Insight in changes in starch and proteins molecular structure of non-wheat cereal flours influenced by roasting and extrusion treatments

Abstract

Barley, rye, triticale, oat, sorghum and millet flours, subjected to roasting or extrusion treatment, were analyzed by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Fourier-transform infrared (FTIR) and Raman spectroscopy with aim to determine structural changes within starch and protein molecules that caused specific rheological properties of heat treated flours. Mixolab was used to determine how changes in starch and protein structure are reflected in rheological properties of dough. Extrusion treatment caused more extensive changes both in starch and protein structure than roasting treatment. Changes of protein secondary structure from α-helix to β-turn aggregated by hydrogen bonds, formed mainly between tyrosyl groups, as well as change in disulphide bond conformation, were more pronounced in extruded flour samples. Changes in the starch structure were also more extensive in extruded flours samples, including complete gelatinization and formation of amylose-lipid complexes. The results obtained by Mixolab showed that all extruded doughs showed resistance at C2 point, which was shifted to approximately 30 min, indicating higher mechanical resistance. It was supposed that this change in dough behaviour is related to protein polymerization during extrusion treatment and starch aggregation during roasting treatment.