Long Term Use of a Cheddar Starter and Development of Phages with Homology to its Bacteria

A mixed, homofermentative, mesophilic starter was used for more than 11 years as the only starter for production of Cheddar cheese at a Danish cheese factory. The activity of the starter at the factory was carefully recorded, and whey samples were regularly tested for bacteriophages. During the years bacteriophages, homologous to an increasing number of the strains of the starter culture, gradually evolved. After 4 years bacteriophages, homologous to more than 50%—and after 6 years to more than 90%—of 62 bacterial isolates from the starter, had appeared. For most of the strains the virulence of their phages was low at first and thereafter increased over several years. It was, however, only after more than 11 years that the cheese factory first began to observe cases of reduced activity of the bulk starter; presumably because the virulence of the bacteriophages had developed to such a degree that very low levels of contamination of the milk for bulk starter could impair the subsequent activity of the bulk starter in the curd.     

Factors affecting solubility of calcium lactate in aqueous solutions

Calcium lactate (CaL2) crystal formation on the surface of cheese continues to be a widespread problem for the cheese industry despite decades of research. To prevent those crystals from forming, it is necessary to keep the concentration of CaL2 below saturation level. The limited data available on the solubility of CaL2 at conditions appropriate for the storage of cheese are often conflicting. In this work, the solubility of L(+)-CaL2 in water was evaluated at 4, 10, and 24 degrees C, and the effects of salt and pH at those temperatures were investigated. The effects of additional calcium and lactate ions on solubility also were studied. The results suggested that temperature and the concentration of lactate ions are the main factors influencing the solubility of CaL2, with the other parameters having limited effect.     

Impact of autolytic, proteolytic, and nisin-producing adjunct cultures on biochemical and textural properties of cheddar cheese

The effect of incorporating a highly autolytic strain (Lactobacillus delbrueckii subsp. bulgaricus UL12) a proteolytic strain (Lactobacillus casei subsp. casei L2A), or a nisin Z-producing strain (Lactococcus lactis, subsp. lactis biovar diacetylactis UL719) into Cheddar cheese starter culture (Lactococcus lactis KB and Lactococcus cremoris KB) on physicochemical and rheological properties of the resultant cheeses was examined. Cheeses were ripened at 7 degrees C and analyzed over a 6-mo period for viable lactococcal and lactobacilli counts, pH, titratable acidity (TA), lipolysis, proteolysis, and textural characteristics. The combination of the nisin-producing strain and autolytic adjuncts significantly increased the production of water-soluble nitrogen, free amino acids, and free fatty acids. The effect of Lc. diacetylactis UL719 alone or of Lb. casei L2A on water-soluble nitrogen and free amino acid contents were also significant, whereas their effect on free fatty acids was not. Viable counts of Lb. bulgaricus UL12 were significantly reduced in the presence of Lc. diacetylactis UL719. Lactobacilli-containing cheeses showed significantly lower values for hardness, fracturability, and springiness. It could be concluded that the addition of Lb. bulgaricus UL12 together with a nisin-producing strain produces a greater increase in cheese proteolysis and an improvement in Cheddar cheese texture.     

Antioxidant activity of Cheddar cheeses at different stages of ripening

The aim of the study was to evaluate the changes in the antioxidant properties of Cheddar cheese at different stages of ripening using different assays: 2, 2'-azinobis (3 ethyl benzothiazoline)-6-sulphonic acid, 2, 2-diphenyl 1, picryl hydrazyl and superoxide radical scavenging activity. Cheddar cheese was prepared with Lactobacillus casei ssp. casei 300 and Lactobacillus paracasei ssp. paracasei 22 and without adjunct cultures. The antioxidant activity of water-soluble extracts of Cheddar cheese was dependent on the ripening period. The changes in the antioxidant activity were related to the rate of formation of soluble peptides (proteolysis) in all the samples of cheeses up to fourth month of ripening.     

复合天然抑菌膜对Cheddar干酪的保鲜效果

使用不同复合天然抑菌膜（无覆膜保鲜（空白）、酪蛋白酸钠-壳聚糖-纳他霉素膜（M1）、酪蛋白酸钠-壳聚糖-纳他霉素/溶菌酶膜（M2））对Cheddar干酪保鲜效果进行研究,在4℃冷藏条件下,对干酪感官、不同贮藏时间的水分含量、p H、滴定酸度、可溶性氮含量、融化性和油脂析出性、质构特性及SDS-凝胶电泳、微生物指标的变化进行测定。结果表明:与空白相比,M1和M2膜包装干酪的各项感官、理化指标较好,质构特性相对较优,并且M1膜包装干酪SDS-凝胶电泳图谱说明其蛋白水解程度相对较低,干酪溶液铺平板培养48 h后的菌落数（3.5×10⁴CFU/m L）少于M2膜（6.8×10⁴CFU/m L）和空白（9.2×10⁴CFU/m L）,因此,M1膜包装明显优于M2膜,并且M1膜和M2膜对Cheddar干酪均具有良好的抗菌保鲜性,可有效延长Cheddar干酪的贮藏期。      

