Dynamic changes in fungal composition during the processing of Hainan areca nut and effects of water activity on dominant mold species

Areca nut, one of the most historically representative chewing products in China, faces challenges from harmful microbial growth that causes both product safety and quality problems. To elucidate the mechanism underlying these microbial threats and develop targeted control strategies, this study analyzed dynamic microbial profiles of Hainan areca nuts during the processing stages. Alpha diversity analysis and total fungal counts (TFC) of Hainan areca nuts were monitored during different processing stages. A significant increase in TFC (1.725 ± 0.046 Lg CFU/g) and diversity of fungal species was observed in the finished product (FP), which might be attributed to manual operation and environmental exposure during the final processing stages. Ten strains of mold with the highest TFC were isolated and further screened on the areca nut powder culture medium. Two dominant mold species were isolated and identified by phylogenetic analysis, and were demonstrated to be Aspergillus ruber and Aspergillus ochraceus. Growth curves under varying water activities (A_w) indicated that the grows of two dominant mold species were inhibited at A_w of 0.798 and 0.815, respectively. Reinoculation of these species in areca nut products (A_w 0.80) further demonstrated that reduced A_w significantly suppressed their growth rates. These results may critically contribute to the prediction and extension of the shelf-life of areca nut products.