酸奶后酸化控制措施的研究进展

酸奶在储存、运输到消费者食用前,乳酸菌会继续产酸,从而使酸奶的酸度增加,出现后酸化现象,影响酸奶的口感和风味。本文简要介绍了酸奶后酸化机理和乳酸菌的耐酸机制,并从物理、化学、生物方法三个方面对目前酸奶后酸化防治措施进行了阐述与展望。     

保存温度对酸奶品质及活性乳酸菌含量的影响

以2种市售酸奶作为研究对象,研究不同保存温度(4、28、37℃)对酸奶品质及活性乳酸菌含量的影响,并分析酸奶酸度、pH值及活性乳酸菌含量的变化趋势。实验结果表明,保存温度为4℃时,酸奶的pH值和酸度具有较高的稳定性及较高的活性乳酸菌含量,但其稳定性却比保存温度为28和37℃时差,很容易发生乳清分离现象。     

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.     

斑马鱼功效模型在验证乳制品补钙和促进肠蠕动中的应用

目的基于斑马鱼补钙和肠蠕动模型,验证和对比不同牛奶补钙和酸奶促进肠蠕动的作用效果。方法选择发育健康且阶段一致的3 dpf野生型斑马鱼,加入不同浓度(2. 5、5. 0、10. 0 mg/m L)的纯牛奶稀释液,同时设置空白对照组。处理至7 dpf后,用2 mg/m L钙黄绿素染色,在荧光显微镜下观察拍照,计算斑马鱼的椎骨荧光强度。选取5 dpf的斑马鱼,用尼罗红染料处理16 h,加入不同浓度(2. 5、5. 0、10. 0 mg/m L)的酸奶和乳酸菌饮料稀释液,同时设置空白对照组。处理24 h后,在荧光显微镜下观察拍照,计算斑马鱼肠道内荧光强度。结果纯牛奶、酸奶和乳酸菌饮料作用效果都随浓度的增加而增强。与空白对照组比较,6种纯牛奶中2种纯牛奶处理的斑马鱼骨骼荧光强度有一定增加; 8种酸奶和乳酸菌饮料都显著引起了肠道荧光强度的减弱,酸奶的效果优于乳酸菌饮料。结论纯牛奶、酸奶和乳酸菌饮料对斑马鱼的最大耐受浓度(MTC)为10 mg/m L,且对斑马鱼起到补钙和促进肠蠕动的作用。     

绿豆酸奶的制作工艺

绿豆酸奶是以绿豆为主要原料制作的一种新型植物蛋白乳酸饮料.本文介绍了绿豆酸奶的制作工艺及方法,通过对产品的分析证明绿豆酸奶是一种营养丰富乳酸菌饮料,含有人体必须的七种氨基酸,又含有医疗保健作用的药用成份黄酮、皂甙、鞣质,是一种较为理想的保健饮料.     

含有缓解花粉症症状乳酸菌的新产品相继上市

2006年12月～2007年2月期间．一批确认具有缓和花粉症症状的乳酸菌新产品相继上市。分别有乳酸菌健康食品（supplement）最畅销品牌——麒麟WellFoods公司的添加KW乳酸菌的“Kirin Noale”系列、卡尔皮斯公司的添加L-92乳酸菌的“Interbalance L-92”系列、在过敏症对策的效果上堪称一流的高梨乳业公司的添加LGG乳酸菌的酸奶等。     

简述酸奶防治肠道疾病的特殊功能

酸奶是鲜牛奶经乳酸菌发酵精制而成的发酵型牛奶,是一种含有大量活性乳酸菌的开胃佳品饮料。当人们饮用时,活性乳酸菌直接进入人体消化道,履行它的“人体肠道健康卫士”职责,因而不仅使酸牛奶营养价值远超过鲜牛奶,而且长期     

