The effects of defaunation on the metabolism of lactic acid in the rumen

Two experiments examined the effects of defaunation on the ruminal metabolism of lactate. Three rumen-cannulated sheep given a diet of molassed sugar beet pulp and barley (80:20) were used to study the effects of defaunation (with manoxol-OT) on the metabolism of lactic acid produced endogenously from rumen fermentation. Defaunation increased mean ruminal concentrations of lactate from 3.4 mmol litre^?1 to 8.9 mmol litre^?1 but other rumen measurements remained virtually unchanged: pH, 6.3 and 6.3; molar proportions of acetic acid, 645 and 645 mmol mol^?1; propionic acid, 189 and 197 mmol mol^?1 and butyric acid 142 and 115 mmol mol^?1 for the faunated and defaunated states respectively. In a second experiment, two groups each of four rumen-cannulated sheep were used to study the effect of defaunation on the ruminal metabolism of added Na-D, L lactate. One group of four was defaunated using a rumen-washing technique whilst the other group of four remained faunated. The animals were given a diet of rolled barley and hay (60:40) and were given a series of intraruminal doses of Na-D, L lactate from 0 to 100 g day^?1, increasing by 20 g day^?1 every third day. Disappearance of added lactate was much more rapid in faunated animals: at the 100 g day^?1 dose rate, L-lactate concentrations had fallen from a peak of 6 g litre^?1 to >1 g litre^?1 after 3 h whereas in defaunated sheep the peak of 6.5 g litre^?1 was reduced to >1 g litre^?1 only after 7 h. In faunated animals lactate addition caused an increase in the ruminal concentration of total volatile fatty acids (VFA) from 147 to 217 mmol litre^?1 between the zero and 100 g day^?1 dose rates, accompanied by an increase in the molar proportion of propionic acid from 190 to 320 mmol mol^?1. However, in defaunated animals there was only a small increase in total VFA concentrations from 94 to 106 mmol ml^?1 with no change in the molar proportion of propionic acid and a small increase in butryric acid from 140 to 180 mmol mol^?1.     

The passage of lactic acid bacteria from silage into rumen fluid, in vitro studies

Inoculated silages sometimes improve cattle performance, possibly because of probiotic effects of lactic acid bacteria (LAB) silage inoculants. The cause of improved animal performance following feeding with inoculated silage is unclear. One issue in studying this phenomenon is to find out whether LAB pass from silage into the rumen fluid and survive in it. The purpose of the present study was to determine whether LAB from inoculated and uninoculated silages pass into the rumen fluid in vitro. Wheat and corn silages, uninoculated or inoculated with 1 of 10 commercial silage inoculant LAB, were prepared in glass jars. After ensiling, a 2.5-g silage sample was added to 25 mL of heat-sterilized or strained rumen fluid together with 5 g/L glucose, and incubated for 48 h at 39 degrees C. Analysis of the incubated rumen fluid included pH measurement, enumeration of LAB, and determination of lactic acid and volatile fatty acids (VFA). The pH of the rumen fluid decreased during incubation; both heat-sterilized and strained rumen fluid contained large numbers of LAB. The heat-sterilized rumen fluid contained lactic acid in addition to VFA, whereas the strained rumen fluid contained only VFA. The results indicate that LAB pass from silage samples into the rumen fluid in vitro and survive there. Their interactions with rumen microorganisms should be studied further to understand how some silage inoculant LAB exhibit probiotic effects in dairy cattle.     

Feeding barley grain steeped in lactic acid modulates rumen fermentation patterns and increases milk fat content in dairy cows

