The separation and technological significance of the outer layers of the wheat grain

A detergent extraction technique was applied to quantitatively separate the outer layers of the wheat grain from the starchy endosperm. These layers were examined under the light microscope which showed that the cellular structures were intact and the contents of the aleurone cells had not been extracted. Milling studies demonstrated that the extraction technique allowed an accurate estimate to be made of the flour-yielding potential of a wheat provided that the milling system was capable of fully realising this flour-yielding capacity. The small-scale nature of the test allows it to be applied in wheat breeding programmes at an early stage as a predictive test for flour yield.     

Total phenolic compounds and antioxidant capacity of wheat graded flours by polishing method

The graded flour fractions, which were milled from whole wheat grain from outer to inner parts without removal of germ and bran, are rich in dietary fibers and minerals, the sources of nutrition for human beings. In this study, the whole waxy wheat was milled into five fractions using the gradual milling method and the phenolic contents and antioxidant capacity of these flours were investigated. The total phenolic and flavonoid contents of free and bound phenolic extracts gradually increased in the order from the inner to the outer fractions. The flours milled from the outer parts of grain contained significantly higher amount of phenolics and exhibited significantly higher antioxidant capacity than did the whole grain. Likewise, the inner flour fractions milled from mostly endosperm part had significantly higher amount of phenolics and exhibited significantly higher antioxidant capacity than did the white flour, which was milled by a conventional milling method. Thus, the graded flours from whole waxy wheat should be encouraged to be used for processing whole-grain foods to improve both qualities of end-use products and health benefits.     

Microbiology of wheat and flour milling in Australia

A survey was undertaken to determine the microbiological status of Australian wheat and the distribution of microorganisms in the flour milling fractions and end products. A total of 650 milling process and end product samples was obtained from nine flour mills located in New South Wales (4), Queensland (2), Victoria (2) and Western Australia (1) during the 1997-1998 and 1998-1999 wheat seasons. Most frequent (modal) counts in wheat and flour were, respectively, as follows: aerobic mesophilic plate count, 10(5) and 10(2) colony forming units/gram (cfu/g); coliforms, 10 and 1 most probable number/gram (MPN/g); Bacillus spp., 10(4) and 10(2) cfu/g; B. cereus, 1 and 0.1 MPN/g; mesophilic aerobic spores, 10 and 1 cfu/g; aerobic thermophiles, both 10 cfu/g; yeasts, 10(3) and 10(2) cfu/g, and moulds, 10(3) and 10(2) cfu/g. Bacillus spp., coliforms, yeasts and moulds were the most frequently detected microorganisms throughout the survey. The most common moulds isolated were Aspergillus, Penicillium, Cladosporium and Eurotium spp. Environmental serovars of Salmonella were isolated from two samples. Escherichia coli and B. cereus were present at very low levels, a majority of positive samples being at the minimum level of detection (3 and 0.3 MPN/g, respectively). As wheat grain layers are separated, surface-adhering contaminants are concentrated in end product bran, wheat germ and pollard, which comprise the outer layers of the grain. Consequently, the inner endosperm fraction contains lower microbial counts, and flour is the cleanest end product of the milling process. Higher microbiological counts midstream in the milling process indicate that equipment contamination may contribute to microbiological contamination; however, the microbiological quality of incoming wheat has a strong influence on the ultimate quality of milling end products.     

新型振动润麦着水机的创新设计和应用

随着我国新建大型粉厂以及老旧制粉车间的改造升级,小麦入磨前的原粮清理和润麦技术日益显得重要,良好的清理和润麦效果不仅可以提高小麦的加工碾磨品质,易于麦麸和胚乳的分离,减少面粉麸屑,而且对于缩短润麦时间,降低小麦表皮菌落种数,减少面粉灰分,生产清洁面粉以及提高加工效率具有重要意义,本文重点介绍了新型振动润麦着水机的创新结构设计和应用。     

小麦籽粒不同部位蛋白质理化特性研究进展

制粉工序不同节点或逐层研磨的小麦粉表示籽粒从外到内不同部位的组分,因其蛋白组分含量和性质各不相同,具有不同的加工特性。明确不同部位蛋白质理化特性,可为制粉、配粉和专用粉生产提供参考。本文综述了小麦蛋白质的分类、蛋白质及其组分在小麦籽粒中的分布,以及不同组分蛋白质的理化性质。小麦籽粒由内向外,蛋白质含量逐渐增大,面筋含量先逐渐增加后降低。越接近外层胚乳或糊粉层,清蛋白、球蛋白、麦醇溶蛋白、麦谷蛋白、十二烷基硫酸钠可溶蛋白、谷蛋白大聚体含量、面筋指数、沉降指数等呈现逐渐增大的趋势,各蛋白质组分的增加幅度不同;面团吸水率和拉伸面积逐渐增加,延伸性逐渐降低;面团形成时间、稳定时间、拉伸阻力等变化规律不明显,总体表现为波动至较大值后降低。     

