Fluorescence Anisotropy Offers New Insights into Food Texture and Structure

In a new study published in the Journal of Food Composition and Analysis, lead author Harshkumar Patel from the University of Copenhagen and the Institute of Agrifood Research and Technology (IRTA) and his team investigated how fluorescence anisotropy (FA) can be used to quantify and assess the structural properties of (semi) solid food matrices (1). The study highlights both the potential and limitations of FA as an analytical tool in food science, particularly for evaluating complex food textures such as plant-based alternatives and traditional dairy products (1).

Food texture plays a crucial role in sensory perception and consumer preference. It is often a key variable that consumers consider when purchasing a particular food item (2). Food texture is also influenced by microscopic and macroscopic levels of structure in a food item (2).

Shredded mozzarella cheese on a cutting board with a grater | Image Credit: © irontrybex - stock.adobe.com

Currently, in the food industry, there has been a gradual rise of plant-based meat and other alternatives. In the United States, approximately 5% of the population adheres to a vegetarian diet and about 4% of the U.S. population is vegan (3). The market is expecting the plant-based protein product market will grow from $14.3 billion in 2024 to $20.5 billion by 2029 (4).

One of the main challenges the plant-based meat industry faces is replicating the fibrous texture of animal-based products. Anisotropy, which refers to the directional dependence of structural properties, is a key characteristic in food formulation, yet it is notoriously difficult to measure and control (1). This study provides a systematic protocol for measuring FA, and the researchers’ goal was to improve its application in the assessment of structural anisotropy in processed food matrices.

As part of the experimental procedure, Patel and the team used fluorescein, which is a classic fluorescent dye, and compared FA values using solutions of tryptophan and bovine serum albumin (BSA) (1). These served as reference points for analyzing more complex food structures. Two primary test systems were investigated in the study: the first was a hybrid extrudate of plant and dairy proteins, and the second was commercially produced cheeses with differing structural characteristics (1).

High-moisture extrusion products made from pea protein isolate (PPI) and whey protein concentrate (WPC) were examined to determine their anisotropic behavior. The researchers found that blends of PPI and WPC (at a 70:30 weight ratio) exhibited greater anisotropy than samples containing only PPI (1). The researchers deduced that the inclusion of dairy proteins may contribute to an improved fibrous structure in plant-based extrudates, potentially enhancing their texture to more closely resemble traditional meat products (1).

The second primary test system assessed anisotropy in mozzarella and cagliata cheese. Mozzarella was chosen for this study because it is known for its characteristic fibrous structure due to the pasta-filata stretching process (1). The researchers found that mozzarella cheese, because of its fibrous structure, displayed higher FA values compared to cagliata (1). These findings confirm that fluorescence anisotropy can effectively distinguish between cheeses based on their textural properties.

Several challenges emerged in the study that indicate the difficulty of applying FA as the tool of choice for this application. First, fluorescence-based measurements often take from a small sampling area; as a result, it can lead to variability in results (1). To obtain reliable quantitative data, the researchers emphasized the need for increasing the number of replicate measurements across homogeneous sample surfaces (1). This is particularly relevant for foods with multiple intrinsic fluorophores, such as extruded plant-based proteins, which complicate direct comparisons across different formulations (1).

FA’s application in food science is limited. As a result, the researchers also suggest that more studies should investigate the technique’s applicability in this industry more, so that researchers have more comparable data to examine in future studies (1).

This study represents a step forward in understanding the complex structural properties of semi-solid foods. Although challenges remain in standardizing FA for widespread use, this research provides a foundation for future studies that could refine and expand its applications in food science. By leveraging fluorescence anisotropy, researchers may unlock new ways to manipulate food structure, paving the way for innovative advancements in both plant-based and dairy product development (1).

References

1. Patel, H.; Barnes-Calle, C.; Rinnan, A.; Engelsen, S. B.; van den Berg, F. W. J. Characterization of the Anisotropy in Proteinaceous Semi-solid Food Matrices Through Polarized Fluorescence Spectroscopy. J. Food Comp. Anal. 2025, 140, 107237. DOI: 10.1016/j.ifca.2025.107237
2. Kilcast, D.; Lewis, D. F. Structure and Texture — Their Importance in Food Quality. Nutr. Bull. 1990, 15 (2), 103–113. DOI: 10.1111/j.1467-3010.1990.tb00073.x
3. Statista, Veganism and Vegetarianism in the United States – Statistics & Facts. Statista.com. Available at: https://www.statista.com/topics/3377/vegan-market/#topicOverview (accessed 2025-02-19).
4. Ethical Globe, The Vegan Market in 2024: Growth, Challenges, and Opportunities. Ethical Globe. Available at: https://www.ethicalglobe.com/blog/the-vegan-market-in-2024-growth-challenges-and-opportunities (accessed 2025-02-19).