Potentialities of plant protein aerogels as innovative food ingredients

Protein aerogels are attracting large attention in the food sector, since presenting appealing characteristics as innovative food ingredients. Being made by proteins, commonly used food ingredients, they are largely accepted by consumers. Moreover, the structure of protein aerogels can be fine-tuned by acting on multiple processing (e.g., drying technique) and formulation (e.g., protein type, pH) factors, thus allowing the engineering of systems with a wide range of tailor-made functionalities. As a result, protein aerogels have been proposed as advanced food ingredients to develop bioactive delivery systems in the gastrointestinal tract, and structure liquid oil into plastic materials able to replace saturated fats in foods. Surprisingly, to date, the potentialities of protein aerogels as innovative food ingredients have been only demonstrated for animal protein-based systems, mainly egg and milk proteins, and studies regarding the development of aerogels from plant proteins are very limited. Nevertheless, the current concern about the poor environmental sustainability of animal proteins and their production is boosting the so-defined “plant-protein transition”, which has been identified as a key strategy to increase of food sustainability. In this context, plant-protein-based aerogels could represent an influential opportunity to favor the inlet of aerogels in the food sector. Based on these considerations, the aim of the present work was to study the possibility of producing food-grade aerogels based on plant proteins (pea and soy) and to collect preliminary data on their compatibility with food systems. To this aim, soy and pea protein isolate (SPI, PPI) hydrogels (10-20% w/w, pH 4.5 or 7.0) were converted into aerogel particles by grinding followed by ethanol solvent exchange and supercritical-CO2-drying. The obtained aerogel particles were analyzed for physical properties (BET surface area, porosity, density), and ability to interact with water and oil, commonly used food solvents. To this aim, aerogel water solubility and water and oil holding capacity (WHC, OHC) were assessed and compared to those of SPI and PPI. Aerogelation of SPI and PPI allowed obtaining porous particles, with BET internal surface and porosity in the range 50-150 m2/g and 60-80% respectively. The lowest values were found, as expected, at pH 4.5, corresponding to the isoelectric point. As compared to SPI and PPI, which presented a water solubility higher than 80%, the corresponding aerogels showed a water solubility around 25%. Aerogelation also significantly increased the WHC and OHC as compared to the protein isolates. The results obtained in this study demonstrate the possibility to produce plant-protein-based aerogels in the form of porous powders. The high ability to absorb water and oil, which can be exploited in the formulation of complex foods requiring rheological modulation (e.g., creams, spreads, dressings), associated with the vegetable origin of the used proteins, can be regarded as key characteristics able to stimulate the interest of the food sector in innovative aerogel ingredients.