Phenolic distribution in apple epidermal and outer cortex tissue by multispectral deep-UV autofluorescence...

Area of Science:

• Plant biochemistry and metabolomics
• Fruit science and quality assessment

Background:

• Phenolic compounds in fruits are crucial for stress responses and sensory qualities.
• Understanding their tissue and subcellular distribution is key to fruit quality and resilience.

Purpose of the Study:

• To map the distribution of phenolic compounds in apple epidermis and outer cortex.
• To investigate the influence of storage conditions on phenolic distribution.
• To differentiate apple varieties based on their phenolic profiles.

Main Methods:

• Deep-UV excitation (275 nm) and fluorescence emission imaging (300–650 nm) of cryogenic apple tissue.
• Analysis of fluorescence signals to identify phenolic compound families (flavanols, hydroxycinnamic acids).
• Comparison of phenolic distribution in 'Douce Moën' and 'Guillevic' cider apple varieties under different storage.

Main Results:

• Monomeric/condensed flavanols were found throughout the tissue, concentrated in the cuticle.
• Hydroxycinnamic acids were primarily located in the outer cortex cell walls.
• Fluorescent pigments were predominantly in the epidermis; variety-specific distributions of flavanols and phenolic acids were observed.
• Storage conditions (cold or room temperature) did not alter phenolic distribution.

Conclusions:

• Fluorescent imaging provides a method to study phenolic distribution at tissue and subcellular levels in apples.
• Phenolic compound distribution varies between apple varieties, distinguishing them.
• This approach can advance research into fruit development, stress resistance, and quality.