Effect of pulsed light on total microbial count and alkaline phosphatase activity of raw milk

The effect of pulsed light (PL) treatments at increasing fluence (0.26–26.25 J cm−2) on total microbial count and inactivation of alkaline phosphatase (ALP) in raw whole milk was investigated. High fluence resulted in a 3.2 log reduction in total microbial count and about 94% inactivation of ALP; concomittantly, milk temperature increased to 55 °C. To determine the photochemical effect of PL treatment only, samples were equilibrated at 0 °C before being exposed to high fluence; this gave a milk temperature of 27 °C, a 1.53 log cfu mL−1 microbial reduction and 44% inactivation of ALP. The effect of temperature increase was determined by heating at 55 °C for 60 s or at 59 °C for 70 s; only the latter yielded a slight reduction in microbial count and ALP activity. This indicated a combined effect between photochemical and photothermal damage for inactivation of both natural microflora and ALP.