Evaluation of the Nanostructure of Pectin, Hemicellulose and Cellulose in the Cell Walls of Pears of Different Texture and Firmness

A Zdunek,J Cybulska,P M Pieczywek,A Kozioł

doi:10.1007/s11947-014-1365-z

Abstract

The nanostructure of polysaccharides is supposed to determine properties such as stiffness or diffusivity of cell walls and their functionality for various tailored properties of food. However, at present, a relation of these nano-properties with sensory texture and firmness remains to some degree unknown. In this work, water (WSP), calcium chelator (CSP) and sodium carbonate (DASP) soluble pectins, hemicellulose and cellulose, extracted from cell walls of two pear cultivars ‘Xenia’ and ‘Conference’ at their harvest times, were studied. An atomic force microscope and image analysis were used to evaluate diameter and branching of the molecules. Sensory texture of ‘Xenia’ was considered as better and its firmness (87 N) was higher than ‘Conference’ (76 N). WSP molecules were present as short molecules with a height of about 0.5 nm for both cultivars. A chain-like and branched CSP fraction had diameter of about 0.3–0.4 nm for both cultivars with a pronounced contribution of molecules with diameter of about 1 nm for ‘Xenia’, which had also higher branching index. DASP revealed similar regular structures for both cultivars however the network was much denser for ‘Xenia’. A rod-like hemicellulose molecules had length of about 20–400 nm and diameter of 1 nm for ‘Xenia’ and 1–4 nm for ‘Conference’. Cellulose diameter for both cultivars was about 23 nm. This study showed that less degraded, thicker and more branched pectin molecules were associated with higher firmness and more favourable texture. Hemicellulose provided a positive contribution to texture when they were thinner and more flexible.

Highlights

The molecular structure of polysaccharides and their assembly are supposed to determine properties such as the stiffness (Geitmann 2010; Gibson 2012) and diffusivity (Fanta et al 2012) of cell walls, and the functionality of these biopolymers for various tailored properties of food (Willats et al 2006) and non-food products (Eichhorn et al 2010)
Liu et al (2009) showed that during storage, firmness did not change with the contents of chelator soluble pectins (CSP) but was consistent with the morphology changes of CSP; the branching structures of CSP decreased, while the frequencies of chains with small width (
This study concerned the structure of individual polysaccharides abundant in the cell walls of pears of distinct texture and firmness

Summary

Introduction

The molecular structure of polysaccharides and their assembly are supposed to determine properties such as the stiffness (Geitmann 2010; Gibson 2012) and diffusivity (Fanta et al 2012) of cell walls, and the functionality of these biopolymers for various tailored properties of food (Willats et al 2006) and non-food products (Eichhorn et al 2010). As a multi-parameter property, is described by such attributes as crispness, hardness, and juiciness (Bourne 2002), which correlate with instrumental parameters such as firmness and acoustic descriptors (Zdunek et al 2010a, 2010b, 2011a, 2011b) These descriptors, both sensory and instrumental, relate directly to mechanical properties and have their origin in the structure of tissue (Aguilera 2005). Depending on the relative strength of cell walls and sheer strength in the middle lamella, tissue may be disrupted throughout cell walls or in-between cells (Waldron et al 1997) The former mode generates acoustic signals and causes a release of juice, which is responsible for crispness and juiciness. It is agreed that in the pant cell walls, cellulose macrofibrils are interlinked with hemicellulose fibrils via hydrogen bonds, whereas pectins form an amorphous matrix

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Conclusion