Antioxidant and free radical scavenging activities of whole wheat and milling fractions

The effects of milling on the phenolic content and antioxidant capacity of two wheat cultivars, namely CWAD (Canadian Western Amber Durum; Triticum turgidum L. var. durum) and CWRS (Canadian Western hard red spring; Triticum aestivum L.) were studied. The milling of wheat afforded several fractions, namely bran, flour, shorts and feed flour. In addition, semolina was the end-product of durum wheat milling. Among different milling fractions the bran had the highest phenolic content while the endosperm possessed the lowest amount and this was also reflected in free radical and reactive oxygen species (ROS) scavenging capacity, reducing power and iron (II) chelation capacity of different milling fractions in the two cultivars. This study demonstrated the importance of bran in the antioxidant activity of wheat, hence consumption of whole wheat grain may render beneficial health effects.     

Wheat (Triticum aestivum L. and T. turgidum L. ssp. durum) Kernel Hardness: II. Implications for End‐Product Quality and Role of Puroindolines Therein

Wheat kernel hardness is a major quality characteristic used in classifying wheat cultivars. Differences in endosperm texture among Triticum aestivum L. or between T. aestivum and T. turgidum L. ssp. durum cultivars profoundly affect their milling behavior, the properties of the obtained flour or semolina particles, as well as the quality of products made thereof. It is now widely accepted that the presence, sequence polymorphism, or absence of the basic and cysteine‐rich puroindolines a and b are responsible for differences in endosperm texture. These proteins show features in vitro, including foaming and lipid‐binding properties, which provide them with a potential impact in the production of wheat‐based food products, where they may improve gas cell stabilization or modulate interactions between starch, proteins, and/or lipids. We here summarize the impact of wheat hardness on milling properties and bread, cookie, cake, and pasta quality and discuss the role of puroindolines therein.     

Conditioning studies on Australian wheat. III. The role of the rate of water penetration into the wheat grain

The penetration of water into the grain of a number of wheat varieties at various time intervals after damping was followed using the technique of autoradiography. Significant varietal differences were noted in the rate of water penetration and these were found to relate closely to the milling behaviour of the respective varieties at the various time intervals after damping.     

Wheat (Triticum aestivum L. and T. turgidum L. ssp. durum) Kernel Hardness: I. Current View on the Role of Puroindolines and Polar Lipids

Wheat hardness has major consequences for the entire wheat supply chain from breeders and millers over manufacturers to, finally, consumers of wheat‐based products. Indeed, differences in hardness among Triticum aestivum L. or between T. aestivum L. and T. turgidum L. ssp. durum wheat cultivars determine not only their milling properties, but also the properties of flour or semolina endosperm particles, their preferential use in cereal‐based applications, and the quality of the latter. Although the mechanism causing differences in wheat hardness has been subject of research more than once, it is still not completely understood. It is widely accepted that differences in wheat hardness originate from differences in the interaction between the starch granules and the endosperm protein matrix in the kernel. This interaction seems impacted by the presence of either puroindoline a and/or b, polar lipids on the starch granule surface, or by a combination of both. We focus here on wheat hardness and its relation to the presence of puroindolines and polar lipids. More in particular, the structure, properties, and genetics of puroindolines and their interactions with polar lipids are critically discussed as is their possible role in wheat hardness. We also address future research needs as well as the presence of puroindoline‐type proteins in other cereals.     

Conditioning studies on Australian wheat. I. The effect of conditioning on milling behaviour

The effect of moisture level and lying time on the milling behaviour of a number of Australian wheat varieties was investigated. Significant differences were noted in the time required to reach optimum milling performance and this was also dependent on the level of water addition. Possible explanations for this behaviour include variations in the rate of penetration of added moisture and the condition of the aleurone/sub-aleurone interface.     

