Why do peach pits have fruit rust

The rust on the surface of peach pits is mainly a natural phenomenon formed by the combined effects of environmental factors, physiological metabolism, and mechanical damage, and usually does not affect food safety. The formation of fruit rust is mainly related to factors such as water retention, temperature differences, fruit maturity, pest infestation, and picking and transportation friction.

1. Water retention

During the growth period of peach trees, when they encounter continuous rainy or high humidity environments, the stomata of the fruit skin remain open for a long time, and water penetrates into the intercellular spaces of the epidermal cells, causing damage to the stratum corneum. Oxidation reaction will gradually form yellow brown rust spots on the damaged area, which are mostly concentrated in the concave areas around the fruit stem.

2. Temperature Difference Changes

During the fruit enlargement period, when subjected to severe diurnal temperature differences, epidermal cells develop microcracks due to thermal expansion and contraction. Phenolic substances seep out under low temperature conditions and undergo enzymatic browning upon contact with polyphenol oxidase, forming a network of rust spots. This phenomenon is more common in mountainous orchards with large temperature differences between day and night.

3. Fruit Maturity

Peaches harvested too early have weaker epidermal protection due to incomplete development of the cuticle layer. As the fruit flesh softens and expands during the ripening process, the incompletely keratinized skin is prone to cracking under tension, and the cracks gradually oxidize to form strip-shaped rust lines.

4. Invasion of pests and diseases

Aphids, spider mites and other piercing sucking mouthparts pests can damage epidermal cells when feeding, and the juice secreted by the wound oxidizes to form spot rust spots. After infection by fungal diseases such as anthrax, concentric wheel like rust stains often appear around the lesions, which need to be distinguished from physiological rust spots.

5. Friction during picking and transportation

Micro wounds caused by pulling the fruit stem during harvesting, or collisions and friction between fruit cores during transportation, can cause the shedding of the wax layer on the skin. After exposed thin-walled cells come into contact with air, phenolic substances oxidize to form irregular sheet-like rust spots, which are commonly found on the protruding parts of fruit shoulders. For peach pits with rust, a soft bristled brush can be used to lightly brush the surface before consumption, and it is safer to peel them after rinsing with running water. When purchasing, pay attention to the absence of obvious disease spots or signs of decay on the fruit. It is normal for the fruit rust to be uniform, light brown, and free of mold. Maintain a ventilated and dry environment during storage to avoid accelerating the expansion of rust spots in humid environments. Proper consumption of peaches in daily diet can supplement vitamin C and dietary fiber, but diabetes patients need to control their intake.