嗜热链球菌和保加利亚乳杆菌混菌生物膜发酵特性及其抗逆性

利用扫描电子显微镜对嗜热链球菌(Streptococcus thermophilus)和保加利亚乳杆菌(Lactobacillus bulgaricus)在不锈钢网布及椰果粒表面形成的混菌生物膜进行观察,并对不锈钢网布表面混菌生物膜发酵特性及其抗逆性进行研究。结果表明:Streptococcus thermophilus和Lactobacillus bulgaricus可在两种载体表面形成典型的混菌生物膜结构,且不锈钢网布表面混菌生物膜的发酵液菌体密度变化曲线与细菌S型生长曲线相似,但在停滞期和对数期不明显,发酵液pH值呈现先下降后趋于平稳的趋势,终止pH值接近4.0;此外,不锈钢网布表面混菌生物膜比游离乳酸菌具有更强的抗性,并且可在15d内稳定地释放较高浓度的游离乳酸菌。     

椰果表面混菌生物膜培养条件优化

为了探明椰果表面混菌生物膜的最优培养条件,采用单因素和正交实验法对保加利亚乳杆菌(Lactobacillus bulgaricus)和嗜热链球菌(Streptococcus thermophilus)在椰果表面形成的混菌生物膜的培养条件进行优化。分别选取培养时间、培养温度、固液比、接种量四个因素。研究结果表明,四个因素对椰果表面形成的混菌生物膜上活菌数的影响效果为:培养温度>培养时间>固液比>接种量。椰果表面混菌生物膜培养条件的优化结果为:培养时间2.5d,培养温度为37℃,椰果与MRS液体培养基组成比例为1∶30(g/mL),接种量为2%。在此培养条件下培养的混菌生物膜,其活菌数达到最大值,为5.79×108CFU/cm2。     

新疆伊犁地区乳制品中乳酸菌发酵和益生特性及其复合发酵方案优化

对7株实验室保存的优良乳酸菌在酸乳发酵过程中的酸化能力、产香能力以及酸乳质构进行测定,并通过抑菌、胃肠液耐受性以及抗生素敏感性等实验探究菌株的益生特性,筛选其中性能较优良的菌株进行组合复配,以获得最优的复合发酵菌株组合方案。单菌株发酵实验结果表明乳明串珠菌Leuconostoc lactis XKN1-5、乳杆菌属Lactobacillus delbrueckii subsp. bulgaricus BSTS6-4凝乳时间短(7 h左右),酸乳酸度可达96°T,酸化能力较其他菌株好;L. delbrueckii subsp. bulgaricus BSTS6-3、Streptococcus thermophilus XSXN1-2发酵制得的酸奶质构特性较好;L. delbrueckii subsp. bulgaricus BSTS6-1、S. thermophilus XSXN1-1产香性能最优,其中菌株XSXN1-1双乙酰质量浓度达到2.02 mg/L,乙醛质量浓度可达16 mg/L,能够明显改善酸奶的风味。益生实验结果表明,乳杆菌菌株Lactobacillus fermentum BST2-3、L. delbrueckii subsp. bulgaricus(BSTS6-1、BSTS6-3、BSTS6-4)能够抑制肠道致病菌的生长;L. fermentum BST2-3、L. delbrueckii subsp. bulgaricus(BSTS6-1、BSTS6-4)的黏附性较好;L. fermentum BST2-3在模拟胃肠液处理9 h后活菌数仍可达10~6 CFU/mL;且7株乳酸菌对大部分所试抗生素表现出敏感,安全性较高。最后按照产酸、产香、质构以及益生特性将菌株分类并进行酸乳复合发酵,获得复合发酵的最优菌株组合为菌株L. delbrueckii subsp. bulgaricus(BSTS6-4、BSTS6-3)、S. thermophilus XSXN1-1、L. fermentum BST2-3。     

