Optimizing Food Packaging Size by Measuring the Tapped Density
2021-11-05Application Note
Optimize food powder packaging & transport costs. BeDensi T1 Pro measures bulk/tapped density of protein powders, helping manufacturers find ideal container sizes for quality control.
| Product | BeDensi T Pro Series |
| Industry | Food and Drink Analysis |
| Sample | Protein Powder |
| Measurement Type | Powder Characteristics |
| Measurement Technology | Powder Characterization |
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Abstract: A reasonable packaging size in the food industry is important not only to ensure the success of the packaging process, but also to decrease the cost of transporting products. This application note explores how the size of the food powder container is determined by measuring the bulk density and tapped density. In this research, three types of protein powders, including whey protein, soy protein and whey-soy protein mixture, were analyzed by an automatic tapped density tester - The BeDensi T1 Pro. The result demonstrates that the instrument relies entirely on providing food manufacturers with reliable information to determine the optimum packing size and choose a container that is satisfying to the customer.
Key words: Tapped Density; Protein Powders; Packaging; Food; Bulk Density; Slack Fill.
1. Introduction
A majority of food industries currently handle particulate food, involving various powders that range from ingredients, such as flours, sugars, and spices, to end products such as protein powder and instant coffee. [1] Great care must be taken during the handling process from production to food packaging and ultimately storage, transportation, and distribution.
Bulk properties, such as the bulk density and tapped density, play a direct and important role in food packaging [2]. Bulk density is the ratio of the mass to the volume of a loose powder. Tapped density is the ratio of the mass to the volume of powder tapped for a defined period. In effect, the tapping process simulates the vibration that all powders endure during production, storage, transportation, and distribution. In Figure 1, it is clear that the interstitial space between the particles is included. [3] After tapping is generated during storage and transit, the amount of interstitial air is reduced, which leads to a smaller volume.
Generally, many powdered foods are packed in a bag or bulk container and then transported over a long distance for consumption after distribution in the shops. The density of the powders is an important parameter to know to establish the optimized size of powder packaging containers. For example, for light bulk density powders, it is an effective method for designing a more compact packaging by removing air from the product during and after filling. Therefore, the optimum packaging size can be accurately calculated by confirming the bulk density and the tapped density, and is highly significant in the economics of transporting powder. Besides, it is crucial to ensure that there is a correct fill volume in each consumer pack. [4] Unreasonable fill volumes, such as those having too much void space in the container on opening by the customer, will dissatisfy the customer and even lead to accusations of misleading the customer based on the Federal Food, Drug & Cosmetic Act (FDCA). [5]
Therefore, it is necessary to figure out the bulk density and tapped density of protein powders so that factories can strike a reasonable balance between the slack-fill and the actual capacity of a container. The aim of this application note is to explore the tapped densities of different protein powders to achieve reasonable and customer-friendly packing sizes for the manufacturers.
2. Method
The whey protein and soy protein were bought off the shelf in a local supermarket in Shenzhen, China. The wheysoy protein was made by mixing the whey protein and soy protein powders. To make density results meaningful, the tapping conditions need to be quoted. The tapping test was performed by the BeDensi T1 Pro in accordance with the ISO standards. [6,7] A 250 ml graduated cylinder with 50 g sample was tapped at room temperature for 625 times using the tapped density tester. The measured density was obtained by the given formula below:
For example, in the protein packaging industry, there is an interesting phenomenon that protein powder containers are rarely filled full, which is caused by slack-fill. Slack-fill is the difference between the actual capacity of a container and the volume of product contained therein. The slackfill covers the appropriate volume that functions for sealing and protection of the product, and is induced by vibration of the powder throughout shipping and storage. Ultimately, when the products arrive on the shelf in a supermarket, it is possible that they may have excessive empty space inside because of tapping.
where x is the number of taps, ρ is the density, m is the mass, and V is the volume. ρ0 and ρ625 are the measured densities, in grams per milliliter, after transfer and after 625 taps, respectively.
To determine the appropriate container size with test results, 500g of whey protein powder was filled in three different slack-fill containers (10, 20, and 30 vol%) before tapping. After tapping 625 times, the feedback on the different-sized containers from twenty Bettersize colleagues was collected.
