Physicochemical, Agronomical and Microbiological Evaluation of Alternative Growing Media for the Production of Rapini (Brassica rapa L.) Microgreens

Background: Peat-based mixes and synthetic mats are the main substrates used for microgreens production. However, both are expensive and non-renewable. Recycled fibrous materials may be low-cost and renewable alternative substrates. Recycled textile-fiber (TF, polyester, cotton and polyurethane traces) and jute-kenaf-fiber (JKF, 85% jute-, 15% kenaf-fibers) mats were characterized and compared to peat and Sure-to-Grow(®) (STG, 100% polyethylene-terephthalate) for the production of rapini (Brassica rapa L.; Broccoletto group) microgreens. Results: All substrates had suitable physicochemical properties for the production of microgreens. Microgreens fresh-yield was on average 1,502 g m(-2) in peat, TF and JKF, and was 13.1% lower with STG. Peat-grown microgreens shoots had higher concentration of K(+) and SO4 (2) (-) , and two-fold higher NO3 (-) concentration [1,959 vs 940 mg kg(-1) of fresh weight (FW)] than those grown on STG, TF, and JKF. At harvest, substrates did not influence microgreens aerobic-bacterial populations (log 6.48 CFU g(-1) FW). Peat- and JKF-grown microgreens had higher yeast-mould counts than TF- and STG-microgreens (log 2.64 vs 1.80 CFU g(-1) FW). Peat-grown microgreens had the highest population of Enterobacteriaceae (log 5.46 ± 0.82 CFU g(-1) ), and E. coli (log 1.46 ± 0.15 CFU g(-1) ). E. coli was not detected in microgreens grown on other media. Conclusion: TF and JKF may be valid alternatives to peat and STG, as both assured competitive yield, low nitrate content, and similar or higher microbiological quality.