We Skyped with the ex-CEO of Avocados Australia and current President of the International Avocado Society, Antony Allen, and explained our project, with the goal of collecting information on how best to tailor our biosensor for industry and human use. Avocados Australia is the leading industry body in Australia for avocados and so they have a wealth of knowledge regarding all parts of the supply chain, from production through to distribution and retail to the customer. During the Skype meeting, we learnt valuable information regarding the ripening process of avocados, the main points of which are outlined below:
• Avocados start producing ethylene when picked from the tree
• Immediately start to ripen if the temperature is above 15°C (59°F)
• Both temperature and ethylene levels are tightly regulated to control ripening
◦ Temperature is kept at 6°C (43°F) and avocados kept for 1-2 days before being shipped.
• Avocados are constantly checked for signs of ripeness and damage, which indicates ethylene production
• When ready to ripen, avocados treated with ethylene and temperature raised to 16-18°C (61-64.5°F)
In the meeting it was confirmed that there are a lack of adequate methods for detecting ethylene during the ripening process. The method that is currently used involves manually handling and inspecting the fruit for signs of damage, as well as feeling for softness and looking for colour change (the latter being particularly important for the Hass variety of avocados). This process is both labour intensive and can lead to unnecessary food wastage.
How will your device work at the consumer level, because that’s where most avocados are damaged?
Let’s make a sticker!
Our biosensor design idea at the time of the Avocados Australia meeting was to have a sticker that could be placed on the avocado. During the ripening process, the sticker would turn blue and allow the consumer to ascertain optimal ripeness. Over the course of our Skype meeting, Antony Allen stated that most of the damage to avocados occurs at the consumer level, when the fruit is softened from the ripening process and therefore susceptible to bruising when squeezed. As our survey found that the more than 95% of consumers do not purchase fruit when it is damaged, the application of a sticker that allows consumers to determine ripeness would save money, prevent food wastage, and make the customer very happy.
Another fruit industry battling against the forces of ethylene is Zespri, a New Zealand based Kiwifruit Company that sells the tasty fruit in more than 53 countries and who manages 30 percent of the global market. During this meeting, we Skyped with Frank Bollen, a technical manager whose team looks after the post-harvest performance of the fruit. This ranges from management of cool-stores (e.g. ethylene levels in these rooms), shipping and the performance of the ships (e.g. cooling rooms on-board), and market performance (e.g. making sure the fruit is “ready to retail” firmness). During the Skype meeting we learnt valuable information regarding the processing of kiwifruits, which is outlined briefly below:
• Fruit ripeness is indirectly measured by a penetrometer
◦ Fruit is picked between 6-8kg (firm)
◦ Quickly softens down to 2kg
◦ Slowly softens down to “ready to eat” firmness (1kg)
• Kiwifruit are very sensitive to ethylene and so produce very little of the gas
• During storage, kiwifruit are packed into 10kg plastic bags and put into boxes
◦ There are 100 boxes on each pallet and the storage rooms are filled with pallets (see images)
• Kiwifruit ripening is accelerated using 100ppm ethylene (highly saturated).
A biosensor for use at the storage level would be very convenient, and a sticker may not be appropriate. What else could you do?
Let’s go back to the drawing board!
Over the course of the meeting it was suggested that a biosensor at the storage level of the production chain would be very beneficial. During the storage process the 10kg bags are opened and manually inspected at random. Fruit is checked for signs of ripening or damage, which roughly indicates ethylene production. In the event of finding softened fruit, the whole bag is emptied and re-packed and the pallet is rearranged. This process is very labour intensive and so we thought that, if there was some sort of ethylene biosensor in each bag or somewhere in the room, any ripening taking place could easily be detected and prevented. This would allow for targeting of specific bags that are producing ethylene, rather than the random process that occurs currently.
See the Applied Design page for how this specification was integrated into the product design process!
Fresh Produce Group receives international and domestic shipments of produce, and process them for distribution to major supermarkets and restaurants. This processing includes quality assurance testing, ethylene ripening phases, and temperature control, as well as packaging. The current ripeness inspection method is manual handling. Workers open a tray of each fruit from each pallet from each shipment, and squeeze each piece of fruit by hand to assess how ripe it is. This handling, however, is also to identify and remove rotted or infected produce, and is essential for sizing the produce as part of quality assurance.
“Manual handling will never be eliminated from our protocol. Is there a way your technology could support current methods rather than aim to replace them completely?”
Any new technology must fulfil a need. Perhaps it is not feasible or practical to implement at this stage of the processing chain, but perhaps it could be redesigned to serve another need. When designing our final biosensor chassis, we included a plate and paper strip design to be used in conjunction with a phone app we developed, for specific applications like these. This technology provides a way for workers of any background to be able to quickly and constantly gain a numerical reading for the ethylene levels inside a storage room or crate. It provides an extra level of accountability, and supports current methods rather than attempting to replace them.
We chatted with OzHarvest volunteers at the Sydney Eat.Think.Save event, then again at a volunteer meeting about parallels between their mission and ours. OzHarvest works to reduce food wastage at the other end of the chain. That is, they recover food that would otherwise be thrown out (including overripe fruits and vegetables) and make new meals to serve to the homeless and disadvantaged.
“Sounds great, but could it be biodegradable?”
When deciding on the final immobilization technique and overall product design, the environmental impact was pushed to the forefront out our minds. The latex nanoporous coating method was chosen due to its biodegradability.
Biofoundry is Australia’s first community lab that aims to make scientific research more accessible by subsidizing costs, and also aims to make science education more accessible to all. Our first outreach project-based presentation was at Biofoundry’s August meeting held at the ATP Innovations Centre right around the corner from our lab. At this presentation there were many things we still had not considered, and it was an extremely valuable opportunity to see which aspects of our initial plan provoked the most questions or comments from an audience with a fundamental scientific background.
“Having a sticker with genetically modified E.coli on fresh produce doesn’t seem like the reward is worth the risk. Could you try to clone the Mycobacterium NBB4 genes into an alternative host, such as yeast?”
An interesting idea…
Using yeast as a host would definitely eliminate the biosafety risk of having E.coli in such proximity to fresh produce. As a future application, it’s definitely worth considering. In the context of iGEM, however, investigating this is not practical for many reasons. Firstly, E.coli is a much more friendly cell to work with in the lab, and familiarity with it’s growth patterns will remove an extra layer of troubleshooting that would be required if we switched to using yeast. Also, and most importantly, it is difficult enough to express Mycobacterium genes in E. coli, let alone in a more complex organism such as yeast. Without codon optimisation methods this would be a task with a low chance of success. Thus, for the scope of our project, we stuck to E. coli, however yeast could be a very interesting way to avoid the main biosafety concern surrounding the application of our technology.