Monitoring changes in the volatiles composition of bottled and refrigerated cow milk by PTR-MS

Transcription

1 Monitoring changes in the volatiles composition of bottled and refrigerated cow milk by PTR-MS Erika Zardin 1, C. Siefarth 1, P. Silcock 2, M. Alothman 2, P. Bremer 2, S. Heenan 2, and J. Beauchamp 1 1 Department of Sensory Analytics Fraunhofer IVV; Freising, Germany erika.zardin@ivv.fraunhofer.de 2 Department of Food Science, University of Otago, Dunedin, New Zealand 5 th International Cold Chain Management Workshop June 2013, Universität Bonn

2 Fraunhofer IVV Fraunhofer Institute for Process Engineering and Packaging IVV Located in Freising (north-east of Munich) One of 66 Fraunhofer Institutes throughout Germany

3 Business Fields of the Fraunhofer IVV

4 Food Quality and Sensory Acceptance Food Quality Sensory Perception and Physiology Intrinsic / Extrinsic changes Chemical Physical Microbiological Analysis (e.g. food quality determination) Identification (e.g. marker/sensor) Knowledge (e.g. food/packaging interaction) Forecast (e.g. food shelf-life) Prevention (e.g. sterilisation/ hygiene) Along the supply chain! Evaluation of the quality of foods by means of sensory analysis as well as the analysis of all factors that influence the physiological composition. Identification of the mechanisms responsible for quality loss and development of prevention strategies.

5 Sensory Analytics department Sensory Analytics Odour, aroma & flavour perception, acceptance, preference characterisation of odorants hedonics / consumer tests sensory assessments mimic analysis off-odour aroma release avoidance strategy development physiological / psychological effects pharmacokinetics of odorants in vivo in vitro

6 Sensory Analytics department Sensory Analytics Odour, aroma & flavour perception, acceptance, preference characterisation of odorants hedonics / consumer tests sensory assessments mimic analysis off-odour aroma release avoidance strategy development physiological / psychological effects pharmacokinetics of odorants in vivo in vitro

7 VOC by Proton Transfer Reaction-Mass Spectrometry H 3 O + + VOC VOCH + + H 2 O Proton transfer reaction when PA(VOC)>PA(H2O)

8 VOC by Proton Transfer Reaction-Mass Spectrometry H 3 O + + VOC VOCH + + H 2 O H 2 O + H + O + H + OH + H + e H 3 O H + H 3 O + 3 O + Proton transfer e H 3 O + H 3 VOC H O + + reaction when e H 3 O H + 3 O + e PA(VOC)>PA(H 2 O) H 2 O H 2 O VOC *

9 PTR-MS performances benefits Very low detection limit: <1 pptv High temporal resolution: down to100 ms per compound Quantitative: calibration (accuracy 10 %) or direct calculation (accuracy 25%) Insensitive to water: sample gas humidity variations have minimal effects No sample preparation : direct (on-line) analyses of gas samples from Headspace drawbacks Low mass resolution: m/ m = 1 isomeric/isobaric species cannot be separated Molecular mass information limited: only low res. MW clues about chem. formula

10 Monitoring changes in the volatiles composition of bottled and refrigerated milk The VOC composition of cow milk changes as milk approaches the end of its shelf-life. Microbial activity is the primary catalyst for such changes. VOC profiles in the headspace of packaged (HDPE), chilled (4.5 C), extended shelf-life cow milk samples were analysed in real-time over a period of 18 days by PTR-MS. PTR-MS static headspace VOC were compared to total aerobic plate count (APC) values Samples re-investigated off-line by SPME-GC- MS to aid chemical identification of the PTRMSdetected signals. Paenibacillus stain Image: retrieved June 2013

11 Materials & method Milk samples: Trim % fat ; Lite % fat, full-cream % fat Refrigerated & kept in the dark throughout the storage period Duplicate series of the milk samples treated with NaN 3 (bacteriostatic agent)

12 Materials & method

13 SPME-GC-MS off-line Later applied to the HS of frozen aliquots of the milk samples Polydimethylsiloxane/Divinylbenzene PDMS/DVB and Carboxen/Polydimethylsiloxane CAR/PDMS fibers Scope: to aid chemical identification of the VOCs detected by the PTR-MS overbrookscientific.com

14 Results n C P S Log APC Yeld point for bacterial numbers: once APC numbers exceed a certain point VOC start to increase. Yield point shift slightly, with m/z 45 & 47 appearing to increase sooner than m/z 89. At high APC numbers there are still low VOC concentrations

15 Results m/z Common name IUPAC name 45 Acetaldehyde (Ethanal) Acetaldehyde 46 Unidentified ( 13 C of above ) 47 Identified Lit. Ref 1: Soukolis et by SPME al. RCMS (this study) ,1(SPME), 2 Ethanol Ethanol 1 Formic acid Formic acid 1 48 Unidentified ( 13 C of above ) 49 Methanethiol Methanethiol 1(SPME) 51 methanol-water cluster 57 Unidentified 59 Acetone 2-propanone 1 60 Unidentified ( 13 C of above ) 61 Acetic acid Acetic acid 1 Ethyl acetate (fragment ) Ethyl acetate 1 Isopropyl alcohol Propan-2-ol 2 1-propanol Propan-1-ol compared the ncps of each mass ions of milk with and without NaN 3 using the nonparametric Mann-Whitney test. 44 m/z identified as being significantly different btw. with and w/o NaN3 SPME attributed identity to ab. 40 of these VOC 62 Unidentified ( 13 C of above ) 63 Dimethyl sulfide DMS Methylsulfanymethan e 1(SPME) 64 Unidentified ( 13 C of above ) 89 Acetoin (3-Hydroxybutanone) (3R)-3-hydroxybutan- 2-one 1 Ethyl acetate Ethyl acetate 2 Butanoic acid Butanoic acid 2 1-Pentanol Pentan-1-ol 1(SPME) 3-Methyl-1-butanol 3-Methyl-1-butanol

16 Results In the presence of NaN 3 bacterial spoilage did not occur any significant differences that were detected can be attributed to bacteria sp. As non-microbiological induced changes to the milk VOCs also occurred, compared samples w. NaN 3 at day 1&18. Differences detected could be attributed to non-microbial sources (i.e. oxygen, auto-oxidation) Additional m/z 33, 109, (111, 122,) 124, (137) not detected in the previous analysis

17 the take-home message use your nose as it will always tell the truth if the milk is off!

18 Light & oxygen influence on milk On-line monitoring of quality changes (by PTR-MS): VOC release from bovine milk during fluorescent light exposure

19 Light & oxygen influence on milk

20 PTR-MS measurements (preliminary results) + sensory analysis (aroma & taste) assessment by trained panel

21 Acknowledgements Collaboration btw. Fraunhofer IVV (Germany) & University of Otago (New Zealand) funded by German Federal Agency for Agriculture and Food (BLE) and The Royal Society of New Zealand ( ) Thank you for your kind attention!