Ultrafiltration of cheese milk: Effect on plasmin activity and proteolysis during cheese ripening

Havarti 45+ cheese was manufactured from milk concentrated 1.8–4.6-fold by ultrafiltration (UF) and from normal milk, and the effect of concentration factor on plasmin activity and subsequent proteolysis in cheese during ripening was examined. There was decreased plasmin activity and a reduced rate of proteolysis of α_S2-casein and β-casein in the UF-cheeses, compared with the corresponding controls, independent of concentration factor. The decreased plasmin activity and slower breakdown of α_S2-casein and β-casein in UF-cheeses compared with traditional cheeses can be partly explained by the inclusion of an increased amount of plasmin inhibitors into the UF-cheeses. However, it is suggested that the differences in plasmin activity and proteolysis arise mainly as a result of inactivation of the plasminogen activation system during UF-concentration, due to a combination of time, temperature and the presence of air in the UF-equipment. The effect of milk treatment on the plasminogen activation system should be further investigated.     

Quality changes in pomegranates during ripening and cold storage

The changes in the quality parameters of Spanish pomegranate fruit (cultivar Mollar) during ripening and during 7 weeks of cold storage at 5°C and 90–95% relative humidity were studied. The fruit and seed weights, as well as the surface colour increased with ripening. Total soluble solids (TSS), pH and titratable acidity (TA) did not show significant differences during the weeks studied (from the 26th to 32nd weeks after flowering), but the seeds' colour (Lab values) and juice colour (absorbance at 510 nm) showed an increase during this period with a maximum during the last 2 weeks. These results indicate that pomegranates should be harvested during the 31st to the 32nd after flowering, in order to get the best pigmentation without a decrease in other quality parameters. The anthocyanin profile changed during the different maturity stages, since the diglucoside derivatives were the prevailing pigments during the early ripening stages, whereas the monoglucoside derivatives were the main pigments in the latter stages. After cold storage of pomegranates harvested at two maturity stages, no differences in TSS, pH, TA and skin colour were observed. In addition, seeds' and juice colour did not decrease during storage. Hence, this study supports the theory that pomegranate is a nonclimacteric fruit and that pomegranates can be stored for at least 45 days without deterioration in the fruit quality.     

The effect of different precooling rates and cold storage on milk microbiological quality and composition

The objective of this study was to measure the effect of different milk cooling rates, before entering the bulk tank, on the microbiological load and composition of the milk, as well as on energy usage. Three milk precooling treatments were applied before milk entered 3 identical bulk milk tanks: no plate cooler (NP), single-stage plate cooler (SP), and double-stage plate cooler (DP). These precooling treatments cooled the milk to 32.0 ± 1.4°C, 17.0 ± 2.8°C, and 6.0 ± 1.1°C, respectively. Milk was added to the bulk tank twice daily for 72 h, and the tank refrigeration temperature was set at 3°C. The blend temperature within each bulk tank was reduced after each milking event as the volume of milk at 3°C increased simultaneously. The bacterial counts of the milk volumes precooled at different rates did not differ significantly at 0 h of storage or at 24-h intervals thereafter. After 72 h of storage, the total bacterial count of the NP milk was 3.90 ± 0.09 log₁₀ cfu/mL, whereas that of the precooled milk volumes were 3.77 ± 0.09 (SP) and 3.71 ± 0.09 (DP) log₁₀ cfu/mL. The constant storage temperature (3°C) over 72 h helped to reduce bacterial growth rates in milk; consequently, milk composition was not affected and minimal, if any, proteolysis occurred. The DP treatment had the highest energy consumption (17.6 ± 0.5 Wh/L), followed by the NP (16.8 ± 2.7 Wh/L) and SP (10.6 ± 1.3 Wh/L) treatments. This study suggests that bacterial count and composition of milk are minimally affected when milk is stored at 3°C for 72 h, regardless of whether the milk is precooled; however, milk entering the tank should have good initial microbiological quality. Considering the numerical differences between bacterial counts, however, the use of the SP or DP precooling systems is recommended to maintain low levels of bacterial counts and reduce energy consumption.     

