Mozzarella干酪加工过程中主要理化指标变化及其产率计算

该文目的在于为干酪功能特性、含水率和产率的控制提供理论依据,使用标准化原料乳经低温巴氏杀菌,采用无盐渍新工艺生产Mozzarella干酪,从添加发酵剂开始,到制成新鲜干酪,测定各阶段干酪凝块的温度、水分含量、pH值和滴定酸度及各阶段乳清和凝块的蛋白和脂肪含量,计算Mozzarella干酪的效能和产率。试验结果表明：在排乳清和粉碎加盐阶段,干酪凝块中的水分含量变化幅度最大,排出乳清中的蛋白和脂肪数量明显增加;干酪的脂肪回收率达到92.22%,实际测得的乳清中脂肪的损失率为7.62%;乳蛋白的回收率达到83.60%,仅有16.72%的蛋白质损失于乳清中;在堆酿阶段pH值有一个从6.3(干酪凝块5.5)至5.25的快速下降过程。Mozzarella干酪的实际产率达到12.38%,达到了同类型干酪的产率要求。Mozzarella干酪的理化指标达到了美国全脂Mozzarella干酪的标准。     

不同因素对羔羊皱胃酶凝乳活性的影响

研究结果表明，羔羊皱胃酶最适凝乳温度为45℃；35℃以上热处理对酶凝乳活性有不同程度的损失，60℃热处理10 min活性完全丧失；pH值为5～8时凝乳活性随乳pH值的降低而增强，酶在pH2.5～7.5之间处理20h凝乳活性稳定；Ca²⁺具有明显的促凝作用；底物浓度对酶活性的影响符合米氏规律。     

外源抗坏血酸与谷胱甘肽对打顶后烟草氧化 还原平衡及烟碱的影响

烟碱含量偏高是我国烤烟的现状。如何有效降低烟叶烟碱含量,提高烤烟工业可用性是烟叶生产中的一个难题。根据烟草打顶导致烟碱含量急剧上升和机械损伤造成细胞氧化迸发的的现象,本试验从打顶创伤引起的一系列生理变化入手,采取打顶后在伤口涂抹抗氧化剂抗坏血酸+谷胱甘肽(As A+GSH)和抗坏血酸(As A)两种方法来抑制活性氧含量的上升,探究茉莉酸刺激烟碱含量上升和活性氧含量之间的关系,并比较两种方法在抑制活性氧及烟碱上升的效果。结果发现,涂抹As A+GSH和As A处理对烟草叶片超氧阴离子、过氧化氢、丙二醛的上升有抑制效果,过氧化氢降解速度慢于超氧阴离子,在烟草内有积累现象。涂抹As A+GSH和As A处理在打顶6 h时茉莉酸含量低于常规打顶,对茉莉酸的产生有抑制效果。其中处理96 h后,打顶后涂抹As A+GSH的处理叶片烟碱含量比常规打顶低21.5%,打顶后涂抹As A的处理叶片烟碱含量比常规打顶低17.5%。且各检测指标之间存在显著或极显著的相关性。另外,打顶后24 h,各处理的活性氧含量回到对照(不打顶)的水平。试验表明,抗氧化型物质(As A+GSH)涂抹打顶后烟草的伤口能有效抑制活性氧、茉莉酸和烟碱含量的上升,且活性氧、茉莉酸、烟碱之间存在着密切联系。As A+GSH比As A有更强的抗氧化性,能更好地抑制打顶后烟碱的上升。     