低脂乳的不同热处理工艺对切达奶酪品质的影响

通过对切达奶酪p H、水分含量、产率、质构和融化性的测定,研究了低脂乳的不同热处理工艺对其品质的影响。结果表明:3个不同热处理工艺下乳清蛋白变性率分别为17.5%、35.1%和68.3%。随着热处理强度的增大,切达奶酪的p H和融化性下降,水分含量和产率提高,质构指标中的硬度、弹性、内聚性和咀嚼度下降,黏着性上升。利用扫描电镜和电泳技术分析不同热处理工艺对奶酪品质造成的差异。结果表明:随着热处理强度的增大,乳清蛋白变性率增大,形成的大分子聚合物被截留在奶酪的网状结构中,影响了酪蛋白的聚集,进而对其品质产成了影响。      

Application of exopolysaccharide-producing cultures in reduced-fat Cheddar cheese: cryo-scanning electron microscopy observations

The microstructure of reduced- and full-fat Cheddar cheeses made with exopolysaccharide (EPS)-producing and nonproducing cultures was observed using cryo-scanning electron microscopy. Fully hydrated cheese samples were rapidly frozen in liquid nitrogen slush (−207°C) and observed in their frozen hydrated state without the need for fat extraction. Different EPS-producing cultures were used in making reduced-fat Cheddar cheese. Full-fat cheese was made with a commercial EPS-nonproducing starter culture. The cryo-scanning electron micrographs showed that fat globules in the fully hydrated cheese were surrounded by cavities. Serum channels and pores in the protein network were clearly observed. Young (1-wk-old) full-fat cheese contained wide and long fat serum channels, which were formed because of fat coalescence. Such channels were not observed in the reduced-fat cheese. Young reduced-fat cheese made with EPS-nonproducing cultures contained fewer and larger pores than did reduced-fat cheese made with a ropy strain of Lactococcus lactis ssp. cremoris (JFR1), which had higher moisture levels. A 3-dimensional network of EPS was observed in large pores in cheese made with JFR1. Major changes in the size and distribution of pores within the structure of the protein network were observed in all reduced-fat cheeses, except that made with JFR1, as they aged. Changes in porosity were less pronounced in both the full-fat and the reduced-fat cheeses made with JFR1.     

Rheological Properties of Cheddar Cheese as Influenced by Fat Reduction and Ripening Time

Fat reduction in Cheddar cheese resulted in an increase in viscoelasticity as evidenced by increases in G’and G”. Proteolysis during ripening led to softening of all cheeses and thus decreases in G’and G” for cheeses containing 34, 27, and 20% fat. Cheese with 13% fat showed a decrease in G’upon ripening, but no change in G”. This lack of change in viscous behavior may be important to the texture of reduced-fat Cheddar cheese and overall acceptability. Dynamic rheological testing was helpful in understanding rheological behavior associated with fat reduction in cheese.     

Reduced-fat Cheddar cheese from a mixture of cream and liquid milk protein concentrate

Reduced-fat Cheddar cheese (RFC) was manufactured from standardized milk (casein/fat, C/F ˜ 1.8), obtained by (1) mixing whole milk (WM) and skim milk (SM) (control) or (2) mixing liquid milk protein concentrate (LMPC) and 35% fat cream (experimental). The percentage yield, total solid (TS) and fat recoveries in the experimental RFC were 22.0, 63.0 and 89.5 compared to 9.0, 50.7 and 87.0 in the control RFC, respectively. The average % moisture, fat, protein, salt and lactose were 40.7, 15.3, 32.8, 1.4 and 0.07%, respectively, in the experimental cheese and 39.3, 15.4, 33.0, 1.3 and 0.10%, respectively, in the control cheese. No growth of nonstarter lactic acid bacteria (NSLAB) was detected in the control or the experimental cheeses up to 3 months of ripening. After 6 months of ripening, the experimental cheese had 10⁷ cfu NSLAB/g compared to 10⁶ cfu/g in the control. The control cheese had higher levels of water-soluble nitrogen (WSN) and total free amino acids after 6 months of ripening than the experimental cheese. Sensory analysis showed that the experimental cheeses had lower intensities of milk fat and fruity flavours and decreased bitterness but higher intensities of sulphur and brothy flavours than in the control cheese. The experimental cheeses were less mature compared to the control after 270 days of ripening. It can be concluded from the results of this study that LMPC can be used in the manufacture of RFC to improve yield, and fat and TS recovery. However, proteolysis in cheese made with LMPC and cream is slower than that made with WM and SM.     

钾盐替代和附属发酵剂对切达干酪品质的影响

为明确降低钠含量和添加在脱脂乳中表现出具有较高血管紧张素转换酶（angiotensin-converting enzyme,ACE）抑制率的Lactobacillus paracasei M3作为附属发酵剂对切达干酪理化性质和体外抗高血压潜力的影响,将部分钾盐替代和L. paracasei M3单独和混合加入到干酪与空白组作对照,以主要成分、微生物、蛋白水解度、质构和风味为理化指标和以ACE抑制率为体外抗高血压潜力指标。结果表明,4 组干酪的主要成分差异不大（P＞0.05）,钾盐替代组、L. paracasei M3组、钾盐替代和L. paracasei M3混合组干酪在乳酸菌总数、pH 4.6可溶性氮、总游离氨基酸上显著高于空白组干酪（P＜0.05）,但是降低了干酪的硬度、pH值和有明显的苦味（P＜0.05）,而在体外抗高血压潜力方面,3 组干酪在成熟6 个月之后ACE抑制率达65.2%、74.3%和78.7%,比空白组分别高19.6%、36.2%和44.4%,由此可知,在切达干酪中钾盐替代和添加L. paracasei M3有助于具有抗高血压潜力的ACE抑制肽的产生,但是后续需要对风味进行补偿性研究。