Exploration of the safe water content and activity control points for medicinal and edible lotus seeds from mildew

Affected by the inner properties and the external environmental conditions, medicinal and edible lotus seeds are susceptible to mildew with fungal infection under suitable temperature and humidity conditions, leading to the production and contamination of various mycotoxins, along with threats to its quality and safety. In this study, the changes of water content (C_w) and water activity (A_w) of lotus seeds stored at 25 °C and different relative humidity conditions, as well as the correlation between them and mildew of this edible and medicinal material were studied, aiming to explore the safe C_w and A_w control points for screening out the suitable storage conditions from mildew. Blank (without fungal conidia) and experimental (artificially added with Aspergillus flavus conidia) groups of lotus seeds were stored at 25 °C and relative humidity of 40%, 50%, 60% and 70% for about 30 days, respectively. The mildew was observed and the changes of C_w, A_w, together with the production of aflatoxins were measured. Results showed that no mildew was found and aflatoxins were not detected in lotus seeds when they were stored for 30 days at 25 °C and relative humidity of 40%, 50% and 60% with C_w < 12% and A_w < 0.6. While, when the relative humidity was up to 70%, the C_w and A_w values rose quickly, and the C_w exceeded the officially-permitted level (14%). Although no mildew was observed, AFB₁ was still detected, increasing the potential risk of lotus seeds regarding aflatoxins. For warranting the quality with economic and safe storage, lotus seeds are suggested to be stored at 25 °C and relative humidity lower than 60% with 12% and 0.6 as the safe C_w and A_w control points, respectively, to prevent medicinal and edible products from mildew and the contamination of aflatoxins.