3. Results
3.1 Pure Protein
The tapped densities of pure whey protein and soy protein powder were obtained. Table 1 denotes that both ρ625 and ρ0 of soy protein are larger than whey protein, which means that a smaller container is appropriate for packing pure soy protein.
| Protein |
ρ0
|
ρ625
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|
(g/ml)
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| Whey | 0.33 | 0.50 |
| Soy | 0.42 | 0.59 |
3.2 Mixed Protein
The tapped density of mixed whey-soy protein powders was also measured by using the automatic tapped density tester. Table 2 presents the densities of mixed protein with 25, 50, and 75 wt.% whey proteins. The soy protein tapped density will increase with the mass fraction of whey protein. It is necessary to determine the applicable containers or bags to store different protein products.
| Protein |
ρ0
|
ρ625
|
|
(g/ml)
|
||
|
Whey-soy (3:1)
|
0.35 | 0.54 |
|
Whey-soy (1:1)
|
0.39 | 0.57 |
|
Whey-soy (1:3)
|
0.41 | 0.59 |
Also, the measured tapped densities are slightly larger than the calculated tapped densities based on the mass weight of the two powders, as shown in Figure 3. The calculated values were obtained by the equation below:
Where the ρmix is the calculated tapped density of the mixture, the ω is the mass fraction. As has been mentioned during tapping or transportation, small particles can be displaced.
| Container Volume (ml) | 500g Loose Protein Powder | 500g Tapped Protein Powder | Customer Emotion | ||
| Volume (ml) | Slack Fill (vol%) | Volume (ml) | Slack Fill (vol%) | ||
| 1683 | 1515 | 10 | 1000 | 41 |  |
| 1893 | 20 | 47 | |||
| 2164 | 30 | 54 | |||
Table 3 shows the slack-fill volumes of the loose and tapped products packed in different volume containers. To easily understand the change, the schematic of the slack-fill changes of the simulated sample is shown in Figure 4. After transit, the slack-fill percentage increased due to an increase in tapped density. For example, the 30 vol% of slack-fill percentage
The air between the larger particles thus reduces the volume and increases the density. It is not an appropriate method to calculate the tapped density of protein powder mixture merely by using a simple model of component properties, since the density is also affected by its particle size and distribution, particle shape, and surface structure. [8]Consequently, a standard tapped density tester is required for manufacturers to scientifically and accurately study the tapped density of the powders.
4. Discussion
The bulk density and tapped density of three types of protein powders were measured successfully. The appropriate container size could be determined from these results for each of the powders. In addition, what a slack-fill percentage would elicit a positive response from customers. The packaging of 500 g whey protein powder was simulated with different container sizes and slack-fill volumes.
The loose product increases to 54 vol% in the tapped product. The larger the packaging size, the higher the slackfill percentage. The feedback result presents that in this case, most of the Bettersize employees were dissatisfied with the 30 vol% initial slack fill, as presented in Table 3.
In this case, when the protein container has a 30 vol% slackfill initially, its tapped slack fill will exceed 50 vol%, which would be contrary to a customer’s expectations. Conversely, customers will be more satisfied if the slack-fill is less than 20 vol%. This suggests that a reasonable packing size can be achieved by controlling the initial slack-fill to less than 20 vol%.
5. Conclusions
The tapped density of the pure and mixed protein powders has been successfully measured by using BeDensi T1 Pro. For pure protein powder, different types of protein powders have different tapped densities, so the packing sizes ought to be confirmed based on the premise of the particle density. With the change of mass ratio in the protein mixture, the tapped density is different. And the tapped density should be measured by a standard tapped density tester rather than calculated by a simple model of component properties. Based on the tapped testing results, a reasonable packing size for the whey protein product can be achieved under a 20 vol% initial slack-fill.
Thus, a standard tapped density tester is an absolute necessity for all manufacturers who wish to study the tapped density of the powder accurately and, from this information, design appropriately sized packaging. The BeDensi T Pro series can provide food powder producers with reliable information to determine an optimum packing volume, which will be useful in determining a packaging that is eye-catching, fit for purpose, and customer-friendly.
6. Reference
[1] Pablo J., Guatavo V. (2010). Food Powder Flowability Characterization: Theory, Method, and Applications. Annual Review of Food Science and Technology, 1(1), pp. 211-239
[2] Malave, J., Barbos-Canovas, G.V. and Peleg, M. (1985). Comparison of the Compaction Characteristics of Selected Food Powders by Vibration, Tapping and Mechanical Compression. Journal of Food Science, 50, pp. 1473-1476
[3] Merkus H. (2009). Particle Size Measurements: Fundamentals, Practice, Quality. 1st ed. The Netherlands: Springer.
[4] Onwulata C. (2005). Encapsulated and Powdered foods. 1st ed. Boca Raton: CRC Press
[5] Federal Food Drug & Cosmetic Act (FDCA) Section 403(d) (21 U.S.C. 343(d)).
[6] ISO8967/IDF134 Dried milk and dried milk products – Determination of bulk density.
[7] Lin R, Wang Y., Selomulya C. (2022) Physical Properties of Dairy Powders. Encyclopedia of Dairy Sciences. pp. 504-520
[8] Merkus, H., Meesters G. (2014) Particulate Products: Tailoring Properties for Optimal Performance. 1st ed. Netherlands: Springer.
About the Authors
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Perfil Liu Senior Engineer @ Application Research Lab, Bettersize Instruments Ltd.
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The BeDensi T Pro Series is a reliable tapped density tester. It excels at intuitive operation while complying with the USP, Ph. Eur., ASTM, and ISO standards.
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