Petfood and its ingredients-for example, meat and meat by-products-are subject to decay by several different processes such as autoxidation, microbial growth, flavor/aroma changes or staling. The period before drastic changes occur from such a process is considered the time of freshness. This period can vary depending on quality of raw ingredients, ingredient processing and storage conditions.
The freshness of petfood ingredients can additionally affect the palatability of the resulting product. One of the primary factors affecting palatability is quality of the ingredients. Off flavors caused by chemical or microbiological deterioration of the ingredients can result in food refusal, since animals rely on their sense of smell and taste to differentiate safe, nutritious foods from those that taste bad or may contain toxic substances.
Role of microbial degradation
One area in which significant opportunities exist to secure freshness is ensuring that ingredients used to produce palatants for dry kibble coating are of high quality. For example, the freshness of poultry viscera is regarded as critical for the quality of products prepared from these viscera. Minimizing the time of shipment between rendering and manufacturing of the palatant is crucial to maintaining freshness.
To demonstrate this, an evaluation of the time between collection of fresh poultry viscera and manufacture of a palatant flavor was conducted. For the first set of experiments, microbial degradation of the viscera with respect to storage time at room temperature was observed. Additionally, the effect of adding a freshness agent to the viscera was assessed.
In the laboratory, fresh intestines were separated from heart, stomach and liver. One portion of the viscera was left untreated while the other portion was treated with a freshness agent ( Figure 1 ). Both portions were incubated at room temperature, and after 24 hours, the untreated material was again divided into two portions. One portion was treated with the freshness agent and the other portion was left as the second control.
All the treatments were further incubated for another 24 hours at room temperature. Both total aerobic counts and total enterobacterial counts were monitored.
Delaying aerobic growth
The initial total aerobic count of the untreated poultry viscera rose significantly by two logs within 24 hours ( Figure 2 ). After 48 hours, no further increase in total count was observed, indicating that quality of the material as measured by total aerobic growth decreases quickly within the initial 24-hour period.
However, when a freshness agent was added to the viscera before storage, development of total aerobes was delayed, with total aerobes in the treated sample only increasing from 2.00 x 107 cfu/g to 7.00 x 107 cfu/g. After 48 hours, total aerobes in the treated sample had further increased to levels similar to that of untreated viscera stored for 48 hours.
It appears that addition of a freshness agent can delay microbial degradation of poultry viscera for at least 24 hours. However, the freshness agent needs to be added as quickly as possible, because treatment of viscera stored for 24 hours at room temperature could not rescue the viscera quality.
Similar to total aerobic count, initial enterobacterial count of the untreated increased after 24 hours of incubation at ambient temperature. No further increase was observed after 48 hours of storage ( Figure 2 ). However, when the ground viscera were treated with the freshness agent, there was minimal change in enterobacterial counts, even after 48 hours.
This is especially important since it is known that enterobacteria are decarboxylase-positive and can therefore be responsible for biogenic amine production in raw materials (Klausen and Huss, 1987). Biogenic amines can be toxic to humans and animals, resulting in a wide variety of symptoms, and their presence in raw ingredients can be an indicator of microbial contamination and reduced quality (Radosevich, 2006).
Interestingly, some rescue of enterobacterial count was observed since treatment of viscera stored for 24 hours resulted in a slight decrease of enterobacterial counts when treated at 24 hours and stored for another 24 hours.
Freshness and palatability
Although analytical measures of factors that influence freshness (such as microbial count) suggest there has been an improvement or control of freshness, freshness must also be evaluated through sensory analysis. Therefore, the effects of time and/or preservation of viscera before flavor production were tested in palatability trials.
At the start of this experiment ( Figure 3 ), viscera were divided into six portions. Five portions of viscera were left untreated while the remaining portion was treated with a freshness agent. Then all samples were stored at ambient temperature for 24 hours.
After 24 hours, flavor was made from the treated sample and one untreated sample to make Flavors H and C, respectively. Another sample was treated with a freshness agent to evaluate the ability of the agent to rescue the stored raw material. This treated sample was divided into two portions, one of which was used to make Flavor D, while the other was stored for an additional 24 hours. At the 48-hour mark, all remaining samples were used to make Flavors E, F and J.
Palatability of the resulting flavors was assessed using a standard two-pan test with 20 dogs over two consecutive days. Each day the position of the two test foods coated with the flavors was switched to avoid influence of position preference over food preference. Both first choice and relative consumption were recorded ( Figure 4 ).
The palatability of flavors prepared from viscera treated immediately after collection of the raw material and stored for up to 48 hours was found to be significantly better than that of digest prepared from untreated viscera stored for the same amount of time. Similar to the microbial results described above, adding the freshness agent needs to happen as quickly as possible, because treatment of viscera stored for 24 hours at room temperature could not rescue the viscera quality and palatability of the flavor.
QA is essential
Ensuring freshness of petfood and ingredients is essential for the health and well-being of companion animals. These results demonstrate the importance of utilizing the freshest raw materials available. Processing and handling measures should be taken to reduce the risk of microbial degradation and loss of palatability in raw ingredients, since preservation of raw material quality results in better quality finished products.
Particular attention needs to be taken to preserve raw material quality since in most cases high quality cannot be rescued once it is lost. Measures such as reducing the collection and transit time before raw material chilling and good hygiene of transfer and processing equipment will reduce the risk of microbial degradation and loss of quality. While sound quality assurance practices are essential, freshness agents may also be considered to retain freshness of the ingredients and performance of the petfood.
Koen Meynen is a research scientist and Jennifer Radosevich, PhD, is director of R&D and regulatory affairs for Kemin Nutrisurance Inc .
N.K. Klausen and H.H. Huss, "Growth and histamine production by Morganella morganii under various temperature conditions," International Journal of Food Microbiology , 5 (1987) 147-156.
Radosevich, J. " Analyzing Amines: Evaluating potential toxicity in petfood ingredients ," Petfood Industry, August 2006.
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