Directing oat groat heat treatment conditions towards increased protein extractability.

Abstract

Oat-based liquid and semi-solid dairy alternatives require extractable proteins for nutritional and technological purposes. However, oats are industrially heat treated ('kilned') to inactivate endogenous lipases thereby avoiding rancidity development. Such heat treatment results in a protein extractability decrease. We here investigated the possibility of directing oat groat heat treatment conditions [oat groat moisture content (13.0-20.0%), heating temperature (80-100 °C) and heating time (15-45 min)] on a lab-scale to achieve complete enzyme inactivation, with peroxidase activity as a marker, while maintaining high protein extractability. Non-heat-treated and industrially heat-treated oats were included as reference samples. The peroxidase activity and protein extractability of lab-scale heat-treated oats decreased with an increase in moisture content, heating temperature and time. Several lab-scale heat-treated oats for which complete peroxidase inactivation was observed, had significantly higher protein extractabilities (31-59%) than industrially kilned oats (21%). The activity of endogenous lipases was determined for a selected sample set. Lipases required milder heat treatment conditions for complete inactivation than peroxidases. Such milder heat treatment led to samples with protein extractabilities between 31 and 65%. A notable observation was that heat treating oats (≥90 °C) caused clumping of the intracellular material of the aleurone cells, likely due to protein aggregation. The main conclusion of this study is that oat heat treatment conditions can be altered successfully to achieve complete enzyme inactivation while maintaining high protein extractability. The obtained insights could lead to the development of oat-based products with higher protein content and desired shelf stability.