大豆蛋白水解物促酸奶乳酸菌增殖及生长动力学

由于乳酸菌缺乏一些生物代谢途径,不能合成生长必需的氨基酸、维生素等物质,营养要求十分苛刻,必需依赖生长环境提供必需氨基酸、维生素等生长因子才能获得高密度生长。应用化学限定培养基进行大豆蛋白水解物、全价氨基酸和生长基本氨基酸3种氮源条件下乳酸菌的生长动力学研究,结果表明:保加利亚乳杆菌和嗜热链球菌在分子量小于5 ku的大豆蛋白水解物培养基中的最大生长速率μmax分别为0.215/h和0.262/h,约为全价氨基酸的2倍,细胞密度增加到5倍。20种全价氨基酸氮源培养基对两种乳酸菌的生长效能很低,保加利亚乳杆菌和嗜热链球菌的最大生长速率分别为0.10/h和0.12/h,pH值只达到pH4.5～5.0。基本氨基酸氮源只能满足乳酸菌生长的最低要求。分子量小于5 ku的大豆蛋白水解物比全价氨基酸对乳酸菌生长具有显著的促进作用,表明乳酸菌生长的最佳氮源是寡肽而不是氨基酸,大豆蛋白水解物可以用作乳酸菌高密度培养添加物。     

保加利亚乳杆菌番茄复合汁增菌培养基的优选研究

研究了在番茄汁基础培养基中添加不同营养物质对保加利亚乳杆菌生长的影响,进一步采用正交试验优化筛选了保加利亚乳杆菌L.b-S1的增殖培养基。结果表明,在番茄汁基础培养基中添加胰蛋白胨、酵母膏、碳酸钙可显著促进试验菌株的细胞生长(P<0.01);利用L933正交试验筛选出增殖培养基的最佳配比为:在番茄汁基础培养基中添加0.5%酵母膏、1.0%胰蛋白胨、0.3%碳酸钙;试验菌株在增殖培养基中经37℃培养18h,活菌数可达为2.25×1010mL-1,较液体MRS培养基的活菌数(4.98×108mL-1)提高了45.18倍,成本较液体MRS培养基降低1500元/t。为工业化大规模培养乳酸菌并研制开发直投式酸奶发酵剂提供了经济廉价的增菌培养基。     

蛋白酶水解脱脂乳培养基的优化

为减少进口发酵剂的使用,降低国内乳制品的生产成本,国内需要自主研发发酵剂,水解脱脂乳培养基的优化是发酵剂制备过程中的一个重要环节。为制备有利于乳酸菌生长的水解脱脂乳培养基,本研究首先以发酵乳杆菌V9为试验菌种,筛选出水解脱脂乳最适的蛋白酶,再通过单因素与正交实验对制备脱脂乳水解液的温度、时间、pH值、加酶量进行优化。结果表明,最适水解条件为:在p H为8.5的12%脱脂乳中按25 U/mL接入碱性蛋白酶,55℃水解1 h,以此水解脱脂乳为培养基培养乳酸菌活菌数达到2.5×109CFU/mL,较脱脂乳培养基中的活菌数提高了1.74倍。利用此优化培养基培养鼠李糖乳杆菌grx19和植物乳杆菌S7,得到的活菌数分别较脱脂乳培养基提高了1.50和1.62倍。     

鸡肉蛋白酶解物对乳酸菌增殖作用研究

利用中性蛋白酶和碱性蛋白酶水解鸡肉蛋白,研究水解物对乳酸菌增殖作用的影响。将不同酶解时间(2、4、6h)的酶解物以1%、2%、3%的添加量添加到四种乳酸菌(嗜热链球菌、保加利亚乳杆菌、嗜酸乳杆菌、干酪乳杆菌)的MRS液体培养基中,37℃恒温培养72h后,通过测定OD622值比较得出对乳酸菌的增殖效果。结果表明,两种蛋白酶解物对四种乳酸菌的增殖作用均有影响,相同酶解时间下,中性蛋白酶和碱性蛋白酶的添加量为3%时,对乳酸菌增殖作用最强;在相同酶添加量下,酶解6h,对乳酸菌增殖作用最强。      