丁二酮乳酸乳球菌发酵对羊奶脂肪酸组成影响分析

为研究乳酸乳球菌乳酸亚种丁二酮变种(Lactococcus lactis ssp.Lactis biovar diacetylactis)在单菌发酵,或与嗜热链球菌(Streptococcus thermophilus)和保加利亚乳杆菌(Lactobacillus bulgaricus)混合发酵条件下对羊奶中脂肪酸含量影响情况,利用气相色谱法进行脂肪酸分析,结果表明:L.diacetylactis发酵显著提高了羊奶中、短链脂肪酸百分含量,降低了长链脂肪酸百分含量(p<0.05);L.diacetylactis接种量对发酵羊奶成品中脂肪酸组成影响不显著;L.diacetylactis与S.thermophilus、L.bulgaricus混合发酵羊奶中脂肪酸组成不受S.thermophilus、L.bulgaricus影响。因此,L.diacetylactis发酵适用于开发风味良好、营养合理的酮香型羊奶保健品。     

SPME-GC-MS结合ROAV分析单菌及复配发酵牛乳中关键性风味物质

采用固相微萃取-气相色谱-质谱联用技术检测分析Streptococcus thermophilus与Lactobacillus delbrueckii subsp.bulgaricus单菌及复配发酵牛乳中的挥发性风味物质,结合相对气味活度值(relative odor activity value,ROAV)探讨发酵牛乳中关键性风味物质。结果表明:本实验共鉴定出100种挥发性风味物质,包括酸类、酮类、醛类、醇类、酯类、烷烃类和芳香族类化合物等。主成分分析表明,表征S.thermophilus单菌发酵乳的关键性风味物质是双乙酰、正壬醛和甲苯;表征L.bulgaricus单菌发酵乳的关键性风味物质是正庚醛、丁酸-2-甲基丙酯和1-庚醇;表征S.thermophilus与L.bulgaricus复配发酵乳的关键性风味物质是乙醛、3-甲基正丁醛、乙偶姻、2-壬酮、2-庚酮、醋酸乙烯酯、碳酸庚基苯基酯、甲酸乙烯酯和2-壬醇。相较于单菌发酵,复配发酵的风味物质组成、各组分相对含量及关键性风味物质均发生改变。     

芹菜IDF 与多菌群益生菌连续共培养的培养物特性

该研究利用生物膜富集微生物的原理,以芹菜中的水不溶性膳食纤维（insoluble dietary fiber,IDF）为载体,保加利亚乳杆菌Lactobacillus bulgaricus(Lb G302)、植物乳杆菌L. plantarum(Lp G304)、副干酪乳杆菌L. paracasei(Lcp G305)、鼠李糖乳杆菌L. rhamnosus(Lr G306)、嗜热链球菌Streptococcus thermophilus(St Q305)为菌株,MRS为营养液,在自主设计的富集培养装置中,富集芹菜IDF中多菌群益生菌,形成富含芹菜IDF与多菌群益生菌的生物膜培养物,研究该生物膜培养物的活菌数、菌群结构、代谢物组成、对消化液的耐受性以及抗氧化活性等。结果表明,37℃富集培养7 d,活菌数可达7.5×1013CFU/g;扫描电镜显示芹菜IDF上形成了较厚的生物膜;0～7 d的Illumina NovaSeq高通量测序分析表明,所接种的乳杆菌和链球菌均被检出;7 d的代谢组学分析结果显示,检出的代谢物有1 398种,其中主要功能物质有神经递质、维生素和辅酶类、肽类等;对DPPH...     

益生菌Lactobacillus plantarum P8与Streptococcus thermophilus混合发酵对发酵乳品质的影响

将益生菌Lactobacillus plantarum P8以不同接种比例分别与Streptococcus thermophilus ND03、ND05和ND07复配发酵牛乳,并以S.thermophilus单菌发酵为对照.于0h、发酵结束(pH=4.5)及4℃冷藏24 h,分别测定发酵乳样品的发酵时间,及pH值、黏度、脱水收缩率和活菌数并进行感官鉴评.结果表明,L.plantarum P8与S.thermophilus ND03复配,发酵时间显著高于其他组,各组样品黏度和脱水收缩率差异不显著；L.plantarum P8与S.thermophilus ND05分别以5×106 mL-1接种1∶1复配时,样品中L.plantarum P8的活菌数为5.26×107mL-1,酸度适宜,无乳清析出,有良好的黏度,产品风味较好,将该组合应用于发酵乳生产,较可行.     

