Shelf life of unpasteurized sour orange juice in Iran

Abstract

Introduction. In Iran, sour orange is available between mid-October and March. Frequently, consumers store a large volume of unpasteurized juice at room or low temperatures for consumption when the fresh fruit is not available. The aim of our research was to determine the shelf life of unpasteurized sour orange juice which was stored under conditions similar to those adopted by consumers at home. Materials andmethods. Sour orange juice was prepared by hand-squeezing fresh fruit; it was filtered, and then poured into clear or dark green glass bottles. Bottles were stored at room temperature [(28 ± 2) °C], in the refrigerator [(4 ± 1) °C] and in the freezer [(–12 ± 1) °C] for 12 weeks. Additional samples were prepared by supplementing juice with 2% (w/w) citric acid and they were stored in the refrigerator. Total soluble solids and pH values were measured every 2 weeks and analysis was carried out on ascorbic acid content by means of the titration method in the presence of 2,6–dichlorophenol indophenol. The study was performed for 12 weeks. Resultsand discussion. Total soluble solids content and pH value of the initial juice were 11.5 °Brix and 3.18, respectively. pH appeared not to be significantly influenced by storage time or conditions; however, total soluble solids content in a few samples was reduced to about 9.5 °Brix. The initial ascorbic acid content was 130 mg·100 mL^–1; after 2 weeks, it was reduced by nearly 50% for all unfrozen samples. The final concentration of ascorbic acid in the juice was approximately 20 mg·100 mL^–1, regardless of storage conditions. The deteriorative reaction of ascorbic acid in the juice at each temperature experienced followed a first-order kinetic model with activation energy of 2.67 kJ·mol^–1.