红参对乳酸菌体外增菌的影响

采用比浊法和活菌计数法研究在基础培养基/菊芋汁基础培养基中添加不同量低聚木糖、低聚果糖、红参提取液及其酸水解物对鼠李糖乳杆菌AS 1.2466T/保加利亚乳杆菌ATCC 11842生长情况的影响。结果表明:不同添加物对鼠李糖乳杆菌AS 1.2466T的增菌效果为红参提取液>红参酸水解物>低聚木糖>低聚果糖。当红参提取液添加量为12.50%时,鼠李糖乳杆菌AS 1.2466T的最大OD600值为1.172,活菌数为2.72×10^8 CFU/mL,比基础培养基中最大活菌数7.75×10^7 CFU/mL增加1个数量级。对保加利亚乳杆菌ATCC 11842的增菌效果为红参提取液>低聚木糖>红参酸水解物>低聚果糖。当红参提取液添加量为6.25%时,保加利亚乳杆菌ATCC 11842的最大OD600值为0.627,活菌数为4.43×10^8 CFU/mL,比菊芋汁基础培养基中最大活菌数1.48×10^7 CFU/mL增加1个数量级。红参提取液比低聚木糖、低聚果糖具有较好的增菌效果,将红参作为益生元研究其益生功能,为研究红参对肠道微生物的影响提供试验依据。     

干酪乳杆菌LC-15的增菌培养基设计及生长动力学研究

对1株具有降胆固醇作用的干酪乳杆菌(Lactobacillus casei)LC-15的增殖培养基进行了筛选和优化,同时对其在分批培养时的生长动力学进行了研究。所得增菌培养基配方为0.1mol/L pH6.8的Na2HPO4-柠檬酸配制经蛋白酶预水解的10%脱脂乳冻干粉,再添加0.5%的葡萄糖,1.5%的胰蛋白胨,0.3%酵母浸膏,在此培养基中的最大菌数可达8.8×109cfu/mL,分别比MRS及脱脂复原乳中提高了1.35倍和0.75倍。得到的干酪乳杆菌在优化培养基中分批培养的生长动力学模型为:N(t)=3.4088/(1+e3.3560-0.3254t)。     

水解大豆蛋白对嗜热链球菌增殖的促进作用

利用胰蛋白酶、胃蛋白酶和碱性蛋白酶分别水解大豆分离蛋白,研究水解物对嗜热链球菌增殖的促进作用。以M17培养基为基础培养基,分别添加3种蛋白水解物作为实验组,以添加大豆分离蛋白作为对照组,培养嗜热链球菌,测定对其产酸和活菌数的影响;并通过蛋白层析技术对3种水解物进行组分分析。结果显示,碱性蛋白酶水解物对嗜热链球菌增殖的促进效果最为显著,使活菌数提高了1个数量级,菌株产酸能力增强。层析结果显示,大豆蛋白碱性蛋白酶水解物(AS)中短肽含量最高,是嗜热链球菌培养的一种理想氮源。     

酵母膏对α溶血性链球菌发酵代谢甘露聚糖肽的影响

研究发酵培养基中酵母膏的添加量对α-溶血性链球菌生长及其代谢甘露聚糖肽的影响规律。结果表明:当酵母膏的添加量小于7g/L时,随着酵母膏添加量的增加,α-溶血性链球菌的菌落数明显增加,最大菌落数为1.9×109,比对照组7.6×108增加了1.5倍,而且α-溶血性链球的延迟期由8h缩短到5h之内,对数期的生长速率由2.83增加到11.02,进入稳定期的时间也由27h以上缩短到23h。当酵母膏添加量大于7g/L时,这一规律就不再明显。同时,酵母膏使菌体量快速增加的时间提前了2~4h,当酵母膏添加量为7g/L时,在发酵4h时,比生长速率最大,为0.38;在发酵27h时,甘露聚糖肽的代谢量最大,为1.04g/L。     

