Numerous investigations have been made on the contribution of butter cultures to the flavor of cultured cream butter, but production of uniform cultured cream butter has not been possible in industry. Therefore, it was desirable to investigate in detail the qualitative and quantitative chemistry of the flavor of high quality butter cultures, and to examine more closely some of the aspects of flavor production by butter culture organisms. Volatile flavor components of high quality butter culture and control heated milk were isolated from intact samples by means of a specially designed low-temperature, reduced-pressure steam distillation apparatus. Most of the flavor compounds present in the resulting distillate fractions were tentatively identified by gas chromatographic relative retention time data. Flavor concentrates obtained by ethyl ether extractions of aqueous distillates were also separated by temperature-programmed, capillary column gas chromatography, and the effluent from the capillary column was analyzed by a fast- scan mass spectrometer. Many of the flavor compounds in the flavor concentrates were positively identified by correlation of mass spectral and gas chromatographic data. In addition, supporting evidence for the identification of some flavor components was obtained through the use of qualitative functional group reagents, derivatives and headspace gas chromatography. Compounds that were positively identified in butter culture include ethanol, acetone, ethyl formate, methyl acetate, acetaldehyde, diacetyl, ethyl acetate, dimethyl sulfide, butanone, 2-butanol, methyl butyrate, ethyl butyrate, methane, methyl chloride, carbon dioxide and methanol; also included were 2-pentanone, 2-heptanone, acetoin, formic acid, acetic acid, lactic acid, 2-furfural, 2-furfurol, methyl hexanoate, ethyl hexanoate, 2-nonanone, 2-undecanone, methyl octanoate and ethyl octanoate. Compounds that were tentatively identified in butter culture include hydrogen sulfide, methyl mercaptan, n-butanal, n-butanol, 2-hexanone, n-pentanal, n-pentanol, 2-mercaptoethanol, n-butyl formate, n-butyl acetate, 2-methylbutanal, 3-methylbutanal, methylpropanal, methyl heptanoate, n-octanal, 2-tridecanone, methyl benzoate, methyl nonanoate, ethyl nonanoate, ethyl decanoate, methyl dodecanoate, ethyl dodecanoate, delta-octalactone and delta-decalactone. Compounds that were positively identified in control heated milk include acetaldehyde, ethyl formate, ethyl acetate, 2-heptanone, 2-furfural, 2-furfurol, 2-nonanone, 2-undecanone, ethyl octanoate and methyl decanoate. Compounds that were tentatively identified in control heated milk include dimethyl sulfide, hydrogen sulfide, ammonia, methyl mercaptan, methyl acetate, acetone, methanol, butanone, butanal, n-butanol, methyl butyrate, ethyl butyrate, 2-pentanone, 2-hexanone, 2-mercaptoethanol, 2-furfuryl acetate, ethyl hexanoate, methyl heptanoate, 2-tridecanone, ethyl decanoate, ethyl dodecanoate, delta-octalactone and delta-decalactone. The data indicated that the qualitative flavor composition of control heated milk and butter culture were very similar. Diacetyl, ethanol, 2-butanol and acetic acid were noted to be consistently absent in the data for the control heated milk. Other compounds were not observed in the heated milk fractions, but were also absent from some of the culture fractions. This was attributed to their presence in low concentrations, chemical instability or inefficient recovery. A modified 3-methyl-2-benzothiazolone hydrazone spectrophotometric procedure was adapted for the determination of acetaldehyde produced in lactic starter cultures. The procedure was applied in conjunction with diacetyl measurements in studying single- and mixed-strain lactic cultures. The diacetyl to acetaldehyde ratio was found to be approximately 4:1 in desirably flavored mixed-strain butter cultures. When the ratio of the two compounds was lower than 3:1 a green flavor was observed. Acetaldehyde utilization at 21°C by Leuconostoc citrovorum 91404 was very rapid in both acidified (pH 4.5) and non-acidified (pH 6.5) milk cultures. The addition of five p.p.m. of acetaldehyde to non-acidified milk media prior to inoculation greatly enhanced growth of L. citrovorum 91404 during incubation at 21°C. Combinations of single-strain organisms demonstrated that the green flavor defect can result from excess numbers of Streptococcus lactis or Streptococcus diacetilactis in relation to the L. citrovorum population. Diacetyl, dimethyl sulfide, acetaldehyde, acetic acid and carbon dioxide were found to be "key" compounds in natural butter culture flavor. Optimum levels of these compounds in butter culture were ascertained by chemical or flavor panel evaluations. On the basis of these determinations, a synthetic butter culture prepared with heated whole milk and delta-gluconolactone (final pH 4.65) was flavored with 2.0 p.p.m. of diacetyl, 0.5 p.p.m. of acetaldehyde, 1250 p.p.m. of acetic acid, 25.0 p.p.b. of dimethyl sulfide and a small amount of sodium bicarbonate for production of carbon dioxide. The resulting synthetic butter culture exhibited the typical aroma, flavor and body characteristics found in natural high quality butter cultures, except that the delta-gluconolactone was found to contribute an astringent flavor. / Graduation date: 1965

