Development of probiotic cheese manufactured from goat milk: response surface analysis via technological manipulation

Production of caprine milk has been rising steadily, partially because of its good nutritional value; the possibility of improving nutritional benefits by adding probiotic species such as Bifidobacterium lactis and Lactobacillus acidophilus was assessed. The manufacturing process of a traditional semi-hard goat cheese was technologically modified to optimize the process. The amount of starter inoculum, the concentration of salt, the addition of a protein hydrolysate, and the ripening time were varied to improve the microbiological, biochemical, and sensory properties of the cheese. Bifidobacterium lactis was able to grow slightly (up to 3 x 10(8) cfu/g), but growth was dependent on the physicochemical characteristics of the cheese. Lactobacillus acidophilus did not grow substantially in any of the experimental cheeses, and maximum numbers did not exceed 6 x 10(7) cfu/g. Concentrations of lactic acid and acetic acid increased throughout cheese manufacture, indicating that production of these acids was uncoupled from growth. Viability of the probiotic strains during ripening was sufficient to yield numbers that were above the accepted threshold (10(6) cfu/g) for a probiotic effect. Both strains contributed significantly to ripening, especially in the formation of low molecular mass peptides and amino acids, but lipolysis was not greatly affected. Statistical analyses using response surface methodology indicated that the manufacture of goat cheese could be optimized by the addition of 0.30% (vol/wt) milk hydrolysate, 3 x 10(7) of viable B. lactis and 7 x 10(6) of viable L. acidophilus cells/ml of milk, respectively, 3.50% (wt/wt) salt, and ripening for 70 d.     

Prolongation of the keeping quality of Mozzarella cheese by treatment with sorbate

An attempt was carried out for prolongation of the shelf-life of Mozzarella cheese by incorporation of potassium sorbate into the cheese. Three manufacturing techniques were used: a) addition of potassium sorbate to kneading water (at level of 6%), b) addition during brine salting (at level of 0.5%) and c) dipping the cheese into potassium sorbate solution (6%) directly prior to packaging. Control cheese was made without potassium sorbate treatment. The resulting cheeses were divided into two portions, one of which was contaminated with Penicillium roqueforti and then packaged, while the second one was packaged without contamination. Both were stored at refrigerator (5 +/- 1 degree C) temperature and analysed periodically until spoilage. The results showed that treatment with potassium sorbate did not affect the organoleptic properties of the cheeses, except that a slight objectionable bitter flavour was observed in fresh cheeses treated with sorbate using the techniques of dipping or in brine salting then it was disappeared during storage. However, the overall acceptabilities of the sorbate-treated cheese were increased up to 10 weeks of storage compared with 4 weeks for untreated cheeses. Treatment with potassium sorbate in kneading water or brine appeared to be more effective than dipping. Addition of potassium sorbate inhibited microbial growth, especially that of moulds and yeasts. The sorbate-treated cheeses had higher moisture, pH values and lower acidity than the control. Fat, salt and total nitrogen were unaffected during storage. Levels of soluble N, non-protein N and total volatile fatty acids in sorbate-treated cheeses were slightly higher than in the control. Furthermore, addition of potassium sorbate increased the meltability and improved the fat leakage of Mozzarella cheese.     

Production of gamma-aminobutyric acid by cheese starters during cheese ripening

Nine mixed-strain starters were examined for their abilities to produce gamma-aminobutyric acid. Six commercial starters were found to produce gamma-aminobutyric acid in a skim milk culture. The bacterium that produced gamma-aminobutyric acid was isolated from the mixed-strain starters, identified as citrate-utilizing Lactococcus lactis ssp. lactis (formerly L. lactis ssp. lactis biovar diacetylactis) and designated as strain 01-7. A cell extract showed glutamate decarboxylase activity, for which the optimum pH was 4.7. In pH-controlled cultivation, gamma-aminobutyric acid was generated at pH 5.0 but not above pH 5.5. Cheeses were prepared experimentally using strain 01-7 to determine the relationship between the pH values and the production of gamma-aminobutyric acid during cheese ripening. gamma-Aminobutyric acid increased linearly in the experimental cheeses as the pH of the cheese decreased. Based on these results, gamma-aminobutyric acid was concluded to be produced by the cheese starters during ripening.     

