杜马斯燃烧法测定油料作物中粗蛋白质含量的 方法优化及其与凯氏定氮法的比较研究

目的建立杜马斯燃烧法测定油料作物中粗蛋白质含量的方法,并与凯氏定氮法进行比较。方法以芝麻、大豆、油菜和花生为研究对象,对杜马斯燃烧法的称样量和氧气系数进行优化。分别用杜马斯燃烧法和凯氏定氮法测定4种样品的粗蛋白含量,并对2种测试方法的结果进行比较分析。结果杜马斯燃烧法的测定值略高于凯氏定氮法,但2种方法的测定值间没有显著性差异(P0.05),杜马斯燃烧法比凯氏定氮法的测定精密度和准确度更高。测定结果的相关性分析表明两种方法的测定值呈显著相关(r~2=0.9988)。结论杜马斯燃烧法的精密度和准确度更好,可以替代凯氏定氮法测定油料作物的粗蛋白质含量。     

杜马斯燃烧法测定食品中总氮含量

以各类食品为试验材料,分析了各种参数对杜马斯燃烧法测定含氮量结果的影响,并比对了杜马斯法和凯氏法的测定结果。结果表明,当通氧量为110～200min/mL,反应炉温度设定900℃以上,样品量在100～150mg时,测定结果理想。大部分食品样品杜马斯和凯氏法无显著性差别。但杜马斯法结果RSD较凯氏法稍大。另改进前处理方法,杜马斯法还可以用于测定液体食品中的氮含量,结果准确。     

The effect of the previous crop on the growth,nitrogen uptake and yield of winter barley intended for malting

Winter barley which received a range of nitrogen rates, was grown at Rothamsted as a test crop after winter oats, winter barley, winter beans, oilseed rape or potatoes, to compare the effects of previous crop on growth and N uptake. In the autumn following the first year crops, the largest amount of residual inorganic N found in the soil was after potatoes, the smallest after oats. Throughout the second season the heaviest crops of barley, which also contained the most N, were after potatoes, and the lightest were after barley. To produce grain with a N concentration of less than 1.8% N (w/w, dry wt), acceptable for malting, it was found that not more than 75 kg N ha⁻¹ after barley and 125 kg N ha⁻¹ after oats, 100 kg N ha⁻¹ after beans and 50 kg N ha⁻¹ after rape or potatoes could be applied. The results demonstrated that barley of acceptable quality for malting can be grown after a break crop, providing that the rate of N fertiliser is suitably adjusted to take account of the residual fertility, but the results do not suggest that residual soil N affects the grain N concentration differently to N applied as fertiliser early in the season.     

杜马斯燃烧法测定牛奶中的蛋白质含量

目的通过对杜马斯燃烧法和凯氏定氮法测定牛奶中的蛋白质含量的比较,建立杜马斯燃烧法测定牛奶中蛋白质的方法。方法杜马斯燃烧法检测条件:称样量100 mg,通氧量80 m L/min,通氧时间80 s;结果选用合适的燃烧条件用杜马斯燃烧法可以准确测定牛奶中的蛋白质含量。结论此方法具有结果准确、精密度高、易于操作的优点,适用于大批量牛奶样品的检测。     

Changes in saccharide,amino acid and S‐methylmethionine content during malting of barley grown with different nitrogen and sulfur status

BACKGROUND: Changes in saccharide, amino acid and S‐methylmethionine (SMM) concentrations and enzyme activities during the malting of barley grown with different nitrogen (N) and sulfur (S) supplementation were investigated in order to clarify their relationship with N and S fertiliser levels. RESULTS: Concentrations of N and S in barley grain were significantly increased by the addition of N to the culture soil. Application of N decreased the starch concentration in grain. On the other hand, higher N fertilisation increased the β‐glucan concentration in grain and malt, thus decreasing the accessibility of β‐glucanase to its substrates. Proteolytic enzyme activity was significantly higher in the absence (?N treatment) than in the presence (+N treatment) of N fertiliser, making the concentration of the majority of amino acids in malt slightly higher in the ? N treatment. SMM was synthesised in grain after imbibition, and application of N increased the SMM content in malt. CONCLUSION: Although SMM can be controlled to a certain extent during kilning, a balanced supply of N and S during cultivation can also be helpful for the production of malt with lower SMM concentration. Adequate soil management is desirable to maintain the balance between good agronomic performance and high malt quality. Copyright © 2010 Society of Chemical Industry     

