In vitro study of the interaction between pectinase and chelate‐soluble pectin in postharvest apricot fruits

Apricots (Prunus armeniaca L.), a kind of climacteric fruits, are favored by consumers for their flavor and texture, but they are highly perishable. Apricots soften rapidly after harvest. Once softened, they are easily damaged such as latent damage, which limits their marketing time [1, 2]. Therefore, a common practice for handling and storing apricots is early harvest and applying postharvest technologies to extend the shelf life [1–4]. The main problem during marketing of apricots is excessive softening. It has been reported that propylene treatment hastens apricots’ softening [5], while it is also known that softening may begin before the peak of ethylene production [6]. Therefore, little is known of the mechanism of softening in these fruits, and even the role of ethylene is unclear. Firmness is a major quality factor affecting the commercial value of apricot fruits. Decreased firmness or softening of fruits was reported to be associated with the depolymerization and solubility of polysaccharides of fruit cell wall [7]. Fruit softening is associated with pectin solubility and sugar loss from cell wall fractions, especially fraction of CSP [8]. Appropriate concentration of calcium can exhibit the textural degradation by connecting ionically bound pectins [3, 4, 9–11]. Appropriate calcium treatment can decrease the loss of CSP and disaggregation of the middle lamella of fruits, thus maintaining the integrity of fruit middle lamella [12]. It is widely accepted that morphology arrangement is critical in determining roles of cell wall materials during postharvest in addition to chemical compositions. However, detailed evolution of fruit CSP is not clear during postharvest considering that what are the major reactions participating in this process is not clear due to the heterogeneous property of the CSP morphology in nanoscale. Abstract Firmness is one of the most important quality attributes of apricot fruits and is associated with chelatesoluble pectin (CSP). To elucidate the changes in CSP during postharvest, in vitro investigation of pectinase effects on CSP of apricot fruits was applied to simulate the in vivo changes in CSP fraction during postharvest. It was found that effects of pectinase (40 U/mg) treatment were similar to those of storage time on CSP nanostructures from the results of atomic force microscopy. Relative frequency of widths less than 31.25 nm was 3.6 % for control group, while it was 16.2, 52.0 and 65.5 %, respectively, for 1:10,000 (pectinase/CSP), 1:1,000 and 1:100 pectinasetreated groups. Most of the CSP lengths were 0.5–1 μm, while it was 0–1 μm for pectinase-treated groups. Pectinase treatment had some similar effects on CSP fraction as storage time.