氯化钙添加量对地衣芽孢杆菌凝乳酶凝乳性能的影响

凝乳酶是生产干酪中极为关键的酶制剂。在凝乳酶作用过程中,添加适量的氯化钙可缩短凝乳时间,增加凝块硬度,减少生产成本,对干酪品质的影响至关重要。本研究利用从甘肃省天祝藏族自治县牦牛牧区土壤中筛选得到的一株高效产凝乳酶的地衣芽孢杆菌菌株D3.11,优化培养后得到凝乳酶,通过分析凝乳过程中相关指标的变化规律、观察比较凝块的微观结构,研究氯化钙添加量对该酶凝乳性能的影响。结果表明,当氯化钙添加量为0.014%~0.022%时,地衣芽孢杆菌D3.11凝乳酶体系的黏度值随凝乳时间的延长先增大后保持稳定;地衣芽孢杆菌D3.11凝乳酶体系和商品酶体系的浊度值均随Ca²⁺浓度的增大而显著增大(P<0.05);地衣芽孢杆菌D3.11凝乳酶体系的粒径主峰分布在136.9~246.7 μm范围内,且粒径值在氯化钙添加量为0.020%时最大;流变学特性分析结果表明,地衣芽孢杆菌D3.11凝乳酶体系达到储能模量G'峰值的时间随氯化钙添加量的增加而缩短;两种酶体系的持水力在氯化钙添加量为0.014%~0.022%范围内显著增大(P<0.05),乳清OD值在氯化钙添加量为0.016%~0.022%范围内变化均不显著(P>0.05);通过激光扫描共聚焦显微镜观察凝块微观结构发现,随着氯化钙添加量的增加,两种酶体系中蛋白微粒均凝结得更紧密。本研究结果为细菌凝乳酶在干酪生产中的应用提供了理论依据。     

富硅稻壳灰施用对土壤镉活性和不同品种水稻镉积累的影响

施硅（Si）可以有效减少水稻镉（Cd）积累,但稻壳灰（rice hull ash,RHA）作为一种广泛易得的富Si材料能否减控水稻Cd积累尚未清楚。为探究RHA对水稻Cd积累的影响,寻找一种可应用到田间的低成本富Si控Cd材料,该试验按土壤质量比分别添加0.2%、1.0%、4.0%的RHA,种植湘晚籼（低Cd积累品种）和玉针香（高Cd积累品种）两种水稻,探究RHA对两个水稻品种Cd积累的影响。结果显示,施加RHA提高了土壤Cd活性,促使铁锰氧化物结合态Cd向可交换态Cd和碳酸盐结合态Cd转换。RHA对水稻Cd积累的影响因水稻品种而异,施加RHA可抑制湘晚籼体内Cd转运,使秸秆Cd含量降低25%～44%,由白根至秸秆、节点I至节间I、节点I至旗叶的转移系数分别降低42%～48%、2%～55%、30%～70%;RHA对玉针香吸收与转运Cd则无抑制作用。该研究结果揭示了RHA对水稻Cd积累的差异影响,为减控水稻Cd吸收提供了一种低成本的富Si材料。     

菌酶协同处理提高脱脂薏米水提取液营养价值

为了高效利用脱脂薏米制备水提取液,该研究采用酸性蛋白酶、木瓜蛋白酶、中性蛋白酶、碱性蛋白酶和风味蛋白酶协同干酪乳杆菌发酵脱脂薏米,考察了菌酶协同处理对薏米水提取液可滴定酸、还原糖、总酚、多肽、氨基酸、抗氧化活性及酪氨酸酶和黄嘌呤氧化酶抑制活性的影响。与干酪乳杆菌单独发酵相比,菌酶协同可促进发酵薏米的蛋白质降解,显著提高水提取液中多肽、还原糖和总酚浓度(P0.05)。菌酶协同处理后水提取液中小分子多肽比例显著增加(P0.05),游离氨基酸含量显著提高(P0.05),必需氨基酸与非必需氨基酸比值达到0.73～1.17。此外,菌酶协同处理后水提取液的铁离子还原能力和ABTS阳离子自由基清除能力较干酪乳杆菌单独发酵显著增强(P0.05),酪氨酸酶和黄嘌呤氧化酶抑制活性分别达到了52.3%～58.1%和36.7%～41.5%,显著高于干酪乳杆菌单独发酵(P0.05)。结果表明,菌酶协同可显著提高脱脂薏米水提取液的营养品质,综合比较后木瓜蛋白酶的增强效果最佳。研究结果可为利用薏米提油后的副产物脱脂薏米开发高附加值薏米水提取液功能食品和化妆品提供参考。     

超低酸预处理结合酶解提高玉米秸秆糖化效率

为提高纤维素酶解糖化的效率,该文采用超低浓度硫酸水解预处理废弃玉米秸秆。重点考察了不同酸浓度、反应温度、反应时间条件下超低浓度酸水解及后续酶解的总还原糖、葡萄糖及木糖的产率,详细叙述了总还原糖及各种单糖在酸水解及酶解过程中的转化规律,通过正交试验确定酸水解的最佳工况为酸浓度0.1%,反应温度160℃,反应时间55 min,搅拌180 r/min,固液比1∶10。酸水解后进行酶解(酶用量5%,pH值4.6,时间24 h,温度50℃)得到还原糖、葡萄糖、木糖产率分别为56.22%、16.97%、18.83%。通过红外光谱和纤维素分析仪对酸水解和酶解后的残渣进行分析可知,纤维素、半纤维素的转化率分别为88.52%、95.18%,进一步计算还原糖、葡萄糖、木糖的转化率为88.11%、44.86%、72.49%。该方法较大程度避免了还原糖在酸水解过程中的降解,保证了半纤维素还原糖的转化效率,进一步提高了总还原糖的产率,为超低酸水解在燃料乙醇领域提供了新的应用途径。     

