Softening of nature ripe fruits is due to

The softening of nature-ripe fruits is primarily attributed to the disassembly of the plant cell wall, specifically the dissolution of the middle lamella [t1][t3]. The middle lamella is the pectin-rich layer that acts as a cement between adjacent plant cells. During ripening, enzymes such as polygalacturonase (PG) and pectin methylesterase (PME) are secreted into the cell wall [t2][t5]. Polygalacturonase specifically catalyzes the degradation of the polyuronide network and pectic materials within the middle lamella [t1][t4]. This enzymatic breakdown leads to the loss of cell-to-cell adhesion and an increase in the solubility of pectic polysaccharides, resulting in the characteristic soft and diffused texture of ripe fruit [t2][t3]. While the primary cell wall also undergoes disassembly, the dissolution of the middle lamella is the hallmark structural change that facilitates cell separation and softening [t1][t3][t4].

Sources

1. [1] https://pmc.ncbi.nlm.nih.gov/articles/PMC2801395/
2. [2] https://www.sciencedirect.com/science/article/abs/pii/S1360138518300189
3. [3] https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/polygalacturonase