Functional Anatomy, Impact Behavior and Energy Dissipation of the Peel of Citrus × limon: A Comparison of Citrus × limon and Citrus maxima

Abstract

This study analyzes the impact behavior of lemon peel (Citrus x limon) and investigates its functional morphology compared with the anatomy of pomelo peel (Citrus maxima). Both fruit peels consist mainly of parenchyma structured by a density gradient. In order to characterize the lemon peel, both energy dissipation and transmitted force are determined by conducting drop weight tests at different impact strengths (0.15–0.74 J). Fresh and freeze-dried samples were used to investigate the influence on the mechanics of peel tissue’s water content. The samples of lemon peel dissipate significantly more kinetic energy in the freeze-dried state than in the fresh state. Fresh lemon samples experience a higher impulse than freeze-dried samples at the same momentum. Drop weight tests results show that fresh lemon samples have a significantly longer impact duration and lower transmitted force than freeze-dried samples. With higher impact energy (0.74 J) the impact behavior becomes more plastic, and a greater fraction of the kinetic energy is dissipated. Lemon peel has pronounced energy dissipation properties, even though the peel is relatively thin and lemon fruits are comparably light. The cell arrangement of citrus peel tissue can serve as a model for bio-inspired, functional graded materials in technical foams with high energy dissipation.

Analysis of the peel structure of different Citrus spp. via light microscopy, SEM and μCT with manual and automatic segmentation

“…Therefore, the peels of citrus fruits can generally act as an inspiration for biologically inspired technical material systems and lightweight structures. 3,4,[9][10][11] Citrus peels typically consist of exocarp (flavedo), mesocarp (albedo), and endocarp 2,12,13 (Fig. 1).…”

“…2,7,14,15 The flavedo, which consists of epidermis, cuticle, and parenchymatous cell tissues, is characterized by its densely packed cells and the oil glands within. 2,13 The albedo makes up a large part of the peel and is a less dense arranged tissue with parenchymatic cells that contains more intercellular spaces than the flavedo. 2,12,13 In addition, lignified vascular bundles run through the albedo and through the flavedo.…”

Damage protection in fruits: Comparative analysis of the functional morphology of the fruit peels of five Citrus species via quasi-static compression tests

“…Besides these morphological and physiological characteristics, the anatomical structure of citrus peels causes some preferable mechanical properties such as a high energy dissipation (Seidel et al, 2010;Thielen et al, 2015;Yang et al, 2022). Even if the proportion and fine structure of individual tissues of the fruit differ, the peel typically consists of an epidermis, a parenchymatous flavedo (exocarp), a thicker, less dense albedo (mesocarp) and a thin endocarp (Ford 1942;Scott and Baker 1947;Jentzsch et al, 2022). In this article, we use quasistatic compression tests to investigate the compression behavior of the peel of pomelo (C. maxima), citron (C. medica), lemon (C. x limon), grapefruit (C. x paradisi) and orange (C. x sinensis) to better understand damage protection properties.…”

“…Towards that end, living nature offers inspiration for apparent auxetic structures, which are characterized, for example, by excellent energy dissipation properties. Examples include the peel of pomelo, which highly dissipates energy under (quasi-) static as well as under dynamic loading (Fischer et al, 2010;Seidel et al, 2010;Thielen et al, 2015;Jentzsch et al, 2022;Yang et al, 2022). In addition, various citrus fruits peels have also been described as biological functionally graded materials (FGM) (Jentzsch et al, 2022).…”

“…Examples include the peel of pomelo, which highly dissipates energy under (quasi-) static as well as under dynamic loading (Fischer et al, 2010;Seidel et al, 2010;Thielen et al, 2015;Jentzsch et al, 2022;Yang et al, 2022). In addition, various citrus fruits peels have also been described as biological functionally graded materials (FGM) (Jentzsch et al, 2022). Wang et al (2018) calculated a Poisson's ratio of 0.08-0.11 ± 0.02 for the pomelo peel, at compression levels of up to 50%.…”