Assessment of the microbial diversity during an industrial‐scale malting process by a polymerase chain reaction‐denaturing gradient gel electrophoresis analysis

Assessing the microbial diversity during malting is an essential step towards process management and optimization. However, microbial characterization of the malting process has mostly been performed using culture‐dependent methods, which has probably led to biased microbial diversity estimates. The aim of this study was to characterize the bacterial communities during an industrial‐scale malting process using polymerase chain reaction–denaturing gradient gel electrophoresis. The main bacterial strains in the malting process were identified as Sphingomonas spp., Enterobacter spp., Neisseria spp., Escherichia spp., Rhodocyclus spp., Erwinia spp. and Klebsiella spp. according to the GenBank database. The results revealed that the bacterial community structure changed during the malting process, and that the diverse microbial community played an active role in the malting ecosystem. Moreover, the dominant species changed with the aeration conditions during malting, and there was a tendency for aerobic bacteria to gradually become the predominant community during malting. An improved understanding of the complex microbial community during malting enables greater process management control and the production of high‐quality malt. Copyright © 2016 The Institute of Brewing & Distilling     

The influence of steep regime and germination period on the malting properties of some hull‐less barley lines

Following field trials in 2008 and 2010, six lines, derived by mutation in the hull‐less barley cultivar Penthouse, were selected to provide a range in grain β‐glucan content. These lines, along with Penthouse and the hulled, malting variety Optic, were then malted, using four different steeping regimes, with samples kilned after 3, 4 and 5 days of germination. The longest steep regime provided samples with optimum modification after 5 days of germination. Samples from the other steep regimes were under‐modified to varying degrees. In particular, the steeps with a single immersion gave poorly modified samples with low extracts and alcohol yields. One line, with low grain β‐glucan, gave higher alcohol yields than either Penthouse or Optic, following a regime comprising two short immersions and a single air‐rest, but there was no clear association, within the lines, between β‐glucan content and malting properties. Copyright © 2012 The Institute of Brewing & Distilling     

Effects of malting on β‐glucanase and phytase activity in barley grain

The effects of malting on β‐glucan and phytate were investigated in one naked and one covered barley by a full factorial experiment with three factors (steeping temperature, moisture content and germination temperature) each with two levels. Analysis of total content of β‐glucan in the malted samples showed small changes after steeping at the high temperature (48 °C), while steeping at the lower temperature (15 °C) gave a significantly lower content. This trend was even stronger for β‐glucan unextractable at 38 °C. Analysis of the activity of β‐glucanase for the samples steeped at 15 °C showed a strong increase over the time of germination, while those steeped at 48 °C had a much slower development. The other two factors influenced the outcome to a small extent, mainly because the steeping temperature was the most important factor overall where any changes in β‐glucan and β‐glucanase were observed. When β‐glucan was extracted at 100 °C, a larger yield was obtained, and this was influenced by the steeping temperature in a much stronger way than for β‐glucan extracted at 38 °C. Determination of average molecular weight for β‐glucan extracted at 100 °C gave a lower value for samples steeped at 15 than at 48 °C. The design did not have any large effects on phytate degradation and phytase activity. However, it indicated that selective control of the enzymes might be possible, since phytase activity was barely affected by the parameters studied, while β‐glucanase was heavily affected. © 2002 Society of Chemical Industry     

Optimising the determination of maize endosperm vitreousness by a rapid non‐destructive image analysis technique

