Functional analysis of polyphenol oxidase 1 gene in common wheat

Polyphenol oxidase (PPO) activity is a major cause of the undesirable brown color of wheat-based products. Ppo1, a major gene for PPO activity, was cloned based on sequence homology in previous studies; however, its function and regulation mechanism remain unclear. In this study, the function and genetic regulation of Ppo1 were analyzed using RNA interference (RNAi) and Targeting Induced Local Lesions IN Genomes (TILLING) technology, and superior mutants were identified. Compared with the control, the level of Ppo1 transcript in RNAi transgenic lines was drastically decreased by 15.5%-60.9% during grain development, and PPO activity was significantly reduced by 12.9%-20.4%, confirming the role of Ppo1 in PPO activity. Thirty-two Ppo1 mutants were identified in the ethyl methanesulfonate (EMS)-mutagenized population, including eight missense mutations, 16 synonymous mutations, and eight intron mutations. The expression of Ppo1 was reduced significantly by 6.7%-37.1% and 10.1%-54.4% in mutants M092141 (G311S) and M091098 (G299R), respectively, in which PPO activity was decreased by 29.7% and 28.8%, respectively, indicating that mutation sites of two mutants have important effects on PPO1 function. Sequence and structure analysis revealed that the two sites were highly conserved among 74 plant species, where the frequency of glycine was 94.6% and 100%, respectively, and adjacent to the entrance of the hydrophobic pocket of the active site. The M092141 and M091098 mutants can be used as important germplasms to develop wheat cultivars with low grain PPO activity. This study provided important insights into the molecular mechanism of Ppo1 and the genetic improvement of wheat PPO activity.

Wheat Grinding Process with Low Moisture Content: A New Approach for Wholemeal Flour Production

The objective of this study was to determine the grinding characteristics of wheat with a low moisture content. Two kinds of wheat—soft spelt wheat and hard Khorasan wheat—were dried at 45 °C to reduce the moisture content from 12% to 5% (wet basis). Air drying at 45 °C and storage in a climatic chamber (45 °C, 10% relative humidity) were the methods used for grain dehydration. The grinding process was carried out using a knife mill. After grinding, the particle size distribution, average particle size and grinding energy indices were determined. In addition, the dough mixing properties of wholemeal flour dough were studied using a farinograph. It was observed that decreasing the moisture content in wheat grains from 12% to 5% made the grinding process more effective. As a result, the average particle size of the ground material was decreased. This effect was found in both soft and hard wheat. Importantly, lowering the grain moisture led to about a twofold decrease in the required grinding energy. Moreover, the flour obtained from the dried grains showed higher water absorption and higher dough stability during mixing. However, the method of grain dehydration had little or no effect on the results of the grinding process or dough properties.

Review of the Sensory and Physico-Chemical Properties of Red and White Wheat: Which Makes the Best Whole Grain?

Establishing sensory and physico-chemical differences between products made from red and white wheat may guide the choice of wheat for use in whole grain and high fibre products. As sensory acceptance is key to consumption, this scoping review aimed to document sensory and physico-chemical research demonstrating quantitative differences in red and white wheat and the associated bran. The following databases were systematically searched following the PRISMA protocol: PubMed, Medline, Scopus, CINHAL and ScienceDirect (1990–2019). Of 16 studies, 13 were sensory studies with 529 participants (six of which included quantitative analysis) and three additional quantitative studies. Overall, 10 studies were in favour of white wheat (seven sensory studies, two focused on quantitative analysis and two with additional quantitative studies). Whole grain (wholemeal) bread, pita bread, crackers, noodles, tortillas, flour, intact grains and bran were examined. Aside from the seed coat colour, levels of bound versus free phenolic compounds and polyphenol oxidase activity appeared most responsible for the differences in red and white wheat. Ensuring the sample size for sensory studies are large enough to detect between-group preferences and linking to physico-chemical analysis are recommended. Attention to blinding techniques in sensory testing and use of food products realistically and consistently prepared with commercial potential are also suggested. This scoping review provides confidence in preference for white wheat for whole grain products, particularly for breads, tortillas and in the choice of white wheat for products suitable for the Asian market.

