Relevant Fusarium Mycotoxins in Malt and Beer

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This entry is adapted from the peer-reviewed paper 10.3390/foods11020246

Mycotoxins are secondary fungal metabolites of high concern in the food and feed industry. Their presence in many cereal-based products has been numerously reported. Beer is the most consumed alcoholic beverage worldwide, and Fusarium mycotoxins originating from the malted and unmalted cereals might reach the final product. This entry aims to describe the possible Fusarium fungi that could infect the cereals used in beer production, the transfer of mycotoxins throughout malting and brewing as well as an insight into the incidence of mycotoxins in the craft beer segment of the industry. Studies show that germination is the malting step that can lead to a significant increase in the level of all Fusarium mycotoxins.

beer craft beer Fusarium mycotoxins brewing

1. Introduction

Fusarium is a fungal genus belonging to the phylum Ascomycota and comprising more than 1500 species ^[1]. Most of them are essential to the environment, but some present certain pathogenicity to animals and humans by producing mycotoxins. Species such as Fusarium graminearum Schwabe, F. oxysporum and F. verticillioides are very common plant pathogens.

Beer is a carbonated fermented beverage obtained from malted cereals. The brewing tradition is one of the oldest ones known to civilized humanity, with historical evidence suggesting it began no earlier than 5000 BC ^[2]. Barley (Hordeum vulgare) is by far the most common cereal used to produce beer; however, in some countries, beer can also be obtained from malted wheat, rye, or sorghum.

Both brewing grains and adjuncts are carefully selected for quality prior to their use. Parameters such as water content (<14.5%), germination energy (>95%), protein content (9.5 to 11.5%), minimum weathering and microbial count, are just a few to consider ^[3]. Contamination with Fusarium or other toxigenic or non-toxigenic fungi can greatly interfere with the plants’ metabolism and therefore alter the composition of the grains and brewing-related enzymes, besides influencing the safety of the final product ^[4]. Among the most occurring Fusarium mycotoxins recorded in beer are zearalenone (ZEN), type B trichothecenes as nivalenol (NIV), deoxynivalenol (DON), deoxynivalenol-3-glucoside (DON-3-Glc), 3- and 15-acetyl-deoxynivalenol (3Ac- and 15-Ac-DON) and, to a lesser extent, type A trichothecenes such as T-2 and HT-2 toxins ^[5].

2. Fusarium Fungi in Brewing Cereals

Fusarium is a filamentous fungus, introduced for the first time by Link in the year 1809 as Fusisporium (Figure 1) ^[6]. It can produce a vast number of plant diseases, including root or stem rots, cankers, wilts, fruit or seed rots and leaf diseases ^[1]. Fusarium infestation is not limited to a particular region, being equally difficult to control in areas with a temperate climate as well as in tropical areas ^[7]. Cereal crops are mainly affected by grain and seed blights, most often caused by F. graminearum and F. culmorum in wheat and barley, F. verticillioides in maize and F. thapsinum in sorghum, leading to yield losses and mycotoxins production ^[7]. Besides the type of cereal, the adopted agricultural practices together with the weather conditions over each year greatly define the Fusarium population to be developed in each geographical region ^[8]. Some researchers also suspect a considerable modification in both the fungal profile and plants’ response to the infection due to climate change ^[9].

Figure 1. Macroconidia of Fusarium sp.

2.1. Barley

Barley (Hordeum vulgare L.) is an important cereal crop. According to the European Commission (2021), it was characterized by a production of 55.6 million tonnes in 2019 in the European Union only. To be suitable for the brewing industry it must fulfil several conditions, such as a high germination capacity, low protein content, high malt extract and diastatic power, low colour level and a uniformity of the grain size. Kaur, Bowman, Stewart and Evans (2015) ^[10] studied how the fungal community of barley malts from different geographical regions correlated with the quality parameters of these malts. They identified significant differences in the fungal population of barley from South Africa and the countries of the Northern Hemisphere, both quantitatively (abundance of the fungi) and qualitatively (type of fungi). These differences were significantly correlated with the usual quality parameters checked in malting barley.

F. graminearum was commonly considered the main species isolated from FHB cereals; however, F. poae has been also increasingly found in recent years’ surveys ^[11]. Both can produce trichothecenes, proved to be responsible for the aggressiveness or virulence of the fungi in the barley plant ^[12]. DON is the most common mycotoxin in malting barley, followed by ZEN, T-2 and HT-2 toxins ^[13]^[14].

