Characterization of antioxidant properties for dried organic fruits in Turkish market and development of novel strategies to increase their potential health benefits

Abstract

In this thesis antioxidant parameters including trolox equivalent antioxidant capacity (TEAC) and total phenolics (TPC) and flavonoid (TFC) contents of major organic dried fruits (raisins, figs, prunes and apricots) produced in Turkey have been determined to understand the bioactive potential of these products. Moreover, a novel method based on controlled rehydration of specified dried fruits in phenolic extracts has been developed to boost the phenolic content and antioxidant activity of dried fruits with low bioactivity and potential health benefits. The TEAC, TPC and TFC of sun dried fruits varied between 35.7 and 74.1 μmol trolox/g (d.w.), 1762 and 4062 μg gallic acid/g (d.w.) and 830 and 2559 μg catechin/g (d.w.), respectively. The TEAC and TPC of prunes were 1.7 to 2.3 fold higher than those for apricots, raisins and figs which showed quite similar TEAC and TPC values. On the other hand, the TFC of prunes and figs were similar and 1.7 to 3 fold higher than those of raisins and apricots. The rehydration studies with raisins conducted in different concentrations (0.5% or 1% (w/w)) of green tea extract (GTE) and walnut shell extract (WSE) at room temperature until reaching of final moisture content of 38.73 % (w/w) showed the possibility of increasing TEAC, TPF and TPC of raisins 1.6-1.8 fold. Similar rehydration strategy applied to figs, prunes and apricots in 1% GTE to bring their moisture content to 39.83, 36.97 and 43.81 % respectively, caused 1.1-1.6 fold increase in TEAC, TPC and TFC of these dried fruits. This work clearly showed the considerably higher bioactive potential of organic dried prunes than organic dried raisins, figs and apricots. However, the application of controlled rehydration process developed in this work enables increasing antioxidant potential and phenolic contents of figs, raisins and apricots to the level of prunes.