蜂蜜酸奶发酵过程中乳酸菌生长动力学的初步研究

本文研究了蜂蜜酸奶发酵过程中乳酸菌双菌的生长规律,同时研究了活菌数、pH、乳酸含量和还原糖转化率与时间变化的相关性。研究表明:在乳酸发酵过程中,保加利亚乳杆菌和嗜热链球菌的生长动力学性质满足典型对数生长曲线规律,且证实了两者之间存在共生作用;并建立了发酵过程中保加利亚乳杆菌和嗜热链球菌的数学模型,确定了世代时间大约为9.3-29.1min;随着发酵的进行,乳酸含量不断增大,体系的pH逐渐下降,还原糖转化率持续升高,在4h达到最高后下降。     

耐酸耐氧双歧杆菌单菌联菌酸奶发酵研究

利用耐酸耐氧双歧杆菌进行了单菌酸奶和联菌酸奶发酵实验,优化出工艺条件.双歧杆菌单菌酸奶,发酵温度37℃,以5%体积比接种双歧杆菌,5%质量比添加蔗糖,在8h内凝乳,酸奶酸度可达80°T,活菌数>10°cfu/mL;双歧杆菌与乳酸菌混合发酵联菌酸奶,双歧杆菌与乳酸菌菌数比1:1,以5%体积比总接种量接种,发酵温度37℃,在4.5h内凝乳,酸度平均在85.T,总活菌数>1×109cfu/mL;双歧杆菌与乳酸菌分别发酵的酸奶,以体积比1:1配比后酸奶口味较佳.     

凝固型绵羊奶酸奶的发酵特性及活菌数变化

研究凝固型的绵羊奶与牛奶酸奶发酵特性和贮存期特性,利用pH计、酸度滴定、质构仪、电子舌、活菌计数及感官评价对其pH值、滴定酸度、质构特性、味觉特点、活菌数和感官评分进行分析。结果表明：在发酵过程中绵羊奶与牛奶有相同的pH值变化规律,即前2.5 h下降非常缓慢,之后迅速下降,在凝乳前0.5 h下降变缓直到凝乳结束,达到发酵终点的时间分别为5 h和4.5 h;在4 ℃贮存0～24 d期间,酸奶的pH值都在逐渐下降,牛奶酸奶比绵羊奶酸奶下降更大;滴定酸度方面起始时绵羊奶比牛奶高,达到发酵终点时也明显高于牛奶;质构测定结果为YSM（添加益生菌干酪-张发酵的凝固型绵羊奶酸奶）、JDM（嗜热链球菌与保加利亚乳杆菌共同发酵的经典凝固型绵羊奶酸奶）具有更高的硬度和稠度,黏聚性和黏性指数也显著高于JDN（嗜热链球菌与保加利亚乳杆菌共同发酵的经典凝固型牛奶酸奶）,奶的种类为影响酸奶硬度、稠度、黏聚性和黏性指数的主要因素,益生菌干酪-张的添加对这些指标的影响很小;电子舌测定结果为丰富性味感值绵羊奶酸奶明显高于牛奶酸奶,酸感值则低于牛奶酸奶,甜、苦、咸、涩、鲜感值差异不明显;感官评价方面绵羊奶酸奶综合评分高于牛奶酸奶,差异性主要体现在滋味、组织状态和喜爱程度上,在色泽和气味方差异不明显;在4 ℃、21 d贮存期间酸奶的活菌数都在逐渐降低,添加益生菌干酪-张的绵羊奶酸奶活菌数最多,第21天时活菌数分别是普通绵羊奶酸奶和牛奶酸奶的10 倍和100 倍以上,干酪-张对绵羊奶酸奶4 ℃贮存期间活菌数的维持有较好作用。同时,实验结果表明：益生菌干酪-张可以作为发酵剂之一与经典的酸奶发酵剂嗜热链球菌和保加利亚乳杆菌搭配用于凝固型绵羊奶酸奶的制作,以增加其功能价值。     

干酪乳杆菌纯种发酵水苏糖合生元酸奶的菌种筛选与工艺

针对目前我国合生元功能性乳制品研发水平低，大多采用益生菌与传统酸奶菌混种发酵的现状，以分离自天然发酵食品、保健品和微生物制剂等的18株新型益生菌和3种商品化发酵剂中所含益生菌为试验菌株，以传统酸奶发酵菌株保加利亚乳杆菌和嗜热链球菌为对照菌株，研究菌株发酵牛乳的凝乳时间、产酸能力、感官品质，分析菌株利用水苏糖的增殖效果，筛选能利用水苏糖作为益生元生产合生元酸奶的益生菌菌株；测定了菌株在纯牛乳基础培养基中的生长曲线；研究了益生元增殖培养基中水苏糖的最适添加量；优化了水苏糖合生元酸奶产品的发酵工艺条件；检测了0 d和贮藏21 d合生元酸奶产品的质量。结果表明：新型益生菌干酪乳杆菌07-211具有发酵牛乳的能力，可利用水苏糖进行显著增殖，活菌数由3.19×108 CFU/mL增至2.05×109 CFU/mL；益生元增殖培养基中水苏糖的最适添加量为0.8%；干酪乳杆菌07-211纯种发酵水苏糖合生元酸奶的最佳工艺条件是：接种量3%，蔗糖添加量4%，发酵温度42 ℃，合生元酸奶凝乳时间4.15 h，pH 4.65，滴定酸度64.27 °T，活菌数3.96×109 CFU/mL，感官品评得分8.78分（10分制）。其中，0 d和贮藏21 d的合生元酸奶的质量均优于国标。本研究结果为工业化生产干酪乳杆菌纯种发酵水苏糖合生元酸奶产品提供理论依据，也为其它功能性合生元乳制品的研发提供借鉴。     

几种乳酸菌的生理特性研究

本文研究了参与酸泡菜发酵生产的几种代表性乳酸菌:植物乳杆菌、肠膜明串珠菌、发酵乳杆菌和小片球菌的发酵产酸曲线和pH 曲线,并探讨了氯化钠与葡萄糖浓度对乳酸菌的生长与心酵产酸量的影响,以及乳酸菌的生长温度范围与耐乙醇的能力。     

发酵肉制品中乳酸菌的分离鉴定及菌种性能的研究

从自然发酵肉制品中分离乳酸菌并对其进行生化试验鉴定，对得到的乳酸菌进行了耐盐、耐亚硝酸盐、产酸能力、生长曲线及抑菌试验。通过分离和鉴定得到5株乳酸菌，3株为乳酸杆菌，2株为乳酸球菌；它们对食盐、亚硝酸盐均具有较好的耐受性，在6％的NaCl、80kg／mg-150kg／mgNaNO2溶液中能生长；对蛋白质，脂肪无分解作用。乳酸杆菌和乳酸球菌对大肠杆菌均有抑制作用，且杆菌的抑制作用大于球菌；乳酸杆菌与乳酸球菌的生长曲线和产酸特性不同，杆菌比球菌生长快，pH值下降快，所需的发酵时间比球菌短。5株乳酸菌都可作为肉制品的发酵剂。     

酪蛋白水解物对酸奶的影响研究

将酪蛋白水解物(含蛋白质7．6％)以2％(w／w)添加到奶液中混合发酵，做空白样对照。研究了二者发酵过程中各发酵参数的变化，并对二者的质构进行了分析比较。研究结果表明：酪蛋白水解物能明显促进酸奶发酵；促发酵作用随所添加的水解物水解程度提高而增强；添加酪蛋白水解物改变了酸奶发酵过程中的pH下降速度，在发酵中期二者的pH下降速度之间存在最大差距；质构分析表明添加2％酪蛋白水解物对酸奶整体质构有所改善。     

甘南牧区犏牛酸奶中优良乳酸菌的分离与鉴定

从甘南牧区采集的犏牛酸奶中分离得到76株乳酸菌。筛选得到3株凝乳快速、产酸力强、凝乳质地优良的乳酸菌菌株,包括1株球菌和2株杆菌。采用16S rRNA基因序列比对分析,鉴定3株乳酸菌分别是屎肠球菌(Enterococcus faecium)、德氏乳杆菌(Lactobacillus delbrueckii)和发酵乳杆菌(Lactobacillus fermentum)。通过球杆菌混合发酵实验,结果表明混合菌株发酵的产酸速率比单菌株发酵明显加快,且后酸化程度较弱,其感官质量也明显优于单菌发酵。     

