Characterization of Oat Endoproteinases that Hydrolyze Oat Avenins

During oat seed germination, the insoluble storage proteins must be solubilized and transported to the embryo for use by the developing plantlet. We showed earlier that pH 6.2 active serine and metalloproteinases were the predominant gelatin‐hydrolyzing enzymes of oats, while the oat globulins were degraded by pH 3.8 active cysteine proteases. The pH of the endosperms of germinating oats is 6.2. We have continued our characterization of the germinated oat proteinases by determining which hydrolyze avenins, the oat storage prolamins. Avenins of resting seeds were purified and hydrolyzed with proteinases that were extracted from oat seeds that were germinated for various periods. The peptides released were analyzed using SDS‐PAGE. The α‐avenins were hydrolyzed at pH 3.8 by cysteine proteinases from four‐day germinated seeds and the β‐avenins were hydrolyzed by similar enzymes from eight‐day germinated seeds. At pH 6.2 or pH 5.0, the avenins were not degraded by any of the germinated oats endoproteinases. It is probable that some kind of pH compartmentalization occurs within germinating oat seed. After four days of germination, either new proteinases form or some preexisting proteinases are activated. The cysteine proteinases are apparently responsible for the majority of the storage protein hydrolysis that occurs during oat germination.     

Effects of Different Lipase Inactivation Treatments on Physicochemical Properties of Naked Oat Globulins

Lipase inactivation is an essential treatment for oat processing, because of the negative effects of lipase on nutrient preservation and storage extension. The effects of different lipase inactivation treatments including hot air roasting, infrared roasting, normal‐pressure steaming, and high‐pressure steaming on the physicochemical properties of oat globulins were investigated. Results showed that normal‐pressure steaming had little effect on solubility of oat globulins; hot air roasting increased foaming capacity of oat globulins but did not change their foaming stability; and all the inactivation treatments increased the surface hydrophobicity and content of total sulfhydryls of oat globulin but decreased exposed sulfhydryl groups. In addition, oat globulin granules from the hot air roasting treatment were distributed more evenly in oat globulin powder compared with the control group. All treatments except normal‐pressure steaming changed the molecular weight of oat globulin subunits, which made the bands of 66,000 and 45,000 disappear from SDS‐PAGE. These results indicated that normal‐pressure steaming was ideal to maintain good solubility of oat globulins, and hot air roasting was ideal to maintain relatively good foaming properties. The treatments changed physicochemical properties of oat globulins by influencing protein aggregation and subunit composition that resulted in different content of sulfhydryl groups and surface hydrophobicity.     

Comparison of Endoproteinases of Various Grains

Two‐dimensional isoelectric focusing (IEF) × PAGE gels were used to compare the endoproteolytic (gelatinase) activities of germinated barley with those of bread and durum wheat, rye, triticale, oat, rice, buckwheat, and sorghum. Barley was used as the standard of comparison because its endoproteinase complement has been studied previously in the greatest detail. The characteristics of the grain proteases were appraised from their migration patterns and by how they were affected by pH levels. All of the germinated grains contained multiple enzyme activities and their separation patterns and pH levels were at least similar to those of barley. The proteinases of the bread and durum wheats, rye, oat, and sorghum were most similar to those of barley, whereas the other grains provided more varied patterns. The rice and buckwheat proteinases developed much more slowly than those of the other grains. The activity patterns of the triticale resembled those of the parents, wheat and rye, but the triticale contained many more activities and higher overall proteolytic activities than any of the other species. These results should be applied to scientific or commercial procedures with caution because grains contain potent endogenous proteinase inhibitors that could inactivate some of these enzymes in various tissues or germination stages.     

