Relation of net portal flux of nitrogen compounds with dietary characteristics in ruminants: a meta-analysis approach

Decrease of N intake (NI) with the aim of increasing efficiency of N utilization and decreasing the negative environmental effects of animal production requires assessment of the forms in which N is absorbed. A meta-analysis was conducted on 68 publications (90 experiments and 215 treatments) to study the effect of NI on net portal appearance (NPA) of nitrogenous nutrients [amino acids (AA), ammonia, and urea] in ruminants. In addition, the effect of several dietary energy and protein factors on this relationship was investigated. These factors were: dry matter intake; proportion of concentrate; diet concentrations and intakes of nonfiber carbohydrates and neutral detergent fiber (NDF); diet concentrations of total digestible nutrients (TDN) and crude protein; rumen-degradable protein and rumen-undegradable protein, as percent dry matter or percent crude protein. The effect of species and physiological stage was also investigated. Within-experiment analyses revealed that the NPA of AA-N and ammonia-N increased linearly, whereas the NPA of urea-N decreased (or recycling of urea-N increased) linearly with NI. Besides NI, many significant covariates could be introduced in each NPA model. However, only TDN and neutral detergent fiber intake (NDFi) were common significant covariates of NI in each NPA model. In this database, ruminants converted 60% of incremental NI into NPA of AA-N with no species effect on that slope. However, at similar NI, TDN, and NDFi, sheep absorbed more AA-N than did cattle and dairy cows. On the other hand, species tended to affect the slope of the relationship between NPA of ammonia-N and NI, which varied from 0.19 for the sheep to 0.38 for dairy cows. On average, the equivalent of 11% of incremental NI was recycled as urea-N to the gut through the portal-drained viscera, which excludes salivary contribution, and no species difference was detected. Overall, at similar TDN and NDFi, sheep and cattle increased their NPA of AA-N relative to NI increment by a similar magnitude. The higher absorption of AA-N observed in sheep compared with cattle, at similar NI, TDN, and NDFi, might result from lower losses of AA through portal-drained viscera metabolism.     

氨基酸营养价值评价方法的研究

通过查阅文献,随机选取31种常见食物氨基酸组成数据,利用统计学软件分析以粗蛋白为基数与以全氨基酸为基数下化学评析法中各项指标与生物价的相关性和离差情况。利用一元回归,求出化学评分法中各项指标与生物价的回归方程,求出值命名为化学生物价。结果表明:CS和SRCAA不随基数选择而改变,其他指标与BV的偏离高低不一。全氨基酸法计算的AAS、EAAI及EAARR与BV的相关性比粗蛋白法强。利用回归方程求得的化学生物价从总体上都消除了与BV的偏离。     

全自动氨基酸分析仪测定支链氨基酸粉中牛磺酸的含量

目的建立全自动氨基酸分析仪测定支链氨基酸粉中牛磺酸。方法样品经上样缓冲液(pH 2.2)溶解提取,按照氨基酸分析仪设定的钠体系程序洗脱,用Na型离子交换色谱柱分离,与茚三酮反应液在135℃下反应,生成可在570 nm和440 nm检测到的蓝色物质,采用外标法定量。结果牛磺酸在4.1065~20.5326μg/mL浓度范围内有良好的线性,r~2=0.999,回收率为101.28%,RSD为2.1%,检出限为15 mg/100 g。结论该方法准确可靠,不需要剧毒衍生试剂,适用于支链氨基酸粉中牛磺酸的测定。     

用氨基酸自动分析仪测定婴幼儿配方奶粉中的16种氨基酸

通过盐酸水解——氨基酸自动分析仪法,测定了婴幼儿配方奶粉中的16种氨基酸。结果表明,在12.5～250μmol/L的线性范围内相关系数均达到0.999以上,6组平行样的重复性变异系数均在2.0%以内,16种氨基酸3个浓度梯度的平均回收率均在95.0%～105.1%之间;应用盐酸水解法得到的待测液常温(20～28℃)放置5h及20h后,除Met外其余15种氨基酸5h后的平均损失率均在1%以下,Met的实际平均损失量也分别在5h0.005nmol/20μL和20h0.020nmol/20μL以下。结论说明,利用该法能得到十分理想的分离效果和相对准确的分析结果。     

几种含氮物质对酱油氨基酸态氮及全氮测定值的影响

按GB 18186-2000酱油检测方法测定几种含氮物质的氨基酸态氮值及测定添加了1％这些含氮物质的酱油氨基酸态氮及全氮含量,分析这些含氮物质对酱油测试结果的影响情况,结果表明:无机铵(氯化铵、硫酸铵),有机铵(柠檬酸铵、草酸铵)等均会导致酱油氨基酸态氮测定值偏高,而三聚氰氨和尿素对酱油的氨基酸态氮测定值无影响;以上几种含氮物质均会提高酱油全氮的测定值.     

