An ADH toolbox for raspberry ketone production from natural resources via a biocatalytic cascade

Aileen Becker,Uwe T Bornscheuer,Karsten Siems,Dominique Böttcher,Werner Katzer,Lutz Müller-Kuhrt

doi:10.1007/s00253-021-11332-9

Aileen Becker, Uwe T Bornscheuer + Show 4 more

Open Access

https://doi.org/10.1007/s00253-021-11332-9

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Abstract

Raspberry ketone is a widely used flavor compound in food and cosmetic industry. Several processes for its biocatalytic production have already been described, but either with the use of genetically modified organisms (GMOs) or incomplete conversion of the variety of precursors that are available in nature. Such natural precursors are rhododendrol glycosides with different proportions of (R)- and (S)-rhododendrol depending on the origin. After hydrolysis of these rhododendrol glycosides, the formed rhododendrol enantiomers have to be oxidized to obtain the final product raspberry ketone. To be able to achieve a high conversion with different starting material, we assembled an alcohol dehydrogenase toolbox that can be accessed depending on the optical purity of the intermediate rhododendrol. This is demonstrated by converting racemic rhododendrol using a combination of (R)- and (S)-selective alcohol dehydrogenases together with a universal cofactor recycling system. Furthermore, we conducted a biocatalytic cascade reaction starting from naturally derived rhododendrol glycosides by the use of a glucosidase and an alcohol dehydrogenase to produce raspberry ketone in high yield.Key points• LB-ADH, LK-ADH and LS-ADH oxidize (R)-rhododendrol• RR-ADH and ADH1E oxidize (S)-rhododendrol• Raspberry ketone production via glucosidase and alcohol dehydrogenases from a toolboxGraphical abstract

Highlights

Raspberry ketone (4-(4-hydroxyphenyl)-butan-2-one) is of high economical relevance (Wang et al 2019) due to its characteristic scent and low odor threshold (Larsen and Poll 1990)
By combining an (S)- and an (R)-selective alcohol dehydrogenase (ADH), such as ADH1E and LK-ADH, high conversion of both rhododendrol enantiomers was attained within 24 h resulting in 71.8±2.1 % raspberry ketone (Fig. 2f and Figure S14)
All ADHs are compatible in terms of pH range (Figure S24) being preferably used between pH 9 and 10 for oxidation reactions (Kosjek et al 2004; Inoue et al 2005a; Quaglia et al 2012)

Summary

Introduction

Raspberry ketone (4-(4-hydroxyphenyl)-butan-2-one) is of high economical relevance (Wang et al 2019) due to its characteristic scent and low odor threshold (Larsen and Poll 1990). The aroma compound is widely applied as flavoring agent in food industry for products like sweets, yoghurts, or soft drinks (Deifel 1989; Beekwilder et al 2007; Wang et al 2019; Milke et al 2020). Deifel 1989) and as a component in perfumes (Dumont et al 1996; Farwick et al 2019), whereas further applications in cosmetic industry, e.g., as skin whitening or hair growth inducing agent, remain controversial (Harada et al 2008; Kim et al 2016). Increasing consumer awareness is demanding for a naturally derived product, especially in food and cosmetic industry (Milke et al 2020; Malik and Rawat 2021). Natural production methods do include the direct isolation from natural sources, and the enzymatic or microbial bioconversion of natural precursors, Appl Microbiol Biotechnol (2021) 105:4189–4197 according to EU regulations (Kosjek et al 2003; European Parliament 2008; Schloesser and Lambert 2018; Milke et al 2020)

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