title: Extending the shelf life of fresh horticultural produce under industrial settings by modified atmosphere packaging systems
Creators: name: Huynh, KN
Publisher: name: University of Tasmania
Year: 2023

description: Fresh horticultural produce is subject to rapid postharvest quality deterioration and senescence due to natural plant physiological processes and microbial degradation. Extending the shelf life of fresh produce has become important to expand market reach, reduce food waste, improve consumer satisfaction and encourage repeat purchases. Postharvest technologies such as modified atmosphere packaging (MAP), sanitisation, ethylene scavenging have been suggested to improve quality retention and extend the shelf life of fruit and vegetables. However, there is a knowledge gap in defining and understanding the opportunity to combine and optimise the different technology options to deliver improved MAP-based shelf life outcomes in industrial settings. This thesis therefore investigated the potential of combination technologies for improving the shelf life of three high-value, perishable produce types: raspberries, blueberries, and broccoli. The modified atmosphere/modified humidity (MA/MH) packaging types studied in this work included microperforated bags with high water vapour transmission rates (WVTR) that were tailored for each study produce, and a mineral-clay impregnated bag with low WVTR. Complementary treatments were chosen to target the major issue limiting shelf life with each produce type such as sanitisation using SO\(_2\) or H\(_2\)O\(_2\) vapour-releasing technologies for raspberries and blueberries, and ethylene scavenging for broccoli. In addition, microperforated lidding film, that develops MAP in unvented punnets was also trialled for raspberries and blueberries. This approach was to help overcome the short shelf life issues with atmospheric conditions used in current vented clamshell systems. In raspberries, MAP reduced mould growth, weight loss and anthocyanin accumulations that led to fruit darkening compared to the current vented clamshells. In the commercial trials over two harvests, a modified atmosphere of 14-15% O\(_2\) &amp; 7-8% CO\(_2\), established in a microperforated bag containing 12 punnets x 125g berries, was found to extend the storability of raspberries to 20-21 days at 2ᵒC. This would add 14 days extra compared to the existing industrial average shelf life of 6 days. The additions of sanitisers to MAP did not provide more benefits to the shelf life of raspberries in this study. In sealed punnets with six 70-μm perforations (creating a percentage of vented area of 5 x 10-9) and containing 125g berries, a passive MAP formed and improved the storability of raspberries to 11 days at 2ᵒC, compared to the vented clamshells and packages with none to five 70-μm perforations. The aroma profiles of the raspberries stored in the MA was closer to that of the berries on day 0 with noticeably smaller peak areas for terpenes/terpenoids than the clamshell fruit. In blueberries, MAP also reduced mould growth and weight loss during 10 weeks of the two commercial trials, as well as 8 weeks of the punnet-scale trial. An atmospheric condition of 16-18% O\(_2\) &amp; 2-4% CO\(_2\), established in both mineral-clay impregnated and microperforated bags packing 12 punnets x 125 g berries, extended the shelf life of ‘Legacy’ blueberries to 6 weeks and ‘Powder Blue’ blueberries to 8 weeks at 2ᵒC. This is equal to 2-4 weeks extra storage compared to the current average shelf life of 4 weeks. At the dose used in this study, SO\(_2\) effectively controlled mould growth but led to softening and bleaching at various degrees of severity. In the sealed punnets of 125g blueberries, the best quality retention was found in packages with two 70-μm perforations (providing a percentage of vented area of 1.68 x 10\(^{-9}\)) plus an initially reduced O\(_2\) level of 17% or 14.5% O\(_2\). Similar to raspberries, blueberries packed in MA had significantly smaller peak areas of terpenes/terpenoids, compared to clamshell fruit. Broccoli is highly perishable with rapid quality loss under abuse temperatures and exposure to ethylene. MAP systems with &gt; 1% O\(_2\) and &lt; 15% CO\(_2\) maintained the chlorophyll contents and GC-MS aroma profiles of broccoli closest to day 0, while minimising weight losses to &lt; 2% under three simulated shipping conditions. The scenarios studied included high-value, long domestic routes (7 days) with either good temperature management (2ºC) or broken cool chain (13ºC) and refrigerated sea-freight for exportation (42 days at 2ºC). In contrast, top-icing adversely affected the visual quality and aroma profiles of broccoli, particularly at 13ºC. Because MA was also developed in the packages with ethylene scavengers, it was not possible to examine the sole effects of ethylene scavenging on broccoli quality in this trial. This research has therefore demonstrated that MAP can extend the storability of raspberries, blueberries, and broccoli beyond current average values under commercial scales and settings. The extended shelf life would allow longer domestic routes and exportation with good end quality. The specific atmospheric conditions, benefits of bulk-pack MAP, the model of retail MAP and considerations for further research have been reported to inform the berry and broccoli industries and help justify establishing new MAP-based extended shelf life offerings. In addition, the design approach used in this Thesis allowed the testings of various MAP designs from one film and one gas mixture. This methodology can benefit future trials and optimisations of retail packaging for other products.