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11140014 PhD Senescent Sweetening

Publication Date: 
28 March 2018
Author/Contact :
Richard Colgan

Contractor :
Natural Resources Institute (University of Greenwich)

Full Research Project Title: Understanding mechanisms and identifying markers for the onset of senescent sweetening
Duration: October 2013 - September 2016


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.


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

Aims and Objectives

Aim: To understand the mechanism(s) underpinning senescent sweetening and to develop predictive tools.


a) To understand the effect of planting location and harvest maturity on senescent sweetening.
b) Tubers will be sampled for biochemical analysis to include: DM content, starch analysis, sugar (fructose, glucose and sucrose) analysis (HPLC).
c) To investigate the integrity of starch granule (amyloplast) membranes.
e) To look at methods to manage senescent sweetening.


The project will use commercial varieties known to have different propensities to develop senescent sweetening selected from different geographical locations, to generate tubers of different maturities at harvest. Changes in sugars, structural carbohydrates, texture, antioxidants, oxygen status and mineral content will be evaluated at harvest and during storage. Changes in the biochemical profile will be related to fry colour and textural properties of tubers.

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].


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