Possible unexpected peaks from oil drop size measurements in milk

Abstract

The shelf life of milk is amongst others dependent on the size of the oil droplets. These droplets can be measured using the laser diffraction (LD) technique. LD is a popular technique to measure particle size distributions (PSD) that has an outstanding broad measuring range capability, is easy-to-use and has a high reproducibility. While this technique is extremely popular, there are some conditions under which LD shows unexpected results in the form of unexpected peaks. The purpose of the current study was to determine under which conditions unexpected peaks appear or do not appear while measuring the PSD of oil droplets on LD equipment. Samples of pasteurized milk were measured on two versions of LD equipment to investigate and identify the conditions under which the LD gives these unexpected peaks, including the variables: pretreatment, sample concentration (i.e. obscuration rate) and dispersing unit stirring speed. A more simplified system (i.e. model emulsion) and a complementary technique (dynamic light scattering) were used to further investigate the unexpected peaks. Results showed that the right sided unexpected peaks are believed to be caused by the incorporation of air. Right sided unexpected peaks can also be caused by dirt in the equipment and a too low sample concentration (i.e. obscuration rate). The second finding of this study is focused on left sided unexpected peaks. These peaks are believed to be caused by a too high sample concentration, which results in the effect of multiple scattering. Another type of left sided unexpected peaks is an increased standard deviation caused by using unoptimized variables of the LD equipment (e.g. too high stirring speed or too low sample concentration). As a result of the increased sensitivity in one of the models of the LD equipment, it was found that it is even more crucial to introduce the adequate optical parameters values (e.g. absorption index). When increasing the absorption index blue light, the discrepancies between different models can be reduced. However, more research needs to be done to confirm this theory. All in all, unexpected peaks can be caused by air, sample concentration, dirt and differences between LD equipment.

Popular Abstract

Chasing unexpected results in the particle size analysis of oil droplets.
Imagine that 90% of the results given by the most popular particle size distribution determination technique are unreliable and a large scientific community have been using these results over the past years without critically thinking about them.
In the engineering world, accuracy and precision are two concepts that are extremely important to consider when measuring the efficiency of any process. In the food industry as well as in many applications, the need to measure small particles has led to different technologies. Some of them used in a major extent compared with others. Together with advances in laser and light technology, especially after the increasing interest of nanoparticles by the pharmaceutical industry, several techniques have been developed in order to improve the accuracy and reliability of the small particle measuring techniques.
Automatized laser diffraction (LD) techniques are the most used and popular instrument to measure particle size distributions. Its high popularity is due to its outstanding broad measuring range capability and its easy-to-use and high reproducibility. These instruments utilize the principle of laser technology. Together with a complex mathematical algorithm the technology interprets the signal and in an indirect way measure macroparticles, microparticles, nanoparticles and mixtures of those. This makes it an all-purpose technique. However, this technique has its problems and limitations, which are not easy to overcome. These are quite often overseen, underestimated or simply unknown to the user.
Having a deeper understanding under which conditions the instrument can give precise, accurate and reliable results will be highly beneficial for most of the scientific community interested in micron and submicron particle populations. For example, product developers, process engineers, food scientists, just to mention some. However, there are some conditions under which the LD technique shows unexpected results in the form of unexpected peaks. To tackle this problem, this study was started.
In this master thesis, conditions are studied under which unexpected peaks appear or do not appear while measuring oil droplets on commonly used LD equipment. A comparison between two commonly used LD models is presented in order to highlight significant differences in volume PSD and the occurrence of unexpected peaks.
Experiments were preformed using primarily pasteurized milk. However, since milk is such a complex system a model emulsion was studied, which is a more basic system to analyze. This also provided insights to discard some of the hypotheses that might cause the appearance of the unexpected peaks. In order to evaluate the accuracy and detection capability of LD equipment, a technique using dynamic light scattering was used as a complementary technique.
Furthermore, this thesis describes usage recommendations and best practices in detail. This can provide insights in how such equipment should be operated to limit the incidence of unexpected peaks and how to interpret the unexpected peaks when they do occur.

• author: Schalkwijk, Laura and Olmedo Sotomayor, Rodrigo
• supervisor: Andreas Håkansson; Fredrik Innings
• organization: Food Technology and Nutrition (M.Sc.)
• course: KLTM01 20201
• year: 2020
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: laser diffraction, oil droplet size, milk, pasteurised milk, unexpected peaks, mastersizer, food engineering, livsmedelsteknik
• language: English
• id: 9016663
• date added to LUP: 2020-06-15 13:50:15
• date last changed: 2020-06-15 13:50:15