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Fast, simple laboratory methods were used to analyze 22 maize samples varying in kernel vitreousness from 50.23% to 76.41%. Samples were analyzed in terms of zein content (53.86–86.37 g/kg endosperm DM), amylose content (190.76–259.77 g/kg endosperm DM), amylose to amylopectin ratio in starch (0.28–0.43), as well as starch granule size (10.95–14.89 μm in equivalent diameter) and starch granule shape (circularity, 0.85–0.94). More vitreous samples had higher zein and amylose content, as well as smaller and less circular starch granules. Nearly all grain traits on their own significantly affected vitreousness, and a multiple regression model to account for their combined effects was able to explain 61.8% of variability in kernel vitreousness. Zein content contributed most to the model, followed by starch granule projected area and circularity. In contrast, the amylose content contributed only 5.1% to the model. These results suggest that starch-protein interactions influence maize kernel vitreousness more strongly than starch molecular properties do. [ABSTRACT FROM AUTHOR]

Relationships between kernel vitreousness and proteins and starch partitioning to the floury and vitreous regions of the endosperm were monitored in a set of 13 maize inbred lines. Decrease of protein contents from the vitreous to the floury endosperms were mainly assigned to α-zeins. Using Raman microspectroscopy, we observed a protein gradient from the periphery to the center of endosperms that well fitted with the inverse relationships between vitreousness and protein content of the vitreous and floury regions. In addition, Raman microspectroscopy highlighted an increase of starch crystallinity from the periphery to the center of the maize endosperms. This agrees with the higher amylose and associated lipid contents within starches of vitreous than in those of floury endosperms. Finally, starch granules from vitreous regions displayed more channels than the floury ones. These channels contain proteins that might favor adhesion of proteins to starch granules or granule–granule contacts to form the close packing of the vitreous endosperm. Therefore transition from vitreous to floury endosperm is at least the result of both protein and starch gradients. These gradients are probably associated with metabolic gradients that have been observed during endosperm development. [ABSTRACT FROM AUTHOR]

Abstract: The proportion of vitreous kernels in a sample is an internationally recognized specification for determining the value of durum wheat (Triticum durum Desf.). Vitreous kernels are mostly related to quality, which affects the pasta performance during cooking. Vitreousness and the amount of shrunken kernels are visually assessed during the grading process. This assessment is subjective and tedious. A machine vision system was developed to determine the percentage of vitreous, starchy, piebald and shrunken kernels in approximately 100 grain samples, using a trans-illuminated image of one layer of non-singulated kernels (in bulk) acquired by a digital camera. Classification models were developed with stepwise Linear Discriminant Analysis, as well as an on-line Bayesian classifier integrated with an image analysis system. The overall correct classification in Starchy classifier was high 98.58% in the Training set, made up of 6679 grains, following the Linear Discriminant Analysis classification, of 30 Italian cultivars harvested in 2005 in three localities. An independent Test set was constituted by samples collected in 30 Sicilian Storage Centres in the 2007 harvest season. The overall classification was 96.03%. For the Shrunken classifier 95.27% of the Training set and 99.58% of the Test set were correctly classified. The image analysis system was more reliable than the human inspectors who validated the system, both for the same samples measured many times and at different times. [Copyright &y& Elsevier]

Abstract: The characterisation of the wheat endosperm by mechanical tests of compression highlighted a relation between the rupture energy and the elasticity modulus for different varieties of wheat; this relation allows us to distinguish mealy and vitreous endosperms. An approach based on the micromechanics of cohesive granular materials is used to analyse these experimental results. A geometrical model of the wheat endosperm made of grains linked by cohesive bonds is proposed. We introduced two parameters, the first one α represents the percentage of active bonds (bonds where the stiffness and strength are non-zero), and the second one β represents the threshold of the bond''s rupture. The parameter β can be related to the cross-section of the bond. This model successfully describes the mechanical tests on the wheat endosperm. The comparison with the experimental tests makes it possible to clearly differentiate vitreous wheats and mealy wheats and then attribute this property to the parameter β. The model shows the same tendency as regards the evolution of the rupture energy and the elastic modulus with the parameter α. The modelling of endosperm by the mechanics of cohesive granular media provides a new theoretical framework to interpret the rheology of endosperm. This approach allows us to connect this rheology to the mechanical actions at the scale of the granules. [Copyright &y& Elsevier]