复合天然防腐保鲜液对Mozzarella干酪贮藏期的影响

采用无盐渍新工艺法制作部分脱脂Mozzarella干酪,使用复合天然防腐保鲜液(0.69%茶多酚+0.013%Nisin和溶菌酶(1∶1)+0.0043%那他霉素)对成熟干酪样品进行浸泡处理,并在4℃冷藏,通过每间隔7d测定干酪不同贮藏时间的水分含量、pH、滴定酸度、可溶性氮含量(SN)、SDS-凝胶电泳、未融化干酪质构特性、融化干酪功能特性、微生物指标和感官评定等一系列指标的变化,评定复合天然防腐保鲜液对Mozzarella干酪贮藏效果的影响。实验结果表明:浸泡处理组4℃冷藏49d时的贮藏效果与对照组28d时相当,复合天然防腐保鲜液的使用可有效延长Mozzarella干酪的贮藏期。     

Plasmin activity, β-lactoglobulin denaturation and proteolysis in high pressure treated milk

The effects of high pressure (HP) on plasmin activity, β-lactoglobulin denaturation and proteolysis during subsequent storage of HP treated milk, were studied. Fresh raw milk samples were exposed to a range of pressures from 50 to 800 MPa, for times of 1, 10 or 30 min, at 20°C. Residual plasmin activity and whey protein denaturation were measured immediately post HP-treatment. Indices of proteolysis were measured during post-HP storage. Treatment at pressures >300 MPa resulted in extensive β-lactoglobulin denaturation. Plasmin activity decreased in milk treated at pressures 400 MPa; the loss of activity was not well correlated with β-lactoglobulin denaturation. Compared to raw milk, treatment at 50 MPa had little effect on proteolysis during storage of treated milk measured as increases in pH 4.6-soluble N and liberation of proteose peptones, but at pressures of 300–400 MPa, proteolysis was increased relative to raw milk. After pressurisation >500 MPa, proteolysis during storage of milk was less than that observed in raw milk. Overall, HP influenced proteolysis in milk in a way which is different from that produced by heat, in terms of subsequent susceptibility of casein to proteolysis during storage or incubation. In particular, HP treatment at pressures of 300–500 MPa can increase proteolysis in milk, possibly through changes in micelle structure facilitating increased availability of substrate bonds to plasmin, which has implications for products prepared from milk thus treated.     

Effect of β-casein concentration in cheese milk on rennet coagulation properties,cheese composition and cheese ripening

Effects of the use of a β-casein powder to enrich cheese milk on rennet coagulation properties of milk, cheese composition and cheese ripening were investigated. Casein content of control milk was 2.5%, whereas that for the three enriched milks was adjusted with β-casein powder at 2.7%, 2.9% and 3.1%. The β-casein to α-casein ratio of these cheese milks was, respectively, 0.70, 0.79, 0.89 and 0.99. Rennet coagulation properties were related not only to casein concentration but also to the proportion of β-casein and α_s-casein presents in milks. Milk with higher concentration of β-casein had poorer coagulation properties. Cheeses could be produced by using a miniature cheese making process. Moisture, ash and calcium contents decreased, while protein content and β-casein increased in cheese as casein and β-casein concentration increased in milk. As a result, hardness was higher in enriched cheeses than in control cheese. During cheese ripening, α-casein was hydrolyzed, but the rate of degradation of α-casein decreased as protein and β-casein concentration increased in cheese. β-Casein seemed to be not hydrolyzed. The rate of decrease of hardness was also slower for enriched cheeses.     

