Hybrid Label-Free Molecular Microscopies for Simultaneous Visualization of Changes in Cell Wall Polysaccharides of Peach at Single- and Multiple-Cell Levels during Postharvest Storage

Abstract

Softening of fruit during the postharvest storage, which is mainly associated with both compositional and spatial changes of polysaccharides within cell wall, affects the texture and quality of fruit. Current research on the fruit softening mechanism lacks an understanding of the overall softening at the cell level. The objective of this work was to investigate the change in the spatial distribution of cell wall polysaccharides in peach flesh cells at both single- and multiple-cell levels in a label-free way during the postharvest storage. Nonmelting peaches (Prunus persica L. Batsch cv.”Zhonghuashoutao”) at commercial maturity were stored at 0 °C and 20 °C. Firmness measurement and chemical analysis were performed at each storage time. In addition, three molecular imaging techniques, namely confocal Raman microspectroscopy (CRM), Fourier transform infrared microspectroscopy (FTIRM), and stimulated Raman scattering microscopy (SRS) were used to visualize changes in the spatial distribution of cell wall polysaccharides of peach fruit in a label-free way during the postharvest storage. The combination of CRM and FTIRM provided complementary spectral information to visualize the spatial changes of cellulose, hemicellulose, and pectin in the cell wall of peach flesh during softening at the single-cell level, and found that the cell wall polysaccharides tended to be concentrated in the cell corner of parenchymal cells at the late stage. Furthermore, SRS, which is an ultrafast Raman imaging technique (approximately three or four orders of magnitude faster than CRM), was used for high-throughput cell wall phenotypes measurement. Different degradation degrees of parenchymal cells during fruit softening were found based on the gray-scale statistical analysis of SRS data. In general, cell wall polysaccharides decreased during softening and tended to be concentrated in the cell corner for most parenchymal cells at the late stage, but there were also some cells not in line with the whole softening trends. The results show that there were differences in the content and spatial changes of cell wall polysaccharides among parenchymal cells of peach fruit during the softening process, and the hybrid use of CRM, FTIRM, and SRS is a promising method for simultaneous visualization of changes in cell wall polysaccharides of peach.

Applications of infrared spectroscopy in polysaccharide structural analysis: Progress, challenge and perspective

“…The degradation rate of pectin was found to be slower than those of cellulose and hemicellulose. Lower storage temperature significantly delayed the degradation process and prolonged the storage life of peach ( Huang et al, 2020 ). Besides the softening process of fruit from hard to soft, FTIR microspectroscopic imaging can also be utilized to investigate the maturation process of nut shell that from soft to hard.…”

Antibacterial activity of molybdenum disulfide and green silver nanoparticles reduced by tea tree essential oil compounds

“…The FTIR spectrum for the AgNPs shows a broad band at 3435 cm −1 that is attributed to the O-H and N-H stretching vibrations. The band at 1383 cm -1 arises from the C-O-H bending that can be attributed to polysaccharides commonly in plants (Bharadwaj et al, 2021;Huang et al, 2020). At 866 cm -1 , a band is attributed to the double bond between C=C carbon atoms, characteristic of essential oils.…”

The calcium-mediated homogalacturonan pectin complexation in cell walls contributes the firmness increase in loquat fruit during postharvest storage

“…Softening and lignification (hardening) are two typical forms of changes in fruit texture during postharvest storage [4] , [6] . Fruit softening usually occurs in many fruits during postharvest storage, such as tomato [7] , peach [8] , and strawberry [9] . On the other hand, some fruits can experience lignification after harvest, including mangosteen [10] , kiwifruit [11] , and loquat [12] .…”