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1.
《Food chemistry》2005,93(1):73-80
Lipolysis was studied during ripening of traditional Feta cheese produced in two small dairies, A and B. The cheeses were made from a thermized mixture of ewes’/goats’ milk by using yoghurt as starter and artisanal rennet from lambs’ and kids’ abomasa (cheese A) or mixed artisanal rennet with calf rennet (cheese B).The acid degree value and the free fatty acids (FFA) contents in both cheeses increased sharply up to 18 d (pre-ripening period at 15 °C) and continued to increase throughout ripening. In both mature cheeses, acetic acid was found at high levels (13–18% of the total FFAs). However, except for this, all FFA contents differed significantly (P < 0.05) between the two cheeses throughout ripening. The levels of individual and total C2:0–C8:0, C10:0–C14:0 and C16:0–C18:2 fatty acids were significantly higher (P < 0.05) in cheese A than in cheese B. Presumably the difference, especially in the C2:0–C8:0 content, was due mainly to the type of the rennet used. Butyric acid was the dominant FFA in cheese A (20% of the total FFAs at 120 d), while the most abundant FFAs in cheese B were capric (18%) and lauric acid (18%). In general, the lipolysis degree of the two cheeses was higher than those reported for the industrially-made Feta cheese.In organoleptic evaluation, cheese A had a piquant taste that was attributed to its high content of butyric acid and showed a significantly (P < 0.05) higher total score than cheese B.  相似文献   

2.
The occurrence and effects of the dry and rainy seasons on yeast populations in traditional Serro Minas cheese, one of the most popular cheeses produced from raw milk in Brazil, were studied over the course of 60 days of ripening. Enzymatic activity exhibited by these yeast isolates was also studied. A total of 19 yeast species were identified via sequence analysis of the D1/D2 domains of the large subunit of the rRNA gene. Fourteen yeast species were obtained from cheese produced during the dry season, and fifteen species were obtained from cheese produced during the rainy season. High diversity indices for the yeast species were determined for cheese manufactured during both seasons (average H′D = 1.7 and H′R = 1.5, respectively). The predominant species in Serro Minas cheese included Debaryomyces hansenii, Kodamaea ohmeri and Kluyveromyces marxianus. D. hansenii 28.12 showed low lipolytic and high proteolytic activity. K. marxianus 83F and 60P demonstrated lipolytic and β-galactosidase activity, respectively. K. ohmeri 88A displayed low lipolytic and β-galactosidase activity. Maximal lipase, β-galactosidase and protease activity was observed at 20 °C and pH 6.0, 30 °C and pH 7.0 and 50 °C and pH 6.0, respectively. Considering that D. hansenii 28.12, K. ohmeri 88A and K. marxianus 60P together showed protease, lipase and β-galactosidase activity in this study, further research on the possibility of including these yeasts as part of a starter culture and research on their effects on the sensory properties of Serro Minas cheese merit more study.  相似文献   

3.
Aqueous extracts obtained from cell suspension cultures of Centaurea calcitrapa were used as proteolytic additive in the manufacture of a commercial bovine cheese, coagulated with animal rennet and typically ripened for 28 d. The cheese was assessed in comparison to standard cheese for two levels of addition of said extract, viz. 0.61 and 1.22 mg of total protein mL−1. The qualitative and quantitative evolutions of the nitrogen fractions were monitored in the experimental cheeses throughout the whole ripening period. In general, the chemical compositions of the cheeses were different depending on the amount of extract used, but no significant differences could be detected in the ripening index. With regard to electrophoretic profiles, the two types of cheese could be distinguished until up to ca. 7 d of ripening, but differences did essentially vanish by 28 d.  相似文献   

4.
《International Dairy Journal》2005,15(6-9):733-740
Fat-derived flavour compounds in four different batches of Gouda cheese were monitored over 2 years of ripening. The total free fatty acid (FFA) concentrations increased from 200–400 to 700–1200 mg kg–1 dry matter, in a fairly linear manner. Long-chain FFAs were predominant in the curds, but relatively more short and intermediate chain fatty acids were released during ripening. The production of δ-lactones was rapid initially, but reached a plateau at 55 mg kg–1 dry matter in about 20 weeks. The production of γ-lactones was slower and also decreased, but was noticeable over a longer time, giving 5.5 mg kg–1 dry matter in 90 weeks. Ethyl ester formation varied substantially. Ketone levels increased only very slightly during ripening; long chain alcohols and aldehydes were not found. Some individual FFAs and lactones exceeded reported flavour thresholds, and are expected to influence the flavour of Gouda cheese.  相似文献   

