71A-7 |
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C. J. KUO and W. J. Harper. Dept. of Food Science and Technology, The Ohio State Univ., 2015 Fyffe Ct., 340-B Parker Food Science Bldg., Columbus, OH 43210-1007 Electronic noses (EN) have been useful in differentiating aromas of cheese, but no method has been available to determine the chemical basis of the differentiation. Using a mass spectrometer with negative chemical ionization (NCI) offers a possible means for identification of the chemical compounds associated with aroma differentiation. NCI gives far fewer fragments than the more common electronic ionization (EI). However, unlike EI, there is no NCI mass library to provide a basis for identification and differentiation of aroma compounds. The objective of this investigation was to build a library database for NCI of Swiss cheese flavor compounds to provide a chemical basis for the application of EN to Swiss-type cheeses. Twenty-four chemicals previously associated with Swiss cheese flavor and representing alcohols, aldehydes, acids, and ketones, were chosen for study. The three most abundant masses and the molecular weight (M) of each compound were tabulated to identify the fragmentation pattern. Methane was used as the reagent gas. One ml of pure chemical was sealed in a 20ml vial and heated at 60 °C for 15 min before the headspace sample was taken for injection. The most common fragment of all the tested chemicals was molecular weight minus 1 (M-1). Nineteen out of 24 compounds had M-1 as the most abundant fragment. The second abundant fragment was dependent on the class of the compound. The alcohols and ketones had M, and the aldehydes had M-1+CH4. Although compounds with the same molecular weight showed some similarity in fragmentation, there were enough different fragments to differentiate between them. Application of the method to 15 Swiss cheeses showed that the NCI mass spectrum library did provide a means for assigning chemical compounds to the cheeses differentiated by EN-NCI. Butyric acid, isobutyric acid, diacetyl, acetic acid, acetaldehyde, and propionic acid were involved in the aroma differentiation.
Session 71A, Dairy Foods: General
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |