Removal of Sulfur Dioxide from Dried Grapes before Handling

Abstract

Dried grapes or raisins are usually treated with sulfur dioxide in high concentrations to prevent enzymatic and non-enzymatic browning reactions and keep golden yellow color of these dried fruits. Sulfur dioxide and sulfite salts are good food preservatives but have high risk on human health especially when using in high concentrations. Thus, this work was achieved to remove sulfur dioxide and sulfite salts from over sulfite raisins before handling in different food industries into lower concentrations by soaking of raisins in water, H<inf>2</inf>O<inf>2</inf> (1%), citric acid (5%) and acetic acid (5%) at 30 and 50^oC for 15 and 30 minutes. These treatments led to removing high amounts of sulfur dioxide and sulfite salts from raisins especially with treatment by citric acid (5%) at 50^oC for 15 min. Comparatively, soaking of raisins in citric acid (5%) was the best treatment followed by acetic acid (5%) and H<inf>2</inf>O<inf>2</inf> (1%) then water. This work also aimed to desulfurization of raisins with minimal effects on their constituents e.g., total phenols, tannins, flavonoids and color features. The loss rates of these constituents from raisins obtained by the soaking treatments in water were lower than those obtained by citric acid (5%) then acetic acid (5%) while the maximum loss rates of these constituents from raisins were obtained by H<inf>2</inf>O<inf>2</inf> because it is oxidizing and bleaching agent. Therefore, this work was achieved to overcome this problem by using citric acid or acetic acid instead of H<inf>2</inf>O<inf>2</inf>