Degradation of histamine and tyramine by Brevibacterium linens during surface ripening of Munster cheese

Red smear formation during fermentation of Munster cheese was started by using three different strains of Brevibacterium linens as surface inocula. The cheeses were produced with and without supplementation of histamine and tyramine. After smearing the cheese surface for the first time with B. linens viable counts of 10(7) CFU/g were detected. At the end of the logarithmic growth phase cell numbers increased to 10(10) CFU/g and remained constant during the whole ripening period. During a 4-week ripening period strains of B. linens reduced histamine and tyramine content by 55 to 70%. B. linens LTH 456 and LTH 3686 degraded histamine and tyramine in a phosphate buffer (pH 7) containing 0.54 M histamine and 0.58 M tyramine when incubated with agitation at 30 degrees C. B. linens LTH 3813 did not reveal any amine degradation activity in a buffer system. The pH on the cheese surface increased from 5 to 7, whereas it increased in the center only to 5.3 after a 3-week ripening period.     

Growth and enterotoxin production of Staphylococcus aureus during the manufacture and ripening of Camembert-type cheeses from raw goats' milk

Tests were carried out to determine the effect of manufacturing procedures for a Camembert-type cheese from raw goats' milk on the growth and survival of Staphylococcus aureus organisms added to milk at the start of the process, and to study the possible presence of staphylococcal enterotoxin A in these cheeses. The initial staphylococcal counts were, respectively, 2, 3, 4, 5 and 6 log cfu ml-1. Cheese was prepared following the industrial specifications and ripened for 41 d. Detection of enterotoxins was done by the Vidas SET test and by an indirect double-sandwich ELISA technique using antienterotoxin monoclonal antibodies. Generally, numbers of microbes increased at a similar rate during manufacture in all cheeses until salting. During the ripening period, the aerobic plate count population and Staph. aureus levels remained stable and high. There was an approximately 1 log reduction of Staph. aureus in cheeses made with an initial inoculum of Staph. aureus greater than 10(3) cfu ml-1 at the end of the ripening period (41 d) compared with the count at 22 h. The level of staphylococcal enterotoxin A recovered varied from 1 to 3.2 ng g-1 of cheese made with an initial population of 10(3)-10(6) cfu ml-1. No trace of enterotoxin A was detected in cheeses made with the lowest Staph. aureus inoculum used in this study.     

Transgenic animal models: new avenues in cardiovascular physiology

Coryneform bacteria and yeasts of 21 brick cheeses from six German dairies, produced by using undefined ripening cultures, were identified. Arthrobacter nicotianae, Brevibacterium linens, Corynebacterium ammoniagenes, Corynebacterium variabilis and Rhodococcus fascians were found in significant numbers. Out of 148 coryneform isolates 36 could not be identified at the species level. With the exception of a large rennet cheese, the coryneform microflora of rennet and acid cured cheeses were similar, but the cheeses had clearly different yeast populations. Debaryomyces hansenii and Galactomyces geotrichum prevailed in rennet cheeses while Kluyveromyces marxianus and Pichia membranaefaciens were the main species found in acid cured cheese. The dominance of Yarrowia lipolytica probably indicates an improper yeast population, resulting in poor cheese quality. Some of the species identified are potential candidates for designing a defined ripening culture for rennet red smear cheese.     

Protective effect of beraprost sodium, a stable prostacyclin analogue, in development of monocrotaline-induced pulmonary hypertension

Commercial cheese products were surveyed for beta-casomorphin peptides. Two extraction methods were compared: 1) water and 2) chloroform and methanol. Peptide profiles were determined using reverse-phase HPLC and multiple wavelength detection. beta-Casomorphin standards were used for comparison with cheese peptide profiles. Results indicated that peptides were present in cheeses with HPLC elution times that were similar to those for beta-casomorphins. However, comparison of absorbancies of the peaks at multiple wavelengths did not indicate peptides similar to beta-casomorphins. Therefore, beta-casomorphins were absent, or concentrations were below the HPLC detection threshold for beta-casomorphin of 2 micrograms/ml of cheese extract. The susceptibility of beta-casomorphins to the proteolytic system of a commercial strain of Lactococcus lactis ssp. cremoris was investigated. beta-Casomorphin standards were incubated at 4 degrees C with bacterial cell lysate at pH 5.0, 5.2, 5.4, and 5.7. Salt concentrations varied among 0, 1.5, and 5%. The concentration of added beta-casomorphins and the degradation products were monitored over 15 wk using HPLC. Enzymatic degradation of beta-casomorphins was influenced by the combination of pH and salt concentrations at cheese ripening temperatures. Therefore, if formed in cheese, beta-casomorphins may be degraded under conditions common for Cheddar cheese.     

