Food ingredients are often derived from plant sources. Because many plant sources are becoming scarce, and are fluctuating in availability, price, and quality, the industry has been looking for alternatives, in particular for those ingredients where constant quality and availability are demanded by the customers. Chemical synthesis based on petrochemical starting materials is the predominant alternative production method. However, as customers aim for natural and sustainable products exhibiting a low product carbon footprint, the utilization of renewable raw material for production of chemicals is increasingly considered [1]. In recent years, microbial fermentation, using sugars as a feedstock, has also been successfully explored to produce food ingredients. One example of ingredients that can be produced via fermentation is terpenoids, which have diverse applications in foods, such as flavoring agents, sweeteners, or vitamins. In this review, the current status of industrial production of terpene ingredients for the food industry by fermentation is reviewed. For a broader view on research activities on microbial terpene production (in academia), the reader is referred to other publications 2, 3, 4. The biosynthesis of terpenes in micro-organisms is shown schematically in Figure 1.

Fermentative production of terpenoids was based on knowledge on the biosynthesis of terpenoids in plants and micro-organisms developed during the 1980s and 1990s. One of the first companies harnessing this knowledge to create microbial platforms for commercial terpene production was the California-based Amyris. The initial technology for producing terpenoids was established in baker’s yeast and Escherichia coli, with the aim of producing a pharmaceutical ingredient, the antimalarial compound artemisinin, which is an oxidized sesquiterpene. The crucial first step in engineering artemisinin production was the overexpression of a plant enzyme, amorphadiene synthase (ADS), in these microbial platforms. This synthase was identified in Artemisia annua, the plant where artemisinin is naturally found. When expressed inside a microbial host such as baker’s yeast, ADS leads to the secretion of amorphadiene from the microbial cells into the culture broth. In addition to ADS, a cytochrome P450 and dehydrogenase enzymes were also overexpressed, with the aim of oxidizing the amorphadiene to dihydroartemisinic acid inside the microbial production host cells. In addition, several steps were taken to overproduce the precursor of sesquiterpenes, farnesyl diphosphate (FPP), in the microbial platforms. This resulted in commercial production of semisynthetic artemisinin in 2013 [5]. As an extension of this research, the same microbial platforms were harnessed to produce a fuel ingredient with a much less modified molecular structure, β-farnesene. Optimization of the strain and the production process has led to the development of a β-farnesene production plant in Brotas, Brazil, capable of producing β-farnesene from sugarcane-derived sucrose at a multiton scale, for single-digit dollars per kg cost price. Companies usually treat the performance indicators of production processes such as yield and product titers as trade secrets. However, published data from Amyris on farnesene fermentation indicate product yields of around 0.18 g farnesene/g glucose and product titers of >80 g/l in lab scale [6]. Possibly, reproducing these titers in production conditions is challenging, and the fermentation performance of terpenoid products other than β-farnesene could be much lower, as farnesene is easily formed from its precursors. In summer 2023, Amyris has declared bankruptcy after months of cost cutting failed to keep the company solvent. It is yet unclear whether low sales prices of the products like farnesene have covered all research and development costs and investments [7]. Parallel with the development of the terpene fermentation technology for artemisinin and farnesene by Amyris, the company Firmenich (now DSM-Firmenich; URL: https://www.dsm.com/corporate/investors/dsm-firmenich.html) from Switzerland started to identify genes in plants, encoding terpene synthases, and cytochrome P450 enzymes for the biosynthesis of commercially interesting terpenoids. Firmenich focused these efforts on terpenes with an application in fragrances, such as patchouli [8], sandalwood, and ambroxide.

From pharmaceuticals, combustables, and fragrance ingredients, it seems a small step to use fermentation technology also for food ingredients. However, challenges for product definition are much different. Food ingredients should comply to food regulations, which differ widely between countries (Regulation (EC) No 178/2002 of the European Parliament and of the Council; URL: https://eur-lex.europa.eu/eli/reg/2002/178/oj). In the United States, food ingredients need to be approved by the Federal Drug Administration (FDA) or should be generally recognized as safe, which means that substance added to food is considered safe by experts under the conditions of its intended use. Ingredients often carry certificates for their compatibility with religious restrictions on food preparations, such as halal or kosher requirements. Moreover, flavor ingredients are often labeled as natural, according to the standards of the European Flavor Association (URL: https://effa.eu/library/guidance-documents). These product labels extend not only to the product itself, or the raw material from which it is made, but also to the whole production line, including process aids such as catalysts, broth ingredients, and other materials used in the same facility. Last, consumer acceptance of microbially produced food ingredients is also much different from pharmaceuticals and fuels [9].

Terpenoids currently used in food industry can be roughly divided into three different categories: flavors, sweeteners, and vitamins. Figure 2 gives a summary on all food ingredients that we discuss. The products are very diverse, not only in their chemical structure and application but also in the stage of their market maturity, which is reflected by their market prices as depicted in Table 1. Although valencene, rebaudioside M (Reb M), and the mogrosides are expensive specialties, some vitamins have already become commoditized. However, it must be considered that prices are only a momentary flash and that they can change a lot over time.