功能性乳酸菌系列产品的研制开发试验Ⅰ活性酸乳发酵工艺的研究

乳酸菌很早就成为人们利用的有益微生物,是人体肠道内极为重要的生理菌群。由乳酸菌发酵制成的食品称为功能性保健食品。本试验是1993年由朝阳市科委下达的科研项目,是运用现代生物技术,研究以乳酸菌为主要对象,以含乳酸菌量最高的酸奶为基础原料,进行了乳酸菌奶粉、乳酸菌奶糖、乳酸菌冷饮、乳酸菌片、乳酸菌饮料、乳酸菌奶酪等系列保健食品的深加工技术研究。现将活性酸乳发酵工艺的研究报告如下：l材料与方法1．1材料1．1．1主要原料鲜牛奶、奶粉、优质白糖、乳酸菌、稳定剂等。1．1．2供试菌株共9株（引自山东、天津、北京等地）。…     

含有缓解花粉症症状乳酸菌的新产品相继上市

2006年12月～2007年2月期间．一批确认具有缓和花粉症症状的乳酸菌新产品相继上市。分别有乳酸菌健康食品（supplement）最畅销品牌——麒麟WellFoods公司的添加KW乳酸菌的“Kirin Noale”系列、卡尔皮斯公司的添加L-92乳酸菌的“Interbalance L-92”系列、在过敏症对策的效果上堪称一流的高梨乳业公司的添加LGG乳酸菌的酸奶等。     

两株乳酸菌的产酸性能及其对抗生素敏感性研究

从市售酸奶中分离出2株乳酸菌,经鉴定为嗜热链球菌(St)与保加利亚乳杆菌(Lb),并对其产酸性能及对抗生素敏感性进行了研究。结果表明:St与Lb 1∶1混合发酵效果优于单菌发酵;乳酸菌对4种抗生素类药物敏感性较弱,服用该类药物对人体肠道内乳酸菌的有益作用产生的影响较小。     

Induction of 2'-5' A synthetase activity and interferon in humans by bacteria used in dairy products.

The production of interferon by fasted human subjects in response to lactic bacteria Lactobacillus bulgaricus and Streptococcus thermophilus was evaluated in vivo and in vitro. The 2'-5' A synthetase activity of blood mononuclear cells was used to estimate interferon production following a single ingestion of 10(11) bacteria in yoghurt or sterile milk (controls). The level of the 2'-5' A synthetase of the yoghurt fed subjects was 83% (p = 0.002) higher than that of the milk fed controls 24 hours after ingestion. The baseline value remained unchanged in the control group. Blood mononuclear cells from a second group of subjects, were cultured with lactic bacteria for 48 hours, their cell-free supernatants contained gamma interferon. These results suggest that a transient production of interferon can be induced in healthy subjects by the lactic bacteria used in food processing.     

酸奶弱后酸化发酵剂乳酸菌育种技术研究进展

后酸化是影响酸奶贮藏期间感官品质和风味特性的重要因素,是决定产品货架期的重要指标。弱后酸化发酵剂菌种的选育是优良发酵剂开发的重要技术手段。通过诱变育种筛选出具有弱后酸化特性的菌株,是延缓酸奶贮藏期间后酸化的技术途径之一。国内外围绕弱后酸化发酵菌株选育,采用诱变育种方法开展了大量卓有成效的研究。本研究针对诱变育种的方法、原理与研究现状,结合本课题组近几年关于发酵剂菌种弱后酸化的研究工作,对弱后酸化乳酸菌菌种的诱变育种进行了简要阐述与展望。     

产黏乳酸菌的发酵特性研究

通过对2株产黏乳酸球菌的发酵特性比较研究,以感观、酸度、活菌数对数值、培养时间、粘度及乳清析出率为考察指标,结果表明:乳酸球菌Q26具备较好的产黏、产香特性,遗传性质较稳定.通过与乳酸杆菌G18进行发酵应用试验,确定G18和Q26存在共生关系,混合发酵的酸牛乳乳清析出率为0.1％,粘度为4 528mPa·s.通过保质期试验,产品在28、20、4℃下保质期分别为3、6、15d.确定Q26和G18为最佳酸牛乳生产用菌种.     

