emulgerende eigenschappen van haverproteïnen

Oats are a valuable source of proteins and the soluble dietary fiber β-D-glucan. Despite this favorable composition, commercially available oat-based drinks and yogurt alternatives generally contain relatively low levels of these oat constituents. To achieve desirable nutritional profiles and product functionality, such products are therefore frequently fortified with refined plant proteins and fibers. This indicates that only a limited fraction of oat protein and β-D-glucan is retained in the oat liquid base used for producing oat-based dairy alternatives, reflecting the low extractability of these components from the oat matrix and a missed opportunity to fully exploit the nutritional and functional potential of oats. The limited oat protein and β-D-glucan extractability is due to a combination of their presence within a complex cellular matrix, and the industrial heat treatment (or 'kilning') oat groats are subjected to. The main aim of this kilning process is to inactivate endogenous enzymes, thereby preventing formation of rancidity and off-flavors, and ensuring product stability during further processing, traditionally focused on flaking and milling. However, in the context of the recent growing interest in oat-based liquid and semi-solid dairy alternatives, the impact of kilning on oat constituent extractability has not been given much attention thus far. Not only the extractability is a relevant aspect for the development of oat-based dairy alternatives, but the colloidal state and functional properties of proteins, once extracted, also play a critical role. However, these factors and the impact of kilning thereon have received limited attention in the currently available literature. This PhD research therefore investigated the effect of kilning on the extractability of key oat constituents, as well as on the colloidal state and emulsifying properties of oat proteins, using oil-in-water emulsions as a model system for oat-based drinks. In a first part of the PhD research, the results demonstrated that kilning markedly reduces the extractability of oat proteins, which was associated with heat-induced alterations in protein secondary structure and aggregation. Importantly, less severe heat treatment conditions could be applied to retain high protein extractabilities, without compromising on shelf stability. Additionally, kilning decreased the oat β-D-glucan extractability, but the extracted β-D-glucans exhibited higher molecular weight and yielded more viscous extracts, potentially offering additional nutritional benefits. In a second part of the PhD research, the impact of kilning and altered environmental conditions on the colloidal state and emulsifying properties of oat proteins was investigated. For this, oat protein isolates were used, thereby minimizing the interference from other oat constituents. Overall, it was observed that samples containing less protein aggregates resulted in emulsions with greater stability. Finally, it was shown that the interplay between oat protein ageing and heat treatment in dispersion was crucial in determining the final protein structures formed. All this shows that it is highly relevant to consider the colloidal state of proteins in relation to understanding their functional properties in foods. Overall, this research elucidates the impact of kilning on oat constituent extractability and protein colloidal and emulsifying properties, offering strategies to better harness the intrinsic nutritional and functional properties of oats in dairy alternative applications.