Influence of the Malt Variety on Lipoxygenase

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Influence of the malt variety on the LOX-activity and potential

Table of contents

List of AbbreviationsII

List of tables and equationsIII

Table of FiguresIV

1 Introduction1

2 The Lipoxygenase2

3 Flavor active compounds formation4

4 LOX activity & potential 5

5 Influence of barley variety and cultivation area on LOX-activity6

6 Influence of malting and malt type on LOX activity & potential7

7 Screenings and studies of LOX-less and LOX-free barley8

8 Summary10

9 Bibliography11

10 Attachments14

List of Abbreviations

e.gfor example

LOXLipoxygenase

LOX-1Lipoxygenase-1

LOX-2Lipoxygenase-2

PUFA polyunsaturated fatty acids

LA linoleic acid

LeA linolenic acid

9-HPOTE9-hydroperoxide-octadecadienoic acid

13-HPOTE13-hydroperoxide-octadecadienoic acid

HPODHydroxyperoxide

THODTrihydroxyoctadenoic acid

T2Ntrans-2-nonenal or (E)-2-nonenal

List of tables and equations

Equation 1: Volumetric activity5

Equation 2: Specific activity5

Equation 3: LOX-Potential5

Table of Figures

Figure 1: Oxidation of linoleic acid by LOX-1 & LOX-2 to 13- & 9-hydroperoxyde2

Figure 2: A. & B. LOX-1 and 2 expression and formation of their products throughout germination …………………………………………………………………………..……….. 3

Figure 3: A. & B. LOX-activity and potential of raw extract and gel fraction differing in barely varieties an growing areas …………………………………………………………....6

Figure 4: Effect of addition of 10% (w/w) caramel and 2% (w/w) black speciality malts on lipoxygenase activity of pale malt during mashing……………………………………..8

Figure 5: A. & B. Amount of T2N formed when using either a normal barley variety Cv. Barke or a novel variety Line D112………………………………………………………… 9

Introduction

Nowadays in every branch of the food industry it is a must to achieve products with a high quality. As for the beer industry where the product can vary from flavor, to color, to alcohol content, etc. so that the customer is able to specify according to his own taste what a good beer is or not, the factor defining a good quality is the maintenance of the beer characteristics. One of the most important characteristics is the flavor. Therefore the term “flavor stability” plays also a major role in the beer quality since it refers to the maintenance of the beer flavor from the moment it is filled into e.g. bottles till its expiration date. The flavor, the flavor stability and other characteristics are partly delimited by the different production steps, from the choosing and preproduction of raw materials to the filling.

It has been stated by many brewers that especially important for the flavor stability in bottled beer, is the influence of lipid oxidation. The lipids contained in beer come from the malt. Malt has plenty of esterified lipids that during mashing are cleaved from glycerol by malt lipases. The then free fatty acids, specifically unsaturated fatty acids are the ones being oxidized into flavor active compounds or their precursors by auto oxidation or mainly by lipoxygenase (LOX) [1]. Furthermore not only flavor active compounds may be formed but also substances which diminish the foam stability of the beer.

LOX is an enzyme exclusively found in the malt. The expression of the LOX is not only genetically dependable but at the same time it depends on the barley variety, its cultivation conditions and the malting process. This been said the aim of these paper is to find more about and present the influence of the malt variety on the LOX-activity and potential. Furthermore new barley varieties showing reduced LOX-activity and their use in the brewery are also...
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