Comparative study of fungal growth in 𝘔𝘺𝘳𝘪𝘴𝘵𝘪𝘤𝘢 𝘧𝘳𝘢𝘨𝘳𝘢𝘯𝘴 (Nutmeg) kernels under varying postharvest storage conditions

Abstract

Fungal population dynamics are influenced by various environmental and handling factors, particularly in postharvest systems. This study investigated the temporal variation of total fungal populations in nutmeg (𝘔𝘺𝘳𝘪𝘴𝘵𝘪𝘤𝘢 𝘧𝘳𝘢𝘨𝘳𝘢𝘯𝘴) kernels, focusing on fungal contamination under different drying and storage conditions, addressing the lack of published research on nutmeg processing in Sri Lanka. Two hundred nutmeg fruits were collected from a commercial grower at Pilimatalawa (7.2595° N, 80.5452° E), Sri Lanka, and divided equally into two treatment groups to compare traditional and improved postharvest practices. Fungal contamination was assessed through culture-based enumeration immediately post-harvest, post-drying, and during storage. Traditional methods involved sun-drying on reused palm mats and storage in dark, poorly ventilated rooms, while the improved method involved hygienic drying at (32±2) °C and storage with adequate lighting and ventilation. Results revealed a significant (𝘱 < 0.05) increase in fungal population with extended storage. Dominant contaminants included 𝘈𝘴𝘱𝘦𝘳𝘨𝘪𝘭𝘭𝘶𝘴 𝘧𝘭𝘢𝘷𝘶𝘴, 𝘈. 𝘯𝘪𝘨𝘦𝘳, 𝘗𝘦𝘯𝘪𝘤𝘪𝘭𝘭𝘪𝘶𝘮 sp., 𝘢𝘯𝘥 𝘙𝘩𝘪𝘻𝘰𝘱𝘶𝘴 sp., 𝘸𝘪𝘵𝘩 𝘈. 𝘧𝘭𝘢𝘷𝘶𝘴, a known aflatoxin producer, particularly abundant in inadequately dried and poorly stored samples. Total fungal colony-forming units (CFU) were significantly (𝘱 < 0.05) higher in nutmegs subjected to open-air sun drying, and storage under poorly ventilated environments at Pilimatalawa, compared to those processed under improved laboratory-controlled hygienic conditions. A. flavus counts increased significantly (𝘱 < 0.05) after two weeks of storage, particularly under conventional conditions, emphasising its ability to thrive under suboptimal postharvest conditions. Water activity of the kernels (0.700 – 0.780) did not directly correlate with fungal counts, suggesting temperature and inoculum exposure during processing play greater roles in fungal growth. Ultraviolet fluorescence spectroscopy and scanning electron microscopy confirmed 𝘈. 𝘧𝘭𝘢𝘷𝘶𝘴 through visible sclerotia formation on shells, indicating potential aflatoxin accumulation. These findings emphasise the need for optimised drying and storage practices to mitigate fungal contamination and ensure nutmeg safety and quality for export.