发酵剂用量对硬质蒙古干酪风味变化的影响

以不同发酵剂使用量制作了一种硬质蒙古干酪,对干酪成熟过程中的风味变化和微生物多样性进行了研究。当发酵剂使用量为1.0 g/L原料乳时,挥发性风味化合物的组分更为丰富,风味更加均匀适中,具有更好的风味体验。在干酪成熟早期,嗜热链球菌和保加利亚乳杆菌生长趋势相同,但到中后期,嗜热链球菌生长速度趋缓,而保加利亚乳杆菌生长速度相对较快。     

Cheddar干酪理化性质变化对其质构及微观结构的影响

在贮藏过程中干酪的理化变化对其质构起到重要作用,由于蛋白质的降解破坏了其网络结构,脂肪水解和氧化使脂肪球发生聚集融合,形成脂肪槽,这些变化促进了干酪质构的变化,使其质地变软.本文系统研究Cheddar干酪在贮藏期的蛋白质水解程度、脂肪水解和氧化程度、质构及微观结构的变化,分析蛋白质水解、脂肪水解对质构和微观结构的影响.     

Gouda干酪在贮藏期蛋白质水解对其质构和微观结构的影响

为了更深入了解贮藏过程中千酪蛋白质水解对其质构的重要影响，系统研究了硬质Gouda千酪在4℃贮藏期的蛋白质水解程度、表面特性和流变学特性变化，分析了蛋白质水解对质构和微观结构的影响，探讨了储存过程中蛋白质水解程度、质构及微结构三者之间的变化关系。     

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。     

不同发酵剂对牦牛乳硬质干酪品质的影响

以新鲜牦牛乳为原料,分别添加嗜温、嗜热和混合(嗜温∶嗜热=1∶1)三种发酵剂制作硬质干酪,研究在1~180 d成熟过程中,不同类型发酵剂制作的干酪中蛋白降解和ACP(酸性磷酸酶)对其品质的影响。结果表明:牦牛乳硬质干酪成熟过程中发挥作用的ACP主要来自发酵剂,且干酪中蛋白降解受ACP影响显著,ACP与PPN(多肽氮)呈强正相关性(r=0.720),与CN(酪蛋白氮)和PN(蛋白氮)呈强负相关性。三种干酪PPN在60~120 d均保持稳定状态。不同类型的发酵剂对干酪蛋白降解强弱不同,过强或过弱均会影响到干酪的品质,嗜温发酵剂对干酪蛋白降解最弱,该干酪风味比较清淡;嗜热发酵剂对干酪蛋白降解能力最强,该发酵剂制作的干酪苦味较重,但组织状态较好;混合发酵剂对蛋白降解适中,该干酪发酵风味浓郁,组织状态较佳。      

一种硬质蒙古干酪的感官评价研究

对蒙古干酪的颜色、质构、微观结构和感官品评进行了研究。蒙古干酪外部亮度稍暗,偏微红色,内部干酪颜色趋向于纯色。在质构上,其硬度、弹性、黏着性和回复性分别为23.18 N、47.25、7.40和5.60,在硬度上和Cheddar干酪类似,但是其他3个方面要差一些。蒙古干酪具有致密的酪蛋白胶束组成微观结构,脂肪脱去形成的孔洞很少。蒙古干酪的综合感官分为69.23分,由于质地和口感的原因使得得分较低,但仍在可接受范围内。     

不同发酵剂对半硬质干酪品质影响研究

利用筛选的一种单一菌株(乳酸乳球菌)和两种混合菌株(乳酸乳球菌干酪乳杆菌(1:1)、瑞士乳杆菌:干酪乳杆菌(1:1))制作发酵剂,然后用于加工半硬质干酪,通过测定成熟干酪的性能指标,研究它们对干酪品质的影响.结果表明,瑞士乳杆菌:干酪乳杆菌(1:1)制作的干酪感官评定值最高,且与另外两种菌株制作的干酪差异显著;结合其他性能指标,确定适于半硬质干酪加工的最佳发酵剂菌株为瑞士乳杆菌:干酪乳杆菌(1:1).     

