Relationships between protein content, starch molecular structure and grain size in barley

Wenwen Yu; Xinle Tan; Wei Zou; Zhenxia Hu; Glen P Fox; Michael J Gidley; Robert G Gilbert

doi:10.1016/j.carbpol.2016.08.078

Relationships between protein content, starch molecular structure and grain size in barley

Carbohydr Polym. 2017 Jan 2:155:271-279. doi: 10.1016/j.carbpol.2016.08.078. Epub 2016 Aug 26.

Authors

Wenwen Yu¹, Xinle Tan², Wei Zou³, Zhenxia Hu⁴, Glen P Fox³, Michael J Gidley³, Robert G Gilbert⁵

Affiliations

¹ Joint International Research Laboratory of Agriculture and Agri-Product Safety, College of Agriculture, Yangzhou University, Yangzhou 225009, Jiangsu Province, China; The University of Queensland, Centre for Nutrition and Food Sciences, Queensland Alliance for Agriculture and Food Innovation, Brisbane, QLD 4072, Australia.
² The University of Queensland, Centre for Nutrition and Food Sciences, Queensland Alliance for Agriculture and Food Innovation, Brisbane, QLD 4072, Australia; Tongji School of Pharmacy, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China.
³ The University of Queensland, Centre for Nutrition and Food Sciences, Queensland Alliance for Agriculture and Food Innovation, Brisbane, QLD 4072, Australia.
⁴ Tongji School of Pharmacy, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China.
⁵ Joint International Research Laboratory of Agriculture and Agri-Product Safety, College of Agriculture, Yangzhou University, Yangzhou 225009, Jiangsu Province, China; The University of Queensland, Centre for Nutrition and Food Sciences, Queensland Alliance for Agriculture and Food Innovation, Brisbane, QLD 4072, Australia. Electronic address: b.gilbert@uq.edu.au.

PMID: 27702512
DOI: 10.1016/j.carbpol.2016.08.078

Abstract

Correlations among barley protein, starch molecular structure and grain size were determined using 30 barley samples with variable protein contents. Starch molecular structure was characterized by fluorophore-assisted carbohydrate electrophoresis and by size-exclusion chromatography (SEC, also termed GPC). The chain-length distributions of amylopectin were fitted using a mathematical model reflecting the relative activities of starch branching enzymes and starch synthase enzymes. Increased protein content significantly and negatively correlated with higher amounts of amylose with longer chains (degree of polymerization, DP 1600-40000) while barley grain sizes positively associated with starch contents. Protein content also positively correlated with the proportion of longer chains of amylopectin (DP 34-100). These results showed that the enzyme activities of starch synthases change with protein content, leading to altered starch contents, structures and grain sizes. From this perspective, selecting for large grain size (or low protein content) does not necessarily relate to starch structure, although may suggest long chains of amylopectin. Measuring starch structure could give a good indication of process performance in human food, animal feed and brewing, as all these structural features contribute to significant functional properties.

Keywords: Barley; Biosynthesis; GPC; Molecular structure; Protein; Starch.