5.
A preparation of exogenous alkaline phosphatase (ALP), containing 17,500 mU L−1, was added to pasteurized milk (PM) to study its role in cheese ripening. Three miniature Cheddar-type cheeses were made from PM containing no added ALP (control), PM plus 23 μL ALP (T1), to give ALP concentration similar to that in raw milk, and PM plus 46 μL ALP (T2). Milk, after addition of ALP, was held at 6 °C for 12 h before cheese manufacture and the experiment was replicated three times. The control, T1 and T2 milks contained ALP activity of 415, 2391 and 4705 mU L−1, respectively. The addition of ALP to PM caused significant (P<0.05) changes in moisture content of miniature cheeses but did not cause any changes in protein content. Levels of water-soluble N during ripening of the cheeses were similar for control, T1 and T2 cheeses. The concentration of amino acids was not affected by the level of ALP present in milk. However, reversed-phase HPLC showed differences in the peptide patterns of control, T1 and T2 cheeses, suggesting a role of ALP in cheese ripening. The results suggest that ALP may play a role in cheese ripening, but further studies are needed to confirm this.  相似文献   

6.
Because of the lytic activity on the cell wall of bacteria like Clostridium tyrobutyricum, hen's egg white lysozyme is used in cheese manufacturing to prevent late blowing. A HPLC method capable to quantify as low as 0.8 ppm lysozyme in milk and cheese is proposed. Lysozyme was extracted with 1 m NaCl at pH 6.0 and the extract was deproteinized at low pH values, reaching a recovery up to 90%. Reversed-phase HPLC was performed on a polymeric column and monitoring lysozyme under fluorescence detection (excitation at 280 nm and emission at 340 nm). The repeatability of this determination tested on a 15-month-aged hard cheese and expressed as relative standard deviation was 1.47 (n=6) and no interference of peptides formed during ripening was observed. Four commercial preparations of egg white lysozyme gave a similar fluorescence response and the partitioning over cheese and whey was studied with one of them. About 80% of the lysozyme added to the cheesemilk at concentrations up to 80 ppm was retained in the cheese and the concentration factor of lysozyme from the cheesemilk to the cheese proved to be 8.2 on average. This HPLC method and the microbiological assay using Micrococcus luteus were compared in cheese analysis, proving the former to be more accurate and reliable than the latter. Eighteen commercial samples including both generic cheeses and cheeses having protected designation of origin, all of them not declared to contain lysozyme, showed concentrations of this enzyme ranging from 0 to 111 ppm.  相似文献   

7.
The effect of high-pressure (HP) treatment (400 MPa, 600 MPa) on ripening of mature 42-day-old Irish blue-veined cheese was studied. Counts of non-starter lactic acid bacteria, lactococci, yeasts, moulds, enterococci and total aerobic bacteria significantly decreased due to HP, with moulds being most sensitive and 600 MPa the most effective treatment. The levels of pH 4.6-soluble nitrogen and (12%) trichloroacetic acid-soluble nitrogen increased immediately after both HP treatments; however, after 28 days of storage, values were lower in HP-treated cheeses than in the control cheese. Urea-polyacrylamide gel electrophoresis showed increased breakdown of β-casein due to HP treatment at both 400 MPa and 600 MPa. Levels of free fatty acids were lower in HP-treated cheese than in the control, but not significantly so, and no significant changes could be observed in the level of flavour compounds of blue-veined cheese. Overall, HP treatment of blue-veined cheese reduced microbiological activity and decelerated proteolysis, with no statistically significant effects on development of flavour compounds.Industrial relevanceHigh-pressure treatment has been studied for the past 100 years; nevertheless, it was not applied in dairy industry, until recently, for a cheese spread. In this study, HP-induced inactivation of microbes and enzymes, which could arrest the ripening of high-quality mature (i.e., ripened) Irish farmhouse blue-veined cheese and thus extend shelf-life at optimal quality, was examined.  相似文献   

