Minimally-Processed Dog Foods
Minimally-processed pet foods are increasing in popularity among dog owners. One sub-category of these foods is raw meat-based diets (aka RMBDs). I have reviewed the current science regarding the safety of these products in previous Science Dog essays (see The Raw Deal and Freeze-dried). In a nutshell, evidence from multiple studies supports a conclusion that because of the inclusion of unprocessed meats from a variety of sources, raw pet foods are at greater risk for microbial contamination, when compared with traditional heat-processed foods.
Although they continue to represent a small portion of the pet food market, raw pet foods are definitely here to stay. The challenge therefore lies in finding non-thermal processing approaches that effectively minimize the safety risks to dogs and humans, yet preserve nutrient integrity and other desired “raw” qualities of these foods.
Recently, Dr. Greg Aldrich of Kansas State University and his graduate student Samuel Kiprotich conducted a systematic review of published studies that examine the use of preservative methods that may be effective with raw food products (1). Let’s review the approaches that are available and where we currently stand with making use of these with raw dog foods.
High Pressure Pasteurization (HPP)
HPP is a non-thermal food processing technique that has been used in the human food industry for many years. Products that are routinely treated with HPP include ready-to-eat meats and meals, fruit juices, packaged dips, and jams and jellies. This type of processing uses high hydrostatic pressure from water compression to process foods without using heat.
In the pet food industry, HPP may be used with raw (frozen), freeze-dried, and most recently, fresh-frozen/gently cooked foods. Microorganisms that are most sensitive to destruction by HPP are molds, yeast and parasites. In contrast, bacteria require higher levels of pressure for inactivation. Currently, both the FDA and the USDA identify HPP as the preferred method for ensuring food safety in raw pet foods (see HPP for more details).
Benefits of HPP
HPP treatment ensures uniform distribution of pressure throughout a product, a feature that improves its effectiveness at controlling contamination. Although there are only a few studies available with RMBDs, the evidence that we currently have shows that HPP effectively reduces (but does not completely eliminate) microbial contamination in raw foods, and can have minimal impact upon food quality characteristics such as flavor, texture and nutrient integrity.
Limitations of HPP
HPP has been found to be more effective at controlling contamination and spoilage when applied to whole chunks/meat cuts than when used with ground/pulverized products. This is an important observation because the majority of commercial raw pet foods are prepared by grinding all of the ingredients into a batter and then forming the batter into patties or chubs (rolls).
Because grinding can distribute microbes throughout a mixture, this type of production necessitates the use of higher pressures to effectively preserve the food. This in turn leads to higher energy/cost inputs for companies and may render HPP to be cost prohibitive. Using very high pressures may also lead to unwanted alterations to food quality, such as off colors and textures, and an increased rate of lipid oxidation (degradation) in the food.
The antimicrobial effects of compounds called organic acidulants have also been studied. These agents are used extensively in human food preparation and are included on the FDA’s Generally Regarded as Safe (GRAS) list. Examples include lactic acid, citric acid, and short-chain fatty acids such as propionic and acetic acid. Organic acidulants exert their antimicrobial action through reductions in product pH, which in turn leads to various negative effects on bacterial cell membranes. In the human food industry, organic acids have been well-studied and are known to effectively reduce contamination to meat surfaces. However, once again, when meats are ground, this poses additional challenges. Similar to HPP, the concentration of acidulants that can be used to preserve raw meats, especially those that are ground, is limited by alterations to meat color and flavors at higher levels.
Essential oils are a broad category of phytochemicals that are produced naturally by aromatic plants. Within the plant, these oils function as a primary defense against microbial invasion. When extracted and concentrated, they can be a potential food additive to be used in preserving RMBDs. Essential oils that are known to have antimicrobial functions in foods include thyme, rosemary, eucalyptus, and even cinnamon. Essential oils have been studied extensively as naturally-derived alternatives to synthetic preservatives. They exhibit a wide range of effectiveness against different food pathogens – some of which cause food spoilage and others, such as Salmonella species, that are potential pathogens.
Perhaps the newest (and most unusual) approach to preventing microbial contamination to RMBDs is the use of bacteriophages, organisms that are essentially viruses of bacteria. (Pretty ingenious, eh?). Similar to bacteria, bacteriophages are numerous and they are everywhere. They are also highly host-specific, a quality that makes them potentially helpful to food manufacturers. To date, the use of bacteriophages to control microbial contamination in foods is found only in liquid products intended for humans. Important limitations of bacteriophages are that bacteria can effectively mutate and become resistant to specific phages, and that some, but not all phages are GRAS listed by the FDA. There are also constraints upon food pH and storage temperatures when attempting to use phages for their antimicrobial effects in foods. To date, phages have not been well-studied either with human foods or in raw foods for pets.
Take Away for Dog Folks
There are several important points that consistently arise in this paper. One of the most consistent has to do with the form of most raw dog foods – the fact that they are ground. Here are several points to think about when you are considering a raw product and what approaches are being used to protect the product from contamination:
- Ground Meats/Raw Mixes: For all of the identified methods for controlling bacterial growth, the fact that most raw diets include ground meats presents a challenge. This is due to the fact that grinding increases the surface area available for microbial infiltration and may also distribute surface-dwelling microbes throughout the mixture.
- Higher Doses Needed: While studies suggest that the challenges posed by ground products can be mitigated by increasing the dosage/level of the preservation method, increases of this type are associated with unwanted colors, flavors and possibly nutritional changes to the food.
- Lack of Consistency: When current studies (most in human foods) are examined collectively, there is a lack of consistent results in terms of the control of contaminating microbes and the production of off-flavors and quality changes to the food when high dosages are used. At this point in time, these variable results suggest that developing a standardized approach using non-thermal methods for ensuring that RMBDs for dogs are safe and free from pathogens remains a challenge.
- The Good News: An approach that nutrition/food science researchers are currently studying is to combine the technologies that are discussed above, with the intent of producing a strong synergistic response. For example, combining HPP with organic acidulants, essential oils or phages may allow the use of lower HPP doses with ground products, while still protecting the food and eliminating unwanted changes to food quality and flavors. Because both organic acidulants and essential oils are GRAS compounds and enjoy a long history of use in human foods, these combinations present a promising approach for use in RMBDs.
Watch this Space (and these researchers at Kansas State University) for more information as it becomes available!
Cited Paper: Kiprotich SS and Aldrich CG. A review of food additives to control the proliferation and transmission of pathogenic microorganisms with emphasis on applications to raw meat-based diets for companion animals. Frontiers in Veterinary Science 2022; Nov 10;9:1049731. doi: 10.3389/fvets.2022.1049731.
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