How Storage Shapes Microbes, Mold, and Toxins
Imagine biting into a crisp, refreshing apple. This popular fruit, a symbol of health and vitality, is the largest temperate fruit crop globally, with production skyrocketing from 41 million tons in 1990 to over 93 million tons in 2021 1 2 . But beneath that shiny surface lies an unseen world—a dynamic ecosystem of fungi and bacteria known as the epiphytic microbiome.
Apples can host up to 100 million bacterial cells, creating a complex ecosystem on their surface that changes dramatically during storage.
This microbial community plays a crucial role in the fruit's postharvest journey, influencing its susceptibility to decay and contamination by harmful toxins. Among the most notorious offenders is Penicillium expansum, a blue mold that produces patulin, a dangerous mycotoxin that can survive processing and end up in our apple juice, compotes, and other products.
93M+
Tons of apples produced annually worldwide
100M+
Bacterial cells on a single apple
Damages immune system
Damages liver
Damages nervous system
Causes gastrointestinal issues
To understand the impact of long-term storage on the apple's microbiome and its relationship with P. expansum and patulin, a comprehensive study was conducted on the 'Golden Delicious' variety 1 2 4 .
| Sampling Stage | Cultivation System | Positive Samples/Total | Patulin Range (μg kg⁻¹) |
|---|---|---|---|
| Beginning of storage | Conventional | 2/9 (2 exceeding EU limit) | ND - 52.5 |
| Beginning of storage | Organic | 0/9 | ND |
| End of storage | Conventional | 2/9 (2 exceeding EU limit) | ND - 62.2 |
| End of storage | Organic | 3/9 (3 exceeding EU limit) | ND - 357.7 |
| Post-conditioning | Conventional | 0/9 | ND |
| Post-conditioning | Organic | 1/9 (1 exceeding EU limit) | ND - 189.2 |
| Before transport | Conventional | 3/9 (2 exceeding EU limit) | ND - 147.2 |
| Before transport | Organic | 2/9 (1 exceeding EU limit) | ND - 46.8 |
ND = Not Detected; EU Limit for solid apple products like compote = 25 μg kg⁻¹ 2
The identification of long-term storage and deck storage as critical control points provides clear targets for intervention. Improving sanitation during these stages and minimizing temperature fluctuations could significantly reduce patulin risk.
Discovery of microbial interactions opens doors to innovative natural solutions. Certain yeasts like Metschnikowia pulcherrima or bacteria like Pantoea agglomerans show promise in suppressing blue mold and patulin accumulation 4 5 .
The simple apple, a staple of diets worldwide, hosts a complex microscopic drama on its surface. The journey from orchard to table, especially prolonged storage, dramatically reshapes its microbial landscape. This can inadvertently favor the growth of Penicillium expansum and the accumulation of its harmful toxin, patulin.
However, through sophisticated science—from toxin quantification to DNA sequencing—researchers are unraveling these complex interactions. By identifying the critical risks in storage and highlighting the power of microbial communities, this work paves the way for smarter, safer food storage practices and natural solutions that ensure the apple you bite into is not only delicious but also safe.