Effect of various dairy packaging materials on the shelf life and flavor of pasteurized milk

Milk from three different dairies (each a separate trial: 1, 2, and 3) was standardized to 2% fat and pasteurized at 92.2, 84.0, and 76.4 degreesC (temperatures 1, 2, and 3, respectively) for 25 s and packaged into six different packaging boards, [standard (A) milk boards with standard seam; juice boards with standard (B) and J-bottom (D) seams; barrier boards with standard (C) and J-bottom (E) seams; and foil (F) boards with J-bottom seam], resulting in 18 different treatments. Standard plate count (SPC) was used to test for microbial quality, and taste a panel was employed for flavor acceptability and difference on the milk stored at 6.7 degreesC at 1, 2, 3, and 4 wk. Statistical analysis of taste panel data showed that the flavor of milk samples A2, B2, and D2 deteriorated faster than the blind control (freshly high temperature, short time pasteurized low fat milk processed at 80.6 degreesC for 25 s). The flavor of milk packaged in standard (A) and juice (B and D) boards deteriorated at a faster rate than milk packaged in barrier (C and E) and foil (F) boards. Microbial counts showed that milk samples stored at 6.7 degreesC in trials 2 and 3 produced high SPC at wk 3 (ranges of bacteria in cfu/ml for trial 2: 9.9 x 10(1) -1.8 x 10(6) and trial 3: 2.5 x 10(5) - 5.5 x 10(8)). In trial 1, high SPC began at wk 4 (9.9 x 10(1) - 5.5 x 10(5) cfu/ml). Milk processed at 76.4 degreesC had the lowest bacterial growth rate, and milk processed at 84.0 degreesC had the highest bacterial growth rate. Different boards had no effects (P > 0.05) on the bacterial growth rates. It appeared that the lower the SPC of the raw milk, the slower the bacterial growth rate after 2 wk of storage. Milk samples stored at 1.7 degreesC maintained low SPC at wk 4, with counts of 0 to 40 cfu/ml for trial 2 and 0 to 200 cfu/ml for trial 3.