2.2. Wheat

Wheat beer is a special type of beer that is fermented from a mix of malted wheat and barley, where wheat represents at least 50% of the malted cereal, according to the present Provisional Act on Purity of Beer (Vorläufiges Biergesetz). The malting procedure of wheat is similar to the one employed for barley; nonetheless, their differences in composition imply significantly different values required for the important malting and brewing parameters (e.g., shorter immersion time during steeping).

As it is in the case of barley, FHB is the main disease affecting wheat fields and has a negative effect on the malting parameters. The coexistence of up to 20 Fusarium species might be causing it, each of them having a different mycotoxin production profile: F. graminearum and F. culmorum produce DON, NIV and ZEN, F. avenaceum produces moniliformin (MON) and beauvericin (BEA), F. poae mainly produces NIV, T-2 and HT-2 toxins ^[15].

2.3. Sorghum

In the case of sorghum cultivars, Fusarium infestation in the field is part of a complex disease, sorghum grain mold, which also includes genera such as Alternaria, Phoma and Curvularia. An internal infection of the grain can result in the digestion of starch and protein contained in the endosperm, overall softening and decay of the seed and, most importantly for the quality and safety of the product, the synthesis of the mycotoxins into the caryopsis ^[16].

Pink, grey, white or black discolourations are the common symptoms visible on the kernels, together with a reduction in grain size, kernel mass and nutritional quality (decrease in soluble carbohydrates and proteins) up to a complete deterioration of the grains ^[17].

3. Fusarium Mycotoxins Transfer from the Cereals to Industrial-Like Beer

From the technological point of view, beer production is considered one of the more complex and delicate processes in the food industry from both a biochemical and physical perspective. It includes steps such as germination, mashing, boiling and fermentation.

3.1. Malting

Malting is a controlled germination process to produce malt. It consists of three stages (steeping, germination and kilning), which are initiated under specific conditions of humidity and temperature. This is one of the most important production stages for brewing because the quality of the obtained malt will define the quality of the wort and, subsequently, of the beer. aims to create favourable humidity conditions for germination, where the activated enzymes will break starch and proteins. The kilning process inactivates the enzymes before excessive hydrolysis can take place. Additionally, kilning is decisive for flavour and colour formation.

3.2. Mashing and Boiling

Mashing is the mix of coarse ground malt with a high amount of water under specific temperatures to reactivate all the enzymes present and to allow the conversion of starches into fermentable sugars and of the proteins into amino acids. It aims to ensure a correct fermentation process and achieve the proposed technological quality of the product. Mashing is followed by wort separation and boiling, accompanied by hops addition. The following processes take place during boiling: enzyme and microorganism inactivation, protein precipitation, isomerisation of hop α-acid, evaporation of water and undesirable volatile compounds (e.g., dimethyl sulphides), etc.

3.3. Fermentation

Yeast is critical to the beer-making process and specifically, the fermentation stage. Its activity is not only limited to transforming malt sugars into alcohol, but its enzymes are also crucial in shaping beer flavour and aroma by creating volatile compounds such as esters and fusel alcohols. Two fermentation styles are known worldwide: ale (top fermentation) and lager (bottom fermentation), performed by two different strains of Saccharomyces yeast.

4. Fusarium Mycotoxins and Craft Beer

From the perspective of the possible presence of Fusarium mycotoxins, the few surveys analysing the presence of different mycotoxins in craft beers suggest that the main contribution to the final level in the product would be made by the malted and unmalted cereals employed in their production. Peters et al. (2017) ^[18] performed the most extensive survey up to date on the occurrence of different mycotoxins in 1000 beer samples from 47 countries, 60% of which were craft beers. They identified the sum of DON and DON-3-Glc to be above 10 µg/L in 406 samples (40%), 73% of which were craft beers, finding a statistically significant correlation between the %ABV (alcohol by volume) and the toxin concentration. FBs were present in concentrations up to 36 µg/L in the craft beer category of the studied samples, which is still considerably lower compared to the levels reported in traditional African beers, which reached above 1000 µg/L in different areas of the continent ^[19]. The Imperial Stout beers showed the highest contamination levels in all the analysed mycotoxins with 83% positive samples. Nonetheless, it is a beer style that is hardly consumed, even by craft beer enthusiasts, mostly due to its higher alcohol content, price and lower accessibility (complex technological steps require a more unique state of the art and knowledge). The hop-forward beer styles are the most popular among the consumers, representing above 20% of the world craft beer production, among them Indian Pale Ale (IPA), Imperial IPA and New England IPA (NEIPA) with bitterness ranging from 30 to 100 IBU (international bitterness units) ^[20].

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