The objectives of the present in vivo and in situ trials were to evaluate whether feeding barley grain steeped in lactic acid (LA) would affect rumen fermentation patterns, in situ dry matter (DM) degradation kinetics, and milk production and composition in lactating dairy cows. The in vivo trial involved 8 rumen-fistulated Holstein cows fed once daily a total mixed ration containing rolled barley grain (27% in DM) steeped for 48 h in an equal quantity of tap water (CTR) or in 0.5% LA (TRT) in a 2 × 2 crossover design. The in situ trials consisted of incubation of untreated rolled barley grain in cows fed CTR or TRT diets and of incubation of 3 different substrates including CTR or barley grain steeped in 0.5% or 1.0% LA (TRT1 and TRT2, respectively) up to 72 h in the rumen. Results of the in vivo trial indicated that cows fed the TRT diet had greater rumen pH during most intensive fermentation phases at 10 and 12 h post-feeding. The latter effect was associated with a shorter duration in which rumen pH was below 5.8 for cows fed the TRT diet (2.4 h) compared with CTR diet (3.9 h). Furthermore, cows fed the TRT diet had lower concentrations of volatile fatty acids at 2 and 4 h post-feeding. In addition, concentrations of preprandial volatile fatty acids were lower in the rumen fluid of cows fed the TRT diet. Results also showed that molar proportion of acetate was lower, whereas propionate tended to increase by feeding cows the TRT diet. Cows fed the TRT diet demonstrated greater rumen in situ lag time of substrate DM degradation and a tendency to lower the fractional degradation rate. Other in situ results indicated a quadratic effect of LA on the effective rumen degradability of substrates whereby the latter variable was decreased from CTR to TRT1 but increased for TRT2 substrate. Although the diet did not affect actual milk yield, fat-corrected milk, percentages of milk protein, and lactose and concentration of milk urea nitrogen, cows fed the TRT diet increased milk fat content and tended to increase fat:protein ratio in the milk. In conclusion, results demonstrated that treatment of barley grain with LA lowered the risk of subacute rumen acidosis and maintained high milk fat content in late-lactating Holstein cows fed diets based on barley grain.     

海南黑山羊瘤胃液中乳酸菌的分离和鉴定

以海南黑山羊瘤胃液为研究对象,对其进行乳酸菌的分离和鉴定,为黑山羊饲料的青贮提供优质的乳酸菌菌株。通过形态学观察及H2O2酶、糖发酵等生理生化试验对所分得菌株进行初步鉴定,并对分离得到的菌株进行16S rDNA基因扩增与测序。结果表明从黑山羊胃液中筛选出15株革兰氏阳性、H2O2酶阴性的乳酸菌疑似菌株,除菌株HBG20不能在pH 3.0条件下生长,其余菌株均能生长;三株代表菌株HBG11、HBG46和HBG86在低温5 ℃和高温55 ℃条件以及pH2.5时均能生长,同时在盐浓度为6.5%时也能生长。16S rDNA基因测序结果表明,菌株HBG11与耐久肠球菌（Enterococcus durans）同源性最高,菌株HBG46与植物乳杆菌（Lactobacillus plantarum）同源性最高,菌株HBG86与干酪乳杆菌（Lactobacillus casei）同源性最高。     

The in-vitro metabolism of D,L-lactic acid by rumen microorganisms

Bacterial and protozoal fractions, isolated by centrifugation and filtration from the rumen of sheep given various diets, were used to examine the in-vitro metabolism of both the D(-) and L(+) isomers of lactic acid. The rate of disappearance of both the D- and L-lactic acid isomers in protozoal incubations was up to 15 × higher than the rate of disappearance in bacterial incubations, which was relatively constant at between 0.04 and 0.073 lactate per g protein per h for cells recovered from animals receiving various diets. However, the rate of lactate disappearance in the protozoal fraction varied from 0.133 g per g protein per h with a barley/hay diet to 1.12 g per g protein per h with a silage diet. L-Lactate disappeared more rapidly than the D-lactate in all protozoal incubations. It was confirmed that the disappearance of lactate associated with the protozoal fraction did not originate from adherent or associated bacteria. Further fractionation of the protozoal population by differential filtration showed that lactate only disappeared when incubated with entodiniomorphid protozoa and not with holotrich protozoa. Endogenous propionate and butyrate production by the entodiniomorphid ciliates was stimulated by 100% in the presence of lactate. It was calculated that on certain diets up to 30% of the volatile fatty acids formed from lactate could be protozoal in origin.     

乳酸大蒜的腌制

用食品生物技术思想设计了一个规模生产乳玻大蒜腌制的方法，并在重要环节做了试验，获得优质新型乳酸糖蒜。     

A model to assess lactic acid bacteria aminopeptidase activities in Parmigiano Reggiano cheese during ripening

