View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Universidade do Minho: RepositoriUM Food and Bioprocess Technology (2018) 11:2217–2228 https://doi.org/10.1007/s11947-018-2180-8 ORIGINAL PAPER Generation of Flavors and Fragrances Through Biotransformation and De Novo Synthesis Adelaide Braga1 & Carlos Guerreiro1 & Isabel Belo1 Received: 8 May 2018 /Accepted: 10 September 2018 /Published online: 19 September 2018 # Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract Flavors and fragrances are the result of the presence of volatile and non-volatile compounds, appreciated mostly by the sense of smell once they usually have pleasant odors. They are used in perfumes and perfumed products, as well as for the flavoring of foods and beverages. In fact the ability of the microorganisms to produce flavors and fragrances has been described for a long time, but the relationship between the flavor formation and the microbial growth was only recently established. After that, efforts have been put in the analysis and optimization of food fermentations that led to the investigation of microorganisms and their capacity to produce flavors and fragrances, either by de novo synthesis or biotransformation. In this review, we aim to resume the recent achievements in the production of the most relevant flavors by bioconversion/biotransformation or de novo synthesis, its market value, prominent strains used, and their production rates/maximum concentrations. Keywords Bioconversion . Biotransformation . De novo synthesis . Flavors . Fragrances Introduction fact, chemical synthesis still represents the cheaper technol- ogy for their production; however, it may require harsh Flavors and fragrances have a wide application in the food, conditions (toxic catalysts, high pressure and temperature, feed, cosmetic, chemical, and pharmaceutical sectors among others) and usually lack adequate regio- and (Vandamme 2003). Nowadays, they represent over a quarter enantio-selectivity to the substrate, resulting in a mixture of the world market for food additives and most of them are of products. Additionally, the compounds generated are la- provided by extraction from natural sources or by traditional belled as Bartificial^ or Bnature identical^, decreasing their methods, as chemical synthesis. The specialized magazine economic value (Longo and Sanromán 2006; Vandamme Perfumer & Flavorist has recently reported that the expected 2003). An increasing in the interest on the biotechnological market for flavors and fragrances will reach US$ 45.6 billion production and use of flavor compounds of (micro) biolog- in 2018 (Bhttp://www.perfumerflavorist.com/fragrance/ ical origin is observed, since the products obtained may be trends/Report-Global-Fragrances-Perfumes-Market-To- labeled as Bnatural^ (Vandamme 2003; Vandamme and Reach-456B-by-2018-197588241.html,^ n.d.) with a good Soetaert 2002).IntheUSAandaccordingtoEuropeanreg- growth rate over the next 5 years. ulations (e.g., CFR 1990 and EEC 1334/2008), compounds The most common processes to produce flavor com- isolated from natural resources or obtained by microbial or pounds are the extraction from natural sources and the enzymatic processes involving precursors isolated from na- chemical synthesis. Nevertheless, extraction from plants ture are classified as Bnatural^ (European Commission has many disadvantages such as low concentration of the 2008;FDA2013). Even though the low yields obtained in product of interest, seasonal variation, risk of plant dis- most of the reported biotechnological processes for flavor eases, stability of the compound, and trade restrictions. In production, in some cases they are economically feasible. Some examples of commercial Bnatural^ flavors biotechno- logically produced are ethyl butanoate, 2-heptanone, β- * Isabel Belo ionone, nootkatone, 1-octen-3-ol, 4-undecalactone, and [email protected] vanillin (Berger 2009; Caputi and Aprea 2011). One of 1 CEB—Centre of Biological Engineering, University of Minho, the main motivations for the microbial production of flavor Campus de Gualtar, 4710-057 Braga, Portugal compounds is its market price, which is normally far above 2218 Food Bioprocess Technol (2018) 11:2217–2228 their synthetic counterparts, but usually lower than those Bioconversion/Biotransformation extracted from nature. For example: synthetic vanillin has a price of around US$ 11 kg−1, natural vanilla flavor ex- Bioconversions/biotransformations can be cheaper, greener, tracted from fermented pods of Vanilla orchids costs US$ and more direct than their chemical analogues. Since the first 1200–4000 kg−1, while Bbiotech vanillin^ is sold for a price discoveries of microbial production of blue cheese-note com- of around US$ 1000 