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During the Christmas period, Brussels sprouts are a traditional addition to a festive meal among many households. With only 43 kcal per 100g and packed with protein and vitamins [1], sprouts offer a nutritious boost during a holiday season often marked by indulgence and excess. Among the vast number of nutrients in the vegetable are vitamin C, potassium, calcium and vitamin B3, all of which have cardiac, bone and cognitive benefits [2].
Unfortunately, due to their seasonal demand, freezing is a necessity, but long-term freezing processes can disturb the biochemical stability of these vegetables. This year, researchers investigated the impact of frozen storage and pretreatment on health-related compounds, including vitamin K1, vitamin C and carotenoids, in Brussels sprouts. A selection of Brussels sprouts of the Sofia variety was harvested in early 2022 and industrially frozen, then subjected to frozen storage at −20°C, −15°C, or −7°C for over a year [3]. Part of these samples were stored at glass transition temperature (GTT) as a control; the GTT has a crucial role in the shelf-life of food and refers to the temperature below which molecular mobility ceases and the product takes on a rigid, glassy appearance. Samples were subjected to different pretreatments, including blanching and pureeing whilst maintaining their macrostructure [3]. After pretreatment, the health-related compounds were quantified using chromatographic methods, including high-performance liquid chromatography with diode-array detection and liquid chromatography with mass spectrometry [3]. Enzyme activity, including ascorbic acid oxidase, alliinase, myrosinase, and lipoxygenase, was determined by measuring absorbance [3]. Pretreatment type did not affect behaviour of the health-related compounds, except for vitamin K1, which was destabilised by pureeing (due to contact with ascorbic acid oxidase in the presence of oxygen) but it was stabilised by blanching [3]. In general, all health-related compounds were more stable when stored closer to the GTT but vitamin K1 was not impacted by temperature or pretreatment type, suggesting that this antioxidant is robust and is stable through long shelf-lives [3].
Fortunately, this research shows that despite concerns about the of loss of biochemical stability when Brussels sprouts are frozen for extended periods of time, beneficial nutrients such as vitamin K1 are stable throughout the process. Therefore, there is no doubt that you will get your nutritional fill from your Brussels sprouts this Christmas.
Written by DWS Microbiologist Kirsty McTear
English