Proteomic analysis of two malting barleys (Hordeum vulgare L.) and their impact on wort quality
Introduction
Barley (Hordeum vulgare) is the fourth cereal most cultivated in Mexico with two grown cycles: Spring-summer cycle (rainfed lands) and Fall-winter cycle (irrigated lands) (Peñalva, 2011). Five varieties meet the quality criteria for brewing industry: Armida, Adabella, Esmeralda, Alina and Esperanza and correspond for the 70% of the total year production in the country (Peñalva, 2011). The use of one or another variety depends on the desired characteristics of the final beer. Malting is a process during which the barley grain is subjected to humid conditions to activate the germination process and then dried. This process induces the enzymes required to transform the grain stock (starch and proteins) into the components required for fermentation.
The qualities of the malt and the final beer are defined by the characteristics of the barley grains and the malting parameters. The barley malt chemical components, germination and viability are mainly determined by the grain characteristics, which are affected by the malting conditions and growing environments (Guo et al., 2016). Each malted barley variety generates unique flavor and body, which is exploited to produce different types of beer. Understanding the biochemical characteristics of the malt to predict the characteristics of the final beer is one of the major goals of the brewing industry.
Many studies have focused on the metabolic proteins present in the malt that influence its quality. The studied plant species have included Arabidopsis thaliana, which is used as a study model, barley (Hordeum vulgare), corn (Zea mays) and rice (Oryza sativa) (Li et al., 2014). Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) is the most popular proteome analysis method. When this method is combined with mass spectrometry identification procedures and enzymatic activity studies using zymography, comparisons can be performed between different malts to find proteins with potential as quality markers.
Some studies, such as the study of Zhao et al. (2013), have related metabolic proteins separated in a pH range of 4–7 with the characteristics of two types of malts with different quality levels for the brewing industry. Other examples of comparative analyses using proteomic techniques include the study of Guo et al. (2016) who compared the proteomes of two barley varieties used for the food and brewing industries with an aim toward identifying the protein content in each variety, and the study by Jin et al. (2013), in which two malts with different degrees of filterability were compared.
Various studies on the hydrolytic systems of malts have been conducted using electrophoretic separations with copolymerized substrates, which are better known as zymograms. These studies have found that distinct malt varieties can contain different band profiles with types of proteolytic activity at different pH values (Wrobel and Jones, 1992).
Due to the importance of studying variations in the proteome and its relationship to the quality of the malt and the beer, the differences in the proteomic profiles of two varieties of malted barleys commonly used in Mexico brewers were studied to obtain information at the proteomic level concerning the differences between the varieties and to relate the proteins found in the malts with wort quality parameters.
Section snippets
Biological samples
The malted barley grains (Hordeum vulgare) samples were provided by the Cuauhtémoc Moctezuma Brewery, Mexico. The malts were called M1 and M2 and were stored at −20 °C prior to use. Malts were produced using two different Mexican barley varieties by a malting company using the same conditions.
Protein extraction
The malts (10 g) were ground into a fine powder (<50 μm). The samples were homogenized in 1 ml of acetate buffer (50 mM, pH 5.0) and extracted by vortex for 30 min, resting in an ice bath every 5 min.
Malt quality
Brewing depends mainly on the biochemical characteristics of the wort, which are directly related to the type of malted barley used in the preparation. In this work, the proteome of two brewing malts and their relation to the wort quality are reported. Both malts are cultivated in different seasons of the year (winter and summer) and both are commonly used in the brewing industry in Mexico. Their use in the process produce different flavor profiles in beer (Cuauhtémoc Moctezuma Brewery). The
Funding source
We thank the National Council of Science and Technology (Consejo Nacional de Ciencia y Tecnología) (CONACYT) for financial support through project PEI 231412. JG. Herrera-Gamboa and CB. López-Alvarado received CONACYT scholarships.
Author contributions
JGHG and CBLA designed and performed the experimental work, BPA directed the project. JGHG wrote the paper with the supervision of BPA. All authors provided critical feedback and helped shape the project and paper. EPO, LCDB and JCCA gave the approval to the final version of the paper.
Conflicts of interest
All authors declare no competing financial interest.
Abbreviations used
M1, Malt 1; M2, Malt 2; 2D-PAGE, Two-dimensional polyacrylamide gel electrophoresis; kVh, kiloVolts per hour; HCl, Hydrochloric acid; SDS, Sodium dodecyl sulfate; DTT, Dithiothreitol; SDS-PAGE, sodium dodecyl sulfate polyacrylamide gel electrophoresis; mA, miliAmpere; kDa, kiloDalton; μg, micrograms; MgCl2, magnesium chloride; FAN, Free amino nitrogen; KI, Kolbach index.
Acknowledgments
We thank Rocío Ortiz López (CIDICS-UANL) and Víctor Aguirre (Facultad de Agronomía-UANL) for their support in conducting the 2D-PAGE technique.
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