处理发酵剂对促熟干酪中生物胺和游离氨基酸的影响

以0、30、60、90 d促熟干酪中生物胺（组胺、色胺、苯乙胺、尸胺、酪胺）和游离氨基酸含量为指标,研究了添加复合处理发酵剂对干酪产生游离氨基酸和生物胺量的影响。结果表明：不同处理发酵剂添加量对各种生物胺产生的影响不同;添加处理发酵剂干酪中生物胺和游离氨基酸含量增加,其含量随着复合处理发酵剂添加量增加而增加。     

修饰发酵剂细胞促熟干酪的研究进展

修饰发酵剂细胞是采用各种物理、化学或基因修饰等方法使发酵剂(主要是乳酸菌)不能生长而不致产生过量的乳酸。同时在干酪中添加时细胞会完整存在，并能在成熟期间释放出活性胞内酶。修饰发酵剂的方法主要有热休克、冷休克、冷冻或喷雾干燥、溶菌酶处理、溶剂处理和基因修饰等。这些方法修饰乳酸菌(包括乳球菌，乳杆菌)与原发酵剂一并加入乳中，可加速干酪中的蛋白质降解和脂肪分解，缩短其成熟期，且增强风味(减少苦味)，在促熟干酪方面取得了较好的实验效果。综述了现有的修饰发酵剂细胞促熟干酪的方法，详述了热休克、冷休克这两种常用的方法，最后对修饰发酵剂细胞促熟干酪的应用前景作以展望。     

植物乳杆菌S72对高达干酪品质的影响

以实验室自主分离的一株具有优良功能特性的植物乳杆菌(Lactobacillus plantarum) S72为辅助发酵剂,制备高达干酪(Gouda),研究植物乳杆菌S72对干酪理化指标、质构、活菌数、游离氨基酸及游离脂肪酸等的影响。结果表明:与商品发酵剂组相比,添加L.plantarum S72作为辅助发酵剂的Gouda干酪,在干酪成熟末期,L. plantarum S72保持较高的活菌数,对干酪的理化指标及质构特性无不良影响。L. plantarum S72提高了Gouda干酪成熟过程中WSE/TN和70%Ethanol-SN的含量,显著增加了PTA-SN的含量。L.plantarum S72后有助于Gouda干酪成熟过程中游离氨基酸的生成。这些结果说明添加L. plantarum S72作为辅助发酵剂不会影响Gouda干酪的质地,并且对Gouda干酪成熟过程中的风味有促进作用。     

快速成熟切达干酪复合发酵剂的筛选

以促进切达干酪成熟为目的,筛选发酵菌种,菌种添加量、菌种比例,确定发酵剂对切达干酪促熟的影响。利用响应面中心旋转组合设计,优化出具有促熟效果的复合发酵剂的最佳配比,即:保加利亚乳杆菌(Lb)添加量为0.92 kg/100 kg原料乳,嗜热链球菌(St)添加量为0.77 kg/100 kg原料乳,瑞士乳杆菌(Lh)添加量为1.08 kg/100 kg原料乳,复合发酵剂的总添加量2.77%。使用优化的复合发酵剂,通过验证试验加工的切达干酪与R704商业发酵剂对照样比对,结果复合发酵剂具有显著的促熟效果(P0.01)。     

干酪促熟附属发酵剂的研究进展

干酪成熟时间较长且费用较高,干酪促熟成为降低生产成本的有效途径之一。干酪促熟常用的方法有酶法、修饰发酵剂细胞、提高成熟温度、高压处理等,但均存在一定的不足,限制了其在干酪工业中的应用。非发酵剂乳酸菌可促进干酪风味的形成并加速成熟．已成为干酪促熟方法的研究热点之一。介绍了干酪生产及成熟过程中微生物的作用,特别介绍了干酪附属发酵剂发展的原由并综述了其在干酪成熟过程中研究进展。     

辅助发酵剂加速Provolone干酪成熟的研究

将瑞士乳杆菌6024作为辅助发酵剂添加到Provolone干酪中,加速Provolone干酪成熟,研究了其对干酪游离氨基酸、游离脂肪酸、质构特性、电镜、风味物质的影响。结果表明,瑞士乳杆菌6024作为辅助发酵剂对干酪中游离脂肪酸质量分数没有显著影响,但能显著增加干酪游离氨基酸质量分数,60 d时达到对照组90 d时的质量分数,此时干酪的质构特性、微观结构、风味物质与对照组90 d时差异不显著。由此可知,瑞士乳杆菌6024作为辅助发酵剂可加速Provolone干酪的成熟,缩短成熟时间。     

