Resin Adsorption and Ion Exchange

Water purification and softening is by far the most important application of absorbent and ion exchange resins, thus providing high quality water, not only for the food industry, but also for a wide range of others industrial sectors. This also covers wastewater treatment, which is gaining increasing interest in reducing organic loads from industrial effluents that accumulate in large quantities.

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Furthermore, numerous biotechnological processes have been described that use resin-based technologies for the enrichment and purification of valuable components, such as polyphenols, which can then be used in fortified foods, beverages, cosmetics and pharmaceuticals (Kammerer et al. , 2011a; Soto et al., 2011).

In the past, the application of adsorbents and ion exchangers in the food industry was dominated by established processes mainly for the removal of phenolic compounds for various reasons. In this context, fruit juice technology is one of the most important areas of application of these resins in the food industry, where they are mainly applied for the stabilization and discoloration of juices and to reduce the bitterness of citrus juices, i.e. to overcome the problems that phenolic compounds usually cause. In this sense, adsorbent technology is an appropriate alternative to conventional clarification methods using, for example, bentonite, gelatin and silica sol, respectively. Therefore, the juices can be standardized and light-colored, almost transparent juices can be obtained by binding the Maillard reaction products formed by the heat treatment of the juices, as well as phenolic compounds, which also contribute to cloud formation. and brown tones of the juices. (Lyndon, 1996; Weinand, 1996). Aside from discoloration, unpleasant tastes and aromas are common problems associated with juice production, which can arise immediately after processing or during storage. In this context, the most obvious example is the bitterness of grapefruit and navel oranges, which is observed prior to storage and is caused by limonin and naringin or hesperidin respectively (Chandler et al., 1968; Johnson and Chandler, 1988; Shaw and Buslig, 1986). Such unwanted bitterness can be effectively mitigated by selectively binding bitter compounds to the surface of the adsorbent resins as a final step in juice production. Consequently, the aromas and flavors that develop during storage are not affected by the absorbent treatment. Such phenomena can be observed when the precursors, which in themselves do not adversely affect the sensory properties of the products, degrade or form unwanted reaction products with other components of the juice. The precursor compounds mentioned above can derive from heating steps carried out for the thermal preservation of the juices or from degradation processes such as the Strecker reaction. This has been shown for ferulic acid, a hydroxycinnamic acid frequently found in plant materials, which can lead to increased release of paravinilguajacol, the latter contributing to an “old fruit” or “rotten” flavor. Therefore, strategies have been developed to address these problems, which are based on the selective binding of the juice precursor compounds using macromolecular resins. In these cases, resin-based technologies can significantly improve the sensory quality of juices without altering their nutritional values ​​and, at the same time, extend the shelf life of the products (Ma and Lada, 2001a, b).

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