Impact behaviour of freeze-dried and fresh pomelo (Citrus maxima) peel: influence of the hydration state.

Thomas Speck,Robin Seidel,Marc Thielen

doi:10.1098/rsos.140322

Abstract

Pomelos (Citrus maxima) are known for their thick peel which—inter alia—serves as energy dissipator when fruits impact on the ground after being shed. It protects the fruit from splitting open and thus enables the contained seeds to stay germinable and to potentially be dispersed by animal vectors. The main part of the peel consists of a parenchymatous tissue that can be interpreted from a materials point of view as open pored foam whose struts are pressurized and filled with liquid. In order to investigate the influence of the water content on the energy dissipation capacity, drop weight tests were conducted with fresh and with freeze-dried peel samples. Based on the coefficient of restitution it was found that freeze-drying markedly reduces the relative energy dissipation capacity of the peel. Measuring the transmitted force during impact furthermore indicated a transition from a uniform collapse of the foam-like tissue to a progressive collapse due to water extraction. Representing the peel by a Maxwell model illustrates that freeze-drying not only drastically reduces the damping function of the dashpots but also stiffens the springs of the model.

Highlights

The thick peel of the pomelo (Citrus maxima) gives rise to the question of its ‘biological purpose’, especially as it constitutes a large amount of the fruit’s volume and is quite costintensive for the plant in terms of material consumption
Free-fall tests with whole pomelos showed that the peel constitutes—besides other functions—an impact protection layer, preventing the fruit from splitting open when impacting on the ground after being shed, and thereby from being afflicted by mould spores or decaying bacteria [1,2]
Freezing of the peel samples via liquid nitrogen led to freeze-cracking of the peel tissue in some cases

Summary

Introduction

The thick peel of the pomelo (Citrus maxima) gives rise to the question of its ‘biological purpose’, especially as it constitutes a large amount of the fruit’s volume and is quite costintensive for the plant in terms of material consumption. Free-fall tests with whole pomelos showed that the peel constitutes—besides other functions—an impact protection layer, preventing the fruit from splitting open when impacting on the ground after being shed, and thereby from being afflicted by mould spores or decaying bacteria [1,2]. This is relevant as on the one hand mould and bacteria reduce the. The cell wall can be regarded as a fibre matrix compound consisting of cellulose fibres and the cell wall matrix, whose main constituents are pectins and hemicelluloses [10]. Extensive work about the hierarchically structured plant cell walls is available [11,12,13] and the mechanical properties of cell walls are reviewed in Agoda-Tandjawa et al [14]

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