Recovery of molecules with healthy properties from orange press liquor by membrane fractionation

Abstract

Fruits and vegetables are widely recognized as an important source of beneficial compounds for the human nutrition. Citrus and juices are widely consumed in the world. Their health benefits have been recognized for a long time now since first cultivated in Asia. The market of oranges is growing constantly, because consumers have become more convenience-oriented and health conscious. Consequently, efforts by researchers and industrial organizations have been made to develop processes more efficient, putting emphasis in food quality and safety. In addition, with the increasing emphasis on water pollution control, industries are establishing programs that will permit disposal of their wastewater without damaging the environment. The citrus fruit industry is no exception. Citrus wastes, such as wet peels and whole rejected fruit, which a great amount of organic matter that can be associated with environmental and health problems due to water runoff and uncontrolled fermentation. Therefore, the development of optimized systems for the treatment of citrus wastes is a crucial factor in the rationalization of the traditional industrial cycle. Membrane operations in the last years have shown their potentialities in the rationalization of production systems. Their intrinsic characteristics of efficiency, operational simplicity and flexibility, relatively high selectivity and permeability for the transport of specific components, low energy requirements, good stability under a wide spectrum of operating conditions, environment compatibility, easy control and scale-up have been confirmed in a large variety of applications and operations in the food industry. Recent R&D efforts aim to convert the potential of wastes into profitable products creating new segments of production and offsetting the disposal costs. Orange peels and pulp contain several bioactive compounds, such as flavonoids and phenolic acids, recognized for their beneficial implications in human health due to their antioxidant activity and free radical scavenging ability. These semi-solid wastes can be pressed to obtain a liquid rich in soluble sugars, named press liquor, that can be concentrated up to citrus molasses grade or alternatively exploited as a natural source for the extraction of phenolic compounds which can be used as natural antioxidants mainly in pharmaceutical, cosmetic and foods industry. This PhD dissertation is based on the opportunity to develop a technical alternative to solve some problems related to the disposal of citrus wastes from an economic and environmental point of view, specifically in terms of recovery of attractive compounds present in orange press liquor. The general aim of the work was devoted to the recovery of phenolic compounds by using an integrated membrane process, in which microfiltration (MF) or ultrafiltration (UF), nanofiltration (NF) and osmotic distillation (OD) processes were involved. MF or UF processes were used for the clarification of the press liquor in order to separate macromolecules, such as pectins, and to obtain a clarified press liquor as permeate stream. In the second step the clarified press liquor obtained from the MF/UF process was treated by NF in order to obtain a retentate stream enriched in phenolic compounds with a low content of sugars. Finally, OD was used as final step to concentrate the NF retentate stream. In the first Chapter, a general overview of membrane operations, including methodologies to evaluate their performance, is reported. The industrial transformation of citrus fruits and the associated production of citrus wastes is reported in Chapter 2. In this Chapter the chemico-physical characterization of citrus press liquor used for the experimental activities performed on membrane laboratory plants is also included. Chapter 3 is focused on the experimental activities concerning the clarification of citrus press liquor by using MF or UF processes. In Chapter 4 the fractionation of clarified press liquor by using NF membranes is analysed and discussed. Experimental activities related to the concentration of the NF retentate by using OD are described in Chapter 5