Enzymatic processing of bioactive compounds

Still more widespread use of bioactive compounds is limited due to issues such as lower solubility and miscibility in more hydrophobic environments. As such, strategies meant to alter the physicochemical properties of hydrophilic bioactives have been developed. One relatively successful approach has been the enzymatic acylation of bioactive compounds with more hydrophobic groups, whereby the addition of such groups impacts on partitioning and even on the emulsification properties of the resulting products (Sasaki et al, 2010 ViUeneuve, 2007). 

Enzymatic acylation to yield bioactive compounds with additional properties and/or altered functionahties generally takes place via esterification or transesterification reactions. In simple esterification, the bioactive compound reacts with a fatty acid (or alcohol, based on its structure) to yield an ester and a molecule of water. In contrast, transesterification reactions involve acyl exchange between an ester and alcohol to yield structurally different ester and alcohol species. Both reactions are typically catalyzed by lipase and can, therefore, benefit from milder reaction conditions, substrate and/or regiospecificity (Chebil et al., 2006). 

Based on current research, some important factors to be considered during enzymatic processing of bioactives include the type of reaction media used, the level and distribution of water in the system, biocatalyst type and loading, reaction temperature, agitation and the type and ratio of substrates selected for use in a particular system. Overall, proper adjustment of the aforementioned parameters can help to push the reaction equilibrium towards the production of modified products and may also result in a more efficient and cost effective reaction set-up (Devi et al., 2008). 

Other parameters of interest in the enzymatic processing of bioactive compounds include reaction temperatnre, agitation level and the selection of substrate types and ratio. Firstly, temperatnre can inflnence not only the activation and denaturation of the enzyme, but also substrate and prodnct solnbility and the viscosity of the reaction media (Chebil et al, 2006 Villenenve, 2007). Particnlarly when viscons snbstrates or ionic liquids are involved, a well mixed system is very important to ensnre proper contact between the biocatalyst and snbstrates. From the preceding brief discnssion, it is clear that the efficiency of enzymatic processing of bioactive componnds is affected by anumber of parameters. Excellent in-depth discnssions of some key parameters can be fonnd in various reviews (Lau et al, 2004 Chebil et al., 2006 Villeneuve, 2007). 

Enzymatic glucosylation (the addition of a sugar moiety) and amidalion (the addition of an amine moiety) are two additional approaches that can be employed to alter the properties and functionalities of bioactive compounds (Villeneuve, 2007 Khare et al., 2009). Finally, many reports also describe approaches involving the enzymatic hydrolysis of various proteins to yield bioactive peptides with novel antioxidative, antimicrobial and health-promoting properties (Wei and Chiang, 2009 Zhang et al., 2009). 

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Table 14.3 Literature compilation on enzymatic processing of bioactive compounds. ...

The aforementioned are brief examples of successful industrial applications of biocatalysts. In the following section, four detailed case studies of enzymatic processing of lipid-based bioproducts, namely partial acylglycerols, bioactive compounds, phospholipids and fatty acid alkyl esters are presented. 

Asymmetric Pummerer rearrangement is a very attractive reaction as previously described. In particular, the reactions induced by SKA work well, and may be synthetically exploited in many cases. The results described here demonstrate that the stereoselective a-deprotonation of the sulfoxide is a prerequisite process for asymmetric induction in the Pummerer reaction. Since many kinds of synthetic and enzymatic preparative methods of optically pure sulfoxides have been developed, the present Pummerer-type reaction will be applicable to many other chiral sulfoxides with one a-substituent, chiral vinylsulfoxides and chiral co-carbamoylsulfox-ides, thus leading to enantioselective syntheses of many new bioactive compounds in the near future. 

Water soluble polymers are well represented in the human environn nt and in food. Thus, our very existence constitutes solid proof of the lack of the physiological effects of many of these compounds. Nevertheless, some water soluble synthetic polymers, even at very low concentrations, influence enzymatic processes that form the basis of the physiology of the body. The reason for a general lack of bioactivity of synthetic polymers on the organism s level is the inability of polymers to penetrate to the location where the body s basic biochemical processes occur. The human body s most prevailing component is water (>fi)%). However, this body of water is not a continuous phase, it is subdivided by lipid membranes into spaces of microscopic size. Lipids constitute about 15% of body weight and a considerable portion of that amount is used to form and maintain cellular membranes, a structural element of the body that diminishes the mobility of hydrophilic polymers in organisms. 

Synthesis of sugar phosphonate analogs, which have attracted much attention for their potential bioactivity as inhibitors and regulators of metabolic processes (Guanti et al. 2000). These compounds are accessible by enzymatic aldolization of tu-diethylphosphonoylated- (3 -hydroxyaldehydes. 

Metabolism, or biotransformation, is the process of ehemical transformation of a toxicant to different structures, called metabolites, which may possess a different toxicity profile than the parent compound. Biotransformation affects both endogenous chemicals exogenous (xenobiotic) entities. Metabolism can result in a transformation product that is less toxie, more toxic or equitoxic but in general more water soluble and more easily excreted. Chemical modification can alter biological effects through toxication of a substance, also called bioactivation, which refers to the situation where the metabolic process results in a metabolite that is more toxic than the parent. If the metabolite demonstrates lower toxicity than the parent compound, the metabolic process is termed detoxication. These processes can involve both enzymatic and non-enzymatic processes, all of which should be familiar to undergraduate and graduate chemists. 

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