Current insights into protein solubility: A review of its importance for alternative proteins

The solubility of proteins plays a key role in determining the physicochemical properties, processing, sensory attributes, shelf life, and nutritional profile of foods formulated with protein-rich materials. At present, there is a renewed interest in understanding the solubility of novel protein sources because of the increased demand for foods formulated without animal-derived proteins. These sources include proteins arising from plants, bacteria, fungi, insects, and precision fermentation. The different solubility characteristics of these proteins make it challenging to create food products that meet the quality demands of food manufacturers and consumers. Consequently, there is a need to gain a deeper understanding of the factors that impact protein solubility, as well as methods to improve protein solubility. In this review, we discuss the fundamental thermodynamical foundations for protein solubility. We base the discussion on the different methods available to measure and analyze protein solubility followed by describing how environmental conditions affect the solubility of alternative proteins (e.g., soy, pea, sunflower, potato, microalgae, mealworm, and others). Finally, the review shows how physical, chemical, and biological methods can be utilized to alter the solubility of proteins. Many novel alternative proteins follow typical solubility patterns, but some show remarkable resistance to precipitation under different environmental conditions. However, there is still a lack of understanding of what exactly determines the solubility of alternative proteins, as well as knowledge about the solubility profiles of individual protein fractions and we conclude by highlighting important knowledge gaps that prevent further innovation.