制粉对小麦粉营养品质影响机理研究现状

小麦制粉是利用机械力作用将小麦胚乳与皮层和胚逐步分离后,再将其胚乳研磨成粉的过程。小麦籽粒中营养物质分布不均匀,在制粉过程中,受制粉系统、机械力作用、筛理分级等因素的影响,胚乳出现不同程度的破碎,不同粒度级的小麦粉营养组分含量及分布也存在着一定差异。同时,随着胚乳的破碎,细胞壁破裂、淀粉与蛋白分离,营养组分和酶的作用位点更多的暴露,从而提高营养组分的消化性和生物利用率。本文综述了制粉过程的相关因素对小麦粉营养品质影响机理研究现状,以了解小麦制粉过程中各营养素的变化和损失,为后续制粉过程中充分保留营养素、提高营养素利用率提供参考。     

Effect of different milling mechanical forces on the structures and properties of wheat flour

Size reduction by milling of endosperm granules produces flour and prompts the heterogeneous distribution of nutrients, changing its properties. The effects of impact milling and frictional milling on the breakage of endosperm granules were evaluated. Comparison of both methods showed that frictional milling initially squeezed larger starch granules out of the endosperm granules, and the flour particles were smaller and exhibited decreased relative crystallinity. Meanwhile, impact milling peeled the protein off the surface of endosperm granules, and the surface of the flour particles had higher S and N contents. Moreover, the content of random coils decreased, and the V-shaped peak disappeared. The weight loss rate of the ground samples and the maximum thermal cracking temperature of the impact-milled samples increased significantly as processing progressed. Different milling mechanical forces can be used in combination to obtain the desired flour.     

The conditioning of wheat. The effect of increasing wheat moisture content on the milling performance of uk wheats with reference to wheat texture

Five UK wheats of similar protein content but widely different degrees of hardness have been conditioned, using two lying times, to give wheat moisture contents in the range 14–16%. The milling performance of the wheats has been assessed in terms of extraction rate, flour moisture content, grade colour figure (GCF) and ash content. Extraction rates all decreased in a linear manner with increasing wheat moisture content. The hard wheats tolerated added water far better than the soft wheats. Hard wheats exhibited a smaller extraction rate loss than the soft wheats for each additional 1% wheat moisture content. Flour moisture contents increase with increasing wheat moisture content and a measure of the moisture losses is obtained for the laboratory milling system. GCF and ash fell with increasing wheat moisture content (decreasing extraction rate). When extraction rates are based on wheat at a fixed moisture content the hard wheats showed very small gains in milling yield but soft wheats suffered a reduction in milling performance as wheat moisture increased.     

Safety of Oxygreen, an ozone treatment on wheat grains. Part 2. Is there a substantial equivalence between Oxygreen-treated wheat grains and untreated wheat grains?

The Oxygreen process is a new process based on wheat grain treatment by ozone (produced in situ), in a closed sequential batch reactor. The Oxygreen process offers a close, homogeneous, and controlled contact between the gas and the grain. It is proposed for use for wheat grain decontamination (insects, fungi, bacteria, mycotoxins, pesticides). It takes place in classical milling diagram, and occurs after grain cleaning and before milling. The aim of the study reported here was to determine if Oxygreen treatment could induce in the grain the formation of processing-related compounds, and if these compounds are specific or could be recognized as classical modifications already used in the cereal industry (milling, baking). Studies were performed in order to evaluate any effect of Oxygreen treatment on vitamins, ferulic acid, phytates, proteins, carbohydrates, and lipids. It was concluded that there was no detectable substantial difference between ozone-treated grains and the untreated ones, although some quantitative differences can occur. The more detectable differences concern concentration of free sugars, and inhibition of some oxidative enzymes. These quantitative differences are very slight compared to the modifications that occur in dough, after addition of oxidative products directly in flour, or during kneading and dough fermentation.     

An autoradiographic technique for the location of conditioning water in wheat at the cellular level

A technique was devised whereby sections of wheat grains, conditioned with tritiated water, were used to produce an autoradiographic pattern of the distribution of this water. This enabled a more precise location of the conditioning water to be made than could be achieved using halves of labelled wheat grains. Within 1 h the labelled water had penetrated into the aleurone cells, and in many cases, into the starchy endosperm to a depth of 50–60 μm. The embryo and scutellum also absorbed the water with great rapidity. Subsequent penetration into the starchy endosperm was delayed for several hours. No morphological changes were observed that could account for the release of water by the aleurone cells. The cells of the embryo and scutellum appeared to bind the water more strongly than those of the aleurone and after 48 h lying time were still more heavily labelled than the other components of the wheat grain.     

