Leafy Asian Vegetables Extending their Shelf Life: Part 2 A report for the Rural Industries Research and Development Corporation by T.J. O’Hare and L.S. Wong January 2002 RIRDC Publication No 02/006 RIRDC Project No DAQ-239A © 2002 Rural Industries Research and Development Corporation. All rights reserved. ISBN 0 642 58405 2 ISSN 1440-6845 Leafy Asian Vegetable – Extending their Shelf Life (Part 2) Publication No. 02/006 Project No. DAQ-239A The views expressed and the conclusions reached in this publication are those of the author and not necessarily those of persons consulted. RIRDC shall not be responsible in any way whatsoever to any person who relies in whole or in part on the contents of this report. This publication is copyright. However, RIRDC encourages wide dissemination of its research, providing the Corporation is clearly acknowledged. For any other enquiries concerning reproduction, contact the Publications Manager on phone 02 6272 3186. Researcher Contact Details Dr Tim O’Hare Gatton Research Station, Queensland Department of Primary Industries, LMB 7, MS 437, Gatton 4343 Queensland Phone: 07-54662222 Fax: 07-54623223 Email: [email protected] RIRDC Contact Details Rural Industries Research and Development Corporation Level 1, AMA House 42 Macquarie Street BARTON ACT 2600 PO Box 4776 KINGSTON ACT 2604 Phone: 02 6272 4539 Fax: 02 6272 5877 Email: [email protected]. Website: http://www.rirdc.gov.au Published in January 2002 Printed on environmentally friendly paper by Canprint ii Foreword Asian leafy vegetables (like other leafy vegetables) tend to have a very short shelf-life if not handled correctly. Modified atmosphere packaging is quite effective in extending their shelf-life as shown in Part 1 of this study (RIRDC Project DAQ-213A), but requires correct packaging and handling conditions for this to occur. The present project investigated the availability of plastic films on the market-place to achieve this aim, and at the same time explored the potential for new technology capable of maintaining leaves in a fresh, green state. Furthermore, this project extends the one-page information leaflet series that was initiated by another RIRDC project (DAV153A Diversifying Asian Vegetable Markets) offering a useful summary of correct handling techniques for pak choy, mizuna, mibuna, Chinese mustard, tatsoi, choy sum and garland chrysanthemum. This report outlines the findings, and provides feedback on the search and development of films for modified atmosphere packaging, as well as providing a useful insight as to what really controls shelf- life in Asian leafy vegetables. This project was funded from RIRDC Core Funds which are provided by the Federal Government. This report, a new addition to RIRDC’s diverse range of over 800 research publications, forms part of our Asian Foods R&D program, which aims to foster the development of a viable Asian Foods industry in Australia. Most of our publications are available for viewing, downloading or purchasing online through our website: • downloads at www.rirdc.gov.au/reports/Index.htm • purchases at www.rirdc.gov.au/eshop Peter Core Managing Director Rural Industries Research and Development Corporation iii Acknowledgements The current project was run in parallel with ACIAR Project PHT9416 (Extending Shelf-life of Leafy Vegetables) and shared resources. iv Contents Foreword .................................................................................................................. iii Acknowledgements................................................................................................. iv Executive Summary................................................................................................. vi Introduction............................................................................................................... 1 Objectives ................................................................................................................. 2 Methodology ............................................................................................................. 3 Plastic film development ......................................................................................... 4 Film availability...................................................................................................................... 4 Film testing............................................................................................................................. 4 Film development................................................................................................................... 5 1-MCP Fumigation .................................................................................................... 8 Background............................................................................................................................. 8 Increasing inherent shelf-life with 1-MCP............................................................................. 8 1-MCP as a protective agent against external ethylene.......................................................... 8 Optimisation of 1-MCP Fumigation Concentration ............................................................... 9 Optimisation of 1-MCP Application Temperature............................................................... 10 Multiple Applications of 1-MCP.......................................................................................... 11 Effect of Physiological Leaf Age on 1-MCP Efficacy......................................................... 11 Factors Controlling Leaf Yellowing ...................................................................... 13 Background........................................................................................................................... 13 Changes in Ethylene and Sugar Levels ................................................................................ 13 Yellowing and Physiological Leaf Age................................................................................ 14 Single-page Leaflets............................................................................................... 16 Pak Choy............................................................................................................................... 17 Mibuna.................................................................................................................................. 18 Mizuna.................................................................................................................................. 19 Chinese Mustard................................................................................................................... 20 Garland Chrysanthemum...................................................................................................... 21 Tatsoi .................................................................................................................................... 22 Choy Sum ............................................................................................................................. 23 General Conclusions.............................................................................................. 24 Publications ............................................................................................................ 25 v Executive Summary The present project DAQ239A flows on from an earlier project of the same name (DAQ213A) in which it was shown that modified atmosphere packaging had potential to almost double storage life of many fresh-processed leafy Asian vegetables. In that project, optimum oxygen and carbon dioxide atmospheres were identified, cool-chain issues were highlighted, and the role of physiological leaf-age influence the rate of leaf yellowing was introduced for the first time. Although it was shown that atmosphere control was potentially a powerful tool for the industry, the next step of using this information to produce modified atmosphere packaging (MAP) was yet to be accomplished. The present project took this further step, along with testing other potential methodologies (eg. 1-MCP fumigation) which, if successful, could make modified atmosphere technology redundant. The practical development of MAP for Asian vegetable leaves proved to be more complex than simply ordering plastic film bags of the appropriate permeability. It was soon realised that other factors came into importance, including aesthetic appearance of the package, film availability, packaging costs, and the unfortunate closure of our industry partner during the project. In the retail market, aesthetic appearance means sales and consequently our science was tempered by consumer demand for a package of high clarity. At this stage, such a bag with optimum permeance characteristics for Asian leafy vegetables does not exist. Polypropylene-based films provide excellent clarity, but the permeance ratio of carbon dioxide to oxygen is not high enough. This results in either one or other of the gases being too high to benefit the leaves. Polyethylene on the other hand has an excellent permeance ratio, but the film clarity is not ideal and looks second-rate to polypropylene. The choice is therefore by necessity a compromise: high clarity with shorter shelf- life, or reduced clarity with optimum shelf-life. Packaging availability also had to be taken into account in the real world of commerce. Due to the small size of the industry, the development of specialised films for Asian leafy vegetables