Understanding the impact of oat groat heat treatment on its protein extractability

Industrially heat treating ('kilning') oats decreases the protein extractability, which is undesirable in oat-based liquid and semi-solid food applications. We investigated the mechanisms by which oat heat treatment influences protein extractability from both whole meal, and bran- and endosperm-enriched sieving fractions. Protein extractability (pH 9.0) decreased from 67% for non-heat-treated to 49% for lab-scale heat-treated and to 23% for industrially heat-treated oats, with similar trends for bran- (66%, 42% and 23%, respectively) and endosperm-enriched (78%, 57%, 23%, respectively) fractions. Prior cryogenic milling showed that heat treatment affected proteins beyond physical barrier-related effects. Interestingly, differential scanning calorimetry indicated no pronounced protein denaturation upon heat treatment. However, protein secondary structure analyses revealed reduced α-helix and random coil contents, accompanied by elevated intramolecular β-sheet formation. Furthermore, protein aggregation state analyses pointed towards aggregation through non-covalent interactions and disulfide bond formation. Thus, protein aggregation, although not denaturation-induced, explains how kilning influences oat protein extractability.