Understanding mechanisms and identifying markers for the onset of senescent sweetening

A significant quantity of potato tubers are processed or consumed soon after harvest, but most of the tubers are stored prior to use. The quality of tubers destined for processing is determined on the reducing sugar (fructose and glucose) content of tubers at processing. Where the crop is stored (6-10°C) beyond 4 months there is a risk that senescent sweetening will develop in some varieties. This is the results of an unpredictable and irreversible rise in glucose and fructose content leading to a darkening of chips and crisps during processing. The biochemical mechanism for aging and sugar accumulation is not fully understood and better predictive tools are needed to aid growers and processors.

Collaboration

Natural Resources Institute, Sutton Bridge Crop Storage Research (SBCSR)

Approach

The research was centred around the study of Lady Rosetta, a variety ‘susceptible’ to sweetening, and VR 808, considered to maintain ‘stable’ sugar profiles, both of them are used in the crisp industry. As additional material, that provided contrasting profiles of sugar accumulation during storage, Pentland Dell (susceptible to sweetening) and Russet Burbank (stable sugar profile), used for chip production were also included in the trial. Changes in tuber respiration, biomechanical and biochemical properties were monitored during storage, to provide a better understanding of the processes leading to senescent sweetening.

Key Findings

• Varietal differences in senescent sweetening observed previously were confirmed.
• The time taken for physical changes in amyloplast membrane integrity observed through SEM analysis were variety and season dependent.
• An increase in respiration is associated with a rise in senescent sweetening. It is essential that when storing potato tubers the concentrations of CO₂ and O₂ in storage should be tracked.
• Increased antioxidant capacity, reduces reactive oxygen species (ROS). Quantifying changes in amyloplast integrity and ROS activity will go some way towards developing diagnostic markers for predicting changes in tuber health.
• The relationship between Ca and senescent sweetening are not fully understood. Further study is required to investigate the relationships between [Ca] and [K], and the ratio of [Ca]: [Mg+K].