Research on even more sustainable mycoprotein

The daily consumption of meat, eggs, and dairy is increasingly under scrutiny. For a variety of reasons, more people are turning to alternative protein sources. Mycoprotein is one such alternative. By default it is frozen immediately after production. Can this process be more sustainable? And what about the food safety of these types of products, especially when pioneering the reuse of byproducts from the food industry.

Proteins play a vital role in our metabolism. They affect the feeling of satiety and can keep the immune system vigilant. While we need proteins, they do not necessarily have to come from animal sources. The consumption of plant-based proteins is linked to an improved cardiovascular system (heart and blood vessels) compared to animal proteins, and generally, their environmental impact is lower—a win-win situation.

Properties

Well-known plant-based protein sources include legumes, nuts, seeds, and grains. Potatoes, mushrooms, leafy vegetables, and seaweeds also contain proteins. Emerging alternative protein sources include 'microbial biomass': products made from microorganisms such as unicellular algae, yeasts, and bacteria. Products consisting of fungi, or 'mycoprotein', also fall into this category.

Mycoprotein is produced by cultivating an edible fungus, fermenting it, and then processing it after several heating steps. By allowing the fungus to grow on side-streams from food production (closing loops), it can also be highly sustainable. It is a high-quality protein, rich in fiber, and low in fat, with a neutral taste, which makes it easy to incorporate into dishes or other products.

However, recent outbreaks and recalls of plant-based drinks made from almonds and oats, and plant-based cheese alternatives from nuts and legumes, show that this group of plant-based products is not free from microbiological hazards. According to standards, potential hazards must be identified in the development of a safe food product. The 'Plenitude' research initiative, of which Wageningen Food & Biobased Research is a project partner, investigates the conditions for bringing a microbiologically safe mycoprotein product to the market that is produced more sustainably than before.

Listeria monocytogenes

Mycoprotein has a pH close to neutral and high water activity. The product contains no preservatives. By default, it is frozen, but this is relatively energy-intensive. Storage at refrigerator temperature could be an alternative. As generally applicable to this type of product, human pathogens that enter the food through post-contamination pose relevant microbiological hazards. For example, Listeria monocytogenes, which causes listeriosis. Pregnant women are a risk group because of the potential for premature birth in the event of an infection. The elderly, individuals with weakened immune systems, and young children are also at risk.

Due to this potential hazard, researchers have decided to subject mycoprotein to a challenge test. This revealed that under vacuum storage conditions at 4°C, L. monocytogenes could increase in numbers by 2 log (a factor of 100) within 8 days. Lowering the temperature and/or altering the atmosphere by adding carbon dioxide (CO₂) to packaged mycoprotein slowed the growth but did not prevent multiplication of the bacteria.
This outcome underscores the necessity of applying strict hygiene measures to control post-contamination in these types of products. It is assumed that there is always a risk of cross-contamination. Only a very short shelf life can then guarantee food safety, unless a sufficient heating step (pasteurization) is chosen in the product packaging.

Pathogen control

Other potential hazards in the form of heat-resistant spore-forming bacteria include Clostridium botulinum and Bacillus cereus. C. botulinum can produce botulism toxin, which binds to nerves and causes muscle paralysis. Although this bacterium needs an anaerobic—oxygen-free—environment to grow, even low numbers of C. botulinum can pose a danger. B. cereus can also cause a form of food poisoning through toxin formation. It is assumed that a higher cell level poses a risk: 5 log (10,000 cells) per gram of product.
For both pathogens, some strains can multiply at refrigerator temperature. With extended storage, cold storage of pasteurized mycoprotein alone is not sufficient. One way to control the germination and growth of C. botulinum spores is to apply a 'botulinum cook', a heating step of 10 minutes at 90°C or equivalent, combined with chilled storage. However, this is not sufficient for B. cereus spores.

Within the Plenitude project, research was conducted on methods suitable for inhibiting the growth of specific cold-loving B. cereus strains on mycoprotein by using a modified atmosphere. Adding sufficient CO₂ ensured that no growth of the pathogen was detected for as long as 34 days at storage temperatures of 10°C or lower. At 12°C, growth was slowed. At 15°C or higher, no inhibition was observed. This may be because CO₂ is less soluble at higher temperatures. It seems that CO₂ suppresses the action of specific enzymes that may play a more active role in the bacteria when B. cereus is exposed to cold temperatures.

Microbiologically safe

This study demonstrates that L. monocytogenes through post-contamination poses a hazard in mycoprotein. Adjusting the process conditions can safeguard this pathogen as well as C. botulinum. Control of B. cereus is possible through MAP with sufficient CO₂ combined with cold storage. It has been shown that mycoprotein can be stored microbiologically safely; using byproducts, without freezing, and without the addition of additives.

Sources:

HTTPS://WWW.WUR.NL/NL/ONDERZOEK-RESULTATEN/ONDERZOEKSPROJECTEN-LNV/SOORTEN-ONDERZOEK/KENNISONLINE/PLENITUDE.HTM
FERRARI ET AL. 2022, HTTPS://DOI.ORG/10.3390/NU14235115
BANACH ET AL. 2022, HTTPS://DOI.ORG/10.1080/10408398.2022.2089625 
VAN BOKHORST-VAN DE VEEN ET AL. MICROORGANISMS RELEVANT FOR SAFETY AND SPOILAGE OF MYCOPROTEIN UNDER DIFFERENT THERMAL TREATMENTS AND PACKAGING CONDITIONS, AND FLAVOR CHANGES AS A RESULT OF THOSE TREATMENTS; submitted to a scientific journal.