Use of milk protein concentrate to standardize milk composition in Italian citric Mozzarella cheese making

To better exploit manufacturing facilities and standardize cheese quality, milk composition could be standardized by fortifying its protein content with a milk protein concentrate (MPC) addition so avoiding partially skimming the milk. With this aim Mozzarella cheese was obtained adding citric acid into milk standardized at 4% protein and a fat to protein ratio of 1.0. Protein fortification was obtained adding MPC produced by ultrafiltration. Milk, whey, curd, cheese and stretching water were weighed and analysed for total solid, fat and protein content, to measure component recovery and yield. Yield increase (from 13.8% to 16.7%) was due to the higher recovery of the milk total solids and proteins in MPC cheese (48.2 and 78.3%, respectively) and to the slightly higher cheese moisture, obtained with a little modification of the cheese technology when adding MPC. Milk fat in cheese was lower than that reported in literature. Hot water stretching of the curd resulted in very low losses (1%) of protein and considerable losses (14%) of fat for both control and MPC cheeses. The likely reasons of this low recovery are discussed and it can be supposed that a further cheese yield increase is possible by changing the curd stretching procedures.     

The effect of storage conditions on the composition and functional properties of blended bulk tank milk

The objective of this study was to investigate the effects of storage temperature and duration on the composition and functional properties of bulk tank milk when fresh milk was added to the bulk tank twice daily. The bulk tank milk temperature was set at each of 3 temperatures (2, 4, and 6°C) in each of 3 tanks on 2 occasions during two 6-wk periods. Period 1 was undertaken in August and September when all cows were in mid lactation, and period 2 was undertaken in October and November when all cows were in late lactation. Bulk tank milk stored at the 3 temperatures was sampled at 24-h intervals during storage periods of 0 to 96 h. Compositional parameters were measured for all bulk tank milk samples, including gross composition and quantification of nitrogen compounds, casein fractions, free amino acids, and Ca and P contents. The somatic cell count, heat stability, titratable acidity, and rennetability of bulk tank milk samples were also assessed. Almost all parameters differed between mid and late lactation; however, the interaction between lactation, storage temperature, and storage duration was significant for only 3 parameters: protein content and concentrations of free cysteic acid and free glutamic acid. The interaction between storage temperature and storage time was not significant for any parameter measured, and temperature had no effect on any parameter except lysine: lysine content was higher at 6°C than at 2°C. During 96 h of storage, the concentrations of some free amino acids (glutamic acid, lysine, and arginine) increased, which may indicate proteolytic activity during storage. Between 0 and 96 h, minimal deterioration was observed in functional properties (rennet coagulation time, curd firmness, and heat stability), which was most likely due to the dissociation of β-casein from the casein micelle, which can be reversed upon pasteurization. Thus, this study suggests that blended milk can be stored for up to 96 h at temperatures between 2°C and 6°C with little effect on its composition or functional properties.     

The effect of homogenization and milk fat fractions on the functionality of Mozzarella cheese

Mozzarella cheese was manufactured from milk containing either a low (olein) or a high (stearin) melting point fraction of milk fat or anhydrous milk fat. The fat was dispersed into skim milk by homogenization at 2.6 MPa before being manufactured into cheese. The melting point of the milk fat did not affect the size or shape of the fat globules, nor was there any effect of homogenization on the polymorphic state of the milk fat. There were no changes in milk fat globule size and shape concomitant with the amount of free oil formed. The polymorphic state of the milk fat did affect the amount of free oil formed and the apparent viscosity of the cheese. The lower melting point fraction yielded a larger amount of free oil. The higher melting point fraction yielded a higher viscosity of melted cheese at 60 degrees C. Mozzarella cheese was also manufactured from homogenized milk, nonhomogenized milk, and a 1:1 ratio of the two, without altering the milk fat composition. Increasing the proportion of homogenized milk yielded a lower free oil content and higher viscosity of the cheese.     