发酵剂添加量和成熟时间对牦牛乳硬质干酪脂肪氧化的影响

为研究发酵剂添加量和成熟时间对牦牛乳硬质干酪中脂肪氧化的影响,试验以添加不同发酵剂质量分数(1%、2%、3%)制得的牦牛乳硬质干酪为材料,对其90 d成熟期内的氧化指标和理化指标进行测定。结果表明:发酵剂添加量和成熟时间对牦牛乳硬质干酪的理化指标和脂肪氧化程度均有显著性影响(P <0. 05),且随发酵剂添加量的增加,干酪中酸度值(acidity value,ADV)、过氧化值(peroxide value,POV)、羰基价(carbonyl value,CV)、硫代巴比妥酸值(thiobarbituric acid value,TBA)增加;随成熟时间的延长,ADV、CV、TBA值增加,POV值先增加后降低。发酵剂添加量为3%时,能够显著增大干酪中脂肪的氧化程度(P <0. 05),同时随成熟时间的延长,脂肪氧化持续进行并且氧化程度也在不断加深。该研究将发酵剂添加量和成熟时间相结合,探讨牦牛乳硬质干酪中脂肪氧化的变化规律,以期从脂肪的氧化机制调控干酪的品质,为实现工业化生产提供理论依据。     

稻米油对涂抹再制干酪微观结构的影响

研究稻米油替代乳脂肪对涂抹再制干酪微观结构的影响。以切达干酪为原料,添加不同比例稻米油制备涂抹再制干酪,测定不同稻米油比例样品的微观结构和脂肪酸含量。结果表明,稻米油替代乳脂肪可以增加再制干酪产品长链脂肪酸,减少其短链脂肪酸、中链脂肪酸比例。稻米油替代对涂抹再制干酪的脂肪酸饱和度和链长的影响,导致再制干酪体系中脂肪球大小和分布的差异。对照组脂肪球小而分布均匀,植物油替代比例增加导致更大的脂肪球,通过微观结构观察,稻米油替代比例增大至50%时,开始出现较大直径且分布不均匀的脂肪球。因此,稻米油替代比例应控制在50%以下较为适宜。     

乳酸菌附属发酵剂的筛选及其对干酪浆蛋白水解的影响

乳酸菌(lactic acid bacteria, LAB)附属发酵剂的添加对干酪的成熟和功能有着重要影响。为了改善天然干酪的成熟特性,对24株LAB的发酵特性进行了评估,包括产酸、自溶度、氨肽酶活力、蛋白水解和脂解活性、耐盐性、产胞外多糖活性以及在低温条件下的生长情况,然后利用干酪浆快速成熟模型,进一步评价筛选菌株对干酪成熟过程的影响。菌株筛选结果表明,24株菌株中,有4株(Lactobacillus fermentum AR497,L.plantarum AR611,L.salivarius AR612和L.salivarius AR809)具有作为附属发酵剂的应用潜力。干酪浆模型结果表明,4株附属发酵剂对干酪浆的pH值及基本成分(水分、脂肪、蛋白质)没有显著影响,4株菌株在干酪浆中增值良好且不影响发酵剂乳酸菌的生长;蛋白质水解分析显示,4株非发酵剂乳酸菌可不同程度地促进干酪浆中pH 4.6可溶性氮(pH 4.6-SN)和12%三氯乙酸可溶性氮(12%TCA-SN)含量的增加,其中菌株AR809对酪蛋白水解的促进效果最显著(P<0.05);RP-HPLC分析显示,菌株AR80...     