Complementary effects of cereal and pulse polyphenols and dietary fiber on chronic inflammation and gut health

Cereal grains and grain pulses are primary staples often consumed together, and contribute a major portion of daily human calorie and protein intake globally. Protective effects of consuming whole grain cereals and grain pulses against various inflammation-related chronic diseases are well documented. However, potential benefits of combined intake of whole cereals and pulses beyond their complementary amino acid nutrition is rarely considered in literature. There is ample evidence that key bioactive components of whole grain cereals and pulses are structurally different and thus may be optimized to provide synergistic/complementary health benefits. Among the most important whole grain bioactive components are polyphenols and dietary fiber, not only because of their demonstrated biological function, but also their major impact on consumer choice of whole grain/pulse products. This review highlights the distinct structural differences between key cereal grain and pulse polyphenols and non-starch polysaccharides (dietary fiber), and the evidence on specific synergistic/complementary benefits of combining the bioactive components from the two commodities. Interactive effects of the polyphenols and fiber on gut microbiota and associated benefits to colon health, and against systemic inflammation, are discussed. Processing technologies that can be used to further enhance the interactive benefits of combined cereal-pulse bioactive compounds are highlighted.

Wheat grain consumption and selection by inbred and outbred strains of mice

Food selection and avoidance are driven primarily by orosensory cues. Previous studies with C57BL/6J mice indicated marked differences in selection and consumption of individual grains of different wheat varieties when presented in binary mixtures. The present study examined the patterns of mouse grain selection across four strains of laboratory mice: two inbred, BALB/c and C57BL/6J, and two outbred, Swiss-Webster and CD1. Four pairs of wheat varieties that were known to vary a priori for consumption preference or seed coat ('bran') color were tested. Two variety pairs were near-isogenic (>98% similar) with contrasting red and white seed coat coloration/pigmentation. All four mice strains exhibited similar preferences between wheat variety pairs, whereas consumption was not highly related to mouse body weight. This result indicates a more generalized phenomenon regarding how mice select and then consume individual wheat grains. The study supported the continued use of C57BL/6J as an effective strain model system to study food perception.

Genetic characterization and expression analysis of wheat (Triticum aestivum) line 07OR1074 exhibiting very low polyphenol oxidase (PPO) activity

Characterized novel mutations present at Ppo loci account for the substantial reduction of the total kernel PPO activity present in a putative null Ppo - A1 genetic background. Wheat (Triticum aestivum) polyphenol oxidase (PPO) contributes to the time-dependent discoloration of Asian noodles. Wheat contains multiple paralogous and orthologous Ppo genes, Ppo-A1, Ppo-D1, Ppo-A2, Ppo-D2, and Ppo-B2, expressed in wheat kernels. To date, wheat noodle color improvement efforts have focused on breeding cultivars containing Ppo-D1 and Ppo-A1 alleles conferring reduced PPO activity. A major impediment to wheat quality improvement is a lack of additional Ppo alleles conferring reduced kernel PPO. In this study, a previously reported very low PPO line, 07OR1074, was found to contain a novel allele at Ppo-A2 and null alleles at the Ppo-A1 and Ppo-D1 loci. To examine the impact of each mutation upon kernel PPO, populations were generated from crosses between 07OR1074 and the hard white spring wheat cultivars Choteau and Vida. Expression analysis using RNA-seq demonstrated no detectable Ppo-A1 transcripts in 07OR1074 while Ppo-D1 transcripts were present at less than 10% of that seen in Choteau and Vida. Novel markers specific for the Ppo-D1 and Ppo-A2 mutations discovered in 07OR1074, along with the Ppo-A1 STS marker, were used to screen segregating populations. Evaluation of lines indicated a substantial genotypic effect on PPO with Ppo-A1 and Ppo-D1 alleles contributing significantly to total PPO in both populations. These results show that the novel mutations in Ppo-A1 and Ppo-D1 present in 07OR1074 are both important to lowering overall wheat seed PPO activity and may be useful to produce more desirable and marketable wheat-based products.

