Abstract
During the ripening process of fruit, the solubilization and depolymerization of cell wall components takes place, which results in the loss of firmness or the softening of fruit. Recently, we reported that two different strawberry cultivars (“Cristal” and “Portola”) exhibit differences in their fruit softening values, with “Cristal” being the firmest and “Portola” being the softest. In the present work, we performed a comparative study of the changes in the physicochemical properties of the cell wall-associated polysaccharide contents of these two strawberry fruit cultivars via thermogravimetric analysis (TGA), combined with the first derivative of the thermogram (DTG) curves and morphological studies using scanning electron microscopy (SEM). The “Cristal” sample showed higher thermal stability than the “Portola” sample. Additionally, differences were observed between the “Cristal” and “Portola” samples at different stages, principally in Region II (temperatures between 200 °C and 350 °C), with a higher thermal stability evident in the green stage of the two cultivars. Notably, a higher thermal stability was observed in the green stage of the “Portola” sample. The highest percentage of cumulative depolymerization (PCD) was observed in the ripe stage of the “Portola” sample. The DTG curve showed four maximum peaks of degradation, which occurred between 170 °C and 350 °C. Finally, the existence of a relationship between fruit firmness and thermal stability was demonstrated for the two cultivars. This relationship was based on the morphological studies conducted using SEM, which provided new evidence through which to understand the changes within the cell wall polymers of these two strawberry cultivars during the ripening process.
Highlights
Commercial strawberry (Fragaria × ananassa Duchesne) is a financially important fruit product that has a short postharvest shelf life due to a rapid softening ratio during ripening [1]
We perform a comparative study of the changes in the physicochemical properties of the cell wall-associated polysaccharides contents of these two strawberry fruit cultivars, grown in the same commercial orchard, via thermogravimetric analysis (TGA) combined with the first derivative of the thermogram (DTG) curves and morphological studies using scanning electron microscopy (SEM); we investigate the percentage of degradation of the cell wall components
“Cristal” and “Portola” showed firmness reduction of 81% and 88%, respectively, from the green stage to the ripe stage; the firmness values were similar to those previously reported for the same cultivars the previous season (2016–2017) [11], indicating that firmness profiles do not change between different seasons, at least during the last 3 years
Summary
Commercial strawberry (Fragaria × ananassa Duchesne) is a financially important fruit product that has a short postharvest shelf life due to a rapid softening ratio during ripening [1]. The disassembly of the cell wall structure principally implies the modification of the pectin fractions because pectins are the major components of fruit cell walls [9] These changes include solubilization, depolymerization, and the loss of neutral side chains; other polymers that exhibit changes include hemicelluloses [9]. The process of fruit ripening requires a complex set of environmental and endogenous signals [16], and in strawberries and other fleshy fruits and fruit products, these signals produce changes in physiology and morphology, which include fruit softening due to textural changes [2,5,11,15,17,18,19,20,21,22] These textural changes are important for achieving the maximum sensory quality, they limit the postharvest life of fruit products [13,23]. Different authors have highlighted that the main decrease in fruit firmness occurs between the large green (G) and white (W) stages in strawberry [2,11,13,21]
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