The impact of heat treatment on oat groat constituent extractability, protein colloidal state and emulsifying properties

Promovendus/a: Ines Pynket

Promotor(en): Prof. dr. Arno Wouters, De heer Frederik Janssen, Prof. dr. ir. Christophe Courtin

Oats are rich in proteins and the soluble dietary fiber β-D-glucan. However, oat-based drinks and yogurt alternatives currently available in the supermarket contain only low levels of these beneficial nutrients. To make up for this, these products are often enriched with other plant proteins and dietary fibers to promote desired end product quality. It is clear that only a limited amount of oat protein and β-D-glucan end up in the oat base that is used for producing these dairy alternatives, highlighting the low extractability of these components from the oat matrix and reflecting the missed opportunity to fully utilize the nutritional and functional benefits of oats.

One reason for this is the industrial heat treatment or kilning process oat groats are subjected to. This heat treatment is performed to improve shelf life, enhance flavor and prepare oats for further processing, traditionally focused on flaking and milling. However, its influence on the extractability of relevant oat nutrients in the context of producing dairy alternatives 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 (i.e. how proteins occur and behave in aqueous media) and functional properties (i.e. how proteins form and stabilize food dispersions) 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. Thus, this PhD research focused on how the kilning process influences the extractability of relevant oat constituents, as well as the oat protein colloidal state and functional properties in oil-in-water emulsions as model system for oat-based drinks.

In a first part of the PhD research, it was shown that kilning strongly impacts the extractability of oat proteins. The decrease in protein extractability upon kilning was due to changes in protein (secondary) structure and aggregation. Less severe heat treatment conditions could be applied to retain high protein extractabilities, without compromising on shelf stability. Additionally, kilning resulted in an oat β-D-glucan extractability decrease, but the extracted β-D-glucans were larger in size and yielded more viscous extracts, which potentially offers additional nutritional benefits.

In a second part of the PhD research, the impact of kilning and altered environmental pH on the colloidal state and emulsifying properties of oat proteins was investigated. For this, a more purified protein sample (an isolate) was 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. In a final study, 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 shows how kilning influences oat constituent extractability and protein colloidal and emulsifying properties, and offers strategies to better utilize the nutritional and functional benefits of oats in dairy alternatives.