Quantification of micro-organisms in binary mixed populations by Fourier transform infrared (FT-IR) spectroscopy

Fourier Transform Infrared (FT-IR) spectroscopy was used for the first time to determine the ratios of different microorganisms in mixtures. Exemplarily, systems composed of two food-associated yeast species (Saccharomyces cerevisiae/Hanseniaspora uvarum) and two yoghurt lactic acid bacteria (Lactobacillus acidophilus/Streptococcus salivarius ssp. thermophilus) were investigated. Determination of the cell number ratio in the lactic acid bacteria system was possible with a minimal prediction accuracy of +/- 16 ratio percentage points while the minimum accuracy of prediction in the yeast two-component system was +/- 4% (both at a 95% confidence level). These results show that FT-IR spectroscopy is potentially a rapid method for the quantification of cell ratios in mixtures of two different microorganisms, provided that the cell ratio does not drop below a certain, system-specific threshold.     

Susceptibility of Cheese and Yoghurt Starter Bacteria to Antibiotics

Eight single-strain lactic streptococci, three commercial cheese starters, and six lactic acid bacteria isolated from yoghurt were examined for their susceptibility to penicillin, cloxacillin, tetracycline-hydrochloride and streptomycin. The ranges of the antibiotics causing 50% inhibition of the bacteria were (mug/ml): penicillin, 0.009 to 0.20; cloxacillin, 0.24 to 2.50; tetracycline, 0.09 to 0.60; and streptomycin, 0.35 to 13.0. The average concentrations required to cause 50 and 100% inhibition of the cheese starters were (mug/ml): penicillin, 0.12 and 0.26; cloxacillin, 1.91 and 3.9; tetracycline-hydrochloride, 0.13 and 0.36; and streptomycin, 0.59 and 2.06. All the cocci were about equally susceptible to tetracycline, and all organisms were more resistant to cloxacillin than penicillin. The yoghurt isolates were more resistant to streptomycin and more susceptible to penicillin than the cheese starters. The 2, 3, 5-triphenyltetrazolium chloride test, using Streptococcus thermophilus BC as assay organism, does not detect low levels of streptomycin in milk. However, it is useful in detecting cloxacillin residues.     

解淀粉乳酸细菌在L-乳酸发酵生产中的应用

对解淀粉乳酸细菌及其产生的淀粉酶和发酵工艺等方面的国内外研究现状进行了综述。解淀粉乳酸细菌具有分泌淀粉酶的能力,可免去原料水解处理工序直接发酵淀粉质原料生产乳酸,可以简化生产工艺,并可节约设备投资,进而降低生产成本。解淀粉乳酸细菌主要分离自传统发酵食品,也可从有机废弃物和厨余垃圾中分离得到。介绍了解淀粉乳酸细菌直接利用淀粉质原料的机理,比较了解淀粉乳酸菌发酵生产L-乳酸的工艺。提出通过诱变育种和基因工程育种等方法获得更加高效的解淀粉乳酸细菌,并结合先进的发酵、分离技术来提高乳酸生产效率。     

Antagonism Between Osmophilic Lactic Acid Bacteria and Yeasts in Brine Fermentation of Soy Sauce

Brine fermentation by osmophilic lactic acid bacteria and yeasts for long periods of time is essential to produce a good quality of shoyu (Japanese fermented soy sauce). It is well known that lactic acid fermentation by osmophilic lactic acid bacteria results in the depression of alcoholic fermentation by osmophilic yeasts, but the nature of the interaction between osmophilic lactic acid bacteria and yeasts in brine fermentation of shoyu has not been revealed. The inhibitory effect of osmophilic lactic acid bacteria on the growth of osmophilic yeasts was investigated. It was recognized that osmophilic shoyu yeasts such as Saccharomyces rouxii and Torulopsis versatilis were inhibited by a metabolite produced by osmophilic lactic acid bacteria (belonging to Pediococcus halophilus) in brine fermentation of shoyu. The primary inhibitor was considered to be acetic acid, although lactic acid was slightly inhibitory.     

