Comparative study of two table grape varieties with contrasting texture during cold storage

Area of Science:

• Plant Science
• Food Science
• Biochemistry

Background:

• Postharvest softening significantly impacts grape quality and export potential.
• Cell wall pectin disassembly is a known factor in fruit softening, but its role in grapes requires further investigation.
• Thompson Seedless (TS) grapes exhibit notable texture loss after cold storage, unlike the firmer NN107 variety.

Purpose of the Study:

• To investigate the biochemical differences in cell wall metabolism between firm (NN107) and softening (TS) grape varieties during cold storage.
• To elucidate the role of pectin polysaccharides and related enzyme activities in maintaining grape berry firmness.

Main Methods:

• Comparative biochemical analysis of cell wall components and enzyme activities (polygalacturonase, pectin methylesterase).
• Analysis of calcium and uronic acid content in grape cell walls.
• Polysaccharide analysis using carbohydrate gel electrophoresis (PACE) to assess pectin fragments.

Main Results:

• NN107 berries showed higher cell wall calcium and less uronic acid reduction than TS during cold storage.
• Polygalacturonase activity was higher in TS, while pectin methylesterase activity was similar between varieties.
• PACE analysis indicated differential pectin metabolism, with TS having fewer pectin fragments after extended storage, unlike NN107.

Conclusions:

• Varietal differences in cell wall metabolism, particularly pectin dynamics and calcium content, are associated with postharvest berry firmness in grapes.
• These findings provide insights into strategies for improving grape storage life and maintaining quality.