Biotechnology: Biotransformation and De Novo Synthesis Fermentation in Bioflavor Production
Biotechnology is widely defined as a method to produce or modify products or to improve functional metabolites value in plants or animal using living microorganisms (or parts of them). Since a long time ago, human has been using biotechnology techniques to produce fermented beverages, breads, and many more. Lately, the technique was developed to manufacture specialty ingredients, such as flavors, oligosaccharides, and many more [1].
Bioflavors
Flavors and fragrances are widely used in the food, cosmetic, chemical, and pharmaceutical industries. There are many compounds that responsible for flavors such as aldehydes, alcohols, esters, ketones, lactones, short- to medium-chain free fatty acids, phenolic and sulphur compounds. To obtain these flavors naturally from distillation or extraction process may be difficult due to low concentration of the flavors compounds of interest from plant or animal source and the high cost of distillation or extraction [2]. While chemically produced of these compounds are usually used a toxic catalyst, higher temperature and pressure, and may left an unwanted residue that may harms human body, the biotechnological production is now being studied as a great solution since the product can be labelled as natural. This Biotechnological production of flavors is called bioflavors [3]. New biotechnological ways to produce bioflavors are based on biotransformation and microbial fermentation - de novo synthesis.
Biotransformation
Biotransformation can be defined as the process of the bioflavor production using microbial cells or the enzyme to perform a specific modifications or interconversions of precursor substances to a structurally similar flavor compound. The biochemical reaction catalyzed by the microorganism or its enzyme can perform a single- or multistep reaction, and each reaction will differ depending on microorganisms, substrates or nutrient supplementations that are used in the fermentation [2].
To give a comparison example with de novo synthesis (to be discussed below), one of popular examples in the biotransformation to produce bioflavour is 2-phenylethanol (2-PE). Through the Ehrlich pathway (transamination, decarboxylation, oxidation and reduction of amino acids to alcohol by enzymes produced by microorganisms), microorganisms like S. cerevisiae can transform the l-phe amino acid to 2-PE directly. The microorganisms do the conversion by producing enzymes and it converts the substrates resulting the desired product without the need to metabolize the substrate like in de novo synthesis.
Another popular example is the biotransformation of vanillin. The biotransformation of lignin, aromatic amino acids, phenolic, ferulic acid, vanillic acid, isoeugenol and curcumin to vanillin have extensively been studied for years. Microorganism like P. cinnabarinus was reported to be able to perform a single-step conversion of ferulic acid to vanillin [3]. Compared to de novo synthesis, biotransformation performed in fermentation yielding a higher level of desired flavor and some of microorganisms do not need to be modified, hence it may offer a more attractive in the feasibility viewpoint in industrial case [2].
De Novo Synthesis
In the fermentation process, several sources of carbohydrates, fats, and protein are catabolized and further converted into the breakdown products of flavor molecules by microbial cells like bacteria, yeasts, and moulds. This fermentation process is called de novo synthesis [2]. The flavors compounds were produced from simple molecules through complex metabolic pathways (whole metabolism).
Giving an example of production of 2-phenylethanol (2-PE), researchers have reported that a genetically modified strain of several yeast like S. cerevisiae and K. marxianus can produce 2-phenylethanol from glucose through the shikimate pathway (seven-step metabolic pathway used in microorganisms) without the addition of its original substrate, the l-phenylalanine (l-phe) amino acid [3].
Other examples are the production of vanillin from the glucose via the shikimate pathway using S. cerevisiae and E. coli. Nevertheless, the production of bioflavors by de novo synthesis still has several challenges because the direct bioconversion of glucose to produce these flavors by microorganisms are limited. This is because they cannot naturally convert the glucose and would require some modification so the strain can metabolize it [3].
Figure refer to ref. [4] and [5].
