MECHANICAL-PROPERTIES OF STARCH, PROTEIN AND ENDOSPERM AND THEIR RELATIONSHIP TO HARDNESS IN WHEAT

Various mechanical properties of whole endosperm, starch granules, and storage protein deposits were compared to determine whether the findings were consistent with the current theories on wheat hardness. All mechanical measurements were performed in situ without the use of solvents, resins, or polishing compounds that could alter the properties of the specimens. The results showed that the starch and protein components had elastic and creep properties. There were no significant differences in any of the mechanical properties of the starch and protein components either within a variety or among soft, hard, and durum wheat types. Tensile strength (S(u)), compressive strength (S(max)), toughness (W(max)), modulus of elasticity (E) and strain to fracture (e(max)) were measured in samples of whole endosperm from various soft, hard, and durum wheats. The mean values for each parameter were highest for durum caryopses and lowest for non-vitreous caryopses of soft wheats. The hard wheat samples were intermediate. The mechanical properties of some vitreous caryopses of two soft wheat varieties were comparable to those of durum and hard wheat caryopses. These results do not support theories that suggest endosperm hardness is directly attributable to a cell product made exclusively in either hard or soft wheat varieties.