发酵乳─最新研究动向

有关发酵乳的研究,目前主要集中于新产品的开发和健康特性的研究。在对近１０年有关文献研究的基础上,介绍了发酵乳的种类,益生菌,乳酸菌的培养、代谢特性、遗传和生物技术,发酵剂的制作,健康特性研究及乳酸菌的安全性等。     

The presence of endotoxin in powdered infant formula milk and the influence of endotoxin and Enterobacter sakazakii on bacterial translocation in the infant rat

Lipopolysaccharide (LPS) is a heat stable endotoxin that persists during the processing of powdered infant formula milk (IFM). Upon ingestion it may increase the permeability of the neonatal intestinal epithelium and consequently bacterial translocation from the gut. To determine the level of endotoxin present in IFM, 75 samples were collected from seven countries (representing 31 brands) and analysed for endotoxin using the kinetic colorimetric Limulus amoebocyte lysate (LAL) assay. The endotoxin levels ranged from 40 to 5.5 x 10(4) endotoxin units (EU) per gram and did not correlate with the number of viable bacteria. The neonate rat model was used to address the risk of endotoxin-induced bacterial translocation from the gut. Purified Escherichia coli LPS was administered to rat pups followed by inoculation with Enterobacter sakazakii ATCC 12868. Bacteria were isolated from the mesentery, spleen, blood and cerebral spinal fluid (CSF) of endotoxin-treated rats due to enhanced gut and blood brain barrier penetration. Histological analysis of the colon showed marked distension of the mucosal and muscular layers. It is plausible that the risk of neonatal bacteraemia and endotoxemia, especially in neonates with immature innate immune systems, may be raised due to ingestion of IFM with high endotoxin levels.     

Antibiotic Resistance in Lactic Acid Bacteria and Micrococcaceae/Staphylococcaceae Isolates from Artisanal Raw Milk Cheeses, and Potential Implications on Cheese Making

ABSTRACT:  Antibiotic susceptibility against 19 antimicrobial agents was evaluated in isolates of the genera  Lactococcus  (46 isolates),  Leuconostoc  (22),  Lactobacillus  (19),  Staphylococcus  (8),  Enterococcus  (7), and  Microccoccus/Kocuria  (5) obtained from the predominant microflora of nonrecent and recent types of artisanal raw cow's milk cheeses. Beta-lactams showed broad activity against all genera, although leuconostocs and lactobacilli were highly resistant to oxacillin (80% to 95.5%). Resistance to aminoglycosides was frequent for lactococci and enterococci (particularly for streptomycin), whereas lower rates of resistance were detected for lactobacilli and leuconostocs. Technologically interesting traits for the food industry were distributed among isolates that showed different degrees of resistance to common antibiotics. However, isolates showing resistance to less than 2 antibiotics were mainly those with properties of greatest technological interest (acidifying activity, proteolytic/lipolytic activities, or diacetyl production).     

含有后生元和β-葡聚糖的乳饮料对小鼠免疫功能的影响

探讨含有后生元和酵母β-葡聚糖的一种乳饮料对小鼠免疫功能的影响.将BALB/c小鼠随机分为乳饮料干预组的低、中、高3个剂量组(1408、3520、8448mg/kg·bw),同时设置一个空白对照组.经口灌胃30 d后,分别进行脏器/体重比值测定、脾淋巴细胞转化实验、迟发型变态反应、抗体生成细胞检测、血清溶血素测定、碳廓...     

超高效液相色谱-同位素稀释质谱法测定配方奶粉中的泛酸

建立测定配方奶粉中泛酸的超高效液相色谱-同位素稀释质谱方法。样品经乙酸铵溶液提取、三氯甲烷除 蛋白后,进行超高效液相色谱-串联质谱分析,采用HSS T3液相色谱柱分离,以10 mmol/L乙酸铵溶液（含0.1%甲 酸）和乙腈为流动相进行梯度洗脱,多反应监测模式,内标法定量。结果表明：方法定量限为0.040 mg/100 g,线 性范围内低、中、高3 个标准添加水平的回收率为96.9%～104.3%,相对标准偏差为3.78%～5.04%。该方法操作过 程简单、分析周期短、灵敏度高、重复性好,适用于奶粉中泛酸的测定。     

植物乳杆菌发酵脱脂牛乳生成共轭亚油酸过程的研究

为提高发酵牛乳共轭亚油酸(CLA)含量,以植物乳杆菌(Lactobacillus plantarum LT2-6)发酵添加亚油酸的脱脂牛乳,并对其生成CLA的过程进行了研究。结果表明,接种后6h CLA开始生成,24h CLA生成量达到最高,再延长发酵时间后CLA生成量缓慢下降。接种3～12h,牛乳滴定酸度快速增加,12h后滴定酸度增加缓慢。发酵18h时CLA的生成速率最大;24h时,牛乳pH降到4.0,CLA生成基本停止。牛乳发酵过程中,pH下降是影响植物乳杆菌LT2-6转化LA生成CLA的主要因素。脱脂牛乳中加入LA,经植物乳杆菌LT2-6发酵、脂肪酸萃取和甲酯化,并用气相色谱检测,结果显示:生成的CLA主要为cis9、trans11/trans9和cis11-CLA。     

