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

Graduation date: 1992

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

Graduation date: 1993

Cheddar Cheese samples (good cheese, weak cheese, cheese made with pasteurized milk, cheese made with heat-shocked milk, cheese from production plant A, cheese from production plant B, cheese made with adjunct culture, and cheese made without adjunct culture), were evaluated during the ripening stage. Proteolysis was studied by a fractionation scheme, resulting in an insoluble fraction analyzed by urea polyacrylamide gel electrophoresis (Urea-PAGE), and a soluble fraction which was further investigated through water soluble nitrogen (WSN), trichloroacetic acid soluble nitrogen (TCA-SN) and phosphotungstic acid soluble nitrogen (PTA-SN) analyzed by total Kjeldahl nitrogen content (TKN). Reversed phase high performance liquid chromatography (RP-HPLC) was used to study the peptide profile of the water soluble fraction. Lipolyisis was studied by levels of individual free fatty acids determined through gas chromatography-flame ionization detection (GC-FID) after isolation employing solid phase extraction (SPE). Volatile sulfur compounds were studied using head space solid phase micro-extraction (SPME) coupled with gas chromatography-pulsed flame photometric detection (PFPD). It was found that Urea-PAGE is capable to differentiate samples according their age, but cannot discriminate samples regarding the treatment assessed, quality or origin of the samples. However, measurements of total Kjeldahl Nitrogen (TKN) of the WSN, TCA-SN, and PTA-SN fractions, and the principal component analysis of the RP-HPLC peptide profile of the WSN fraction, revealed differences in the rate and pattern of proteolysis for each one of the manufacturing cases. Good cheese, cheese produce in plant TCCA, cheese made in plant CRP with adjunct culture isolated from plant TCCA cheese, and cheese made with heat-shocked milk developed higher level of total nitrogen for the WSN, TCA-SN and PTA-SN fractions, indicating that primary and secondary proteolysis were faster for these samples. This is supported by a PCA model with three principal components that account for the 80-83% of the variability of the data from the RP-HPLC peptide profile analysis, which discriminates the samples according to age and manufacturing practice. In addition, FFA profiles demonstrated higher levels of low and medium chain free fatty acids for good cheese, cheese produce in plant TCCA, cheese made in plant CRP with adjunct culture, and cheese made with heat-shocked milk samples, which suggest faster lipolysis during ripening. The Volatile Sulfur Compounds (VSC) analysis showed higher levels of DMS and MeSH and lower levels of H2S, suggesting faster catabolism of sulfur containing amino acids in good cheese, cheese produce in plant TCCA, cheese made in plant CRP with adjunct culture, and cheese made with heat-shocked milk. / Graduation date: 2013