Extraction, characterisation and functional applications of sustainable alternative protein sources for future foods: A review

• Alternative protein sources are viewed to be more sustainable than animal proteins. • Potential replacers for animal proteins need to have similar functional properties. • There are opportunities and challenges of incorporating alternative proteins in food processing and manufacturing. • Food waste needs to be addressed as key to food security. For many centuries, animal proteins have been used as the conventional food proteins in the food industry to produce a variety of food products due to their functional properties that range from gelation, water holding and binding capacity, foaming ability and stability, solubility, and emulsification. However, the production of proteins from animal sources does come at a cost due to its impact on the environment. Thus, the search for potential replacers for animal proteins that are sustainable, cheaper, and environmentally friendly has resulted in the exploration and the incorporation of alternative proteins in different food product formulations. Even though studies have been carried out to investigate the functional properties of several alternative protein sources, there are technological, sensorial, and nutritional challenges that still need to be overcome in order to make alternative protein sources a more feasible exchange for animal-based proteins. Additionally, the impact of processing on the functional and structural characteristics of alternative proteins in addition to the health impact still need to be understood. Therefore, this review discusses alternative protein sources that have been researched and documented as potential substitutes for animal-based protein sources. The extraction, characterisation, functional properties, and the nutritional quality of alternative proteins in comparison to the conventional animal-based protein sources will also be discussed. Additionally, this review aims to highlight opportunities and challenges of incorporating alternative proteins in food processing and manufacturing.