Water and cell wall contributions to apple mechanical properties

Area of Science:

• Food Science
• Plant Physiology
• Biophysics

Background:

• Apple texture is crucial for consumer acceptance and is influenced by complex interactions between cellular structure, water dynamics, and cell wall composition.
• Understanding these relationships is key to improving apple quality and storage potential.

Purpose of the Study:

• To investigate the relationship between apple cortex viscoelastic properties, water dynamics, histological, and chemical characteristics.
• To compare discrete and continuous methods for decomposing multi-exponential T2 curves obtained from low-field NMR relaxometry.
• To identify key factors influencing apple texture, particularly the role of cell wall components.

Main Methods:

• Low-field NMR relaxometry was used to study water mobility in four apple genotypes before and after plasmolysis.
• Multi-exponential T2 relaxation curves were decomposed using both discrete and continuous methods.
• Viscoelastic properties (storage modulus, E') and cell wall sugar content (galactose, arabinose) were measured.

Main Results:

• Both discrete and continuous methods effectively discriminated between apple genotypes based on water mobility, even after plasmolysis.
• No specific NMR relaxation component directly correlated with apple viscoelasticity.
• Galactose and arabinose cell wall content showed correlations with the storage modulus (E'), with opposite signs before and after plasmolysis.

Conclusions:

• Water dynamics, as measured by T2 relaxometry, can distinguish apple genotypes but do not directly correlate with viscoelastic properties.
• Pectin RGI side chains may play a significant role in regulating apple texture in turgid tissues, as indicated by the correlations between specific sugars and storage modulus.