酸水解-全自动氨基酸分析仪测定方格星虫中氨基酸

目的:优化测定方格星虫氨基酸的实验条件。方法:研究以酸水解-全自动氨基酸分析仪分析法对海南东方方格星虫中18种氨基酸含量进行分析测定,为确保该实验结果的有效性与可行性,辅以线性关系,加标回收率实验,精密度实验,方法检出限的计算分析。结果:实验发现方格星虫样品中含有18种氨基酸,其中,鲜方格星虫中天门冬氨酸、精氨酸含量较高,分别为2.02%、1.26%,胱氨酸、色氨酸含量最低,分别为0.21%。方格星虫干中谷氨酸、精氨酸含量最高,分别为11.89%、7.94%,而胱氨酸、色氨酸含量最低,分别为0.45%、1.07%;结论:实验方案具备可操作性及数据有效性,仪器的精密度高,相对标准偏差在0.21%以下,检出限低,最低达到0.00000001 ng/kg,线性范围宽,且相关系数在0.9999以上,操作简便,结果令人满意。      

两种测定酱油中氨基酸态氮方法的探讨

该研究探讨了酱油中氨基酸态氮测定的两种方法：酸度计法和比色法。因两种方法间有无差异尚未有定论,依据GB 5009.235-2016《食品中氨基酸态氮的测定》标准,通过探讨影响测定结果的关键因素和操作注意事项来保证方法的准确性,再抽取市售10种酱油,分别用两种方法测定其氨基酸态氮含量,试验结果显示,两种方法检测结果无显著性差异（P＞0.05）。     

Plasma essential amino acid concentrations in response to casein infusion or ration change in dairy cows: A multilevel,mixed-effects meta-analysis

The objectives of the current meta-analysis were to review the relationships between plasma individual essential AA concentrations and their respective AA digestible flows (AADI) in 2 independent sets of studies. The first set of studies included 36 casein infusion studies (CN; 83 treatment means) and was regarded as the best comparison standard available, because differences in AADI achieved by casein infusion (up to 40% of total metabolizable protein supply) did not rely on any model assumptions and were directly estimated from casein infusions. The second set of studies included 42 feeding trials (FT; 94 treatment means) in which AADI were predicted using the 2001 National Research Council model. The 2 sets of studies were not balanced for dry matter intake and the supplies of metabolizable protein and net energy for lactation; therefore, a subset of 17 CN studies (35 treatment means) and 19 FT trials (49 treatment means) balanced for these variables was assembled to allow the comparison of linear terms from CN and FT studies. In the subset of data set, the linear terms of individual AA did not differ between CN and FT studies except for Met and Thr, with a slope lower by 23 and 62%, respectively, in CN versus FT studies. The agreement in linear slopes between CN and FT studies indicates, indirectly, that AADI were predicted accurately by the National Research Council model. In the large data set, the relationships between plasma concentrations of Ile, Leu, Val, and their sum (branched-chain AA; BCAA) and their respective AADI shared common characteristics that distinguished them from the other AA. For the plasma concentration of BCAA, the linear terms were significant in CN and FT studies, but the quadratic terms were significant only in FT studies. This decline in the response of plasma concentration of BCAA to increased BCAA digestible flow in FT studies was associated with diets rich in energy, diets with a high concentrate level, or diets based on corn silage. These dietary conditions can stimulate insulin secretion and decrease plasma concentration of BCAA. For the non-BCAA, a quadratic term was significant for plasma His, Lys, Met, and Thr in each set of studies, indicating an increased removal of these AA by the liver as AADI increased.     

