Extended storage of raw milk. i. effect on microbiological quality

Abstract

Quality of industrial and fluid raw milk was assessed by Standard Plate Count (SPC),. Psychrotrophic Bacterial Count (PBC), proteolytic count, Tyrosine Value (TV) and lipase activity. Of the 360 milk samples tested, 78% had PBC of < 10,000/mL, 92%<50,000/mL and 8% > 100,000/mL. The same raw milk supplies showed SPC distribution of 63% < 10,000/mL, 86% < 50,000/mL and 14% > 100,000/mL. Wide variations in TV were obtained, ranging from 0.32mg/mL to 0.78mg/mL. Counts generally exceeded 106/mL before a definite increase in TV could be observed indicating that the application of this test as a sole indicator of microbiological quality would be limited.Examination of SPC and PBC for industrial milk samples showed that there was no significant (P=0.05) increase in counts during three-day holding periods in farm bulk tanks. Fluid milk samples which were pooled and stored at 4°C after every-other-day collection, were held for two additional days before any marked increase in bacterial count and TV occurred. It is suggested that under proper sanitation and storage conditions, raw milk may be held for up to four days before processing without sacrificing quality.