Effect of the metabolism of urea on the acidifying activity of Streptococcus thermophilus

One of the main functions of Streptococcus thermophilus strains used in the dairy industry is the production of lactic acid. In cheese and fermented milk manufacturing processes, the pH evolution kinetics must be reproducible in order to ensure the good quality of the final products. The objective of the present study was to investigate the effect of the metabolism of urea on the acidifying activity of fast- and slow-acidifying strains of S. thermophilus. Milk treatment with a purified urease and utilization of the urease inhibitor flurofamide revealed that urea metabolism by S. thermophilus influences the pH evolution kinetics through 2 distinct means. First, ammonia production from urea tends to increase the pH. This effect is greater when lactic acid concentration is low due to a lower buffering capacity of milk. Second, urea metabolism also modifies growth and lactic acid production by S. thermophilus. Depending on the strains and the growth stage of the cultures, consumption of urea induces either a faster or a slower pH decrease. For the slow-acidifying strain RD678, suppression of urea metabolism by adding flurofamide decreased the time necessary to reach pH 6 by 195 min. This effect was less pronounced for the 2 fast-acidifying strains RD674 and RD677. These results show that urea metabolism may have a considerable influence on the acidifying properties of S. thermophilus strains.     

In vitro studies on microbial incorporation of nitrogen from [15N2] urea and [15N]ammonium chloride by human intestinal flora

6 typical bacteria species of the human intestinal flora (E. coli, Klebsiella pneumoniae, Proteus vulgaris, Streptococcus faecalis, Bacteroides fragilis, Bifidobacterium sp.) were incubated in a liquid medium for 48 h with [15N2]-urea and [15N]-ammonium chloride. The rates of [15N]-incorporation were calculated. They depend reproducible on the species examined, on the kind of the offered NPN-substance and on the amount of NPN-substance in the medium. With [15N2]-urea the minimal rate of incorporation was 3.8% (E coli) and the maximal one 95.6% (Bifidobacterium sp.). With [15N]-ammonium chloride the corresponding figures were 31.0 (Proteus vulg.) and 98.0% (Bifidobacterium sp.). The findings are discussed with regard to a possible enteral detoxification in uremic patients by bacterial utilization and elimination of urea and ammonia.     

叶蛋白资源的开发与利用

着重综述了植物叶蛋白的定义、营养价值、生产工艺及其在食品工业上的应用,并指出植物叶蛋白具有开发利用前景。     

菜籽磷脂脱色的动力学研究

以过氧化氢为脱色剂,对菜籽磷脂进行脱色,获得了有关动力学参数。研究结果表明,过氧化氢浓度对脱色效果的反应级数为0.6199,色素浓度对脱色效果的反应级数为0.3329,脱色反应的活化能为52.88kJ/mol。     

15N tracer kinetics of the utilization of yeast nitrogen

The utilization of nitrogen from 15N-labeled Saccharomyces cerevisiae cells was studied in 6 infants by means of oral pulse labeling, comparing native and heat-treated yeast cells. The 15N dose used was 3 mg/kg. The body weight of the subjects varied between 5500 and 9400 g. The yeast cells were harvested from a culture medium which contained 15N ammonium chloride as the only source of nitrogen. The 15N-enrichment of the cells amounted to 95 atom-%. In the course of 48 h following the administration of the native yeast cells, 11% of the tracer dose were renally excreted. The corresponding value after labeling with heat-treated yeast cells was 17.9%. The cumulative renal excretion of the tracer tended to be faster as compared with pulse labeling of the native yeast cells. A paired comparison with labeled native and heated yeast cells in 3 subjects did not reveal any differences in the retention rate of 15N. When untreated 15N yeast cells were administered, 13.2% of the tracer dose were excreted in the urine and 10% respectively in the faeces. The retention was 76.8%. After single pulse labeling with 3 mg 15N/kg from heat-treated yeast cells the corresponding values were 19.4%, 4.4% and 76.2%, respectively. The kinetic of the renal 15N excretion points at the partial absorption of the yeast nitrogen from the colon.     

