Adsorption of Oxygen Gas by Hydrated Wheat Flour

A pilot scale process involving microfiltration followed by osmotic evaporation was used to prepare concentrated orange and passionfruit juices. Both juices were concentrated 3-fold to 33.5 and 43.5 °Brix, respectively. Quantitative headspace gas chromatographic analysis of 20-35 volatile components showed a loss of about 32% of the volatile components in orange and about 39% in passionfruit juices. For both orange and passionfruit, sensory evaluations using triangle difference tests showed a significant difference between the initial juice and the reconstituted concentrate. In orange juice, a trained taste panel was used to evaluate six specific flavour characteristics in the two juices. The characteristics evaluated were green, fresh orange, fruity/floral, peel oil, cooked/processed and terpene. There were no significant differences found by the panel between the juices in any one characteristic, but the average flavour score for each characteristic was slightly lower in juice from concentrate that in the initial juice. This study demonstrates the feasibility of using osmotic evaporation combined with microfiltration to prepare concentrated orange and passionfruit juices of intermediate concentration degree with high flavour quality.