Homogenization

Setting quality specifications and improving shelf life

Text by Julie Nguyen

The National Milk Marketing plan was created in 1970 to enforce strict quality standards throughout the production and processing chain of Canadian dairy products. According to the Canadian Dairy Information Centre (CDIC), more than 2.5 billion litres of milk and cream were produced in 2015. Because this beverage is important for the health of both consumers and the economy, special focus needs to be given to the supply chain, since it plays a critical role in determining the shelf life of the product.

Raw liquid milk is a mixture of fat globules, proteins, and other nutrients such as vitamin A, D, E, and K, just to name a few. The particle size of fat globules, in particular, plays a crucial role in determining the shelf life in addition to the taste and texture of the milk. When left to age, fat globules present in whole raw milk will rise to the top, creating a layer of cream. When kept continuously at the optimal temperature of 2 C to 3 C, the shelf life of non-homogenized milk can last about seven days, while homogenization can prolong the shelf life to at least twice as long. For that reason, commercial milk is most often homogenized.

Homogenization is a two-stage mechanical (not chemical) process developed in the late 19th century. It reduces fat globules into smaller droplets by forcing milk through a tiny orifice under high pressure. In doing so, fat droplets are reduced in size and will thus stay suspended in liquid milk longer. This process is used to produce whole milk (approximately 3.6% fat), 2% milk, and skim milk. Some research studies have even shown that homogenization also improves the digestibility of milk. There is, however, a downside. Decreasing fat droplet size increases the available surface area, and when available surface area of the fat droplets becomes excessively large there is insufficient protein to completely cover the surface of the droplet. The result can be flocculation or coalesce of fat droplets. In order to achieve a perfect balance, food scientists need to monitor and control the homogenization process through real-time feedback.

HORIBA Instruments offers two options for monitoring the homogenization process; the LA-350 Laser Particle Size Analyzer and the LA-960 Laser Particle Size Analyzer.

The LA-960 is the high performance laser diffraction analyzer with a wide dynamic size range from 10 nm to 5 mm. While some may feel that a size range from 10 nm to 5 mm is overkill for assessing particle size of fat globules, many have found that the LA-960 can provide additional sub-micron information on milk. This data in the nanometer size range can provide information on the protein constitution (casein micelles) of the milk. The LA-960 also offers unique accessories that are well-suited for a wide variety of dairy applications, such as spray-dried milk powder, chocolate and coffee creamer.

The Partica mini LA-350 is a laser diffraction analyzer with a size range from 100 nm to 1000 µm. This lower cost LA-series analyzer is compact (297 mm x 420 mm) and portable (23 kg). This offers the added advantage of being able to be placed at each milk plant, providing immediate feedback on optimization of the final product. For that reason, the LA-350, or its predecessor, the LA-300, has become the standard in the industry.

Above is a typical of the example of the overlay of store-bought non-homogenized milk and homogenized whole milk obtained using the
LA-350**.

The distribution shows the presence of much larger fat globules in non-homogenized milk versus the distribution of stable, homogenized whole milk. Particles for non-homogenized milk range from approximately 1-10um whereas particles for homogenized milk range roughly from 0.2-2um. From the analysis result, we can see that the homogenization process reduces particle median (D(v0.5)) from 3.71um to 0.81um. This critical parameter is often utilized by milk producers when setting quality specification thus improving shelf life.

**Note that the amount of fat dominates the amount of casein (protein) in whole fat milk such that the presence of protein is not even apparent in this particle distribution. For full detail, please visit www.horiba.com and go to the Applications Note on Milk Homogenization.

Reference
[1] www.dairyinfo.gc.ca

Julie Nguyen is a consultant at

HORIBA Scientific