A rapid non‐destructive image analysis technique was developed and optimised for the determination of maize endosperm vitreousness without the need for sample preparation. Maize kernel translucency measurements were optimised for a light system consisting of positioning whole kernels on top of round illuminated areas smaller than the projected areas of the kernels, allowing light to shine through the kernels. A correction factor to allow for constant illumination of kernels was developed to adjust for kernel size variation in relation to constant light area. The intensity of translucency in maize is linearly correlated to the percentage of kernel illumination (r = 0.99, p < 0.001). Significant correlations were found between corrected translucency values and endosperm yields determined by hand dissection. These were: translucency as a percentage of the whole kernel and vitreous endosperm (mass%), r = 0.77; translucency as a percentage of the whole kernel and opaque endosperm (mass%), (r = ?0.72); translucency as a percentage of endosperm and vitreous endosperm (mass%), r = 0.81; and translucency as a percentage of endosperm and opaque endosperm (mass%), r = ?0.77; with n = 245 in all instances. Translucency varied by 29.5% between the lowest and highest values, and vitreous endosperm (mass%) varied by 16.8% between the lowest and highest values. Correlations increased significantly after corrections for kernel thickness. A thickness increase of 1 mm in the maize will cause a decrease of 21.86% in translucency and vice versa. The method allows for large samples (at least 49 kernels min^?1) to be analysed for individual vitreous and opaque endosperm contents with no interferences with kernel structure. With further development of suitable automated sampling techniques, it could become a suitable potential method for in‐line quantification of maize endosperm contents. Copyright © 2004 Society of Chemical Industry     

分光光度法测定牦牛不同脏器中左旋肉碱方法优化及含量分析

对牦牛脏器中左旋肉碱的分光光度法测定进行优化,并对其脏器中左旋肉碱含量进行分析。在单因素实验的基础上,以加酶反应时间、缓冲体系pH、酶反应温度为自变量,以吸光度为响应值,进行响应面分析。确定最优工艺条件为:酶反应温度37℃、缓冲体系pH7.6、加酶反应时间16min,在此条件下,左旋肉碱吸光度值为0.321。通过对牦牛心、肝、肺、肾中左旋肉碱测定值的分析发现,肝脏中左旋肉碱含量最高,为28.35mg/kg;肺脏中左旋肉碱含量为22.75mg/kg;心脏中含左旋肉碱14.61mg/kg;肾脏中左旋肉碱的含量最低,为5.22mg/kg。      

Evaluation of the potentials of millet,sorghum and barley with similar nitrogen contents malted at their optimum germination temperatures for use in brewing

Studies on the malting physiology of barley have led to similar studies on millet and sorghum. This study compares the outcomes of the malting physiology of millet, sorghum and barley. Results show that optimal development of diastatic power, soluble nitrogen, hot water extract and the wide range of amino acids of these three cereals is related to optimal malting conditions and appropriate mashing procedures. Transfer of the nitrogen/extract/soluble nitrogen/diastatic concepts of barley malt do not apply to millet and sorghum. However, all the cereals studied produced the range of amino acids required by yeast for fermentation. Sorghum malt released the highest amounts of group 1 amino acids, usually taken up faster by yeast. It also produced and released the highest amounts of amino acids, classified as group 2, which are assimilated more slowly than group 1 amino acids. It also produced and released more of the amino acids that are slowest to be assimilated during fermentation, as well as very high levels of proline. Optic barley malt produced and released the least amount of proline. The fate of proline during yeast fermentation is not clear, but it is believed that proline is not utilized during fermentation. Copyright © 2013 The Institute of Brewing & Distilling     

热分解-电化学法测定印染废水中的总氮

为解决总氮测量方法(HJ 636—2012)存在的问题,建立了热分解-电化学法并应用于检测印染废水。结果表明,热分解-电化学法的检测范围为0～200.00 mg/L,检出限为0.025 mg/L,测量印染废水水样的相对标准偏差为3.0%～4.1%,加标回收率为98.9%～101.5%。与HJ 636—2012方法比较,热分解-电化学法具有测量简便快捷、干扰因素少、检测范围广和灵敏度高等优点。     