Acetaldehyde is known to be responsible for the green or yogurt-like flavor defect of lactic cultures. This study was undertaken to extend the knowledge of acetaldehyde production and utilization by microorganisms normally found in mixed-strain butter cultures. It is anticipated that the resulting information will contribute to a more thorough understanding of the development of a green flavor defect; hence, to methods of avoiding and overcoming this defect. Acetaldehyde production by single-strain cultures of S. lactis, S. cremoris, and S. diacetilactis was found to parallel the increase in microbial population. S. lactis and S. cremoris were found to remove some of the acetaldehyde produced on continued incubation at 21°C. S. diacetilactis did not remove any of the acetaldehyde produced. The ratio of diacetyl to acetaldehyde in the strains of S. diacetilactis studied was found to be unfavorable for a good culture flavor at all times up to 22-24 hr incubation. All of the cultures studied produced a distinct green flavor when grown in milk media. All of the lactic streptococci studied produced both ethanol and acetone when grown in a boiled milk medium. No evidence of acetone utilization by S. diacetilactis was observed. A tentative mechanism for the formation of acetone from pyruvate via acetoacetate was proposed. Single-strain cultures of Leuconostoc dextranicum and Leuconostoc mesenteroides were shown to be capable of utilizing added acetaldehyde under a variety of culturing conditions. These two organisms, along with L. citrovorum were combined into two-strain mixtures with various lactic streptococci. The production and utilization of acetaldehyde varied widely among different two-strain mixtures. The ratio of different lactic organisms comprising the flora of a desirably flavored commercial mixed-strain butter culture was determined. The microbial shift occurring when this culture developed a green flavor defect was found to be an overgrowth of the homo-fermentative lactic streptococci by the S. diacetilactis population. It was found that the concentration of acetaldehyde in a ripened single-strain lactic culture could be significantly reduced by adding a large inoculum of a culture of L. citrovorum and continuing incubation at 21°C or by cooling and holding the culture at 5°C after the addition of L. citrovorum. / Graduation date: 1966

Call number: LD2668 .T4 1931 A34

No description available.