kg−1 (Schrader et al. 2004;Xuetal. pounds in 1950 (Patton 1950), several bioflavor synthetic 2007). Equivalent data are also observed for other aroma paths have been unveiled and exploited throughout the de- compounds, such as γ-decalactone (synthetic = US$ cades. In the next topic, microbial production of today’skey 150 kg−1; natural = US$ 6000 kg−1; Bbiotech^ =US$ flavor compounds in food, beverage, and cosmetic industry 300 kg−1) and ethyl butyrate (synthetic = US$ 4 kg−1;nat- will be addressed. ural = US$ 5000 kg−1; Bbiotech^ =US$180kg−1)(Dubal et al. 2008). Flavor compounds can be biotechnologically Phenolic Aldehydes produced in two basic ways: through de novo synthesis or by biotransformation. De novo synthesis refers to the pro- The most important flavors and fragrances from the class of duction Bfrom the new^, i.e., the synthesis of substances phenolic aldehydes are anisaldehyde and some derivatives of from simple building block molecules (sugars, amino acids, protocatechu aldehyde (3,4-dihydroxybenzaldehyde), such as nitrogen salts, minerals, among others), which will be me- vanillin, veratraldehyde, and heliotropin. In fact, vanillin is tabolized by organisms to form a different and complex one of the most popular flavors in the world. Vanillin is the structure. Biotransformations, in turn, are single reactions primary component of the extract of the vanilla bean. These catalyzed enzymatically (as pure enzymes or within micro- flavors can be extracted from the beans of Vanilla species such bial cells). Therefore, the substrate is metabolized by the as Vanilla planifolia and Vanilla tahitensis (Gallage et al. organism (usually a breakdown or an oxidation/reduction 2014); however, total world consumption of vanilla beans process) in a single (bioconversion) or a few has been affected due to its very high price (US$ 20 per kg (biotransformation) reactions to produce a structurally sim- in 2010 and US$ 500 in 2016) (Berger 2007; Eurovanille ilar molecule (Bicas et al. 2015). The production of aroma 2017). In 2017, the record price of vanilla beans was due to compounds by de novo synthesis usually generates a mix- a cyclone that hit Madagascar (world’s main producer of ap- ture of products, whose maximal concentrations are nor- proximately US$ 100 million) and consequently destroyed the mally below 100 mg L−1 (Bicas et al. 2015). Therefore, plant cultures. This compound is not only widely used as biotransformations have higher potential for the production flavor enhancer in sweet foods such as ice creams, cookies, of Bbioflavors^ on a commercial scale (Bicas et al. 2015). or cakes, but also in soft beverages, cosmetics, or as precursor for pharmaceutical preparations, and as food preservative. Also, synthetic vanillin is used in the production of deodor- Biotechnological Production of Flavors ants, air fresheners, cleaning products, antifoaming agents, or herbicides (Ramachandra Rao and Ravishankar 2000; Sinha Considering the disadvantages of chemical production, re- et al. 2008; Walton et al. 2003). garding the quality of the product, health and environmental Over the years, most of the studies extensively addressed issues and the inability of natural production at industrial the biotransformation of lignin, aromatic amino acids, pheno- scale, the need to address an alternative way for flavor pro- lic stilbenes, ferulic acid (FA), vanillic acid, isoeugenol, or duction through low-cost and environmentally friendly pro- curcumin for the vanillin production, in a concentration range cesses became crucial. Consumer perception that everything of 0.13 to 32.5 g L−1 (Huang et al. 1993;Kaurand natural is better is causing an increase demand for natural Chakraborty 2013;Priefertetal.2001;Zhaoetal.2005). In flavor additives and biotechnological routes may be, if they 2010, Tilay et al. (2010) investigated the effects of media exclude any chemical steps, a way to get natural products composition and environmental factors such as pH on vanillin (Longo and Sanromán 2006). De novo synthesis should be production from FA by one-step biotransformation using fun- therefore used for complex targets or product mixtures, where- gus Pycnoporous cinnabarinus. In optimized conditions, van- as bioconversions/biotransformations are able to carry out illin production reached a maximum of 126 mg L−1. single-step processes. In general, microorganisms are able to Regarding FA biotransformation, in 2016, Fleige et al. produce a wide range of flavor compounds by de novo syn- (2016) used a metabolic engineered strain, Amycolatopsis thesis. However, the production levels are very poor, and thus sp. ATCC 39116, in a fermentative process where vanillin constitute a limit for industrial exploitation. degradation was