嘧菌酯水解动力学研究

为指导合理使用嘧菌酯以及评价其环境特性提供依据,并为处理该药剂废水的研究提供基础参数,研究了嘧菌酯在不同温度和pH条件下水溶液中的降解情况。结果表明,嘧菌酯在水中相对稳定,温度和pH是影响嘧菌酯在水环境中降解的两个主要因素;在不同温度条件下,嘧菌酯的半衰期分别为56.1、37.7、15.5、13.6 d,水解速率常数随温度的升高而增加,说明嘧菌酯的水解受温度影响较大,低温抑制水解,高温促进水解;在不同pH值缓冲溶液中,嘧菌酯的半衰期分别为47.9、29.6、17.2 d,水解速率依次为pH9〉pH7〉pH5,说明嘧菌酯在偏碱性环境中稳定性较差。     

Rheological Characterization of a New Oat Hydrocolloid and Its Application in Cake Baking

A new oat hydrocolloid containing 20% β‐glucan, called C‐trim20, was obtained from oat bran concentrate through steam jet‐cooking and fractionations. The rheological characterization of the C‐trim20 was conducted using steady and dynamic shear measurements. The C‐trim20 suspension exhibited a shear‐thinning behavior that was more pronounced at high shear rates and high concentrations. Its dynamic viscoelastic moduli increased with increasing concentration while the frequency at which G′ and G″ crossover decreased. The C‐trim20 suspension at various concentrations followed the Cox‐Merz rule. C‐trim20 was also evaluated for potential use in baked products, specifically cakes. The baking performance of C‐trim20 was tested by incorporating it into cake formulations. The inclusion of this hydrocolloid gave increased elastic properties to cake batters and produced cakes containing 1 g of β‐glucan per serving with volume and textural properties similar to those of the control cake.     

The Impact of Oat Quality on White Salted Noodles Containing Oat Flour

This research compared the physicochemical properties of six milling oat cultivars from Western Australia over two growing seasons (2011 and 2012). Variations among the cultivars in physicochemical properties, particularly β‐glucan content, were assessed to determine their suitability for incorporation into white salted noodles at a level of 30% of the flour component. The average across six oat cultivars grown in 2012 was significantly higher (P < 0.05) for protein content, lipid content, and volume of smaller sized particles (<100 µm) and significantly lower for ash content, starch damage, and volume of larger particles (>100 µm) in comparison with the average across the same oat cultivars grown in 2011. The year of cultivation by cultivar interaction was significant (P < 0.05) for ash content, protein content, β‐glucan content, starch damage, and particle size. Oat cultivar Mitika had the highest peak viscosity for 100% oat flour (whole groat) and 30% oat–wheat (OW) flour blend, which may be owing to lower amylose percentage, high protein content, and greater volume of smaller particles. The effect of growing season had greater impact on OW noodle firmness than the genetic effect of cultivars. The eating and cooking quality attributes of OW noodles, such as color, color stability, firmness, and cooking solid loss were superior for those incorporated with 2012 oat flour (whole groat) compared with 2011 oat flour. Among the six oat cultivars, Williams produced noodles with poor cooking and eating quality, and Mitika was easier to handle during processing and produced noodles with superior brightness and color stability in comparison with other oat cultivars evaluated.     

Stability of Oat Avenanthramides

The three main oat avenanthramides, N‐(4′‐hydroxy)‐(E)‐cinnamoyl‐5‐hydroxyanthranilic acid ( Bp ), N‐(4′‐hydroxy‐3′‐methoxy)‐(E)‐cinnamoyl‐5‐hydroxyanthranilic acid ( Bf ), and N‐(3′,4′‐dihydroxy)‐(E)‐cinnamoyl‐5‐hydroxyanthranilic acid ( Bc ), and their corresponding cinnamic acids, p‐coumaric ( P ), ferulic ( F ), and caffeic ( C ), were investigated for stability to pH, temperature, and UV‐light treatment. The retention of the avenanthramides after processing of oat‐based food products was also analyzed. The avenanthramide Bc and the cinnamic acid C were sensitive to alkali and neutral conditions, especially in combination with heat treatment, whereas the other compounds studied were more stable. The cinnamic acids but not the avenanthramides were isomerized when irradiated with UV‐light. The avenanthramides were restored after processing of oat‐based products.     