培养条件对奇异变形杆菌生物膜生长的影响

采用改良微孔板培养,结晶紫染色、平板计数以及电镜扫描方法研究不同初始菌浓度、培养环境(温度、气体环境)、培养基成分(pH、氯化钠浓度、碳源种类和浓度),培养基用量及接触材料对奇异变形杆菌(Proteus mirabilis,P. mirabilis)生物膜生长的影响。经过24 h培养,初始菌浓度10 CFU/cm2时,生物膜形成量较低,初始菌浓度102~108 CFU/cm2时,生物膜形成量明显;37 ℃有氧条件适宜P. mirabilis生物膜形成;培养基组成(2.0% NaCl,1.0%麦芽糖,pH8.0)和加倍用量对P. mirabilis生物膜形成具有明显的促进作用;粗糙的木制表面最易使P. mirabilis粘附并形成生物膜,硅胶次之,聚丙烯塑料和盖玻片表面比较光滑,菌体不易粘附,生物膜难以形成;不同接触材料形成的P. mirabilis生物膜结构和形态不同,硅胶上生物膜为蘑菇状,盖玻片上生物膜成扁平状。本文研究结果可为食品生产加工过程中P. mirabilis污染防控提供理论依据和技术支撑。     

豆汁的加工工艺研究

以绿豆为原料,选取加水比例、加菌量、发酵时间3个因素,采用单因素和正交实验获得豆汁最佳工艺参数,为今后豆汁产品的生产提供参考。研究结果表明,在豆水比1∶10,加菌量1.676×107CFU/mL,发酵时间24h的条件下,豆汁的可溶性固形物达到1.002%,酸度为10.92g/kg,微生物浓度7.38×107CFU/mL,可溶性蛋白质含量达40.104g/L。     

甘孜藏族自治州传统牦牛发酵乳中乳酸菌的分离鉴定及多样性分析

从甘孜藏族自治州11个县采集40份传统牦牛发酵乳样品,采用稀释倾注法分析乳酸菌数量,通过选择性分离,采用生化试验与16S r DNA基因序列测定方法分析传统牦牛发酵乳中乳酸菌的多样性。结果表明:甘孜地区乳酸菌平均含量在(6.48~7.90)lg CFU/mL,共分离出乳酸菌78株,其中乳杆菌属(Lactobacillus)43株、明串珠菌属(Leuconostoc)3株、肠球菌属(Enterococcus)15株、链球菌属(Streptococcus)12株、片球菌属(Lactococcus)5株,鉴定出的种或亚种分别是:L.delbrueckii subsp.bulgaricus、L.helveticus、L.fermentum、L.casei、L.plantarum、L.brevis、P.acidilactici、Leu.mesenteroides subsp.mesenteroides、E.faecalis、E.faecium和S.thermophilus,其中嗜热链球菌12株,占菌株总数15.38%,为甘孜地区优势菌,分离出肠膜明串珠菌肠膜亚种3株,在乳酸菌分离株中所占比例最小,仅为3.85%。     

不同环境条件对隆德假单胞菌生物被膜形成能力的影响

为研究环境条件对食品腐败菌隆德假单胞菌（Pseudomonas lundensis,PL）生物被膜形成能力的影响,采用微孔板结晶紫法测定不同的营养条件、接种浓度、pH、NaCl和Mg2+浓度条件下其生物被膜量,用激光共聚焦扫描显微镜观测其在不锈钢材料上的黏附和结构特征。结果表明,PL生物被膜的形成量在营养胁迫下降低,稀释TSB培养基50倍造成的营养胁迫使其生物被膜量从1.75±0.35降低至0.24±0.17。PL接种量从1.3×107 CFU/mL降至2.5×104 CFU/mL时,其生物被膜的形成量无显著差异（P>0.05）,在pH为8.0时PL形成生物被膜量最多,1.25%以上的葡萄糖、4%以上的NaCl和0.5%的Mg2+能够显著（P<0.05）抑制PL生物被膜的形成。激光共聚焦显微镜观测结果表明该菌在一定浓度下具有在不锈钢表面形成典型生物被膜的能力。PL生物被膜形成能力受营养条件、葡萄糖浓度、pH、NaCl浓度、Mg2+等环境因子的影响。     

Effect of surface roughness and stainless steel finish on Listeria monocytogenes attachment and biofilm formation