Wheat bran-based biorefinery 1: Composition of wheat bran and strategies of functionalization

Wheat, together with maize and rice, accounts to about 90% of the world's cereal production. During the milling process, wheat bran, besides other valuable compounds such as wheat germ and parts of the endosperm, remains as major by-product. Wheat bran is composed of various histological cell layers, called the pericarp, testa, hyaline and aleurone layer and its weight ratio to milled wheat is about 25%. Annually, over 650 million tons of wheat are produced in the world, of which more than 69% are used for food. The thereby accruing biomass of wheat bran can be estimated as 150 million tons, which are basically used in the feed industry. Even if numerous studies have investigated potential health benefits of consuming more whole grain foods, the addition of bran to existing food systems may confer difficulties in terms of processing, nutrition or sensory acceptance by consumers. This review will summarize state-of-the-art technological approaches such as mechanical, thermal or enzymatic treatment used to modify the functional properties of wheat bran and coincidently describe the impact on the food system.     

Dye-binding capacity as a sensitive index for the thermal denaturation of wheat protein. A test for heat-damaged wheat

The influence of the thermal denaturation of wheat proteins on their dye-binding capacity has been studied for a wide range of wheat varieties and growing conditions. A strong correlation has been established between dye-binding capacities of sound and heated wheats and this has been used as the basis of a rapid diagnostic test for heatdamaged wheat. The test is of an empirical nature and is independent of wheat variety. The Research Association Protein Indicator Device (RAPID-meter) can now be used to determine both wheat protein content and the extent of thermal denaturation of the protein. In addition to protein dye-binding capacity a number of other heat-sensitive indices within wheat have been investigated. Control systems are required for any heatdamage test to compensate for initial differences of the index within different wheat samples. The only heat-sensitive index to which reference samples could be applied was protein dye-binding capacity.     

小麦中呕吐毒素的影响因素和污染特性分析

以小麦为研究对象,分析影响呕吐毒素,即脱氧雪腐镰刀菌烯醇（deoxynivalenol,DON）含量的相关因素,研究小麦不同粒型及籽粒不同部位DON的污染特性、分布差异。结果表明,小麦籽粒染病、破损,籽粒粒径及虫蛀类型对DON污染均有影响,DON含量与不完善粒含量呈显著的弱正相关,与赤霉病粒含量呈显著的强正相关。相同品种的小麦样品,小麦不同粒型和籽粒不同部位,DON含量存在很大差异,其中赤霉病粒显著高于未染病粒,破损粒显著高于完整粒,小颗粒显著高于大颗粒,籽粒胚部显著高于胚乳,粒面DON含量占35.2%～52.1%。胚乳结构越靠近外层,DON污染越严重,越靠近籽粒中心,DON污染越轻,制粉后外层麸皮DON含量较高,而可食用的小麦粉含量较低。小麦通过分级、分选、水洗和制粉加工可有效降低DON的污染。     

Distribution of soft wheat kernel lipids into flour milling fractions

Samples of whole and manually degermed Atou wheat were milled on a micro-mill to give straight-run flour, coarse offal, fine offal, finished bran and bran finisher flour. The non-starch lipids in these products were compared with non-starch lipids in the aleurone-free starchy endosperm, and with lipids in the germ and aleurone of the original wheat. About half of the triglyceride in flour was derived from the germ; no glycolipids or phospholipids were derived from germ, and no lipids of any kind were derived from the aleurone. Non-starch lipids in the aleurone-free endosperm of a mixed English soft wheat grist were then compared with the non-starch lipids in 11 flour streams from a commercial mill. All flours had much more triglyceride than the endosperm. In flours from the reduction system there were significant correlations between flour colour grade, sterylester, triglyceride, diglyceride, free fatty acid and diacylphospholipids, but none between ash or protein and colour or any class of lipid. Analysis of the principal components of variation in a simplified matrix describing all 11 flours placed triglyceride, diglyceride, free fatty acid, and diacylphospholipids close together in one group, and all glycolipids and N-acylphospholipids in a separate unrelated group. Sterylester and colour were loosely associated with the first group but could also be regarded as part of a third loose group with ash and protein. The results are interpreted in terms of lipid distribution within the wheat kernel, and their significance in milling and baking practice.     

Improved wheat for baking

To bakers, wheat quality means the performance characteristics of the flour milled from the wheat when used in specific wheat products. The tremendous increase in the number of wheat cultivars grown in the U.S. in recent years, along with the unusual climate, new advances in milling technology, and increased automation of baking lines, have resulted in bakery production problems partly attributed to wheat flour quality. In this review various factors affecting wheat quality are explained. Concerns of bread and cookie/cracker manufacturers on deterioration of the wheat quality are discussed, and, finally, some solutions are proposed.