Call number: LD2668 .T4 1978 S515 / Master of Science

Numerous attempts have been made to identify the flavor compounds in Blue cheese, however, duplication of Blue cheese flavor has not yet been accomplished. Therefore, it was desirable to make a qualitative and quantitative investigation of Blue cheese flavor compounds and to study the effect of certain microorganisms on Blue cheese flavor. The aroma fraction of Blue cheese was isolated by centrifugation of the cheese and molecular distillation of the recovered fat. The volatiles were separated by gas chromatography on packed columns containing polar and nonpolar phases and by temperature programmed capillary column gas chromatography. Relative retention time data and fast scan mass spectral analysis of the capillary column effluent were used to identify compounds in the aroma fraction. Compounds positively identified were as follows: 2-pentanone, 2-hexanone, 2-heptanone, 2-octanone, 2-nonanone, 2-decanone, 2-undecanone, 2-tridecanone, 2-propanol, 2-pentanol, 2-heptanol, 2-octanol, 2-nonanol, methyl butanoate, methyl hexanote, methyl octanoate, methyl decanoate, methyl dodecanoate, ethyl formate, ethyl acetate, ethyl butanoate, ethyl hexanoate, ethyl octanoate, ethyl decanoate, ethanal, 3-methyl butanal, 2-methyl butanol, 3-methyl butanol, 1-pentanol, benzene, and toluene. Tentatively identified compounds included acetone, delta-octalactone, delta-decalactone, methyl acetate, isopropyl hexanoate, 3-methylbutyl butanoate, pentyl hexanoate, ethyl-2-methylnonanoate, isopropyl decanoate, furfural, 2-methyl propanal, methanol, ethanol, 2-phenylethanol, cresyl methyl ether, dimethylcyclohexane, diacetyl, methyl mercaptan, and hydrogen sulfide. A combination of liquid-liquid column chromatography and gas-liquid chromatography was utilized to quantitate the major free fatty acids in Blue and Roquefort cheese samples. The average concentration (mg acid/kg cheese) in three Blue cheese samples was as follows: 2:0, 826; 4:0, 1, 448; 6:0, 909; 8:0, 771; 10:0, 1,318; 12:0, 1,588; 14:0, 5,856; 16:0, 12,789; 18:0, 4,243; 18:1, 12,455; 18:2, 1,072; 18:3, 987. Roquefort cheese was found to be proportionately more abundant in 8:0 and 10:0 acids and low in 4:0 acid compared to Blue cheese. No formic, propionic, or isovaleric acid was detected in any of the cheeses tested. A quantitative procedure involving adsorption chromatography, liquid-liquid chromatography and absorption spectrophotometry was used to isolate and measure the concentration of the C₃, C₅, C₇, C₉, and C₁₁ methyl ketones in the fat of Blue and Roquefort cheese. The average methyl ketone concentration (micromoles ketone/10 g cheese fat) of five Blue cheese samples was as follows: acetone, 1.7; 2-pentanone, 5.9; 2-heptanone, 11.2; 2-nonanone, 9.3; 2-undecanone, 2. 4. Considerable variation in ketone concentration was noted between samples, but no consistent differences were observed between Blue and Roquefort cheese. One Roquefort sample contained no acetone. The annount of ketone formed during cheese curing does not depend directly on the amount of available fatty acid precursor. There appears to be a selective conversion of the 8:0, and to a lesser extent the 6:0 and 10:0, fatty acids to methyl ketones by the Penicillium roqueforti spores. The concentration of the C₅, C₇, and C₉ secondary alcohols was determined in the same cheeses used for ketone analysis. The previously measured ketones acted as internal standards and facilitated a semi-quantitative calculation of alcohol concentrations from peak areas of gas chrorriatograms. The average alcohol concentration (micromoles alcohol/10 g cheese fat) in five Blue cheese samples was as follows: 2-pentanol, 0. 3; 2-heptanol, 2. 1; 2-nonanol, 0. 8. The alcohols were present in approximately the same ratios as their methyl ketone analogs, but at much lower concentrations. A synthetic Blue cheese flavor was prepared using a blend of butterfat, dry curd cottage cheese, cream, and salt as a base. The most typical flavor was obtained using the following' compounds: the 2:0, 4:0, 6:0, and 8:0 fatty acids at two-thirds the average concentration found in cheese; twice the average concentration of the C₃, C₅, C₇, C₉, and C₁₁ methyl ketones and C₅, C₇, and C₉ secondary alcohols found in cheese: 2.0 mg/kg of base of 2-phenylethanol; 1.5 mg/kg of base of ethyl butanoate; 6.0 mg/kg of base of both methyl hexanoate and methyl octanoate. Incorporation of higher acids caused a soapy flavor. The presence of 2-phenylethanol and the esters was judged as very important in duplicating Blue cheese flavor. The mycelia of Penicillium roqueforti appear to be more active in the reduction of methyl ketones to secondary alcohols than the spores. Yeasts associated with Blue cheese are capable of reducing methyl ketones to secondary alcohols. Yeasts also may play a role in Blue cheese flavor by producing ethanol and other alcohols and certain esters. / Graduation date: 1966

