Chemical and microbiological changes in fluid milk as affected by packaging conditions

Changes in chemical and microbiological quality parameters of whole pasteurized milk stored under fluorescent light at 4 degrees C in pouches made of (a) low density polyethylene (LDPE, clear and TiO2 pigmented, 60 micrometer in thickness), (b) coextruded (LDPE/polyamide/LDPE, clear and TiO2 pigmented, 60 micrometer in thickness) and (c) coextruded (LDPE + 2% TiO2/LDPE + 2% TiO2/LDPE + 4% carbon black pigment/LDPE + 2% TiO2/LDPE + 2% TiO2), 60 and 110 micrometer in thickness were monitored for a period of 7 days. Milk packaged in coated paperboard cartons and stored under the same experimental conditions served as the "control" sample. Data were obtained for lipid oxidation, lipolysis, proteolysis, vitamin A and riboflavin content and microbial growth including mesophilic and psychrotrophic counts. Results showed good protection of milk packaged in all pouches with regard to microbiological and chemical parameters assessed over the 7 day period with the exception of vitamin retention. In both clear and TiO2 pigmented LDPE and LDPE/polyamide/LDPE pouches, a high degree of vitamin degradation was observed ranging from 50.9% to 73.6% for vitamin A and from 34.4% to 45.3% for riboflavin. In coextruded (LDPE + 2% TiO2/LDPE + 2% TiO2/LDPE + 4% carbon black pigment/LDPE + 2% TiO2/LDPE + 2% TiO2) pouches, vitamin retention was significantly higher (increasing vitamin protection with increasing pouch thickness); the losses ranged between 15.1% and 18.9% for vitamin A and between 18.8% and 21.5% for riboflavin as compared to 15.1% for vitamin A and 19.5% for riboflavin in the control sample. It is concluded that coextruded pouches containing both white (TiO2) and black (carbon black) pigments, 110 micrometer in thickness, prevent excessive vitamin degradation and may be used as an inexpensive, attractive and convenient milk packaging alternative to the coated paperboard carton.