Novel optimal temperature profile for acidification process of <Emphasis Type="Italic">Lactobacillus bulgaricus</Emphasis> and <Emphasis Type="Italic">Streptococcus thermophilus</Emphasis> in yoghurt fermentation using artificial neural network and genetic algorithm

The acidification behavior of Lactobacillus bulgaricus and Streptococcus thermophilus for yoghurt production was investigated along temperature profiles within the optimal window of 38–44 °C. For the optimal acidification temperature profile search, an optimization engine module built on a modular artificial neural network (ANN) and genetic algorithm (GA) was used. Fourteen batches of yoghurt fermentations were evaluated using different temperature profiles in order to train and validate the ANN sub-module. The ANN captured the nonlinear relationship between temperature profiles and acidification patterns on training data after 150 epochs. This served as an evaluation function for the GA. The acidification slope of the temperature profile was the performance index. The GA sub-module iteratively evolved better temperature profiles across generations using GA operations. The stopping criterion was met after 11 generations. The optimal profile showed an acidification slope of 0.06117 compared to an initial value of 0.0127 and at a set point sequence of 43, 38, 44, 43, and 39 °C. Laboratory evaluation of three replicates of the GA suggested optimum profile of 43, 38, 44, 43, and 39 °C gave an average slope of 0.04132. The optimization engine used (to be published elsewhere) could effectively search for optimal profiles of different physico-chemical parameters of fermentation processes.     

Effects of yoghurt intake on plasmid transfer and colonisation with transconjugants in the digestive tract of mice associated with human faecal flora

This study deals with the effects of yoghurt intake on wild-type and recombinant plasmid transfer from an exogenous Escherichia coli K12-derivative donor strain to an endogenous recipient strain in the digestive tract of mice associated with human faecal flora. We showed that the self-transmissible plasmid R388 was efficiently transferred to recipient strain PG1 in mice associated with human faecal flora (HFF-PG1) and that the resulting transconjugants (PG1-R388) became established at a high and maximal population level without any selective pressure. Using HFF-PG1 mice made it possible to determine whether yoghurt consumption decreases R388 transfer efficiency and the ability of transconjugant PG1-R388 to successfully colonise the digestive tract. Results indicated that yoghurt consumption had two effects: it reduced the efficacy of plasmid transfer 10-fold and decreased the transconjugant PG1-R388 population density 100-fold, compared to the control group. We also describe another HFF mouse model in which recipient PG1 was replaced by EM0 with which no plasmid transfer was observed. This model made it possible to demonstrate the potential promoting effect of yoghurt intake on transconjugant formation and establishment. Our results indicated no yoghurt effect; no transconjugants appeared in the digestive tract of HFF-EM0 mice fed on yoghurt or on standard food. In both mouse models, HFF-PG1 and HFF-EM0, yoghurt intake did not promote the mobilisation of either the non-self-transmissible plasmid pUB2380 or the recombinant plasmid pCE325.     

Nutritional aspects of fermented milk products

Abstract Fermented milk products are a palatable and economical source of a wide range of nutrients. The nutrient composition is similar to that in milk, but concentrations of vitamins are in general a little lower, with the possible exception of folic acid. Concentrations of lactic acid, galactose, free amino acids and fatty acids are increased as a result of the fermentation. Lactose-intolerant individuals tolerate lactose when it is consumed in yoghurt better than when it is taken in the equivalent quantity of milk. The mechanism of this effect has not been clearly established. By far the greatest proportion of published material freely available in the West concerns yoghurt; reference is made to other cultured products where results are available to indicate interesting differences.     

微量量热法研究酸奶菌种的适宜生长温度及最佳生长温度

测定酸奶菌种保加利亚孔杆菌、嗜热链球菌及二者混合菌在乳中生长的热谱图曲线,确定了各菌种及混合菌的适宜生长温度范围,计算出了各菌种在不同温度下的生长速率常数。用计算机拟合k-T方程,求出各菌种的最佳生长温度。     

环境因素对酸奶菌株自溶的影响

本论文探究了培养条件对德氏乳杆菌保加利亚亚种KLDS 1.9201和唾液链球菌嗜热亚种KLDS 3.021自溶的影响.结果表明,随着培养温度(30℃～55℃)、盐浓度(0%～5%)以及酸度值(pH5.0～7.5)的升高,KLDS 1.9201和KLDS 3.0201不仅自溶度相应增大,而且在磷酸缓冲液中释放的核酸和蛋白含量也呈递增趋势.高温55℃,pH 7.5和5%乳酸盐浓度的培养环境使KLDS 1.9201和KLDS 3.0201在培养45 h后的自溶度分别达到了55%和36.3%,显著高于低自溶培养环境下(30℃、pH 5.5和0%乳酸盐)KLDS 1.9201和KLDS 3.0201的自溶度9.96%和8.6%(P<0.05).透射电镜观察表明高自溶和低自溶培养条件对酸奶菌株菌体形态的影响是截然不同的,且酸奶菌株自溶时发生的细胞壁降解程度与自溶光密度值相对应.     

酸奶中乳酸菌含量的检测

目的检测酸奶发酵前后以及贮藏期间的乳酸菌活菌数及酸度变化,以对酸奶的质量进行控制.方法应用高层半固体琼脂试管法. 结果酸奶中乳酸菌含量极高,达2.65×1010个/ml以上,并随贮藏时间的延长而发生变化. 糖对酸奶的含菌量无明显影响.双菌酸奶比单菌酸奶含菌量高,常可达到倍增,pH值随发酵和贮藏进程而下降.结论高层半固体琼脂试管法操作简便、快速、准确、活菌检出率高.     

酸奶发酵剂和乳酸菌生物技术育种

由新鲜牛奶制成的酸奶由于其丰富的营养、特殊的风味、爽滑的质构和良好的生理功能 ,倍受人们青睐。对酸奶乳酸菌的微生物种类、功能及其组成的酸奶发酵剂进行了综述 ,并简要介绍了乳酸菌生物工程育种方面的研究进展及酸奶乳酸菌研究领域一些令人感兴趣的课题。     

酸奶中保加利亚乳杆菌的抗药性实验研究

测定了10种常用抗菌药物对市售酸奶中分离的57株保加利亚乳杆菌的MIC,结果显示泰能、克林霉素、林可霉素、头孢唑啉和红霉素对乳杆菌的抗菌活性最强,MIC90值为0.25～2.0mg/L,敏感率为96.5%～86.0%。其次是阿莫西林、复方新诺明、青霉素,其MIC90值为2.0～4.0mg/L,敏感率为84.3%～78.9%。庆大霉素、氯霉素其MIC90值为4.0～16.0mg/L,敏感率为63.2%～59.7%。可见,酸奶中的保加利亚乳杆菌存在抗药性,其抗药性基因是否具转移性有待于进一步研究。