8.
Four batches of Serra da Estrela cheese originating from as many dairy farms were sampled throughout the ripening period, and assayed for the evolution of free amino acid (FAA) content, total nitrogen content (TN), water-soluble nitrogen content (WSN), trichloroacetic acid-soluble nitrogen content (TCASN) and phosphotungstic acid-soluble nitrogen content (PTASN). The WSN content increased from 1% (on the day of manufacture) up to 43% of TN by 180 d of ripening, thus reflecting the intense proteolytic activity of the enzymes contributed by the plant coagulant utilized. The TCASN was also found to be high in this cheese by the end of ripening (16–20%), which suggests a high extent of FAA release throughout maturation. The major FAA by 180 d of ripening were Glu, Val, Leu and Lys, representing 56–70% of the total in all four dairies sampled. Cheeses produced from refrigerated milk possessed higher amounts of γ-amino-n-butyric acid (Gaba) and lower amounts of Glu when compared with those manufactured with non-refrigerated milk.  相似文献   

9.
《International Dairy Journal》2003,13(2-3):221-230
The physico-chemical characteristics, proteolysis (classical nitrogen fractions, caseins and their degradation products and free amino acids), and lipolysis (fat acidity and free fatty acids) were studied throughout the ripening of three batches of Babia-Laciana cheese, a Spanish traditional variety made from raw goats’ milk. The main compositional characteristics of this cheese at the end of the ripening are its high content of total solids (TS) (78.0±2.4 g 100 g−1 of cheese) and fat (61.1±1.2 g 100 g−1 of TS), the presence of residual lactose (1.6±0.8 g 100 g−1 of TS) and its low content of sodium chloride (1.1±0.7 g 100 g−1 of TS) and ash (2.8±0.5 g 100 g−1 of TS). Its pH values (4.44±0.72) are extraordinarily low. The evolution and final values of the different nitrogen fractions show that this cheese undergoes a very slight proteolysis, a fact which was corroborated when the caseins and their degradation products were quantified: β-casein did not undergo any modification throughout ripening, while only 21% of the αs-caseins were degraded. Free amino acids content increased by a factor of about 7 throughout ripening, resulting in a high content of γ-amino butyric acid and a low content of glutamic acid at the end of the process. Fat acidity increased very slightly, approximately 4.5 times, during ripening, reaching final values of 3.5±2.2 mg KOH g−1 of fat. The total free fatty acids content showed a similar evolution to fat acidity. At the end of the ripening process, the main free fatty acid was C18:1, followed by C16 and C10.  相似文献   

10.
In a preliminary study with commercial ewe's milk cheeses, there were statistically significant differences in the sensory evaluation scores and the amounts of short-chain (C4–C10) free fatty acids (FFAs) between cheeses made with lamb rennet paste or bovine rennet. Experimental ewe's milk cheeses were manufactured with 2 levels of artisanally produced lamb rennet paste and 2 levels of bovine rennet in 50 L vats, with a manufacturing replicate done within 1 week. Total coagulating activity was 2500 RU for cheeses manufactured with a high amount of rennet or 1000 RU for cheeses manufactured with a low amount of rennet. The two batches of lamb rennet pastes used had 4.0 (early Spring) and 6.5 U g−1 lipase (late Spring), whereas no lipase activity was detected in bovine rennets. The total concentration of FFAs in cheeses manufactured with lamb rennet paste was significantly higher than in cheeses manufactured with bovine rennet, regardless of ripening time and time of the year. Lipolysis in the former cheeses increased with the total units of lipolytic activity added. The increase in lipolysis in cheeses made with lamb rennet was primarily due to higher amounts of short-chain fatty acids (C4–C10). Butyric acid was the main FFA in cheeses made with lamb rennet paste, representing 34.5 μmol 100 μmol−1 (low level of rennet) and 44.2 μmol 100 μmol−1 (high level of rennet) of the total FFAs, whereas it represented only 17 μmol 100 μmol−1 of the total FFAs in all cheeses made with bovine rennet. The concentration of individual FFAs of chain length <C12 were significantly higher in cheeses made with lamb rennet paste than in cheeses made with bovine rennet. Cheeses made with lamb rennet paste received significantly higher intensity scores for odour and flavour intensity, sharp odour, ‘piquant’ and bitter flavours and ‘natural rennet’ odour and flavour.  相似文献   

