Effects of potassium metabisulfite pre-treatment and different drying temperatures on some chemical properties and color retention of Russian olive (Elaeagnus Angustifolia) fruit

Silverberry fruit is an important medicinal fruit that used for reducing pain. The present work was carried out to study the effect of potassium meta-bisulfite (KMS) and air drying temperature on quality of Russian olive fruit. Different KMS levels (0, 1, 2 and 4%) and drying temperatures (45, 60 and 75°C) were used and some traits such as weight loss (WL), rehydration ratio (RH-R), TSS (total soluble solids), TA (total acidity), TSS/TA ratio, ascorbic acid, color parameters (L*, a*, b*, chroma and Hue, TEPL, TEPa and TEPb, ΔE and BI), total phenol (TP), and potassium were measured. WL, RH-R and total color change (ΔE) increased with increment of pre-treatment concentration. All traits except TSS, were significantly affected by drying temperature. TA, ascorbic acid and TP raised by increasing air temperature from 45°C to 60°C. Temperature higher than 60°C increased ΔE. Increment of temperature from 45°C to 75°C led to an increasing trend of browning index, a*, b* and C* (chroma), however, L* (lightness) and hue angle decreased. In general, using higher KMS concentrations as pre-treatment improved weight loss during drying, however, significant color change observed and color retention significantly reduced. Drying temperature higher than 60°C also increased browning index of Russian olive fruit, however, total phenols increased in parallel. Thus, it is suggested that drying temperatures lower than 60°C may be good treatment for drying silverberry fruits.