Orange capsicums contain the richest source of the orange pigment zeaxanthin, which is vital for central vision, according to a plant physiologist at The University of Queensland (UQ).
Associate Professor Tim O’Hare is helping to address the lack of zeaxanthin in Australian’s diets through research based at the Queensland Alliance for Agriculture and Food Innovation (QAAFI).
“When it comes to orange zeaxanthin and health, the compound accumulates in our macula,” he said. “It protects against blue light, which is particularly damaging as it can oxidise our photoreceptors, which leads to macular degeneration.”
O’Hare’s research found 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.
“Our bodies can’t make zeaxanthin, which means we rely exclusively on dietary sources or on artificial supplements,” he said.
O’Hare’s comparative analysis of different fruit and vegetables identified orange capsicums as the richest source of zeaxanthin. One capsicum (typically 450 grams) was found to contain levels equivalent to 30 supplement tablets, with two milligrams of zeaxanthin the daily recommended dose, according to UQ.
“Each zeaxanthin tablet is roughly equivalent to 10 grams of orange capsicum flesh – that’s how rich the capsicums are in this pigment,” he said.
“The trouble at the moment is that orange capsicums are not always available in shops, something we are looking to overcome.”
O’Hare’s analysis also compared zeaxanthin levels among the different orange capsicum varieties available in Australia.
A total of eight orange varieties of capsicum were analysed, with seven proving to be rich sources of zeaxanthin; the eighth owes its orange colouring to a mix of red and yellow pigment but does not contain zeaxanthin.
He found readily available ‘traffic light’ capsicums – coloured red, yellow and green – contain no zeaxanthin.
According to UQ the ultimate 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 eye health benefits, thereby creating demand.
O’Hare’s colleague at QAAFI, PhD candidate Rimjhim Agarwal, is working towards producing genetic tools to help select and breed orange capsicums for higher zeaxanthin production.
O’Hare is also 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. However, it cannot rival the levels found in orange capsicums.