Effect of degradability of dietary protein and fat on ruminal, blood, and milk components of Jersey and Holstein cows

Twelve Holstein cows and 12 Jersey cows were used in six 4 x 4 Latin squares to investigate the effects of the degradability of dietary protein and supplemental dietary fat on milk components. Dietary dry matter contained 16% crude protein with two concentrations of ruminally undegradable protein (RUP) obtained by substituting blood meal for a portion of the soybean meal. Treatments were 1) 29% RUP, 0% added fat; 2) 29% RUP, 2.7% added fat (Ca soaps of fatty acids); 3) 41% RUP, 0% added fat; and 4) 41% RUP, 2.7% added fat. The dry matter of the total mixed ration fed at 1000 and 1400 h consisted of 30% corn silage, 29% alfalfa haylage, and 41% concentrate. Supplemental dietary fat depressed dry matter intake by 6.2%. Plasma urea N was greater at 0700 and 1600 h for Jerseys fed diets containing added fat and greater at 0700 h for Holsteins fed diets containing 41% RUP than for Holsteins fed 0% added fat and 29% RUP. When averaged across both breeds, milk production increased 7.1%, and production of 4% fat-corrected milk by Jerseys increased 8.4%, in response to added dietary fat. Milk protein was reduced when Holstein diets contained 41% RUP. Milk protein content was reduced 7.1 and 3.9%, and milk urea N was increased 4.9 and 8.5%, by added fat and 41% RUP in both breeds, respectively. Added fat reduced the concentration, but not the yield, of milk components. Substitution of blood meal decreased the concentration and yield of milk protein and casein N.     

Rapid determination of cholesterol in milk and milk products by direct saponification and capillary gas chromatography

The level and nature of the albendazole residues in milk of treated cows were determined as a function of the time of milking (12-h intervals), and the fate of those residues during cheesemaking, ripening, and storage was examined when the obtained milk was used for making Teleme cheese. Ion-pair liquid chromatographic analysis with fluorescence detection showed that the albendazole sulfoxide metabolite reached its maximum (523 +/- 199 micrograms/kg) at the 1st milking and declined below the detection limit by the 4th milking. The sulfone metabolite attained its highest level (812 +/- 99 micrograms/kg) more slowly (at the 2nd milking) and declined below detection limit by the 13th milking. The 2-aminosulfone metabolite, which was present in the milk obtained at the 1st milking, reached its maximum (128 +/- 36 micrograms/kg) at the 3rd milking, and slowly declined to a level below detection limit by the 15th milking. Whey and cheese analysis revealed that about 70% of each major metabolite initially present in milk could be distributed in the whey. The remaining 30% occurred in the cheese at residue levels higher than those initially present in the milk of the 1st or 2nd milking (688 versus 445 or 450 versus 230 micrograms/kg for albendazole sulfoxide; 890 versus 608 or 1502 versus 783 micrograms/kg for albendazole sulfone; 19 versus 15 or 161 versus 105 micrograms/kg for albendazole 2-aminosulfone). Ripening and storage of the cheeses made from milks from the 1st or 2nd milkings results in a decrease of the sulfoxide metabolite (to 225 or 206 micrograms/kg), an increase of the sulfone metabolite (to 1,181 or 1,893 micrograms/kg), and no effect on the 2-aminosulfone metabolite.     

