15B-12 |
Compounds responsible for musky off-odor of rennet casein |
Y. KARAGUL-YUCEER1, K. N. Vlahovich2, M. A. Drake1, and K. R. Cadwallader2. (1) Dept. of Food Science, North Carolina State Univ., Southeast Dairy Foods Research Center, Box 7624, Raleigh, NC 27695, (2) Dept. of Food Science & Human Nutrition, Univ. of Illinois, Urbana-Champaign, 1302 W. Pennsylvania Ave., Urbana, IL 61801 Rennet casein, produced by enzymatic (rennet) precipitation of casein from pasteurized skim milk, is used in both industrial (technical) and food applications. The principal food use of rennet casein is as a functional ingredient in processed cheese analogues and spreads. The flavor of rennet casein is an important quality parameter. However, it has been observed that during storage rennet casein powder develops an off-odor described as musky/wet dog-like. The exact chemical nature of this off-odor has not been previously reported. The objective of our study was to determine the predominant odorants responsible for the typical off-odor of rennet casein powder. Two commercial rennet casein powders were evaluated. Each sample was hydrated, mixed with sodium chloride and then extracted with ether. Aroma extracts were obtained by high vacuum distillation of the ether fraction. Aroma extracts were separated into neutral/basic and acidic fractions and analyzed by gas chromatography-olfactometry (GCO), aroma extract dilution analysis (AEDA) and GC-mass spectrometry (MS). Cool on-column injection was employed to minimize degradation of any thermally labile components. Compounds were identified by GC-MS data, retention indices on two columns and odor properties against reference standards. Odorants detected by GCO were typical of those previously reported in nonfat milk powders and consisted of short chain volatile fatty acids, phenolic compounds, lactones, furanones, etc. Results of AEDA revealed that 2-aminoacetophenone (AAP; musky, grape-like) and indole (mothball, fecal) were primarily responsible for the typical musky/wet-dog-like off-odor of rennet casein. AAP may be especially important since it was the most potent odorant among those detected by GCO and AEDA. Both AAP and indole may have been derived by degradation of the amino acid tryptophan. This study provides information on the chemical nature of the musty/wet dog-like off-odor associated with rennet casein. Results may aid scientists in detection and prevention of this flavor defect.
Session 15B, Dairy Foods: Chemistry, microbiology and sensory analysis of various cheeses
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