植物乳杆菌ST-Ⅲ的生长特性与保存性能研究

对植物乳杆菌ST-Ⅲ与酸奶发酵剂在不同温度混合发酵时的生长特性以及在不同pH值发酵乳中的保存活性进行了研究。结果表明,与酸奶发酵剂在37℃或40℃混合发酵时,植物乳杆菌ST-III不出现明显生长,活菌数始终保持在5.0×106 mL-1左右;在酸奶冷藏(0~6℃)保存2周的过程中,植物乳杆菌ST-III具有良好的存活性能,酸奶的初始pH值(4.00~5.00)不影响其存活性能。     

酸奶冻干发酵剂制备中保加利亚乳杆菌不同菌株特性的研究

研究了不同来源的7株保加利亚乳杆菌在乳中的生长与发酵特性、后酸化活性以及抗冷冻干燥特性。结果表明,7菌株在乳中42℃发酵,L.b-S1和L.b-DR凝乳时间最短,为3 h,凝乳后的活菌数、pH值、滴定酸度均无显著差别,活菌数均达1×108 mL-1以上,pH值均达4.5～5.0,滴定酸度均达90～100°T;7菌株在发酵后的酸乳中冷藏期间,L.b-S1和L.b-DR的后酸化活性最低,4℃冷藏21 d,酸度上浮不足10°T,pH值下降0.2～0.4,活菌数下降1个log数量级左右;7菌株在以脱脂乳为保护剂的冷冻干燥试验中,L.b-S1抗冻干性最强,其次为L.b-DR,其冻干存活率分别达31.46%和20.39%。     

美国大杏仁风味酸乳的研制

将美国大杏仁浆添加到牛乳中,通过利用保加利亚乳杆菌和嗜热链球菌(1∶1)混合的发酵剂生产杏仁酸乳。通过正交试验得到的结果显示,杏仁酸乳优化发酵工艺参数如下:美国大杏仁浆和牛奶比例为2∶8,蔗糖8%,保加利亚乳杆菌和嗜热链球菌(1∶1)混合发酵剂2%,发酵温度42℃,发酵时间4.5h。结果表明通过优化制得的杏仁酸乳兼有杏仁和酸乳的营养与风味。     

自然发酵牛乳中乳酸菌和酵母菌的活菌动态变化

构建三批次各100 kg牛乳自然发酵体系，通过分析乳酸菌和酵母菌的活菌动态变化，对两者间的相互作用进行研究。结果表明，在（20±1）℃的自然发酵温度下，持续发酵56 h，pH值下降至4.6～5.0，发酵牛乳逐渐分层并形成上层奶嚼口和下层凝乳。连续三个批次发酵牛乳中奶嚼口和凝乳的乳酸菌平均活菌数分别为（12.02±1.21）lg（CFU/mL）和（11.54±1.30）lg（CFU/mL），差异不显著（P＞0.05）；而凝乳中酵母菌平均活菌数[（6.39±0.60）lg（CFU/mL）]显著低于奶嚼口[（4.56±0.30）lg（CFU/mL）]（P＜0.05）。活菌动态变化表明，在牛乳自然发酵过程中，乳酸菌的生长具有延迟期、对数期、稳定期三个典型阶段，而酵母菌没有明显的对数期，随着乳酸菌的生长反而抑制酵母菌的生长。     

乳酸菌混菌发酵制备豆清液多肽动力学模型的建立

为探究乳酸菌混菌发酵豆清液制备多肽的动态过程及钙螯合活性变化，建立描述菌体生长、多肽生成及蛋白质消耗动力学模型，测定了发酵过程中的pH值、蛋白酶酶活和钙螯合活力。结果表明，动力学模型具有良好可靠性；乳酸菌混菌发酵过程中多肽含量在对数期达到5.31 mg/mL，pH值下降至3.5左右后稳定；酸性蛋白酶酶活在4～8 h较高，最大酶活为3.6 U/mL；钙螯合活力总趋势为先升高后降低，在14 h达到最高值33.35%。     