Status and prospects of the dairy goat industry in the United States

Among the major classes of U.S. livestock, dairy goats have yet to achieve USDA statistical reporting of their numbers, amounts of milk produced and processed, and cheese and other products marketed. However, the USDA has published buck proofs of approximately 16,000 does annually from Dairy Herd Improvement Association (DHIA) records of the Alpine, LaMancha, Nubian, Oberhasli, Saanen and Toggenburg breeds, thereby encouraging genetic progress. This represents a 1% participation in DHIA of the estimated 1.5 million U.S. dairy goats. Annual breed registrations are led by Nubians (11,000), and the leading states in descending order are California, Texas, Ohio, New York, and Pennsylvania. Breed average milk yields range from 960 kg of milk for Saanen to 726 kg of milk for Oberhasli. Average milk contents range from 4.5% fat and 3.69% protein for Nubian to 3.3% fat and 2.98% protein for Toggenburg. Leading lactation records are 3,023 kg of milk (Toggenburg) and 174 kg of fat (Nubian). Total annual registrations are 45,000+ animals by 16,000+ member breeders. Estimated total U.S. goat milk commercial production is 24,000+ t, with half going into commercial farm goat cheese production of 640+ t. Recent years have seen significantly increased numbers of dairy goat research projects and publications from Oklahoma, Texas, California, Georgia, Alabama, Florida, Louisiana, New York, Connecticut, Delaware, and Massachusetts. Furthermore, annual national and international symposia, annual national goat cheese judging competitions and workshops, an active national goat research foundation, representation on the National Interstate Milk Shippers Committee and Mastitis Council, and formation of a national association and council for the development and promotion of dairy goat products indicate an evolution from former emphasis on purebred breed development to a focus on market development. The conclusion is that dairy goats are emerging as a necessary and recognized U.S. industry.     

Influence of sorghum grain processing on performance and nutrient digestibilities in dairy cows fed varying concentrations of fat

Forty Holstein cows averaging 85 +/- 50 d in milk were assigned to five dietary treatments for 56 d to determine the effects of ruminal starch degradability and supplemental fat on milk yield and composition and nutrient digestibilities. Treatments were 1) dry-rolled sorghum, no added fat; 2) dry-rolled sorghum plus 2.5% prilled fatty acids; 3) steam-flaked sorghum, no added fat; 4) steam-flaked sorghum plus 2.5% prilled fatty acids; and 5) steam-flaked sorghum plus 5% prilled fatty acids. Fat supplementation at 2.5 and 5% increased the content of fatty acids in diets from 3.0 to 5.4 and 7.7%, respectively. Milk yield was increased 2.0 kg/d when steam-flaked sorghum plus 0 or 2.5% added fat was fed and was 2.4 kg/d higher when prilled fatty acids were fed at 2.5 versus 0%. Cows fed supplemental fat at 5% did not increase milk yield over that of cows fed no added fat. For cows fed 2.5% fat, steam-flaking decreased dry matter intake 12% and increased efficiency of conversion of feed to milk 11%. Milk composition was unaffected by treatments, except that lactose was depressed by fat supplementation. Milk protein yield and efficiency of conversion of dietary protein to milk protein were increased when steam-flaked sorghum was fed. Starch digestibilities were increased from 92.6 to 98.2% when sorghum was steam-flaked compared with dry-rolled and fat supplementation tended to decrease digestibility of neutral detergent fiber. Steam-flaking tended to improve, and the addition of 2.5% fat did improve, the lactational performances of the cows. These effects appeared additive, but 5% fat appeared to be excessive.     

Effects of level and type of energy source (volatile fatty acids or glucose) on milk yield, composition and coagulating properties in dairy cows

Four fistulated Holstein cows were arranged in a 4 x 4 Latin square design to study the effects of level and type of energy source on milk yield and composition. Treatments consisted of a basal diet fed alone (low energy treatment) or with 3.3 Mcal of net energy for lactation from extra nutrients perfused either into the rumen (either propionic acid or a mixture of volatile fatty acids) or into the duodenum (glucose). Increasing the energy input without changing the volatile fatty acid profile improved milk yield and slightly increased milk protein and fat yields. Compared with the isoenergetic mixture of volatile fatty acids, both propionic acid and glucose infusions significantly decreased fat content (-4.5 g/kg) and yields (respectively, -111 and -160 g/d), but affected fatty acid proportion and yield differently (more elongation process and less C18 with glucose infusion). Protein yield was slightly increased by propionic acid infusion but not by glucose because of the counterbalanced effects on milk yield (-1.3 kg/d) and protein content (1.5 g/kg). The coagulating properties of milk were directly linked to variations in protein, casein and mineral contents. In conclusion, propionic acid or glucose scarcely affected milk protein content, but induced a similar decrease in milk fat content probably through different metabolic pathways.     