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

Typescript (photocopy). / Digitized by Kansas Correctional Industries

A method for the assessment of volatile compounds in dairy products was developed using solvent desorption dynamic headspace sampling. The method was first applied to assay for diacetyl and acetoin in buttermilk. Major buttermilk volatiles recovered included diacetyl, acetic acid, and acetoin. Normalized detector responses were linear over the range of concentrations tested for diacetyl and acetoin. The method enabled quantitative estimation of diacetyl and acetoin in <30 min, including sample preparation time. Next, the ability of stabilizing and emulsifying agents to inhibit the release of diacetyl from a model dairy matrix was examined using modified purge parameters. Stabilizers (guar, xanthan, and carrageenan) and emulsifiers (lecithin, carboxymethyl cellulose, and Tween 80) were examined for their effects on headspace available diacetyl at 0.05, 0.10, and 0.20% (wt/wt) in a 5% milkfat model system. Guar gum and carrageenan exhibited similar diacetyl release inhibition when corrected for viscosity. Xanthan gum exhibited the greatest decrease in headspace available diacetyl after correction for viscosity at increasing gum levels. Tween 80 imparted no significant viscosity and had no effect on recoverable diacetyl. Lecithin had no effect on viscosity, however it did inhibit the release of diacetyl as a function of lecithin level. Carboxymethyl cellulose increased viscosity and inhibited diacetyl release. Finally, a rapid dynamic headspace sampling technique was evaluated for its ability to differentiate between Cheddar cheese samples for volatile aroma compounds. Seven samples of Cheddar cheese were examined ranging in flavor from mild to extra sharp. A total of 14 volatile compounds were tentatively identified with published retention indices and retention times of known standards. Major volatiles recovered were 2-butanol, acetoin, propanoic acid, butyric acid, and caproic acid. Other identified compounds were 2-butanone, diacetyl, ethyl butyrate, 1-butanol, ethyl caproate, hexanol, acetic acid, 2,3-butanediol, and octanoic acid. The application of solvent desorption dynamic headspace sampling of dairy volatiles is a simple, rapid method for the determination of volatile compounds previously shown to influence flavor and aroma of dairy products. This research was conducted to demonstrate the optimized application of this technology to tracking dairy products aroma compounds. / Graduation date: 1996

During the course of ripening, Cheddar cheese frequently develops a flavor defect described as fruity. Recent work has indicated that the use of certain starter cultures ultimately results in the development of the defect as the cheese ages. The flavor compounds responsible for the defect, however, have not been elaborated. The purpose of this investigation was to isolate and identify the components responsible for the fruity flavor defect and to evaluate the role of certain cheese starter cultures in the development of the defect. Since the fruity character of the defect is apparent in the aroma of the cheese, the compounds responsible for the defect were expected to be reasonably volatile. Volatile constituents were isolated by a distillation technique from fat expressed from a typically fruity cheese by centrifugation. The volatile constituents were then separated by gas-liquid chromatography. By monitoring the odor of the effluent stream of the column, it was possible to determine which components had fruity odors, and these were subsequently identified by mass spectral analysis and coincidence of retention time with the authentic compounds. Ethyl butyrate, ethyl hexanoate, and ethyl octanoate were found to be the only compounds with detectable fruity odors. The volatiles from the fat of four cheeses possessing varying degrees of the defect and their matching non-fruity controls were analyzed by a gas entrainment, on-column trapping, gas-liquid chromatographic technique. The manufacturing and curing conditions of each fruity cheese and its matching control were identical, except for the use of different starter cultures. Ethanol, ethyl butyrate, and ethyl hexanoate were more abundant in each of the fruity samples. The approximate concentration range of these compounds was as follows: In fruity cheese; ethanol 400 to 2,040 ppm, ethyl butyrate 1.6 to 24 ppm, ethyl hexanoate 0.9 to 25 ppm. In non-fruity cheese; ethanol 36 to 320 ppm, ethyl butyrate 0.7 to 4.7 ppm, ethyl hexanoate 0.3 to 2.2 ppm. In ten commercial Cheddar cheeses selected at random from the market, the concentration of ethanol ranged from 5.5 to 620 ppm. Single-strain cultures of Streptococcus lactis, Streptococcus diacetilactis, and Streptocococcus cremoris as well as three mixedstrain commercial cultures were evaluated for ethanol and acetaldehyde production in non-fat milk medium. Among the single-strain cultures there appeared to be no correlation between ethanol production and species, although considerable variation was noted for strains within a species. The mixed-strain cultures were designated A, B, and C. Cultures B and C had been implicated in the development of the fruity flavor defect in Cheddar cheese, while culture A produced normal cheese of good quality. Cultures B and C produced approximately 40 times more ethanol than culture A when incubated in non-fat milk medium for one month at 7°C. Certain single-strain cultures and the three mixed-strain cultures were tested for their ability to reduce acetaldehyde and propanal, and to catalyze the formation of ethyl butyrate when ethanol and butyric acid were provided as substrates. Acetaldehyde and propanal were reduced to the corresponding alcohols by all cultures, but the formation of ethyl butyrate was not observed in any culture. A good correlation between high levels of ethanol and high levels of ethyl butyrate and ethyl hexanoate in the fruity cheeses suggests that the quantity of ethanol present in the cheese may determine the amount of ester formed. Further, starters resulting in the defect produced considerably more ethanol than cultures resulting in normal cheese when incubated at 7°C, a normal temperature for curing Cheddar cheese. This observation adds weight to the hypothesis that certain cultures are directly responsible for the defect. / Graduation date: 1966

