Quantitative and Qualitative Composition of Bacterial Communities of Malting Barley Grain and Malt during Long-Term Storage

Soňa Felšöciová,Štefan Dráb,Przemysław Łukasz Kowalczewski,Miroslava Kačániová,Tomáš Krajčovič

doi:10.3390/agronomy10091301

Abstract

In the grain samples of three malting barley varieties harvested in 2016, and in the malt made from them, we observed microbial changes during storage. Analyses were performed after 0, 3, 6, and 9 months of storage in floor warehouses and silos. We monitored microbial changes based on the quantitative determination of microorganisms using a plate dilution method and qualitative determination of microorganisms, where we identified a particular species of bacteria using the MALDI-TOF MS Biotyper instrument (Bruker Daltonics, Bremen, Germany). Based on the quantitative determination of microorganisms, we found that the total plate counts of microorganisms was higher in malts than in barley grains. The storage period had the greatest impact on the number of coliform bacteria, which gradually increased with the growing months in storage. The number of lactic acid bacteria in barley grains with the growing months in storage and malt produced from them decreased slightly, and the content of the sporulating bacteria in all the samples fluctuated slightly. Differences in the numbers of observed microorganisms were negligible during storage between floor warehouses and silos. In the samples of barleys, the most commonly identified species were Pantoea agglomerans, which was also present in malt samples but did not belong to the dominant species. A diverse species representation appeared in the samples, whereas predominating species belonged to the Enterobacteriaceae family.

Highlights

Barley is an important feed crop, but it is the predominant raw material for the production of malt for brewing purposes
The initial total plate count on barley had the highest counts compared to other monitored groups of bacteria, and the storage time had not activated their growth yet
Trials carried out proved significant impact of the time of barley storage and the type of barley storage

Summary

Introduction

Barley is an important feed crop, but it is the predominant raw material for the production of malt for brewing purposes. Many intrinsic and extrinsic factors, including plant variety, climate, soil type, agricultural practices, storage, and transport influence the diversity and structure of the microbial community present n barley grains [2,3,4]. The indigenous microbial community of barley harbors a wide range of microorganisms, including numerous species of Gram-negative and Gram-positive bacteria, yeasts, and filamentous fungi [3], and is often associated with unwanted trends such as variability in malt batches, grain dormancy, undesirable aromas, and interference with barley respiration [5] or by producing mycotoxins [6]. Bacteria numerically dominate in the culturable microbial community of pre-harvest barley [2]. The most common and abundant bacterial species during growth is Erwinia herbicola ( Pantoea agglomerans) [3]

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