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The seasonality of fruits and vegetables makes it impossible to consume and use them throughout the year, thus numerous processing efforts have been made to offer an alternative to their fresh consumption and application. To prolong their availability on the market, drying has received special attention as currently this method is considered one of the most common ways for obtaining food and pharmaceutical products from natural sources. This paper demonstrates the weakness of common drying methods applied for fruits and vegetables and the possible ways to improve the quality using different drying techniques or their combination with an emphasis on the microwave energy. Particular attention has been drawn to the combined drying with the assistance of vacuum-microwaves. The quality of the dried products was ascribed by chemical properties including the content of polyphenols, antioxidant capacity and volatiles as well as physical parameters such as color, shrinkage, porosity and texture. Both these fields of quality classification were considered taking into account sensory attributes and energy aspects in the perspective of possible industrial applications. In conclusion, the most promising way for improving the quality of dried fruit and vegetable products is hybrid drying consisting of osmotic dehydration in concentrated fruit juices followed by heat pump drying and vacuum-microwave finish drying.

Conselho Nacional de Desenvolvimento Científico e Tecnológico A concurrent flow dryer with pneumatic load, revolving and discharge, that was compatible with either production and the investment capacity of the small enterprise for drying the pulped coffee was projected, built and evaluated. Because the pneumatic system would be overdimensioned when it would not be moving the product during the drying phase, the fan was also used through a bifurcation to insufflate the hot air in a pre-dryer constructed according to SILVA et al. (2001). Thus, the new dryer was separately evaluated and in a combined system containing both pre-dryer and drying bin. For evaluating the concurrent flow dryer, four tests were accomplished. as being three tests with complete load and one with half load, whereas the air flow was 23.15 m3 min-1 and 33.41 m3 min-1, respectively. For evaluation of the combined drying system composed by the pre-dryer, concurrent flow dryer and storer-dryer bin, four tests were accomplished, from which three were with complete load and one with half load, whereas the air flows of 58.5 m3 min-1 and 64.3 m3 min-1 were respectively used. When operating separately, the prototype showed the values 3,022 and 3,886 kJ kg-1 of evaporated water for specific energy consumption in the tests FT1 and FT2, respectively. Those values are below the consumption limits foreseen in the available literature for this dryer type. In test FT3, however, the average specific energy consumption was 3,856 kJ kg-1 of evaporated water, which was within the consumption limits foreseen in the literature, therefore energetically efficient. When the pneumatic dryer operated with half load (FTM4), the specific energy consumption was 7,041 kJ kg-1 evaporated water, therefore superior to the other tests, as showing to be operable with lower load for which it was dimensioned. In the combined drying system composed by pre-dryer, concurrent flow dryer and storer-dryer bin, the system showed a total specific energy consumption of 4,250; 5,712 and 4,690 kJ kg-1 evaporated water in the tests FD5, FD6 and FD7 respectively, which are below in comparison with some traditional drying processes. When the pre-dryer and the pneumatic dryer operated with half load (FTM4), the total specific energy consumption (6,954 kJ kg-1 evaporated water) was compatible to the other tests, as being energetically efficient. The developed dryer is easily operated during loading, drying and discharge, as well as requires little maintenance and labor, and works efficiently with the coffee amount available. The coffee processed in the new dryer showed good quality concerning to the type and beverage. The combined drying system (hybrid dryer, concurrent pneumatic flow dryer and storer-dryer bin) is a technique that provided a high-qualified product that was also economically viable. Um secador de fluxos concorrentes com carga, revolvimento e descarga pneumáticos, compatível com a produção e a capacidade de investimento do pequeno produtor para a secagem de café pergaminho foi projetado, construído e avaliado. Visto que o sistema pneumático ficaria superdimensionado quando não estiver movimentando o produto durante a fase de secagem, o ventilador foi usado também, por meio de uma bifurcação, para insuflar ar quente em um pré-secador construído segundo Silva et al. (2001). Portanto, o novo secador foi avaliado separadamente e em um sistema combinado contendo um pré-secador e silo secador. Para avaliação do secador pneumático de fluxos concorrentes, foram realizados quatro testes, três testes foram com carga completa e um teste com meia carga, sendo que a vazão de ar utilizada foi igual a 23,15 m3 min-1 e 33,41 m3 min-1, respectivamente. Para a avaliação do sistema de secagem combinada, composto por pré-secador, secador pneumático de fluxos concorrentes e silo secador-armazenador, foram realizados quatro testes, sendo três deles com carga completa e um com meia carga. A vazão de ar utilizada foi igual a 58,5 m3 min-1 e 64,3 m3 min-1, respectivamente. O protótipo apresentou, operando sozinho, consumo específico de energia igual a 3.022 e 3.886 kJ kg-1 de água evaporada, testes FT1 e FT2, respectivamente. Estes valores estão abaixo dos limites de consumo previstos na literatura para este tipo de secador e, no teste FT3, o consumo específico médio de energia (4.856 kJ kg-1 de água evaporada) esteve dentro dos limites de consumo previstos na literatura, mostrando-se eficiente energeticamente. No teste em que o secador pneumático operou com meia carga, FTM4, o consumo específico de energia (7.041 kJ kg-1 de água evaporada) foi superior aos demais testes, mostrando ser operável com carga inferiores para a qual foi dimensionado. No sistema de secagem combinada composto por pré-secador, secador pneumático de fluxos concorrentes e silo secador-armazenador nos testes FD5, FD6 e FD7 o sistema apresentou consumo específico total de energia de 4.250; 5.712 e 4.690 kJ kg-1 de água evaporada, respectivamente. Cujos valores são menores do que alguns processos tradicionais de secagem. No teste em que o pré-secador e o secador pneumático operaram com meia carga, FTM4, o consumo específico total de energia (6.954 kJ kg-1 de água evaporada) foi compatível com os demais testes, sendo eficiente energeticamente. O secador desenvolvido é de fácil operação durante o carregamento, secagem e descarga e exige pouca manutenção e mão-de-obra, funciona eficientemente com a quantidade de café disponível. O café processado no novo secador foi de boa qualidade quanto ao tipo e bebida. O sistema de secagem combinada (secador híbrido, secador pneumático de fluxos concorrentes e silo secador armazenador) é uma técnica com a qual foi obtido um produto de ótima qualidade, além de ser economicamente viável.