Consumer interest in plant-based foods has increased rapidly in the past decade. This growth is not solely driven by increased rates of vegan and vegetarian diets in the population. Rather, consumer demand in this category is fueled by various trends, including environmental sustainability concerns, desire for variety in protein sources, and animal welfare concerns.^1,2

In recent years, significant innovation has resulted in the development of plant-based meat alternatives that aim to mimic the texture, mouthfeel, and feeling of satiety provided by animal-derived foods. Perhaps the prime example of this is the launch of plant-based burger patties and breaded nuggets by food manufacturers who aim to create products that are close to indistinguishable to traditional beef or chicken products.

The rapid rise of plant-based meat alternatives means that knowledge of the food safety risks of these products is still limited. In particular, microbial growth and inactivation kinetics, well known and long established in traditional meat and poultry products, is not well understood in relation to the variety of protein sources and matrices that have been developed in recent years. Additionally, consumers face a learning curve in understanding how to safely handle plant-based meat alternatives.

General Process

Production of plant-based meat alternative products starts with the extraction of the protein source from plants. The extracted proteins may be processed further (e.g., by hydrolysis) to improve functionality. Proteins are then combined with other dry and wet ingredients and extruded, whereby the mixture is forced through a barrel via a screw system and then released out of a small opening (die). The combination of thermal and mechanical stress during extrusion produces a product with an altered protein structure that mimics the texture of meat. Conditions of extrusion and cooling die setup can be varied to produce the desired product.³

In the case of plant-based burger patties, the extruded protein is ground up and mixed with binders, additives, flavors, and colors to achieve the desired texture, look, and mouthfeel. Nutrients also may be added to boost the nutrient profile. Cutting, forming, and/or shaping is then performed to produce the product's desired format.^4,5 For breaded products, the formed product is coated in a batter and breading layer prior to a par-fry process to set the breading. Many plant-based meat alternative products are packed and distributed frozen to maintain quality and a long shelf life. Products intended for a refrigerated shelf life are often packaged in modified atmosphere packaging (MAP) or vacuum-packed to prevent growth of aerobic spoilage bacteria and molds.

Each of the steps during manufacturing and distribution introduce potential challenges and opportunities for maintaining food safety and quality of plant-based meat alternative products.

Raw Materials

Manufacturers of plant-based meat alternatives generally strive to formulate a product that simulates the look and mouthfeel of a traditional meat or poultry product. Product texture is of particular importance. To mimic the texture of meat, plant proteins must be bound together in a way that simulates muscle fibers and the interstitial spaces between them. The sensation of juiciness comes from the release of water that is trapped between the fibers.⁵

Protein from soy and pea are commonly used plant proteins, but a range of other plant proteins are also used, including mycoprotein, wheat gluten, mung bean, fava bean, chickpea, potato, and rice proteins. The different plant proteins provide a range of functional properties that are important in creating the structure and mouthfeel of the finished product.⁶ This is a landscape that is constantly evolving, as new protein sources become available at a consistent industrial scale and as consumer trends and demands evolve. Mixtures of proteins in a product can be beneficial to enhance texture and to improve the amino acid profile for more balanced nutrition. It also brings more complexity, especially with challenges in ensuring continuous supply of raw materials. As the number of ingredients grows, so do the potential sources of microorganisms to the product. As such, the microorganisms present in plant-based meat alternative products may vary significantly from those found in traditional meat products. This issue is exacerbated by the different nutrient profile of plant-based meat alternatives, which will affect the types of microorganisms that thrive and create spoilage and/or food safety challenges over shelf life.

Protein sources can also provide quality and food safety challenges. In times of high demand, the availability of plant-based protein sources may be limited, leading to variability in ingredient quality. To ensure consistent supply at an industrial scale, food manufacturers may source proteins from new and various suppliers and regions around the world. An impact of sourcing from different areas of the world is that moisture levels, microbiological load, and even pH of material may be affected and vary widely. Each of these factors can impact the effectiveness of downstream food safety controls, such as thermal processing and product hurdle system for maintaining refrigerated shelf life.

Factory Hygiene

While hygienic conditions in a facility producing plant-based meat alternatives need not be substantially different from those in traditional food processing environments, some specific challenges may be experienced. During the surge of consumer demand in plant-based meat alternatives in recent years, many large, established food producers added new lines to existing factories or retooled existing lines to make plant-based products.

