Development of anti-caking agents: Using powder testing to identify candidates |

2021-11-12 10:53:13 By : Ms. Vancey Geng

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Laura Shaw, Freeman Technology; Dr. Renata Negrini, Omya International AG; Marcel Lex, Omya International AG; Jamie Clayton, Freeman Technology; Lalit Sharma, Omya International AG | 2021 October 25

Food processing and processing industries rely heavily on anti-caking agents to ensure production efficiency and maintain the value of powdered ingredients and products. Driven by innovation and changing customer preferences, this is a healthy expansion of the industry. It is expected that the food handling and processing equipment market will have a compound annual growth rate (CAGR) of 6.5% by January 2026

In this context, there is an increasing demand for new high-performance additives that meet changing needs, especially to replace controversial or poorly sourced ingredients. For example, silica is an effective and widely used anti-caking agent, but due to concerns about nanoparticles, its use has become increasingly controversial. 2

In this article, we describe the development of new anti-caking agents by Omya (Ottlingen, Switzerland), the world's leading calcium carbonate producer, and Freeman Technology (Tewkesbury, UK), a global leader in powder characterization technology. Cooperative work. A major focus is the application of advanced powder testing (FT4 powder rheometer) to evaluate uneven agglomeration behavior-crusts-to rigorously evaluate potential candidates.

If the powder is left undisturbed for a long time, it will increase its strength and lose the flow characteristics that define its value in many cases. This process is called agglomeration, and it can be carried out through a series of chemical, electrical and mechanical mechanisms; for food ingredients, the absorption and migration of water almost always play a decisive role. Moisture adsorbed on the surface of the powder particles or the powder body can cause chemical agglomeration—for example, through hydration, partial dissolution, and recrystallization—or through modification of the particle surface, which in turn triggers plastic flow and particle-particle interaction. Multiple mechanisms may occur simultaneously or sequentially, and the end result ranges from soft fragile aggregates to irreversibly fused materials whose properties are far from those of the original materials.

The powdered ingredients used in the food industry range from dry ground spices and extracted seasonings to core ingredients such as cocoa and milk powder. These components show considerable diversity in surface chemical and physical properties, and the agglomeration behavior is correspondingly complex. For any given material, the absorption of moisture is directly affected by the storage conditions (relative humidity, temperature and pressure), but the stored powder usually has only one surface exposed to the surrounding environment. Therefore, the agglomeration behavior is complicated by the ease with which moisture can migrate through the powder or other means, even if the properties of the powder bed are changed by, for example, liquid bridging or recrystallization. The assumption that clumping is always uniform is unreliable; crusting is commonplace.

The consistent processing and ease of use of powdered ingredients depend on their flow characteristics. Agglomeration may affect key operations such as hopper discharge, mixing, batching, and in some cases, dissolution. Therefore, it is essential to control the agglomeration to an acceptable level. The goal is to develop strategies to keep the ingredients in top condition without incurring unnecessary costs. Although storage under controlled temperature and humidity conditions may be essential, anti-caking agents can change the sensitivity to moisture and make fluidity easier to maintain. Therefore, they are an important class of additives in the food industry.

The source and safety of food ingredients are constantly being reviewed and are an important driving force for innovation and reformulation. Regarding anti-caking agents, silica is generally considered the "gold standard" and has the potential to reduce caking in the following ways:

Through these mechanisms, adding different concentrations of silica can improve the caking behavior of all types of powders-dry/hard, wet, and soft/high-fat materials, respectively. However, the use of silica is becoming more and more controversial. The silica anti-caking agent has a fine particle size distribution, which can give a high specific surface area, thereby consolidating its effect. Although usually composed of aggregated nanoparticles with a diameter of more than 100 nm, there are concerns that this material may expose users to particles below this "nano threshold". Regulations on nanoparticles and their associated potential health risks continue to evolve, but some countries have now banned silica as an anti-caking agent. Cooperation with the European Food Safety Authority (EFSA), for example, requires better characterization and specifications to provide Ensure safety. 2

The state of silica provides the impetus for the introduction of new anti-caking agents with stronger safety. Calcium carbonate has considerable potential in this regard. It is a natural material with established safety and has been used in fortified foods, including dairy products and non-dairy products. Replicating the impressive performance of silica is a major challenge, but Omya has made considerable progress in this regard with its expertise in the development of calcium carbonate products. The following study illustrates the level of performance achieved with the new functionalized calcium carbonate (FCC) anti-caking agent.