Effect of dietary forage concentration and buffer addition on duodenal flow of trans-C18:1 fatty acids and milk fat production in dairy cows

The objective of the study was to determine the effects of dietary fat source on duodenal flow, apparent absorption, and milk fat incorporation of trans-C18:1 fatty acids. Four ruminally and duodenally cannulated multiparous Holsteins cows in mid to late lactation were fed a basal diet containing 36% corn silage, 24% alfalfa haylage, and 40% concentrate (dry matter basis). Diets contained 0% supplemental fat (control diet), 3.7% high oleic sunflower oil, 3.7% high linoleic sunflower oil, or 3.7% partially hydrogenated vegetable shortening; treatments were administered in a 4 x 4 Latin square design with 3-wk experimental periods. The flow of trans-C18:1 to the duodenum was higher for cows fed diets supplemented with fat than for cows fed the control diet (283 vs. 64 g/d). Incomplete biohydrogenation accounted for the increased flow of trans-C18:1 to the duodenum in cows fed diets containing high oleic and high linoleic sunflower oil. Increased flow of trans-C18:1 in cows fed the diet containing partially hydrogenated vegetable shortening most likely originated from the trans-C18:1 in the diet. Milk fat percentages were 3.48, 3.07, 3.18, and 3.38% for cows fed the control diet and diets containing high oleic sunflower oil, high linoleic sunflower oil, and vegetable shortening, respectively. Milk trans-C18:1 increased from 2.9 to 11.2% of the total fatty acids for cows fed the control diet and the diets supplemented with fat, respectively. Milk trans-C18:1 were equal across all diets supplemented with fat. Ruminal and total tract digestion of organic matter, neutral detergent fiber, and N did not change with fat supplementation. Results showed that trans-C18:1 is increased in the milk of cows with reduced milk fat; however, excessive amounts of trans-C18:1 in milk do not necessarily correspond directly to milk fat depression.     

Development of a probiotic cheddar cheese containing human-derived Lactobacillus paracasei strains

Cheddar cheese was manufactured with either Lactobacillus salivarius NFBC 310, NFBC 321, or NFBC 348 or L. paracasei NFBC 338 or NFBC 364 as the dairy starter adjunct. These five strains had previously been isolated from the human small intestine and have been characterized extensively with respect to their probiotic potential. Enumeration of these strains in mature Cheddar cheese, however, was complicated by the presence of high numbers (>10(7) CFU/g of cheese) of nonstarter lactic acid bacteria, principally composed of lactobacilli which proliferate as the cheese ripens. Attempts to differentiate the adjunct lactobacilli from the nonstarter lactobacilli based on bile tolerance and growth temperature were unsuccessful. In contrast, the randomly amplified polymorphic DNA method allowed the generation of discrete DNA fingerprints for each strain which were clearly distinguishable from those generated from the natural flora of the cheeses. Using this approach, it was found that both L. paracasei strains grew and sustained high viability in cheese during ripening, while each of the L. salivarius species declined over the ripening period. These data demonstrate that Cheddar cheese can be an effective vehicle for delivery of some probiotic organisms to the consumer.     

Growth reduction of Listeria spp. caused by undefined industrial red smear cheese cultures and bacteriocin-producing Brevibacterium lines as evaluated in situ on soft cheese

The undefined microbial floras derived from the surface of ripe cheese which are used for the ripening of commercial red smear cheeses have a strong impact on the growth of Listeria spp. In some cases, these microbial consortia inhibit Listeria almost completely. From such undefined industrial cheese-ripening floras, linocin M18-producing (lin+) (N. Valdés-Stauber and S. Scherer, Appl. Environ. Microbiol. 60:3809-3814, 1994) and -nonproducing Brevibacterium linens strains were isolated and used as single-strain starter cultures on model red smear cheeses to evaluate their potential inhibitory effects on Listeria strains in situ. On cheeses ripened with lin+ strains, a growth reduction of L. ivanovii and L. monocytogenes of 1 to 2 log units was observed compared to cheeses ripened with lin strains. Linocin M18 activity was detected in cheeses ripened with lin+ strains but was not found in those ripened with lin strains. We suggest that production of linocin M18 contributes to the growth reduction of Listeria observed on model red smear cheeses but is unsufficient to explain the almost complete inhibition of Listeria caused by some undefined microbial floras derived from the surface of ripe cheeses.     