超细粉碎辅助提取裸燕麦多糖工艺研究

以燕麦麸皮为原料,研究了超细粉碎辅助提取裸燕麦多糖的工艺技术。对裸燕麦麸皮进行超细粉碎,采用X射线小角散射法检测了麸皮的粒度分布,并通过单因素实验和正交实验优化了裸燕麦多糖的提取条件。确定超细粉碎后的燕麦麸皮的平均粒度为397.6nm,中位粒径为408.9nm,分布散度为134.8nm;裸燕麦多糖的提取条件为:提取时间0.5h,料液比为1:20,提取4次,提取温度60℃;该工艺条件下多糖的得率为0.126 g·g-1。本研究为裸燕麦的精深加工提供了理论依据,并为进一步研究裸燕麦多糖的结构效应关系奠定了基础。     

Preparation and Characterization of Films Using Barley and Oat β‐Glucan Extracts

Films for potential food use were prepared from aqueous solutions of β‐glucan extracted from hulled barley, hull‐less barley, and oats. The extracts (75.2–79.3% β‐glucan) also contained proteins, fat, and ash. Glycerol was used as a plasticizer. The films were translucent, smooth, and homogeneous in structure on both sides. Water vapor permeability of films prepared from 4% solutions of β‐glucan extracts were higher than those from 2% solutions, despite similar values for water vapor transmission rate. Mechanical properties were influenced by both β‐glucan source and concentration. The oat β‐glucan films showed higher tensile strength and water solubility, and lower color, opacity, and deformation values than those of barley. Films prepared from hull‐less barley cv. HLB233 remained intact upon immersion in water for 24 hr.     

Application of Oat Oil in Breadbaking

Lipids, especially polar lipids, can improve loaf volume, grain and texture, and delay staling in bread. Oats (Avena sativa L.) are rich in total and polar lipids. We have investigated the effect of oat lipids in a bread formulation on loaf volume, appearance, and bread staling. Oat oil was fractionated into polar and nonpolar fractions by water‐degumming. Crude oat oil and shortening (at 3%) increased loaf volume by ≈11% over the zero lipid formulation. The polar lipid fraction increased loaf volume by nearly the same amount when added at only a 0.5% level. The addition of 3% crude oat oil or 0.7% oat oil polar fraction significantly delayed bread firming and starch retrogradation; the difference between oat lipids and shortening was more evident at the end of a four‐day storage period. Oat lipids had a stronger relative effect on bread from a weak flour (10% protein) than from a strong flour (14% protein). The effects of oat oil in the bread formulation could be related to the amphipathic character of polar lipids in oats that enables them to interact with starch, proteins, and other bread components.     

Polar Lipids from Oat Kernels

Oat (Avena sativa L.) kernels appear to contain much higher polar lipid concentrations than other plant tissues. We have extracted, identified, and quantified polar lipids from 18 oat genotypes grown in replicated plots in three environments to determine genotypic or environmental variation in these lipids. Validation experiments indicated a solid phase silica gel extraction step elution provided excellent and clean separation of extracted lipids into neutral lipid, glycolipid, and phospholipid fractions. Analysis of phospholipids by HPLC (normal phase, diol column) indicated phosphatidylethanolamine, phosphatidylcholine, phosphatidic acid, phosphatidylglycerol, phosphatidylinositol, and lyso‐ forms but very little genotypic or environmental variation. Di, tri and tetragalactosyl‐diacylglycerols were quantified in the glycolipids, along with their mono‐, di‐, and triacyl estolides. Most of these exhibited significant genotypic variation. Molecular species analysis of the glycolipids in the Morton cultivar by direct infusion electrospray ionization tandem mass spectrometry confirmed the enormous diversity of galactosyl‐lipids in oats. Analyses indicated total lipid of ≈8.3% (dry weight basis), of which ≈10% was phospholipid and 11% was glycolipids. These results indicate that oats are a rich source of polar lipids and contain an extremely rich diversity of galactosyl‐lipids.     

Structure and Pasting Properties of Oat Starch

Following a period of declining food use, oats are now increasing in importance because of perceived nutritional benefits. The pasting properties of oat starch were regarded as similar to those of other cereal starches until the development of instruments with a more rapid mixing system than the amylograph showed characteristic differences in oats. These differences in pasting properties offer opportunities for novel products in both food and industrial areas. The structure, composition, and pasting properties of oat starch are reviewed, with particular emphasis on methods of measurement. Future directions of research in this area are suggested.     

