| Important psychrotrophs encountered in raw milk are Gram-negative rods with Pseudomonas spp. comprising 65 to 70% of the genera. Some Gram-positive bacteria are also present, with Bacillus being the most important genera. Spoilage bacteria found in raw milk produce heat-resistant lipases and proteinases that are not destroyed by pasteurization. In general, microbial counts in excess of 1 × 106 cfu/ml are enough to produce defects in milk.; Serious off-flavors in milk, such as bitter, putrid, unclean, rancid, and sour, have been associated with psychrotrophic microorganisms. Traditional microbial evaluation of milk is time consuming. Faster methods are desirable. The electronic nose is a promising technology that can be used as a fast screening tool. It enhances objectivity of flavor evaluation, requires minimal sample preparation, generates reproducible and reliable results, is easy to operate, and results can be obtained rapidly. The objectives of this study; were to test an electronic nose for odor assessment of milk inoculated with Pseudomonas fluorescens and/or Bacillus coagulans , to correlate microbial loads and sensory results with electronic nose readings, and to attempt to predict the shelf life based on microbial loads of milk samples in an accelerated study.; Parmalat® whole, reduced-fat, and fat-free milk were used. Sterile milk samples were inoculated with P. fluorescens and/or B. coagulans, stored at 1.7°, 7.2°, and 12.8°C, and evaluated at days 0, 3, 5, 7, and 10 using an electronic nose. Counts for P. fluorescens were performed using aerobic plate count 3M Petrifilm. Those for B. coagulans were performed using nutrient agar plates. The odor of milk samples was evaluated by a 10-member untrained sensory panel. Electronic nose readings, microbial counts, and sensory data were analyzed using discriminant function analysis. The electronic nose discriminated differences in odor due to microbial load, storage temperature, and sensory data. This research demonstrated the potential use of electronic nose to detect odor differences in milk due to microbial loads. Electronic nose readings can be correlated with sensory panel perception. This may lead to a new rapid method for determining sensory evaluation and microbial loads of milk. |
