Oxidative stress plays an essential role in the pathogenesis of chronic diseases such as cardiovascular diseases, diabetes, neurodegenerative diseases, and cancer. Long term exposure to increased levels of pro-oxidant factors can cause structural defects at a mitochondrial DNA level, as well as functional alteration of several enzymes and cellular structures leading to aberrations in gene expression. The modern lifestyle associated with processed food, exposure to a wide range of chemicals and lack of exercise plays an important role in oxidative stress induction. However, the use of medicinal plants with antioxidant properties has been exploited for their ability to treat or prevent several human pathologies in which oxidative stress seems to be one of the causes. In this review we discuss the diseases in which oxidative stress is one of the triggers and the plant-derived antioxidant compounds with their mechanisms of antioxidant defenses that can help in the prevention of these diseases. Finally, both the beneficial and detrimental effects of antioxidant molecules that are used to reduce oxidative stress in several human conditions are discussed.

Naringenin is a flavonoid belonging to flavanones subclass. It is widely distributed in several Citrus fruits, bergamot, tomatoes and other fruits, being also found in its glycosides form (mainly naringin). Several biological activities have been ascribed to this phytochemical, among them antioxidant, antitumor, antiviral, antibacterial, anti-inflammatory, antiadipogenic and cardioprotective effects. Nonetheless, most of the data reported have been obtained from in vitro or in vivo studies. Although some clinical studies have also been performed, the main focus is on naringenin bioavailability and cardioprotective action. In addition, these studies were done in compromised patients (i.e., hypercholesterolemic and overweight), with a dosage ranging between 600 and 800 μM/day, whereas the effect on healthy volunteers is still debatable. In fact, naringenin ability to improve endothelial function has been well-established. Indeed, the currently available data are very promising, but further research on pharmacokinetic and pharmacodynamic aspects is encouraged to improve both available production and delivery methods and to achieve feasible naringenin-based clinical formulations.

Several inorganic materials are potentially suitable for enzymatic covalent immobilization, by means of several different techniques. Such materials must meet stringent criteria to be suitable as solid matrices: complete insolubility in water, reasonable mechanical strength and chemical resistance under the operational conditions, the capability to form manageable particles with high surface area, reactivity towards derivatizing/functionalizing agents. Non-specific protein adsorption should be always considered when planning covalent immobilization on inorganic solids. A huge mass of experimental work has shown that silica, silicates, borosilicates and aluminosilicates, alumina, titania, and other oxides, are the materials of choice when attempting enzyme immobilizations on inorganic supports. More recently, some forms of elemental carbon, silicon, and certain metals have been also proposed for certain applications. With regard to the derivatization/functionalization techniques, the use of organosilanes through silanization is undoubtedly the most studied and the most applied, although inorganic bridge formation and acylation with selected acyl halides have been deeply studied. In the present article, the most common inorganic supports for covalent immobilization of the enzymes are reviewed, with particular focus on their advantages and disadvantages in terms of enzyme loadings, operational stability, undesired adsorption, and costs. Mechanisms and methods for covalent immobilization are also discussed, focusing on the most widespread activating approaches (such as glutaraldehyde, cyanogen bromide,

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Agarose is a polysaccharide obtained from some seaweeds, with a quite particular structure that allows spontaneous gelation. Agarose-based beads are highly porous, mechanically resistant, chemically and physically inert, and sharply hydrophilic. These features-that could be further improved by means of covalent cross-linking-render them particularly suitable for enzyme immobilization with a wide range of derivatization methods taking advantage of chemical modification of a fraction of the polymer hydroxyls. The main properties of the polymer are described here, followed by a review of cross-linking and derivatization methods. Some recent, innovative procedures to optimize the catalytic activity and operational stability of the obtained preparations are also described, together with multi-enzyme immobilized systems and the main guidelines to exploit their performances.Keywords: enzymes; immobilization; stabilization; agar-agar; agarose; cross-linking; functionalization Enzyme Immobilization: An OverviewAs biological catalysts, enzymes are biological macromolecules able to increase the rate of biochemical reactions without changing the reaction equilibrium [1]. Their distinctive features are very intriguing from the perspective of the economical effectiveness of large scale processes, drawing the interest of various industrial sectors. Enzymes are, in fact, very efficient catalysts, operating under mild conditions (aqueous environment, physiological pH, ambient temperature/pressure), and performing very precise reactions due to their outstanding chemo-, stereo-or regio-specificity and selectivity [1][2][3][4][5].Accordingly, enzymatic large scale processes usually feature lower demands both in terms of cost and time [2,6], allowing enzymes to find applications in several fields, such as biosensor production [7], detoxification of pollutants [8][9][10][11][12], production of biofuels and other bioproducts [13][14][15][16][17][18], and the food and pharmaceutical industries [4,19].However, the use of enzymes in homogenous catalysis suffers from numerous limitations hampering the economic feasibility of the processes [20]. The large scale production of enzymes, for instance, is very costly, and they are usually rather unstable. Moreover, after the reaction, soluble enzymes contaminate the reaction products, since their recovery is very challenging and expensive.Many of these drawbacks can be overcome by making the enzyme insoluble in the reaction medium. The term "enzymatic immobilization" refers to the numerous techniques aimed to attach enzymes on solid matrices, retaining at least part of their catalytic activity [21][22][23][24].Despite the additional costs related to the developments of the process, heterogenized enzymes overshadow the use of their soluble native forms for several reasons [25][26][27][28]. The recovery of the catalyst after the reaction, for instance, is efficient and immediate. Contamination of the products is minimized, and the enzymatic catalytic activity can be completely exploited...