The unique flavor of high quality Swiss cheese is difficult to reproduce in commercial market cheese. Swiss cheese flavor has never been duplicated or thoroughly understood. New techniques and advances in flavor research have enabled better definition and understanding of food flavors. Therefore, it was desirable to make a detailed investigation of Swiss cheese flavor. Neutral volatile flavor compounds were isolated from Swiss cheese fat by low-temperature low-pressure distillation. The compounds were separated by temperature programmed gas chromatography. Direct analysis of cheese fat and whole cheese from four domestic and two imported good flavored cheeses by gas entrainment and on-column trapping provided a further means of isolation of volatile flavor compounds in Swiss cheese. Gas chromatography in conjunction with rapid scan mass spectrometry and relative retention time data were used to identify compounds. Compounds positively identified by the distillation and on-column trapping techniques were as follows: methanol, ethanol, 1-propanol, 1-butanol, 2-pentanol, trans-2-hexene-1-ol, 2-phenylethanol, acetaldehyde, 2-methyl propanal, 2-methyl butyraldehyde, benzaldehyde, phenylacetaldehyde, acetone, butanone, 2-pentanone, 2-hexanone, 2-heptanone, 2-nonanone, 2-undecanone, 2-tridecanone, 2-pentadecanone, hexane, octane, 1-octene, nonane, 1-nonene, dodecane, pentadecane, toluene, α-pinene, methyl acetate, methyl hexanoate, methyl octanoate, methyl decanoate, ethyl propionate, ethyl butanoate, ethyl hexanoate, ethyl octanoate, ethyl decanoate, ethyl dodecanoate, butyl acetate, 3-methyl butyl acetate, γ-valerolactone, γ-dodecalactone, δ-octalactone, δ-decalactone, δ-dodecalactone, dimethyl sulfide, diacetyl, benzothiazole, o-dichlorobenzene, 1, 2, 4-trichlorobenzene, di-isobutyl adipate, and chloroform. Compounds tentatively identified include an aromatic hydrocarbon, pinane, α-fenchene, ethyl benzene, a di-methyl benzene, methyl benzoate, 2-phenyl-2-methyl butane, 5-methyl-5-ethyl decane, 3-methyl butyl octanoate, 2, 5-dimethyl tetra decane, methyl vinyl ether and 2-methyl propenal. The concentration of selected volatile compounds identified by the on-column trapping technique were determined by relating their peak heights to known quantities of compound. Average concentrations calculated from the mean values for all the six cheeses and expressed in parts per million were as follows: dimethyl sulfide. 0.107; diacetyl, 0.8; acetaldehyde, 1.4; acetone, 1.6; butanone, 0.3; 2-methyl butyraldehyde, 0.42; 2-pentanone, 0.98; 2-heptanone, 0.45; ethanol, 16.3; 2-butanol, 0.3; 1-propanol, 2.9; 1-butanol, 0.7; methyl hexanoate, 1.5; and ethyl butanoate, 0.6. Liquid-liquid partition chromatography and gas chromatography were utilized to determine quantitatively the major free, fatty acids in the six Swiss cheeses. 2-Methyl butyric acid was detected in all cheeses and varied from 9.0 to 100.0 mg/kg cheese. The other isomeric acid, 3-methyl butyric, was detected in only two cheeses. Formic acid was detected in only one cheese. No n-valeric or 2-methyl propionic acids were detected. A synthetic Swiss cheese flavor was prepared utilizing the data obtained in this investigation and that available in the literature for free amino acids. A satisfactory reproduction of Swiss cheese flavor could be achieved only if the mixture contained free fatty acids, volatile constituents, and free amino acids and was adjusted to the pH of natural cheese. / Graduation date: 1966