Short communication: Bovine α-casein is a ferritin-binding protein and inhibitory factor of milk ferritin immunoassay

Commercial bovine milk α-casein, but not β- and κ-caseins, bound to bovine spleen ferritin, as determined by an immunoassay for ferritin. In contrast, α-casein did not bind to apoferritin. The binding of α-casein to bovine spleen ferritin was strongly inhibited by increasing ionic strength by the addition of 0.5 M (NH₄)₂SO₄. The addition of α-casein to a known amount of bovine spleen ferritin resulted in significantly lower recovery (78-80%) of added ferritin, although β- and κ-caseins showed little inhibitory effect in the ferritin immunoassay. These results indicate that bovine α-casein is a specific ferritin-binding protein that may inhibit milk ferritin immunoassay.     

Inactivation of Enterobacter sakazakii in infant milk formula by gamma irradiation: determination of D10-value

ABSTRACT:  Enterobacter sakazakii is an emerging foodborne pathogen that has caused several cases of meningitis and necrotizing entercolitis in infants and has been associated with infant formulas. Five strains of E. sakazakii were inoculated individually into brain heart infusion broth and rehydrated or dehydrated infant milk formula and exposed to ionizing radiation. E. sakazakii strains in brain heart infusion broth and rehydrated infant milk formula (RIMF) were exposed to irradiation dose of up to 1 kGy while strains in dehydrated infant milk formula (DIMF) were exposed to irradiation dose of up to 9 kGy. The D₁₀-values were determined by using a linear regression model. Average calculated D₁₀-values ranged from 0.21 to 0.29 kGy, 0.24 to 0.37 kGy, and 1.06 to 1.71 kGy in brain heart infusion broth, RIMF, and DIMF, respectively. The results obtained from this study will be useful for powdered infant milk formula industries to reduce the risk associated with E. sakazakii .     

羊奶粉生产环节阪崎肠杆菌分离鉴定及其毒力基因和药敏检测

目的:分析羊奶粉生产环节阪崎肠杆菌的污染状况,分离株毒力基因携带情况以及耐药性。方法:采自某羊奶粉加工厂空气过滤车间、液态奶车间、流化床车间、喷雾干燥车间和包装车间的生产样品及环境样品共180份,按国标GB4789.40-2010和PCR方法进行阪崎肠杆菌的分离鉴定;采用PCR方法检测cpa、hly、sip和omp X毒力基因;采用琼脂稀释法测定药敏性。结果:27个采样点中有14个阪崎肠杆菌阳性点,检出率为51.9%;180份样品中有29份检出阪崎肠杆菌,污染率为16.1%;阳性样品主要为粉状和棉签涂抹样品,污染率分别为23.5%和16.9%。毒力基因检出率为100%,毒力基因类型有cpa-omp X和cpa-hly-omp X,检出率分别为79.3%,20.7%。29株菌对利福平、甲氧苄啶/磺胺甲恶唑、头孢西丁钠、阿莫西林、阿莫西林/克拉维酸的耐药率依次为100%,75.9%,6.9%,3.4%和3.4%;对其它11种抗生素均敏感,多重耐药率为6.9%。结论:羊奶粉加工厂存在阪崎肠杆菌的污染。空气流动、粉尘污染、操作人员交叉污染及生产设备清洗消毒不彻底可能是加工过程中该菌的污染途径。分离株毒力基因携带率较高,对大多数供试抗生素敏感,出现多重耐药现象。     

山羊乳酪蛋白酶解物制备及体外抗氧化活性研究

以自由基清除能力、金属离子螯合能力和抗脂质过氧化能力为指标,采用均匀试验研究山羊乳酪蛋白酶解物的制备及其体外抗氧化活性,并且比较自由基清除能力的方法。结果表明：山羊乳酪蛋白适宜的酶解工艺为在60g/kg的底物浓度下,中性蛋白酶和碱性蛋白酶的添加量分别为4000U/g和250U/g,45℃、pH7.5条件下酶解24h。山羊乳酪蛋白经酶解后其体外抗氧化活性显著增强。山羊乳酪蛋白酶解物 ·OH清除率的EC50值是其蛋白的3.59倍,ABTS＋ ·的清除能力是其蛋白的158.72倍,螯合Fe2＋的能力是其蛋白的5.44倍;在亚油酸体系中抗脂质过氧化能力强于TBHQ,与VE相当。清除 ·OH、DPPH自由基、O2－ ·和ABTS＋ ·的方法不能相互替代。