17B-4 |
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H.-Y. CHUNG1, J. A. Partridge2, and B. R. Harte1. (1) School of Packaging, Michigan State Univ., 130 Packaging Bldg., East Lansing, MI 48824-1223, (2) Dept. of Food Science & Human Nutrition, Michigan State Univ., 2100-B Anthony Hall, East Lansing, MI 48824-1225 Light-oxidized off-flavors in milk occur while exposed to fluorescent light in retail dairy cases. Degradation of sulfur containing amino acids causes burnt feather like off-flavors from low molecular weight sulfur volatiles. Oxidation of unsaturated fatty acids generates cardboardy, metallic off-flavors from aldehydes and ketones. Reduced fat (2%) milk in 237 ml glass bottles was stored at 5oC and exposed to 0, 2, 4, 8, 12, 24, 36 and 48 hours of fluorescent light (1000 lx). The electronic nose equipped with 12 metal-oxide semiconductor sensors was used to analyze the headspace generated at 45, 70 or 95oC for 15 minutes. Models based on sensor responses (max dR/R0) using Linear or Quadratic Discriminant Function Analysis (LDA or QDA) or k-Nearest Neighbor (k-NN) were evaluated. A series of triangle tests were performed by 24 consumer panelists, to determine the sensory threshold of light-oxidized off-flavors. It showed that light exposure caused significant olfactory change in 8 hours (p < 0.05). Canonical discrimination scatter plots indicated a partial differentiation in LDA models based on sensor responses of the electronic nose. Headspace temperature at 95oC offered better differentiation for moderately oxidized samples (0 to 12 hours), though 45oC headspace differentiated highly oxidized samples (36 and 48 hours). Among several supervised statistical learning techniques, LDA and 1-NN had the highest correct identification rates for test data. When harmful light exposure was defined as 8 hours, the LDA of 95oC headspace samples correctly recognized 97% of the oxidized samples. The electronic nose detected light-oxidized off-flavors in reduced fat milk, with comparable sensitivity to triangle sensory tests.
Session 17B, Dairy Foods: General
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