Location: Food Quality Laboratory2011 Annual Report
1a. Objectives (from AD-416)
(1) Develop spectroscopic imaging procedures (hyperspectral or multispectral) that can be used to assess quality of small grains (emphasizing wheat, rice, and barley) and oilseeds in bulk for grade, class, foreign material, and damage (mold, black point, heat, frost, and insect). (1a). Develop hyperspectral image analysis algorithms for determination of the level of mold damage from Fusarium Head Blight on wheat kernels. This will involve the development of image processing routines that identify the infected kernels in representative samples of intact wheat kernels and determine the regions of Fusarium damage within each infected kernel. (1b) Develop hyperspectral image analysis algorithms for identification of wheat kernels damaged by heat, frost, black point, and insects, as defined by official inspection criteria. (1c) Develop hyperspectral image analysis algorithms for the prediction of flour yield and break flour yield in soft red winter wheat. (2) Develop optical and mechanical methods and instrumentation for grain quality measurement that are applicable at points of sale, such as elevators, terminals, and mills. (2a) Develop rapid and objective optical methods for prediction of starch quality indicators in wheat, such as the ratio of amylose-to-amylopectin, and the identification of wheat into three states of waxiness: waxy, partial waxy, and wild type. (2b) Develop a near-infrared (NIR) spectroscopy procedure for wheat gluten quality determination for use in commerce.
1b. Approach (from AD-416)
Fusarium-inoculated hard red spring and hard red winter wheat samples will be imaged using an in-house near-IR hyperspectral system. Image analysis will be a multistep process. First, for each kernel a mask will be created from one of the images whose wavelength creates a strong contrast between kernel and background. The mask will be applied to the images at all other wavelengths in order to remove the background. Principal component analysis (PCA) loadings from images of damaged and normal regions will be examined to identify the wavelengths at local minima and maxima, which inherently possess the greatest contrast between Fusarium damage and healthy endosperm. Hyperspectral image analysis will also be used to examine three wheat milling properties: milling yield (% straight grade flour) defined as the percent by mass of all flour fractions recovered through a 94-mesh screen; solvent retention capacity in 50% (w/w) sucrose solution, a measure of the water affinity of the macro-polymers (starch, arabinoxylans, gluten, and gliadins); and solvent retention capacity in 5% (w/w) lactic acid, an indicator of gluten strength. Near-IR spectroscopy will explored as a method for measuring the degree of waxiness in hexaploid wheat. Wild type, partial waxy (waxy null alleles in one or two genomes), and waxy samples (null alleles in all genomes), drawn from breeders' advanced lines of hexaploid wheat, will be used. Gel electrophoresis will be used to identify the waxy protein (granule bound starch synthase, GBSS) in each sample. Lastly, a near-IR procedure for wheat gluten quality will be developed in conjunction with a rheological procedure. The wheat samples consist of approximately 50 lines grown in field replicated (3x) plots over three consecutive seasons. Half of these lines are transgenic, in which the gene construct modifies the length of the central repeat region within the high molecular weight (HMW) glutenin subunits. Different levels of gene expression, hence, level of glutenin protein, are represented as a function of the transgenic ancestor. Thus, this set will contain a much wider range in the ratio of glutenin-to-gliadin than naturally encountered. Flour from these samples will be evaluated for glutenin and gliadin contents by SE-HPLC another ARS laboratory. At Beltsville, the flour will be scanned in the NIR and FT-mid-IR regions. Rheological properties, such as the recovery response for a gluten specimen subjected to a controlled regiment of compressive force and hold time, will be measured at a third laboratory. Spectral calibrations for glutenin and gliadin concentrations, as well as calibrations for the rheological parameters (percent recovery and recovery time constant), will be developed using partial least squares regression. Additionally, classification algorithms (PLS discriminant analysis and SVM) algorithms will be developed that will identify the genetically modified lines based on their spectral response.
3. Progress Report
The final stages of fabrication of a near-infrared (NIR) spectroscopic (hyperspectral) imaging system were completed. Begun in the previous year, the system was optimized during 2011 for seed-sized (cereal grain) objects by giving special attention to lighting and close-up imaging for quality evaluation of cereal grains. The system was tested on about 160 samples of soft red winter wheat (30 kernels/sample) arising from a study whose objective is to develop a rapid and nondestructive procedure for determining milling quality (yield, softness, and solvent retention capacities). Image processing routines were written to transform raw spectral image data into usable characterizations of internal physical and chemical properties of the cereal grains (wheat, barley) for assessment of quality and potential safety (mold) concerns. Work is nearly complete on applying linear discriminant analysis (LDA) to categorize (poor to excellent) wheat according to the milling characteristics as measured on a pilot mill housed at the USDA Soft Wheat Quality Laboratory. A study was completed on using NIR reflectance spectroscopy to distinguish waxy and partial waxy states in common (bread) wheat. Waxiness is a condition of endosperm starch that chemically describes the lack of branching in the molecule, with long linear chains of the repeating unit attributed to the waxy condition. The degree of branching in turn affects the processing characteristics of wheat starch, either for food or industrial purposes. From the genetic standpoint, waxiness is controlled by just one gene that encodes for synthesis of the enzyme, granule bound starch synthase, which in turn regulates the production of the linear form of the starch molecule. Because common wheat is hexaploid (three sets of chromosome pairs), eight genetic combinations exist. For the study, all combinations were available, these being the fully waxy condition, the six intermediate (‘partial’) waxy states, and the wild type condition. Using LDA (see above) on NIR spectra of three forms (ground, whole, and single kernel), the findings showed that the fully waxy wheat is recognizable at 90-100% accuracy. However, accuracy drops off with the other states, even when the intermediate waxy states are combined. The spectral sensitivity to the amylose-lipid complex is suggested as the major contributing factor to waxiness classification success. Research began on developing a single kernel imaging system that captures images of wheat kernels cascading in air from a feeder. The system allows for the simultaneous viewing of two opposing sides of a kernel. Morphological (size and shape) and kernel surface (texture) properties are addressed. This real time imaging system is to be used in inspection operations and its principles can be applied to online operations in flour mills for removing damaged and diseased kernels from the mainstream. Design of hardware, optics, and software to capture images was completed, and work continues on reducing image processing time. The targeted conditions are fusarium damage, black point, and heat damaged kernels.
1. Improvements on measuring wheat hardness. Wheat endosperm hardness, a genetically controlled property, is largely responsible for determining the use of wheat lots in bread, crackers, noodles, and cakes. Parallel to the biological and genetic understanding of hardness, knowledge of the physical or engineering strength, defined as the force and energy needed to break apart a kernel, is fundamental to improving the efficiency of milling and processing operations. Through mathematical description of the mechanics that define the crush procedure, followed by a three-laboratory study using two genetically related wheat cultivars (one hard and one soft), ARS scientists in Beltsville, Maryland, and Pullman, Washington, were successful in reducing the variability in lab-to-lab strength property values by as much as tenfold. This standardization of the measurement procedure will result in more accurate designations of a wheat lot’s suitability, as well as a better estimation of the energy requirements of milling. Plant breeders, traders, and processors will benefit from this research.
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.