Changes in protein digestibility during processing of oats, peas and faba beans from raw material to texturized protein

Plant proteins are a sustainable and promising source of protein and can be used to produce meat analogues resembling animal meat in taste, texture, and appearance. In the context of today’s controversial debate about ultra-processed food, meat analogues have come under criticism and their nutritional value has not been thoroughly investigated. Therefore, this study aimed to investigate how processing changes the protein digestibility of yellow peas, faba beans and oats during different processing steps, and to give an answer to the question whether it is advisable to give preference to minimally processed food over ultra-processed products from a protein nutrition perspective. Different samples were prepared by dehulling of legumes, defatting of oats and dry fractionation into a protein fraction. Furthermore, thermal treatments, such as heating in a rapid visco analyzer (RVA), traditional cooking and extrusion cooking, were applied. The sample materials were characterized in terms of their contents of protein, phytic acid and non-starch polysaccharides (NSP), as well as their particle size distribution. Next, the static in vitro digestion model INFOGEST was combined with size-exclusion chromatography to determine the protein digestibility after three different time points of simulated digestion. Boiled chicken breast was used as reference sample. Dehulling and dry fractionation improved the total protein digestibility due to an increased protein solubility, which in turn was attributed to the decreased particle size and further purification of the protein fraction upon these two processing steps. Heat-treated samples were equally or better digestible, which might have resulted from heat-induced protein unfolding enhancing proteolytic susceptibility and the elimination or reduction of heat labile antinutritional factors, such as phytic acid or trypsin inhibitors. Dry and wet texturized protein products were less digestible as compared to the starting material of the extrusion process, mainly because of the decreased protein solubility, which could be attributed to the crosslinked texture. It was concluded that ultra-processed samples, especially dry texturized protein products, were better digestible as compared to the minimally processed raw material, which was only traditionally cooked. Further research is needed to optimize the protein digestibility of texturized protein products by selecting different extrusion conditions and improve their availability of essential amino acids by combining different plant sources. In addition, texture and sensory analyses should vi be conducted in conjunction with the digestion experiments, to pursue the goal of a plantbased meat analogue with high nutritional value and optimized taste and texture, which are essential for a successful market launch of these products.