A number of challenges are presented in this scenario. New allergens may be introduced to the facility, adding complexity and requiring an update to the allergen management plan, including validated cleaning and sanitation. Effect on culture within a facility must be considered and an appropriate management plan should be in place to prepare employees for the production of a new product that may be significantly different to that currently produced. Vegan certification and regulatory considerations may be impacted when adding a non-meat product into a facility or line that traditionally produces meat products. Lastly, in the case of products with refrigerated shelf life, new food safety hurdle systems may be introduced, requiring significant focus on process capability to ensure appropriate application and consistent distribution throughout the product.

Microbiological Concerns During Refrigerated Shelf Life

The microbial load of plant-based meat alternative products tends to be relatively low at the start of shelf life in comparison to their traditional meat counterparts, likely due to the thermal processing applied to the ingredients.^7,8 A challenge for maintaining food safety and quality of plant-based meat alternatives is due to the intrinsic properties of these products. With pH often ranging from 6.0–7.0 and water activity > 0.98, plus high protein and high moisture content, these products provide ideal conditions for rapid microbial growth and are prone to microbial and enzymatic spoilage.⁹

Refrigerated shelf life may be maximized by incorporating frozen distribution of product prior to retail display. In the U.S., products may be frozen at the manufacturer for distribution and then thawed by retailers as they transfer to the refrigerated display case, where the refrigerated shelf life date is applied in the form of a date label. In other regions around the world, bulk product is distributed frozen to co-packers, where it is packed into the final retail pack with the chilled use-by date printed on the label and immediately slacked (refrigerated) for refrigerated distribution to retail stores.

Identifying microorganisms of concern can be challenging in plant-based meat alternatives due to the range of ingredients added compared to traditional meats. Product spoilage during refrigerated storage is commonly caused by lactic acid bacteria and yeasts, especially in vacuum packaging or MAP. Mold spoilage is more common in products with lower water activity and/or if oxygen is present in the atmosphere inside the package. Appropriate controls should be implemented to inhibit microbial growth and maintain a suitable refrigerated shelf life.

Plant-based meat alternatives are not exempt from contamination via microbial pathogens. Incoming plant-based dry raw materials may be a source of bacterial spores that have survived the thermal processing steps during manufacture. A recent study investigated the prevalence of Clostridium botulinum in frozen and chilled plant-based sausages sampled in retail locations in Finland and Germany.¹⁰ Of 74 vegetarian sausages sampled, 32 percent were found to contain C. botulinum, including Group I (proteolytic) and Group II (non-proteolytic, capable of growth at refrigerated temperatures). The ability of C. botulinum to grow and produce neurotoxin in the products was not determined; however, the study indicates the need for food producers to evaluate C. botulinum as a potential food safety hazard.

The processing environment, often kept chilled to ensure optimal product quality, may lend itself to potential contamination by Listeria monocytogenes. Recent outbreaks and recalls of plant-based food products highlight the potential for microbial contamination, and the need to implement appropriate processing controls and hurdle formulation to prevent outgrowth during shelf life.^11–17

Use of Hurdles in Product Design

Control of pathogen growth during refrigerated shelf life is a critical aspect of product design. Yet many consumers are already concerned that plant-based meat alternatives are highly processed. Use of artificial preservatives may be viewed negatively by consumers, especially in this product category, which is marketed as a positive alternative to meat. Thus, the demand for natural preservatives remains high. Innovative ingredients that meet this need continue to be developed, with the goal of achieving an effective microbiological hurdle that maintains maximum refrigerated shelf life without additional labeling.

Finding the appropriate ingredient that can contribute to the hurdle system without imparting a significant flavor is a challenge. Organic acids, cultured dextrose, extracts from different plant sources, and combinations of these ingredients are only a few examples of the increasing options commonly added to form a hurdle system in plant-based meat alternatives.

Of the organic acids, acetic acid is commonly used. While providing an effective antimicrobial effect against pathogen growth, it also increases sourness. Modified vinegar products, including buffered or powdered vinegars, have a more neutral pH, which allows them to be used in foods while imparting a lower impact on taste. The pH of modified vinegar is increased by the addition of a buffering agent. The reaction between the buffering agent and the acetic acid in vinegar forms acetate and increases pH.¹⁸ The acetate, remaining acetic acid, and pH in the product combine as an effective preservative with lower taste impact on a food compared to vinegar alone.

There are several considerations when using modified vinegar. First, there is still a sensory impact resulting from its use; modified vinegar may contribute a sour note to the product. Second, plant-based meat alternatives are well-buffered systems, and in order to achieve acceptable preservation, a substantial amount may need to be added to the product. This impacts the cost of the finished product and the taste profile in the form of increased sourness.

