Determination of texture properties of banana fruit cells with an atomic force microscope: A case study on elastic modulus and stiffness.

Characterization of biological materials with their elasto-mechanical properties is considered essential for understanding their nature. In addition, elasto-mechanical studies at the macroscale are frequently used to determine these characteristics by a resistance measurement such as the Magness-Taylor penetration test or compression test using an Instron Universal Mechanical Testing Machine. In this regard, the atomic force microscopy (AFM) was presented as a new method for identifying the alterations of elasto-mechanical properties at a nanoscale. Therefore, the present study estimated the elastic modulus and stiffness of the cell walls which were isolated from the banana mesocarp with AFM-based nanoindentation. Then, the elastic modulus of a cell and stiffness were determined by analyzing the force-separation curves using the theory of Hertz and the mechanics of Sneddon. Using two tips of the distinct radius of the curvature (10 and 10,000 nm), it was revealed that the tip geometry significantly affected the measured elasto-mechanical properties. Further, the elastic modulus was around 95 ± 45 and 18.5 ± 12.5 kPa for the sharper tip (R = 10 nm) and a bead (R = 10,000 nm) tips, respectively. Furthermore, a large variability was considered regarding the elasto-mechanical property (>100%) among the cells which were sampled from the same region in the fruit. Therefore, the AFM can be highly suitable for evaluating the structure-related properties of biological materials at the cellular and subcellular scales by combining nano elasto-mechanical properties with topography imaging.