FORMATION OF MOUSY OFF-FLAV IN WINE BY LACTIC ACID BA by PETER JAMES COSTELLO,Bsc, Msc A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy Department of Horticulture, viticutture and oenology The UnÍversity of Adelaide The Australian Wine Research Institute November 1998 Declaration I hereby declare that this thesis contains no material which has been accepted for the award of any other degree or diploma at any university. To the best of my knowledge and belief, no material described herein has been previously published or written by any other person except when due reference is made in the text. If accepted for the award of Doctor of Philosophy, this thesis will be available for loan or photocopy. Peter Costello 11 THESIS SUMMARY Formation of mousy off-flavour in wine by lactic acid bacteria. Mousy off-flavour is an infrequent yet serious spoilage phenomenon in wine and other fermented beverages, which is commonly associated with the growth and metabolism of certain lactic acid bacteria (LAB) and the spoilage yeast Dekkera / Brettanomyces. Two compounds known to cause the characteristic and offensive mousyJike off-flavours are the N-heterocyclic volatile bases 2-acetyltetrahydropyridine (ACTPY) and 2- etþltetratrydropyridine (ETPY). Since there is no satisfactory method for the removal of mousy off-flavour, this spoilage can invoke substantial economic loss to the wine producer. The aims of this thesis were to investigate the following aspects of the formation of mousy off-flavour by wine LAB: 1. Development of a sensitive and reliable procedure for the quantification of N-heterocyclic compounds causing mousy off-flavour in wine; 2. Survey the abilities of wine LAB and other wine bacteria to produce mousy off-flavour and the causative mousy compounds; 3. Investigate the substrates and metabolism of mousy compound formation by LAB. Difficulties were encountered in the analysis of ACTPY due to its chemical and chromatographic instability, suggesting why previous research efforts have failed to quantify mousy compounds. Of several procedures assessed for the reliable extraction and quantification of low concentrations (pgl[- level) of mousy compounds, a continuous liquid - liquid extraction (CLLE) method was developed and used in association with gas chromatography - mass spectrometry (GC-MS). The CLLE / GC-MS method was validated by demonstrating efficient and artefact-free recovery of mousy compounds from spiked Riesling wine. Using this procedure, three structurally related compounds, ACTPY, ETPY and a newly discovered and highly potent N-heterocycle,2-acetyl-1-pyrroline (ACPY), were found to be unique components of mousy wines. Of the three mousy compounds, ACTPY was the most common and occurred at the highest concentration (106 WgtL), whereas ACPY and ETPY occurred less frequently and at maximum concentrations of 7.8 and 4.5 ¡tglL, respectively. The mousy aroma properties of ACPY were confirmed by GC-sniff analysis. Thirty five LAB were screened for the ability to produce mousy off-flavour by a qualitative alkaline test strip procedure. In addition to Lactobacillus brevis and L. cellobiosus, which were known to be associated with mousy off-flavour, a diversity of LAB species, particularly heterofermentative Lactobacilløs spp. and Oenococcus oeni, exhibited this ability in a range of ethanolic and wine-bascd mcdia. Thc homofermentative Pediococcus spp., however, were generally lacking in this ability. lll Selected wine bacteria were tested for the production of mousy compounds in nutritionally complex (Can-MEt) and chemically defined (Sl) media. In Carr-MEt medium, strains of Lactobacillus spp., O. oeni, Pediococcus spp. and Gluconobacter oxydans each produced one or more of ACTPY, ACPY and ETPY generally in the concentration range of <0.1 to 30 þgI-. Exceptionally high concentrations of ACTPY (259 ¡tgtL) were produced by the type strain L. hilgardü DSM 20176. In contrast, synthetic (Sl) medium supported only limited production of mousy compounds, despite similar growth characteristics to those with Can- MEt medium. The metabolism of mousy compounds by LAB was studied utilising a high cell density incubation (HCDI) technique with a basal assay (BA) medium, the main components of which were D-fructose (50 glI-), ethanol (5Vo v/v), LJysine (5gl[-), L-ornithine (5 glI-), metal salts and organic acids. Essential substrates of ACPY and ACTPY formation by L. hilgardü DS}l4 20176 were the availability of a fermentable carbohydrate (e.g. D-fructose), ethanol and iron (ferrous sulfate). In addition, L-ornithine stimulated the formation of ACPY and repressed ACTPY, whereas L-lysine stimulated the formation of ACTPY and repressed ACPY. The formation of ETPY, however, was little influenced by the availability of carbohydrate, L ornithine or L-lysine. Other nutritional factors found to affect the formation of ACPY and ACTPY by L. hilgardü DSitl4 20176 in BA medium included the presence of malic acid and acetaldehyde, and the source of carbohydrate and amino acid. Replacement of ethanol with n - propanol led to the formation of propionyl-tetrahydropyridine, although