The purpose of this study was to evaluate the effect of surface roughness (Ra) and finish of mechanically polished stainless steel (Ra = 0.26 +/- 0.05, 0.49 +/- 0.10, and 0.69 +/- 0.05 microm) and electropolished stainless steel (Ra = 0.16 +/- 0.06, 0.40 +/- 0.003, and 0.67 +/- 0.02 microm) on Listeria adhesion and biofilm formation. A four-strain cocktail of Listeria monocytogenes was used. Each strain (0.1%) was added to 200 ml of tryptic soy broth (TSB), and coupons were inserted to the mixture for 5 min. For biofilm formation, coupons with adhesive cells were incubated in 1:20 diluted TSB at 32 degrees C for 48 h. The experiment was performed by a randomized block design. Our results show that the level of Listeria present after 48 h of incubation (mean = 7 log CFU/cm2) was significantly higher than after 5 min (mean = 6.0 log CFU/cm2) (P < 0.01). No differences in initial adhesion were seen in mechanically finished (mean = 6.7 log CFU/cm2) when compared with electropolished stainless steel (mean = 6.7 log CFU/cm2) (P > 0.05). Listeria initial adhesion (values ranged from 5.9 to 6.1 log CFU/cm2) or biofilm formation (values ranged from 6.9 to 7.2 log CFU/cm2) was not significantly correlated with Ra values (P > 0.05). Image analysis with an atomic force microscope showed that bacteria did not colonize the complete surface after 48 h but were individual cells or grouped in microcolonies that ranged from 5 to 10 microm in diameter and one to three cell layers in thickness. Exopolymeric substances were observed to be associated with the colonies. According to our results, electropolishing stainless steel does not pose a significant advantage for food sanitation over mechanically finished stainless steel.     

Salmonella enterica Enteritidis biofilm formation and viability on regular and triclosan-impregnated bench cover materials

Contamination of food contact surfaces by microbes such as Salmonella is directly associated with substantial industry costs and severe foodborne disease outbreaks. Several approaches have been developed to control microbial attachment; one approach is the development of food contact materials incorporating antimicrobial compounds. In the present study, Salmonella enterica Enteritidis adhesion and biofilm formation on regular and triclosan-impregnated kitchen bench stones (silestones) were assessed, as was cellular viability within biofilms. Enumeration of adhered cells on granite, marble, stainless steel, and silestones revealed that all materials were prone to bacterial colonization (4 to 5 log CFU/cm(2)), and no significant effect of triclosan was found. Conversely, results concerning biofilm formation highlighted a possible bacteriostatic activity of triclosan; smaller amounts of Salmonella Enteritidis biofilms were formed on impregnated silestones, and significantly lower numbers of viable cells (1 × 10(5) to 1 × 10(6) CFU/cm(2)) were found in these biofilms than in those on the other materials (1 × 10(7) CFU/cm(2)). All surfaces tested failed to promote food safety, and careful utilization with appropriate sanitation of these surfaces is critical in food processing environments. Nevertheless, because of its bacteriostatic activity, triclosan incorporated into silestones confers some advantage for controlling microbial contamination.     

Modelling the survival of starter lactic acid bacteria and Bifidobacterium bifidum in single and simultaneous cultures

The inactivation kinetics at 4 degrees C of Bifidobacterium bifidum, Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus, cultured alone or consociated in a laboratory medium (modified MRS broth), were modelled through the Weibull model and a second-order polynomial equation. The initial cell number of S. thermophilus and L. delbrueckii subsp. bulgaricus was approximately 6-7log (CFU/ml); the viability loss after 30 days of storage was 2.87 and 1.99log (CFU/l) for L. delbruckii subsp. bulgaricus and S. thermophilus, cultured alone, respectively; whereas the consociation of lactobacilli and streptococci with bifidobacteria reduced viability loss during storage (0.28 and 0.54log CFU/l for lactobacilli and streptococci, respectively). Finally, the consociation of lactobacilli and streptococci with B. bifidum improved their oxygen uptake.     

Behavior of Listeria monocytogenes in a Pseudomonas putida biofilm on a condensate-forming surface

