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Palatability is a crucial aspect of pet food: pet parents want their companion animals to enjoy their meals and are more likely to purchase highly palatable pet food, thus enhancing brand loyalty.
In this article, we will explain how Free Fatty Acids (FFA) are related to the freshness of certain poultry raw materials used in complete dry kibbles recipes and how FFA influence palatability in pet food.
Fat is largely present in pet food: it is coated onto kibbles to increase caloric intake and enhance palatability (in conjunction with palatability enhancers). Fat is also present in Processed Animal Proteins (PAP or animal meals) included in pet food recipes. PAP and animal fat used in pet food production are mainly produced via rendering, where they are extracted from Category 3 Animal By-Product (ABP) from human food meat production (Viscera, Carcasses, Skin, Heads, legs…)1.
Triglycerides are the primary fat molecules: they are esters made of glycerol molecules and long carbon chain carboxylic acids, the fatty acids. Free Fatty acids (FFAs) are released upon enzymatic or pH-dependent non-enzymatic hydrolysis2.
In enzymatic hydrolysis, the bond between fatty acids and glycerol can be broken by lipases, enzymes produced by bacteria naturally present on crude raw materials before fat and PAP production in the rendering process3.
The ester bond can also be broken during the rendering process itself. This article will focus on the FFAs produced before the rendering process takes place.
It is also worth noting that, once the animal fat is well-separated, purified and stored in good conditions, the content of free fatty acids in fat should remain constant. In addition, FFAs in finished PAP meal are normally stable after rendering processes.
FFAs in fats are measured by titrating the sample with a solution of 0.1N potassium hydroxide in the presence of a phenolphthalein indicator to monitor the endpoint of the volumetric titration. The results are often expressed as % of Oleic acid4, commonly referred to as percentage of acidity.
To test the effect of raw material freshness on palatability, several batches of fat were produced from the same batch of crude raw material but with different levels of freshness. This has been possible thanks to the Kemin rendering pilot plant, specifically designed to replicate the rendering process conditions (Raw materials recipe, cooking temperature/duration conditions...).
Chicken viscera, heads, and legs were collected from a nearby slaughterhouse. The original batch of raw material was split into several batches, stored at room temperature for several days, and rendered at different time periods. This gave time for the bacteria to grow in the crude ABP and produce more lipases, increasing the FFAs amount over time. Initial fat extracted from the original batch of raw material was fresher and with fewer FFAs, while fat extracted later was less fresh and with a higher amount of FFAs. The fat extracted was then combined to obtain the desired inclusion of FFA (%Oleic acid 1.1, 3.3, 4.9, 7.5, and 10).
The fats obtained were coated onto dog and cat kibbles at 4%. The dog kibbles were also coated with a 2% liquid palatability enhancer, while the cat kibbles were coated with a 1.5% dry palatability enhancer. The coated diets were then tested for oxidation parameters (Peroxides Values (P.V.), Hexanal, and 2,4-Decadienal in extracted fat) to ensure there was no bias in the test results, since different oxidative statuses can generate different palatability results.
All the diets were under oxidation control, as can be seen by the low level of all the oxidative parameters.
The kibbles were then tested for palatability in expert kennels and catteries.
To assess palatability, a two-bowl test has been chosen for our trials. Groups of 20 trained animals were presented with two diets to choose from, and the food consumed of each type was weighted. The two diets were presented again on the following day, swapping positions to the bowl from left to right to avoid any side bias.
The amount consumed was recorded for each animal, and data analysis was completed according to a one-tailed t-test. The goal of the trial is to identify if a preference exists between diets. Results are given as intake ratio (IR): the amount of a ration consumed divided by the total amount consumed and expressed as the average of 2 days.
The target of the palatability trials was to assess the impact on the palatability of the raw material freshness, using FFAs as a marker. The trials were designed to test the freshest fat available (3.3% acidity for dogs, 1.1 % acidity for cats) in comparison to the other fats produced.
A total of 3 palatability trials for dogs were conducted; the results are shown in the graph below.
The blue bar represents the intake ratio of the diet coated with fat having 3.3 % Oleic acid FFA compared to the other 3 diets produced for dog trials with 4.9%, 7.5%, and 10% Oleic acid FFAs coated Fats respectively.