Abstract: The reduction of coarse farina during milling from five representative hard and soft French bread wheat cultivars was followed step by step. Particle size distribution of the milled products and energy required to dissociate wheat farina revealed large differences between cultivars. A grinding index (required energy to produce 1kg of flour), K′, corresponding to the energy necessary to obtain a given amount of flour, was found to be related with both grain hardness and vitreousness. Analysis of particle size distribution suggested a major influence of hardness in the production of fine particles <50μm during the reduction process. On the other hand, vitreousness appeared to impact on the extent of coarse particle size reduction. Differences in farina reduction behaviour of the wheats analysed were related to their endosperm mechanical properties as determined by compression tests and structural characteristics as measured by Hg intrusion porosity. Vitreousness appeared to affect the endosperm extensibility and degree of porosity. The profile of the different lipid and protein classes in the reduction products of two cultivars showing opposite behaviour as well as different PINA/PINB ratio were determined. The results suggest that the most resistant parts of the grain are enriched in glycolipids, whereas phospholipids appear associated with the most friable parts, at least in the soft wheat grains tested. [Copyright &y& Elsevier]

This review summarizes the results of studies on near-isogenic common wheat lines differing in the Pinb-D1 allele encoding puroindoline B or durum wheat into which both wild-type puroindoline genes were introduced. The material was grown in different environments to evaluate the respective effect of puroindoline genes or of the environmental factors on grain characteristics and milling behavior. Environmental conditions were found to impact grain porosity (=1/vitreousness) and the presence of both wild-type puroindoline genes was found to reduce the vitreousness threshold under 60%. Hardness measurements with single kernel characterization system were found to differ from near-infrared reflectance spectroscopy analysis and were linearly related to vitreousness but differently depending on the puroindoline allele carried. Puroindoline genes were found to play a major role in the grain porosity, breaking energy, size of generated particles and in the concentration of phytic acid and damaged starch into flour whereas vitreousness introduced variations in the ability to break and in the level of damaged starch. Finally, the highest flour yield is obtained from either vitreous common wheat grains carrying the wild-type puroindoline alleles or carrying mutated alleles and displaying low vitreousness. This result was confirmed using common French wheat cultivars whose puroindoline genes were identified. Image 1 • Effect of environmental conditions on grain porosity (vitreousness) are demonstrated. • Pinb-D1 allele appears to affect both porosity and grain hardness. • SKCS or NIRS hardness measurements methods are not equivalent. • Highest total flour yield at milling was obtained for grain SKCS values around 30-60. • Puroindoline genes and grain porosity both affects flour biochemical composition. [ABSTRACT FROM AUTHOR]

Maize kernel color and carotenoid concentration are traits valued by the food industry to ensure the quality of their products. Correlations between color and carotenoid concentration have been extensively reported. Based on the concept that chromaticity is modified differently by opaque and translucent materials, we tested the hypothesis that maize kernel color is not only the result of total carotenoid concentration but also a consequence of kernel hardness. Kernel hardness (test weight, vitreousness, and floaters percentage), carotenoid concentration, and color (HunterLab) were measured in thirteen commercial hybrids. Genotypes showed significant differences in all analyzed kernel hardness traits, carotenoid concentration (24.7–39.4 mg kg−1), and HunterLab color dimensions. Kernel color values and kernel hardness were correlated. Genotype differences in b (yellowness) were observed in kernels with similar total carotenoid concentration but contrasting hardness. For a similar carotenoid concentration harder genotypes always showed lower b values. When whole kernels were milled and color was measured on the resulting flour, genotype differences in yellowness disappeared, further supporting that the kernel vitreous structure affects kernel color. Our results sustain the notion that the genotype capacity to form larger proportions of vitreous endosperm impacts color regardless of total carotenoid concentration. Image 1 • Endosperm vitreousness affects the optical expression of kernel color. • Maize kernel hardness impacts color regardless of total carotenoid concentration. • Assuming carotenoid concentration based only on kernel color may be misleading. • Higher carotenoid concentrations were found in harder kernels. [ABSTRACT FROM AUTHOR]