Listeria monocytogenes has been isolated from condensate-forming surfaces in food processing plants. The objective of this research was to observe the behavior of L. monocytogenes on condensate-covered stainless steel with a Pseudomonas putida biofilm. L. monocytogenes-containing biofilms, either with or without added chicken protein, were incubated in a high humidity chamber at 12 degrees C to allow formation of condensate. Samples were analyzed for attached and unattached L. monocytogenes and total plate count periodically for 35 days. Samples were also taken for microscopic observation of Listeria and bacterial extracellular polymeric substances (EPS). L. monocytogenes attached in significantly greater numbers (> 3-log difference) to surfaces with preexisting P. putida biofilms than to Pseudomonas-free surfaces. L. monocytogenes survived in the presence or absence of P. putida with no added nutrients for 35 days, with numbers of survivors in the range of 3 to 4 log CFU/cm2 in the presence of P. putida and less than 2.9 log CFU/cm2 in pure culture. Attached and unattached L. monocytogenes were at similar levels throughout the incubation under all conditions studied. The addition of protein to the biofilms allowed growth of L. monocytogenes in pure culture during the first 7 days of incubation. Numbers of L. monocytogenes were not affected by the presence of P. putida when protein was present. Unattached L. monocytogenes were at levels of 3.6 to 6.7 log CFU/cm2 on the protein-containing surfaces. Microscopic observation of the condensate-covered biofilms indicated that L. monocytogenes formed microcolonies embedded within an EPS matrix over a 28-day period. This research demonstrates that L. monocytogenes can survive on condensate-forming stainless steel in low and high nutrient conditions, with or without the presence of Pseudomonas biofilm. The Listeria can detach and, therefore, have the potential to contaminate product.     

Survival of foodborne pathogens on stainless steel surfaces and cross-contamination to foods

The retention of bacteria on food contact surfaces increases the risk of cross-contamination of these microorganisms to food. The risk has been considered to be lowered when the surfaces are dry, partly because bacterial growth and survival would be reduced. However, some non-spore-forming bacteria might be able to withstand dry conditions on surfaces for an extensive period of time. In this study the survival of Salmonella enteritidis, Staphylococcus aureus and Campylobacter jejuni on stainless steel surfaces at different initial levels was determined at room temperature. The transfer rates of these pathogens from kitchen sponges to stainless steel surfaces and from these surfaces to foods were also investigated. Staph. aureus was recovered from the surfaces for at least 4 days when the contamination level was high (10(5) CFU/cm2) or moderate (10(3) CFU/cm2). At low levels (10 CFU/cm2), the surviving numbers decreased below the detection limit (4 CFU/100 cm2) within 2 days. S. enteritidis was recovered from surfaces for at least 4 days at high contamination levels, but at moderate level, the numbers decreased to the detection limit within 24 h and at low level within 1 h. C. jejuni was the most susceptible to slow-air-drying on surfaces; at high contamination levels, the numbers decreased below the detection limit within 4 h. The test microorganisms were readily transmitted from the wet sponges to the stainless steel surfaces and from these surfaces to the cucumber and chicken fillet slices, with the transfer rates varied from 20% to 100%. This study has highlighted the fact that pathogens remain viable on dry stainless steel surfaces and present a contamination hazard for considerable periods of time, dependent on the contamination levels and type of pathogen. Systematic studies on the risks of pathogen transfer associated with surface cleaning using contaminated sponges provide quantitative data from which a model of risks assessment in domestic setting could lead.     

模糊综合评判结合响应面法优化鹰嘴豆酸奶发酵工艺

以鹰嘴豆、椰浆为主要原料,白砂糖为辅料,嗜热链球菌(Streptococcus thermophilus)、保加利亚乳杆菌(Lactobacillus bulgaricus)为发酵菌种,制备鹰嘴豆酸奶。以持水力及感官评分的模糊综合评判值为评价指标,采用单因素试验及响应面法对其发酵工艺进行优化。结果表明,鹰嘴豆酸奶的最佳发酵工艺为鹰嘴豆浆添加量68%、椰浆添加量16%、白砂糖添加量7%,在42℃条件下发酵7 h,其口感嫩滑,酸甜可口,具有独特风味,感官评分为89.20分,持水力为57.39%,模糊综合评判值为0.97,其乳酸菌活菌数(8.33×10⁶ CFU/g)、糖度(7.17°Bx)、蛋白质含量(2.14 g/100 g)、pH(4.22)均符合中国卫生监督协会发布的团体标准T/WSJD 12—2020《植物蛋白饮料植物酸奶》中对复合植物酸奶的品质指标要求。     

Effect of temperature, pH, and water activity on biofilm formation by Salmonella enterica enteritidis PT4 on stainless steel surfaces as indicated by the bead vortexing method and conductance measurements

