15C-36 |
Microbial and sensory quality evaluation of reduced-fat and fat-free milk with an electronic nose |
F. KOREL, Food Engineering Department, Celal Bayar University, Engineering Faculty, Manisa, 45140, Turkey and M. O. Balaban, Food Science and Human Nutrition Department, University of Florida, P.O. Box 110370, Gainesville, FL 32611.
Psychrotrophs are the major spoilage organisms in milk. Bacterial spoilage produces metabolites which cause off-odors. Psychrotrophic counts exceeding 1x106 cfu/ml are generally reqiured to produce adverse effects on quality. Traditional microbial evaluation of milk is time consuming. A fast, simple, and inexpensive method for reliable detection of pyschrotrophs would be a valuable quality control tool for the dairy industry. The electronic nose is a promising technology that can be used as a fast screening tool. The objectives of this study were to determine the changes in microbial and sensory quality of reduced-fat and fat-free milk inoculated with P. fluorescens or B. coagulans, stored at different temperatures, and to correlate e-nose data with microbial loads and sensory results. Sterilized Parmalat® reduced-fat and fat-free milk were inoculated with P. fluorescens (ATCC 948) or B. coagulans (ATCC 7050). They were stored at 1.7°, 7.2°, and 12.8°C up to 10 days, and evaluated at days 0, 3, 5, 7 and 10 using an e-nose (e-NOSE 4000). Microorganisms were enumerated using aerobic plate count 3M Petrifilm and standard plate count agar. The odor of milk samples was evaluated by a 10-member untrained sensory panel. Data were analyzed using discriminant function analysis (DFA). Discrimination of microbial loads by e-nose readings gave classification rates of 100% for each temperature and type of milk. Sensory scores of samples were predicted from e-nose readings with accuracies of 100%. When grouped by days, DFA of e-nose readings gave correct classification rates of 100% for all treatments. This study demonstrated the potential use of the electronic nose to detect odor differences due to microbial load. E-nose readings can be correlated with sensory evaluations. This may lead to a new rapid method to determine the quality of milk.
Session 15C, Dairy Foods
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