The aim of this work was to investigate in which phases of ripening of Parmigiano Reggiano cheese lactic acid bacteria aminopeptidases present in cheese extract could be involved in release of free amino acids and to better understand the behavior of these enzymes in physical-chemical conditions that are far from their optimum. In particular, we evaluated 6 different substrates to reproduce broad-specificity aminopeptidase N, broad-specificity aminopeptidase C, glutamyl aminopeptidase A, peptidase with high specificity for leucine and alanine, proline iminopeptidase, and X-prolyl dipeptidyl aminopeptidase activities releasing different N-terminal amino acids. The effects of pH, NaCl concentration, and temperature on the enzyme activities of amino acid β-naphthylamide (βNA)-substrates were determined by modulating the variables in 19 different runs of an experimental design, which allowed the building of mathematical models able to assess the effect on aminopeptidases activities over a range of values, obtained with bibliographic data, covering different environmental conditions in different zones of the cheese wheel at different aging times. The aminopeptidases tested in this work were present in cell-free Parmigiano Reggiano cheese extract after a 17-mo ripening and were active when tested in model system. The modeling approach shows that to highlight the individual and interactive effects of chemical-physical variables on enzyme activities, it is helpful to determine the true potential of an amino-peptidase in cheese. Our results evidenced that the 6 different lactic acid bacteria peptidases participate in cheese proteolysis and are induced or inhibited by the cheese production parameters that, in turn, depend on the cheese dimension. Generally, temperature and pH exerted the more relevant effects on the enzymatic activities, and in many cases, a relevant interactive effect of these variables was observed. Increasing salt concentration slowed down broad-specificity amino-peptidase C, glutamyl aminopeptidase A, proline iminopeptidase, and peptidase with high specificity for leucine and alanine. Interestingly, this variable did not affect broad-specificity aminopeptidase N and positively affected X-prolyl dipeptidyl aminopeptidase. The models elaborated varying pH, temperatures, and salt concentration and were a useful, low cost, and fast tool to understand the role of the main peptidases in the different phases of cheese ripening in relation to the major environmental factors influencing enzyme activity.     

卤制鸭脖中乳酸菌生长预测模型初步研究

以卤制鸭脖为试验材料,研究不同贮藏温度下鸭脖中乳酸菌的生长状况,构建乳酸菌生长预测模型.结果表明,Gompertz模型能较好地描述卤制鸭脖中乳酸菌在不同温度下的生长.温度与最大比生长速率和延滞时间的关系,用平方根模型描述呈现良好线性关系,统计分析结果表明二级模型非常显著.建立的生长预测一级和二级模型可有效地描述5℃～25℃温度范围内卤制鸭脖中乳酸菌的生长,为卤制鸭脖的品质评价提供理论支撑.     

金属离子对啤酒酵母发酵中生成乳酸的影响

通过对不同啤酒酵母发酵中Na+、K+、Ca2+、Mg2+浓度梯度添加实验,采用高效液相相色谱法对乳酸生成的影响进行了分析。实验结果表明:与空白发酵液相比,在不同菌种作用下随着添加金属离子浓度梯度,乳酸生成表现出较明显的变化趋势性,分析结果对于啤酒生产具有一定的指导意义。     

卤制鸭头中乳酸菌生长预测模型的建立与验证

为快速预测和监控卤制鸭头中微生物的生长,建立和验证卤制鸭头基质上5～25℃温度条件下乳酸菌的生长预测模型。结果表明:利用Gompertz模型建立不同温度下卤制鸭头中乳酸菌的一级模型,得到的乳酸菌一级生长预测模型的偏差因子和准确因子都在1左右;利用平方根模型描述温度与最大比生长速率和延滞期的关系,得到乳酸菌生长预测的二级模型,R2分别为0.9923和0.9031,模型的总体显著,初步说明生长预测模型能有效地预测5～25℃下卤制鸭头中乳酸菌的生长。      

向日葵籽乳酸饮料的研制

以向日葵为籽原料，磨浆后经乳酸发酵制取乳酸饮料，并通过对其制造过程的研究以及感观和风味的探讨，最终确定了向日葵籽乳酸饮料的最佳工艺和配方。     

高效液相色谱法检测贝类中的乳酸和琥珀酸

研究探讨利用高效液相色谱测定贝类中乳酸和琥珀酸的样品处理方法和测定方法,结果显示:与乙醇沉淀法、国标法相比,流动相提取法更适合作为样品的提取方法,在检测条件中,流动相为pH2.5的2.0%NH4H2PO4,流速在1.0mL/min,波长为205nm为最优条件。此方法具有较好的线性、较高的准确度和精密度,加标实验回收率为94.0%～99.9%,相对标准偏差为0.09%～0.14%。也测定了两种贝类中乳酸和琥珀酸的含量。     