大豆蛋白限制性酶解模式与产品胶凝性的相关性

为了改善大豆蛋白的胶凝性,对大豆浓缩蛋白、大豆分离蛋白进行限制性酶解处理,并考察相应产品的蛋白酶酶解模式与胶凝性变化的相关性。该研究以蛋白质的水解度为指标,通过中性蛋白酶、胰蛋白酶的酶解作用,水解大豆浓缩蛋白、大豆分离蛋白至蛋白质水解度(DH)为1%、2%,考察酶性质、蛋白质的DH对产品胶凝性影响,并利用SDS-凝胶电泳进行确认。结果表明:大豆浓缩蛋白经中性蛋白酶、胰蛋白酶的酶解后,产品胶凝性均显著下降;大豆分离蛋白经中性蛋白酶的酶解后,产品胶凝性在DH为1%时增加,但在DH为2%时下降;大豆分离蛋白经胰蛋白酶酶解后,胶凝性显著改善。SDS-凝胶电泳确认,蛋白质的酶水解模式和水解度不同是导致产品胶凝性产生不同变化的原因。     

Mozzarella干酪成熟中蛋白水解与功能特性的变化

为控制干酪的质量,对Mozzarella干酪成熟过程中蛋白质的水解(测定SDS凝胶电泳和可溶性氮)和未融化干酪的质构变化以及融化干酪功能特性变化进行了研究,干酪成熟过程中由于凝乳酶和乳酸菌酶的作用使蛋白水解,从而使pH 4.6可溶性氮(SN)和12% TCA SN逐渐增加;凝乳酶主要影响酪蛋白的水解范围,乳酸菌及其酶,不但影响酪蛋白的水解范围,而且主要影响酪蛋白的水解深度。干酪中的残留凝乳酶和乳酸菌酶使酪蛋白水解为大分子量的肽段,而乳酸菌酶还可将大分子量的肽段进一步降解为小分子量的肽段和游离氨基酸。由于酪蛋白的水解,使干酪的硬度和弹性下降,融化性和油脂析出性增加,随着小分子量肽和游离氨基酸的增加,干酪的褐变性提高。     

红茶在超微-酶解反应器中的萃取特性研究

本文通过研究红茶在超微－酶解反应器(超微粉碎与酶解反应耦合)中作用所得茶汤的品质变化情况,探讨超微－酶解反应器在红茶萃取方面的优越性,并寻求一条生产茶汤的新途径。结果表明：经过超微－酶解反应器后的茶汤的可溶性固形物含量和茶多酚含量,随着剪切温度、剪切频率、剪切时间、加酶量的增大呈增大的趋势;较过胶体磨后的茶汤,二者含量分别提高了6.7%～12.6%和1.5%～8.0%;较直接热水萃取,二者含量分别提高了16.0%～20.1%和6.2%～24.4%。红茶加酶后在反应器中反应较不加酶所得茶汤茶多酚含量显著提高23.3%～35.6%。     

Physicochemical variables affecting the rheology and microstructure of rennet casein gels