The purpose of the anti-caking agent is to maintain the fluidity of the powder. Therefore, the comparative evaluation of the performance of the new anti-caking agent relies on the measurement of powder flowability. The use of a powder rheometer for dynamic powder testing is particularly suitable for this purpose because it provides:

The figure at the beginning of this article shows how to use the FT4 powder rheometer to measure basic flow energy (BFE), a baseline dynamic powder characteristic. When the instrument rotates downward through the powder bed, the axial and rotational forces acting on the blades of the instrument are recorded every 40 milliseconds to construct an energy gradient map as a function of the height of the bed. The value of BFE is generated by integration, by determining the area under the curve. However, since the position of the blade can be determined with high accuracy at any given time, it is easy to detect the difference in flow characteristics within the sample. Through dynamic testing, skin formation can be detected, the influence of moisture migration through the powder bed can be tracked, and the strength of aggregated materials can be quantified. Through the humidity cycle experiment, it can also be determined whether the agglomeration is reversible. These features make dynamic testing very valuable for all types of agglomeration studies.

An experimental study was conducted to compare the performance of two FCC anti-caking agents (Agent 1 and Agent 2) with commercially available silica products. The dynamic powder properties of four samples were measured: milk powder and milk powder containing 1% w/w silica, 1% w/w reagent 1 and 1% w/w reagent 2. The baseline powder characteristics test was performed under ambient conditions (FT4 powder rheometer) and the caking behavior was then passed through repeated tests after storage under controlled relative humidity conditions, after 4.5 days at 63% RH, and after 2.5 days at 74% RH Quantify.

In the preliminary analysis of the data, the agglomeration index (CI) was determined, where CI is the ratio of the total energy (TE) of the agglomerated material to the BFE of the fresh powder before storage. Given that silica is known to be effective in preventing caking, it was found that the CI of the sample containing the silica anti-caking agent was unexpectedly high. Figure 1 shows the data supporting these calculations.

Image courtesy of Freeman Technology

Figure 1: Energy vs. height graph of milk samples containing silica anti-caking agent showing obvious signs of crusting.

These results show that after 4.5 days of storage at 63% relative humidity, scabs appear in the top ~10 mm sample, and the peaks in the graph indicate greater flow resistance in this area. Storage at a higher RH (74%) will produce a stronger enclosure in a shorter period of time. However, in both cases, the crust is relatively thin, and the underlying material has no change in flow characteristics; both trajectories return to close to the baseline curve. Picture courtesy of Freeman Technology Picture courtesy of Freeman Technology Picture 2: Crustal depth and strength data of the four samples show that the new anti-caking agent results in a thicker but weaker crust compared to silica products.

Comparable data for each sample quantifies the difference in the depth and strength of the crust (see Figure 2). In the absence of anti-caking agents, milk powder will agglomerate extensively, with a depth of about 23-33 mm, depending on the storage conditions, but the strength of the agglomerated material is relatively small. The shell formed with reagent 1 and reagent 2 is thinner than when no anti-caking agent is used, but thicker than silica, especially after storage at low RH (63%). However, under high relative humidity, the strength of the crust formed by using reagent 1 and reagent 2 is lower than using silica; at lower relative humidity, the strength of the developed crust is more comparable.

These data indicate that all anti-caking agents promote the formation of a relatively impermeable shell at the air-powder interface, thereby inhibiting the migration of moisture to the rest of the powder. They also provide evidence that the performance of the new reagents is relatively better compared to silica, resulting in the formation of thicker shells with comparable or lower strength, depending on storage conditions.

In the last extension of the study, the observed agglomeration parameters are related to the characteristics of the new mixed sample and are measured under environmental conditions before agglomeration to investigate the feasibility of predicting the agglomeration behavior from this baseline analysis. The analysis revealed two particularly powerful and interesting relationships:

* It is found that the depth of the crust is closely related to the stability index (SI-R2, 63% RH = 0.9542, 74% RH = 0.9267), where SI is the ratio of the BFE to the initial BFE measured after seven measurement cycles. The instability of the BFE measurement may be due to the moisture absorbed during the measurement process, which provides a rationale for this correlation.

* The maximum energy in the earth's crust, an indicator of the strength of the earth's crust, was found to be closely related to permeability, which was quantified by the pressure drop of the sample at 15 kPa (R2, 63% RH = 0.8954, 74% RH = 0.9570). A basic principle of this relationship is that low permeability inhibits water migration and promotes the development of a stronger crust at the air-powder interface.

The results of this research are put together to show how dynamic data can sensitively characterize and distinguish Agent 1 and Agent 2 through multiple related indicators to evaluate their performance relative to silica and have the potential to predict behavior. This is in sharp contrast to alternative technologies, such as moisture absorption measurement, which cannot distinguish between Agent 1 and Agent 2, and has limited insight.

A second set of experiments was performed to compare the performance of the anti-caking agent with two different substrates: powdered milk and commercial flavor blends. Measure the dynamic powder properties of the original powder and the mixture of each powder with 1% w/w silica or reagent 2 (as in case study 1). The baseline characterization was performed under environmental conditions, and the caking behavior was quantified by repeating the test after milk and flavor samples were stored at 75% RH for two and six days, respectively. This reflects the storage time required to observe significant skin formation on each substrate.