The diet coated with fat having 3.3% acidity showed a palatability comparable to the diet coated with fat having 4.9% acidity and superior palatability compared to the diet coated with fat at 7.5% acidity; the comparison between the diet coated with fat at 3.3% acidity and the diet coated with fat at 10% acidity showed a consumption trend towards the diet with less FFA, but not a statistically significant result.
A total of 4 palatability trials for cats were conducted; the results are shown in the graph below.
The blue bar represents the intake ratio of the diet coated with fat having 1.1 % Oleic acid FFAs compared to the other 4 diets produced for cat trials with 3.3%, 4.9%, 7.5% and 10% Oleic acid FFAs coated Fats.
The diet coated with fat having 3.3% acidity was the only one showing superior palatability when compared to the diet coated with fat having 1.1% acidity. The other results obtained seem to indicate a trend for a reduction of palatability when increasing FFA inclusion in the fat used for coating.
From the palatability results obtained, it is demonstrated that a higher FFA amount in the fat used for coating might lead to a decrease in palatability, especially for cats.
Considering the impact to palatability that freshness might have, it is crucial to ensure that the crude ABP is managed in a proper way so that freshness is preserved. Good manufacturing practices are pivotal in reducing bacterial activity that could accelerate raw material decay. A clean and hygienic production environment is critical for the finished product’s quality.
Another crucial aspect is crude ABP management: transportation inside slaughterhouses, storage duration and conditions, the timing needed for the raw material to reach the rendering plant, and rendering storage conditions, especially when the external temperature exceeds 18°C.
In a separate study at the Kemin rendering pilot plant, the efficacy of a preservative solution to control raw material decay was tested.
Chicken viscera, heads, and legs were collected from a nearby slaughterhouse; the initial batch was divided in two. One part was treated with 0.5% of preservative solutions, while the other was left untreated. The material was stored at room temperature (25 °C) and processed to extract fat and meals after 0, 1 and 3 days. FFA content in fat and meals were tested.
FFA development in fat and meals followed a similar behavior. The impact of the preservative solution is clear in decreasing the development of FFAs already after 24 hours.
Since in the European Union, Category 3 crude APB stored at ambient temperature must be rendered within 24 hours10, preservatives are considered a good tool for controlling freshness and palatability. A natural preservative solution must be selected based on the efficacy of organic acid combinations and to avoid its potential negative impact on palatability. They need to be applied correctly at the right dosage and at the right moment in the process.
In these series of experiments, it was clearly demonstrated that FFA recoveries in animal fat and PAP are correlated with the freshness level of crude, rendered ABP.
It was further shown that raw material freshness impacts palatability.
Understanding that controlling raw material freshness can be challenging, we have also been able to validate the efficacy of a preservative solution in reducing FFA formation.
1. Aldrich, G. (2006). Rendered product in pet food. In D.L. Meeker (Ed.), Essential Rendering: All About the Animal By-Products Industry (pp. 159-177). Arlington, VA: Kirby Lithographic Company, Inc.
2. Gupta, M. K. (2017). Practical Guide to Vegetable Oil Processing, AOCS press (Second Edition). Chapter 2: Basic Oil Chemistry, pp. 7-25.
3. Martins, A.A., Andrade, S., Correia, D., Matos, E., Caetano, N.S., & Mata, T.M. (2021). Valorization of Agro-Industrial Residues: Bioprocessing of Animal Fats to Reduce Their Acidity. Sustainability, 13(19), 10837.
4. Dijkstra, A. J. (2016). Vegetable Oils: Composition and Analysis. Encyclopedia of Food and Health, 357–364.
5. Internal Kemin document: CLS KNE #470139
6. Internal Kemin documents: TD-23-9337; TD-23-9338; TD-23-9339
7. Internal Kemin documents: TD-23-9340; TD-23-9341; TD-23-9342; TD-23-9343
8. Internal Kemin documents: CLS KNE #19456, #19479, #19523, #19531
9. Internal Kemin documents: CLS KNE #19456, #19479, #19523, #19531
10. COMMISSION REGULATION (EU) No 142/2011, Annex VIII, Chapter1, Section 2.
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