The third consideration is the regulatory impact. Some regions of the world require specific labeling for these products. The U.S. Department of Agriculture (USDA) states, "Buffered vinegar can be labeled as vinegar without declaring the individual buffering agents used, because those buffering agents are considered as processing aids."¹⁹ Different approaches are taken in other parts of the world, where modified vinegar is to be specifically labeled so that consumers understand that this ingredient differs from regular vinegar.

Ingredient companies continue to develop promising natural preservatives, but challenges remain prior to their widespread use. Some ingredients have significant taste impact, which is often unacceptable in products aiming to imitate the taste of meat. Flavor systems (providing the "meat" taste to plant-based alternatives) may weaken over refrigerated storage, revealing flavor notes from the plant-based proteins and/or preservatives, which often impart acidic, fruit, or floral notes.

Validation of Microbial Hurdles

Inoculated challenge studies may be required to confirm and understand efficacy against microbial growth during refrigerated shelf life. Such studies will be the responsibility of the producer of the finished product, since efficacy of a preservative may vary across different products with different formulations.

Predictive modeling can provide a useful tool for estimating potential microbial growth during refrigerated shelf life, but may not be fully relied upon if the tool has not been validated in the product of interest. The EU Reference Laboratory (EURL) for Listeria monocytogenes published a technical guidance document providing useful guidance to follow in designing a challenge study and using predictive modeling to assess pathogen growth potential.²⁰

Knowledge of the chilled distribution system of the product is required so that the conditions of storage can be accurately represented in the study. This is particularly important when designing products to be distributed in different regions of the world that may employ different levels of temperature control during distribution. Acceptable distribution and storage temperatures vary depending on market and customer requirements, and deviations to these temperatures must be considered when designing shelf life and inoculated challenge studies.

Consumer Use

Plant-based meat products that are sold refrigerated are primarily positioned in the meat section in retailers, which likely signals to a consumer that these products are to be handled in the same manner as their meat-containing counterparts. As the category matures, this placement may change. Marketing is a critical aspect of the communication to consumers on how to safely handle and prepare the products. Consumers' views regarding safety of plant-based meat alternatives will vary, and may consider these products safe to consume if not cooked or undercooked due to the plant-based description and health-related benefits marketed for these products.²¹

Consumer preparation instructions vary across the range of products on the market. This is primarily due to the variability in products between manufacturers. Factors that may affect the preparation instructions include protein source and nutrient content, serving size, product shape and thickness, as well as quality attributes specified by each manufacturer to ensure optimal sensorial experience for the consumer.

As this product category continues to grow and innovate further, the food industry should work closely with academia and regulatory authorities to build and share knowledge regarding the food safety risks posed by plant-based meat alternatives. This will foster a collaborative approach to addressing industry-wide issues and ensure a foundation of science-based risk mitigation tools that can be employed to support manufactures as they continue to innovate and design new products to meet consumer demand.

