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 (te mperatures 1, 2, and 3, respectively) for 25 s and packaged into six differ ent packaging boards, [standard (A) milk boards with standard seam; juice b oards with standard (B) and J-bottom (D) seams; barrier boards with standar d (C) and J-bottom (E) seams; and foil (F) boards with J-bottom seam], resu lting in 18 different treatments. Standard plate count (SPC) was used to te st for microbial quality, and taste a panel was employed for flavor accepta bility 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 de greesC 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 sto red 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 g rowth 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 tr ial 2 and 0 to 200 cfu/ml for trial 3.