OPTICAL AND MECHANICAL INSTRUMENTATION FOR QUALITY ASSESSMENT OF SMALL GRAINS
Location: Food Quality Laboratory
Title: Starch waxiness in hexaploid wheat (Triticum aestivum L.) by NIR reflectance spectroscopy
Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 9, 2011
Publication Date: March 14, 2011
Citation: Delwiche, S.R., Graybosch, R.A., St Amand, P., Bai, G. 2011. Starch waxiness in hexaploid wheat (Triticum aestivum L.) by NIR reflectance spectroscopy. Journal of Agricultural and Food Chemistry. 59:4002-4008.
Interpretive Summary: Starch, the primary energy storage compound in plants, consists of two large polysaccharide molecules, amylose and amylopectin. The relative portions of these two molecules have a direct effect on the processing characteristics of starch in food and industrial formulations. Traditionally, starches with extremely low levels of amylose, called ‘waxy’ starches, have been produced in maize (corn). Recent plant breeding efforts have been successful in developing this trait in wheat as an alternative crop. Full commercialization of waxy wheat will be enhanced by rapid methodologies that can distinguish waxy from conventional wheat. One mainstay technology in wheat commerce quality inspection, near-infrared (NIR) reflectance spectroscopy, was examined for this purpose. Results from this study, which utilized a genetically diverse set of hard winter wheat, indicate that the NIR technique is able to identify the waxy condition (in ground meal, bulk kernel, or individual kernel format) 95 percent of the time or better. This technology has immediate application to wheat country elevators and other downstream sale points that need rapid and accurate devices for identity preservation of waxy wheat lots.
Starch, the primary energy storage component of plants, consists of two large macromolecules, amylose and amylopectin. Each molecule is composed of long chains of alpha-D-glucopyranosyl units, with branching present in amylopectin and absent in amylose. The relative abundance of these two molecules affects starch gelatinization during processing and hence the suitability of this ingredient for various food and industrial uses. Wheat (Triticum aestivum L.) breeding programs are currently active in the development of varieties that are free of amylose, also known as waxy wheat, and varieties with reduced amylose content, known as “partial waxy” types. Successful introduction of waxy wheat varieties into commerce is predicated to some extent on a rapid methodology at the commodity point of sale that can test for the waxy condition. Near-infrared reflectance spectroscopy of ground meal, intact bulk kernels, and single kernels was applied to a set of hard winter (hexaploid) wheat breeders’ lines representing all eight genotypic combinations of alleles at the wx-A1, wx-B1 and wx-D1 loci. These loci encode the granule bound starch synthase, the enzyme responsible for amylose synthesis. Linear discriminant analysis of the scores associated with principal components 1-4 was successful in identifying the fully waxy samples at typically greater than 90 percent accuracy, regardless of sample format. Classification accuracy among wild type and partial waxy samples was much lower, typically ranging between 40 and 60 percent. It is suggested that the spectral basis for waxy identification lies in differences in CH bond strengths at the C-6 site of the D-gylucopyranosyl unit of amylopectin where branching occurs.