一种植物乳杆菌对干酪模型成熟中微生物及蛋白质水解的影响

采用无菌条件下生产的新鲜干酪凝块制作干酪模型,以WSN,12%TCASN和氨基酸含量等为指标测定植物乳杆菌SP-3对其的促熟作用。微生物测定表明SP-3在干酪模型的成熟过程中(12d)能保持较高的浓度;WSN结果表明SP-3对干酪中蛋白质的初级水解无显著影响;12%TCASN的结果表明SP-3影响了干酪中小肽的形成;5%PTA-SN和总游离氨基酸浓度测定结果表明植物乳杆菌SP-3促进了体系中游离氨基酸的产生;游离氨基酸的分析显示谷氨酸、亮氨酸、组氨酸的含量明显高于对照组,而丝氨酸、赖氨酸、脯氨酸的含量低于对照组。以上结果表明,植物乳杆菌SP-3能加快干酪体系中蛋白质的水解进程,具有促进干酪成熟的作用。     

发酵剂对牦牛乳硬质干酪蛋白降解和苦味关系的影响

用甘肃天祝新鲜牦牛乳为原料分别添加嗜温、嗜热和混合发酵剂制作硬质干酪,以pH 4.6-可溶性氮（soluble nitrogen,SN）、12%三氯乙酸氮（trichloroacrtic acid-N,TCA-N）、游离氨基酸（free amino acid,FAA）含量和疏水性肽/亲水性肽（S/Q）为蛋白水解度指标,研究3 种牦牛乳硬质干酪在6 个月内成熟过程中苦味和蛋白质降解之间的关系。结果表明：3 种干酪在成熟过程中pH 4.6-SN、12% TCA-N和FAA含量均呈上升趋势,苦味值与pH 4.6-SN、12% TCA-N和FAA含量成正相关,相关系数分别为0.400、0.412和0.458。3 种干酪成熟过程中S/Q的变化趋势和程度不同,嗜温发酵剂干酪中S/Q呈现降低趋势;嗜热和混合发酵剂干酪中S/Q均呈现先降低后增大的趋势,但在这两种干酪中S/Q的变化程度不同,嗜热发酵剂干酪在1～3 个月S/Q略有降低,在3～6 个月S/Q快速增大,而混合发酵剂干酪正好相反。S/Q与苦味值成极显著正相关（r=0.895）,S/Q可很好地反映干酪中苦味的强弱。而干酪中苦味强弱与蛋白质降解强弱密切相关,对蛋白降解程度越大的发酵剂制作的干酪越容易产生苦味,其中,嗜热发酵剂对干酪蛋白降解程度最大,混合发酵剂次之,嗜温发酵剂最小。     

不同凝乳酶生产干酪成熟期间氨基酸的变化

以鲜奶为原料,以进口的EZAL、MAOLL作发酵剂(由乳油连球菌和乳酸链球菌组成),以微生物酶、羔羊皱胃酶、小牛皱胃酶和猪胃蛋白酶、木瓜蛋白酶、无花果蛋白酶作为凝乳酶生产硬质干酪,研究不同凝乳酶对干酪成熟期间氨基酸变化的影响。结果表明:不同凝乳酶生产干酪成熟期间氨基酸(FAA)含量的变化趋势:羔羊皱胃酶>小牛皱胃酶>微生物凝乳酶>无花果蛋白酶>猪胃蛋白酶>木瓜蛋白酶。     

凝乳酶对牦牛乳硬质干酪成熟期间蛋白降解的影响

以新鲜牦牛乳为原料,采用小牛皱胃酶、木瓜蛋白酶和微生物凝乳酶制作硬质干酪,探讨凝乳酶种类对牦牛乳硬质干酪成熟期间蛋白质降解的影响。结果表明:三种凝乳酶牦牛乳硬质干酪成熟过程中,不同凝乳酶牦牛乳硬质干酪在成熟期间蛋白质降解能力存在较大差异,总氮（TN）、p H4.6水溶性氮（p H4.6-SN/TN）、12%的三氯乙酸氮（12%TCA-N/TN）、5%磷钨酸氮（5%PTA-N/TN）含量、游离氨基酸均随成熟时间延长不同程度的增加,蛋白氮和酪蛋白氮逐渐降低,多肽氮呈先升高后下降趋势,且微生物凝乳酶降解牦牛乳硬质干酪蛋白能力显著（p<0.05）高于木瓜蛋白酶和小牛皱胃酶。      