An assay was developed in an effort to elucidate the effect of important environmental parameters (temperature, pH, and water activity [aw]) on Salmonella Enteritidis biofilm formation on stainless steel surfaces. To achieve this, a modified microbiological technique used for biofilm studying (the bead vortexing method) and a rapid method based on conductivity measurements were used. The ability of the microorganism to generate biofilm on the stainless surfaces was studied at three temperatures (5, 20, and 37 degrees C), four pH values (4.5, 5.5, 6.5, and 7.4), and four aw values (0.5, 1.5, 5.5, and 10.5% NaCl). Results obtained by the bead vortexing method show that maximum numbers of adherent bacteria per square centimeter (106 CFU/cm2) were attained in 6 days at 20 degrees C. Biofilm formation after 7 days of incubation at 20 degrees C was found to be independent of the pH value. In addition, the high concentration of sodium chloride (10.5% NaCl, aw = 0.94) clearly inhibited the adherence of cells to the coupons. Conductance measurements were used as a supplementary tool to measure indirectly the attachment and biofilm formation of bacterial cells on stainless steel surfaces via their metabolic activity (i.e., changes in the conductance of the growth medium due to microbial growth or metabolism). Results obtained by conductance measurements corresponded well to those of the bead vortexing method. Furthermore, we were able to detect cells that remained attached on the metal surfaces even after vortexing via their metabolic activity. The results, except for demonstrating environmental-dependent Salmonella Enteritidis biofilm formation, indicated that traditional vortexing with beads did not remove completely biofilm cells from stainless steel; hence, conductance measurements seem to provide a more sensitive test capable to detect down to one single viable organism.     

A psychrotrophic Burkholderia cepacia strain isolated from refrigerated raw milk showing proteolytic activity and adhesion to stainless steel

The proteolytic activity of a psychrotrophic strain of Burkholderia cepacia isolated from refrigerated raw milk was characterized. Bur. cepacia produced proteolytic activity during growth at refrigeration temperature, with maximum activity at pH 6-7. The enzyme showed relative thermal stability in the range 40-50°C during 25 min, and maintained 80% its initial activity at 76°C/30 s. Milk coagulation assay showed that the crude protease from Bur. cepacia caused coagulation from day 2 for skimmed milk, whereas coagulation was observed from day 5 for whole milk. The adherence of this strain to stainless steel was evaluated, and the substrata had around 107 CFU/cm2 after 15 to 60 min incubation. Results on biofilm development suggest that this bacterium could adhere and to form biofilms even at refrigeration temperatures. These results indicate that Bur. cepacia may represent a potential hazardous to milk and dairy products.     

Effect of carbon dioxide under high pressure on the survival of cheese starter cultures

A new processing method that rapidly forms curds and whey from milk has the potential to improve cheesemaking procedures if cheese starter cultures can tolerate the processing conditions. The survival of Lactobacillus delbrueckii ssp. bulgaricus, Lactococcus lactis ssp. lactis, or Streptococcus thermophilus through this new process was evaluated. Inoculated milk containing 0, 1, or 3.25% fat or Lactobacillus MRS broth or tryptone yeast lactose broth (depending on microorganism used) was sparged with CO2 to a pressure of 5.52 MPa and held for 5 min at 38 degrees C. Broth contained 7.93 to 8.78 log CFU/ ml before processing and 7.84 to 8.66 log CFU/ml afterward. Before processing, milk inoculated with L bulgaricus, L. lactis, or S. thermophilus contained 6.81, 7.35, or 6.75 log CFU/ml, respectively. After processing, the curds contained 5.68, 7.32, or 6.50 log CFU/g, and the whey had 5.05, 6.43, or 6.14 log CFU/ml, respectively. After processing, the pHs of control samples were lower by 0.41 units in broth, 0.53 units in whey, and 0.89 units in curd. The pH of the processed inoculated samples decreased by 0.3 to 0.53 units in broth, 0.32 to 0.37 units in whey, and 0.93 to 0.98 units in the curd. Storing curds containing L. lactis at 30 degrees C or control curds and curds with L. bulgaricus or S. thermophilus at 37 degrees C for an additional 48 h resulted in pHs of 5.22, 5.41, 4.53, or 4.99, respectively. This study showed that milk inoculated with cheese starter cultures and treated with CO2 under high pressure to precipitate casein-produced curds that contained sufficient numbers of viable starter culture to produce lactic acid, thereby decreasing the pH.