References

1. Elkin, E. "Plant-based food sales are expected to increase fivefold by 2030." August 11, 2021. https://fortune.com/2021/08/11/plant-based-food-sales-meat-dairy-alternatives-increase-by-2030/.
2. Szenderák, J., D. Fróna, and M. Rákos. "Consumer Acceptance of Plant-Based Meat Substitutes: A Narrative Review." Foods 11, no. 9 (April 27, 2022): 1274. https://doi.org/10.3390/foods11091274.
3. McHugh, T. "How Plant-Based Meat and Seafood Are Processed." Food Technology Magazine. October 1, 2019. https://www.ift.org/news-and-publications/food-technology-magazine/issues/2019/october/columns/processing-how-plant-based-meat-and-seafood-are-processed.
4. Rubio, N.R., N. Xiang, and D.L. Kaplan. "Plant-based and cell-based approaches to meat production." Nature Communications 11 (2020): 6276. https://doi.org/10.1038/s41467-020-20061-y.
5. Caldwell, J.M. "How Safe Are Plant-Based Meat Alternatives?" Food Technology Magazine. February 1, 2021. https://www.ift.org/news-and-publications/food-technology-magazine/issues/2021/february/columns/food-safety-and-quality-how-safe-are-plant-based-meat-alternatives.
6. Ahmad, M., S. Qureshi, M.H. Akbar, S.A. Siddiqui, A. Gani, M. Mushtaq, I. Hassan, and S.B. Dhull. "Plant-based meat alternatives: Compositional analysis, current development and challenges. Applied Food Research 2, no. 2 (December 2022): 100154. https://doi.org/10.1016/j.afres.2022.100154.
7. Geeraerts, W., L. De Vuyst, and F. Leroy. "Ready-to-eat meat alternatives, a study of their associated bacterial communities." Food Bioscience 37 (October 2020): 100681. https://doi.org/10.1016/j.fbio.2020.100681.
8. Tóth, A.J., A. Dunay, M. Battay, C.B. Illés, A. Bittsánszky, and M. Süth. "Microbial Spoilage of Plant-Based Meat Analogues." Applied Sciences 11, no. 18 (September 8, 2021): 8309. https://doi.org/10.3390/app11188309.
9. Liu, Z., M. Shaposhnikov, S. Zhuang, T. Tu, H. Wang, and L. Wang. "Growth and survival of common spoilage and pathogenic bacteria in ground beef and plant-based meat analogues. Food Research International 164 (February 2023): 112408. https://www.sciencedirect.com/science/article/pii/S0963996922014661.
10. Pernu, N., R. Keto-Timonen, M. Lindström, and H. Korkeala. "High prevalence of Clostridium botulinum in vegetarian sausages." Food Microbiology 91 (October 2020): 103512. https://doi.org/10.1016/j.fm.2020.103512.
11. U.S. Food and Drug Administration (FDA). "Lavva Voluntarily Recalls a Single Lot of Blueberry Plant-Based Yogurt." January 11, 2021. https://www.fda.gov/safety/recalls-market-withdrawals-safety-alerts/lavva-voluntarily-recalls-single-lot-blueberry-plant-based-yogurt.
12. FDA. "Outbreak Investigation of Salmonella: Jule's Cashew Brie (April 2021)." July 7, 2021. https://www.fda.gov/food/outbreaks-foodborne-illness/outbreak-investigation-salmonella-jules-cashew-brie-april-2021.
13. FDA. "Lyons Magnus Expands Voluntary Recall to Include Additional Nutritional and Beverage Products Due to the Potential for Microbial Contamination." August 16, 2022. https://www.fda.gov/safety/recalls-market-withdrawals-safety-alerts/lyons-magnus-expands-voluntary-recall-include-additional-nutritional-and-beverage-products-due.
14. EU Rapid Alert System for Food and Feed (RASFF). "Notification 2022.2311: Listeria monocytogenes in vegan organic cheese alternative from France." Notified April 20, 2022. https://webgate.ec.europa.eu/rasff-window/screen/notification/545435.
15. FDA. "Reckitt Recalls Two Batches of Prosobee 12.9 oz Simply Plant Based Infant Formula Because of Possible Health Risk." February 20, 2023. https://www.fda.gov/safety/recalls-market-withdrawals-safety-alerts/reckitt-recalls-two-batches-prosobee-129-oz-simply-plant-based-infant-formula-because-possible.
16. Food Standards Australia New Zealand (FSANZ). "JS Health x Inside Out Almond Milk and Oat Milk 1 L." February 16, 2023. https://www.foodstandards.gov.au/food-recalls/recalls/Inside-Out-Almond-Milk-Collagen-Calcium-Prebiotics-1-L.
17. RASFF. "Notification 2023.0500: Listeria monocytogenes in vegan organic cheese and foie gras alternative." Notified January 20, 2023. https://webgate.ec.europa.eu/rasff-window/screen/notification/591930.
18. Health Canada. "Health Canada's Proposal to Enable the Use of Modified Vinegar as a Preservative in Certain Meat and Poultry Products and Preparations." December 22, 2020. https://www.canada.ca/en/health-canada/services/food-nutrition/public-involvement-partnerships/notice-proposal-enable-use-modified-vinegar-preservative-meat-poultry-products-preparation/document.html.
19. U.S. Department of Agriculture (USDA). "askFSIS Public Q&A: Buffered Vinegar as an Antimicrobial: Part 2 of 2." January 31, 2023. https://ask.usda.gov/s/article/Buffered-Vinegar-as-an-Antimicrobial-Part-2-of-2.
20. EU Reference Laboratory (EURL). "EURL technical guidance document on challenge tests and durability studies for assessing shelf-life of ready-to-eat foods related to Listeria monocytogenes." Version 4. July 1, 2021. https://food.ec.europa.eu/system/files/2021-07/biosafety_fh_mc_tech-guide-doc_listeria-in-rte-foods_en_0.pdf.
21. USDA. "For Safety's Sake, Handle Plant-Based Meat Alternatives Safely." July 27, 2022. https://www.usda.gov/media/blog/2022/07/27/safetys-sake-handle-plant-based-meat-alternatives-safely.

Stephen F. Grove, Ph.D., is the Senior Manager, Food Safety at McCain Foods. He provides technical food safety and microbiology leadership to support new product innovation, and he co-leads the Food Safety and Quality Culture Committee for McCain North America.