71A-29 |
|
W. BANG, D. A. Clare, G. Cartwright, and M. A. Drake. Dept. of Food Science, North Carolina State Univ., Schaub Hall, Box 7624, Raleigh, NC 27695-7624 Shelf life remains a crucial economic issue for pasteurized fluid milk. The Feldmeier system is a tubular heat exchanger that functions as a piggyback system on a conventional high temperature short time (HTST) plate pasteurizer, allowing higher heat treatment of the milk. The system may provide an alternative economical way to increase the shelf life of fluid milk. The objective of this study was to determine the impact of different heat treatment temperatures using the Feldmeier system on the microbiological and sensory shelf life of fluid milk. Raw milk (1000 kg) was obtained from the NCSU dairy farm on three occasions, standardized to 1.5% fat (w/v) and pasteurized at one of five different temperatures (75 °C for 20 sec only (control) or with the additional heat treatments of 103, 114, 125, or 136 °C for 3 sec). Milk was packaged in paperboard cartons and stored at 4 °C. Pasteurized milks were tested following 0, 7, 14, 21, 28, 42, 49, 66, 80, and 101 days. Microbiological quality (total plate counts, spores, psychrotrophs, coliforms) as well as enzymatic quality (reactive sulfhydryls and sulfhydryl oxidase) were determined. Descriptive sensory analysis was conducted with a trained panel (n=7). Conventionally pasteurized milks reached shelf life failure (> 10E6CFU/mL and sensory failure) within 38 days, while all Feldmeier milks retained microbiological and sensory shelf life through 80 days. Sulfhydryl oxidase activity was detected in raw milk, control, and 103 °C milks. The reactive sulfhydryl concentration of the 114, 125, or 136 °C milks was less than that of the 103 °C milk, due to protein precipitation. Trained panelists detected higher cooked flavors in the Feldmeier system milks compared to control milks, but these flavors and differences decreased with storage time. The Feldmeier system may be an economically feasible method to increase the shelf life of pasteurized milk.
Session 71A, Dairy Foods: General
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |