Efficient Synthesis of Phenylacetate and 2-Phenylethanol by Modular Cascade Biocatalysis

Derivation of Kokumi γ-Glutamyl Peptides and Volatile Aroma Compounds from Fermented Cereal Processing By-Products for Reducing Bitterness of Plant-Based Ingredients

Current food production methods and consumption behaviours are unsustainable and contribute to environmental harm. One example is food waste-around 38% of food produced is wasted each year. Here, we show that two common food waste products, wheat bran and brewer's spent grain, can successfully be upcycled via miso fermentation. During the fermentation process, kokumi γ-glutamyl peptides, known to increase mouthfulness, are produced; these include γ-ECG (oxidized), γ-EVG, γ-EV, γ-EE, γ-EF, and γ-EL. The profiles of kokumi peptides and volatile aroma compounds are correlated with koji substrate, pH, and enzymatic activity, offering straightforward parameters that can be manipulated to increase the abundance of kokumi peptides during the fermentation process. Correlation analysis demonstrates that some volatile aroma compounds, such as fatty acid ethyl esters, are correlated with kokumi peptide abundance and may be responsible for fatty, greasy, and buttery aromas. Consumer sensory analysis conveys that the bitter taste of vegetables, such as that in endives, can be dampened when miso extract containing kokumi peptides is added. This suggests that kokumi peptides, along with aroma volatile compounds, can enhance the overall flavour of plant-based products. This study opens new opportunities for cereal processing by-product upcycling via fermentation, ultimately having the potential to promote a plant-based diet.

Biotransformation of the Proteogenic Amino Acids Phenylalanine, Tyrosine and Tryptophan by Yarrowia Species: An Application to the Preparative Synthesis of Natural Phenylacetic Acid

The biotransformation of the aromatic amino acids phenylalanine, tyrosine and tryptophan originates a number of bioactive compounds. Yeasts are the most used microorganisms for the transformation of (L)-phenylalanine into the flavour phenylethanol. Here, we reported a study on the biotransformation of the proteogenic aminoacids phenylalanine, tyrosine and tryptophan by yeast strains belonging to Yarrowia genus. We found that the latter microorganisms, in high aerobic conditions, metabolise the aromatic amino acids (L)-phenylalanine and (L)-tyrosine with the almost exclusive formation of phenylacetic acid and 4-hydroxyphenylacetic acid, respectively. Differently, the biotransformation of (L)-tryptophan with Y. lipolytica, gave anthranilic acid as the main product. As stated by the European and USA legislations concerning natural flavour production, phenylacetic acid obtained by microbial conversion of phenylalanine of natural origin can be commercialised as a natural flavour. Accordingly, our findings were exploited in a new process, based on the Yarrowia strains-mediated biotransformation of natural (L)-phenylalanine, that allows the large-scale preparation of the high-value, natural flavour, phenylacetic acid.

Artificial multi-enzyme cascades for natural product synthesis

Artificial multi-enzyme cascades bear great potential for offering sustainable synthesis of useful and valuable natural molecules. In the past two years, many new cascades were developed to produce natural alcohols, acids, esters, amino compounds, fatty acid derivatives, alkaloids, terpenoids, terpenes and monosaccharides from natural substrates and simple chemicals, respectively. These artificial cascades were constructed by combining individual enzymes designed using the retro-synthesis strategy and based on the available natural substrates and simple chemicals. While performing the cascades in vivo is often simple and straightforward, in vitro cascades usually require cofactor regeneration that was achieved by introducing one or more cofactor-regeneration modules in one pot. Protein engineering is frequently used to improve the performances of some enzymes in the cascades.

Microbial synthesis of 4-hydroxybenzoic acid from renewable feedstocks

4-Hydroxybenzoic acid (4HBA) and its esterified forms can be used as preservatives in the pharmaceutical and food industries. Here, we reported the establishment of a coenzyme-A (CoA) free multi-enzyme cascade in Escherichia coli to utilize biobased _L-tyrosine for efficient synthesis of 4HBA. The multi-enzyme cascade contains _L-amino acid deaminase from Proteus mirabilis, hydroxymandelate synthase from Amycolatopsis orientalis, (S)-mandelate dehydrogenase and benzoylformate decarboxylase from Pseudomonas putida, and aldehyde dehydrogenase from Saccharomyces cerevisiae. The whole-cell biocatalysis afforded the synthesis of 128 ± 1 mM of 4HBA (17.7 ± 0.1 g/L) from 150 mM _L-tyrosine with > 85% conversion within 96 h. In addition, the artificial enzymatic cascade also allowed the synthesis of benzoic acid from 100 mM _L-phenylalanine with a conversion ∼ 90%. In summary, our research offers a sustainable alternative for synthesizing 4HBA and benzoic acid from renewable feedstocks.

Enzymatic synthesis of fluorinated compounds

Fluorinated compounds are widely used in the fields of molecular imaging, pharmaceuticals, and materials. Fluorinated natural products in nature are rare, and the introduction of fluorine atoms into organic compound molecules can give these compounds new functions and make them have better performance. Therefore, the synthesis of fluorides has attracted more and more attention from biologists and chemists. Even so, achieving selective fluorination is still a huge challenge under mild conditions. In this review, the research progress of enzymatic synthesis of fluorinated compounds is summarized since 2015, including cytochrome P450 enzymes, aldolases, fluoroacetyl coenzyme A thioesterases, lipases, transaminases, reductive aminases, purine nucleoside phosphorylases, polyketide synthases, fluoroacetate dehalogenases, tyrosine phenol-lyases, glycosidases, fluorinases, and multienzyme system. Of all enzyme-catalyzed synthesis methods, the direct formation of the C-F bond by fluorinase is the most effective and promising method. The structure and catalytic mechanism of fluorinase are introduced to understand fluorobiochemistry. Furthermore, the distribution, applications, and future development trends of fluorinated compounds are also outlined. Hopefully, this review will help researchers to understand the significance of enzymatic methods for the synthesis of fluorinated compounds and find or create excellent fluoride synthase in future research.Key points• Fluorinated compounds are distributed in plants and microorganisms, and are used in imaging, medicine, materials science.• Enzyme catalysis is essential for the synthesis of fluorinated compounds.• The loop structure of fluorinase is the key to forming the C-F bond.