Total phenolics, antioxidant capacity, colour and drying characteristics of date fruit dried with different methods

Abstract

Date slices were dried with the three drying methods convective (60, 70 and 80 °C), microwave (120 W) and freeze drying to determine drying characteristics and to compare the dried fruit quality. All colour parameters changed depending on the drying method and colours closest to the fresh sample were obtained with freeze drying. It is interesting to note that the total phenolic content and antioxidant capacity in each sample rose when looked at in relation to the fresh sample. In particular, microwave-dried samples were recorded as having the highest total phenolic content and the highest antioxidant capacity. To explain the drying kinetics of the date slices, nine thin-layer drying models were also attempted. Based on statistical tests, the model developed by Midilli et al. model was found to be the best model for convective and microwave drying, but the Two Term model was the best for freeze drying. This study shows that microwave drying can produce high quality date slices with the additional advantage of reduced drying times compared to convective and freeze drying.Keywords: drying methods; thin-layer; date slices; colour; total phenolic content.Practical Applications: Microwave drying at 120W can improve the final quality of dried date slices.

Modelling of drying kinetics and comparison of two processes: forced convection drying and microwave drying of celery leaves (Apium graveolens L.)

“…Indeed, it is clear from the curves that the decrease in the moisture content becomes faster with the increase of both temperature and power levels. Thus, the drying time required to achieve the lowest moisture content was reduced from 338 to 10.83 min for temperatures ranging from 40 to 120 °C and from 48.5 to 2.66 min for powers ranging from 100 to 1000 W. These results have shown that an increase of temperature or power levels leads to a reduction of drying time, which are in accordance with reported observations on convective drying (Faal et al, 2015;İZlİ, 2017;Nguyen et al, 2015;Xiao et al, 2015) as well as those on microwave drying (Amiri of different food products other than celery. When comparing processes in terms of reduced drying time, a significant reduction has been observed when applying the microwave drying process, especially when applying high power levels; this could be explained by the fact that one of the advantages of microwave drying is a short processing time (Amiri Chayjan et al, 2015).…”

Potentially bioaccessible phenolics, antioxidant capacities and the colour of carrot, pumpkin and apple powders – effect of drying temperature and sample structure

“…However, a direct comparison of phenolics in fruit and vegetables between the studies is difficult due to many factors, for example cultivation conditions, varieties and different methods of sample preparation and extraction. Some authors have reported loss of phenolics due to convective drying, concluding that the long drying times may promote degradation of antioxidant compounds (Garau et al, 2007) and formation of Maillard products (Yang et al, 2010;_ Izli, 2017). However, in other cases, the total content of phenolics in samples dried by hot air increased, as that observed in this study.…”

Influence of microwave and microwave‐convective drying on the drying kinetics and quality characteristics of pomelo

“…While the highest value (the closest to the fresh sample) was found for the samples dried at 90 W–55 °C, the lowest value was determined for the samples dried at 160 W microwave alone treatment (Table ). The darker appearance of the microwave‐dried slices compared to other dried samples might be because of the non‐enzymatic browning (Izli, ; Maskan, ). Similar findings were reported by some authors (Reyes, Ceron, Zuniga, & Moyano, , Izli & Isık, ).…”