Prediction of Shelf-Life of Pasteurized Milk and Other Fluid Dairy Products in 48 Hours

Abstract

The objectives of this study were to provide early shelf-life information about various dairy products and to eliminate the need for flavor analysis to detect microbiological spoilage. Two combinations of milk and media volumes (5 and 20 ml) and two preincubation times (18 and 24 h) were evaluated. An improved impedance method to predict potential shelf-life of whole milk, skim milk, chocolate milk, and half and half was developed. A mixture of 20 ml of product and 20 ml of plate count broth, preincubated for 18 h at 18°C, followed by impedance testing at 21°C, gave consistent results in the least time. Traditionally the impedance method required the input of a taste panel for calibration of the impedance detection times to flavor-related shelf-life. A simpler method replaces flavor analysis by impedimetric determination of each sample's last day of use. Last day of use was defined as the day after the impedance detection time was ≤2.0 h. On this day, standard plate counts were usually in the 1.0 × 106 to 1.0 × 107 cfu/ml range, indicating spoilage. Correlation coefficients between impedance detection times and days to last day of use or Moseley plate counts were r = .89 and r = .71, respectively. A field trial at a commercial dairy research center verified that impedance detection times correlate very closely to flavor-related shelf-life and that last day of use determination is useful in replacing flavor analysis when necessary. This method provides potential shelf-life prediction within 48 h. The last-day-of-use concept allows users to calibrate the impedance method without a plate count procedure or taste panel. © 1987, American Dairy Science Association. All rights reserved.