How Safe Are My Plant Proteins?

The world population is estimated to reach around 10 billion by 2050. As the global demand for proteins grows, producing sustainable and nutritional alternative proteins will shape the future of the food industry. Consumers are including more alternative proteins in their diet. Among the alternatives, plant-based proteins have the highest acceptance rate compared to meat from animals, whereas insect-based proteins have the lowest rate.

As food companies invest more time and resources in developing a variety of alternative protein products to meet consumer demand, sourcing and incorporating optimal plant-based ingredients is key. Most commonly, texturized vegetable proteins (TVP) are used as a potential replacement for conventional meat and to emulate animal-based meat sensorial properties. Since plant-based proteins in their unprocessed form do not have the same texture, mouthfeel, or fullness as animal-based proteins, food companies combine binders, additives, and functional ingredients with plant protein sources to create meat-like sensory characteristics.

Product developers have multiple options when innovating alternative plant protein products. Soy, pea, and wheat proteins are the most used plant protein sources for food product formulation. Proteins from potato, mung bean, and rice are used to enhance texture. Plant-based oils such as sunflower, canola, and sesame oils, and fats extracted from coconut and cocoa beans are added to create mouthfeel and a marbling effect. Crude fibers, starches, and hydrocolloids are included to bind water and reduce syneresis. Functional ingredients such as yeast extract, pigments, sugars, and spices are added for flavor, color, and texture. Carrageenan derived from seaweed is commonly used as a thickening, gelling, or stabilizing agent. Potassium carbonate and alginate are used to achieve sensorial properties of plant-based meat that are comparable to meat.

Plant-based ingredients also are used to promote other desired outcomes in the final product. For example, some plant-based ingredients may be included in formulations to mask the strong off-flavors produced during processing of soybeans. Vitamins B12 and D, calcium, zinc, iron, and long-chained n-3 (omega-3) fatty acids also are incorporated to increase the nutritional value of plant-based proteins. Antioxidants are added to reduce rancidity during storage. Organic acids and phosphates are used to extend the shelf life.

However, as novel plant-based protein foods are developed, many new safety, quality, and nutritional challenges arise. For example, unlike meat products, plant-based proteins may contain multiple allergens at high levels. In addition, microorganisms that are common in plant-based ingredients may pose the risk of growth and toxin production in finished products. Product developers should be aware of several potential food safety risks and quality concerns when designing, formulating, and testing plant-based products to help prevent processing and storage issues later in production.

Microbiological Risks and Watchouts

Recent foodborne illness outbreaks show the importance of considering the microbiology of plant-based ingredients. In 2022, a plant-based cheese brand was linked to five cases of Listeria infections in France, Germany, Belgium, and the Netherlands. No related deaths have been reported, but the five cases included four pregnant women who gave birth prematurely. In 2016, a multistate outbreak of Salmonella Virchow infections was linked to a low-moisture powdered meal replacement containing about 40 raw organic ingredients, including plant-based proteins (Gambino-Shirley et al. 2018).

Many plant-based proteins come from crops such as legumes, seeds, grains, and tubers that are sourced close to the soil and can be contaminated with a large spectrum of microorganisms that were initially present in raw products or from the environment. A range of other microorganisms can be introduced to food during harvesting, as well as during processing and storage. The addition of multiple plant-based ingredients and other ingredients may introduce new pathogens and spoilage organisms that are not commonly found in animal-based meats.

A high protein and moisture content, as well as a near neutral pH, make most plant-based protein alternatives susceptible to microbiological growth. Both foodborne pathogens such as Salmonella, Escherichia coli, L. monocytogenes, S. aureus, B. cereus, and C. botulinum and spoilage microorganisms such as lactic acid bacteria, yeasts, and molds may be introduced into plant-based protein with contaminated raw materials or in a poor hygienic processing environment. These microorganisms can grow if products are handled and stored under abuse conditions. S. aureus and spore-forming bacteria C. botulinum and Bacillus cereus may produce heat-stable toxins that can survive even high heat treatments. C. botulinum is ubiquitously distributed in soils and detected in plants. Plant-based meat analogues provide the nutritional requirements for the growth of C. botulinum. Vacuum-packaged products especially pose a high risk of C. botulinum growth and toxin production.

Among the risks that product developers should consider are microbial contaminants, processing, and cooking.

Microbiological Contaminants. In 2010, Salmonella Tennessee was identified in a hydrolyzed vegetable protein that is used in other products. Staphylococcus species have been identified in plant-based ingredients, indicating possible post-process contamination. In a survey, elevated levels of B. cereus were found in 4.1% of the plant-based protein powder samples in the range of 100–10,000 CFU/g. C. perfringens was found in 0.8% of the plant-based protein powder samples in the range of 100 to 1,000 CFU/g (CFIA 2019).

