Question: Lots of recipes, from soups to frittatas, encourage us to use up forgotten “tired” vegetables such as carrots, pumpkin, cabbage, etc. We’re told greens quickly lose nutritional value, but what about root veges? Does soup boiled for ages or frittata made with tired veges have any food value?
Answer: In an ideal world, we’d all pop out to the greengrocer every few days for the freshest fruits and vegetables. But with time at a premium, less frequent stock-ups often replace regular shopping trips, and those veges in the fridge may end up a little tired. While it’s true that veges lose nutrients over time, the good news is that many key micronutrient groups – such as minerals and specific vitamins – remain stable even with prolonged storage.
For instance, a 2007 study in the Journal of Food Science found broccoli’s vitamin C content declined by about 39% when stored at 6°C for 35 days.
While this might sound like a lot, the flip side is that broccoli retained 60% of its vitamin C content after languishing in a fridge for more than a month. Vitamin C is particularly susceptible to degradation and loss during storage and processing, so the fact that the broccoli retained much of its vitamin C after over a month suggests it would have retained a significant proportion of its hardier nutrients, too. Indeed, the researchers found 70% of the broccoli’s sulforaphane content was retained.
Sulforaphane is a type of glucosinolate – phytochemicals thought to reduce cancer risk and boost the effects of other antioxidants. Similarly, another 2007 study published in Food and Chemical Toxicology revealed that broccoli, Brussels sprouts, cauliflower and green cabbage lost only 9-26% of their glucosinolates after storage for seven days in a fridge.
Nutrient losses vary between vegetables, with some experiencing more significant losses than others. For example, a 2005 study in the International Journal of Food Sciences and Nutrition found green capsicum refrigerated at 4°C for 20 days retained all of its vitamin C. Red capsicums lost about 15% over that time, but remained a rich source of vitamin C, at 70mg per half cup.
Baby spinach is an example of a particularly delicate vegetable. Because the leaves have a very high respiration rate, their post-harvest quality is affected mainly by tissue decay. In a 2015 study published in HortTechnology, researchers stored baby spinach leaves in a refrigerator for up to 12 days. The leaves’ antioxidants and vitamin C content stayed stable for six days of storage at 4°C and then declined. Similarly, magnesium, zinc and iron levels decreased after six days of storage.
‘Tired’ vegetables retain a surprising amount of nutritional value, even after extended storage.
In general, minerals and dietary fibre are stable during processing, storage and cooking. They are more likely to be lost during peeling and other removal steps during food preparation or processing.
Pumpkins, cabbage and root vegetables such as carrots have a lower respiration rate than vegetables such as broccoli and asparagus. The respiration rate of vegetables is a measure of how quickly they consume oxygen and produce carbon dioxide, which affects their freshness and shelf life. Veges with a lower respiration rate tend to stay fresh for longer when stored correctly, thus retaining more of their nutrients.
Storage conditions, such as temperature, humidity and light, significantly affect shelf life and nutrient content. Proper storage helps to prevent wilting, which is closely tied to nutrient loss. To maximise nutrients, refrigerate vegetables promptly and keep ethylene-producing items (such as avocados and tomatoes) away from ethylene-sensitive ones such as beans, broccoli, cabbage and leafy greens. Ethylene causes veges to ripen faster.
So, although fresh vegetables are ideal, “tired” veges retain a surprising amount of nutritional value, even after extended storage in the fridge. Root vegetables are resilient, holding on to minerals, dietary fibre and some vitamins and antioxidants. Whether they are boiled in a soup or baked in a frittata, rest assured they still contribute valuable nutrients.
