A Study on Consecutive Changes of Milk Quality by Different Containers.

포장용기별우유의 경시변화에 관한 연구

A study on consecutive changes of milk was carried out to determine the changes of milk components and microorganisms by different containers. The containers included in this study were glass bottles, polyethylene packs, polystyrene bottles and aluminum foils. The number of total microorganisms and coliforms, contents of milk fat and vitamin A were tested. The results obtained were as follows: 1) The number of total microorganisms exceeded the legal criteria within 2-3 days at 4$\circ$C, 24 hours at room temperature (20-23$\circ$C) and 3 hours at 35$\circ$C. 2) The number of coliforms in milk contained in glass bottles exceeded the legal criteria within 3 days at 4$\circ$C, that of glass bottles and polyethylene packs within 12 hours at room temperature (20-23$\circ$C), that of polyethylene packs and polystyrene bottles within 6 hours at 35$\circ$C, and that of glass bottles within 9 hours at 35$\circ$C respectively. 3) The milk fat contents by di'fferent containers were not changed at all. 4) Vitamin A contents were reduced by a slight exposure to sunlight. The destruction rates of all containers were the highest in an hour after exposure to sunlight. The rates by different containers were 50.1% in glass bottles, 47.6% in polyethylene packs, 30.4% in polystyrene bottles in an hour after exposure respectively. After an hour exposure, the destruction rates gradually decreased. The vitamin A destruction rate of glass bottles were the highest, and that of polyethylene packs were next, and that of polystyrene bottles were the lowest 5) The changes of pH of milk were high in the following order: the milk in glass bottles, polyethylene packs, and polystyrene bottles. pH of milk in aluminum foils were not changed.