提高酵母抽提物得率及氨基氮含量的研究

本文以新鲜面包酵母为原料,通过研究高压均质,外加蛋白酶及酵母抽提物,搅拌条件,离心次数等对酵母自溶的影响,得出了提高酵母抽提物得率臁氨基氨含量的优化工艺条件,产品最终得率为75．9％,氨基氮含量为4．75％。     

酱中总酸、氨基酸态氮和食盐的连续测定

对酱的总酸、氨基酸态氮和食盐的测定方法进行了改进,将几个单独测定的项目合并为一个连续测定过程,测定了三个样品中的总酸、氨基酸态氮和食盐含量.结果显示,一次性连续测定法RSD在0.4%～1.9%(n=6)之间,平均回收率100.4%,具有简便、快速、准确等优点,令人满意.     

坛子肉中氨基酸和脂肪酸营养品质评价

目的评价坛子肉中氨基酸和脂肪酸的营养品质。方法运用多种方法对坛子肉中氨基酸和脂肪酸的组成及含量进行测定,并用必需氨基酸指数法(essential amino acid index method,EAAI)、氨基酸评分法(amino acid score, AAS)、化学评分法(chemical score, CS)评价坛子肉中蛋白质的营养价值。结果坛子肉中氨基酸总量为20.76%±0.21%, 8种必需氨基酸占氨基酸总量的42.60%, 4种鲜味氨基酸占氨基酸总量的36.90%,AAS和CS均表明第一限制性氨基酸为色氨酸。坛子肉中粗脂肪含量为28.15%±0.31%,不饱和脂肪酸占脂肪酸总量的70.79%±0.31%。必需氨基酸占氨基酸总量的38.15%,必需氨基酸与非必需氨基酸的比值为61.68%。结论坛子肉是一种具有独特风味的优质蛋白源以及具有均衡脂肪酸的高营养价值的肉制品。     

大曲中总酸和氨基酸态氮的连续滴定

对目前大曲酸度和氨基酸态氮的测定方法进行了改进,在滴定过酸度的试样中直接加入中性甲醛溶液以继续滴定试样中的氨基酸态氮。对同一曲样分别用两种方法进行对照试验表明,改进后的方法与原方法测得的结果一致。在实际测定工作中,连续滴定法只需配制一种浓度的氢氧化钠标准溶液,并且每个曲样的测定由原来的4个平行样减少到2个平行样,从制备样液到一次性测定2个理化指标总共只需40min左右,与原方法相比更简便省时。     

花边骡鸭理想氨基酸模式的研究

研究应用氨基酸扣除法原理,根据现有氨基酸需要量标准和目前的研究结果规划出一种氨基酸模式来确定对花边骡鸭生产性能和血液生化指标的影响.结果表明:花边骡鸭在1～3周龄4种必需氨基酸理想比例为赖氨酸∶蛋氨酸∶色氨酸∶苏氨酸=100∶37∶67∶19;花边骡鸭在4～8周龄4种必需氨基酸理想比例为赖氨酸∶蛋氨酸∶苏氨酸∶色氨酸=100∶33∶64∶18.     

酸度计法测定酱油中氨基酸态氮的不确定度评价

该文分析了滴定法测定酱油氨基酸态氮不确定度来源,对不确定度各分量进行评估与合成。结果表明,样品移取、定容和滴定引入的体积不确定度以及pH计示值误差和分辨率引入的不确定度分量是影响酱油氨基酸态氮测定的主要来源。试验对酱油样品进行10次重复测定,测得氨基酸态氮为0.813 g/100 mL,扩展不确定度为0.046 g/100 mL（P=95%,k=2）。该不确定度评定适用于滴定法测定酱油中氨基酸态氮的过程分析,对检测结果准确度的控制具有指导意义。     

氨基酸折算法计算婴幼儿配方粉中乳清蛋白含量方法的评估

目的评价以氨基酸折算法计算婴幼儿配方粉中乳清蛋白含量的方法。方法本实验使用自配的流动相,采用酸水解氨基酸自动分析仪测定婴幼儿配方粉中氨基酸含量,再根据乳清蛋白中天冬氨酸/天冬酰胺、丙氨酸、苯丙氨酸和脯氨酸4种特征氨基酸含量的经验公式折算出婴幼儿配方粉中乳清蛋白占总蛋白的百分比。结果对我国市售多种品牌的婴幼儿配方粉中的水解氨基酸进行了检测,再计算出乳清蛋白含量,发现仅1阶段乳基婴儿配方粉基本符合大于60%的国标规定。结论该氨基酸折算法对婴幼儿配方粉中乳清蛋白含量的定量研究具有参考价值,但对掺有大豆蛋白的产品无法进行准确测定。     