Repeatability of Mice Consumption Discrimination of Wheat (Triticum aestivum L.) Varieties across Field Experiments and Mouse Cohorts

Whole grain wheat (Triticum aestivum L.) foods can provide critical nutrients for health and nutrition in the human diet. Potential flavor differences among varieties can be examined using consumption discrimination of the house mouse (Mus musculus L.) as a model system. This study examines consistency and repeatability of the mouse model and potentially, wheat grain flavor. A single elimination tournament design was used to measure relative consumption preference for hard red spring and hard white spring varieties across all 3 experiments in combination with 2 mouse cohorts. Fifteen replicate mice were used in 24-h trials to examine differences in preference among paired wheat varieties until an overall "winner" was established as the most highly preferred variety of wheat. In all 3 experiment-cohort combinations, the same varieties were preferred as the "winner" of both the hard red spring and hard white spring wheat varieties, Hollis and BR 7030, respectively. Despite the consistent preference for these varieties across experiments, the degree (magnitude) to which the mice preferred these varieties varied across experiments. For the hard white spring wheat varieties, the small number of varieties and confounding effects of experiment and cohort limited our ability to accurately gauge repeatability. Conversely, for the hard red spring wheat varieties, consumption preferences were consistent across experiments and mice cohorts. The single-elimination tournament model was effective in providing repeatable results in an effort to more fully understand the mouse model system and possible flavor differences among wheat varieties.

PRACTICAL APPLICATION

The mouse model system used here is effective in identifying wheat varieties that may be more or less desirable to humans in whole wheat foods. The system identifies consistent differences across different mouse cohorts and crop years.

The house mouse (Mus musculus L.) exerts strong differential grain consumption preferences among hard red and white spring wheat (Triticum aestivum L.) varieties in a single-elimination tournament design

Wheat (Triticum aestivum L.) plays a central role in the health and nutrition of humans. Yet, little is known about possible flavor differences among different varieties. We have developed a model system using the house mouse (Mus musculus L.) to determine feeding preferences as a prelude to extending results to human sensory analysis. Here, we examine the application of a single-elimination tournament design to the analysis of consumption preferences of a set of hard red and hard white spring wheat varieties. A single-elimination tournament design in this case pairs 2 wheat varieties and only 1 of the 2 is advanced to further tests. Preferred varieties were advanced until an overall "winner" was identified; conversely, less desirable varieties were advanced such that an overall "loser" was identified. Hollis and IDO702 were the winner and loser, respectively, for the hard red varieties, and Clear White 515 and WA8123 were the winner and loser, respectively, for the hard white varieties. When using the more powerful protocol of 14 mice and a 4-d trial, differences in mean daily consumption preferences of 2 varieties were separated at P-values as small as 2 × 10(-8) . The single-elimination tournament design is an efficient means of identifying the most and least desirable varieties among a larger set of samples. One application for identifying the 2 extremes in preference within a group of varieties would be to use them as parents of a population to identify quantitative trait loci for preference.

Optimizing experimental design using the house mouse (Mus musculus L.) as a model for determining grain feeding preferences

There is little research evaluating flavor preferences among wheat varieties. We previously demonstrated that mice exert very strong preferences when given binary mixtures of wheat varieties. We plan to utilize mice to identify wheat genes associated with flavor, and then relate this back to human preferences. Here we explore the effects of experimental design including the number of days (from 1 to 4) and number of mice (from 2 to 15) in order to identify designs that provide significant statistical inferences while minimizing requirements for labor and animals. When mice expressed a significant preference between 2 wheat varieties, increasing the number of days (for a given number of mice) increased the significance level (decreased P-values) for their preference, as expected, but with diminishing benefit as more days were added. However, increasing the number of mice (for a given number of days) provided a more dramatic log-linear decrease in P-values and thus increased statistical power. In conclusion, when evaluating mouse feeding preferences in binary mixtures of grain, an efficient experimental design would emphasize fewer days rather than fewer animals thus shortening the experiment duration and reducing the overall requirement for labor and animals.