Cannabis (Cannabis sativa L.) one of the oldest cultivated plants [1] is valued for its diverse array of applications, including fiber, textiles, fuel, therapeutics, and pharmaceuticals [2,3,4]. Owing to the history of global prohibition, cannabis has been broadly classified as either hemp, which is characterized by low Δ9-tetrahydrocannabinol (THC) content and permitted for cultivation, or cannabis plants with higher THC levels that remain strictly regulated. The legal classification of hemp varies by jurisdiction. In the United States, hemp is defined as containing no more than 0.3% THC by dry weight [5], whereas in Switzerland, the allowable THC limit can be as high as 1% [6]. Cannabis flower is the major source of the plant’s diverse array of phytochemicals, including cannabinoids, terpenes, and phenolic compounds, which contribute to its pharmacological and therapeutic properties. Hemp, in particular, serves as a rich source of cannabidiol (CBD), a non-psychoactive cannabinoid that is less abundant in high-THC cultivars [7,8,9]. Similar to the broad medical applications for high-THC medical cannabis, such as in treatments for chronic pain, inflammatory diseases, and chemotherapy-induced nausea [10], hemp flower and CBD-rich extracts have been recognized for their therapeutic potential [11]. Many studies have demonstrated the potential of CBD in alleviating pain [12,13,14,15] and anxiety [16], and in management of seizures associated with epilepsy [17]. Hemp and medical cannabis are primarily consumed by inhalation, either through vaporization or smoking of the dried flower [18]. However, during cultivation, processing, and packaging, hemp can become contaminated by pathogenic fungi such as yeasts and molds [19], which pose safety concerns, especially when inhaled [20,21,22,23]. Previous studies have linked fungal contamination in cannabis products to serious health outcomes [24,25,26,27,28], underscoring the need for improved microbial safety standards for hemp flower.

For medicinal cannabis, consumer safety concerns have led to regulations in Europe, Canada, and certain U.S. jurisdictions that mandate microbial load testing. Under Dutch regulations, medicinal cannabis must contain <100 colony-forming units (CFUs) per gram, a threshold that approaches sterility [29]. In contrast, Canada permits a higher limit of up to 1000 CFUs per gram. Furthermore, the European and United States Pharmacopoeias have set strict microbiological safety standards for inhalable cannabis products, requiring the complete absence of pathogens such as Staphylococcus aureus, Pseudomonas aeruginosa, and bile-tolerant Gram-negative bacteria such as Escherichia coli [19,30]. Notably, in the United States, the standards for both recreational and medical cannabis are inconsistent across states [31]. Compared to this regulatory patchwork, microbial safety standards for hemp flower are even less consistent, often lacking clear oversight altogether, leaving hemp flower largely unregulated with respect to microbial load [24]. Furthermore, knowledge gaps remain regarding the impact of post-harvest treatments on flower quality and microbial load reduction, underscoring the need for studies to support evidence-based policymaking and standard-setting.

Given that maintaining sterile conditions in cannabis cultivation is both challenging and costly, effective post-harvest decontamination remains essential for consistently meeting safety requirements [32]. Post-harvest treatment methods, such as electron beam (EB), cold plasma, and gamma irradiation, have been thoroughly reviewed for their effectiveness in reducing fungal contaminants in medical cannabis [33,34,35,36]. Unlike gamma irradiation, EB technologies deliver ionizing radiation without relying on radioactive sources [37], making it a safer and more accepted technology within the industry [32]. While research has shown that EB irradiation can effectively sterilize cannabis flower, less is known about its impact on long-term storability, chemical integrity, and microbiological stability post-treatment [36]. This method, widely used in food safety, effectively sterilizes food ingredients and extends product shelf life [38], is regulated in the European Union, the United States, Australia, and Canada [37].

In addition to microbial safety, previous work has shown that the phytochemical composition of cannabis flowers changes during long-term storage. Cannabinoids such as Δ9-tetrahydrocannabinolic acid (THCA) and cannabidiolic acid (CBDA) undergo slow decarboxylation to their neutral forms, while THC can oxidize to cannabinol (CBN) under exposure to heat, light, or oxygen, whereas CBD is comparatively stable [7,30,39,40]. Terpenes are more vulnerable due to their volatility and susceptibility to oxidation; monoterpenes such as myrcene and limonene typically degrade more rapidly than sesquiterpenes, leading to measurable losses in aroma and quality over time [30,36,39]. Although packaging in sealed or vacuum-protected containers minimizes volatilization and oxygen exposure, several studies report significant declines in total terpene content over months of storage [30,39,41,42]. Recent work by Lumu et al. [40] demonstrated that hemp flowers stored for six months at different moisture levels retained higher total cannabinoid content when stored at lower moisture, while CBD and Δ9-THC levels remained statistically unchanged; however, elevated storage temperatures and light exposure accelerated cannabinoid decarboxylation [40]. These chemical dynamics are increasingly recognized as critical for product quality and consumer experience, yet systematic data on the combined effects of irradiation and storage on hemp flower phytochemistry remain limited.

This study evaluated the impact of EB irradiation and storage time on cannabinoid and terpene profiles, as well as microbial loads in hemp inflorescences of 2 cultivars over a 12-week storage period. Specifically, this research assesses the suitability of EB irradiation for sterilization, focusing on its effectiveness in preserving the chemical stability and microbial safety of hemp flowers during extended storage. Moreover, the study provides insights into the stability of hemp-specific secondary metabolites during storage and shows that microbial load decreases over time under the tested storage conditions. These findings highlight a potential avenue for further research into consumer safety standards.