Biotechnological Production of Flavour Active Lactones

Ian L. Gatfield

Haarmann & Reimer GmbH, Postfach 1253, D-37601 Holzminden, Germany

1 Introduction 222

2 Fermentative Production of Lactones 224

2.1 4-Decanolide 224

2.2 5-Decanolide 228

2.3 4-Octanolide 230

2.4 5-Octanolide 231

2.5 4-Hexanolide 231

2.6 4-Dodecanolide 231

2.7 6-Pentyl-2-pyrone 232

2.8 Macrocyclic Lactones 232

3 Enzymatic Synthesis of Lactones 233

3.1 Via Intramolecular Esterification 233

3.2 Via Enantioselective Hydrolysis 234

3.3 Via Baeyer-Villiger Type Reaction 234

4 Conclusions 236

5 References 237

Biotechnology lends itself to the production of natural flavour materials, which can either be obtained as complex mixtures or pure, individual flavour components. Examples of the latter category are acids, alcohols, esters, aldehydes, ketones and lactones. Biotechnological processes are reviewed which can be used to produce those y- and 8-lactones which are important to the flavour industry. Emphasis is placed upon fermentative processes using microorganisms capable of performing p-oxidative degradation reactions. The preferred substrates in this type of biotransformation are hydroxy fatty acids which can themselves be obtained enzymatically or extracted from natural sources. Certain microorganisms are capable of hydroxylating fatty acids, thereby giving rise to the immediate precursors of y- and 8-lactones. The intramolecular esterification of hydroxy fatty acids can be catalysed by certain lipases. The lipase from Candida antarctica is also capable of converting some cyclic ketones to the corresponding lactones via the Baeyer-Villiger reaction.

Advances in Biochemical Engineering/ Biotechnology, Vol. 55 Managing Editor: T. Scheper © Springer-Verlag Berlin Heidelberg 1997

1 Introduction

Lactones are ubiquitous in nature and have been isolated from all major food systems [1], The naturally occurring, organoleptically important lactones generally have y- or 5-lactone structure, and are straight-chained, while a few are even macrocyclic (Fig. 1).

The importance of aliphatic lactones as aroma components of foods is based on their characteristic organoleptic properties. Among these are oily, peachy, creamy, fruity, nut-like, coconut, honey and so-on. Due to their mostly low odour thresholds averaging about 0.1 ppm [2], lactones often have a high flavour value. Whereas y-lactones preferentially occur in plants, 5-lactones are mainly found in animal products.

Sensorily important lactones usually possess eight to twelve carbon atoms and some are very important flavour components in a number of foods such as strawberries, peaches, apricots, milk products and fermented foods. They are produced in plants in minute amounts when the fruit ripens, probably by catabolic processes involving the structurally related fatty acids [3]. However, the fact that both the optical purity and the absolute configuration can vary for identical lactones isolated from different sources supports the idea of the presence of different biosynthetic pathways, involving either anabolic or degra-dative mechanisms.

4-decanolide (y-decalactone)

5-octanolide (8-octalactone)

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