Background

The mechanical properties of parenchyma cell walls and the strength and extension of adhesion areas between adjacent cells, jointly with cell turgor, are main determinants of firmness of fleshy fruits. These traits are modified during ripening leading to fruit softening. Cell wall modifications involve the depolymerisation of matrix glycans and pectins, the solubilisation of pectins and the loss of neutral sugars from pectin side chains. These changes weaken the cell walls and increase cell separation, which in combination with a reduction in cell turgor, bring about textural changes. Atomic force microscopy (AFM) has been used to characterise the nanostructure of cell wall polysaccharides during the ripening and postharvest storage of several fruits. This technique allows the imaging of individual polymers at high magnification with minimal sample preparation.

Scope and approach

This paper reviews the main features of the cell wall disassembly process associated to fruit softening from a nanostructural point of view, as has been provided by AFM studies.

Key findings and conclusions

AFM studies show that pectin size, ramification and complexity is reduced during fruit ripening and storage, and in most cases these changes correlate with softening. Postharvest treatments that improve fruit quality have been proven to preserve pectin structure, suggesting a clear link between softening and pectin metabolism. Nanostructural characterisation of cellulose and hemicellulose during ripening has been poorly explored by AFM and the scarce results available are not conclusive. Globally, AFM could be a powerful tool to gain insights about the bases of textural fruit quality in fresh and stored fruits.

中文翻译：

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原子力显微镜在果实成熟和收获后储存过程中细胞壁拆卸过程的纳米结构图

背景

薄壁组织细胞壁的机械性能以及相邻细胞之间粘附区域的强度和延伸以及细胞膨大是决定肉质果实坚挺度的主要因素。这些性状在成熟过程中被修饰，导致果实变软。细胞壁修饰涉及基质聚糖和果胶的解聚，果胶的增溶和果胶侧链中性糖的损失。这些改变削弱了细胞壁并增加了细胞分离，这与细胞膨大的减少相结合，引起了质地的改变。原子力显微镜（AFM）已用于表征几种水果的成熟和收获后贮藏过程中细胞壁多糖的纳米结构。

范围和方法

本文从纳米结构的角度回顾了与水果软化相关的细胞壁拆卸过程的主要特征，正如AFM研究提供的那样。

主要发现和结论

AFM研究表明，在果实成熟和贮藏期间，果胶的大小，分枝和复杂性降低了，并且在大多数情况下，这些变化与软化有关。事实证明，提高果实品质的采后处理可以保留果胶结构，这表明软化和果胶代谢之间存在明确的联系。AFM对纤维素和半纤维素在成熟过程中的纳米结构表征研究不足，可用的稀缺结果尚无定论。在全球范围内，AFM可能是获得有关新鲜和储藏水果中质地水果质量基础的见解的强大工具。