The effect of hot air, vacuum and microwave drying on drying characteristics, rehydration capacity, color, total phenolic content and antioxidant capacity of Kumquat (Citrus japonica)

Azime OZKAN-KARABACAK,Omer Utku COPUR,Canan Ece TAMER,Gulsah OZCAN-SINIR

doi:10.1590/fst.34417

Abstract

Abstract Sliced kumquats were dried by using three different drying methods, microwave (375 W), hot air (70 and 80 °C), and vacuum (70 and 80 °C with 100 and 300 mbar) to determine drying characteristics, antioxidant capacity and total phenolic content and color. All color parameters (L, a, b, Cab, ΔE and h° ) changed depending on the drying methods. Page and Modified Page models are the best fitted drying methods with the highest value of R2 (0.9994) and the lowest values of RMSE (0.000635-0.000735) and χ2 (0.000010-0.000013) compared to other models. Effective moisture diffusivity values for dried kumquats ranged from 1.54 × 10-8 to 8.24 × 10-8 in vacuum drying at 70 °C-300 mbar and microwave drying at 375 W, respectively. In comparison to the fresh sample, the dried samples showed an increase in both total phenolic content and antioxidant capacity. The total phenolic content (3095.71 ± 101.41 mg GA/100g d.w) and antioxidant activity (10.51 ± 0.19 µmol TE/g d.w) with DPPH assay showed the highest levels for the vacuum drying at 70 °C-100 mbar method. Microwave dried samples had the highest antioxidant activity with CUPRAC assay as (17.58 ± 0.63 µmol TE/g d.w.). This study indicated that microwave drying and vacuum drying at 70 °C-100 mbar were able to yield high-quality kumquat slices.

Highlights

Kumquats (Citrus japonica) the smallest of the citrus fruits (Young, 1986), can be eaten as fresh, pickled, candied, marmalade or jelly
The drying time of kumquats which were hot air dried were respectively 195 and 190 minutes at drying air temperatures of 70 and 80 °C at a constant relative humidity (20%) while vacuum drying at 70 °C-100 mbar, vacuum drying at 80 °C-100 mbar, vacuum drying at 80 °C-300 mbar were respectively 285, 210 and 300 minutes (Figure 1)
The effective moisture diffusivity (Deff) values for different drying methods, calculated from Equation 6, ranged from 1.54 × 10-8 to 8.24 × 10-8 m2/s in vacuum drying at 70 °C-300 mbar and microwave drying at 375 W respectively

Summary

Introduction

Kumquats (Citrus japonica) the smallest of the citrus fruits (Young, 1986), can be eaten as fresh, pickled, candied, marmalade or jelly. The nutrient profile of raw kumquat (exclude seeds) was determined and reported as: water 80.85 g, energy 71 kcal, carbohydrate 15.90 g, total sugars 9.36 g, total dietary fiber 6.5 g, protein 1.88 g, total lipid 0.86 g, ash 0.52 g, per 100 g edible portion. It is rich in minerals and vitamins; it contains potassium 186 mg, calcium 62 mg, magnesium 20 mg, phosphate 19 mg, sodium 10 mg, vitamin C 43.9 mg per 100 g edible portion (United States Department of Agriculture Agricultural Research Service, 2016). Cultivation of this fruit become widespread in south regions of Turkey as it is rich in several nutritious and bioactive compounds

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