Proteolysis and Lipolysis in Ripening Cheddar Cheese Made with Conventional Bulk Starter and with Frozen Concentrated Direct-to-the-Vat Starter Culture

Samples taken at the beginning and after 1, 2, and 3 wk of ripening were assayed for total dipeptidase activity and individual free amino acids. Protein dye-binding values and fat acidity titers were used to assess and monitor proteolysis and lipolysis at 4 days and 1, 2, 3, 6, 9, and 12 months. Results indicated higher dipeptidase activity in the bulk starter cheese for the fist 3 wk of ripening. Total free amino acids at the initial stages of cheese ripening were slightly lower in the cheeses made with the frozen concentrated culture. Studies using the protein-dye binding technique showed significantly higher-dye binding capacity by the 3-month-old cheese made with the bulk starter. The differences, however, became minimal in cheeses at 6, 9, and 12 months of age. Higher fat acidity levels were also obtained in the 3, 6, 9, and 12 month cheeses made with the bulk starter.     

Ripening of cheddar cheese with added attenuated adjunct cultures of lactobacilli

We made Milled curd Cheddar cheese with Lactococcus starter and an adjunct culture of Lactobacillus helveticus I or Lactobacillus casei T subjected to different attenuation treatments: freeze shocking (FS), heat shocking (HS), or spray drying (SD). Proteolysis during cheese ripening (0 to 6 mo), measured by urea-PAGE and water-soluble nitrogen, indicated only minor differences between control and most adjunct-treated cheeses. However, there were significant differences in the effect of Lactobacillus adjuncts on the level of free amino nitrogen in cheese. Cheeses made with FS or HS Lb. helveticus adjunct exhibited significantly greatest rates of free amino group formation. Lipolysis as measured by total free fatty acids was consistently highest in adjunct-treated cheeses, and FS Lb. casei-treated cheeses showed the highest rate of free fatty acid formation followed by FS Lb. helveticus treated cheeses. Mean flavor and aroma scores were significantly higher for cheeses made with Lb. helveticus strain. Freeze-shocked Lb. helveticus-treated cheeses obtained the highest flavor and aroma scores. Sensory evaluation indicated that most of the adjunct-treated cheeses promoted better texture and body quality.     

Changes in the free amino acid content during ripening of Idiazabal cheese: influence of starter and rennet type

The effect of starter and rennet type on free amino acid release during ripening of Idiazabal cheese was studied. Four batches of cheeses were manufactured depending on the rennet used, commercial calf rennet or artisanal lamb rennet, and the addition or not of starter culture. Cheese samples contained 24 individual free amino acids Leu, Glu, Val and Phe showing the highest contents during the ripening. The results indicated that the release of the free amino acids during ripening was strongly affected by starter added to the cheeses, and that this effect varied markedly with the rennet used for cheesemaking. Total amounts of free amino acids were higher for the cheeses made with commercial calf rennet than for those made with artisanal lamb rennet, regardless of starter addition. Likewise, the highest total free amino acid levels were found in the cheeses made with starter, regardless of the type of rennet used.     

Ripening time estimation of Kariesh cheese

Kariesh cheese is a popular cheese in Egypt produced by acid coagulation of milk. It can be consumed fresh or after ripening. Proteolysis in cheese was measured by determining soluble nitrogen (SN), amino acid nitrogen (AAN), total amino acids (TAA) and free amino acids (FAA). SN, AAN and FAA increased during ripening. Free amino acids profile revealed in total 16 amino acids and the same distribution of free amino acids. Cheese ripening was influenced by the type of milk and the method of production. The mildly acid sweet flavour was attributed to the concentration of glutamic acid, aspartic acid, proline and valine. Linear regression analysis was carried out to estimate the ripening time of this cheese. A positive correlation between the accumulation of amino acid and ripening time was established. The highest coefficient of determination near one resulted from glutamic acid (R² = 0.99) followed by lysine (R² = 0.97–0.99), then aspartic acid (0.90–0.98). From the linear regression equation for glutamic acid, lysine, aspartic acid or proline, the ripening time of Kariesh cheese in weeks was determined as follows: Time of ripening [weeks] = mg amino acid 100 g cheese-a/b where b = slope and a = intercept of regression straight line at 0 time.     

