Evaluation of Low-Pressure Cold Plasma Effect on Phytonutrients, Drying and Microstructural Characteristics, and Changes in Microbial Load of Fresh and Hot-Air-Dried ‘Heidi’ Mango

Abstract

Alternative pre-treatment strategies before drying offer the prospect to minimize drying time, replacing the use of chemicals, and preserving quality of dried fresh products. This study explored the application of low-pressure atmospheric cold plasma (CP) for 5- and 10 min (CP5 and CP10) as pre-treatments prior to processing and hot air drying (60 °C) of ‘Heidi’ mango, while non-treated samples served as control. Changes in tissue microstructure and physicochemical properties, bioactive compounds, and microbial load were evaluated, and seven thin layer drying models were applied. Scanned electron microscope images showed that CP pre-treatments altered the tissue microstructure of dried mango slices compared to control. ‘Heidi’ mango slices with the initial moisture content of 80 ± 0.2% on a wet basis was reduced by 81% and 76% in dried CP5 and CP10 samples, respectively. Drying time was reduced by 20% for CP pre-treated samples in comparison to control samples, and the drying behavior of ‘Heidi’ mango slices was best described by the Logarithmic model (R2, 0.9999 and RMSE, 0.0122). Colour attributes were best retained by sodium metabisulphite (SMB) pre-treated samples, followed by CP5 pre-treated, which performed better than CP10 and control (p ≤ 0.05). Highest total flavanols (15.0 ± 0.4 mg CE 100 g−1) and higher total phenolics (1528.2 ± 23.6 mg GA 100 g−1) were found in CP5 pre-treated samples compared to the control (p ≤ 0.05). Lowest antioxidant activities were found in CP10 pre-treated samples compared to the control (p ≤ 0.05). CP-pretreatment and drying resulted in ≥ 2 Log reduction in microbial load on mango slices. These results demonstrate to the role players in mango value addition chain, the potential of low-pressure CP pretreatment in enhancing/maintaining the bioactive compounds, reducing drying time and microbial load.