Microbiological and Sensory Stability of Pasteurized Milk in Brazil

The purpose of this study was to investigate the influence of storage temperature on the microbiological and sensory stability of homogenized whole pasteurized milk (75 degrees C/15 s), packaged in high density polyethylene (HDPE) bottle and low density polyethylene (LDPE) pouch, both were monolayer materials pigmented with titanium dioxide (TiO2). The storage temperatures investigated were 4, 9, and 14 degrees C. Microbiological evaluation was based on the results of mesophilic and psycrotrophic counts, with 7 log CFU/mL and 6 log CFU/mL, respectively, set as upper limits of acceptability for the keeping quality of milk. Sensory shelf life was determined based on the ratings assigned to the attributes appearance, aroma, flavor and overall appreciation of milk samples (17 +/- 1 degrees C) by 40 panelists using a 7-point hedonic scale (1 = dislike very much, 4 = neither like nor dislike, 7 = like very much). The average scores > 4 and percentage of approval > 50% were used as threshold values for all the attributes assessed. The microbiological shelf life estimated for pasteurized milk packaged in HDPE bottle and stored at 4, 9, and 14 degrees C were 36, 8, and 5 days, respectively. For milk samples packaged in LDPE pouch, shelf life was estimated at 35, 7, and 3 days, respectively. According to pre set criteria for sensory stability, shelf life for milk in bottle stored at 4, 9, and 14 degrees C were 28, 9, and 4 days, respectively. For milk in pouch, sensory shelf life obtained was 28, 7, and 2 days, respectively. The results achieved in this study confirmed that exposure to abusive storage temperature (14 degrees C) dramatically reduced the shelf life of pasteurized milk and that the temperature around 4 degrees C can be considered ideal for maintaining the microbiological and sensory quality and integrity of the product. Based on the results of this study, HDPE bottle were found to produce better results when compared to LDPE pouch, mainly for abuse storage temperature.