Pyrazines: Synthesis and Industrial Application of these Valuable Flavor and Fragrance Compounds

Abstract

Alkyl pyrazines—other than being extracted from various natural sources such as coffee beans, cocoa beans, and vegetables—can be synthesized by chemical methods or by certain microorganisms. The importance of pyrazines for the food industry is expected to grow in the upcoming years due to the higher demand for convenience products. The roasty, nutty, and earthy smell is reminiscent of coffee and cocoa, depending on substitution and concentration of pyrazines. The growing awareness of people about the ingredients and the origin of their daily food has strongly influenced the market with labels like “organic” and “natural.” Many flavor ingredients prepared by biotechnological methods have conquered the market recently and are destined to replace the ineffective (0.01% pyrazine kg−1 biomass) extraction from plants or animal sources. This review focuses on the achievements and challenges in pyrazine synthesis. The major part deals with an overview of methods such as the extraction of natural products, the chemical and biocatalytic synthesis, and fermentation by microorganisms. The different types of production are decisive for the declaration and value of the final product and span from 200–3500 US$ kg−1 for the synthetically produced or the naturally extracted 2,5‐dimethylpyrazine, respectively.

Sensory and Chemical Characteristic of Two Insect Species: Tenebrio molitor and Zophobas morio Larvae Affected by Roasting Processes

“…Pyrazines occur naturally in heat-treated food products and are produced on a mass scale by extraction from natural products, chemical synthesis, and biocatalysis (enzymatic, microbiological) [ 66 ]. They are used as flavor- and aroma-enhancing compounds.…”

Multicomponent syntheses of 5- and 6-membered aromatic heterocycles using group 4–8 transition metal catalysts

“…Despite the wide utility of pyrazines, 134,135 there are few examples of catalytic MCRs for their synthesis. Hypothetically, pyrazine could be divided into one alkyne and two nitriles in [2 + 2 + 2] cycloaddition just like pyrimidines.…”

Aroma active alkylated pyrazines are produced by Basfia succiniciproducens as by‐products of succinic acid production

“…14 Currently, natural alkylated pyrazines are typically extracted from food, such as potatoes, coffee or nuts. 13 To the best of our knowledge, there is no industrial production for these alkylated pyrazines based on fermentation.…”

“…For example, 1 kg of synthetically produced 2,5-dimethylpyrazine costs ~200 US$, while its natural counterpart is currently sold for ~3,500 US$/kg. 13 Because of the immense amounts of fermentation broth resulting from the industrial succinic acid fermentation process, the extraction of valuable natural flavour compounds from this broth might be a promising idea. For the first time, an aroma analysis of a fermentation broth of this microorganism was carried out, whereby compounds of interest were subsequently quantitated.…”

“…H, t) 13. C NMR (CDCl 3 , 100 MHz): δ 151.9, 148.4, 148.1, 147.7, 36.6, 22.4, 22.2, 14.1, 14.1. , 100 MHz): δ 152.2, 148.5, 148.2, 147.8, 34.6, 31.2, 22.9, 21.6, 21.5, 21.1, 14.1.…”