Understanding the correlation between molecular structure of chilled dairy creams and the risk of environmental stress cracking in Tetra Pak® carton packages

Abstract

Multilayer food packaging are lined with an inner layer of plastic and has excellent barrier properties. However, plastics lose their mechanical properties after being exposed to certain conditions; the combination of factors generates failures in the material such as the appearance of cracks, this phenomenon is known as environmental stress cracking (ESC). Tetra Pak® has been interested in research on the formation of cracks in the bottom. Previous investigations have been carried out on packaging such as Tetra Top® and products with a high fat content as dairy creams and it was found that in some cases there were “aggressive” agent that accelerate the formation of cracks and increase the risk of ESC. This research focused on the study of chilled dairy creams, investigating the effect of unit operations in the production process (heat treatment: direct or indirect, and homogenization: downstream, upstream, and no apply) that could substantially influence the molecular structure and physicochemical properties of the final dairy cream. Therefore, three different phases were developed in the project; the first was the production of five batches of chilled dairy cream using a lab mini-UHT (with 5 different formulations). In the second, physical and chemical analyses of the dairy cream batches, and in the third phase, the indicative tests of food package interaction as the main objective of investigating the ESC. It is important to note that these tests were carried out on a laboratory scale, the purpose was to simulate the process conditions that occur in the dairy industry, but there are more factors to control, such as the flow speed, the homogeneity of the raw materials, among many other variables that are difficult to control. Nevertheless, the objective of finding significant differences in the final product depending on the applied process was fulfilled

Popular Abstract

This is Environmental stress cracking (ESC) is one of the most common problems in polymers, this phenomenon usually occurs regardless of the time of polymer use, therefore, it can occur immediately after starting to use or it can occur in days, months, or years later. It is difficult to establish an analysis methodology that allows early detection of the fractures or cracks formation in the polymer before they are visible to the human eye. This problem has been detected in certain Tetra Top®, Tetra Pak carton packaging, used to package high-fat and refrigerated dairy creams.
Theoretically, it is known that the formation of cracks can begin previously when the plastic material is subjected to stress, or bent, or sealed and increase the risk of cracks formations when it comes in contact with aggressive agents that accelerate the crack formation process. Cracks form and spread resulting in leaks, which is a problem for food producers due to loss of food product and loss of packaging, due to the loss of integrity of the packaging and the product exposed to environmental conditions. The objective of this study was to be able to predict which factors among processing line such as heat treatment and homogenization have a significant influence on the molecular structure of the dairy cream that are packed in the Tetra Top® that can accelerate the formation of cracks and obtain a correlation between the dairy cream product and the ESC in the bottom in the packaging.
In this thesis, it was tried to find relationships between the characteristics of the molecular structure and the responses of the Tetra Top® packaging and its risk factor of ESC. For this reason, the production of chilled dairy cream is proposed using a mini-UHT laboratory scale, controlling variables of traceability of raw materials, the heat treatment and homogenization, as well as cooling phases and storage, among others. As a second phase, it was proposed to carry out an analysis of the dairy cream product obtained previously, such as fat and protein content, as well as analysis of particle size distribution, viscosity, emulsion stability and microscopy with protein staining.
On the other, the heat load of the dairy cream was estimated by measuring the lactulose concentration, also it was carried out viscosity analysis at two temperatures of 6°C and 20°C. Moreover, the stability of the emulsion was analysed in a time of 70 minutes at 23°C using the technology based on the measurement of transmittance as the backscattering of near-infrared light at 880 nm, this study allows knowing the movement of the particles in the dairy creams and creating a prediction model on time of the stability of the emulsion.
As a third phase, analyses were carried out to verify the food-packaging interaction, such as the puncture test using a setup in a force machine, this equipment is used to evaluate the ESC in the inside layer of the package as indicative test. The equipment gives as a result of tip displacement at failure in mm.
The red-ink test was also carried out, which is a dye penetration test widely applied as a leak detection method. The result after to remove the cardboard layers of the material by hand is to visualize if it is the appearance of leak, points, or spots.
Official ESC evaluation tests such as that specified by ASTM D1693, for example the Bell telephone or the Notch Constant Load Test (NCLT), are based on generating biaxial tension and at the same time putting the material in contact with the "aggressive" substance, thus evaluate the crack formation time, managing to quantify the risk of ESC. But these tests are unreliable and slow, they also require the use
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of special equipment that quantifies the application of quantifiable forces, in addition to the fact that it is more complex to analyse the data obtained and to be able to generate possible solutions from this.
In conclusion, the risk of ESC depends on many factors, among the main ones are the plastic material, the environmental conditions and the chemical agents that accelerate the formation of cracks. Therefore, in this study, the main focus was to evaluate and summarize all the possible factors associated with the "chemical agent", which in this case is chilled dairy cream, since it is considered a priority to establish correlations between the chemical and molecular structure of the product and the risk of ESC, and thus be able to generate certain recommendations to dairy cream producers that help them reduce the risk of ESC in Tetra Top® packages.

• author: Fernandez Castaneda, Alejandra
• supervisor: Frida Lewerentz; Maria Glantz; Helena Wijkander; Jannika Timander
• organization: Food Technology and Nutrition (M.Sc.)
• course: KLGM01 20221
• year: 2022
• type: H2 - Master's Degree (Two Years)
• subject: Agriculture and Food Sciences
• keywords: Cream, microestructure, environmental stress cracking, food technology and nutrition
• language: English
• id: 9088645
• date added to LUP: 2022-06-17 08:40:16
• date last changed: 2022-06-17 08:40:16