Field estimation of ammonia volatilisation from 15N-labelled urea fertiliser

Granules of ¹⁵N-labelled urea (150 kg N ha^?1), with or without the urease inhibitor hydroquinone, were broadcast on to small plots of winter oilseed rape in March. Ammonia volatilisation losses were estimated by a ¹⁵N balance procedure in which the amount of ¹⁵N in the plants, plus that in the soil to 70 cm depth, was determined 18 days after urea application. All the urea-N was recovered in soil and plants from plots given either urea alone or urea plus hydroquinone; hence there was no volatilisation of ammonia. Although the soil pH was high enough (7.7 to 8.0) for ammonia loss, this did not occur because the soil was too cold, too wet and had a high cation exchange capacity.     

Interaction between dietary content of protein and sodium chloride on milk urea concentration,urinary urea excretion,renal recycling of urea,and urea transfer to the gastrointestinal tract in dairy cows

Dietary protein and salt affect the concentration of milk urea nitrogen (MUN; mg of N/dL) and the relationship between MUN and excretion of urea nitrogen in urine (UUN; g of N/d) of dairy cattle. The aim of the present study was to examine the effects of dietary protein and sodium chloride (NaCl) intake separately, and their interaction, on MUN and UUN, on the relationship between UUN and MUN, on renal recycling of urea, and on urea transfer to the gastrointestinal tract. Twelve second-parity cows (body weight of 645 ± 37 kg, 146 ± 29 d in milk, and a milk production of 34.0 ± 3.28 kg/d), of which 8 were previously fitted with a rumen cannula, were fitted with catheters in the urine bladder and jugular vein. The experiment had a split-plot arrangement with dietary crude protein (CP) content as the main plot factor [116 and 154 g of CP/kg of dry matter (DM)] and dietary NaCl content as the subplot factor (3.1 and 13.5 g of Na/kg of DM). Cows were fed at 95% of the average ad libitum feed intake of cows receiving the low protein diets. Average MUN and UUN were, respectively, 3.90 mg of N/dL and 45 g of N/d higher for the high protein diets compared with the low protein diets. Compared with the low NaCl diets, MUN was, on average, 1.74 mg of N/dL lower for the high NaCl diets, whereas UUN was unaffected. We found no interaction between dietary content of protein and NaCl on performance characteristics or on MUN, UUN, urine production, and renal clearance characteristics. The creatinine clearance rate was not affected by dietary content of protein and NaCl. Urea transfer to the gastrointestinal tract, expressed as a fraction of plasma urea entry rate, was negatively related to dietary protein, whereas it was not affected by dietary NaCl content. We found no interaction between dietary protein and NaCl content on plasma urea entry rate and gastrointestinal urea entry rate or their ratio. The relationship between MUN and UUN was significantly affected by the class variable dietary NaCl content: UUN = −17.7 ± 7.24 + 10.09 ± 1.016 × MUN + 2.26 ± 0.729 × MUN (for high NaCl); R² = 0.85. Removal of the MUN × NaCl interaction term lowered the coefficient of determination from 0.85 to 0.77. In conclusion, dietary protein content is positively related to MUN and UUN, whereas dietary NaCl content is negatively correlated to MUN but NaCl content is not related to UUN. We found no interaction between dietary protein and NaCl content on performance, MUN, UUN, or renal urea recycling, nor on plasma urea entry rate and urea transfer to the gastrointestinal tract. For a proper interpretation of the relationship between MUN and UUN, the effect of dietary NaCl should be taken into account, but we found no evidence that the effect of dietary NaCl on MUN is dependent on dietary protein content.     

