The threat of Salmonella contamination is present at multiple points in the feed-to-food chain – from raw ingredients at the feed mill through delivery of the finished food product.
Feed manufacturing is a critical area to address Salmonella risk, and hydrothermal treatment, hydrating solutions and potent organic acids are three tools that can help to reduce Salmonella contamination and recontamination in poultry feed.
The threat of reactivated Salmonella
Feedstuffs arriving at the mill with no detectable indications of Salmonella can be contaminated or re-contaminated with Salmonella during processing, should environmental conditions facilitate the activation of dormant Salmonella. Although the water activity level in a typical feedstuff is too low to support Salmonella growth (optimal >0.8), the dormant bacteria can survive and reactivate under certain conditions.
Conditions that may allow dormant Salmonella bacteria metabolisms to reactivate include exposure to rising moisture levels in production processes such as grinding, mixing and conditioning, and on-farm practices. For example, when farmers begin grinding the grain, the exposed nutrients present a point of access for Salmonella to enter and proliferate.
Enterobacteriaceae counts in barley and wheat surge upon grinding, but whether Salmonella is present upon arrival at the mill or is reactivated during feed processing, there are tools that can help support a comprehensive Salmonella management program.
1. Hydrothermal treatment
Hydrothermal treatment refers to the addition of heat and moisture to feed mash before it is processed through a pelletizer. Controlling moisture in conjunction with temperature can reduce the presence of Salmonella in poultry feed during processing.
Within a feedstuff, the term “D-value” refers to the decimal reduction time, or the time required at a specific temperature, under specified conditions, to reduce the microbial population by one decimal.
When it comes to reducing Salmonella, moisture value and temperature are inversely related. Figure 2 shows that at a higher moisture level (15 percent), an increased log reduction in Salmonella can be realized compared with a (10 percent) moisture level.
For a conventional feed mill, Figure 3 shows that optimizing the moisture profile and temperature throughout the poultry feed production process may make it easier to control Salmonella.
Heat treatment during fermentation can also help to reduce the degradation of expensive nutrients in the feed. For example, researchers in Denmark compared the free lysine concentration of un-inoculated liquid feed and the same liquid feed inoculated with 103, 105, and 107 Escherichia coli/ml, and concluded that the loss of free lysine in fermented liquid feed was due to metabolism by E. coli.
The researchers found degradation of free lysine occurred to a high extent when fermenting non-pelleted-non-heated feed. However, limited degradation of free lysine occurred during the fermentation of pelleted-heated feed.(Figure 4)
2. Hydrating solutions
The moisture profile of feed is a summary of the different process states including mixing, conditioning, pelletizing and cooling.
Adding a hydrating solution containing a pre-mixture of water and a feed additive may help to achieve an optimum moisture profile in the production plant. Introducing a hydrating solution can also benefit monogastric feed production by inhibiting the growth of microorganisms in feed and recovering shrinkage losses.
In addition, a hydrating solution can assist in improving microbial control, moisture profile and shelf life, while reducing gram-negative bacteria; e.g. Salmonella in raw materials and compound feeds with a long-lasting effect. The surfactants in hydrating solutions reduce water surface tension, leading to better absorption and distribution of the hydrating solution into the feed particles prior to pelletizing.
3. Potent organic acids
In addition to fluctuating moisture profiles and environmental conditions during processing, other opportunities for Salmonella contamination and recontamination are present around the mill.
For example, poultry feed may be contaminated with Salmonella via raw materials whose high buffering capacity can make Salmonella control more difficult. Historically, high dosages of chemicals have been required to achieve adequate Salmonella reduction in raw materials. But alternative options are emerging.
Potent synergistic blends of organic acids and surfactants may reduce Salmonella and the risk of recontamination. These organic acids and surfactants present several benefits. Buffering makes the acids less liable for evaporation. These acids may also reduce re-contamination of feed and raw materials compared to non-buffered organic acids and other volatile products used to manage Salmonella. Applied at the mill, they safeguard against recontamination on the farm by lowering microbial counts in feed materials.
An effective Salmonella control program addresses the numerous ways Salmonella may be transmitted across the feed-to-food chain. Hydrothermal treatment during feed processing, the introduction of hydrating solutions to reduce Enterobactiaceae, and application of potent organic acids at the mill can help control Salmonella and potentially reduce the risk of reactivated Salmonella.