贮存温度和贮存时间对复原乳稳定性的影响

研究了贮存温度和贮存时间对复原乳的pH值、流变特性、粒径、乳析率和离心沉淀率的影响,在此基础上分析了贮存过程中乳浊液粒径与乳析率、离心沉淀率之间的相关性。结果表明:随着贮存温度的升高,复原乳的pH值与表观黏度逐渐降低,而随着贮存时间的延长,二者均先升高后降低,其中25℃和37℃下贮存在第15天时达到最大值,而55℃下贮存在第7天时达最大值;贮存过程中乳浊液顶部粒径d4,3与乳析率有较好的相关性(P<0.05),二者均随着贮存温度的升高和贮存时间的延长而增大;贮存过程中乳浊液底部粒径d4,3与离心沉淀率有很好的相关性(P<0.05),二者随着贮存温度的升高先增大后减小,在37℃时达最大值,随着贮存时间的延长均有所增大。     

Effect of camel chymosin on the texture,functionality, and sensory properties of low-moisture,part-skim Mozzarella cheese

The objective of this study was to compare the effect of coagulant (bovine calf chymosin, BCC, or camel chymosin, CC), on the functional and sensory properties and performance shelf-life of low-moisture, part-skim (LMPS) Mozzarella. Both chymosins were used at 2 levels [0.05 and 0.037 international milk clotting units (IMCU)/mL], and clotting temperature was varied to achieve similar gelation times for each treatment (as this also affects cheese properties). Functionality was assessed at various cheese ages using dynamic low-amplitude oscillatory rheology and performance of baked cheese on pizza. Cheese composition was not significantly different between treatments. The level of total calcium or insoluble (INSOL) calcium did not differ significantly among the cheeses initially or during ripening. Proteolysis in cheese made with BCC was higher than in cheeses made with CC. At 84 d of ripening, maximum loss tangent values were not significantly different in the cheeses, suggesting that these cheeses had similar melt characteristics. After 14 d of cheese ripening, the crossover temperature (loss tangent = 1 or melting temperature) was higher when CC was used as coagulant. This was due to lower proteolysis in the CC cheeses compared with those made with BCC because the pH and INSOL calcium levels were similar in all cheeses. Cheeses made with CC maintained higher hardness values over 84 d of ripening compared with BCC and maintained higher sensory firmness values and adhesiveness of mass scores during ripening. When melted on pizzas, cheese made with CC had lower blister quantity and the cheeses were firmer and chewier. Because the 2 types of cheeses had similar moisture contents, pH values, and INSOL Ca levels, differences in proteolysis were responsible for the firmer and chewier texture of CC cheeses. When cheese performance on baked pizza was analyzed, properties such as blister quantity, strand thickness, hardness, and chewiness were maintained for a longer ripening time than cheeses made with BCC, indicating that use of CC could help to extend the performance shelf-life of LMPS Mozzarella.     

The effect of two types of mould inoculants on the microbiological composition,physicochemical properties and protein hydrolysis in two Gorgonzola‐type cheese varieties during ripening

The aim of this paper was to investigate the role of two types of Penicillium roqueforti moulds (type esportazione and dolce) in the ripening of two Gorgonzola‐type cheese varieties. Cheeses were analysed after 4, 14, 30 and 60 days of ripening. Microbiological analysis showed high numbers of total bacterial count, yeasts and moulds in both 60‐day‐old cheese varieties. The concentration of water‐soluble N, nonprotein N and 5% phosphotungstic acid‐soluble N increased significantly during ripening. Patterns of proteolysis by urea‐polyacrylamide gel electrophoresis showed that rind‐to‐core gradients and age‐related changes in moisture and salt content influenced mould and other enzyme activities, which are reflected in various rates of protein degradation. The hydrolysis of αs₁‐ and β‐caseins was more extensive in the core than under the rind of both cheese varieties.     