11.
The antimicrobial activity of two pediocin-producing transformants obtained from wild strains of Lactococcus lactis on the survival of Listeria monocytogenes, Staphylococcus aureus and Escherichia coli O157:H7 during cheese ripening was investigated. Cheeses were manufactured from milk inoculated with the three pathogens, each at approximately 6 log cfu mL−1. Pediococcus acidilactici 347 (Ped+), Lc. lactis ESI 153, Lc. lactis ESI 515 (Nis+) and their respective pediocin-producing transformants Lc. lactis CL1 (Ped+) and Lc. lactis CL2 (Nis+, Ped+) were added at 1% as adjuncts to the starter culture. After 30 d, L. monocytogenes, S. aureus and E. coli O157:H7 counts were 5.30, 5.16 and 4.14 log cfu g−1 in control cheese made without adjunct culture. On day 30, pediocin-producing derivatives Lc. lactis CL1 and Lc. lactis CL2 lowered L. monocytogenes counts by 2.97 and 1.64 log units, S. aureus by 0.98 and 0.40 log units, and E. coli O157:H7 by 0.84 and 1.69 log units with respect to control cheese. All cheeses made with nisin-producing LAB exhibited bacteriocin activity throughout ripening. Pediocin activity was only detected throughout the whole ripening period in cheese with Lc. lactis CL1. Because of the antimicrobial activity of pediocin PA-1, its production in situ by strains of LAB growing efficiently in milk would extend the application of this bacteriocin in cheese manufacture.  相似文献   

12.
《International Dairy Journal》2000,10(5-6):383-389
The mesophilic lactobacilli colonizing Fiore Sardo ewe's milk cheese were characterized. They seemed to be the dominant non-starter lactic acid bacteria composing its natural microflora, with a viable cell number varying from 105 CFU g−1 (1-day-old cheese) to 108 CFU g−1 (30-day-old cheese) and then slowly decreasing up to 104 CFU g−1 after 7 months’ ripening. Considering the relevance of mesophilic lactobacilli in affecting the cheese ripening, a PCR-based taxonomic identification of the Lactobacillus species isolated was performed. Cheese samples were collected from 3 farms and 457 isolates from cheeses at different ripening times were analysed with species-specific primers for L. plantarum, L. casei group, L. paracasei, L. casei, L. rhamnosus, L. pentosus, L. paraplantarum, L. curvatus, L. graminis and L. sake. L. plantarum and L. paracasei were the most frequently detected species. Moreover, the development and the evolution during ripening of the facultatively heterofermentative Lactobacillus species (FHL) were different in the three batches of cheese.  相似文献   

13.
Phenotypic and genotypic methods were used to identify filamentous fungi that characterize traditional Italian Fossa cheese and its ripening environment. After ageing for 60 days at a dairy, it was ripened for an additional three months in a pit. In the fully ripened cheese, moulds ranged from 3 to 3.4 log cfu g?1 and Penicillium was the prevalent species. Pit environmental fungi ranged from 530 to 750 cfu m?3 (air) and from 130 to 340 cfu cm?2 (surfaces). The dominant pit strains were Alternaria spp., Aspergillus spp., Cladosporium spp. and Penicillium spp. Phylogenetic analyses of 18S rRNA gene and ITS1-5.8S-ITS2 regions highlighted Penicillium camemberti, Aspergillus nidulans and Aspergillus versicolor as traceable species occurring in both the cheese and pit environment, suggesting their involvement in the development of typical Fossa cheese characteristics. This approach may be used for the identification of microflora on other cheese varieties to better understand the fungal contribution in cheese ripening.  相似文献   

14.
A microbiological, compositional, biochemical and textural characterisation of the pasta filata Caciocavallo Pugliese cheese during ripening is reported. Fully ripened cheese contained a total of ca. log 8.0 cfu g−1 mesophilic bacteria and ca. log 6.0 cfu g−1 presumptive staphylococci, while the number of thermophilic and mesophilic rod and coccus lactic acid bacteria varied during ripening. A two-step RAPD-PCR protocol was used to differentiate biotypes. The natural whey starter was composed mainly of Lactobacillus delbrueckii, Lb. fermentum, Lb. gasseri, Lb. helveticus and Streptococcus thermophilus strains. After day 1 of ripening, Lb. delbrueckii became dominant and some strains of Enterococcus durans and E. faecalis appeared. Non-starter lactic acid bacteria, such as Lb. parabuchneri and Lb. paracasei subsp. paracasei formed a large part of the lactic microflora at 42 and 60 d of ripening. The level of pH 4.6-soluble nitrogen increased from the outer to the inner of the cheese and also increased in each section as ripening progressed, attaining values of 18–15%. Urea-PAGE electrophoresis showed that degradation of αs1-casein was more rapid than that of β-casein throughout ripening and the rates at which both caseins were degraded greatly increased from the outside to the inside of the cheese. Based on the primary proteolysis products, both chymosin and plasmin appeared to be active. RP-HPLC profiles of the 70% ethanol-soluble, pH 4.6-soluble nitrogen, showed a large number of peaks, indicating a heterogeneous mixture of proteolytic products. There were both age- and section-related changes in the area of the different peptide peaks. Butyric (C4:0), caproic (C6:0), palmitic (C16:0) and oleic (C18:1) acids were the free fatty acids found at the highest concentrations. The level of short chain fatty acids (e.g., butyric and caproic) decreased from the middle and inner to outer sections of the cheese. Peptidase activity in the curd was pronounced, increased during ripening and varied with the cheese section. The greatest increase of the peptidase activity coincided with a change in the lactic microflora and with the prevalence of non-starter lactic acid bacteria. Microbial esterases were supposed to be active together with rennet paste. Little change in the firmness and fractures stress during maturation were found by textural analyses of the raw cheese. The flowability was similar to that of typical low-moisture Mozzarella cheese, while stretchability was lower. The heat-induced changes in phase angle of Caciocavallo Pugliese cheese indicated a phase transition from largely elastic rheological characteristics in unheated cheese to a more viscous and fluid character in melted cheese.  相似文献   