氨基酸自动分析仪测定游离L-半胱氨酸

目的对比讨论含硫氨基酸的传统测定方法过甲酸氧化法,针对添加了L-半胱氨酸的保健食品,提出一个操作简便、计算准确的测定游离L-半胱氨酸含量的方法。方法称取试样用上机缓冲液超声溶解,微孔滤膜过滤,应用氨基酸自动分析仪分析,用Na型离子交换色谱柱分离,L-半胱氨酸标准品定量计算其含量。结果L-半胱氨酸浓度在0.3861~3.0648 mg/m L的范围内与峰面积的线性良好,相关系数r0.999。在80%、100%、120%添加水平下,L-半胱氨酸的平均回收率为97.2%。结论该方法操作简便、准确、重现性好,适用于保健食品中游离L-半胱氨酸的含量测定。     

杂环氨基酸酯的合成与表征

以三种杂环结构的氨基酸、二氯亚砜、甲醇/乙醇为原料,合成L-色氨酸甲/乙酯盐酸盐、L-组氨酸甲酯盐酸盐以及L-脯氨酸甲/乙酯盐酸盐,产率较高,并通过核磁共振谱、红外光谱、元素分析对其盐酸盐进行了结构表征,所得到的氨基酸酯盐酸盐分别用饱和碳酸钠溶液中和、二氯甲烷萃取,最终得到了三类杂环氨基酸酯。     

An in vivo stable isotope–based approach for assessment of absorbed amino acids from individual feed ingredients within complete diets

Accurate assessment of the nutritional content of feed ingredients is required for precise diet formulation. Characterizing ingredients in terms of absorption and digestibility of individual AA is challenging, and this information often relies on indirect methods. The purpose of this research was to evaluate an in vivo stable isotope–based method of determining plasma entry rates of individual AA from feather meal (FM), blood meal (BM), and a rumen-protected AA (RPMet). Abomasal infusions of unprotected Ile, Leu, Met, and sodium caseinate were used as control treatments to assess technique reliability and accuracy. Isotopic enrichment of plasma AA in response to a 2-h constant jugular infusion of a mixture of ¹³C labeled AA was measured and modeled using a dynamic 4-pool model, which was fitted to each AA by infusion to derive diet entry rates. The resulting entry rate matrix was used to derive plasma entry rates of individual AA from each ingredient by regression. The mean of plasma AA entry for abomasally infused Ile, Leu, and Met was 93.4 ± 7.35% of that infused, indicating that 6.6% was used by splanchnic tissues during first pass. The mean of the plasma essential AA entry for abomasally infused casein was 86.7 ± 4.81% of that present in the source protein, which represents a mean of 8.7% first-pass use assuming 95% digestibility. Individual AA appearances ranged from 86 to 93% of the source content except Ile, which was 73%. These fractional appearance percentages were similar to those previously reported when using a dietary regression approach. The mean plasma essential AA entry rate for FM was 52.7% of the AA in the source ingredient, with a range across AA of 48 to 58%. The mean plasma essential AA entry rate for BM was 47.5%, with a range of 30 to 61%. However, estimated Met availability from the RPMet was lower (9.9%) than expected (42%). This may be due to the relatively larger errors of measurement for Met entry rates and a small change in RPMet inclusion. Assuming that rumen-undegraded protein absorption is reflective of aggregated essential AA entry rates after correction for first-pass use, 52.6 and 61.2% of dietary FM and BM CP was absorbed from the intestine, respectively, which yielded an estimated intestinal digestibility of 70 and 66%, respectively. This method appears to provide an accurate and precise in vivo assessment of individual AA plasma entry rates that can be used to better characterize individual feed ingredients in ruminants. Such information will result in more robust economic assessments of feeds and increased precision of diet formulation.     

烟草中游离氨基酸的分析方法及研究方向

游离氨基酸是烟草中的重要化合物,对烟草香味物质的形成有着重要的作用。烟草游离氨基酸的分离和定量鉴定方法主要有：9－芴氯甲酸甲酯作为预柱衍生试剂的高压液相色谱法、氯甲酸乙酯作为衍生试剂的毛细管气相色谱法以及氨基酸自动分析仪法。其中,氨基酸自动分析仪更适合分离和鉴定烟草游离氨基酸。同时指出,对低焦油混合型卷烟－白肋烟进行氨基酸分析,以期找出最佳工艺,可以更有效地提高我国混合型卷烟的质量。