10 takeaways from a mini-course on managing moisture and water activity

Managing moisture and water activity (aw) during feed production is essential for supporting feed safety, and achieving important quality standards like texture, palatability and shelf-life. Recently, Trouw Nutrition teamed up with scientists and feed mill authorities from METER Group, Inc. and NEF Feed Milling Consulting to present a mini-course exploring how optimizing water activity and moisture management can support safe, high-quality animal feed. Below, we share key course takeaways:

Dr. Prince Nanda
Global Programme Manager
Trouw Nutrition

1. Water activity and moisture content are different
During the mini-course, scientists Dr. Zachary Cartwright and Mary Galloway of METER Group Inc. explained the difference between moisture content vs. water activity and considered strategies for managing aw at the feed mill. As a principle of thermodynamics, aw is the measure of the energy status of water in a system. A higher water activity is indicative of more energy available for water to influence factor such as microbial growth, moisture migration or chemical and physical reactions in feed.

As ingredients with higher aw encounter ingredients with lower aw, water will move to achieve balance, potentially influencing finished feed attributes like texture. Chemical and physical bonding are two ways to restrict water’s ability to move. Some common methods used to control aw include dehydration, edible films or surface coatings, and additives such as humectants and emulsifiers.

As opposed to aw, “moisture content” refers to a qualitative amount of water. While increasing or decreasing the amount of moisture in a product can affect its quality (i.e. the texture & durability of feed may improve palatability), moisture content is not a driving force when it comes to the reactions occurring in the feed.

Figure 1: Isotherms can show the water activity in different types of feeds or pinpoint specific elements within a feed.

2. Isotherms portray the relationship between water activity and moisture content
A moisture sorption isotherm graphically shows how aw fluctuates as water is adsorbed into and desorbed from a product held at a constant temperature. The fluctuations are complex and unique for each product. While aw almost always increases as moisture content increases, the relationship is not linear. Isotherms are a useful way to illustrate the effect that will occur when water is added or removed to feed. Isotherms are helpful tools to help support actions to achieve attributes like, feed safety, texture and shelf-life or packaging requirements.

Calculating isotherms highlights the variability in moisture content and aw in different feeds. Specific isotherms can pinpoint the ideal level of moisture required to avoid quality loss, reduce microbial growth, and determine the point at which rapidly increased moisture uptake begins.

Isotherms can also be used to improve consistency across batches in feed mills. The ability to slightly increase moisture content without negatively affecting the feed quality can significantly improve operational efficiencies/economics at the feed mill.

Innovations in isotherm technology to produce dynamic dewpoint curves allow researchers to understand product adsorption and desorption as samples are exposed to humidified or desiccated air respectively. Such high resolution curves can be used to pinpoint critical water activities and environmental conditions where caking, clumping or loss of texture might occur during feed production.

Figure 2. Some types of organic acids are better at preventing the growth of different kinds of fungi, including moulds, yeasts, and other microorganisms.

3. Blended organic acids can provide synergistic effects
During the mini-course, Trouw Nutrition shared research showing how the selection and application of organic acids can support feed safety as well as operational efficiencies at the mill. As fungi are able to proliferate in very low aw, common fungi present a risk for spoilage, and reducing shelf-life, while also compromising feed’s essential nutrients, and palatability. A study examining nutrient loss in non-mouldy and mouldy feed corn found that total energy, crude protein and fat declined for the mouldy corn. Furthermore, common fungi such as Aspergillus, Fusarium and Penicillium are known to generate mycotoxins, which can have a negative impact on animal health and performance.

While adding organic acids can provide an anti-microbial effect to inhibit moulds in feeds, individual organic acids may not provoke consistent responses in various fungi. For example, testing found that formic acid is more effective against Salmonella and E. coli than against other organisms, while sorbic acid is equally effective against multiple fungus types.

Beyond the type of acids used, it is also important to consider blending of acids used to support feed safety. Improper blending can be highly corrosive for humans working in the feed mill and on plant equipment used to manufacture feed. Proper blending, precise dosing and correct application are essential to ensure that acids deliver the desired inhibitory effect on mould or fungi growth. Extensive research on the use of organic acids against various fungi led Trouw Nutrition to develop a patent-pending technology, ActiProp®. The technology includes a buffering agent, emulsifier, phytochemical compounds, and propionic acid to target moulds. Trouw Nutrition includes ActiProp® technology in its Fylax Forte HC solutions, which are developed to inhibit moulds in animal feed.

4. Validate interventions to support feed safety
Validation is an essential step in evaluating the efficacy of solutions designed to support safety at the mill. Research conducted with Westerdijk Fungal Biodiversity Institute, explored the individual use of buffered propionic acid, an emulsifier and phytochemical blend and ActiProp compound against Aspergillus chevalieri and Penicillium lanosocoeruleum.

Individually, the buffered propionic acid infiltrated about 16.9% and 10.9% of the aspergillus and penicillium cells, respectively, while the blended emulsifier and phytochemical penetrated about 4.1 and 2.5% of the respective mould cells. While the blend of all ingredients was expected to target about 21% and 13.4% of aspergillus and penicillium cells, respectively, a synergistic rather than additive effect was observed, with the blend penetrating 32.5% and 40.7% of mould cells. When examining the application of various amounts of activated – rather than buffered – propionic acid, research showed the ActiProp ingredient was 2-3 times more effective than buffered propionic acid alone.