this reaction did not occur with iso-propanol. The incorporation of deuterated ethanol (d6-ethanol) into the acetyl side chain ACTPY and ACPY, and of deuterated acetaldehyde (d4-acetaldehyde) into the acetyl side chain of ACTPY, confirmed that ethanol and acetaldehyde were precursors of these mousy compounds. These results also suggested that the attachment of the carbonyl side chain involved prior reduction of a primary alcohol to the corresponding aldehyde. A pathway for the formation of ACPY and ACTPY by heterofermentative LAB is proposed. In this scheme, the co-metabolism of exogenous carbohydrate and ethanol force the accumulation of C-2 intermediates of the heterolactic fermentation of sugars (e.g. acetyl- coenzyme A). These C-2 compounds may then concurrently acetylate N-heterocyclic intermediates of L-ornithine and L-lysine metabolism, thus leading to the production of ACPY and ACTPY. 1V Acknowledgments I wish to sincerely thank my supervisors, Dr Paul Henschke and Prof. Terry Lee, and more recently Dr Madimir Jiranek for their guidance, inspiration and encouragement which has made this project possible. I also thank the current Director of The Australian Wine Research Institute, Prof. Peter Hpj, for his support in completing this project. The Adelaide University (Australian Postgraduate Research Award) and the Grape and Wine Research and Development Corporation are thanked for financial support. I am also indebted to my colleagues at the Australian Wine Research Institute who were involved in this project, in particular Dr. Markus Herderich (visiting post-doctoral fellow) who gave invaluable guidance in the GC and GC-MS techniques and extraction procedures, and Dr. Paul Grbin, whose friendship during this project was highly appreciated. Other personnel (past and present) of the chemistry department at the Australian Wine Research Institute are thanked for their support and advice on the chemistry and analysis of the mousy compounds, especially Dr. Patrick Williams, Dr. Mark Sefton, Mr Yoji Hyasaka, Dr. George Skouroumounis, Mr. Alan Pollnitz and Dr. Bob Simpson. In particular, Dr. Mark Sefton is thanked for his advice and editing of the chapter on the analysis and quantification of mousy off-flavour compounds, and also Mr. Yoji Hyasaka for his unfailing support and expertise with the Finnigan GC-MS. 'Wine I also thank the staff of the microbiology group of the Australian Research Institute, especially Dr. Eveline Bartowsky for her valuable advice, kind support and editing of most of this thesis. Dr. Miguel de Barros Lopes and Mr. Holger Gockowiak are gratefully acknowledged for their constructive advice and support on the microbiological content and other aspects of this work, and Mr. Jeff Eglinton is also thanked for his valuable assistance. Other staff at the Institute, especially Mrs. Janet Currie, aÍe thanked for their kind support, as well as Dr. Andrew Markides from The Dept. of Horticulture, Viticulture and Oenology for his encouragement and invaluable assistance. I also thank my parents, John and Joan, and parents-in-law, Joe and Margaret Smith, for their support and encouragement. Finally, and most importantly, I wish to thank my wife, Angela, for her constant love, support and patience, without which this project would not have been possible, and to my children Claire and Matthew, who constantly provided a source of inspiration to complete this work. V Publications Part of the work described in this thesis of Peter James Costello has been published: 1. Costello, P.J.; Stockley, C.S.; Lee, T.H.; Henschke, P.A. Current selection criteria of lactic acid bacteria for malolactic fermentation. Stockley, C.S.; Johnstone, R.S.; Leske, P.A'; Lee, T.H., eds. Proceedings of the eighth Australian wine industry technical conference; 25- 29 October 1992;}r'f¡elbourne Vic.: Adelaide SA: Winetitles; 1993: 142-147. 2. Herderich, M.; Costello, P.J.; Grbin P.R.; Henschke, P.A. Occurrence of 2-acetyL-l- pyrroline in mousy wines. Nat. Prod. Lett. 7;1995: 129-132, 3. Grbin, P.R.; Costello, P.J.; Herderich, M.; Markides, A.J'; Henschke, T.H.; Lee, T'H' Developments in the sensory, chemical and microbiological basis of mousy taint in wine. Stockley, C.S.; Sas, A.N.; Johnstone, R.S.; Lee, T.H., eds. Proceedings of the ninth Australian wine industry technical conference; 16-19 July 1995; Adelaide, SA: Adelaide SA: 'Winetitles; 1996: 57 -61. VI TABLE OF CONTENTS Declaration u Thesis Summary üi Acknowledgments V Publications vi Table of contents vii 1.. INTRODUCTION AND AIMS 1 2. LITERATURE REVIEW 2.1 Wine spoilage caused by bacteria 4 2.1.1 Wine spoilage by acetic acid bacteria 5 2.1.2 Wine spoilage by lactic acid bacteria 9 (Ð Acidification 10 (iÐ Mannitol taint t2 (iiÐ Ropiness and slime t3 (iv) Diacetyl production t3 (v) Acrolein formation and bitterness I4 (vi) Decomposition of tartaric acid t4 (vii) The geranium off-odour 15 2.2 Mousy off-flavour wine spoilage t6 (Ð Early studies ll (iÐ Recent studies on the nature and origin of mousy off-flavour 22 2.3 Occurrence of Z-acetyltefiahydropyridine and related compounds in other foods 29 3.