益生菌切达干酪成熟过程中细菌群落的多样性分析

采用选择性培养基和聚合酶链式反应和变性梯度凝胶电泳（polymerase chain reaction-denaturing gradient gelelectrophoresis,PCR-DGGE）技术,研究益生菌切达干酪成熟过程中（6 ℃,180 d）细菌群落构成及益生菌（干酪乳杆菌LC2W）的存活情况。结果表明：SBM和MSE等选择性培养基存在选择专一性不强的缺点,不能客观反映干酪内各种微生物的动态变化;随着切达干酪成熟时间的增加,发酵剂嗜热链球菌和乳酸乳球菌的数量明显下降,而非发酵剂菌群乳杆菌的数量和主要种类呈上升趋势;干酪成熟180 d后,干酪乳杆菌LC2W的存活量仍高于1×108CFU/g。切达干酪能作为干酪乳杆菌LC2W存活的良好载体;PCR-DGGE技术和选择计数法联用更加适合干酪细菌群落结构的分析。     

The effects of using a starter culture,lipase, and protease enzymes on ripening of Mihalic cheese

The purpose of this study was to determine the effects of fungal lipase from Mucor miehei and a bacterial neutral protease from Bacillus subtilis alone and combined with a starter culture on ripening properties of traditional Turkish Mihalic cheese. The use of protease with lipase (Cult + Prot + Lip) resulted in better flavour and texture with accelerated ripening. The obtained results pointed out that the gross compositions of the cheeses were changed by the type of enzymes and ripening time (P < 0.01). The acid degree value (ADV) of all cheeses showed a linear increase with ripening. The highest lipolysis rate was noted in lipase‐added cheese batch (as 5.56 ADV) with highest γ‐CN ratio and β‐CN degradation. At the end of ripening time, it was observed that αs‐CN ratios decreased in starter‐added (Cult), starter + protease–added (Cult + Prot), and protease‐added (Prot) cheese batches. The use of protease with lipase (Cult + Prot + Lip) resulted in better flavour and texture with accelerated ripening. Protease‐added cheeses, which were characterized by bitterness and crumbly textural properties owing to the intense breakdown of β‐casein, scored lower than lipase‐added cheeses. It was determined that the use of mesophilic aromatic starter culture with lipase and protease could be used to accelerate ripening of Mihalic cheese made from pasteurised milk.     

Ripening of extra-hard cheese made with mesophilic DL-starter

Extra hard cheese is commonly made with thermophilic starters using high temperatures to stimulate expulsion of whey. In this work, microflora, proteolysis and volatiles were investigated in an extra-hard cheese made with mesophilic DL-starter, produced using challenging cooking temperatures for the starter bacteria over several hours. Cheese from six commercially produced vats was investigated over 56 weeks. The number of starter bacteria decreased after three weeks of ripening. Casein breakdown was characterised by chymosin and plasmin activity on α_s1- and β-caseins, respectively. Peptide profiles showed accumulation of Lactococcus derived peptides from α_s1-CN f1–23, and the peptide β-CN 29–93 as a result of joint plasmin and chymosin activity and absence of highly proteolytic thermophilic Lactobacillus, commonly present in extra-hard cheese. The composition of amino acids depended mainly on starter during the first 26 weeks of ripening. The content of volatiles depended both on ripening time and the starter used.     

Formation of biogenic amines in raw milk Hispánico cheese manufactured with proteinases and different levels of starter culture

Two proteinases, a neutral proteinase from Bacillus subtilis and a cysteine proteinase from Micrococcus sp., were used to accelerate the ripening process of raw cow's milk Hispánico cheese, a semihard variety. Two levels (0.1% and 1%) of a commercial starter culture containing Lactococcus lactis subsp. lactis and L. lactis subsp. cremoris were added for cheese manufacture. The influence of both factors, proteinase addition and level of starter culture, on the growth of amino acid-decarboxylating microorganisms and on the formation of biogenic amines during cheese ripening was investigated in duplicate experiments. The population of tyrosine decarboxylase-positive bacteria, which represented less than 1% of the total bacterial population in most cheese samples, and tyrosine decarboxylase-positive lactobacilli was not influenced by proteinase addition or level of starter culture. Tyramine was detected in all batches of cheese from day 30. Its concentration was significantly (P < 0.05) influenced by proteinase addition but not by the level of starter culture and increased with cheese age. After 90 days of ripening, 103 to 191 mg/kg of tyramine was found in the different cheese batches. Histamine was not detected until day 60 in cheese with neutral proteinase and 1% starter culture and until day 90 in the rest of the cheeses. The concentration of this amine did not exceed 20 mg/kg in any of the batches investigated. Phenylethylamine and tryptamine were not found in any of the samples.