Development of detection medium for hard-to-culture beer-spoilage lactic acid bacteria

Abstract

Aims: To develop a detection medium for hard‐to‐culture beer‐spoilage lactic acid bacteria (LAB). Methods and Results: Four hard‐to‐culture beer‐spoilage strains of LAB, belonging to Lactobacillus paracollinoides and Lactobacillus lindneri, have been obtained by repeatedly subculturing the wild‐type strains in beer. To develop a countermeasure against these hard‐to‐culture beer‐spoilage LAB, a beer‐based medium was modified. As a consequence, the supplementation of a small amount of de Man Rogosa Sharpe medium was found to enhance the growth of hard‐to‐culture beer‐spoilage LAB strains obtained in this study. In addition, sodium acetate was shown to improve the selectivity of this beer‐based medium. Further comparative study was performed with five other media widely used for the detection of beer‐spoilage LAB in the brewing industry. This study revealed that the newly developed medium, designated advanced beer‐spoiler detection (ABD) medium, possessed superior sensitivity for hard‐to‐culture beer‐spoilage LAB and comparable sensitivity with easy‐to‐culture beer‐spoilage LAB. Moreover, ABD medium was found to suppress the growth of nonspoilage micro‐organisms, and thereby allow the selective growth of beer‐spoilage LAB. Conclusions: Advanced beer‐spoiler detection medium is considered as an effective tool for comprehensive detection of beer‐spoilage LAB in breweries. Significance and Impact of the Study: The detection by ABD medium can be used as an indicator for differentiating the beer‐spoilage ability of LAB without further confirmatory tests in breweries.

Sake and Beer Spoilage Lactic Acid Bacteria - A Review

“…It has been increasingly recognized that microorganisms too deeply associated with a particular environment tend to exhibit hard-to-cultivate characteristics 50,56 . These lines of evidence therefore suggest the profound association of these species with beer brewing environments and indicate that the physiological characteristics of beer spoilage LAB living in beer brewing environments are drastically different from those of laboratory strains maintained in nutrient-rich media 103 . It should be also noted that, due to the hard-to-cultivate nature of L. lindneri, L. paracollinoides and P. damnosus, these LAB species may have been underreported as causative agents of microbiological incidents in the beer brewing industry.…”

“…Interestingly, recent studies have shown that repeated passages in beer gradually reduce the culturability of originally easy-tocultivate strains of L. lindneri and L. paracollinoides, eventually leading to the acquisitions of hard-to-cultivate strains that mimic the state of primary isolates of these species 103,105 . Strikingly, it was observed that highly adapted strains of beer spoilage L. lindneri and L. paracol- linoides die swiftly on MRS agar (Fig.…”

“…Furthermore, strains belonging to these three species show hard-to-cultivate characteristics on primary isolation, and often fail to grow on MRS agar 5,103 , a detection medium widely recommended for beer spoilage LAB by major brewery associations 15,21,27 . Interestingly, recent studies have shown that repeated passages in beer gradually reduce the culturability of originally easy-tocultivate strains of L. lindneri and L. paracollinoides, eventually leading to the acquisitions of hard-to-cultivate strains that mimic the state of primary isolates of these species 103,105 .…”

“…A recent study showed that some strains of beer spoilage LAB are too excessively adapted to beer environments to be detected by a conventional media (Fig. 4) 103 . This study also suggested that many nutrients included in conventional media are inhibitory for the growth of hard-to-cultivate beer spoilage LAB strains.…”

Effects of Lysozyme on the Microbiological Stability and Organoleptic Properties of Unpasteurized Beer

“…Among them the most important spoilage organisms are, according to brewing literature, L. brevis, L. lindneri, L. paracollinoides and P. damnosus 2,30,32,34 . In addition, L. backi and P. inopinatus have been reported as potential beer spoilers 7,22,33 .…”