Concentration of citrus fruit juices in membrane pouches with solar energy Part 1: How solar drying setup and juice pretreatment determine the drying flux

Abstract

AbstractThe aim of this study was to investigate how solar drying setup and choice of juice pretreatment determine the drying flux in a fruit juice concentration process called solar assisted pervaporation. With this process, hygienic membrane pouches and solar energy are used to concentrate and preserve fruit juices. In this study, the feasibility of concentrating citrus (tangerine) juice into marmalade under realistic conditions in rural Mozambique was assessed with three solar drying setups and four juice pretreatments. The main findings were (a) tangerine marmalade with a soluble solids content ≥65° Brix could be produced with all solar drying setups tested within 3–6 days, (b) sucrose addition as a juice pretreatment did not impact drying time and is recommended to increase yield, and (c) direct active and tilted passive solar drying reduced the drying time considerably; however, passive drying was more sensitive to poor weather conditions.Practical applicationsCitrus fruits have high spoilage rates on a global level due to their juicy nature and short ripening period. They are difficult to handle and transport to urban markets and are also difficult to preserve by traditional solar drying practices. An alternative approach is to preserve citrus fruits with membrane pouches that are filled with citrus juices and then placed in the sun to dry. Water passes through the membrane pouch as vapor, allowing for the juices to be concentrated into marmalade. The membrane pouch also protects the juice from microorganisms in the surrounding air during drying. The process is driven by solar energy and is suitable for small‐scale producers in rural areas of tropical countries. The aim of this study was to further investigate the process in rural Mozambique under realistic weather conditions. The main results are recommendations to small‐scale producers on how to optimize the process.