The determination of ALP activity is often used for the evaluation of treatment efficiency for HTST heated and microfiltered ESL milk. The results of ALP activity tests (Table 5) show that all HTST and microfiltered ESL samples had received an adequate heat treatment, i.e. in the referred samples, the activities measured are far below the threshold value of 350 mU⁄L for pasteurised milk. Generally, ALP activities of 0.02–0.07 U⁄L are found in HTST-heated milk (Lorenzen et al.2010). LPO is appropriate for assessing the heating efficiency in directly and indirectly heated ESL milk. The results in Table 5 proved that a sufficient heat load was applied. The indigenous milk enzyme LIP is relatively thermolabile compared with ALP and LPO. In previous heating experiments (Martin et al. 2005) with bulk raw milk (LIP activity: 236 U⁄ L), at 70C⁄ 9.5 s, a LIP activity of 16 U⁄L was observed, corresponding to approximately 8% residual activity. However, at 75C⁄ 9.5 s no quantifiable activity could be determined. The present examination shows that LIP activities were below the measurement limit of