Increasing interest has been shown in the irradiation sterilization and irradiation pasteurization of foods, but problems of off-flavors and odors are still unsolved, especially in the case of dairy products. From the flavor chemistry point of view, milk lipids are very highly susceptible to irradiation effects. Therefore, this investigation was designed to study some irradiation induced reactions involving flavor changes in the milk fat and to identify the volatile components produced in the milk fat upon irradiation. Milk fat, prepared from raw sweet cream and washed free of phospholipids, was first irradiated in the presence of air and under vacuum in glass vials at 4.5 Mrad with gamma rays from cobalt-60. The irradiation resulted in increase in TBA number, peroxide value, total monocarbonyls, bleaching of color, slightly rancid and typical candle-like off-flavors. Free fatty acids were also produced upon irradiation. The changes were more drastic in air along with production of a slight oxidized flavor. The monocarbonyls identified by column and paper chromatographic methods in irradiated milk fat include: C₁ through C₁₂, C₁₄ , and C₁₆ n-alkanals; C₃ through C₉, C₁₁, C₁₃ and C₁₅ alk-2-ones with only traces of C₆ and C₈ alk-2- ones; and C₅, C₆, C₉, and C₁₂ alk-2-enals. Irradiation of milk fat that had been dried over calcium hydride also caused free fatty acid production, especially short chain fatty acids. Methyl octanoate treated with calcium hydride and irradiated at 1.5, 3.0, 4.5, and 6.0 Mrad yielded small quantities of free octanoic acid, confirming that irradiation caused fission of the ester linkage even when traces of water were removed. The quantities of octanoic acid formed increased with increasing dose of irradiation. For identification of volatile components, the milk fat was irradiated in 307x409 'C' enameled cans under vacuum. The headspace analysis showed some air still left in the cans. Irradiation resulted in consumption of oxygen and production of hydrogen, carbon monoxide, carbon dioxide, and methane as identified in the headspace gases. The volatiles were isolated from the irradiated and control milk fats by low temperature, vacuum steam distillation at 40°C and 1-2 mm Hg. The volatile components were then extracted from the aqueous distillate with ethyl ether. The ethyl ether extract exhibited the typical candle-like defect. The ethyl ether concentrate was analyzed by combination of GLC and fast-scan mass spectrometric techniques. Identification of various components was achieved on the basis of mass spectral data and coincidence of gas chromatographic retention times. In the case of the components for which only GLC t[subscript r]/t[subscript r] evidence was available or the mass spectra obtained were not satisfactory, the identity assigned was only tentative. The volatile compounds that were positively identified to be present in irradiated milk fat are given below: n-Alkanes C₅ through C₁₇ 1-Alkenes C₅, C₇ through C₁₇ Fatty acids C₄, C₆, C₈ and C₁₀ n-Alkanals C₅ through C₁₁ Others γ-decalactone, δ-decalactone, 2-heptanone, benzene, ethyl acetate, chloroform, and dichlorobenzene. The tentative identification was obtained for the following compounds: γ-lactones C₆ and C₈ δ-lactones C₆, C₈, C₁₁, and C₁₂ 1, ?-alkadienes C₁₀, C₁₁, C₁₂, C₁₆ and C₁₇ iso-alkanes C₁₀, C₁₁, C₁₂, and C₁₃ Others methyl hexanoate, 2-hexanone, 4-heptanone and n-dodecanal. The compounds present in unirradiated control milk fat included: short chain fatty acids (C₄, C₆, C₈, and C₁₀), C₈, C₁₀, and C₁₂ δ-lactones, 2-heptanone, chloroform, dichlorobenzene, benzene, toluene, and ethyl-benzene. Only tentative identity was established for most of these components in control milk fat. Possible reaction mechanisms are presented for the formation of the compounds in irradiated milk fat. / Graduation date: 1966