Yoghurt: an unlikely source of Campylobacter jejuni/coli

Knowledge of the relative insensitivity of Campylobacter jejuni to moderately acid environments prompted us to study its survival in different batches of yoghurt of pH range 4.2–5.3 and the role of organic or inorganic acid in the die-off of this pathogen. None of the 11 strains of C. jejuni or C. coli survived more than 25 min in yoghurt. Suspecting that this rapid die-off cannot be accounted for by the pH of the yoghurt we compared the survival rates of C. jejuni in milk, whose pH had been adjusted by lactic, propionic and hydrochloric acid respectively, with that of yoghurt. Even for an inoculum of 10⁵–10⁸ cfu/ml propionic acid was bactericidal in minutes. Lactic acid reduced the bacterial populations by 3–5 logs in 30 min. Strong inorganic acid HC1, by contrast, had little or no effect on the populations. Although lactic acid is quite bactericidal for C. jejuni , it is apparently not the only factor to which the prompt elimination of this pathogen from yoghurt could be attributed.     

青藏高原垂穗披碱草青贮饲料中乳酸菌的多样性及低温发酵菌株的筛选

【目的】探究青藏高原垂穗披碱草青贮饲料中乳酸菌的多样性,筛选在低温条件下(10、15和25°C)生长性能较好的优良菌株。【方法】将垂穗披碱草青贮饲料中分离纯化的乳酸菌进行形态特征观察及16S r RNA基因测序鉴定;用MRS液体培养基在10、15和25°C条件下分离、初筛乳酸菌,选取高吸光度值的菌株作为优势菌株。用绿汁发酵液在10、15和25°C条件下培养测定其p H值,选取低p H值菌株作为优势菌株,并综合MRS培养基筛选结果确定优良菌株。【结果】从不同温度和发酵阶段的垂穗披碱草青贮饲料中共分离得到108个乳酸菌菌株,它们分属于6个属、18个种。其中,清酒乳杆菌LS-24在15°C条件下发酵液p H值显著降低(P0.05),戊糖片球菌PP-63在发酵初期生长速度较快,植物乳杆菌LP-21在15°C条件下发酵液p H值降至3.9且有最大活菌数。【结论】在青藏高原垂穗披碱草青贮饲料中发现的乳酸菌属基本涵盖了前人在常温青贮饲料中发现的所有属,但种数略少;在108株菌中,清酒乳杆菌LS-24、戊糖片球菌PP-63和植物乳杆菌LP-21在低温条件下均表现出较好的繁殖和发酵特性,可作为青贮饲料低温发酵的备选菌株。     

Protective effect of casein toward Salmonella typhimurium in acid-milk

Lactic acid is the inhibitory agent in yoghurt responsible for the inhibition of Salmonella typhimurium. Casein, however, may exert a protective effect toward the survival of the salmonella in acid-milk products. Salmonella typhimurium was found to die-off 21.2% more rapidly in 18-h yoghurt-whey than in 18-h yoghurt at 37 C with a pH of 3.85 and 1.42% lactic acid. When casein was added to yoghurt-whey, the die-off rate of the salmonellas was reduced to that found in yoghurt. The rate remained unchanged when 4.8% sodium caseinate was added to the whey. When 0 to 14% casein was added to the acid-whey the die-off rate changed from 9.7 to 24.0 min/log reduction of cells, respectively. There was a direct correlation between the increase in casein concentration and length of survival of the salmonellas. At a pH of 3.85, 4.2 or 4.5, the die-off rate was 6.5, 13.0 or 40 min/log reduction of cells in milk containing 1.42% lactic acid, and was 4.0, 10.0 or 33.3 min/log reduction, respectively, in whey with 1.42% lactic acid. Thus, the protective effect of casein toward Salm. typhimurium incieased as the pH increased. This indicated that casein exerts a protective effect on Salm. typhimurium in acid dairy products and the degree of protection depends on the casein concentration, the form of the casein molecule and the pH.