How to evaluate the quality of fresh pet food providers: Processing methods

For veterinary professionals, navigating the rapidly expanding "fresh" pet food market with clients can be a frustrating exercise in deciphering marketing jargon. While owners often seek these diets with the best intentions for their pets' health, it falls to the clinical team to evaluate the genuine nutritional quality and safety of these products.

The "fresh" definition gap

Despite its surging popularity, there is no legal or regulatory definition for a fresh complete diet in the UK. According to the FEDIAF 2025 nutritional and labelling guidelines, fresh may "be used to describe pet food ingredients that have not been subjected to any treatment except refrigeration" (FEDIAF, 2025).

As a food category, it is widely understood by consumers to mean frozen or chilled, fresh-like meals from providers such as Butternut Box, Marro, Different Dog, KatKin, and Tuggs. However, this definition gap has turned "fresh" into a highly effective marketing halo. Diet providers producing shelf-stable products frequently co-opt this buzzword to elevate their positioning. In this article, we mean fresh to mean mildly cooked and frozen - let's look at how you can help pet owners to evaluate the differences in diet types.

Thermal processing: 90°C vs. Retort (121-130°C)

When evaluating true frozen or chilled fresh products against shelf-stable alternatives, understanding the manufacturing process—specifically the thermal load applied to the ingredients—is critical.

• Gentle Pasteurisation (90°C): Genuine frozen fresh diets are typically cooked at 90°C. This targeted pasteurisation is sufficient to destroy pathogenic bacteria (mitigating the infectious risks associated with raw feeding) without excessively degrading the food matrix. The meal is then rapidly frozen, allowing for natural preservation without artificial additives.
• The Retort Process (121-130°C): Shelf-stable wet foods (cans, pouches, and cartons) must undergo commercial sterilisation via a retort process. This involves subjecting the sealed product to extreme heat (121-130°C) and pressure. Because the heat must penetrate to the very centre of the product, the outer layers undergo prolonged "heat soaking," enduring these extreme temperatures for extended periods.

Nutrient stability and bioavailability

The thermal load of the retort process has a profound impact on nutrient stability, whereas the 90°C pasteurisation method offers superior preservation of essential compounds:

• Heat-Sensitive Vitamins: B vitamins (particularly thiamine, riboflavin, and pantothenic acid) and Vitamin C are highly thermolabile. The extreme temperatures and heat soaking of the retort process lead to significant degradation of these vitamins, requiring manufacturers to heavily supplement the formulas post-processing to meet minimum FEDIAF requirements (Fascetti & Delaney, 2012).
• Amino Acid Integrity: Lysine, an essential amino acid, is uniquely vulnerable to heat damage due to its reactive epsilon-amino group. Gentle cooking at 90°C largely preserves lysine's bioavailability, whereas retort temperatures significantly reduce it (Tran et al., 2008).

The Maillard Reaction, AGEs, and chronic inflammation

The degradation of lysine during high-heat processing is primarily driven by the Maillard reaction—a chemical reaction between amino acids and reducing sugars that causes browning. The Maillard reaction is exponentially accelerated at retort temperatures (121-130°C) (van Rooijen et al., 2014).

Clinical Note: The end products of the Maillard reaction are known as Advanced Glycation End products (AGEs).

Because of the intense heat soaking required for commercial sterilisation, retort-processed, shelf-stable diets typically contain vastly higher concentrations of dietary AGEs and their precursors (such as α-dicarbonyl compounds) compared to gently pasteurised fresh diets. A recent 2026 study evaluating commercial dog foods confirmed that wet (retort) foods contained significantly higher levels of Maillard-derived compounds compared to fresh diets (Kocadağlı et al., 2026).

The clinical reality of AGEs: from human ultra-processed foods to canine chronic disease

The discussion surrounding Advanced Glycation End products (AGEs) has historically been clouded by speculative pseudoscience, but it is now a rigorously researched area of mainstream veterinary and human medicine. To understand the impact of AGEs on our patients, we must first look at the wealth of data emerging from human nutrition regarding Ultra-Processed Foods (UPFs).

Human medical research heavily implicates the thermal processing of UPFs in the widespread consumption of dietary AGEs (dAGEs). These compounds are now recognized as primary mediators of metabolic syndrome, cardiovascular disease, and premature aging in humans (Akkaya et al., 2026; Claudino et al., 2024; McIntosh et al., 2022). Veterinary literature has established that this same pathophysiology applies to companion animals consuming highly processed, high-heat diets.

The mechanism of AGE-induced damage

Systemically absorbed dAGEs can cause havoc on the body through two primary, evidence-backed mechanisms:

• Protein Cross-Linking: AGEs physically bind to and cross-link with body proteins, particularly structural proteins like collagen. This alters the protein's structure and function, leading to tissue stiffening and loss of elasticity.
• RAGE Activation and Oxidative Stress: AGEs bind to a specific cellular receptor appropriately named the Receptor for Advanced Glycation End products (RAGE). Research demonstrates that RAGE activation acts as a cellular alarm system, triggering a cascade of oxidative stress and releasing pro-inflammatory cytokines.

Systemic implications in the canine patient

Over time, the continuous intake of dAGEs from heat-soaked commercial diets drives chronic, low-grade inflammation. This persistent inflammatory state is heavily implicated in the pathogenesis of several prevalent age-related conditions:

• Osteoarthritis (OA): AGE-induced cross-linking of collagen in the articular cartilage makes the joint matrix brittle and highly susceptible to mechanical degradation. Furthermore, localized RAGE activation within the joint capsule aggressively drives synovial inflammation, accelerating disease progression (Akkaya et al., 2026).
• Chronic Kidney Disease (CKD): The kidneys are the primary route of excretion for circulating AGEs. A high dietary AGE burden chronically overworks the nephrons. Evidence shows that AGE accumulation within renal tissues induces glomerulosclerosis and interstitial fibrosis, acting as a potent catalyst for CKD (McIntosh et al., 2022).
• Cognitive Decline: Similar to research linking UPFs and AGEs to Alzheimer's disease in humans (Claudino et al., 2024), veterinary studies indicate that AGEs cross the blood-brain barrier. There, they induce neuroinflammation and contribute to the amyloid plaque formation associated with Canine Cognitive Dysfunction (CCD).

The clinical takeaway

The recent 2024 study by Bridglalsingh et al. (2024) confirms that the processing method of pet food directly dictates the concentration of dietary AGEs, which directly correlates to the levels of circulating AGEs in a dog's bloodstream.

By advising clients on the fundamental biochemical differences between a frozen diet gently pasteurised at 90°C and a shelf-stable product subjected to 121–130°C retort heat soaking, veterinary teams can practice proactive medicine. Guiding owners toward genuinely fresh, low-heat diets is a tangible way to mitigate unnecessary inflammatory burdens and support the long-term health of our patients.