Analysis of wheat grain development using NIR spectroscopy

Abstract

The scope of the present investigation was to detect maturation processes in wheat seed non-destructively with special respect to changes in moisture, carbohydrate and protein content and natural hydration/dehydration processes. During seed development, many biochemical, enzymatic and morphological changes occur under highly hydrated conditions.The ratio of different water species (high density water (HDW) with weaker hydrogen bonding and low density water (LDW) with stronger hydrogen bonding) changed drastically during maturation and their transitions could be followed with high sensitivity in specific regions of NIR spectra. In the maturing seed, two combination bands (Water I and Water III) were strong indicators of changes in water content while a first overtone (Water II) band gave a weaker response to change in moisture content.Three carbohydrate absorption bands showed different dynamics of carbohydrate (starch, fructan) accumulation and breakdown. Carbohydrate I represents starch accumulation during maturation based on the vibrations of intermolecular hydrogen-bonded O–H groups in polysaccharides. Carbohydrate II peak represents the of O–H stretching and C–C stretching vibrations in water-soluble carbohydrates while Carbohydrate III peak describes the changes in C–H stretching and deformation bands of poly-and mono-/oligosaccharides.Two protein absorption bands were identified (at 2055–2065 nm identified as amide A/II and at 2175–2180 nm identified as amide I/III). These showed characteristic changes related to the accumulation of proteins and formation of the gluten network. The Amide A/II peak represents protein network formation during maturation based on the vibrations of inter-chain hydrogen-bonded N–H groups in polypeptides. The Amide I/III absorption band describes protein accumulation and the interactions of gliadins and glutenins that form the gluten network. NIR spectroscopy is shown to be effective in monitoring plant physiological processes both qualitatively and quantitatively, while the spectra also contain hidden information that can be used to define the stage of development of the wheat seed.