Influences of grain and protein characteristics on in vitro protein digestibility of modern and ancient wheat species

Authors: MA, FENGYUN - The Ohio State University; Baik, Byung-Kee

Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/21/2021
Publication Date: 1/21/2021
Citation: Ma, F., Baik, B.V. 2021. Influences of grain and protein characteristics on in vitro protein digestibility of modern and ancient wheat species. Journal of the Science of Food and Agriculture. 101(12):4578-4584. https://doi.org/10.1002/jsfa.11100.
DOI: https://doi.org/10.1002/jsfa.11100

Interpretive Summary: Durum, hard red winter, hard red spring, soft club, and soft red winter wheats that are grown in the U.S. are characterized by the differences in their genetic backgrounds and production regions, which all contribute to wide variations in the physical and compositional characteristics of grain, such as hard or soft kernel texture, high or low protein content, and strong or weak gluten. Ancient wheat classes including spelt, emmer and einkorn are also known to possess unique genetic backgrounds and grain characteristics different from those of the modern wheat classes. These differences could have considerable influences on the digestibility of protein, and subsequently the sensitivity and adverse responses of consumers to wheat protein. Protein molecules resistant to digestion could act as allergens and, therefore, high digestibility of proteins in wheat products is desired to avoid their potential immunogenic effects. A better understanding of the relationship between wheat characteristics and digestibility of protein in flour would be valuable for the identification and development of wheat varieties that cause decreased adverse responses stemming from low protein digestibility. The seven classes of modern and ancient wheat showed substantial variations in grain characteristics as well as the protein digestibility of flour, and isolated albumins, globulins and gluten. Soft red winter wheat varieties exhibited the highest protein digestibility of flour and albumins, while durum wheat varieties exhibited the lowest. Isolated gluten exhibited the highest protein digestibility, followed by flour and flour devoid of albumins and globulins, suggesting that albumins and globulins (as well as flour components other than protein) have substantial influences on flour protein digestibility. Kernel hardness and albumin proportion, exhibiting negative and positive relationships with flour protein digestibility, respectively, play pivotal roles in protein digestion and need to be considered for developing wheat cultivars with higher protein digestibility. Information about the protein digestibility of modern and ancient wheat species and the grain and protein characteristics influencing protein digestibility, and subsequently wheat protein allergenicity, would benefit consumers and food processors by providing them with selection tools, and would be valuable to food processors and wheat breeding programs for the identification and development of wheat varieties, respectively, with improved protein digestibility and potentially low allergenicity.

Technical Abstract: Five modern wheat classes including 17 wheat varieties, and three ancient wheat classes including 9 wheat varieties, were analyzed for kernel hardness (KH) and flour protein characteristics as well as in vitro protein digestibility (IVPD) of cooked flour, flour without albumins and globulins (FWOAG), gluten, albumins and globulins to identify the factors influencing protein digestibility of flour. IVPDs of flour, FWOAG, gluten and albumins of wheat varieties ranged from 86.5% to 92.3%, 85.8-90.3%, 90.6-94.6% and 74.8-85.1%, respectively. The IVPD of gluten was significantly higher than the IVPDs of flour and FWOAG, indicating that non-protein components substantially affect protein digestibility. Eight wheat classes were significantly different in IVPDs of flour and albumins, but not in IVPDs of FWOAG, gluten and globulins. The highest and lowest IVPDs of flour and albumins were observed in soft red winter and durum wheat, respectively. There were apparent differences in undigested protein bands and intensities of wheat classes with low and high flour IVPDs. KH and albumin proportion exhibited negative and positive relationships, respectively, with flour IVPD. These results demonstrate that KH, non-protein components and albumin proportion play pivotal roles in protein digestion and need to be considered for developing wheat cultivars with higher protein digestibility.