HMF formation, diastase activity and proline content changes in bee pollen dried by different drying methods

Abstract

Bee pollen, as a protein rich and energy enhancing food source, can be used as a valuable complement to our daily diet. In this study, multifloral bee-pollen was dehydrated to a moisture content less than 8% by hot-air (HAD) and vacuum (VD) (300, 500 mbar) drying at 35, 50 and 65 degrees C, microwave (MWD) and microwave assisted vacuum drying (MW-VD) (500, 675 mbar) at 300, 450, 600 and 900W power levels and freeze drying. The water activity, diastase number (DN), proline and 5-hydroxymethyl-2-furfural (HMF) contents in fresh and dried pollen samples were determined and compared. A greater reduction was observed in DN of samples subjected to MWD and MW-VD at 600 and 900W as compared to other drying treatments. Drying by microwave irradiation at 900W power level caused the highest, almost 72-76%, reduction in DN values. A higher retention of enzyme activity, ranging between 87 and 93%, was observed at 50 degrees C during HAD and VD. Proline and HMF content were affected by the power level during MWD and MW-VD. A significant reduction in proline content was observed only in microwave treated samples at the highest power level. Except for the highest power level, MW VD leads to a significant increase in HMF levels ranging between 4.9 and 9.2 mg/kg while HAD and VD provided similar HMF content in samples as compared to fresh pollen.