牛奶发酵过程中阪崎克罗诺杆菌可形成活的非可培养状态

该研究以保加利亚乳杆菌为牛奶发酵剂,研究了牛奶发酵过程中阪崎克罗诺杆菌与保加利亚乳杆菌的相互作用以及阪崎克罗诺杆菌存活量的变化情况,并结合16S rDNA高通量测序技术和PMA-qPCR方法分析阪崎克罗诺杆菌在牛奶发酵过程中是否形成“活的非可培养”状态。结果显示,保加利亚乳杆菌在牛奶中发酵48 h后pH值可达到3.40,酸度值可达212.00。在发酵前期接种阪崎克罗诺杆菌,48 h后pH值和酸度值分别为3.50和193.30;在发酵中期接种阪崎克罗诺杆菌,48 h后pH值和酸度值分别为3.47和214.30。发酵前期阪崎克罗诺杆菌的污染对保加利亚乳杆菌发酵结果的影响更大。阪崎克罗诺杆菌在牛奶中生长48 h后菌浓度可稳定在9.08 lg(CFU/mL);不论在牛奶经发酵前期或中期接种阪崎克罗诺杆菌,发酵后期平板计数法均检测不到阪崎克罗诺杆菌,但16s rDNA和PMA-qPCR技术均可检测到阪崎克罗诺杆菌活菌的存在。该研究结果说明,阪崎克罗诺杆菌在牛奶发酵后进入了“活的非可培养”状态,该状态的存在会导致该菌检测时活菌数量的低估,从而引发乳及乳制品的安全隐患。     

Applicability of a bacteriocin-producing Enterococcus faecium as a co-culture in Cheddar cheese manufacture

Two strains, Enterococcus faecium RZS C5 and E. faecium DPC 1146, produce listericidal bacteriocins, so-called enterocins. E. faecium RZS C5 was studied during batch fermentation in both a complex medium (MRS) and in milk to understand the influence of environmental factors, characteristic for milk and cheese, on both growth and bacteriocin production. Fermentation conditions were chosen in view of the applicability of in situ enterocin production during Cheddar cheese production. Enterocin production by E. faecium RZS C5 in MRS started in the early logarithmic growth phase, and enterocin activity decreased during the stationary phase. The effect of pH on enterocin production and decrease of activity was as intense as the effect on bacterial growth. Higher enterocin production took place at pH 5.5 compared with pH 6.5. The use of lactose instead of glucose increased the production of enterocin, and at higher lactose concentration, production increased more and loss of activity decreased. The production in skimmed milk compared to MRS was lower and was detected mainly in the stationary phase. When casein hydrolysate was added to the milk, enterocin production was higher and started earlier, indicating the importance of an additional nitrogen source for growth of E. faecium in milk. For co-cultures of E. faecium RZS C5 with the starters used during Cheddar cheese manufacture, no enterocin activity was detected during the milk fermentation. Furthermore, the applicability of E. faecium RZS C5 and E. faecium DPC 1146 strains was tested in Cheddar cheese manufacture on pilot scale. Enterocin production took place from the beginning of the cheese manufacturing and was stable during the whole ripening phase of the cheese. This indicates that both an early and late contamination of the milk or cheese can be combated with a stable, in situ enterocin production. The use of such a co-culture is an additional safety provision beyond good manufacturing practices.     

枇杷酒醋化过程醋酸菌的生长、产酸及耗氧的关系

以枇杷果酒为原料,以沪酿1.01为发酵菌,研究了枇杷果醋酿造过程中菌株生长、产酸及耗氧的关系。结果表明,枇杷果醋发酵过程中菌株的生长可分为低菌量的对数增长期、醋化缓冲期、高菌量对数增长期和衰减期4个时期;高菌量对数增长期为主要产酸期,总酸含量与菌量的增长对数值呈线性相关;耗氧水平同产酸率、总酸含量与产酸率的交互项呈显著相关;影响耗氧水平的主要因素为产酸率,同时基质中总酸量越大,产酸所需的耗氧水平越高。     

