Elsevier

Food Chemistry

Volume 118, Issue 3, 1 February 2010, Pages 566-574
Food Chemistry

Construction of a novel beer proteome map and its use in beer quality control

https://doi.org/10.1016/j.foodchem.2009.05.022Get rights and content

Abstract

Beer proteins were analysed by two-dimensional gel electrophoresis (2DE). The protein species associated with major spots on 2DE gels were identified by mass spectrometry followed by a database search to construct a comprehensive beer proteome map. As a result, 85 out of 199 protein spots examined were positively identified and categorised into 12 protein species. A total of 11 beer samples were brewed from the malt of eight cultivars having different levels of protein modification. This experiment was designed to demonstrate the influences of barley cultivar and malt modification on beer protein composition and beer quality characters. The beers produced from these brewing trails were subsequently analysed by 2DE and their proteomes were compared. Cultivars and malt modification affected the concentration of several proteins in beer. Beer protein concentration was associated with differences in the desirable beer quality trait, foam stability. In addition, expression of yeast derived proteins were observed that may also influence beer quality. Overall, the application of a comprehensive beer proteome map provides a strong platform for detection and potential manipulation of beer quality related proteins.

Introduction

Beer foam quality is one of the important characteristics that a consumer uses to determine beer quality. Foam quality is defined by its stability, lacing, whiteness, intensity, strength, and creaminess (Bamforth, 1985). In clear beer, colloidal haze formation is also a serious quality problem. Consumers judge a beer as stale or not fit to drink if it displays colloidal haze. Foam stability (Bamforth, 1985, Evans and Sheehan, 2002) and haze formation (Asano et al., 1982, Iimure et al., 2009, Siebert, 1999) have been assumed to be major quality traits controlled by proteins. In beer foam stability, several beer proteins have been identified as either foam-positive or negative. Previous reports suggested that protein Z (Evans et al., 1999, Evans et al., 2003, Kaersgaard and Hejgaard, 1979, Maeda et al., 1991) and lipid transfer protein 1 (LTP1) (Jégou et al., 2000, Sorensen et al., 1993) play important roles in beer foam stability. In addition, recent studies have suggested that barley dimeric α-amylase inhibitor-1 (BDAI-1) and yeast thioredoxin are foam-positive and foam-negative proteins, respectively (Iimure et al., 2008, Okada et al., 2008). In beer colloidal haze, CMe component tetrameric α-amylase inhibitor (CMe), BDAI-1 and hordein were suggested as haze active (Asano et al., 1982, Evans et al., 2003, Iimure et al., 2009, Robinson et al., 2007, Siebert, 1999). However, conclusive identification of protein factors causing beer foam stability and haze formation still requires validation. One of the reasons for the poor understanding of protein factors may come from the lack of knowledge of the spectrum of proteins in beer. Thus, comprehensive analysis of beer protein identity is necessary to reveal the relationship between beer proteins with respect to quality characters including foam stability and haze formation.

Barley cultivar and the level of protein modification during malting are also known as important malting related factors that can modify beer quality (Evans et al., 1998, Iimure et al., 2008). Protein modification is judged by malt modification which is conventionally measured in the brewing industry as the Kolbach index (soluble nitrogen/total nitrogen × 100). Therefore, the understanding of beer protein also requires an understanding of the effect of different barley cultivar and malt modification combinations in important quality proteins (i.e., hordeins, protein Z).

Proteome analysis, which separates a sample of proteins by two-dimensional gel electrophoresis (2DE) which is followed by mass spectrometry analysis and database searches, is a powerful tool to comprehensively detect the spectrum of proteins present in a beer sample. In several reports, proteins from barley grain and malt were analysed by 2DE and major protein spots were identified (Bak-Jensen et al., 2004, Østergaard et al., 2004). Also major beer proteins were identified by mass spectrometry (Hao et al., 2006, Perrocheau et al., 2005). Similarly, Iimure et al., 2008, Iimure et al., 2009 identified foam proteins and haze active proteins using a proteome analysis.

To expand these pioneering analyses, this study develops a comprehensive proteome map of beer for Japanese style lager beer. Recent advancements in protein analysis enable the development of a proteome map with greater resolution by identifying relatively minor spots. The use of the proteome map is applied practically, to assess eleven beer samples that were prepared with different barley cultivars and levels of malt modification. The efficient application of protein spot intensities on 2DE images is discussed to control foam stability and haze formation.

Section snippets

Barley sample, malting and malt quality analysis

The barley-malt materials used in this study are described in Table 1. Each 75 kg barley grain sample from a single cultivar (>2.5 mm screen) was processed according to Okada et al. (2008). For cultivars F, G and H, two different ex-steep moisture levels, i.e., low (36–37%) and high (43–44%), were used to influence malt modification, thus assess its influence on beer protein composition. Malt quality characters were analysed according to the standard methods of the European Brewery Convention (

Identification of major beer proteins on the 2DE gels

Proteins in standard beer samples (i.e., Beer F(L)), were separated by 2DE (pI 4–7 and 6–9) (Fig. 1) and individual protein spots were analysed by MALDI-TOF-MS or LC-MS/MS followed by database searches to determine spot identity. The search engines identified 85 out of 199 protein spots which were categorised into 12 protein species (Table 2). According to the source of sequences on the databases, 8 out of the 12 protein species were derived from Hordeum vulgare subsp. vulgare and the remaining

Discussion

A total of 85 protein spots on 2DE gels (Fig. 1 and Table 2) together with data set for the 2DE images were identified in the current proteome analysis. Perrocheau et al. (2005) also analysed beer proteins by 2DE and mass spectrometry but resulted in identification of only 31 protein spots. Hao et al. (2006) identified major proteins in beer foam by mass spectrometry following sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS–PAGE), which made protein composition comparison

Acknowledgements

We are grateful to T. Yazawa, K. Ito and N. Yatabe, the Bioresources Research and Development Department, Sapporo Breweries Ltd. for their technical assistance. We are also grateful to K. Takoi for the beer sample preparation. This study was supported by the Program for Promotion of Basic Research Activities for Innovative Biosciences, Japan (PROBRAIN).

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