Carbohydrate, peptide and lipid metabolism of lactic acid bacteria in sourdough

The metabolic pathways of lactic acid bacteria that influence bread quality are coupled to the central carbon flux by the availability of cofactors influencing the cellular and environmental redox potential. Homo- and heterofermentative metabolism differ fundamentally with respect to the requirement for regeneration of reduced cofactors, NADH or NADPH. The utilization of co-substrates such as oxygen or fructose as electron acceptors by obligate heterofermentative lactobacilli is coupled to an increased production of acetate in dough. Recently, several oxidoreductases involved in cofactor regeneration were characterized and glutathione and short-chain aldehydes derived from lipid oxidation were identified as substrates for cofactor regeneration by Lactobacillus sanfranciscensis. Based on the different metabolic requirements for cofactor regeneration, homo- and heterofermentative lactobacilli exert divergent effects on redox-reactions in sourdough that influence bread quality beyond the formation of acetate. Proteolysis, followed by peptide or amino acid metabolism by LAB is one of the key routes of flavour formation in bread flavour, and enables the strain-specific formation of antifungal metabolites. Peptide metabolism as well as the metabolism of cysteine, arginine, and phenylalanine in Lactobacillus plantarum, L. sanfranciscensis, and Lactobacillus pontis is increasingly understood and these insights provide new opportunities for the directed application of sourdough LAB for improved bread quality.     

A mechanistic model of small intestinal starch digestion and glucose uptake in the cow

The high contribution of postruminal starch digestion (up to 50%) to total-tract starch digestion on energy-dense, starch-rich diets demands that limitations to small intestinal starch digestion be identified. A mechanistic model of the small intestine was described and evaluated with regard to its ability to simulate observations from abomasal carbohydrate infusions in the dairy cow. The 7 state variables represent starch, oligosaccharide, glucose, and pancreatic amylase in the intestinal lumen, oligosaccharide and glucose in the unstirred water layer at the intestinal wall, and intracellular glucose of the enterocyte. Enzymatic hydrolysis of starch was modeled as a 2-stage process involving the activity of pancreatic amylase in the lumen and of oligosaccharidase at the brush border of the enterocyte confined within the unstirred water layer. The Na⁺-dependent glucose transport into the enterocyte was represented along with a facilitative glucose transporter 2 transport system on the basolateral membrane. The small intestine is subdivided into 3 main sections, representing the duodenum, jejunum, and ileum for parameterization. Further subsections are defined between which continual digesta flow is represented. The model predicted nonstructural carbohydrate disappearance in the small intestine for cattle unadapted to duodenal infusion with a coefficient of determination of 0.92 and a root mean square prediction error of 25.4%. Simulation of glucose disappearance for mature Holstein heifers adapted to various levels of duodenal glucose infusion yielded a coefficient of determination of 0.81 and a root mean square prediction error of 38.6%. Analysis of model behavior identified limitations to the efficiency of small intestinal starch digestion with high levels of duodenal starch flow. Limitations to individual processes, particularly starch digestion in the proximal section of the intestine, can create asynchrony between starch hydrolysis and glucose uptake capacity.     

自制蛋白胨在乳酸菌培养中的应用

为了提高乳酸菌培养过程中的活菌总数,利用自制蛋白胨取代对照培养基中的氮源对乳酸菌进行培养。采用微生物菌液浊度测定法和微生物活菌计数法对培养结果进行测定。结果表明,用自制蛋白胨作为氮源取代对照培养基中的部分氮源培养植物乳杆菌、干酪乳杆菌、嗜热链球菌、双歧杆菌时的菌液浊度和活菌总数均高于对照培养基,但在培养保加利亚乳杆菌时的培养效果不如对照培养基。自制蛋白胨作为氮源培养大部分乳酸菌时的培养结果要优于对照培养基,自制蛋白胨可以取代对照培养基中的部分氮源制作新的培养基,并降低培养基的制作成本。      

瘤胃内共轭亚油酸(CLA)的形成

对瘤胃内共轭亚油酸（CLA）的形成机制、参与氢化的微生物及影响氢化的因素进行了综述，并对如何提高牛乳中CLA含量进行简要概述。     

基因工程改良乳酸菌发酵剂品质的研究进展

综述了近5年来利用基因工程技术改良乳酸菌发酵剂蛋白质水解能力、产生双乙酰能力、合成胞外多糖能力、抗杂菌病源菌污染能力4个方面研究的最新进展，并简要介绍了基因食品可能存在的不安全问题及解决方法。