The rheology and microstructure of a rennet casein system were studied in the pH range from 5.8 to 12.0 during cooling from 80 to 5 degrees C at four cooling rates: 0.5, 0.1, 0.05, and 0.025 degrees C/min. A dramatic increase in storage modulus with pH was observed during cooling at a fixed cooling rate. Continuous networks were formed for gels at pH 7.2 and above, while a discontinuous network was observed for gels below pH 6.5. The monotonic increase in storage modulus with pH could be correlated to the number of net (negative) charges and the strength of the hydrophobic interactions. At a higher pH, the protein micelles were larger due to weaker hydrophobic interactions and stronger repulsive electrostatic interactions resulting from more charges. When these protein micelles aggregated into flocs during cooling, the flocs had similar sizes at different pH values but a smaller fractal dimension at a higher pH. Consequently, for systems of the same protein and salt concentrations, more flocs were present in the gels at a higher pH, which subsequently generated more cross-links and a higher storage modulus. The pH also determined how the cooling rate affected the gel properties. At pH 5.8 and 6.5, the gels were firmest at the fastest cooling schedule, and the cooling rate did not show a trend in affecting the gel strength at the other three rates. On the other hand, a slower cooling rate generated a firmer gel at pH 7.2 and 12.0. The analysis of casein interactions suggests that the cooling rate affected the casein floc size only when repulsive interactions enabled a slow flocculation (at higher pH values) comparable with temperature change rates during cooling. For rennet casein gels of pH within the range of processed cheese products (pH 5.8 and 6.5), particle or cluster rearrangements created more uniform networks for gels cooled at slower schedules and weakened the structure.     

Use of recombinant cyprosin in the manufacture of ewe's milk cheese

A recombinant cyprosin from the cardoon (Cynara cardunculus L.) was assayed and compared with calf rennet in batches of ewes' milk cheese by determining different chemical, biochemical, and microbiological parameters over 4 months of ripening. There were no differences between the two types of coagulants in most chemical parameters, a(w), and pH. Proteolysis was more marked and rapid in cheese containing recombinant cyprosin as coagulant, the soluble nitrogen content of which was significantly higher (p < 0.01) than that of the cheese obtained with animal rennet; at the end of ripening the nonprotein nitrogen of cheese produced with recombinant cyprosin was slightly higher (p > 0.05) as compared with that in cheeses obtained with animal rennet. Microbial counts in the milk used for making cheese were high in most of the groups analyzed. Despite slight differences in counts, the main microbial groups analyzed were similar in cheese produced with both types of coagulants throughout ripening.     

Formation of early and advanced Maillard reaction products correlates to the ripening of cheese

The present study deals with the characterization of the ripening of cheese. A traditional German acid curd cheese was ripened under defined conditions at elevated temperature, and protein and amino acid modifications were investigated. Degree of proteolysis and analysis of early [Amadori compound furosine (6)] and advanced [N(ε)-carboxymethyllysine (4), N(ε)-carboxyethyllysine (5)] Maillard reaction products confirmed the maturation to proceed from the rind to the core of the cheese. Whereas 6 was decreased, 4 and 5 increased over time. Deeper insight into the Maillard reaction during the ripening of cheese was achieved by the determination of selected α-dicarbonyl compounds. Especially methylglyoxal (2) showed a characteristic behavior during storage of the acid curd cheese. Decrease of this reactive structure was directly correlated to the formation of 5. To extend the results of experimental ripening to commercial cheeses, different aged Gouda types were investigated. Maturation times of the samples ranged from 6 to 8 weeks (young) to more than 1 year (aged). Again, increase of 5 and decrease of 2 were able to describe the ripening of this rennet coagulated cheese. Therefore, both chemical parameters are potent markers to characterize the degree of maturation, independent of coagulation.     

Controlled proteolysis and the properties of milk gels

Milk gels induced by partial proteolysis of the kappa-casein followed by acidification were studied, and their gelation behavior was compared to that of milk gels induced by simultaneous acidification and renneting, using dynamic rheology. There were generally two stages (at pH values below and above 5.0) in the gelation of the milk whose kappa-casein had been partially proteolyzed and acidified. The onset of gelation was at higher pH as the degree of kappa-casein proteolysis increased. The development of G' immediately after the onset of gelation was faster in the milk gels induced by simultaneous acidification and renneting, because of the continuing kappa-casein proteolysis. Preheat treatment caused the onset of gelation to occur at higher pH than for unheated milk. However, the maximum tan delta during gelation always occurred at the same pH (for a given concentration of acidulant), and its value and position were independent of the extent of renneting and whether the milks had been heat treated. The results are discussed in terms of the interactions between casein micelles occurring during gelation.     

Factors affecting the retention of rennet in cheese curd

The coagulant retained in cheese curd is a major contributor to proteolysis during ripening. The objective of this study was to quantify the effects of several milk-related factors and parameters during cheese manufacture on the retention of coagulant in cheese curd. The amount of coagulant retained in curd was determined by its activity on a synthetic heptapeptide (Pro-Thr-Glu-Phe-[NO2-Phe]-Arg-Leu) using reversed-phase HPLC. The retention of chymosin in cheese curd increased significantly when the pH of milk was reduced at rennet addition below pH 6.1, the pH at whey drainage below pH 5.7, or the average casein micelle size in milk and when the ionic strength of milk was increased. The casein content of milk and the quantity of chymosin added to milk had no significant effect on the retention of chymosin in curd; the quantity of coagulant bound per gram of casein remained unchanged.     

