Quality deterioration of packaged fruits caused by mechanical damage : a study on 'Cavendish' banana supply chain in Australia

Background: Banana (Musa spp.) is the largest horticultural product in Australia with a farm gate value of over AU$ 600 million in 2017. Quality deterioration of bananas in postharvest supply chains (SC) due to mechanical damage results in economic loss to both growers and retailers. However, the mechanism of damage occurrence in packaged bananas, and the underlying causes for deteriorated fruit quality, remains unclear. Over 95% of Australia's banana production is concentrated in the region of far North Queensland and the road supply chains to major markets can extend thousands of kilometres across the continent. This results in prolonged exposure of packaged bananas to transient shocks and vibration intransit. This research aimed to identify the causes of mechanical damage along the post-harvest SC and to provide recommendations for mitigating the damage and improving the quality of bananas in the retail markets. Methodology: To achieve the research objectives, mixed research strategies and methods were used. Field research was conducted to investigate the occurrence and extent of damage and identify risk factors along the post-harvest SC. The laboratory experiments were then followed to establish the causes and effects and, develop possible solutions to improve banana quality. Firstly, the mechanical damage levels in packaged bananas were assessed across the SC to understand the frequency and severity of different types of cosmetic defects in bananas. A field observation study along the post-harvest SC was conducted in parallel to damage assessment to identify the risk factors for mechanical damage. Secondly, the mechanisms of damage development in packaged bananas were characterized by using simulated vibration, top-load compression and drop-impact tests. Field vibration data collected during the interstate transport of bananas were used to develop vibration test profiles that were then used in laboratory-based simulation experiments. The performance of a range of packaging alternatives was then tested on the vibration simulator and the results were compared. The compression strength and basesagging levels in different package types under high relative humidity (RH) ripening conditions were experimentally tested. Finally, the effectiveness of vacuum-tightening banana clusters to minimize mechanical damage caused by simulated vibration was also examined. Findings: It was revealed that the increase in cosmetic defects caused by mechanical damage was progressive along the SC, resulting in deteriorated appearance quality of bananas in retail stores. Different mechanical stresses on packages such as top-load compression, vibration and drop-impact resulted in markedly different damages in bananas including bruising, abrasion and neck injuries. Both bruising and neck injuries occurred due to top-load compression and were influenced by the package position in a pallet. Neck injuries were also associated with the handling of packages during the last -mile distribution of ripe bananas. Abrasion damage was the most prominent type of damage in packaged bananas across the SC, mainly caused by vibration during transport. Mechanical damage caused by vibration was influenced by the intensity of the input vibration from the truck floor, the vibration transmissibility in a stacked pallet and the freedom of movement of packaged bananas inside the package. Simulated package testing revealed that both vibration transmissibility and the construction material of packaging influenced the mechanical damage levels in bananas. The structural integrity of the corrugated cartons was weakened with exacerbated base-sagging levels due to the moisture absorption in the high RH environment, causing mechanical damage in ripe bananas during the distribution to retail stores. The one-piece corrugated carton showed a better protective performance under simulated vibration, higher compression strength and reduced base-sagging levels compared to the widely used two-piece carton. Improvements in work practices including optimal packing of clusters in pack houses and stacking arrangements of packages in retail stores were highlighted to further minimize mechanical damage to bananas. Finally, column-stacking of packages in the pack houses and careful handling during the pallet consolidation in the distribution centre may further reduce damage to bananas during the 'last -mile' distribution. Significance: This study made several contributions to the industry practice and field of research. Knowledge of the mechanisms of damage occurrence and the causes of damage along the SC resulted in several practicable interventions for the industry to improve the quality of bananas in the post-harvest SCs. The contributions to the field of research include the introduction of an objective damage estimation method, improved understanding of the vibration characteristics of multi -trailer road trains and the influence of vibration transmissibility in a column of stacked packages, on the development of mechanical damage in packaged fruits. The research developed a method of modelling damage levels in packaged bananas using vibration intensity and exposure duration. This method makes accelerated vibration simulation testing for package fruits realistic and reliable. Limitations and Future Research: The study showed that the vibration damage can be reduced by vacuum-tightening of bananas. However, additional research is warranted to make it a commercially viable application. Solutions targeted at vibration dampening in pallets can be further researched to reduce the transmission of high-frequency vibration to the lower tiers in the pallet. The protective performance of one-piece carton can be improved through adjusting package height for optimal headspace to allow a quasi-static compression on the fruits while avoiding excessive compression caused by the transfer of weight from the top-tiers of the pallet. The enhancement of moisture-resistant can be considered to further strengthen the carton. RPCs in the current form were not suitable for packing bananas. However, further investigations on improved side-wall cushioning could be considered to reduce the damage levels. Finally, the proposed advances to the industry practice for improving the quality of bananas require other socio-economic evaluations such as the financial feasibility and the environmental sustainability before the implementation of the proposed recommendations.