Effects of a polymer-coated urea product on nitrogen metabolism in lactating Holstein dairy cattle

The purpose of this study was to evaluate the impact of polymer-coated urea on nitrogen retention, rumen microbial growth, and milk production and composition. Coated urea (CU) that is more slowly hydrolyzed to ammonia than unprotected urea could potentially be used more efficiently by rumen microorganisms. Eight cows were offered each of three diets in a randomized crossover design. Each treatment period consisted of a 14-d adjustment period and a 5-d collection period. Diets were formulated to maintain milk production while reducing plasma urea nitrogen concentrations and urinary nitrogen excretion. Diets consisted of corn silage, mixed grass/legume haylage, chopped alfalfa hay, corn meal, protein, vitamin and mineral supplements, in a total mixed ration and fed ad libitum. The diets contained 17.9%, 18.1%, and 16.4% CP and 0, 0.77%, and 0.77% CU (dry matter basis) and are denoted as CP18-CU, CP18+CU, and CP16+CU, respectively. Individual feed intakes were measured, and total fecal, and urine collections were conducted. Cows were milked twice daily at 0500 and 1700 h, and the milk sampled for composition and milk urea N analysis. Dry matter intake averaged 23.5 +/- 0.2 kg/d and was not altered by diet. Also, milk fat and true protein were not altered by diet and averaged 3.72 and 3.07%, respectively. Milk yield was highest for diets CP18-CU and CP18+CU. Significant differences were observed in N intake and excretion in urine, feces, and milk between dietary treatments. Cows fed CP16+CU consumed 11% less N than in CP18-CU. Cows fed CP18+CU showed the highest excretion of N in urine, and together with CP16+CU, the lowest N excretion in feces. Nitrogen excretion in milk was lower for cows fed CP16+CU. Calculated N balance was not significantly different between diets nor was it significantly different from zero. Efficiency of N capture in milk protein as a function of N intake was higher for animals on CP16+CU. Urinary excretion of purine derivatives was not different between diets, and estimated microbial CP was also similar. Coated urea was not effective at reducing nitrogen excretion by dairy cattle.     

The effect of gestation and of protein quality on the nutritive utilization of protein

A study was made of the effect of protein quality on gestation and on digestive and metabolic utilization in Wistar rats. The protein level of the diet was 14%, and the protein sources used were: casein, beans and a mix of beans and wheat, in order to complement the essential amino-acids deficient in both protein sources. Gestation increased food intake in the 3 groups of experiments, in which distinct protein sources were used. Protein quality did not affect food intake in the two physiological situations under study (gestation and non-gestation). In pregnant animals, the greatest weight gains were obtained with the casein diet, while in non-pregnant ones the weight increases were greater with the diet of beans and wheat. The smallest gains recorded were those of pregnant and non-pregnant rats fed a diet of beans. Gestation did not affect protein-absorption. The digestive utilization of protein was superior with the casein diet. The study of nitrogen retention showed: 1. The pregnant animals retained more nitrogen than the non-pregnant animals with all of the diets under study. 2. In pregnant animals, the greatest metabolic utilization took place with the casein diet, with little difference between the bean and bean-wheat mix diets, although in the latter it was slightly superior.     

海洋鱼蛋白可控酶解动力学模型的研究

应用数学推导结合实验研究的方法，以沙丁鱼蛋白为底物．研究胰蛋白酶可控酶解过程的动力学模型及其相关参数，结果如下：DH=9.804ln[1 (1．701E0／S0-0．00367)]和R=(16．678E0-0．036S0)exp[-0．102(DH)]，动力学常数k2=16．678／min和Kd=1.7015／min，最低临界初始蛋白酶浓度E0=c0S0，最大临界底物初始浓度S0=E0／c0，c0=2.159x10^-3。与实验结果相比较，证实动力学模型与实验结果非常吻合，说明它具有很好的实际应用价值。     

油料蛋白质的综合利用

一、不同油料蛋白质营养互补性强 油料蛋白的种类很丰富,具体有：大豆蛋白、棉籽蛋白、芝麻蛋白、花生蛋白、菜籽蛋白、葵花籽蛋白及无毒棉蛋白等。据研究,油料中蛋白质特性有４点：一是蛋白质中必需氨基酸丰富,结构配比接近人体需要。二是油料蛋白质对人体的生理功能作用既能克服禾谷类粮食蛋白质生物价低的缺点,又可从根本上解决过量食用动物蛋白质对人体负效应大的“富贵病”问题。三是利用油料蛋白质经济意义很大,既可充分节约现有蛋白质资源,又与生产动物蛋白质比,有投入小产出大的特点。四是油料蛋白质是人类普遍适用的蛋白质…     