酪蛋白水解物对瑞士乳杆菌生长的影响

利用胰蛋白酶水解酪蛋白,以水解物对瑞士乳杆菌增殖效果为指标,优化水解条件,并研究最佳增殖效果。 结果表明：胰蛋白酶水解酪蛋白的最佳水解条件为水解温度37℃、底物质量分数5%、酶与底物质量比1:600、pH8.0,此条件下制备的水解产物添加量为1g/100mL 时对瑞士乳杆菌生长增殖效果最好,而添加量大于4g/100mL 时,对瑞士乳杆菌生长呈现抑制作用。     

乳酸菌饮料

一、乳酸菌饮料的制造方法 1、乳酸菌饮料原液的制造工序见下图 2、操作要点 (1) 原料乳:通常使用脱脂乳和脱脂奶粉。原料乳的品质要求是耐热性强、含耐热性细菌少、产酸量大。 (2) 培养基的调制:在脱脂乳中添加脱脂奶粉,无脂乳固形物的浓度应调整为15—     

Evaluation of de-lipidated egg yolk and yeast autolysate as growth supplements for lactic acid bacteria culture

Four strains of lactic acid bacteria (LAB) were cultivated on deproteinated whey supplemented with yeast autolysate (YA) and/or de-lipidated egg yolk (DEY). Growth was compared to that recorded on the widely used MRS medium. The feasibility of the use of YA in place of yeast extract was confirmed. In the presence of YA in the medium, cell numeration gained nearly 1 log for only 0.4% DEY added in the culture medium, namely 0.1 g/L additional nitrogen, showing that DEY also supplies LAB growth in trace elements and growth factors like vitamins. If compared to the MRS medium, final cell numerations were about 1 log lower on deproteinated whey supplemented with YA and DEY, while the protein nitrogen ratio of both media was 2.7, showing the high potential of the tested supplements, and especially DEY. Subsequent works with higher and hydrolysed DEY may be therefore useful.     

Calcium-Aggregated Milk: a Potential New Option for Improving the Viability of Lactic Acid Bacteria Under Heat Stress

Heat-induced inactivation of viable cells restricts a wide range of application of spray drying in producing dried lactic acid bacteria (LAB) products. In the present study, an effective method to enhance the stability of LAB under heat stress has been identified. This was done by enhancing the heat stability of skim milk as the carrier. Here, skim milk was supplemented with 10 mM CaCl₂ and heated to 90 °C for 10 min to induce protein aggregation. Using this Ca-aggregated skim milk as carrier, the survival of five LAB strains tested was found two orders of magnitudes higher than that of an untreated milk after the heating at a rising temperature from about 25 to 70 °C within 45 s. Possible mechanisms of the protection were explored by comparing the residual viability, microstructure of the cell-contained milk, and changes of suspension particle sizes caused by heat treatment of the four carriers, i.e., untreated milk, Ca-added milk, heat-treated milk, and Ca-aggregated milk. Ca-aggregated milk induced the highest microbial heat stability among them, providing a thick and compact encapsulation around LAB cells before the heat treatment for inactivation. The viable cells could stay in a comparatively more stable extracellular environment. This work reveals potentially a new option for using milk protein aggregates as a protectant of microorganisms. A series of calcium-enriched probiotic products may be developed based on the described principles of the finding of the Ca-aggregated milk.     

Production of β-galactosidase for lactose hydrolysis in milk and dairy products using thermophilic lactic acid bacteria

The aim of this work was to establish optimal conditions for the maximum production of β-galactosidase using an industrially suitable medium. Lactobacillus delbrueckii subsp. bulgaricus ATCC 11842 was cultivated in skim milk, whey and whey permeate basal media, supplemented with whey protein products, yeast extract or De Man–Rogosa–Sharpe (MRS) broth, at pH 5.6 and 43°C. All supplementations of the whey and whey permeate basal media resulted in the enhancement of the specific growth rates, rate of lactic acid production and β-galactosidase activity. However, unsupplemented skim milk gave the greatest rate of lactic acid production (3.50±0.269 mg lactic acid ml⁻¹ media h⁻¹) and the highest β-galactosidase activity (5.491±0.116 U activity ml⁻¹ media); far superior to the best whey-based medium supplemented with MRS (2.71±0.176 mg lactic acid ml⁻¹ media h⁻¹ and 3.091±0.089 U activity ml⁻¹ media, respectively). A technologically feasible approach for the reprocessing of the spent skim milk was tested and a conceptual process scheme is proposed.     

