Prevalence of mycotoxins in food by-products

The transition to a circular economy requires the prevention of microbiological and chemical risks to guarantee the physicochemical and microbiological stability of reused food by-products. Sustainable solutions for their management remain a great challenge for several industries, mainly due to their potential contamination by mycotoxins, which are natural toxins produced by diverse fungi as secondary metabolites. Aflatoxins (AFs), Ochratoxins (OTs), Fumonisins (FBs), Zearalenone (ZEA), and Trichothecenes constitute the main toxins that have been described to potentially occur in a variety of foods, from crops to animal products, but with limited information on their counterpart by-products.

A review study* summarises studies on the assessment of mycotoxins in food by-products commonly used for animal feed, namely distiller dried grain with solubles (DDGS), brewer’s spent grain and yeast, grape pomace, and sugar beet pulp. In brief, researchers in this study published in the journal Toxins highlight the prevalence of mycotoxins in food by-products and indicate the gap in the mycotoxin legislation limits of the by-products as extrapolated from the corresponding food materials.

Distiller Dried Grain with Solubles (DDGS)

DDGS is the main by-product of the distilled ethanol industry (beverage or biofuel), being the ground residue of cereal grains, such as maize, rice, and other grains, that are left over after ethanol production via the grains’ starch. The assessment of mycotoxins in DDGS revealed high levels of contamination despite its relatively low moisture content (7.1%). A variable degree of DDGS contamination was reported. Despite this variability, the most significant content appeared to occur for Fumonisin B1 (FB1) and Fumonisin B2 (FB2), Deoxynivalenol (DON), Zearalenone (ZEA), and Beauvericin (BEA), while high variability was observed in Aflatoxins. The 3 most prevalent mycotoxins were:

• ZEA (35%, average 167.6 µg/kg),
• DON (29%, average 3.0 mg/kg), and
• FBs (25%, average 1.0 mg/kg).

Other articles showed the existence of co-contamination with 30% of samples being contaminated with 2 mycotoxins, and 9% with 3 or more mycotoxins; in these samples, toxin levels were generally high, with mean levels of 9080.0 µg/kg for FB1, 5950.0 µg/kg for FB2, 1160.0 µg/kg for DON, 910.0 µg/kg for ZEA, and 350.0 µg/kg for BEA.

Brewer’s Spent Grain (BSG) and Yeast (BSY)

BSG and BSY are by-products of the brewing industry. When analysed for Aflatoxin (AFs) content, BSY and BSG samples from EU breweries contained only trace levels of AFs. The researchers suggest that EU-derived BSG and yeast could be considered for the development of new food products. Higher content of AFB1 was assessed in BSG samples of Argentinian origin and the following was discovered:

• AFB1 content in fresh BSG samples had an average level of 11.76 µg/kg and 57% prevalence, which increased up to 257.0 µg/kg after seven days of storage;
• AFB1 in BSG destined for pig feed revealed 50.4 µg/kg with a prevalence of 31.3% .

A survey on the presence of Fumonisins (FBs) in BSG from Brazil destined for inclusion in dairy cattle feed revealed that approximately 72.5% of all samples (out of a total of 80) were contaminated with FBs, with average levels of 227.0 µg/kg. 10 samples of Brazilian BSG and BSY were also evaluated for their DON and ZEA contents. BSG samples presented an average of 1068.0 µg/kg, and DON and ZEA showed an average of 1429.0 µg/kg, respectively, while BSY contained 166.0 µg/kg of DON and no ZEA contamination.

Grape pomace (GP)

Grape pomace is the wine-making industries’ main by-product, representing 20–30% of waste generated during the wine-making process in the form of skin, some pulp, stalks, and grape seeds. It is a by-product rich in carbohydrates, protein, and phenolics. However, it is currently mainly used in low-value applications, such as animal feeds, due to its high moisture content (58–82%). In piglet diets, the inclusion of grape pomace benefits overall blood constituent metabolism and helps maintain piglet health by increasing the polyphenol content in blood plasma and antioxidant activity in the liver, spleen, and kidneys. In the current study, the OTA prevalence in grape pomace was high as the occurrence was detected in 12 of the 13 analysed samples; however, trace levels of OTA were quantified with a mean concentration of 0.07 µg/kg.

Sugar beet pulp (SBP)

In the last few years, sugar beets have risen as an alternative to sugarcane in the production of sugar. SBP is a sugar-depleted sugar beet by-product which is rich in carbohydrates and protein. It possesses a high moisture content and becomes a burden to store and properly use, and, thus, rarely has applications beyond animal feeding. In the current study, the presence of various mycotoxins was observed; 40 samples from 5 regions in France were analysed for their content of AFB1, OTA, DON, ZEA, patulin (PTL), mycophenolic (MPA), roquefortine C (RQC), gliotoxin (GLT), and penicillic acid (PEA). The results showed that only 8 out of 40 samples were found to be positive, thus indicating that 80% of samples were free from any mycotoxin contamination. In the contaminated samples, ZEA and MPA were the most prevalent. ZEA was found in three samples at concentrations of 1023, 4862, and 6916 µg/kg, whereas MPA was found in five samples (up to 1436 µg/kg) and OTA was detected in one sample at 15 µg/kg.

Mycotoxin legislation on food by-products

The European Commission, which has established maximum permitted levels of mycotoxins in different foodstuffs, has provided guidance values concerning maximum mycotoxins in animal feeds, but, according to the researchers, no legislation exists regarding the mycotoxin content in food by-products. The researchers suggested the establishment of mycotoxin legislation for food by-products, including legislation for emerging mycotoxins such as Mycophenolic acid, Roquefortine C, Gliotoxin, and Patulin, among others. Besides the legislation, it was also suggested that there should be strict and efficient strategies that reduce mould growth, as well as hygienic precautions to prevent mycotoxins during by-product storage.

The by-products that were assessed had a high mycotoxin prevalence which, in most cases, exceeded the limits established for human consumption, which is a drawback for their reliable valorisation and may hamper their range of applications as ingredients in the food and feed industry. It was concluded that the mycotoxins commonly occurring in food industry by-products are Aflatoxin B1, Ochratoxin A, Fumonisins, Deoxynivalenol, and Zearalenone.

*This article is based on an original article by Paloma Lopes, M. Madalena C. Sobral, Guido R. Lopes, Zita E. Martins, Claúdia P. Passos, Sílvia Petronilho, and Isabel M. P. L. V. O. Ferreira. 2023. Mycotoxins’ Prevalence in Food Industry By-Products: A Systematic Review. Toxins, Vol 15: 249.