Effect of the Cooling Rate and the Surface Film Composition on the Colloidal Stability of Whey Protein Based Emulsions of Triacylglycerols

Abstract

The goal of this project was to investigate the effect and interplay of formulation and processing parameters on the colloidal stability of emulsified triacylglycerols from a product quality perspective. Different methods to quantify and monitor this effect over time were evaluated. The results of this study were intended to lead to the development of industry relevant recommendations to optimise the processing conditions and formulation of a range of different products.
Many commercially important products, including cosmetics, pharmaceuticals and foods such as UHT milk and heavy cream are based on triacylglycerols emulsified in a protein-rich continuous phase. Temperature fluctuations during long-term storage and distribution of these products can cause uncontrolled crystallisation of the disperse fat phase. This impairs the functional and sensory characteristics and the stability of the emulsion system. Product defects and product waste could be reduced by gaining a systematic understanding of the factors that govern the crystallisation behaviour of emulsified triacylglycerols and by finding mechanisms to induce a guided crystallisation process.
In this study, a liquid emulsion system was produced from hydrogenated palm oil, consisting nearly entirely of triacyglycerols, and an aqueous continuous phase, containing !-lactoglobulin as emulsifier. Diffraction analysis, microscopic and calorimetric measurements were used to determine the colloidal stability of the model system over eight weeks of isothermal storage at 22 °C. Based on previous research, it was expected that the surface film composition of the dispersed palm oil droplets and the rate at which the emulsions are cooled from processing to storage temperature, would impact the stability of the system. Thus, the influence of a high, moderate and low cooling rate and the addition of two phospholipids, acting as complementary emulsifiers to !-lactoglobulin, were tested.
No significant effect of the cooling rate on the stability of the emulsion system was noted over a storage period of eight weeks. The addition of phospholipids seemed to have altered the composition and thereby the properties of the emulsion interfaces. The emulsions showed a more uniform fat crystal size but also more extensive flocculation. It is therefore questionable whether the benefit of using phospholipids does not outweigh the costs. One of the two phospholipids even appeared to inhibit the crystallisation of the hydrogenated palm oil, which is unfavourable, when aiming for a fully crystalline fat phase.
The results of this project suggest that a formulation without phospholipids and a slow cooling process are most cost and resource efficient to produce a stable emulsion system. Independent of the formulation or processing, there were signs for the migration of fat molecules between the emulsion particles. This can adversely affect the particles’ physicochemical properties and raises the need for further research into mechanisms to prevent mass transport processes in triacylglycerol emulsions.

Popular Abstract

What crystals have to do with the quality of stored food products
Some food components can form crystals when the foodstuff is stored over an extended period of time. These crystals can impair the product’s texture and appearance. It is therefore important to control crystallisation in foods to preserve their quality.
When you think of a crystal, you might have a shiny objects in mind, maybe made from water, like snowflakes or ice cubes or made from carbon, like a diamond on an engagement ring. In chemical terms, the crystalline state is one of two solid states that a compound can exist in. Food components such as fats, proteins and sugars can form crystals. In some applications, as for instance ice cream and margarine, crystals are necessary to provide a certain texture.
However, crystals can also form unintentionally in foods such as UHT milk and heavy cream. In these products, the milk fat is initially present as liquid droplets floating around in an aqueous medium. When these products are stored or shipped, the liquid fat droplets can crystallise over time. The fat crystals can grow really big and form sharp edges. The large fat crystals tend to get entangled when they collide. Then they stick together and merge. Eventually, the fat crystals may form one big layer, which floats up. This might make you think that the product has turned bad and make you discard it.
This project was aimed at finding mechanisms to control the fat crystallisation during storage of high fat liquid dairy products. Milk fat is a highly complex natural fat with a varying composition depending on seasonal factors and cow genetics. Therefore, hydrogenated palm oil was used as a model fat. It has a known composition and similar key features to milk fat. After screening the literature, two approaches to control the fat crystallisation were chosen: (a) rapidly cooling the product from the temperatures at which it is processed, i.e. temperatures above the melting point of the fat, to the temperature at which the product is stored and (b) adding certain fats, called phospholipids, because these allow to induce a controlled crystallisation process. Both approaches were expected to lead to the formation of small, equally sized, roundish fat crystals, which would not easily get entangled.
Approach (a) showed no significant effect on any product parameter. Approach (b) on the other hand led to a more uniform crystal size. The benefit of this effect is however outweighed by the costs, that the addition of phospholipids incurs. This is especially true since the quality and the stability of the products were acceptable even without following either approach (a) or (b).
The results of this project suggest that a product formulation without added phospholipids and a cooling process that is not intentionally accelerated are most efficient to reach a stable high fat liquid dairy product.

• author: Schüler, Charlotte
• supervisor: Björn Bergenståhl
• organization: Food Technology and Nutrition (M.Sc.)
• course: KLGM01 20222
• year: 2022
• type: H2 - Master's Degree (Two Years)
• subject: Agriculture and Food Sciences; Technology and Engineering
• keywords: Emulsion technology, Fat crystallization, Emulsified triglycerides, Colloid science, Food technology
• language: English
• id: 9103560
• date added to LUP: 2022-12-06 09:35:58
• date last changed: 2022-12-06 09:35:58