Plants contain antinutritional factors (ANFs) with negative impact on protein digestibility and nutritional quality. We aim to highlight the importance of extraction method on the coextraction of different ANFs to put focus on this challenge regarding the usability of plant-protein ingredients. We mainly focus on the research behind the established, industrial techniques, wet extraction and dry fractionation, in relation to ANFs. These methods give protein powders differing considerably in protein concentrations and ANF contents. Wet extraction offers the highest protein concentration (typically >85%) and lowest ANF content (reduction between 75% and 96%, depending on the type of ANF). Usage of chemicals and energy has pushed the development of new extraction techniques; hence dry fractionation is explored. However, it was typically found that dry fractionation resulted in an accumulation of some ANFs in the resultant protein concentrates. Innovative separation methods, like selective electrodialysis, forward osmosis, immobilized metal affinity, and zinc reductants, are suggested to be effective processes for concentration, purification, and selection of proteins. In general, more research is needed, and strategies to sophisticate extraction methods, for example by combining with pre- and postprocessing, and ensure high quality of the protein fractions are mandatory.

As the plant-based food market grows, demand for plant protein is also increasing. Proteins are a major component in foods and are key to developing desired structures and textures. Seed storage proteins are the main plant proteins in the human diet. They are abundant in, for example, legumes or defatted oilseeds, which makes them an excellent candidate to use in the development of novel plant-based foods. However, they often have low and inflexible functionalities, as in nature they are designed to remain densely packed and inert within cell walls until they are needed during germination. Enzymes are often used by the food industry, for example, in the production of cheese or beer, to modify ingredient properties. Although they currently have limited applications in plant proteins, interest in the area is exponentially increasing. The present review first considers the current state and potential of enzyme utilization related to plant proteins, including uses in protein extraction and post-extraction modifications. Then, relevant opportunities and challenges are critically discussed. The main challenges relate to the knowledge gap, the high cost of enzymes, and the complexity of plant proteins as substrates. The overall aim of this review is to increase awareness, highlight challenges, and explore ways to address them.