常量法测定螺旋藻片中氮含量的不确定度评定

评定螺旋藻片中氮含量测定的不确定度。方法 采用《中国药典》2015年版第四部氮测定法中第一法(常量法),测定出螺旋藻片中的含氮量。根据测量不确定评定的要求与表示的要求,通过获得的检测数据对螺旋藻片中氮含量测定的不确定度进行评定。结果 当氮含量的结果为：20.59mg/片时,常量法测定螺旋藻片氮含量的合成标准不确定度为0.196mg/片,扩展不确定度为0.39mg/片,螺旋藻片中氮含量测定的结果为：(20.59±0.39)mg/片,（k=2,p=95%）。结论 在测定过程中,测量不确定度的主要来源于试样测定重复性实验引入的不确定度和试样滴定过程引入的不确定度。因此, 对常量法测螺旋藻片氮含量的不确定度评定时, 应控制好试样的消化、蒸馏,同时控制好试样的滴定,以确保数据的准确可靠。     

Applicability of neutron activation analysis (NAA) in quantitative determination of some essential and toxic trace elements in food articles

Accurate and reliable data on microgram and nanogram quantities of some essential and toxic elements in most food articles are very scarce. Neutron activation analysis (NAA), with its essentially blankfree advantage, is a valuable approach in the field of determination of trace elements in different foodstuffs and diets. Accordingly, various radiochemical (RNAA) and instrumental (INAA) approaches have been developed in our laboratory for the elements As, Cd, Co, Cu, Hg, I, Mo, Ni, Sb, Se, Sn, Th, U, V, and others, and verified by the analysis of compositionally appropriate certified reference materials.This communication was presented as a poster at EURO FOOD CHEM VIII, Vienna, September 18–20, 1995, and was one of three such posters which were awarded as being outstanding     

利用韦氏分析预测刀豆货架寿命并确定感官评分标准切分点

实验中刀豆通过韦氏分析,获得不同温度下(0、5、20、25℃)的货架寿命终点,并由感官评定线性回归方程计算得感官评定标准中切分点的交集区间为(4.70,4.90),为感官评定切分点以及货架寿命终点判断提供了理论依据。实验研究也表明,在设定切分点为4.80情况下,温度与货架寿命的对数呈现非常好的相关性(R2=0.997)。     

Rapid instrumental methods and chemometrics for the determination of pre‐crystallization in chocolate

Three rapid instrumental methods for the determination of the pre‐crystallization stage in six types of chocolate were studied. The methods were near‐infrared (NIR) spectroscopy, fluorescence spectroscopy and tri stimulus colour measurements. The chocolates were tempered into five categories: two levels of under‐tempered, two levels of over‐tempered and one level of well‐tempered chocolate. A temper meter was used as the reference method. NIR and fluorescence data were orthogonalized before modelling in order to remove the chocolate type characteristics. NIR spectroscopy was capable of discriminating between the five tempering groups when the principal component analysis (PCA) model was used on all chocolate types. A partial least squares discriminant analysis on the NIR spectra with the three main tempering groups (over‐, well‐, and under‐tempered) as the dependent variable showed perfect separation of the groups. Using fluorescence spectroscopy it was possible to separate the chocolates into the three main tempering groups in a PCA model, while the colour measurements did not reflect the degree of pre‐crystallization.     

Comparative study of the effects of 1‐MCP treatment on apple quality by instrumental and multivariate analysis

BACKGROUND: The main aim of this work was to define how 1‐methylcyclopropene (1‐MCP) treatment affects apple fruit quality by two complementary approaches. RESULTS: The results confirmed that 1‐MCP treatment maintained firmness and acidity of the fruit. Multivariate analysis distinguished treated and untreated fruits and showed that a relationship exists between 1‐MCP treatment and firmness, and also between 1‐MCP and the physiological disorder, ‘diffuse skin browning’ (DSB). Relationships for acidity were low and absent for soluble‐solids concentration (SSC). The PCA model built only with 1‐MCP treated fruit showed a positive correlation between DSB incidence and firmness, and a negative correlation between DSB and SSC or a* values. Collectively, these correlations indicated that the more immature fruits are more susceptible to DSB. This last model also characterised acidity as the best parameter to discriminate the 1‐MCP fruits. CONCLUSION: It is the first time that such a comparative study has been conducted on 1‐MCP treated fruits. The results are of interest because they (1) help to discriminate treated and untreated fruits, and (2) allow discrimination of 1‐MCP‐treated fruit during storage. Copyright © 2008 Society of Chemical Industry