Effects of increasing dietary protein on nutrient utilization in heifers

Four prepubertal Holstein heifers, average age 146.0 +/- 3.6 d and 152.8 +/- 8.6 kg of body weight (BW), fitted with rumen cannulae were used to evaluate increasing levels of dietary protein with a constant metabolizable energy intake on rumen ammonia N concentrations, N balance, total tract apparent digestibility, and urinary excretion of purine derivatives in a 4 x 4 Latin square design with 20 d periods. Heifers were fed dietary crude protein levels (CP) of 11.9, 16.7, 18.1, and 20.1% CP with similar amounts of metabolizable energy (ME) (2.6 Mcal per kg of dry matter) at 2.0% BW as dry matter intake. Resulting protein to ME ratios (CP:ME) were 45.0, 63.3, 69.4, and 77.3 g of dietary CP per Mcal of ME. Rumen ammonia N and plasma urea nitrogen increased as CP level increased. Rumen pH, volatile fatty acids, and the acetate-to-propionate ratio were not affected with increasing CP levels. Greater urinary N excretion resulted in an increase in total N excretion with increasing CP levels. Apparent dry matter digestibility was similar for all diets, while apparent total tract N digestibility was lowest for the 11.9% CP level. Microbial N calculated from urinary excretion of purine derivatives increased with increasing CP levels. Holstein heifers between 153 and 196 kg consuming a diet at 2.0% BW as dry matter intake containing a CP level of 16.7% achieved a better synergistic relationship of dietary protein to energy (CP:ME of 63.3 g of CP per Mcal of ME) than the diets lower or higher in CP that were studied.     

尿素改性制备芝麻蛋白胶黏剂的研究

以芝麻蛋白为原料,用尿素改性制备芝麻蛋白胶黏剂。以尿素浓度、料液比、反应时间、反应温度进行单因素试验,研究其对芝麻蛋白胶黏剂表观黏度、胶合强度的影响。通过正交试验进行优化,得出最佳制备工艺条件为:尿素浓度3 mol/L,料液比1∶8,反应时间4 h,反应温度25℃。在最佳条件下,芝麻蛋白胶黏剂的湿胶合强度为0.78 MPa,满足国家标准Ⅱ类(≥0.70 MPa)胶合板的要求。     

蚕蛹蛋白过敏与综合利用的研究进展

蚕蛹蛋白是一种营养价值很高的天然动物蛋白,富含有18种氨基酸,其中八种人体必需氨基酸含量超过总氨基酸的40%,且比例均衡,具有非常高的利用价值,近年来被广泛利用于多个行业中。本文介绍了蚕蛹蛋白的种类和含量,进一步汇总了过敏原的相关信息,在此基础上总结了蚕蛹蛋白在食品、饲料、医药、纺织、生物等行业中的开发利用。      

Influence of synchronizing protein and starch degradation in the rumen on nutrient utilization and microbial protein synthesis

A 4 x 4 Latin square design with four multiparous cows in midlactation fitted with duodenal cannulae was used to determine the effect of synchronization of protein and starch degradation in the rumen on nutrient availability in lactating cows. As major starch and protein sources, diets contained: barley plus cottonseed meal; barley plus brewers dried grains; milo plus cottonseed meal; and milo plus brewers dried grains. Experimental periods were 12 d and consisted of 8 d adjustment and 4 d collection. Chromium oxide was used as the marker to determine digestibility and nutrient flow from the rumen. Microbial protein synthesis was estimated from nucleic acid content in duodenal samples. Apparent and corrected rumen digestibilities of DM, organic matter, CP, and starch were higher for diets containing barley than milo but were not affected by protein source. For diets containing barley and milo, starch digested postruminally averaged 820 and 2190 g/d and percentage digestibility was 70 and 77%. No difference among diets was found in DM, organic matter, and CP flow to the small intestine; however, microbial N synthesis was higher in diets containing barley than in diets containing milo.