Abstract
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 (Cw) and water activity (Aw) 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 Cw and Aw 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 Cw, Aw, 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 Cw < 12% and Aw < 0.6. While, when the relative humidity was up to 70%, the Cw and Aw values rose quickly, and the Cw 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 Cw and Aw control points, respectively, to prevent medicinal and edible products from mildew and the contamination of aflatoxins.
Highlights
Foods including medicinal and edible products, feeds and medicinal plants are vulnerable to fungal conidia and mildew if improperly treated in the processes of growth, harvest, processing, storage and transportation (Giorni et al 2018; Liu et al 2015b; Zhang et al 2019)
Affected by the nature of their components and the external environmental conditions, lotus seeds are susceptible to mildew with fungal infection under suitable temperature and humidity conditions, especially during the plum rain season, leading to the production and residue of various mycotoxins, such as aflatoxins, ochratoxins, etc
It could be found that when the relative humidity was lower than 70%, the C w values were all not more than 12%, which might be suggested as the suitable water content control point for safe storage of lotus seed in practice
Summary
Foods including medicinal and edible products, feeds and medicinal plants are vulnerable to fungal conidia and mildew if improperly treated in the processes of growth, harvest, processing, storage and transportation (Giorni et al 2018; Liu et al 2015b; Zhang et al 2019). Similar results were reported by Wei et al (2019) Taking their prominent medicinal value and edible function, as well as the high occurrence of mildew and aflatoxins contamination into consideration, a maximum residue level (MRL) of 5 μg/kg for AFB1 and 10 μg/kg for the total amount of AFB1 + AFB2 + AFG1 + AFG2 in lotus seeds (Chinese Pharmacopoeia Commission 2015a) have been officially set. It is of great significance and urgency to prevent lotus seed from mildew and aflatoxins production through controlling the crucial factors or conditions, such as water content (Cw), water activity (Aw) and environmental temperature and humidity, to ensure their quality and safety
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