Short communication: Comparison of growth kinetics at different temperatures of Streptococcus macedonicus and Streptococcus thermophilus strains of dairy origin

Within the genus Streptococcus, S. thermophilus and S. macedonicus are the 2 known species related to foods. Streptococci are widely used as starter cultures to rapidly lower milk pH. As S. macedonicus has been introduced quite recently, much less information is available on its technological potential. Because temperature is an important factor in fermented food production, we compared the growth kinetics over 24 h of 8 S. thermophilus and 7 S. macedonicus strains isolated from various dairy environments in Italy, at 4 temperatures, 30°C, 34°C, 37°C and 42°C. We used the Gompertz model to estimate the 3 main growth parameters; namely, lag phase duration (λ), maximum growth rate (µ_max), and maximum cell number at the stationary phase (N_max). Our results showed significant differences in average growth kinetics between the 2 species. Among the strains tested, 37°C appeared to be the optimal temperature for the growth of both species, particularly for S. macedonicus strains, which showed mean shorter lag phases and higher cell numbers compared with S. thermophilus. Overall, the growth curves of S. macedonicus strains were more similar to each other whereas S. thermophilus strains grew very differently. These results help to better define and compare technological characteristics of the 2 species, in view of the potential use of S. macedonicus in place of S. thermophilus in selected technological applications.     

应用于羊肉脱膻的三种发酵剂筛选及发酵特性研究

为筛选出适合发酵羊肉制品的优质发酵剂，对肉葡萄球菌（Staphylococcus carnosus）、植物乳杆菌（Lactobacillus plantarum）和戊糖片球菌（Pedicoccuspentosaceus）的发酵特性进行研究，通过耐盐、耐亚硝酸盐、产酸能力、蛋白质和脂肪分解能力、膻味脂肪酸降解能力、抑菌能力、菌种间拮抗作用等试验对其筛选。结果表明，三株菌对食盐和亚硝酸盐具有较好的耐受性，能在6%的食盐溶液和150 mg/L亚硝酸盐溶液中存活，具有一定产酸能力，除植物乳杆菌无脂肪酶活性，其他两株菌具有蛋白质和脂肪降解能力，膻味脂肪酸降解率可达60%～80%，能抑制病原微生物的生长，且三株菌间无拮抗作用，对羊肉制品的风味和品质无负面影响。因此肉葡萄球菌、植物乳杆菌和戊糖片球菌可进一步应用于发酵羊肉制品的生产和开发。     

高耐受酿酒酵母的筛选及酵母曲制备工艺的优化

本文以大曲为研究对象,选育出了1株耐受p H2.0、45℃、18%vol的优良酿酒酵母。将该酵母应用于酵母曲制备,通过酵母曲工艺优化,试验在小麦粉添加量为10%、培养24 h、培养水分达到60%时,制备出的酵母曲中酵母菌含量提高了50%。     

木糖葡萄球菌和肉葡萄球菌混合发酵剂对腊肉品质的影响

以不添加发酵剂的腊肉为空白对照,从理化特性、微生物分析、感官评价、香气活性化合物组成及电子鼻分析角度,研究木糖葡萄球菌和肉葡萄球菌混合发酵剂对腊肉品质的影响。结果表明,添加葡萄球菌混合发酵剂对产品的品质影响较大。与空白组比,葡萄球菌混合发酵剂可显著提高产品的酸价(2.12→3.28 mg/g)、蛋白质降解指数(16.32%→19.24%)、红度值a*(9.25→11.08)、香气和接受度得分及氨基酸代谢源香气活性化合物的种类和含量(3-甲基丁醛、3-甲基丁酸),同时显著降低产品的过氧化值(0.15→0.07 g/100 g)、硫代巴比妥酸反应物含量(0.25→0.17 mg/kg)和脂肪氧化源香气活性化合物的含量(己醛和壬醛),而对成品的基本理化指标(水分含量、水分活度、pH值)没有显著影响。电子鼻传感器能够将2组产品区分开,说明加入发酵剂后,腊肉的风味有所改变。因此,通过添加木糖葡萄球菌和肉葡萄球菌混合发酵剂可以显著促进腊肉中蛋白质和脂肪的水解、改善产品的色泽,促进发酵风味快速形成,同时延缓脂肪氧化。     

直投式纳豆菌发酵剂制备工艺优化

为探索出一种工艺简便、成本低且活菌数高的直投式纳豆菌（Bacillus natto）发酵剂的制备方法，该研究以大米粉为基质替代传统的种子液培养基培养纳豆菌后直接将其烘干制成直投式纳豆菌发酵剂，通过单因素及正交试验优化直投式纳豆菌发酵剂的制备工艺。结果表明，用含1.5%蛋白胨的大米粉作为培养基，在接种量4.0%、加水量40%、培养温度43 ℃条件下培养纳豆菌28 h，菌体生长良好，将培养物烘干后制成的直投式纳豆菌发酵剂中的活菌数含量达4.71×109 CFU/g。此技术操作简便，可推广至工业生产中，简化生产过程。     

