Lipase in oat endosperm: The effect of freeze-drying and oven-drying

Abstract: The project was carried out in collaboration with Lantmännen with the aim to analyse the lipase activity in oat endosperm, non-heat-treated whole grain oat flour and heat-treated whole grain oat flour and to investigate whether lipase activity could be inactivated in oat endosperm by reducing water activity by various methods such as oven drying and freeze drying to extend oat shelf life. Lipase activity was measured by a wet extraction of the flour and an artificial substrate that gives a coloured product if lipase enzymes are active in the extract. The formation of the product was measured during five minutes at room temperature or 37 °C using a spectrophotometer, and the enzyme activity in units/g of flour was calculated. It was not possible to measure the enzyme activity in the flour directly. The obtained results for the different oat fractions indicated differences in lipase activity between the oat fractions. Lipase activity for oat endosperm was 0.183 U/g, lipase activity for non-heat-treated whole grain oat flour was 0.088 U/mg and the heat-treated whole grain oat flour had no lipase activity. The differences were statistically significant since the p-value was <0.0001. The results from the analysis that compared whether oven-drying and freeze-drying as methods had an effect on lipase activity indicated that oven drying had the greatest effect when assay was performed at room temperature. However, when the assay was performed at 37 °C the lipase activity in oven-dried and freeze-dried oat endosperm were similar to non- treated samples. This indicates that temperature has a great impact on the lipase activity. Thus, oven drying and freeze drying could not completely inactivate the lipase activity, but probably reduce it.