Listeria meningoencephalitis is a rare condition, occurring mainly in immunocompromised patients. We present two cases of Listeria monocytogenes meningoencephalitis in immunocompetent children, with successful treatment with betalactam/aminoglycoside combination. Unpasteurized cheese was postulated as the source of infection.

This thesis considered the potential benefits of employing linear programming in cheese manufacturing plants as a decision tool for management. Its potential has been enhanced by the recent approval of acid orange 12 as a chemical for testing the percent protein in milk; therefore, a practical test is now available for monitoring protein as well as milk fat in milk manufacturing and fluid milk plants. Seven models, each one differing only in the milk fat and protein percentages or means of standardizing the cheese milk, were manipulated individually and simultaneously to test the managerial benefits of linear programming under various plant and market conditions. Each model consisted of five cheese activities or variables, two butter activities, three powder activities, and a selling activity for each product produced. The maximum price that could be paid the farm producer per hundred-weight of milk and the minimum wholesale rice per pound of manufactured product, to cover variable costs were determined for each variety of cheese and composition of milk. There was a definite interaction between each of the activities. This caused the cost to produce a Pound of cheese to vary according to the alternative uses for milk, cream, skim milk, and whey. When the simulated plant was being utilized at or near full capacity and the cheese milk was standardized with non fat dry milk powder, total cheese yield increased as did total profits. When the plant was not being utilized to full capacity, profits were higher by not standardizing.

The flavor, quality and composition of market brick cheese varies greatly. Its moisture content often ranges from 37 to 43 per cent. The flavor may be similar to Limburger or it may even resemble that of Cheddar. Such a great variation in a specific food product tends toward disappointment for the consumer. It is believed that a more uniform standard of quality for this product is needed to materially increase its consumption. Therefore, a detailed study of some of the factors involved in the manufacture of brick cheese may help to improve the quality and aid in determining a satisfactory standard.

