MECHANICAL PROPERTIES OF WHEAT GRAIN BY AFM AND NHT TESTING SYSTEM AND COMPRESSION TEST

MENDEZ-MENDEZ J; RIBOTTA PD; QUIROGA FM; BARRERA GN; CALDERÓN-DOMINGUEZ G; ARZATE-VAZQUEZ I

CORDOBA

Congreso; VI Congreso Internacional de Ciencia y Tecnología de Alimentos (CICYTAC 2016); 2018

Ministerio de ciencia y tecnologia de Córdoba

The objective of this study was to evaluate the changes of mechanical-properties of wheat grains at different pre-moistening conditions by indentation and compression tests. Hard (ACA315) (HW) and soft (Buck-Amancay) (SW) wheat cultivars were evaluated. Wheat samples were conditioned at 10% and 15% moisture content and the surface of the whole wheat grains and their cross-section surfaces were studied. The Bio-AFM (Bioscope-Catalyst, Bruker, USA) and Nano-Hardness (NHT) (CSM Instruments, Switzerland) testers were used to the indentation evaluations and the kernel breaking strength was measured by Instron (Universal Testing Machine 3342, USA). The first pericarp outer layer of the whole kernels was indented by AFM. The Young´s modulus (E) of the SW and HW pericarps at 10% and 15% were 2.66 and 1.72 GPa, and 1.49 and 1.34 GPa, respectively. The SW outer layer structures were stiffer than the HW at 10% moisture, however, no differences were found at 15% moisture. E values of wheat samples were similar at 15% moisture. In relation to the cross-section areas, the pericarp regions showed greater measurement heterogeneity than the endosperm due to their complex structure. The AFM stiffness values were ranged between 1.93-0.69 GPa (pericarp regions) and 1.41-1.19 GPa (endosperm regions) and the NHT stiffness values were ranged between 4.7-3.9 GPa (pericarp regions) and 5.1-4.1 GPa (endosperm regions). The AFM and NHT results indicated that the cross-sections of the wheat cultivars did not present significant differences in the pericarp and endosperm stiffness at the same moisture content. Higher moisture content caused a reduction in the E of the pericarp regions in both wheat cultivars (AFM test). However, only the stiffness of the endosperm regions in SW was reduced when moisture increased (NHT test). The hardness of the pericarp regions did not show differences at 10%; however, the hardness of the endosperm regions of HW was greater than the SW at 15% moisture. Regarding to the compression test, the increment of moisture decreased the E values in both samples (HW10%: 0.192 GPa; HW15%: 0.114 GPa; SW10%: 0.172 GPa; SW15%: 0.102 GPa) and the SW grains presented lower fracture force than HW sample, at both moisture levels (HW10%: 89.3 N; HW15%: 67.6 N; SW10%: 78.5 N; SW15%: 58.5 N).