酸马奶中具有潜在共生性乳酸菌和酵母菌的筛选

对内蒙古锡盟地区酸马奶中分离出的8株乳酸菌和7株酵母菌进行潜在共生菌的筛选。在各自培养基中交互添加代谢物作为实验组,以各自培养基中添加等量生理盐水作为对照,分析比较稳定期的浊度值。筛选出3对具有相互促进作用的乳酸菌(LC)和酵母菌(YE)：LC1和YE3,LC4和YE3,LC5和YE4,其中LC5和YE4相互促进作用极显著(P＜0.01)。LC5和YE4在脱脂乳培养基中共同培养和二者在各自培养基中交互添加代谢物培养都表明其具有相互促进作用,YE4的代谢物促进LC5的生长,使LC5发酵液的滴定酸度值增大,而对pH值变化没有影响;LC5的代谢物促进YE4的生长,使YE4发酵液pH值增大,接近酵母菌最适生长pH值。     

酸马奶中乳酸菌与酵母菌的共生发酵特性

对内蒙古锡盟地区酸马奶中分离出的1株乳酸菌和1株酵母菌进行混合培养,初步确定双菌混合发酵的最佳培养条件：双菌发酵计数乳酸菌活菌数的最佳发酵温度为30℃摇床培养12h再转到37℃静置培养,最佳发酵时间为20h,脱脂乳中添加的营养成分最优配方为蛋白胨1g/100mL、蔗糖0.5g/100mL、酵母浸粉0.5g/100mL;双菌发酵计数酵母菌活菌数的最佳发酵温度为37℃静置培养8h再转到30℃摇床培养,最佳发酵时间为32h,脱脂乳中添加的营养成分最优配方为蛋白胨0.5g/100mL、蔗糖0.5g/100mL、酵母浸粉0.5g/100mL;选用乳酸菌与酵母菌质量比1:1作为菌种配比。 同时在最佳生长条件下探讨乳酸菌与酵母菌的相互作用关系以及后发酵对二者共生作用的影响,结果表明,促进乳酸菌生长的活性物质生成的时间为12h以前(即将酵母菌在5号配方中30℃摇床培养),促进酵母菌生长的活性物质生成的时间应为16h以前(即将乳酸菌在1号配方中37℃静置培养),在后发酵过程中,乳酸菌与酵母菌双菌培养的活菌数都极显著高于单菌培养(P＜0.01)。     

Fermented milk obtained with kefir grains as an ingredient in breadmaking

The objectives of this research were to study the effect of the addition of lyophilised kefir milk to premixes for household production of bread and evaluate the quality attributes of them. Four lyophilised samples were obtained from the followings: skim milk, acidified skim milk, fermented skim milk and neutralised fermented skim milk. Breads were prepared with commercial wheat flour, lyophilised milk samples and yeast through a straight dough process. Quality was assessed through loaf volume, crumb porosity and moisture, crumb texture and crust colour. Changes in texture and starch recrystallisation by X‐ray diffractometry were determined after 1 and 3 days of storage at room temperature. Breads with acidified milks showed the highest specific volumes and crumbs with the best texture properties. Crystallinity in bread with fermented milks was higher than for skim milk sample. This would indicate that there would be a certain effect of the type of milk processing on the promotion of starch retrogradation.     