Some studies have reported the high prevalence of Enterococcus faecium and Enterobacteriaceae, indicating a post-process contamination of heat-treated plant-based meat alternatives. A survey of commercial tofu in the Netherlands showed that the aerobic plate counts were above 10⁶ CFU/g in 95% of the samples, Enterobacteriaceae exceeded 10³ CFU/g in 86% of the samples, and the number of E. coli was above 10² CFU/g in 36% of the samples. Yersinia enterocolitica was detected in 11% of the samples. B. cereus was identified in one of 154 samples and S. aureus in another, at levels above 10⁵ CFU/g (van Kooij and de Boer 1985).

Geeraerts et al. (2020) showed that bacterial counts in vegetarian, vegan, and insect imitations of meat products were relatively low but ranged from <2.0 to 8.7 log CFU/g. Vegetarian and vegan meat substitutes consisted primarily of Lactobacillus sakei, E. faecium, and Carnobacterium divergens. The insect-derived product mainly contained E. faecium, besides the presence of Macrococcus caseolyticus and Cronobacter sakazakii.

Processing. The process of transforming plant proteins into meat-like proteins requires several major processing steps. TVP alternatives are extruded at a high temperature and high pressure to create the desired texture. Novel plant ingredients may require milder processing as high temperature treatments may adversely affect the functional or nutritional properties. While the microbiological load is reduced during the process (e.g., <100 CFU/g), plant-based meat alternatives are susceptible to post-processing contamination with pathogens. Besides, endospores such as Bacillus and Clostridium may survive thermal processes. Especially in low-moisture protein powders, bacterial pathogens such as Salmonella. Listeria, Cronobacter, and Bacillus can survive for extended periods of time during storage. These pathogens pose a potential health risk for foodborne illnesses if these products are consumed without further processing.

Cooking. Plant-based meat alternatives should be handled just like raw meat products since plants can contain high levels of foodborne pathogens. Thermal processing at the manufacturing facility or proper cooking at the restaurant or home prior to consumption is crucial to ensure that they are microbiologically safe to consume. Plant-based burgers should be cooked to the internal temperature of 160°F (71.1°C) just like raw beef burgers.

Protein Quality and Other Watchouts

While consumers are looking to increase their consumption of plant proteins in their diets, essential nutrients may be missing from a vegetarian diet. To evaluate protein quality, a joint FAO/WHO Expert Consultation on Protein Quality Evaluation developed the Protein Digestibility Corrected Amino Acid Score (PDCAAS). This scoring method is based on the essential amino acid requirements of preschool-aged children. PDCAAS results either are expressed as decimals or multiplied by 100. PDCAAS scores less than 1.0 (i.e., <100%) indicate that the protein is suboptimal. The PDCAAS of most animal-based protein sources, such as milk and whey, are at or very near 1.00. Plant proteins, however, may have insufficient amounts of indispensable amino acids. The PDCAAS score for soy protein isolate is near 1.0, while the reported values for peas are in the range of 0.66–0.91, lentils 0.68–0.80, and wheat 0.45–0.54.

In addition to PDCAAS scores, other risk factors that product developers should consider when using plant-based ingredients include:

Allergens. Besides nine major food allergens in the United States, more than 160 foods have been identified as causing food allergies in sensitive individuals. Most plant-based proteins contain at least one food allergen among their ingredients. Soy, wheat, pea, and lupin proteins are known allergens. In many plant-based meat alternatives, high levels of protein isolates such as soy protein isolates (containing >90% soy protein) and soy protein concentrates (70%–90% soy protein) are present, resulting in much higher levels of allergens.

Gut Microbiomes. A plant-based diet appears to promote the development of diverse and stable gut microbiomes. However, it is uncertain how ultra-processed plant-based meat alternatives might affect gut microbiota composition. For example, carrageenan, a polysaccharide used as a thickening, gelling, or stabilizing agent, may cause gastrointestinal inflammation and alterations in intestinal microflora.

Fat, Sodium, and Antinutritional. Some meat analogues have relatively high amounts of sodium compared to unprocessed meats. Plant-based products formulated with high levels of coconut oil may have saturated fat levels comparable to or higher than meat products. Plants contain antinutritional protein inhibitors. For example, phytic acids in legumes can reduce the bioavailability of minerals through the formation of indigestible salts.

Other Risks. Carcinogens such as polycyclic aromatic hydrocarbons, nitrosamines, and heterocyclic aromatic amines are produced in meats cooked at high temperatures and may also occur in plant-based meat products. Heavy metals, pesticides, aflatoxins, and hexanes used in processing soy protein isolates are chemical contaminants of concern in plant-based meat alternatives.

Conclusion

Ultimately, it is imperative that food quality and safety is considered at every stage of the food chain, from the ingredients to the formulation, the process, the finished product, the packaging, and all points along the distribution chain.