Impact of Gum Arabic Coating Pretreatment on Quality Attributes of Oven-Dried Red Raspberry (Rubus idaeus L.) Fruit

The present study evaluated the effect of gum arabic (GA) edible coating pretreatment on the quality of dried red raspberries. Red raspberries were independently pretreated with varied concentrations of GA (3, 5, and 10% (w/v) by dipping for 2 min before oven-drying at 60 °C until the moisture content was below 8% (18–24 h). Raspberries dipped in distilled water were used as the control samples. Quality attributes including colour, moisture content, water activity (a_w), hardness, hygroscopicity, rehydration capacity, total soluble solids (TSS), titratable acidity (TA), pH, anthocyanin composition, ascorbic acid (AA) content, total phenolic content (TPC), antioxidant activity, peroxidase (POD), and polyphenol oxidase (PPO) enzyme activity were investigated. GA pretreatment of the raspberries improved the a_w (lower), hardness (lower), TSS, TSS/TA ratio, BrimA, AA content, and TPC, whilst it significantly (p < 0.05) reduced the colour properties (redness, chroma, hue angle, and total colour differences) and the total anthocyanin content when compared with the control samples. The DPPH radical scavenging activity, POD, and PPO enzymes residual activities were not significantly (p > 0.05) affected by GA pretreatment. Five different types of anthocyanins, including cyanidin dihexoside, cyanidin 3-O-galactoside, cyanidin 3-O-glucosyl-rutinoside, and cyanidin 3-O-rutinoside were identified and quantified with cyanidin dihexoside being the primary anthocyanin, varying from 951.18–1053.70 µg/g DM. GA pretreatment of raspberries between 3 and 5% could result in improved physicochemical, antioxidant properties and minimum loss of anthocyanins.