Polymerization and gelation of whey protein isolates at low pH using transglutaminase enzyme

Dynamic and steady shear rheology is used to examine the synthesis of low-pH (approximately 4) whey protein gels obtained through a two-step process. The first step involves cross-linking of whey proteins at pH 8 and 50 degrees C using transglutaminase enzyme, while the second step entails cold-set acidification of the resulting solution using glucono-delta-lactone (GDL) acid. During the first step, the sample undergoes enzyme-catalyzed epsilon-(gamma-glutamyl)lysine bond formation with a substantial increase in viscosity. Acidification in the second step using GDL acid leads to a rapid decrease in pH with a concomitant increase in the elastic (G') and viscous (G' ') moduli and formation of a gelled network. We examine the large strain behavior of the gel samples using a relatively new approach that entails plotting the product of elastic modulus and strain (G'gamma) as a function of increasing dynamic strain and looking for a maximum, which corresponds to the yield or fracture point. We find the enzyme-catalyzed gels to have significantly higher yield/fracture stress and strain compared to cold-set gels prepared without enzyme or conventional heat-set gels. In addition, the elastic modulus of the enzyme-catalyzed gel is also higher than its non-enzyme-treated counterpart. These results are discussed in terms of the gel microstructure and the role played by the enzyme-induced cross-links.     

Removal of cholesterol from Cheddar cheese by beta-cyclodextrin

This study was carried out to determine the cholesterol removal rate and resulting changes in flavor, fatty acid and bitter amino acid production in reduced-cholesterol Cheddar cheese, made by cream separation followed by 10% beta-cyclodextrin (beta-CD) treatment. The cholesterol removal from the cheese was 92.1%. The production of short-chain free fatty acids (FFAs) increased the ripening time in control and cream-treated cheeses. The quantity of short-chain FFAs released between treatments during ripening was different, while not much difference was found in the production of neutral volatile compounds in the samples. Reduced-cholesterol cheese produced much higher levels of bitter amino acids than the control. In sensory analysis, the texture score of control Cheddar cheese increased significantly with ripening time; however, that of the cream treatment group decreased dramatically with ripening time. On the basis of our results, we conclude that the cheese made from beta-CD-treated cream had a higher rate of cholesterol removal and ripened rapidly.     

Phenological Disorder Induced by Atmospheric Nitrogen Deposition: Original Causes of Pine Forest Decline over Japan. Part I. Phenological Disorder,Cold Death of Apical Shoots of Red Pine Subjected to Combined Exposures of Simulated Acid Rain and Soil Acidification,and Implications for Forest Decline

Seeds of red pine (Pinus densiflora Sieb. and Zucc.) were sown in red-yellow soil artificially adjusted to pH (H₂O) 4.10, 4.60 or 5.90 by adding H₂SO₄ solution to the soil (pH 5.90), and the three-month seedlings were exposed to simulated acid rain at pH 2.0, 3.0 or 5.6 for 10 minutes once, 3 times a week, for 12 months from 4 August 1994 to 3 August 1995 alone or in combination. Significant interactive effects between acid rain and soil acidification on growth and whole-plant net photosynthetic rate, and cold death ratio of new apical shoots following a cold snap were observed in a quadratic response pattern. The simulated acid rain increased budburst, new needle spread and elongation, and new apical shoot death percentage following a cold snap, but did not induce visible injury. In the highest soil acidity treatment at a soil pH 4.1, whole-plant net photosynthetic rate and seedling height exhibited a quadratic responses with increasing rain acidities. On the other hand, soil acidification caused leaf yellowing. The death percentage of new apical shoot of seedlings exposed to rain pH 2.0 following a cold snap was linearly enlarged with increasing soil acidities. With increasing soil acidity, height and whole-plant net photosynthesis of the seedlings exposed to rain pH 3.0 exhibited a linear increase response, while height of seedlings exposed to control rain exhibited a quadratic response. It is suggested that the results provide experimental evidency for phenological disturbances and an enhancement of frost risk by direct acid rain and indirect longterm soil acidification which may be significant in forest decline.