The effect of chemical parameters on cheese structure and functionality was studied by modifying the calcium, salt content, and pH of cheese. Cheese blocks were high-pressure injected from zero to five times with water, solutions of different salts, or an acid solution 14 d after manufacture. Successive injections were performed 24 h apart. After 40-42 d of refrigerated storage, cheese structure was studied by using scanning electron microscopy and digital image analysis, and cheese functionality was characterized by texture profile analysis and melting test. Increased salt content of cheese (2.7 versus 0.1%) caused the protein matrix to become more hydrated and to expand (P < 0.1 ), though the occurrence of syneresis resulted in decreased moisture content of cheese (P < 0.05). Salt injection increased cheese hardness and the initial rate of cheese flow, but it decreased cheese cohesiveness (P < 0.05). Increased calcium content (1.8 versus 0.3%) and decreased pH of cheese (4.7 versus 5.3) caused contraction of the protein matrix (P < 0.05) and release of serum. Thus, the matrix became less hydrated, and the moisture content and weight of cheese decreased (P < 0.05). Calcium injection decreased the pH and melting of cheese, but it increased cheese hardness (P < 0.05). Acid injection promoted calcium solubilization and decreased calcium content of cheese (P < 0.05). Above pH 5.0 (5.0-5.3), acid injection decreased cheese hardness and increased the initial rate of cheese flow (P < 0.05). Below pH 5.0 (5.0-4.7), acid injection decreased cheese cohesiveness, and the initial rate and extent of cheese flow (P < 0.05). In conclusion, modifying the chemical composition of cheese alters protein interactions, resulting in cheese with different structural and functional properties. Increased salt content of cheese (up to 2.7%) impairs protein-to-protein interactions, and its effect is most significant when salt content increases from 0 to 0.5%. Below 5.0 (5.0- 4.7), the effect of pH predominates over calcium content, and decreased cheese pH promotes protein-to-protein interactions. Increased calcium content of cheese (up to 1.8%) also promotes protein-to-protein interactions, and the content of protein-bound calcium may be the major factor controlling the functionality of most cheeses.

Importance of project: In recent years many antibiotics have come to the foreground as a treatment for mastitis. Aureomycin is one of the more recent antibiotics that has been used for this purpose. Aureomycin has been reported to be successful in curing some types of mastitis, but milk produced by cows that have been treated with Aureomycin does not act normal in the cheese manufacturing process. The most noticeable effect in milk from cows treated with Aureomycin has been slow or complete cessation of acid production by bacteria in cultured dairy products; this has been especially true in the cheese manufacturing process. In the even of slow acid production, or complete cessation of acid production, the cheese produced is either of lower quality than would normally be exected, or the entire vat of cheese may be lost. In either case there is a definite advers effect on the dairy industry. Purpose of investigation: The purpose of this problem is to determine the percentage of Aureomycin necessary in milk to cause slow or complete cessation of acid production in the cheese manufacturing process, and to find a chemical or heat treatment that can be used to inactivate the aureomycin so that there will be no harmful effect in milk used to manufacture cheese.

The regulatory standards set by food authorities globally for probiotic foods such as Cheddar cheese makes it essential to have reliable enumeration media that will accurately monitor the survival of probiotic bacteria over the shelf life of Cheddar cheese. This study therefore investigated various selective and differential media for reliable enumeration of Lactobacillus acidophilus, Bifidobacterium spp., starter lactic acid bacteria (SLAB) and non-starter lactic acid bacteria (NSALB) from Cheddar cheese using pure cultures and commercial probiotic Cheddar cheese. All media showed variation in counts and selectivity. Some reported selective media failed to inhibit SLAB and NSLAB. The media that were reliable and also gave good recovery were, Reinforced Clostridium Agar with Bromocresol green and Clindamycin (RCABC), which was selective for L. acidophilus spp. and Reinforced Clostridium Agar with Aniline blue and Dicloxacillin (RCAAD), which was differential for Bifidobacterium spp. and SLAB. Reinforced Clostridium Agar with Bromocresol green and Vancomycin (RCABV) was found suitable for NSLAB. Additionally, an enzyme based colorimetric assay was modified successfully and used as a confirmatory test to check the presence of bifidobacterial colonies on enumeration media. Six batches of probiotic Cheddar cheese were manufactured with the incorporation of LAFTI L10 (L. acidophilus) and LAFTI B94 (B. lactis). The survival of probiotic bacteria, SLAB and NSLAB were monitored over a six-month ripening period using the selected media. The survival of free probiotic bacteria throughout the ripening process decreased consistently in all the six batches. In order to enhance the survival of probiotic bacteria, the effect of microencapsulation on the viability of LAFTI L10 and LAFTI B94 in Cheddar cheese was studied. Six batches of Cheddar cheese were manufactured with the incorporation of alginate-starch encapsulated and free cells of LAFTI L10 and LAFTI B94. The survival of both the encapsulated and free probiotic bacteria was studied over a six month ripening period. The survival of encapsulated LAFTI L10 and LAFTI B94 (107 cfu/g) was found to be significantly better than that of free bacteria (105 cfu/g) at the end of six months of ripening period in Cheddar cheese. / Master of Applied Science (M. App. Sci.) (Biotechnology)