Recurrence of hemolytic-uremic syndrome in renal transplant recipients: a meta-analysis

To identify contributing factors for cheese-associated outbreaks, we reviewed all cheese-associated outbreaks of human illness reported to the Centers for Disease Control and Prevention (CDC) with onsets during 1973 to 1992. The infrequency of large, cheese-associated outbreaks was notable because such outbreaks had been a frequent public health problem before the mid-20th century. Of 32 reported cheese-associated outbreaks, 11 attributed to manufacturing errors caused most of the illnesses and hospitalizations and all 58 deaths. Important factors in these 11 outbreaks were manufacturing cheese with raw or improperly pasteurized milk and postpasteurization contamination. If current Food and Drug Administration sanitary requirements for cheesemaking had been met, these outbreaks would have been preventable. In two outbreaks of Salmonella infections, fewer than 10 Salmonella per 100 g of cheese were detected. In two outbreaks of Brucella infections, efforts to recover the pathogen from the implicated cheese were unsuccessful, emphasizing the inadequacy of end product testing for assuring consumer safety. Curing cheeses kills most bacteria present in cheeses; however, evidence from sources other than the CDC Foodborne Disease Outbreak Surveillance System suggests that curing alone may not be a sufficient pathogen control step to eliminate Salmonella, Listeria, and E. coli O157:H7 from cheese.     

Determination of biogenic amines in cheese

A liquid chromatographic (LC) procedure for determining 10 biogenic amines in cheese is described. The method is based on ion-pair chromatography on a reversed-phase column with postcolumn derivatization with o-phthaldialdehyde and fluorometric detection. It allowed simultaneous determination of 10 amines in < 80 min: histamine, tyramine, tryptamine, 2-phenylethylamine, serotonin, agmatine, spermine, spermidine, putrescine, and cadaverine. Linearity for each amine was observed between 0.5 and 6.0 micrograms/mL. Detection limits ranged form 0.004 to 0.009 micrograms/20 microL, and determination limits ranged from 0.066 to 0.149 mg/100 g. Amino acids and other amines did not interfere with determination of biogenic amines. Three extractants--methanol, hydrochloric acid, and trichloroacetic acid--were compared in their efficiency to recover amines from spiked samples. Purification of the cheese extract was required prior to LC to avoid interference from compounds in the cheese matrix. Hydrochloric acid extraction followed by purification with diethyl ether gave best recoveries for all the amines (75.5-112.3%). The method is simple, fast, and reliable. It can be used to study the technological and toxicological implications of biogenic amines in cheeses.     

The SUVIMAX (France) study: the role of antioxidants in the prevention of cancer and cardiovascular disorders