Effect of whey pH at drainage on physicochemical, biochemical, microbiological, and sensory properties of Mozzarella cheese made from buffalo milk during refrigerated storage

The objective of this research was to determine the effect of drainage pH on physicochemical, biochemical, microbiological and sensory properties of Mozzarella cheese made from buffalo milk during refrigerated storage. Four vats of cheese were made at 4 different whey drainage pH (6.2, 5.9, 5.6, and 5.2). Lower drainage pH caused higher pH 4.4-soluble N and pH 4.4-soluble N:total N. Interaction of drainage pH at d 1 and 30 of storage on all soluble nitrogen fractions was significant. Degradation of caseins in samples made at a drainage pH of 6.2 was lower than that of other cheese samples. The decreasing whey drainage pH significantly increased counts of thermophilic and mesophilic lactobacilli of the samples during refrigerated storage. No coliforms or Escherichia coli were detected in the cheeses. The average sensory property scores of all cheese samples were very close, and, as expected, storage time had a negative effect on all sensory scores.     

Influence of calcium, pH, and moisture on protein matrix structure and functionality in direct-acidified nonfat Mozzarella cheese

Influence of calcium, moisture, and pH on structure and functionality of direct-acid, nonfat Mozzarella cheese was studied. Acetic acid and citric acid were used to acidify milk to pH 5.8 and 5.3 with the aim of producing cheeses with 70 and 66% moisture, and 0.6 and 0.3% calcium levels. Cheeses containing 0.3% calcium were softer and more adhesive than cheeses containing 0.6% calcium, and flowed further when heated. Cheeses with the same calcium content (0.6%), the same moisture content, but set at different pH values (pH 5.3 and 5.8), exhibited no significant differences in melting or firmness. Increasing cheese moisture content from 66 to 70% produced a softer cheese but did not increase meltability. Such differences in functionality corresponded with differences in structure and arrangement of proteins in the cheese protein matrix. Microstructure of cheese with 0.6% calcium had an increase in protein folds and serum pockets compared with the 0.3% calcium cheeses that had a more homogeneous structure. Protein matrix in the low-calcium cheese appeared less dense indicating the proteins were more hydrated. In the 0.6% calcium cheeses, the proteins appeared more aggregated and had larger spaces between protein aggregates. Thus, between pH 5.3 and 5.8, calcium controls cheese functionality, and pH has only an indirect affect related to its influence on the calcium in cheese.     

成熟温度对Mozzarella干酪蛋白水解和质构的影响

研究了温度为4,7,10℃时对干酪成熟过程中蛋白水解和质地的影响。结果表明,随着干酪成熟温度的升高,成熟期间干酪中可溶性氮与总氮的比值增加较快,干酪的硬度下降速度也较快。说明在较高的成熟温度下,干酪在较短的时间内能够达到成熟的状态。     

Effects of Penicillium roqueforti and whey cheese on gross composition,microbiology and proteolysis of mould‐ripened Civil cheese during ripening

Four different types of mould‐ripened Civil cheese were manufactured. A defined (nontoxigenic) strain of a Penicillium roqueforti (SC 509) was used as the secondary starter with and without addition of the whey cheese (Lor); in parallel, secondary starter‐free counterparts were manufactured. Chemical composition, microbiology and proteolysis were studied during the ripening. The incorporation of whey cheese in the manufacture of mould‐ripened Civil cheese altered the gross composition and adversely affected proteolysis in the cheeses. The inoculated P. roqueforti moulds appeared to grow slowly on those cheeses, and little proteolysis was evident in all cheese treatments during the first 90 days of ripening. However, sharp increases in the soluble nitrogen fractions were observed in all cheeses after 90 days. Microbiological analysis showed that the microbial counts in the cheeses were at high levels at the beginning of ripening, while their counts decreased approximately 1–2 log cfu/g towards the end of ripening.     

