Abstract
Press liquors are typical by-products of the citrus juice processing characterized by a high content of organic compounds and associated problems of environmental impact, which imply high treatment costs. However, these wastes contain a great number of health promoting substances, including fibers, carotenoids and phenolic compounds (mainly flavonoids), whose recovery against waste-destruction technologies is very attractive for new business opportunities. In this work, the clarification of orange press liquor by using microfiltration (MF) membranes is studied as a preliminary step to obtain a permeate stream enriched in antioxidant compounds which can be further processed to produce extracts of nutraceutical and/or pharmaceutical interest. MF poly(vinylidene fluoride) (PVDF) hollow fibers were prepared by the dry/wet spinning technique. A series of fibers was produced from the same polymeric dope, in order to investigate the effect of selected spinning parameters, i.e., bore fluid composition and flowrate, on their properties. The morphology of the produced fibers was analyzed by Scanning Electron Microscopy (SEM). Fibers were further characterized for their mechanical properties, porosity, bubble point, pore size distribution and pure water permeability (PWP). Some of the produced fibers exhibited high permeability (pure water permeability ~530 L/m2·h·bar), coupled to good mechanical resistance and pore size in the range of MF membranes. These fibers were selected and used for the clarification of press liquor from orange peel processing. In optimized operating conditions, the selected fibers produced steady-state fluxes of about 41 L/m2·h with rejections towards polyphenols and total antioxidant activity of 4.1% and 1.4%, respectively.
Highlights
Citrus is one of the world’s major fruit crops largely developed in tropical and sub-tropical countries
The recovery of these compounds and their reuse as natural antioxidants is of great interest to valorize these by-products and offer new opportunities for the formulation of products of interest in food, pharmaceutical and cosmetic industry
Experimental results showed that suspended solids were completely removed by the hollow fiber (HF) membranes, while total soluble solids and pH remained quite unchanged in comparison to the unclarified liquor
Summary
Citrus is one of the world’s major fruit crops largely developed in tropical and sub-tropical countries. U.S.A., India, Mexico, and Spain are the world’s leading citrus fruit-producing countries, representing close to 60% of the global production [1]. The citrus juice production is accomplished by a huge amount of waste material such as peels and seeds. These wastes are traditionally spread on soil producing dried peel by natural evaporation which can be used as swine or cattle feed [2]. This method of handling presents environmental and health problems due to uncontrolled fermentation and produced leachates containing high concentrations of organic matter which can contaminate surface and ground waters. The resulting press liquor, with an average total soluble solids (TSSs) content of 10 ̋ Brix, can be concentrated up to 65–70 ̋ Brix by Membranes 2016, 6, 9; doi:10.3390/membranes6010009 www.mdpi.com/journal/membranes
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