Amino Acids and Derivatives

Amino acids are organic compounds that contain both amino and carboxylic acid functional groups (figure 1). Amino acids are known as the building blocks of protein and they find various applications in the production of foods, animal feeds and pharmaceuticals. Recently, with the fast development of metabolic engineering and synthetic biology technologies, the metabolic engineering for production of amino acids has been flourishing.

Fig. 1 Structure of amino acids

Types of Amino Acids

There are over 500 amino acids in nature, while only 20 of them directly code with human genetics (Figure 2). Broadly, these 20 amino acids can be sorted into two groups: essential and non-essential. Essential amino acids, also known as indispensable amino acids, are amino acids that humans and other vertebrates cannot synthesize from metabolic intermediates. Whereas non-essential amino acids can be synthesized by the body.

Fig. 2 Non-essential and essential amino acids

Preparing Methods of Amino Acids

At present, amino acids are mainly produced through three different routes, namely, extraction from protein-hydrolysates, chemical synthesis and microbial processes (enzymatic synthesis and fermentation). The different amino acids production methods are compared in table 1 ^[1].

Table 1 Comparison among different amino acid production methods

Methods	Principle	Advantages	Disadvantages
Extraction from protein hydrolysates	An amino acid can be separated from the others present in the protein-hydrolysates if its properties are different from the others	Large scale industrial production Can use industrial by-products or waste Common reagents such as hydrochloric acid and sodium hydroxide	Few kinds of amino acids Depend on the availability of natural protein rich resources By-products Wastewater generation Possible protein degradation
Chemical synthesis	Amino acids obtained through a chemical reaction	Produce achiral-amino acids	Production of racemic mixtures additional optical resolution step is necessary to obtain only the L-forms Price of the catalyst Hazardous sources
Enzymatic synthesis	Application of proteases to peptide hydrolysis	Produce optically pure D and L-amino acids Very few amounts of by-product Simple process downstream	Price and instability of the enzyme Not favorable for production of L amino acids at industrial scale
Fermentation	Microorganisms convert the sugars present in a substrate into amino acids	Large scale industrial production of most of L-amino acids Economic method Production of L-amino acids form Mild conditions Low plant maintenance costs	Sterility has to be ensured Energy required for oxygen transfer and mixing High operational costs

The fermentation process is becoming one of the most promising processes for amino acids commercial production because of the new genetic engineering tools applied to maximize yield, specificity and productivity of the target compounds. An example of the fermentation process is showed in figure 3 ^[2].

Fig. 3 Example of amino acid fermentation and downstream process flowchart

Applications

Amino acids can be used to enhance the flavor of food and enhance nutrition. Additionally, amino acids are widely used in the medical and healthcare industry, cosmetic industry, and biopharmaceutical industry. Common applications are as followings.

Applications

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References

Martina D'Este, Merlin Alvarado-Morales, Irini Angelidaki, Amino acids production focusing on fermentation technologies-A review, Biotechnology Advances, Volume 36, Issue 1, 2018, Pages 14-25.
Leuchtenberger, W.; Huthmacher, K.; Drauz, K. Biotechnological Production of Amino Acids and Derivatives: Current Status and Prospects. Appl. Microbiol. Biotechnol. 2005, 69, 1–8.