INITIALLY, PROTEIN ASSESSMENT involves gathering evidence necessary to support protein claims on food labels. In his presentation titled “The Impact of Processing on Protein Quality Measurements: Implications for Protein Content Claims,” James D. House, Ph.D., of the University of Manitoba, relayed that two key parameters are: 1) how well does the amino acid composition of the protein source match to human amino acid needs; and 2) how well is the protein digested, and are the amino acids absorbed to support the needs of the consumer.
“Regulatory frameworks for protein content claims in Canada and the U.S. are underpinned by the protein efficiency ratio (PER) and protein digestibility-corrected amino acid score (PDCAAS), respectively,” explained House. The digestible indispensable amino acid score (DIAAS) is a novel approach to measuring protein quality. The EU uses an expression of protein content relative to energy content.
The PER method utilizes a rat bioassay that measures weight gain/protein intake over 28 days and adjusted relative to a reference protein (casein). “The advantage,” according to House, “is it’s simple and provides a summative biological response to protein intake.” But using rodents is not reflective of human AA needs, and there are ethical constraints. There is limited data available; 47 entries are in the CFIA PER table and 247,326 foods in USDA Food Composition Databases. “Also, the values are non-additive, so it is limited in its use to predict values for new food products,” he explained.
The PDCAAS is determined from the product of the AAS (calculated by dividing the food AA by the AA in the reference pattern) and true fecal protein digestibility (determined by fecal nitrogen output divided by the dietary nitrogen input), with a correction for endogenous losses. Protein content claims for foods are based on the product of the PDCAAS and the protein content of the representative amount customarily consumed (RACC). House stated that “a value of 5-9.9g is a ‘good source’ of protein; 10g or greater is an ‘excellent source.’”
House also explained: “The advantages of the PDCAAS are that it’s simple; there are robust AA datasets; and values are additive to permit calculations of PDCAAS values for mixtures of proteins. However, as with the PER, the PDCAAS is determined using a rodent bioassay. Also, fecal protein digestibility is impacted by gut microbiota, and values are truncated at 1.00, so proteins of higher quality are not identified.”
The DIAAS has been proposed but has not yet been adopted by any jurisdiction. It has advantages, because it treats AA as individual nutrients; uses ileal (relating to the ileum) digestibility values; and scores are not truncated. But, stated House, “It is a bioassay with its associated ethical constraints; multiple analyses are required for one DIAAS value; and it has an arbitrary cut off of 75% for protein source claims.”
Various factors, including plant genetics and growth, as well as processing, affect the quality of plant proteins. (See chart “Factors Influencing Plant Protein Quality.”)
House’s research has found that digestibility values for fava, pea and lentil protein isolates were greater than concentrates—most likely due to reduced antinutrient factors. Despite having a higher protein content, the final PDCAAS values of the isolates were lower than concentrates for lentil and pea, due to lower AAS. This suggest that the isolation process altered the AA composition. Extrusion of flours from buckwheat and pinto beans resulted in higher PER, increased digestibility and greater PDCAAS than baked products. A correlation was found between digestibility and PDCAAS values generated from in vitro and in vivo methods. House suggested that “the use of in vitro digestibility analysis could be a potential replacement for current rodent assay for nutrient content claims.” (Nosworthy, MG et al. J. Agri. Food Chem. 2017/ http://bit.ly/2XrA2eA).
Another study showed that the PDCAAS for processed beans was higher than the DIAAS (61 vs. 45%). Extrusion/cooking of various beans resulted in higher PDCAAS (66% average) and DIAAS values (61% average) than baked (52 and 48%). A significant correlation was found between PDCAAS and in vitro PDCAAS (R2 = 0.7497). (Nosworthy, MG et al. Nutrients. 2018/ http://bit.ly/2IyzoUw)
“Protein quality plays an important role in communicating protein messages to consumers,” concluded House. “But, given the many sources of variability in assessment methods, we need new practical approaches for its determination.”
“The Impact of Processing on Protein Quality Measurements: Implications for Protein Content Claims,” Dr. James D. House, Dept. of Food and Human Nutritional Sciences, University of Manitoba
This presentation was given at the 2019 Protein Trends & Technologies Seminar. To download free presentations and the Post-conference summary of this event, go to https://globalfoodforums.com/store/protein-seminars/
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