Protein: Difference between revisions

The mature [[barley]] grain contains a spectrum of proteins that differ in function, location, structure, and other physical and chemical characteristics. The level of protein is a critical aspect of the quality of [[malt]] and [[beer]], and it is influenced by [[grain]] variety, soil conditions, crop rotation, fertilization, and weather conditions.<ref name=steiner/><ref name=picariello/><ref name=mahalingam/> Generally, the protein content in barley grain represents approximately 8–16% of its total mass.<ref name=mashing>Evans E. [[Library|''Mashing.'']]  American Society of Brewing Chemists and Master Brewers Association of the Americas; 2021.</ref><ref name=silva>Silva F, Nogueira LC, Goncalves C, Ferreira AA, Ferreira IMPLVO, Teixeira N. [https://www.sciencedirect.com/science/article/abs/pii/S0308814607006085 Electrophoretic and HPLC methods for comparative study of the protein fractions of malts, worts and beers produced from Scarlett and Prestige barley (''Hordeum vulgare'' L.) varieties.] ''Food Chem.'' 2008;106(2):820–829.</ref><ref name=mahalingam>Mahalingam R. [https://bmcgenomics.biomedcentral.com/articles/10.1186/s12864-016-3408-5 Shotgun proteomics of the barley seed proteome.] ''BMC Genomics.'' 2017;18(44).</ref> Brewers prefer lower protein levels as long as there is plenty of soluble nitrogen for good yeast nutrition and beer foam potential.<ref name=crit>Bamforth CW, Fox GP. [https://www.brewingscience.de/index.php?tpl=table_of_contents&year=2020&edition=0009%2F0010&article=92781 Critical aspects of starch in brewing.] ''BrewingScience.'' 2020;73(9/10):126–139.</ref> This is because excessive protein content decreases the relative amount of [[carbohydrates]] (mainly [[starch]]) and also has other negative influences on the [[brewing]] process.<ref name=yu/> The barley used for [[malting]] should generally fall at the lower end of this range, with about 9–11% protein.<ref name=fix/><ref>Yu W, Tao K, Gidley MJ, Fox GP, Gilbert RG. [https://www.researchgate.net/publication/328971139_Molecular_brewing_Molecular_structural_effects_involved_in_barley_malting_and_mashing Molecular brewing: Molecular structural effects involved in barley malting and mashing.] ''Carbohydr Polym.'' 2019;206:583–592.</ref> Six-row barley tends to have more protein content and thus less starch than two-row.<ref name=mahalingam/> Hordeins (storage proteins) are the most abundant proteins found in a barley grain, and they form a matrix around the [[starch]] granules, increasing grain hardness.<ref name=celus>Celus I, Brijs K, Delcour JA. [https://www.sciencedirect.com/science/article/abs/pii/S0733521006000762 The effects of malting and mashing on barley protein extractability.] ''J Cereal Sci.'' 2006;44(2):203–211.</ref><ref name=iimure/> These storage proteins are created specifically to be broken down and used as a source of amino acids for building other proteins during seed germination, facilitating the plant's growth. A large variety of other proteins are present in barley, with over a thousand unique proteins identified.<ref name=kerr>Kerr ED, Fox GP, Schulz BL. [https://www.sciencedirect.com/science/article/pii/B9780081005965228692 Grass to glass: Better beer through proteomics.] In: Cifuentes A, ed. ''Comprehensive Foodomics.'' Elsevier; 2020:407–416.</ref> Notable among these are [[lipid transfer protein]]s (LTP) and [[protein Z]], which are the two major proteins in finished beer.