ChileanJAR

Three milk samples were obtained in a monthly scheme, in 10 selected upper level dairy farms, from the Region Metropolitana (Chile). Milk samples were collected, at the end of thefirst milking,when received in the tank, keeping them in flasks and afterwards held for 48 hr at 4ºC,simulating a cooling tank; methylene blue reduction test (MBRT; hr), total bacterial (TBC), psychrotrophic (PC) and coliform (CC) counts/ml were determined, at time 0, 24 and 48 hr, in each sample. The differences between milk bacteriological quality variables due to storage time were analysed through ANOVA, in a complete random pattern. The average results were: TBC: 36,750 b, 38,983 ab, and 79,516 a (P < 0.05); PC: 2,975 c, 6,905 b, and 84,480 a (P < 0.05); CC: 1,073 a, 1,157a, and 1,369a; MBRT: 6.32a, 6.32a, and 6.13a. Considering different standards of bacteriological quality, milk stored for two days was appropiate in 68.9 - 100; 30 - 73.3; 10 - 36.6; and 23.3 - 33.3% of the samples, according to MBRT, TBC, PC and CC, respectively. Consequently, milk collection every other day would be severely restrained because of strong PC development during the last 24 hr of storage and, to a less extent, because of TBC; although CC was numerically constant, it would also limit collection every other day, duetothe high initial contamination by these microorganisms. Furthermore, these results would show a remarkable overestimation of the bacteriological quality in refrigerated milk, as MBRT is the official test used in Chile to classify raw milk.