Plant protein digestibility: Methodology to study the impact of genetics, environment and processing on measures of protein quality

Two key components that define the nutritional quality of dietary proteins, including plant-based proteins, are the respective amino acid profile and the extent to which the protein is digested, absorbed and utilized to meet the needs of the consumer. For plant proteins in particular, numerous factors are known to influence both parameters, including genotypic, environmental, and processing factors, and their interactions. An understanding of overall protein digestibility is critical for establishing data in support of protein content claims on foods. In both Canada and US, data from in vivo rodent bioassays is currently required from a regulatory perspective. However, given the cost and challenges of using animal tests, it is not practical to generate data on the various factors known to impact digestibility. Alternative approaches include the use of in vitro digestibility methods that can yield data for both protein and amino acid digestibility. These methods have been used to explore factors including the impact of milling, isolation, and processing methods, in addition to genetic and environmental factors on digestibility. As such, they are useful techniques for generating comparative data and for product formulation purposes, even if they can’t be currently used to substantiate protein content claims in Canada and the US. A current limitation with in vitro methods, however, is the lack of standardization of existing methods. Ring trials are currently underway to validate and standardized methods, including AOCS protocols to measure protein digestibility using established pH Drop and pH STAT methods. The availability of such methods and their subsequent validation against in vivo data will assist in developing strong arguments to move away from animal testing as official methods for measuring digestibility, while providing the research community validated protocols to assess the multitude of factors known to impact protein and amino acid digestibility.