15.
Cheese ripening acceleration is of continuous interest for the industry. High-pressure (HP) treatment of starter cultures used in cheese-manufacturing offers the potential to accelerate ripening by increasing the activity of their intracellular peptidases that contribute in the development of desired cheese organoleptic characteristics.The objective of the present research was the investigation of the effect of HP treatment (200 MPa-20 °C - 20 min) directly on white brined cheese or on the starter culture used for its manufacture (Str. thermophilus:L. lactis:L. bugaricus 2:1:1). For this purpose, the microbial, textural, physicochemical and organoleptic characteristics and proteolysis were assessed during the 2nd stage of ripening in cold stores. Control cheese without any treatment was also studied.Cheeses made with HP-treated starters had increased secondary proteolysis. Organoleptic scoring of these cheeses was higher during the whole storage period compared to control and HP-treated cheese. Their superiority was evident even at the early stages of ripening in cold stores, since no bitterness was detected. On the contrary, although HP treated cheeses showed the highest increase in aminopeptidases activities, this was not correlated with the studied ripening indices or the organoleptic characteristics.According to the results, HP-treated starter culture can accelerate proteolysis and potentially the ripening of cheese-in-brine.Industrial relevanceThe data obtained from this work suggest that application of HP treatment under optimized conditions on cheeses in brine starter cultures or on whole cheeses can be effectively used for the production of products with reduced ripening time. This is of great importance for the cheese industries, since the storage period for ripening is long (higher than two months), while applying HP treatment as suggested in this study, this time may be reduced to less than one month, producing cheeses of superior quality.  相似文献   

16.
The contributions of the coagulant Cynara cardunculus and of the microflora of raw milk to the volatile-free fatty acid profile of Serra da Estrela cheese were evaluated. The experimental design included both a model system and, dual cheeses. The study in the model system showed that isovaleric acid was the predominant volatile compound after 7 d of ripening. The systems inoculated with Enterococcus faecium produced the highest amount of this volatile (ca. 135.8 mg kg−1 curd), while those inoculated with Lactobacillus plantarum produced the least (21.4 mg kg−1 curd); Lactococcus lactis produced moderate amounts (ca. 34.2 mg kg−1 curd) but a total amount of volatile-free fatty acids similar to those found in control samples. This is considered advantageous since this volatile fatty acid confers a harsh, piquant, mature flavour to cheese, coupled with the realisation that excess volatiles may result in off-flavours. The addition of cultures in experimental cheeses helped reduce ripening time to about one half. Inclusion of Lb. plantarum led to cheeses containing the highest amounts of volatiles, and exhibiting an aroma closest to that of typical Serra da Estrela cheese.  相似文献   