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。      

Effect of CO2 addition to raw milk on proteolysis and lipolysis at 4 degrees C

Fresh raw milks, with low (3.1 x 10(4) cell/ml) and high (1.1 x 10(6) cells/ml) somatic cell count (SCC), were standardized to 3.25% fat, and from each a preserved (with 0.02% potassium dichromate) and an unpreserved portion were prepared. Subsamples of each portion were carbonated to contain 0 (control, pH 6.9) and 1500 (pH 6.2) ppm added CO2, and HCl acidified to pH 6.2 Milk pH was measured at 4 degrees C. For the preserved low- and high-SCC milks, two additional carbonation levels, 500 (pH 6.5) and 1000 (pH 6.3) ppm, were prepared. Milks were stored at 4 degrees C and analyzed on d 0, 7, 14, and 21 for microbial count, proteolysis, and lipolysis. The addition of 1500 ppm CO2, but not HCl, effectively delayed microbial growth at 4 degrees C. In general, in both the low- and high-SCC unpreserved milks, there was more proteolysis and lipolysis in control and HCl acidified milks than in milk with 1500 ppm added CO2. Higher levels of proteolysis and lipolysis in the unpreserved milks without added CO2 were related to higher bacteria counts in those milks. In preserved low- and high-SCC milks, microbial growth was inhibited, and proteolysis and lipolysis were caused by endogenous milk enzymes (e.g., plasmin and lipoprotein lipase). Compared with control, both milk with 1500 ppm added CO2 and milk with HCl acidification had less proteolysis. The effect of carbonation or acidification with HCl on proteolysis in preserved milks was more pronounced in the high SCC milk, probably due to its high endogenous protease activity. Plasmin is an alkaline protease and the reduction in milk pH by added CO2 or HCl explained the reduction in proteolysis. No effect of carbonation or acidification of milk on lipolysis was observed in the preserved low- and high-SCC milks. The CO2 addition to raw milk decreased proteolysis via at least two mechanisms: the reduction of microbial proteases due to a reduced microbial growth and the possible reduction of endogenous protease activity due to a lower milk pH. The effect of CO2 on lipolysis was mostly due to a reduced microbial growth. High-quality raw milk (i.e., low initial bacteria count and low SCC) with 1500 ppm added CO2 can be stored at 4 degrees C for 14 d with minimal proteolysis and lipolysis and with standard plate count < 3 x 10(5) cfu/ml.     

Lipolysis and proteolysis in Ragusano cheese during brine salting at different temperatures

The influence of temperature (12, 15, 18, 21, and 24 degrees C) of saturated brine on lipolysis and proteolysis in 3.8-kg blocks of Ragusano cheese during 24 d of brining was determined. Twenty-six 3.8-kg blocks were made on each day. The cheese making was replicated on 3 different days. All blocks were labeled and weighed prior to brining. One block was sampled and analyzed prior to brine salting. Five blocks were placed into each of 5 different brine tanks at different temperatures. One block was removed from each brine tank after 1, 4, 8, 16, and 24 d of brining, weighed, sampled, and analyzed. Both proteolysis and lipolysis in Ragusano cheese increased with increasing brine temperature (from 12 to 24 degrees C), with the impact of brine temperature on proteolysis and lipolysis becoming progressively larger. Proteolysis was highest in the interior of the blocks where salt in moisture content was lowest and temperature had more impact on proteolysis in the interior position of the block than the exterior position. However, the opposite was true for lipolysis. The total free fatty acid content was higher and temperature had more impact on lipolysis at the exterior position of the block where salt in moisture was the highest. This effect of increased salt concentration on lipolysis was confirmed with direct salted cheeses in a small follow-up experiment. Lipolysis increased with increasing salt in the moisture content of the direct salted cheeses. It is likely that migration of water-soluble FFA from the brine into the cheese and from the interior portion of the cheese to the exterior portion of the cheese also contributed to a higher level of FFA at the exterior portion of the blocks. As brine temperature increased the profile of individual free fatty acids released from triglycerides changed, with the proportion of short-chain free fatty acids increasing with increasing brine temperature. This effect was largest at high salt in moisture content.     

Lipolysis and proteolysis profiles of fresh artisanal goat cheese made with raw milk with 3 different fat contents

The objective of this study was to describe the proteolysis and lipolysis profiles in goat cheese made in the Canary Islands (Spain) using raw milk with 3 different fat contents (0.5, 1.5, and 5%) and ripened for 1, 7, 14, and 28 d. β-Casein was the most abundant protein in all cheeses and at all ripening times. Quantitative analysis showed a general decrease in caseins as ripening progressed, and degradation rates were higher for α_S1-casein than for β-casein and α_S2-casein. Furthermore, the degradation rate during the experimental time decreased with lower fat contents. The α_S2-casein and α_S1-casein levels that remained in full-fat and reduced-fat cheeses were less than those in low-fat cheese. In contrast, β-casein also showed degradation along with ripening, but differences in degradation among the 3 cheese types were not significant at 28 d. The degradation products increased with the ripening time in all cheeses, but they were higher in full-fat cheese than in reduced-fat and low-fat cheeses. The free fatty acid concentration per 100 g of cheese was higher in full-fat cheese than in reduced- and low-fat cheese; however, when the results were expressed as milligrams of free fatty acids per gram of fat in cheese, then lipolysis occurred more rapidly in low-fat cheese than in reduced- and full-fat cheeses. These results may explain the atypical texture and off-flavors found in low-fat goat cheeses, likely the main causes of non-acceptance.