The present investigation was undertaken to characterize a number of strains of Lactobacillus bulgaricus and Streptococcus thermophilus intended for use by a commercial starter supply company. Thorough characterization of each culture was required in order to combine compatible strains so that their usefulness in Mozzarella cheese manufacture would be maximized. In this regard, cocci were assayed for formate and carbon dioxide production, rods for proteolysis, and both types for salt and phosphate tolerance as well as rate of acid production. In addition, certain combinations of cocci and rods were assayed as mixtures for these characteristics. Analyses of the various strains of lactobacilli and S. thermophilus were performed. Proteolysis, as determined by the Church method, for the rods (L. bulgaricus , L. helveticus and L. lactis ) varied from as low as 11.3 to as high as 34.7 mM when incubated for six hours. Proteolysis analyses for S. thermophilus also revealed a wide range of values from a low of 18.5 to a high of 46.4 mM. However, when strains were incubated for 16 hours, rods were shown to be nearly twice as proteolytic as cocci. When mixed cultures were tested for proteolysis, results were dependent on strain synergism. Values ranged from a low of 5.1 mM to 70.5 mM in mixed cultures. Various strains of S. thermophilus and mixed cultures were assayed for formate production. The S. thermophilus strain values were from a low of 4.2 to as high as 20.3 mg/L. Formate production in mixed cultures varied from traces of formate in one culture to quantities two and a half times that produced by the single S. thermophilus strains tested. Carbon dioxide production for the rods (L. bulgaricus , L. helveticus , and L. lactis ) varied from as low as 0 μl to as high as 376 μl when incubated for six hours at 44 °C. Carbon dioxide production for S. thermophilus ranged from 5 μl to 1259 μl. Also, S. thermophilus strains produced significantly more carbon dioxide than rod cultures, with only three exceptions. All mixtures were weak producers of carbon dioxide. Nine of 19 L. bulgaricus strains were stimulated by 0.1% phosphate ion and one strain showed stimulation at 0.3% phosphate ion. Thirteen of 19 strains were severely inhibited by 0.5% phosphate. Three of 10 L. helveticus strains were stimulated by 0.1% phosphate and another three strains were unaffected. All strains were inhibited by 0.5% phosphate. Two L. lactis strains showed stimulation at 0.1% phosphate, but inhibition at 0.3% and 0.5%. Acid production by strains of S. thermophilus was inhibited in 11 of 13 cases at 0.1% phosphate. The two strains not inhibited were slightly stimulated by 0.1% and 0.3% phosphate and unaffected by 0.5% phosphate. The mixed cultures of L. bulgaricus CR 14/ S. thermophilus 2 and L. bulgaricus Ql S. thermophilus 2 were not inhibited by 0.1% phosphate, but inhibition occurred at higher concentrations. Mixed cultures of L. bulgaricus C, E/ S. thermophilus 7, 12 and L. bulgaricus C, G/ S. thermophilus 4, 12 were stimulated by all three concentrations of phosphate salts tested. Sodium chloride produced toxic effects on the rods at concentrations ranging from 2.5% to 3.0%, and acid production was stimulated 7 of 32 strains by low salt concentrations(0.5%). In general, cocci were more sensitive to NaCl, with 6 of 13 strains showing sensitivity at 0.5%. Sensitivity to salt was a more gradual effect in the cocci as revealed by a gradual reduction in rate of acid production as NaCl concentrations increased. Mixed cultures were more tolerant to NaCl with no inhibition occurring at concentrations of 1.0%. Culture L. bulgaricus C, GIS. thermophilus 4, 7 were stimulated at concentrations through 1.5%. The synergistic properties of the mixed strains increased NaCl tolerance. / Graduation date: 1993

Thesis (Ph.D.)--Brown University, 2008. / Vita. Adviser: David I. Kertzer. Includes bibliographical references (leaves 359-379).