Concentration of pineapple juice by osmotic evaporation

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Abstract

The aim of this work was to evaluate the process of osmotic evaporation to concentrate pineapple juice. In order to study the effect of pulp content on the performance, clarified and single strength pineapple juices were successively concentrated up to 57 g 100 g−1 total soluble solids (TSS). Trials were carried out with a laboratory unit using saturated calcium chloride brine as the extracting phase. Under the operating conditions, the difference in temperature between the juice and the brine had a large influence on the water evaporation rate. The highest flux was obtained at 35 °C in the juice compartment and 20 °C on the brine side. Flux ranged from 2 to 13 kg h−1 m−2. It significantly decreased when the TSS content of the juice increased. For the same operating conditions, higher flux values were obtained when processing the clarified juice, which indicated an effect of pulp content on performance. At no time were significant changes observed in the quality of the products obtained from raw juices and juices from concentrates.

Section snippets

introduction

Fruit juice concentration is a fundamental factor for the competitiveness of products and the conquest of new markets as it reduces costs related to operation logistics (packing, storage and transport). The concentration of juices is traditionally accomplished by the use of thermal evaporation. Thermal processes can greatly affect the sensorial and nutritional quality of fruit juices, as these attributes are mainly conferred by heat-sensitive compounds. There is, indeed, a rising demand for

Pineapple juices

A commercial pasteurised, pulpy pineapple juice was used as the raw material. The characteristics of the juice are shown in Table 1. The concentration experiments were carried out with this single strength juice and with the clarified one. For the latter case, the single strength juice was clarified in a micro-filtration system with tubular ceramic membranes of 0.1 μm average pore diameter at 20 ± 1 °C, 2 bar trans-membrane pressure and 6 m s−1 crossflow velocity without enzymatic treatment (

Effect of operating conditions

Some tests were performed before concentrating the pineapple juice in order to evaluate the effect of the temperature difference between both compartments and brine velocity on the evaporation flux. These experiments were carried out with the single strength pineapple juice circulating with a tangential velocity of 1.25 m s−1.

As shown in Table 2, an increase in the temperature of the juice from 20 °C to 35 °C approximately doubled the evaporation flux, whereas the increase in velocity slightly

Conclusion

The concentration of both single strength and clarified pineapple juices using osmotic evaporation achieved TSS contents of at least 56 g 100 g−1. The average evaporation flux was about 6.1 kg h−1 m−2 for the single strength juice and 8.5 kg h−1 m−2 for the clarified juice. The higher flux rate for clarified juice compared with single strength juice indicated some effect of pulp on the evaporation flux. Characterisation of the juice showed no significant changes in the main properties of the pineapple

Acknowledgements

The authors wish to thank CAPES program from the Brazilian Ministry of Education for its financial support and M. Guy SELF (CIRAD, France) for his valuable help in the edition of this article.

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