Image courtesy of Freeman Technology Image courtesy of Freeman Technology

Figure 3: Energy vs. height plots of milk (left) and flavor (right) samples with and without anti-caking agents show that the substrate has a significant effect on the caking behavior.

As expected, the milk powder data (Figure 3-left) is comparable to the data generated in Case Study 1. However, a different behavior was observed using the fragrance mixture (Figure 3-right). Here, silica limits agglomeration to the upper half of the sample, but the baseline energy value of the silica-fragrance mixture is significantly higher than the raw material or reagent 2 mixture. In addition, although both the original fragrance and Agent 2 mixture showed obvious peak energy values, in either case, the fluidity failed to converge to the baseline value; the energy value was higher after storage in the entire sample. This caking behavior can be described as mixing, between the crusts and uniform agglomeration in the entire powder sample, which indicates that in the case of mixed fragrance, a larger proportion of the powder bed will be affected by any agglomeration.

Image provided by Freeman Technology Image provided by Freeman Technology Image provided by Freeman Technology

Figure 4: The dynamic data measured on the milk and spice mixture show that the effect of the anti-caking agent depends on the substrate.

In the presence and absence of silica and Reagent 2, a complete comparison of the data for the two substrates shows a significant difference. Generally speaking, compared with milk powder, the spice mixture will form a stronger shell. However, when compared to silica, Agent 2 significantly reduces the energy and strength of the crust; the relative increase in the depth of the crust is less pronounced. Relative to the absence of caking agent, Reagent 2 has a positive effect on the CI of the fragrance mixture, although the CI value of silica is the lowest.

As with case study 1, this set of experiments was extended by analyzing the dynamic and volume characteristics of the fresh mixture before storage. These data (Figure 5) illustrate how the addition of anti-caking agents affects the characteristics of raw powders, provides useful insights about the potential for process performance changes, and helps to rationalize the observed caking behavior.

Image provided by Freeman Technology Image provided by Freeman Technology Image provided by Freeman Technology Image provided by Freeman Technology

Figure 5: The dynamic and volume characteristics of the milk and spice mixture show that the effect of anti-caking agents varies from substrate to substrate.

The addition of silica significantly reduces the compressibility of the milk powder and flavor mixture. Reagent 2 reduces the compressibility of milk powder, although it is not a fragrance mixture, but the degree is lower than that of silica. Lower compressibility is associated with more effective particle filling and makes the powder less prone to changes in fluidity during storage. However, it can also lead to high BFE values, because powders with lower compressibility tend to have poor flowability under the mandatory conditions associated with BFE measurement. This effect was observed in perfume-silica mixtures, but not so much in similar powdered milk samples. A strong correlation was observed between compressibility and CE (caking energy) (R2, milk powder = 0.9981, R2, fragrance mixture = 0.9275).

The SE data provides another example of the contrast behavior observed with different substrates. Although both anti-caking agents reduced the SE of the milk powder, the opposite effect was observed in the flavor mix. SE quantifies how easy it is for the powder to flow in an unconstrained, low-stress state. Therefore, higher values ​​may be directly related to performance impairments in unit operations where powder flows under gravity, such as in filling or metering applications.

Finally, in case study 1, a strong correlation between the SI and shell energy of the two powders (R2, milk powder = 0.9970, R2, spice blend = 0.9860) was observed, and it is reasonable to rationalize this trend as before , Refer to SI's ability to provide an indication of water absorption tendency.

This second set of data further demonstrates the complexity of agglomeration behavior and the insight of dynamic powder properties on the relative applicability of crusts and different anti-caking agents to different substrates. 

The food processing industry relies heavily on anti-caking agents to achieve the required manufacturing efficiency and product performance. Improving and updating the additive package is essential to respond to changing needs, formulate new foods, and eliminate ingredients with undesirable sources or health conditions. The work presented here proves the value of dynamic powder testing in comparing the performance of anti-caking agents and the efficacy of the new functionalized calcium carbonate anti-caking agents on two different substrates. A key feature of dynamic testing is the ability to detect and characterize heterogeneous agglomerations or crusts to provide unique and rigorous insights that directly support the introduction of additives with targeted performance characteristics. The results show that the performance of the functionalized calcium carbonate anti-caking agent is close to that of silica (a gold standard anti-caking agent), so it has considerable potential in food processing applications.

Laura Shaw is an application expert at Freeman Technology; Dr. Renata Negrini is a food technology service manager at Omya International AG; Marcel Lexis, a former consumer product innovation engineer, Omya International AG; Jamie Clayton is an operating director at Freeman Technology; Lalit Sharma is a food innovation at Omya International AG manager.

1 McKinsey and Co. "Food Processing and Handling: Subversive Maturity"

2 N Michail "EFSA raises red flags that silica is safer than nanoparticles"

3 Brockbank K, Armstrong B, Clayton J. The measurement and quantification of agglomeration in excipients and foods focuses on the non-uniform interaction with environmental moisture. Microparticles 2020, 56: 75-83

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