Sources of Variation in Oat Kernel Size

Oat kernel size uniformity is important to the oat milling industry because of the size fractionations that occur in the milling process. We measured frequency of single, double, and triple kernel spikelets and kernel mass of primary, secondary, and tertiary kernels from each spikelet type (for a total of six kernel types) to determine relative influence of kernel type, panicle position, genotype, and environment on oat kernel size for 10 oat cultivars grown at four locations. Kernel type was the most important factor affecting kernel size. Primary kernels from triple kernel spikelets were larger than primary kernels from double kernel spikelets. Tertiary kernels were the smallest. Environments that produced larger kernels also produced higher frequencies of triple kernel spikelets. Some genotypes produced no triple kernel spikelets in any environment, whereas others produced varying proportions, depending on the environment. Kernels closer to the top of the panicle were larger than those near the base. The presence of tertiary kernels was neither associated with lower groat percentages nor with increased proportions of undersized kernels. Most undersized kernels were kernel types other than tertiary.     

不同品种燕麦对镉胁迫响应的差异性研究

利用实验室水培模拟试验,研究了轻度镉胁迫条件下10个燕麦品种生长及吸收积累镉的差异性。结果表明,经5μmol·L-1的镉处理后,供试燕麦品种的株高、根长、地上部与地下部生物量、叶绿素含量、类胡萝卜素含量均出现不同程度的下降,不同品种间存在明显的差异,有的甚至达到极显著水平;不同品种燕麦对镉的吸收与积累也存在明显差异;燕麦镉的吸收转运与耐性没有直接的联系。按照镉胁迫下燕麦耐镉性和镉含量的冠根比进行聚类分析,可将10个品种分为4类：①镉转运少且耐性强;②转运多但耐性强;③转运多且耐性弱;④转运较少但耐性弱。其中品5号地上部生长抑制率最小,并且镉含量、镉转运量较少,表现出较强的耐镉性,在轻度镉污染土壤上种植品5号有利于降低镉污染对人类健康的风险。     

Effects of Natural Chelating Agents on the Solubility of Some Physiologically Important Mineral Elements in Oat Bran and Oat Flakes

The solubility of mineral elements from oat bran and flake samples was studied by a method using equilibrium dialysis after enzymatic digestion of starch and proteins. The effects of six potential chelating agents common in food were tested on the solubility of mineral elements. The minerals studied were calcium, magnesium, iron, manganese, zinc and potassium, and the chelating agents were citric, lactic, malic, and ascorbic acids, glucose and xylitol. The mineral elements were tightly bound to the dietary fiber of the samples. Bran fiber bound even the zinc and calcium contributed through the enzymes used. Adding citric, malic, or lactic acids increased the solubility of the mineral elements studied, except for potassium which was easily dialyzable as such. Iron was insoluble in all situations. Citric acid was the most efficient chelating agent in solubilizing the mineral elements. The effect of malic and lactic acids on the solubility of minerals was small. No effect was found with glucose, ascorbic acid, and xylitol. Thus, the intestinal availability of mineral elements may be affected by dietary hydroxy acids such as citric and malic acids in high dietary fiber diets.     

Factors Affecting Viscosity of Slurries of Oat Groat Flours

Oat grain is routinely kilned and steamed before milling to develop flavor and to inactivate lipid-degrading enzymes. Heat treatments can significantly affect viscous properties, which have functional and nutritional importance. Oat flour slurries (23%, w/w, solids dry basis) made from steamed (for 20 min) or autoclaved (at 121°C, 15 psi, for 10 min) grain developed high viscosities, whereas flour slurries made from raw or kilned (105°C for 90 min) oats did not. Flour slurries made from raw groats, surface-sterilized by 1% hypochlorite, were more viscous than untreated raw groat flour slurries, suggesting that β-glucan hydrolases on the surface of the groat caused the viscosity losses observed in raw or kilned groats. However, because viscosities developed by surface-sterilized groats were not as great as in steamed oat-flour slurries and because some roasting treatments also inactivated enzymes without enhancing viscosity, it appears steaming might also affect the β-glucan polymer, resulting in its greater hydration in solution. Smaller particle size and higher incubation temperature also resulted in increased flour slurry viscosity, presumably because of increased hydration of the β-glucan. Rmoval of lipids from steamed oat flour significantly increased the oat flour slurry viscosity, apparently by increasing the β-glucan concentration in the flour.     