Comparison of the rheology of mozzarella-type curd made from buffalo and cows’ milk

Curd rheology and calcium distribution in buffalo and cows’ milk, were compared at their natural pH and during acidification (pH 6.5–5.6). Buffalo milk displays a curd structure and rheology different from that of cows’ milk and the casein-bound calcium, as well as the contents of fat, protein and calcium, are also higher. Due to these higher amounts of casein-bound calcium, the overall curd strength with buffalo milk (as indicated by the dynamic moduli) was higher, at similar pH values, than those of equivalent gels produced from cows’ milk. The curd rheology was adversely affected at lower pH (5.8–5.6) in both of the milk types, due to the loss of casein-bound calcium from casein micelles. The degree of solubilisation of calcium in buffalo milk during acidification is quite different from that observed in cows’ milk with a lower proportion of the calcium being solubilised in the former. The maximum curd firmness was obtained at pH 6.0 in both milk types. For both species, these rheological and micellar changes were qualitatively the same but quantitatively different, due to the different milk compositions.     

The influence of ripening temperature and sampling site on the proteolysis in Reggianito Argentino cheese

The effects of elevated ripening temperature and sampling site on proteolysis in Reggianito Argentino cheese were evaluated. Cheeses ripened at 12 or 18 °C and 85% relative humidity were analysed at 2, 4 and 6 months in 2 sampling zones (central and external). Samples were analysed to determine the physicochemical and proteolysis parameters through the urea-PAGE of the urea-soluble fraction, RP-HPLC analysis of the water-soluble fraction at pH 4.6, and the free amino acid analysis. Proteolysis was significantly affected by ripening temperature and sampling site. Urea-PAGE analysis showed that elevated temperature increased the degradation of α_s1- and β-casein. The degradation of α_s1-casein was larger in the central zone than in the external one, while β-casein degradation was similar in both zones. The majority peaks detected by RP-HPLC of the water-soluble fraction at pH 4.6 and free amino acids were significantly affected by ripening temperature and sampling site. Glu, His, Val, Leu, and Lys had the higher concentrations. Principal component analysis showed useful groupings when results from chromatograms were studied. In conclusion, the results obtained not only are useful to characterise the ripening of an Argentinean hard cheese, but also to evaluate the effect of an increase of ripening temperature on Reggianito Argentino cheese proteolysis.     

The effect of application of cold natural smoke on the ripening of Cheddar cheese

The present study was undertaken to study the effects of application of natural wood smoke on ripening of Cheddar cheese, and to determine the effects of smoking before or after ripening on cheese quality. A 20-kg block of Cheddar cheese obtained immediately after pressing was divided into six approximately 3-kg blocks and ripened at 8 degrees C for up to 270 d. One 3-kg block was taken after 1 d, 1, 3, 6, or 9 mo and smoked for 20 min, then returned to the ripening room for further ripening. Cheeses were sampled at intervals for lactobacilli counts, moisture, pH, and proteolysis. Sensory analysis was conducted on 6 and 9-mo-old cheeses by a trained sensory panel (n = 7). Results show that application of natural wood smoke did not significantly affect cheese pH or primary proteolysis during ripening. However, secondary proteolysis as assessed by the concentrations of free amino acids was generally higher in smoked cheeses than in control cheeses after 6 mo of ripening. Cheese smoked after 6 mo of ripening had better smoked flavor than that smoked after 9 mo of ripening. Cheese smoked after 3 mo of age and further ripened for 6 mo had the highest smoked flavor intensity. It is concluded that it is best to smoke cheese after ripening for at least 3 mo.     

The effect of substitution of NaCl with KCl on chemical composition and functional properties of low-moisture Mozzarella cheese

The effect of NaCl substitution with KCl on chemical composition, organic acids profile, soluble calcium, and functionality of low-moisture Mozzarella cheese (LMMC) was investigated. Functionality (meltability and browning), organic acids profile, and chemical composition were determined. Chemical composition showed no significant difference between experimental cheeses at same storage period, and same salt treatment. Meltability of LMMC salted with 3NaCl:1KCl, 1NaCl:1KCl, and 1NaCl:3KCl was higher compared with only NaCl (control). The amount of soluble Ca and P increased significantly during storage, with no significant difference between salt treatments. Organic acids profile did not differ between salt treatments at the same storage time.