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I like cabbage. It’s not a glamorous vegetable, but it’s tasty and versatile – even if it is easy to overcook and get the dreadful school canteen cabbage water smell. It’s also good for you, containing a range of medically relevant chemicals, including the potentially antibacterial and anticancer 4-methylsulfinylbutyl glucosinolate (4MSO).
But how can you get the best from your cabbage? According to new research published in Current Biology, it may be as easy as eating it at the right time of day.
A team of US scientists, led by Danielle Goodspeed at Rice University in Houston, has demonstrated that shop-bought cabbages, even days after harvest, responded to a day–night cycle that regulated concentrations of defensive chemicals such as glucosinolates and the hormone jasmonate. When growing in the wild, this strategy offers an advantage, serving to increase protective chemicals in anticipation of daily attack from insect herbivores. However, it hasn’t been clear if this process would continue after harvest, on supermarket shelves or even in your fridge.
To find out, Goodspeed took samples of shop-bought cabbage and exposed it to a regulated cycle of 12 hours of light followed by 12 hours of darkness. After several cycles, the team looked at the variable chemical profile as well as the plant’s vulnerability to being nibbled by cabbage looper moth caterpillars.
The results showed that glucosinolate levels, including that of 4MSO, did indeed vary by two to three fold with the day/light cycle, peaking between 4 and 8 hours into the ‘day’. Plants that experienced the same circadian pattern as their caterpillar pests also fared better in the nibble test – where plant and caterpillar had opposite day/night cycles, the cabbages experienced far more grazing and the caterpillars got fat. This pattern was evident until around a week after harvest, and even when the plants were refrigerated to 4°C (though the total levels of glucosinolate were lower in refrigerated veg).
So what does this mean for cabbage eaters like me? It shows that the way we store vegetables, and even the time of day at which we eat them, may alter their nutritional value and possibly change the way they taste. The team suggest that we should think about such clock-mediated chemical behaviours when considering harvesting, preserving, transport, storage of food, and in scientific research into plant crops.
But what if you don’t like cabbage? They found the same behaviour in lettuce, spinach, courgette, sweet potato, carrot and blueberry, so there’s a clock-mediated crop for every palate!
Reference: Goodspeed et al., Postharvest Circadian Entrainment Enhances Crop Pest Resistance and Phytochemical Cycling, Current Biology (2013), http://dx.doi.org/10.1016/j.cub.2013.05.034