Immobilisation of lipases by adsorption and deposition: High protein loading gives lower water activity optimum

Two different immobilisation techniques for lipases were investigated: adsorption on to Accurel EP-100 and deposition on to Celite. The specific activities were in the same order of magnitude, 2.9 (μmol min ^-1 mg protein) when Celite was used as support and 2.3 (μmol min ^-1 mg ^-1 protein) when Accurel EP-100 was used as support, even if the amount of lipase loaded differed by 2 orders of magnitude. Immobilisation on Accurel EP-100 was the preferred technique since 40-100 times more protein can be loaded/per g carrier, thus yielding a more active catalyst. The water activity profiles in lipase catalysed esterification were influenced by the amount of protein adsorbed to Accurel EP-100. Higher protein loading (40 mg g ^-1) resulted in a bell-shaped water activity profile with highest specific activity (6.1 μmol min ^-1 mg ^-1 protein) at a(w) = 0.11, while an enzyme preparation with low protein loading (4 mg g ^-1) showed highest specific activity at a(w) = 0.75.