Effects of freeze drying and convective hot-air drying on predominant bioactive compounds, antioxidant potential and safe consumption of maoberry fruits

The effects of freeze drying and convective hot-air drying of maoberry fruits (Antidesma bunius L.) on their phenolic and ascorbic acid contents and antioxidant activities, as well as the levels of 5-hydroxymethylfurfural (HMF) and food-associated microorganisms, were investigated. Results showed that fruits dried to the desired final moisture content (∼15%) using convective hot-air drying at 50–100 °C exhibited lower retention of ascorbic acid, total phenolics, total flavonoids and total anthocyanins compared with fruits dried using the freeze drying process, with greater retention observed in fruits exposed to lower temperatures. Lower drying temperatures also resulted in dried fruits with higher antioxidant activities, and no significant differences in antioxidant potential were observed in freeze-dried and 50 °C-dried fruits. All dried fruit products obtained from the studied conditions showed negligible HMF levels (<100 ppm) and possessed lower pathogen loads than the microbiological limits for ready-to-eat products. Therefore the products should cause no adverse health effects. As suggested by a principal component analysis, convective hot-air drying at 50 °C could be a potentially inexpensive drying method for preserving bioactive compounds and inactivating key pathogens in maoberry fruits, despite its low efficiency in reducing fungal contamination of the dried products.