Proteins recovered from acid whey/skim milk mixtures heated at alkaline pH values

Skim milk and mixtures prepared by combining acid whey with skim milk at volume ratios of 2:1, 1:1, 1:2, 1:3 and 1:4 were adjusted to pH 7.5 and heated at 90°C × 15 min. Protein was isolated from these heated samples by precipitation at pH 4.6 and it was found that 65% of the whey protein was recovered in each case. Non-recovered proteins included the proteose peptones and small quantities of β-lactoglobulin, α-lactalbumin and bovine serum albumin. The solubility of these isolates, which contained from 10–25% whey protein, decreased to > 95% when the whey protein exceeded ˜16%. Further characterization of the isolate, prepared from the 1:1 volume ratio of acid whey and skim milk, showed that ˜50% of the whey protein was insoluble, bound to casein and non-functional while the other ˜50% was complexed with casein and was soluble. The addition of a reducing agent suggests that sulphydryl bonding alone is not responsible for complex formation.     

Preparation of a Yogurt-like Product Containing Egg White

The fermentation of liquid egg white by lactic acid bacteria, Lactobacillus bulgaricus and Streptococcus thermophilus , to develop a new yogurt-type product has been studied. Egg white was prepared by pasteurization, blending, and neutralization to minimize antimicrobial activity, and by combining additives to make the media more suitable for growth of lactic acid bacteria. Skim milk, gums (guar gum, CMC, xanthan gum), soymilk, and glucose were studied. Optimum results were obtained when 47.4% egg white was combined with 28.4% alkali treated soymilk. 19.0% skim milk. 1.9% glucose, 2.8% sucrose, 0.5% xanthan gum, and 0.01% vanilla extract. The composition per 100 gram of the final product included 7.52% protein, 0.57% fat, and 62 calories. Microbiological and sensory tests showed the product to be free of pathogens and to have an extended shelf life at refrigeration temperature.     

Effect of thermophilic lactic acid bacteria on the viability of Salmonella serovar Typhimurium PT8 during milk fermentation and preparation of buffalo's yogurt

Viability of dairy-borne Salmonella enterica ssp. enterica serovar Typhimurium PT8 was studied during the fermentation of skim milk by thermophilic lactic acid bacteria (LAB). Longer generation times of Salmonella were found in mixed cultures of skim milk containing Streptococcus thermophilus, Lactobacillus delbrueckii ssp. bulgaricus or a mixture of them (1:1), as compared with single cultures of the pathogen. Salmonella was less able to survive in mixed cultures with these LAB during prolonged incubation at 41°C and also during cold storage of the fermented milk. L actobacillus ssp. bulgaricus and its mixture with S. thermophilus were more inhibitory to the growth and survival of Salmonella than was S. thermophilus . This was associated with higher ability of L . ssp. bulgaricus and the mixture to develop acidity in milk than S. thermophilus . Examining the antibacterial activity of these LAB towards Salmonella showed that other factors including heat-resistant and heat-labile compounds were involved in inhibiting the pathogen by these cultures. The viability of the same Salmonella strain during the preparation and cold storage of buffalo's yogurt was also examined. Salmonella was found to survive longer in yogurt made with starter containing probiotic bacteria than in that prepared with the traditional starter. This was ascribed to the development of lower pH by the traditional starter.     

Cottage Cheese from Ultrafiltered Skim Milk Retentates in Industrial Cheese Making

Ultrafiltered skim milk retentates were transported to a large industrial cottage cheese plant for milk supplementation leading to cottage cheese. The resulting industrial products were observed for composition, yields, whey component losses, and quality.Ten lots of small curd cottage cheese were made in vats containing up to 6593 kg skim milk. Retentate supplemented skim milks, concentrated approximately 10% (1.1:1) and 20% (1.2:1) in total protein, were very similar in initial composition to the controls. Mean cheese yield values from milks supplemented to 1.2:1 total protein were significantly higher than mean unsupplemented control milk values. Cheese yield efficiencies, per kilogram total solids, were also significantly higher in the retentate cheese but not when calculated per kilogram total protein.Total solids, total protein, and ash were higher in cottage cheese wheys from retentate supplemented cheese and were directly related to retentate supplementation concentration. Mean whey component loss per kilogram cheese exhibited significant decreases from milks of higher retentate supplementation. Retentate supplemented skim milk produced industrial cottage cheese of comparable quality to cheese made from unsupplemented control skim milks.