Effects of hot air and freeze drying methods on antioxidant activity, colour and some nutritional characteristics of strawberry tree (Arbutus unedo L) fruit

Antioxidant activity, colour and some nutritional properties of hot air and freeze-dried strawberry tree (Arbutus unedo L.) fruits were investigated. Additionally, the effects of two pre-treatments, namely ethyl oleate and water blanching, were compared in terms of drying characteristics. For determination of antioxidant activities in ethanol extracts, two different analytical methods were used: 1,1-diphenyl-2-picrylhydrazyl scavenging activity and beta-carotene bleaching activity. As a result, the ethyl oleate pre-treatment shortened the drying time by hot air method and gave a higher 1,1-diphenyl-2-picrylhydrazyl scavenging activity (82.16 +/- 0.34%), total phenolic content (7.62 +/- 1.09 mu g GAE/g extract), ascorbic acid content (236.93 +/- 20.14 mg/100 g), besides hydromethylfurfural was not observed. Freeze- dried fruits exhibited higher ascorbic acid content (368.63 +/- 17.16 mg/100 g) than those fresh fruits (231.33 +/- 19.51 mg/100 g) and nearly 1,1-diphenyl-2- picrylhydrazyl activity (93.52 +/- 0.41 %) to fresh fruits (94.03 +/- 1.18%). Colour characteristics, sugar content and mineral contents of fruits were significantly affected by pre-treatments and drying methods (p < 0.05). It is concluded that the drying of strawberry tree fruits should bring a valuable and attractive foodstuff to food industry due to the rich nutritional components, antioxidant activity and colour. Another conclusion from this study is that the freeze-drying is the best drying method to keep the nutritional value, antioxidant activity and sensory properties of fruits