17.
Seventeen strains of mesophilic lactic acid bacteria, isolated from cheese (non-starter lactic acid bacteria, NSLAB) or sourdough, were used individually as adjunct cultures in a Caciotta cheese model system. Adjunct cultures were monitored by randomly amplified polymorphic DNA analysis and their cell counts mainly varied from ca. 9.0 to 8.0 log cfu g−1 throughout 36 days of ripening. Adjunct cultures influenced differently cheese proteolysis. Both NSLAB and sourdough strains caused an extensive secondary proteolysis; however, some NSLAB strains produced the highest concentration of free amino acids. Principal component analysis (PCA) differentiated cheeses manufactured with NSLAB strains Lactobacillus parabuckneri B9FST, Lb. paracasei B61F5, Lb. curvatus 2768 and Lb. rhamnosus ATCC 7469 based on the accumulation of Lys, Glu, Phe, Hist, Asp and Met. Assessment of cheese lipolysis showed that: (i) highest concentrations of free fatty acids (FFA) were found with NSLAB strains Lb. rhamnosus ATCC 7469 and Lb. casei subsp. pseudoplantarum 2742 (ca. 10 500 mg kg−1); (ii) PCA differentiated cheeses manufactured with NSLAB strains Lb. rhamnosus ATCC 7469 and Lb. casei subsp. pseudoplantarum 2742 based on the accumulation of palmitic (C16:0) and linoleic (C18:2) acids, and those with Lb. curvatus 2768 and Lb. parabuckneri B9FST based on the high concentration of short chain FFA; (iii) the cheese made with sourdough strain Lb. sanfranciscensis CB1 had the highest levels of unsaturated FFA.  相似文献   

18.
《International Dairy Journal》2000,10(5-6):359-367
The rheological properties of high-pressure-treated (50–400 MPa, 1 h) and untreated Gouda cheese were compared. Immediately after pressure release, oscillation measurements gave lower storage and loss moduli from 50 MPa onwards. Simultaneously, tan δ was higher, indicating a relatively less solid-like behaviour of the pressurized samples. Creep measurements showed that samples treated at 400 MPa got less rigid, less solid-like, and more viscoelastic; from 50 MPa onwards, the samples had less resistance to flow at longer times. Texture profile analysis revealed that samples treated at 225 and 400 MPa showed no macroscopical breakage. Relaxation measurements gave a higher level of stress decay at long relaxation times and a higher rate at which the stress relaxes. During further ripening after pressure release, differences between pressure-treated and untreated samples became smaller. At 42 days of ripening, any or only a slight difference could still be observed. Dissolution experiments showed that hydrophobic interactions in Gouda cheese were weakened by pressure treatment. This possibly led to structural changes of the paracasein network causing the rheological property changes. These pressure effects on proteins in Gouda cheese are possibly reversible as hydrophobic interactions and rheological properties were restored during ripening.  相似文献   

19.
Reggianito is a typical variety of grana-type hard cheese produced in Argentina. It is the most exported and due to its organoleptic characteristics is very appreciated by the consumers. The objective of this study was to characterise the global composition, lipolysis, proteolysis and volatile compound profiles of commercial Reggianito cheeses from different dairy plants.Statistical differences (P ? 0.05) in some physicochemical parameters, nitrogen fractions and FFA levels among commercial brands were detected. The volatile profiles were studied by SPME–GC–MS/FID. A total of 53 compounds were identified, the majority belonging to the groups of ketones, alcohols, acids, esters and aldehydes. All these compounds have been reported in Italian grana-type cheeses. Visualization of the analytical results was performed by principal component analysis. This analysis clustered cheese samples according to dairy plants. This fact could be, among other factors, consequences of differences in technologies and ripening time of different manufacturers.  相似文献   

20.
《International Dairy Journal》2005,15(10):1026-1033
The effect of proteolytic enzymes from somatic cells on cheese quality was studied. In preliminary experiments, milk and two sodium caseinate systems (pH 6.5 and pH 5.2, the latter in the presence of 5% NaCl) were used as substrates to investigate the proteolytic activity of somatic cells recovered from mastitic milk. Urea-polyacrylamide gel electrophoretograms of hydrolysates suggested that somatic cell extracts contributed directly to proteolysis both in buffer and in milk, but that such activity was reduced by batch pasteurisation (63 °C for 30 min). Sodium caseinate was readily hydrolysed by somatic cell extracts; hydrolysis of αs1-casein was greater at pH 5.2 and increased with level of somatic cells, suggesting that somatic cells contain proteolytic enzymes which are more active at acidic pH values. Subsequently, miniature Cheddar-type cheeses were made from batches of milk to which somatic cells were added (at levels of levels of 3×105 or 6×105 cells mL−1), either before or after pasteurisation. Proteolysis during ripening of cheese (as measured by levels of pH 4.6-soluble nitrogen) increased with somatic cell addition, although this effect was reduced by pasteurisation after cell addition. Somatic cells may also have directly influenced cheese moisture content, which has been established as a principal indicator of quality of Cheddar-type cheese. Proteolytic enzymes of somatic cells from milk were shown to contribute directly to proteolysis in milk and cheese.  相似文献   

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