Evaluation of White Salted Noodles Enriched with Oat Flour

Oat consumption is regarded as having significant health benefits. The enrichment of white salted noodles with oat flour would provide a potential health benefit but may affect the texture and sensory quality. Oat cultivars grown in Western Australia (Yallara, Kojonup, Mitika, Carrolup, and new line SV97181‐8) and a commercial oat variety were milled into flour and added to wheat flour at 10, 20, and 30% to produce oat‐enriched white salted noodles. The purpose of the study was to determine the quality characteristics of the oat flours and to assess the influence the oat flour blends had on noodle texture, color, and sensory characteristics. In addition, another goal was to determine whether the different oat cultivars had similar potential to provide health benefits by measuring the β‐glucan content before and after processing. The results indicated that protein, ash content, and noodle firmness increased with the increased percentage of oat flour in the noodle formulations, whereas the pasting properties of the noodle wheat–oat flour blends did not differ significantly. The color of raw noodle sheets and boiled noodles changed significantly with oat incorporation and resulted in lower lightness/brightness, higher redness, lower yellowness, and lower color stability in comparison to standard wheat white salted noodles. Noodles made with the lowest oat percentage (10%) scored highest for all sensory parameters and were significantly different in appearance, color, and overall acceptability compared with noodles made with 20 and 30% oat flour. The β‐glucan content of the flour blends increased with the increase in the level of oat incorporation but subsequently decreased during processing into noodles. The decrease in the β‐glucan content varied across the different oat cultivars and levels of incorporation into the noodles. A new oat cultivar, SV97181‐8, exhibited the least β‐glucan loss during processing. In this study, the quality characteristics of white salted noodles enriched with oat flour from Western Australian cultivars were determined to provide essential information for the commercial development of healthier noodles.     

燕麦AsKUP1的克隆与功能分析

植物钾离子转运蛋白中的Na~+不敏感性KUP/HAK/KT转运蛋白对植物耐盐胁迫起着重要作用。为了阐明钾离子转运蛋白基因AsKUP1在燕麦中响应盐胁迫的表达模式和鉴定其生物学功能,从燕麦中克隆了AsKUP1,利用RACE方法获得AsKUP1全长序列,并对其进行生物信息学分析;构建了pCAMBIA1301-AsKUP1植物过表达载体,转化拟南芥,并运用实时荧光定量PCR方法分析AsKUP1在拟南芥中的表达情况。结果表明,AsKUP1全长2 951bp,包含2 334bp的ORF序列,预测编码777个氨基酸,等电点为8.55,分子量为87.0k D。序列分析表明,AsKUP1与山羊草和小麦KUP/HAK/KT家族亲缘关系较近,预测该蛋白有14个疏水跨膜结构域,位于细胞质膜的概率较大。此外,盐胁迫下,T2转基因种子萌发率为57%,野生型为43%;经潮霉素筛选分离比为3∶1的2个转基因株系后代T3转基因株系根长分别是野生型的1.46倍和1.34倍,T3转基因植株鲜重、干重分别是野生型的1.56倍和1.44倍,Na~+含量无显著差异,而K~+含量为野生型的1.25倍,说明AsKUP1的表达提高了拟南芥植株的耐盐性。本研究结果为揭示钾离子转运蛋白家族基因AsKUP1在植物中的耐盐机制和通过转基因技术提高植物耐盐能力奠定了基础。     

Antioxidant Activity and Phenolic Contents of Oat Groats and Hulls

Research was initiated to measure antioxidant activity of extracts from oat (Avena sativa L.) groats and hulls and the concentrations of phenolic substances that may contribute to antioxidant activity. Antioxidant activity of ethanolic extracts of four cultivars was evaluated by an in vitro assay that measures the inhibition of coupled autoxidation of linoleic acid and β-carotene. Total phenolic content was determined using Folin and Ciocalteau's phenol reagent and was expressed as gallic acid equivalents. Phenolic compounds were separated by reversed-phase HPLC and detected at 290 nm. Peaks were identified by comparing retention times and spectra with known standards and verified with internal standards. Groats had significantly higher antioxidant activity than hulls. For two cultivars, total phenolic content was similar in groats and hulls, whereas one cultivar had higher and another lower total phenolic content in groats than hulls. Ten phenolic compounds were separated and identified in extracts, and one flavan-3-ol and three avenanthramides were tentatively identified. The concentrations of many of these compounds differed among cultivars and between fractions. In general, caffeic acid and the avenanthramides were predominantly found in groats, whereas many of the other phenolics were present in greater concentrations in hulls.