Osmotic Evaporation Research Articles

PINEAPPLE JUICE CONCENTRATED BY OSMOTIC EVAPORATION1

AbstractPasteurized pineapple juice was concentrated by osmotic evaporation to produce a 51 d̀Brix concentrate that was reconstituted to single strength juice for evaluation. Headspace gas chromatography (HSGC) showed that the concentrate retained an average of 62% of the volatile components present in the initial juice. A sensory panel preferred initial juice over reconstituted concentrate, and noted a decrease in desirable flavor top notes as well as development of some processed flavor in the concentrate. Similar HSGC analysis of four other commercial juice samples showed a wide range of quantitative values for volatile components, with the initial juice being similar to the weakest of these commercial juices. Analysis of concentrated juice extracts permitted identification of additional less‐volatile components not monitored directly by HSGC of the juice. Relatively low levels of these components were also present in the initial juice. Although this nonthermally produced concentrate retains more volatile components than when traditional thermal processing methods are used, addition of aqueous aroma to the concentrate may be required for satisfactory flavor.

Evaluation of Concentrated Orange and Passionfruit Juices Prepared by Osmotic Evaporation

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.

Concentration of passion fruit juice on an industrial pilot scale using osmotic evaporation

Osmotic evaporation to concentrate clarified passion fruit juice was tried out on an industrial scale. A pilot plant that was equipped with a module containing 10.2 m 2 of polypropylene hollow fibres was used to concentrate passion fruit juice up to a total soluble solids (TSS) content higher than 60 g/100 g at 30°C. Tangential velocity, temperature and concentration of solutions significantly influenced evaporation flux. An average evaporation flux of almost 0.75 kg h −1 m −2 was obtained with water, 0.65 kg h −1 m −2 when juice was concentrated to 40 g TSS/100 g and 0.50 kg h −1 m −2 when it reached 60 g TSS/100 g. A long-term trial, lasting 28 h, was successfully carried out without membrane fouling. Osmotic evaporation can be also conducted as a multistage procedure, giving a constant evaporation flux of around 0.62 kg h −1 m −2 when juice was concentrated from 14 to 60 g TSS/100 g. Sensory quality and vitamin C content were well preserved in the concentrated juice.

Osmotic evaporation through macroporous hydrophobic membranes: a survey of current research and applications

The principle of osmotic trans-membrane evaporation is exposed and compared to other membrane contactors. The origin and the current description of the vapour flux are critically reviewed as well as the importance of the boundary layers near the membranes. Furthermore, a compilation of results obtained on the laboratory and on the industrial scale is given and the disagreements between the conclusions of different research groups are discussed.