植物乳杆菌发酵梨原汁饮料的研究

乳酸菌发酵果蔬汁,因其绿色、健康、营养,成为日常生活中必不可少的食物。我国梨种植业广泛、产量高,并且梨果自身营养素全面。因此,该研究利用3种复合益生菌研制一款发酵梨浆饮料。对发酵优势菌株进行发酵剂制备并优化工艺,保护剂配比为:谷氨酸钠2%、海藻糖5%、乳糖5%、脱脂乳10%、保护剂添加量与菌泥为3∶1(mL/g),在这些条件下,得到菌粉发酵剂菌活为8.48×10^9cfu/g;在发酵梨浆应用的工艺进行优化,最佳工艺为:植物乳杆菌299、保加利亚乳杆菌717、嗜热链球菌176体积比为4∶1∶1、接种量为8%、发酵温度为37℃、发酵时间72 h。此条件下梨浆得到充分发酵,口感突出,风味酸甜;测定梨浆发酵前后有机酸的变化:酵前梨浆中含量较为丰富的有机酸为:柠檬酸、苹果酸、乳酸、草酸。其中苹果酸、柠檬酸有优势有机酸,含量分别为:36.49、38.59 mg/100 g。经3种复合乳酸菌发酵后,梨浆中有机酸含量发生变化,有机酸含量依次为:乳酸、柠檬酸、苹果酸、草酸。其中乳酸含量由1.65 mg/100 g升高为116.27 mg/100 g。     

Metaproteomic analysis of enzymatic composition in Baobaoqu fermentation starter for Wuliangye baijiu

Wuliangye is one of the most famous brands of baijiu in China. The typical flavours of Wuliangye baijiu are mainly formed by the multifarious enzymes in fermentation starter (Baobaoqu, BBQ). As the enzymes remained poorly understood, the detailed enzymatic composition of BBQ was analysed by metaproteomics for the first time. It is worth noting that the enzymes from plant, animals and micro-organisms were detected together and oxidoreductases were the dominant enzymes. Next, the analysis of function showed that the enzymes were mainly involved in carbon metabolism and the biosynthesis of amino acids. Additionally, the relationship between differential abundant enzymes and formation of typical flavour substances in premium and normal BBQ was established. Furthermore, the activities of classic enzymes in BBQ were examined to verify the reliability of metaproteomic results. This study will provide clues to further improve the manufacturing technology for Wuliangye baijiu.     

Milk feeding level and starter protein content: Effects on growth performance,blood metabolites,and urinary purine derivatives of Holstein dairy calves

The objective of this study was to investigate the effects of milk allowances equal to 526 g/d as moderate (MOD) versus 790 g/d of milk dry matter as high (HI), and starter diets containing 18% or 23% crude protein (CP), on growth performance, blood metabolites, and purine derivative (PD) excretion in the urine of dairy calves. A total of 52 female Holstein dairy calves (40.8 kg of body weight) were randomly assigned to the experimental diets. The treatments were (1) moderate milk and 18% CP starter diet (MOD-18CP); (2) MOD and 23% CP starter diet (MOD-23CP); (3) high milk and 18% CP starter diet (HI-18CP); and (4) HI and 23% CP starter diet (HI-23CP). Calves had free access to a starter feed and water and were weaned on d 53 but remained in the study until d 73. Urine samples were collected during the preweaning period (for 6 consecutive days between d 35 and 40) and postweaning period (for 6 consecutive days between d 65 and 70) to investigate urinary excretion of PD. Starter feed intake, β-hydroxybutyrate (BHB), and blood urea concentrations were reduced; however, average daily gain (ADG) and blood glucose levels increased in calves fed HI before weaning compared with MOD. During the preweaning period, high milk feeding increased total urinary PD excretion but decreased it after weaning. The 23CP diet resulted in higher feed intake and ADG before weaning and higher excretion of allantoin and total excretion of PD compared with the 18CP diet. The HI-23CP treatment resulted in the greatest withers and hip heights at weaning and final measurement, as well as the highest preweaning blood insulin concentrations. In terms of rumen development, MOD-23CP showed the greatest benefits based on starter intake, blood BHB concentration, and urinary excretion of PD. Based on the higher urinary excretion of PD found in HI-fed calves before weaning, it is possible that milk feeding overestimates estimated microbial yield. The results suggest that feeding starters with a higher proportion of CP may help maintain a more balanced ratio of CP to ME during high milk feeding, to avoid protein deficiency due to low starter intake. When calves are fed a high milk allowance, urine excretion of PD may be misinterpreted as a measure of estimated microbial growth and rumen development; this should be considered during calculations of estimated microbial yield in milk-fed calves.     

海洋平台吊机软启动器设计应用与优化研究

软启动器作为大型电动机常采用的启停控制装置之一,越来越多地应用到海洋钻井生产过程中。该文从电动机启停特点、软启动器控制方式、接线,并结合海洋钻井平台吊机的设计思路及应用来分析,结合现场相关故障维修实例对软启动器升级改造方案进行了研究。