Orange capsicums on the menu for long-term eye health
A five-year cross-industry project, Naturally Nutritious is researching the development of innovative food products and varieties that are nutritious, delicious and visually appealing. Project Lead Dr Tim O’Hare provides an update, with the focus on developing orange capsicums.
First it was carrots; now capsicum has been identified as good for your eyes – and it is the nutrient linked to the orange colour that counts.
Just as carrots were found to promote night vision through a nutrient called beta-carotene, now another orange vegetable has been found to be pivotal for eye health.
Research by Dr Tim O’Hare from the University of Queensland has identified orange capsicums as the richest source of the orange pigment zeaxanthin, which is vital for central vision.
He is now helping to address the lack of zeaxanthin in our diets through research based at the Queensland Alliance for Agricultural and Food Innovation (QAAFI) and funded by Hort Innovation.
The findings are part of the Naturally Nutritious project, which is seeking to increase the level of nutrients in fruit, vegetables and nuts.
Nutrition you can see
Dr O’Hare explained that he and his project team are interested in products that can be visually identified by consumers as containing vital nutrients.
“A number of nutrients we are interested in for human health are actually pigmented. In most cases, it’s the zeaxanthin itself that gives orange capsicums their vivid orange colour,” Dr O’Hare said.
Another example of this is the purple pigment anthocyanin, found in purple sweet corn (more about purple sweet corn can be found on page 54 of Vegetables Australia – Spring 2019).
“With these nutrients, what you see is what you get – the more intensely coloured the product, the more nutrients it contains,” Dr O’Hare said.
When it comes to orange zeaxanthin and health, Dr O’Hare said the compound accumulates in our macula, at the back of our eyes. It protects against blue light, which is particularly damaging as it can oxidise our photoreceptors and leads to macular degeneration.
As such, zeaxanthin deficiency leaves eyes susceptible to age-related macular degeneration, which in Australia affects one in seven people over 50 years of age and one in three over 80.
Too much blue light can damage the light receptors (called cones) in the retina that are responsible for high-resolution central vision and colour perception. The more zeaxanthin in your macula, the more blue light is naturally screened from hitting the back of the eye.
Dr O’Hare stressed that food is essential to achieve this protection.
“Our bodies can’t make zeaxanthin, which means we rely exclusively on dietary sources or on artificial supplements,” he said.
A comparative analysis of different fruits and vegetables identified orange capsicums as the richest source of zeaxanthin by far. One capsicum (typically 450 grams) was found to contain zeaxanthin levels equivalent to 30 supplement tablets, with two milligrams of zeaxanthin the daily recommended dose.
“Each zeaxanthin tablet is roughly equivalent to 10 grams of orange capsicum flesh – that’s how rich the capsicums are in this pigment,” Dr O’Hare said.
“The trouble at the moment is that orange capsicums are not always available in shops. This is something we are looking to overcome.”
In contrast, the ‘traffic light’ capsicums – coloured red, yellow and green – contain no zeaxanthin.
The analysis also compared zeaxanthin levels among the different orange capsicum varieties that are available in Australia.
A total of eight orange varieties of capsicum were analysed, with seven all proving to be rich sources of zeaxanthin. The eighth, however, owes its orange colouring to a mix of red and yellow pigment.
“Mix these two colours together and you get a dark orange fruit, but sadly no zeaxanthin,” Dr O’Hare said.
At the University of Queensland’s QAAFI institute, PhD candidate Rimjhim Agarwal is working to better understand how orange capsicums accumulate zeaxanthin, with the goal of producing genetic tools to help select and breed for higher zeaxanthin production.
Ultimately, the goal of the research is to make it agronomically viable and profitable for growers to produce more orange capsicums, and to alert consumers to their special health benefit of preserving eyesight – thereby creating demand.
The trick is to coordinate the increase in demand with supply, which includes ensuring that there are no constraints on Australian farms to growing orange capsicums.
Dr O’Hare has a tip for consumers who already include zeaxanthin-producing capsicums in their diets.
“Zeaxanthin is fat-soluble, so it’s best served with a helping of olive oil or salad dressing to aid absorption,” he said.
“Raw works well, although cooking the capsicum can also help by breaking down the cell walls to better release the zeaxanthin. But don’t overcook them, as overcooking will cause some of the zeaxanthin to break down.”
While zeaxanthin does occur in other vegetables, the levels tend to be quite low. However, Dr O’Hare is exploring ways to increase zeaxanthin production in other vegetables, and he has produced orange-coloured corn that contains 10 times more zeaxanthin than its yellow counterpart. Even so, it cannot rival the levels found in orange capsicums.
As capsicum and chilli belong to the same species, Dr O’Hare is also exploring opportunities to make and accumulate zeaxanthin into chillies. For those who like it hot, one high-zeaxanthin chilli a day could be enough to help stave off macular degeneration.
Find out more
Please contact Dr Tim O’Hare, Senior Research Fellow, Queensland Alliance for Agriculture and Food Innovation (QAAFI), The University of Queensland at email@example.com or 0408 148 049.
More information about Naturally Nutritious can be found here.
Naturally Nutritious is funded by the Hort Frontiers Health, Nutrition and Food Safety Fund, part of the Hort Frontiers strategic partnership initiative developed by Hort Innovation, with co-investment from the University of Queensland and contributions from the Australian Government.
The Queensland Alliance for Agriculture and Food Innovation (QAAFI) is a research collaboration between University of Queensland and the Queensland Government through the Department of Agriculture and Fisheries.
Project Number: HN15001
This article has appeared in Vegetables Australia – Summer 2020/21. To read the full publication, please click here.