Michèle Desmet

Determination of puncture injury susceptibility of tomatoes

Abstract Puncture injury leads to large qualitative and quantitative losses of loose tomatoes ( Lycopersicon esculentum Mill.) when they pass through handling operations. Some cultivars are less susceptible to puncture injury, which is a desirable characteristic for tomato quality. It is, therefore, important that the puncture injury susceptibility of a new tomato cultivar is known, prior to commercialisation and large-scale production. In this research, a pendulum was designed to evaluate the puncture injury susceptibility of tomato cultivars in an objective way. Logistic regression was used as a statistical tool to model the influence of the impact energy on the incidence of puncture injury. This methodology was applied to two cultivars with different susceptibilities to puncture injury, ‘Tradiro’ (less susceptible) and ‘Blitz’ (very susceptible). Their susceptibilities to puncture injury were measured as a function of storage time and colour stage. It was found that: (i) tomatoes at harvest were less susceptible to puncture injury than after storage for several days; and (ii) colour at harvest had no effect on the susceptibility for puncture injury. This research revealed that the pendulum test in combination with logistic regression is a suitable method and a promising measurement tool to determine the puncture injury susceptibility of tomato cultivars.

Modelling fruit characteristics during apple maturation: A stochastic approach

At present, mathematical models to predict the change of fruit quality attributes during apple maturation are deterministic and do not take into account the large natural variability of fruit quality attributes during the growing season. In this work a stochastic system approach was developed to describe the quality evolution of fruit. The basic dynamics of fruit quality evolution was represented by means of a stochastic system, in which the initial conditions and the model parameters were specified as random variables together with their probability density functions. A fundamental approach from stochastic systems theory was used to compute the propagation of the probability density functions of fruit quality attributes, which requires the numerical solution of the Fokker–Planck equation.

Numerical solution of the Fokker-Planck equation for postharvest applications

In recent years many mathematical models have been developed to predict the change of fruit quality attributes such as firmness during maturation and cold storage. Instead of modelling the full chain of underlying biochemical processes, typically models of minimum complexity are developed to describe the basic dynamics of fruit quality attributes by means of a limited number of state variables. However, these models are deterministic and do not take into account the large natural variability of fruit quality attributes. In this research the evolution of fruit quality attributes was represented by means of a system of differential equations in which the initial conditions and the model parameters were specified as random variables together with their probability density functions. A fundamental approach from stochastic systems theory is used to compute the propagation of these probability density functions through a dynamic model for apple firmness during maturation. This approach considers the solution of the Fokker-Planck or forward diffusion equation. Because the Fokker-Planck equation is a first order partial differential equation of hyperbolic type, usually the solution can not be derived in closed form. Numerical tools are developed to discretise the computational domain and are based on special finite difference schemes. The main features of this stochastic approach were demonstrated for the time evolution of soluble solids content during apple maturation.

Uncertainty of Measurements of the Fruit Impacts

During harvest and handling, fruits and vegetables suffer from different impacts, which may cause bruises and other quality degradations. Besides impacts, bruises can result from vibrations, static loads and friction. Today’s high quality demands urge a screening of the entire handling chain from grower to consumer in order to locate critical parts responsible for fruit damage (Hilton, 1998).