5. Dose to deliver smaller droplet size
Dosing equipment is an important component to ensure the uniform application of active ingredients. Using a system like sensor-based moisture management or a moisture-based dosing system to add feed additives can help provide safe, accurate dosing of products. While a range of nozzles can be used to apply liquid additives, the smaller the droplet size used when dosing, the better the bacterial and mould control.

6. Steam during pelletizing supports quality and production efficiencies
Steam can contribute to optimal moisture during pelleting. A well-designed steam system adds dry saturated steam as early as possible in the conditioner and applies temperatures above 80°C (176°F). Steam conditioning and moisture regulation are primary processes used during pelletizing to support ingredient and mash quality. The steam conditioning process helps plasticize individual particles and creates liquid bridges in feed. Benefits of this process include reducing energy requirements, supporting partial gelatinization of starch, improving moisture balance, lowering production costs, killing pathogenic bacteria, improving throughput rate and reducing equipment wear.

Thermal properties must also be supported and mechanical considerations can support production efficiency. For example, conditioner rotors should have overlapping paddles minimize feed residues and support thermal properties. Heated housing helps to avoid the risk of condensation and consequently recontamination. Retentioners must show a ‘first in, first out’ concept to guarantee a uniform heat exposure to all particles.

Increased conditioning temperatures in general improve pellet quality, however quality tends to plateau around 80-85°C (176-185°F). The recommendation remains that constant throughput rates rather than constant motor load leads to better results in terms of pellet quality.

7. Ensure consistency and optimal moisture levels
Ernst Nef, an authority with decades of experience in feed milling addressed the importance of achieving consistency in moisture levels especially at the pelleting process. He noted that moisture variability in feed ingredients is strongly related to origin, type and state of the raw material, but also affected by various in-house proceses. Achieving moisture consistency during pelleting will help manage energy use, support good and constant pellet quality, and reduce risks for spoilage.

Technologies and diagnostic tools like NIR or microwave sensors can measure moisture levels during mixing and help ensure desired moisture levels are reached before mash enters the pellet mill. Applications at the processing line also have a role to play in achieving moisture targets during production. For example, a hydrating solution can be sprayed in the mixer based on pre-set formulas or pre-set batch volumes, and digital flow meters can monitor moisture levels. However, pre-set moisture amounts may fail to consider variation in feed ingredients, resulting in feed that is too dry, less palatable, or concentrated leading to nutrient waste. And too much moisture can dilute nutrient levels, choke the pellet mill or increase mould risk.

Sensor-based moisture addition offers millers more control and allows moisture amounts to be targeted in real-time, batch by batch compared to fixed moisture addition.

8. Reduce surface tension
Surface tension is the film on a liquid caused by the attraction of particles from the bulk of the liquid. This effect tends to minimize surface area. Adding surfactants can reduce surface tension thereby reducing the droplet size, which helps provide more surface area and better moisture penetration into the feed.

Regardless of how much surfactant is added, surface tension reduction is limited and eventually stabilizes. Reducing droplet size helps ensure uniform moisture addition and absorption, smooths operation and reduces lumps, facilitating better moisture addition and retention. Using process moisture management during production and including a surfactant to reduce surface tension can lower process loss, improve throughput pace and support pellet quality while contributing to energy savings.

9. Manage starch gelatinization
Feed ingredients typically contain amylose or amylopectin starch types. When exposed to heat and moisture, starch starts to breakdown or become gel-like. The amount of starch in ingredients can vary. For example, corn is 71-74% starch while wheat contains 66-72%. Starch in feed ingredients starts to gelatinize during various temperature ranges with ingredients like barley seeking temperatures from 52-60°C (125-140°F) while sorghum requires temperatures up to 78°C (172.4°F).

Different types of feed processing produce different amounts of gelatinization and require separate levels of thermal processing – in general, gelatinization increases as more heat and moisture are added. Both the pelleting and extrusion processes use moisture & heat to gelatinize the starch in feed ingredient. Steam gelatinization during pelleting may only alter about 10-20% of the starch available. Along with temperature, the amount of moisture in feed prior to processing influences the amount of gelatinization that occurs. Research has shown that when more moisture is present in ingredients prior to conditioning more starch gelatinization occurs.

10. Steering moisture levels can support feed hygiene
Adding moisture during conditioning helps improve thermal conductivity, as moisture helps carry heat into feed ingredients. The D-value for feed conditioning represents the decimal reduction for an organism or the amount of time needed at a specific temperature to kill 90% of that organism – like Salmonella. Research examining the links among temperature, moisture content and D-value found that the higher the moisture level, the less time was needed to reach the desired D-value, regardless of temperature. Similarly, expanding moisture content from 5% to 15% also helped heighten the rate of reduction for unwanted organisms like Salmonella enteritidis as temperatures increased. The importance of raising feed moisture levels in the conditioning process to 15 – 17% comes from the fact that it drastically reduces how long it takes to kill pathogens without requiring much more heat.

The 10 takeaways above spotlight how the work of companies representing animal nutrition, water technology and feed milling innovation are advancing the science and business of feed production. Managing water activity and moisture in feed ingredients can improve the quality and safety of animal feed as well as production economics.

References available upon request.