半硬质干酪加工工艺条件的研究

通过单因素试验和正交优化试验,研究发酵剂添加量、CaCl2添加量、凝乳酶添加量、凝乳温度和盐水浓度对半硬质干酪感官品质的影响,从而得出加工半硬质干酪的最佳工艺条件。结果表明,其最佳工艺参数为发酵剂添加量5%、CaCl2添加量0.02%、凝乳酶添加量3.0 g/100 L、凝乳温度36 ℃、盐水质量分数18%。此最佳工艺条件下得到干酪的感官评分最高为93.25分,干酪产率为10.37%,含盐量为0.74%,含水量为43.58%。香味浓郁、组织细腻、软硬适度、呈现乳白色且有光泽。     

Ultrafiltered milk reduces bitterness in reduced-fat Cheddar cheese made with an exopolysaccharide-producing culture

The objectives were to reduce bitterness in reduced-fat Cheddar cheese made with an exopolysaccharide (EPS)-producing culture and study relationships among ultra-filtration (UF), residual chymosin activity (RCA), and cheese bitterness. In previous studies, EPS-producing cultures improved the textural, melting, and viscoelastic properties of reduced-fat Cheddar cheese. However, the EPS-positive cheese developed bitterness after 2 to 3 mo of ripening due to increased RCA. We hypothesized that the reduced amount of chymosin needed to coagulate UF milk might result in reduced RCA and bitterness in cheese. Reduced-fat Cheddar cheeses were manufactured with EPS-producing and nonproducing cultures using skim milk or UF milk (1.2×) adjusted to a casein:fat ratio of 1.35. The EPS-producing culture increased moisture and RCA in reduced-fat Cheddar cheese. Lower RCA was found in cheese made from UF milk compared with that in cheese made from control milk. Ultrafiltration at a low concentration rate (1.2×) produced EPS-positive, reduced-fat cheese with similar RCA to that in the EPS-negative cheese. Slower proteolysis was observed in UF cheeses compared with non-UF cheeses. Panelists reported that UF EPS-positive cheese was less bitter than EPS-positive cheese made from control milk. This study showed that UF at a low concentration factor (1.2×) could successfully reduce bitterness in cheese containing a high moisture level. Because this technology reduced the RCA level (per g of protein) to a level similar to that in the control cheeses, the contribution of chymosin to cheese proteolysis would be similar in both cheeses.     

随机扩增多态性法分析西藏牦牛奶酪中乳酸菌的遗传多样性

目的：利用随机扩增多态性（randomly amplified polymorphic DNA,RAPD）法对西藏地区牦牛奶酪中27 株乳酸菌基因型进行同源性分析。方法：利用5 个随机引物对Mg2+浓度、dNTP用量、退火温度、模版用量/引物用量（ng/pmol）4 个条件做单因素梯度试验,建立最佳反应条件,筛选最佳引物,然后对27 株乳酸菌和4 株乳酸菌标准菌株进行随机扩增,用NTsys 2.10e软件对扩增条带进行聚类和遗传相似性系数分析,分析结果与16S rRNA测序得到的菌种鉴定结果进行对比。结果：31 株菌遗传相似系数在0.72～1.00之间,当相似性系数在0.82时,菌株被分成了8 组,菌株按照不同种属聚类,聚类结果同16S rRNA测序结果基本一致,同时成功将Lactobacillus casei和Lactobacillus paracasei两个亚种区分开。结论：RAPD技术可以较好地应用于西藏地区牦牛奶酪中乳酸菌亲缘性关系分析。     

乳化盐在重制奶酪生产中的作用

阐述了乳化盐在重制奶酪中的作用，以及常用乳化盐的主要特性、实际应用和重制奶酪经常出现的质量缺陷、原因分析、采取的措施等。     

Initial pH influences in-batch hydrogen production from scotta permeate

We studied the influence of initial pH on hydrogen (H₂) production using permeate from scotta (a partially deproteinized cheese whey from ricotta production) as substrate (51 g L^?1 lactose). Dark fermentation was carried out at 35 °C in laboratory batch reactors, in an unbuffered system. Hydrogen production and metabolite (volatile fatty acids, ethanol, and lactic acid) evolution during a 96-h period were monitored in reactors with initial pH varying in the range 4–10. In all reactors, H₂ production started only when pH fell below 6. However, it was much higher (+31%) in the reactors with initial alkaline pH. We conclude that H₂ production occurs only at acidic pH values, but initial alkaline pH values increase the overall H₂ production in dark fermentation of lactose-rich substrates.     

