This article appears in the Winter 2018 edition of Talking Avocados (Volume 29 No 2).

Reducing bruising in avocado

By Melinda Perkins, Muhammad Mazhar, Daryl Joyce, Noel Ainsworth, Lindy Coates and Peter Hofman

As we near the end of the Supply chain quality improvement – Technologies and practices to reduce bruising (AV15009) project, it is timely to reflect on the findings to date and outline the research being undertaken in the final stages of the study.

Background

Recent surveys suggest that a large proportion of Australian avocado consumers are disappointed with the quality of the fruit that they receive. Encounters with flesh bruising are a major cause of consumer dissatisfaction.

This project was established to collate and evaluate current knowledge of factors that contribute to flesh bruising in avocado and to identify strategies to reduce it.

What we know about flesh bruising in avocado

A series of comprehensive literature reviews were conducted in the early stages of the project. The findings from these were communicated to industry via three Talking Avocados articles (details below), presentations at some recent Avocados Australia regional meetings, and a workshop at the Brisbane Markets (Figure 1).

Figure 1. A workshop held at the Brisbane Markets in May allowed researchers to present project findings (top panels) and gain the perspectives of industry stakeholders via group discussions (bottom panels).

Appropriate post-harvest temperature management was highlighted as a most important factor in controlling not only the expression of flesh bruising (Figure 2), but fruit quality in general.

Figure 2

The prompt cooling of Hass fruit to 5°C after harvest and minimising temperature fluctuations throughout the supply chain (except during ripening) are strongly recommended. The reviews also highlighted the following key points.

Flesh bruising arises when susceptible fruit are exposed to mechanical injury, including impact, compression and vibration. Susceptibility to bruising in avocado increases as fruit ripen and soften. To avoid bruising, softening fruit should not be exposed to drop heights of more than 10 cm.  In fact, firm-ripe and soft-ripe fruit should be ‘handled like eggs’ and not dropped at all.

Freshly harvested fruit generally do not bruise if dropped. However, our research suggests that they become more prone to body rots upon ripening. A 30cm drop height at harvest versus no impact at harvest caused increased body rots at the soft-ripe stage. More research is needed to quantify the relationship, but the initial findings do indicate that even hard mature green fruit require careful handling.

Hass fruit should be harvested when dry matter is above 23%, as increasing dry matter has been linked with lower bruise susceptibility in this cultivar.

Passing fruit through the supply chain as quickly as possible is recommended because stored fruit are more susceptible to bruising upon ripening than un-stored fruit.

Squeezing of fruit by retail staff, shoppers and consumers is the predominant cause of flesh bruising. Possible solutions include educating these groups about appropriate handling techniques, arranging retail displays into relative ripeness categories (eg ‘ripe and ready to eat now’ or ‘ready to eat in 2-3 days’), providing fruit in pre-packed formats (eg net bags, clam shells), and/or developing decision aid tools (DATs) that can used to objectively determine fruit firmness (ripeness) in a non-bruising manner. Research by our team has shown that shoppers responded positively to a prototype DAT, indicating that such devices would be readily adopted by shoppers if made available.

Pre-harvest factors including tree nutrition, irrigation regime, rootstock cultivar, tree vigour, crop load and canopy management are known to affect avocado fruit quality in terms of ripening time, physiological disorders and/or post-harvest disease. These factors are highly likely to also affect bruise susceptibility, although there is next to no published research in this area.

Where to next?

During the next few months, the project team will monitor fruit quality through actual supply chains in the field and through simulated supply chain scenarios in the laboratory. The applied aim is to gain a better understanding of the quantitative extents to which some abovementioned factors, including post-harvest temperature and fruit dry matter at harvest, affect final fruit quality.

The focus will be on flesh bruising susceptibility, incidence and severity. However, body rot susceptibility, incidence and severity will also be carefully assessed. Crucially, the effect of impact injury at harvest on final fruit quality in terms of rots as well as bruising will be investigated.  Fruit subjected to a controlled impact at the beginning of the supply chain will be compared and contrasted to fruit that receive no impact. In doing so, we aim to clearly demonstrate how careful handling at harvest can help deliver high-quality fruit to consumers.

Want more information?

For more information, our previous Talking Avocado articles are also online:

• Factors affecting avocado flesh bruising susceptibility, Winter 2017 edition
• Best practice handling to reduce flesh bruising, Summer 2018 edition
• Does impact injury at harvest increase body rots at retail?, Autumn 2018 edition.

Acknowledgements

The Supply chain quality improvement – Technologies and practices to reduce bruising (AV15009) project is funded by Hort Innovation using the Hort Innovation Avocado research and development levy with co-investment from the Queensland Department of Agriculture and Fisheries, The University of Queensland, Avocados Australia and contributions from the Australian Government.