Fermentation of reconstituted milk by Streptococcus thermophilus: Effect of irradiation on skim milk powder

The growth of Streptococcus thermophilus ST12 (ST12) in milk reconstituted from non-irradiated and irradiated at 10 kGy low-heat skim milk powders (RSM and irrRSM, respectively) at 40 °C was monitored by microcalorimetry. Statistically significant differences of the growth patterns of ST12 in RSM and irrRSM were found. Distinctively diauxic growth curves in RSM were replaced by one-stage growth curves in irrRSM. The final pH in RSM was 5.56 while in irrRSM samples it was 4.41. The time of initiation of gel formation was about 36 min shorter; however, the gels were considerably weaker in irrRSM than in RSM. The front-face fluorescence spectra were also used to characterise the differences in acidification processes. The microcalorimetric data together with the concentrations of metabolites determined during fermentation, rheological and fluorescence measurements indicated the substantial changes in the growth of ST12 in irrRSM in comparison with RSM.     

干酪乳杆菌对柑橘汁发酵的工艺研究

研究了干酪乳杆菌发酵柑橘汁的发酵过程.接入柑橘汁后的0～10h内干酪乳杆菌处于迟滞期;第10h开始发酵进入对数期,并在第52h结束,发酵终点的活菌数为1.31×109 cfu/mL;发酵液pH值从起点的6.11降至终点的3.69;发酵液最高总酸达到1.48 g/100mL.进一步研究了干酪乳杆菌营养源的优化,结果表明添...     

Effects of ultrasound on the fermentation profile and metabolic activity of lactic acid bacteria in buffalo's (Bubalus bubalis) milk

In this study, the ultrasound was applied at the lag phase and logarithmic phase of the growth of Streptococcus thermophilus subsp. Salivarius (6.76 ± 0.15 log cfu/mL) and Lactobacillus bulgaricus (6.36 ± 0.22 log cfu/mL) in buffalo's milk. The results revealed that S. thermophilus entered into the logarithmic phase after 45 min of incubation. Ultrasound application during lag phase (1685 J mL⁻¹) and logarithmic phase (561.6 J mL⁻¹) reduced the fermentation time by 32 min (12.5%) and 40 min (15.7%), respectively. Ultrasound treatment (1684.8 J mL^-1) during the lag phase resulted in fractures (approximately 0.1–0.2 μm) on the cell membrane of S. thermophilus. Application of ultrasound for a 2–6 min period enhanced (P < 0.05) the microbial growth while increasing (P < 0.05) the β-galactosidase activity. The lactose hydrolysis was increased up to 49.2% compared to that of the control. Ultrasound treatment during the lag phase showed higher (P < 0.05) storage modulus, yield point and consistency index compared to the logarithmic phase. It can be concluded that ultrasound has huge potential to improve the fermentation rate of buffalo's milk.Industrial relevanceConventional food fermentation is one of the most time and resources consuming processing steps in the food industry. In this work, it was shown that the appropriate application of ultrasound during different stages of microbial growth reduced the fermentation time of buffalo milk by 13% to 16% by enhancing the metabolic activities of lactic acid bacteria. Therefore, ultrasound has great prospects in the food processing industry to improve process efficiency. Scaling-up of laboratory applications of US in to industrial scale through designing new power transducers with high capacity and greater acoustic filtration is necessary to enhance its potential to be used at large scales.     

一株费氏丙酸杆菌生长特性及其代谢物抑菌作用分析

对一株费氏丙酸杆菌生长特性及其代谢物抑菌作用进行研究。结果表明:该菌株生长周期约为10 d,第1~3天为其对数生长期,第4~8天为菌体生长的稳定期,第9~10天为衰亡期。在生长过程中,菌体利用糖的速率很快,还原糖在发酵1 d内几乎被消耗殆尽,发酵液pH值在发酵的第1天下降到4.6左右,此后一直到第10天,pH值基本稳定在4.6左右。在同等条件下,该丙酸杆菌代谢物对大肠杆菌的抑制作用优于对金黄色葡萄球菌和酵母菌的抑制作用。对代谢产物的分析结果表明,发酵产物中抑菌物质除了丙酸之外,还存在其他物质,初步判定为细菌素。