Nutritional stress suppresses nitrate content and positively impacts ascorbic acid concentration and phenolic acids profile of lettuce microgreens

In the last twenty years, horticulture has focused on producing high-quality food while improving resource use efficiency. The application of nutritional stress is an effective tool to increase the phytochemical content of vegetables while reducing environmental footprint. Microgreens represent an emerging functional food characterized overall by higher levels of phytonutrients than their mature counterparts. The current study examined the effect of using nutrient solution or only distilled water on the nutraceutical performance of lettuce (Lactuca sativa L.) microgreens grown in a peat-based substrate. Our results showed that lettuce microgreens can be effectively grown using only substrate nutrients, incurring a 27% decrease in fresh yield, but a significant increase in total ascorbic acid (+187%), anthocyanins (+35%), and total phenolic acids content (+26%). Of utmost interest, is the near absence of nitrates in water-treated microgreens, which renders this category of fresh vegetables ideal for the production of food dedicated to consumers highly sensitive to nitrates, such as infants. Growing microgreens without providing additional nutrients to those found in a typical peat-based substrate is an important potentiality that adds value to this new class of vegetables and also renders them particularly suitable for home cultivation.