转谷氨酰胺酶交联乳蛋白对新鲜干酪特性的影响

利用转谷氨酰胺酶(TG)交联酪蛋白,研究其对新鲜干酪凝乳的成分和质构特征的影响。结果表明,TG能够加速凝乳发酵过程,提高乳中蛋白质和脂肪的回收率,并显著降低了乳清中的蛋白含量,对凝乳的质构特征也具有明显修饰作用。但与凝乳酶同时作用时,TG酶对凝乳的修饰作用不显著。     

Effect of Free or Encapsulated Recombinant Aminopeptidase of Lactobacillus rhamnosus S93 on Acceleration of Cheddar Cheese Ripening

The use of recombinant aminopeptidase (PepN) from Lactobacillus rhamnosus S93 in free or encapsulated form was investigated to shorten the duration of Cheddar cheese ripening. Proteolysis was determined by measuring the soluble nitrogen as phosphotungstic acid (PTA-N) derivatives and free amino acids (FAA) over a 6-month period. The experimental cheeses received higher scores for sensory properties than the control cheese. The amounts of PTA-N and total FAA in the cheese with the encapsulated enzyme after 2 months of ripening were close to those of the control cheese after 6 months, suggesting the acceleration in proteolysis by about 4 months.     

Physical and processing properties of milk,butter, and cheddar cheese from cows fed supplemental fish meal

Physical, chemical, sensory and processing properties of milk produced by feeding a rumen-undegradable fish meal protein supplement to Holstein cows were investigated. The supplement contained (as fed basis) 25% soft-white wheat, 60% herring meal, and 15% feather meal. The total fat level in the milk decreased to 2.43%. For both pasteurized and ultra-high temperature processed drinking milk, no difference was found between fish meal (FM) milk and control milk in terms of color, flavor and flavor stability; in particular, no oxidized flavor was observed. Cheddar cheese made from FM milk ripened faster after 3 mo of ripening and developed a more desirable texture and stronger Cheddar flavor. The yield efficiencies for FM and control cheese, 94.4 (+/- 2.44 SE) and 96.4 (+/- 2.26 SE), respectively, were not different. Relative to controls, average fat globule size was smaller in FM milk and churning time of FM cream was longer. FM butter had softer texture and better cold spreadability, and butter oils from FM enriched milk had lower dropping points compared to control butter oil (average 32.89 versus 34.06 degrees C). These differences in physical properties of butter fat were greater than expected considering that iodine values were not different. This study demonstrates the feasibility of producing high quality products from milk naturally supplemented with FM, but the results also show that dietary changes affect processing properties.     

国内外干酪发酵的研究进展

简介了国内外干酪的产量和分布情况，综述了干酪的研究现状和技术问题，并对我国干酪的生产开发进行了展望。     

Effect of soy protein supplementation on the quality of ripening Cheddar-type cheese

The impact of soy protein isolate on the proteolysis and organoleptic properties of Cheddar-type cheese during ripening was studied. Cheese was prepared from cow's milk (control) and cow's milk plus soy protein isolate by using a starter culture of Streptococcus thermophilus and Lactobacillus delbrueckii subsp . bulgaricus, and then ripened at 12  ±  1°C for 3 and 5 months. The molecular weight range and peptide fraction in the cheeses were determined by high-performance liquid chromatography (HPLC), and the microstructure was observed by scanning electron microscopy (SEM). Sensory evaluation was used to compare the flavour, body, texture and appearance of the cheeses. The results show that the molecular weight range (9924–9966  Da) in the control cheese was larger than that (6954–6957   Da) in the soy protein-treated cheese and the microstructure in the latter was less compact than in the control cheese. In the sensory evaluation, higher scores were given for some experimental cheese than the control cheese. After 5 months of ripening, the organoleptic properties of the cheese had markedly improved and no bitter off-flavour was detected in the treated cheeses. It was concluded that soy protein could be used to improve the quality of cheese and the addition of 5% soy protein isolate could be recommended for improving the flavour and texture of Cheddar-type soy supplemented cheese.