Legumes are very important components in the diet of many countries, mainly those of the Mediterranean region. They are also highly versatile and culturally diverse foods found all over the world, serving as a basic protein source in certain countries. Recently, there has been a growing interest in the technological functionalities of legume proteins in view of their use as food ingredients, mainly as alternative substitutes for meat, egg, dairy, and wheat proteins.
Throughout the legume agro-industrial processing chain, large amounts of by-products and wastes are generated, particularly during harvesting and processing in the field, when defective legumes are disposed of. In addition, pods and other seed residues are left over after cleaning and splitting operations during industrial processing. The amount of wastes originated from legume processing ranges from 5% to 25% of the initially harvested crop. However, these by-products can still be a rich source of useful compounds, such as proteins, fibres, minerals, and other bioactive molecules (e.g., phenols and carotenoids) that have been shown to have a beneficial impact on human health.
At present, there has been a growing interest in the food industry towards the potential utilization of legume by-products, mainly due to the presence of high amounts of protein that could be incorporated into various types of food (e.g. pasta with high protein, hamburgers, nuggets, beverages, baby and sport foods, meal replacements, baked goods, etc.) to increase their nutritional value and/or to provide specific and desirable functional or technological properties, making agricultural practices more profitable and reducing human dependence on animal products. In fact, vegetarian and vegan diets have become increasingly popular, and many consumers see themselves as partial vegetarians and greatly restrict their intake of animal products. This has led to an increase in the demand for alternative sources of dietary protein, mainly from legumes and their processed products.
In the work carried out within the ALEHOOP project, alkaline extraction followed by isoelectric precipitation has been used to obtain protein extracts from by-products of four legumes: lentils, beans, peas, and lupines. They consist of defective seeds, which due to their size, appearance, or any other type of defect, do not meet the quality standards necessary to be placed on the market
The protein extracts obtained have been characterized in terms of their biochemical (moisture, protein, sugar and fat content, mineral analysis, and amino acid composition), and technofunctional properties (solubility, water and fat holding capacities, gelling, emulsifying and foaming capacity), as well as antioxidant activity and antinutritional factors, since their subsequent application as ingredients in different products intended for human consumption will depend on all of them.
Likewise, these protein extracts have been hydrolysed using enzymes, in order to modify some functional properties, especially to improve the water solubility of the original extracts.
Finally, an exhaustive characterization of the residual streams from protein extraction process has been carried out, and different alternatives for their use have been proposed.
Therefore, efficient utilization of these agro-industrial by-products can help reduce the overall economic and environmental impact of agro-industrial and food processing pipelines. The extraction of waste and subsequent exploitation will lead to achieving, hopefully in the near future, a zero-waste economy and a more sustainable circular and bio-based society.