Endospores of Clostridium spp. capable of producing gas in a lactate-containing medium were enumerated from 14 pasteurized milk samples from Wisconsin cheese plants. Concentrations of endospores of lactate-fermenting, gas-producing Clostridium spp. were between 5.0 x 10(-2) and 1.7 x 10(0) MPN ml(-1). Concentrations of presumptive C. tyrobutyricum endospores (defined by subterminal endospore position and lactate dehydrogenase activity) were lower, not exceeding 2.0 x 10(-2) MPN ml(-1). Based on subterminal endospore position, lactate dehydrogenase activity, and a carbohydrate fermentation profile identical to C. tyrobutyricum strain ATCC 25755, five isolates (Ct) were initially characterized as C. tyrobutyricum, a known cause of late-blowing in high-pH cheeses. Twenty-eight other isolates (Cx) produced gas from lactate, but differed from ATCC 25755 in either endospore position, lactate dehydrogenase activity or carbohydrate fermentation profile. When inoculated at high concentrations in Gouda cheese, strain ATCC 25755, two Ct isolates and 18 Cx isolates tested produced gas during ripening. Among the five Ct isolates obtained and two reference strains confirmed as C. tyrobutyricum, there were four qualitatively different volatile organic acid byproduct profiles. Each of the two confirmed C. tyrobutyricum reference strains and five Ct isolates had distinct quantitative cell membrane fatty acid (CMFA) profiles. The Cx isolates represented 14 different volatile organic acid byproduct profiles and each isolate had a unique CMFA profile. Pulsed field gel electrophoresis (PFGE) of DNA from the two confirmed reference C. tyrobutyricum strains, four Ct and three Cx isolates, showed a low degree of relatedness. The results of this study suggest that a heterogeneous group of lactate-fermenting, gas-producing Clostridium spp. may be found in milk. Gas chromatographic analysis of volatile organic acid byproducts or CMFA, and PFGE of DNA are highly discriminating methods for differentiating Clostridium spp. that may cause late blowing in high-pH cheeses.     

OXA-16, a further extended-spectrum variant of OXA-10 beta-lactamase, from two Pseudomonas aeruginosa isolates

Pooled whey from the production of one variety of ovine cheese and two varieties of caprine cheeses was studied for gross composition and individual whey protein composition over one production season. Individual proteins were quantified by sodium dodecyl sulfate-PAGE and digital imaging technology. The mean proportion of alpha-lactalbumin (LA) from caprine wheys from the manufacture of Chevre and Cheddar-type cheeses was higher than values previously reported for bovine whey from Cheddar cheese; proportions of serum albumin, immunoglobulin (Ig)G, and beta-lactoglobulin (LG) were lower. Ovine whey from Manchego-type cheese showed a higher proportion of beta-LG, about the same proportion of alpha-LA, and lower proportions of serum albumin and IgG than did the bovine whey. Relative amounts of alpha-LA decreased throughout the season, but beta-LG rose in midlactation and then gradually decreased toward the end of lactation. Relative proportions of serum albumin remained fairly stable throughout the year, and IgG decreased.     

Lipoprotein lipase activity and its relationship to high milk fat transfer during lactation in grey seals

Lipoprotein lipase regulates the hydrolysis of circulating triglyceride and the uptake of fatty acids by most tissues, including the mammary gland and adipose tissue. Thus, lipoprotein lipase is critical for the uptake and secretion of the long-chain fatty acids in milk and for the assimilation of a high-fat milk diet by suckling young. In the lactating female, lipoprotein lipase appears to be regulated such that levels in adipose tissue are almost completely depressed while those in the mammary gland are high. Thus, circulating fatty acids are directed to the mammary gland for milk fat production. Phocid seals serve as excellent models in the study of lipoprotein lipase and fat transfer during lactation because mothers may fast completely while secreting large quantities of high fat milks and pups deposit large amounts of fat as blubber. We measured pup body composition and milk fat intake by isotope (deuterium oxide) dilution and plasma post-heparin lipoprotein lipase activity in six grey seal (Halichoerus grypus) mother-pup pairs at birth and again late in the 16-day lactation period. Maternal post-heparin lipoprotein lipase activity increased by an average of four-fold by late lactation (P = 0.027), which paralleled an increase in milk fat concentration (from 38 to 56%; P = 0.043). Increasing lipoprotein lipase activity was correlated with increasing milk fat output (1.3-2.1 kg fat per day) over lactation (P = 0.019). Maternal plasma triglyceride (during fasting) was inversely correlated to lipoprotein lipase activity (P = 0.027) and may be associated with the direct incorporation of long-chain fatty acids from blubber into milk. In pups, post-heparin lipoprotein lipase activity was already high at birth and increased as total body fat content (P = 0.028) and the ratio of body fat: protein increased (P = 0.036) during lactation. Although pup plasma triglyceride increased with increasing daily milk fat intake (P = 0.023), pups effectively cleared lipid from the circulation and deposited 70% of milk fat consumed throughout lactation. Lipoprotein lipase may play an important role in the mechanisms involved with the extraordinary rates of fat transfer in phocid seals.