Methyl jasmonate-loaded composite biofilm sustainably alleviates chilling lignification of loquat fruit during postharvest storage.

In this work, the MeJA-loaded gelatin/pullulan/chitosan composite biofilm was prepared to inhibit the chilling lignification of the loquat fruit during storage at 0 °C. The firmness and lignin content were decreased by 89 % and 81.77 % after MeJA-loaded biofilm treatment. Malondialdehyde (MDA) production was almost completely suppressed and chilling injury of loquat fruit was significantly reduced. Enzyme activity results show that the biofilm alleviated chilling lignification mainly by inhibiting peroxidase (POD) activity in the phenylpropanoid pathway (PCCs = 0.715, with lignin content). Also, the conventional MeJA vapor treatment only alleviated lignification on day 3, but the biofilm treatment had a better and more sustained effect throughout the whole storage due to its sustained release ability. Besides, the biofilm had good mechanical properties, transparency and water vapor transmission rate. This work indicates that loading preservatives into biofilms has a promising application prospect for inhibiting the postharvest quality deterioration of fruit and vegetables.

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

INTRODUCTION: Postharvest textural changes in fruit are mainly divided into softening and lignification. Loquat fruit could have severe lignification with increased firmness during postharvest storage. Pectin is mainly associated with the postharvest softening of fruit, but some studies also found that pectin could be involved in strengthening the mechanical properties of the plant. OBJECTIVES: This study focused on characterizing the dynamics of pectin and its complexation in the cell wall of lignified loquat fruit during postharvest storage, and how these changes could influence fruit firmness. METHODS: The homogalacturonan (HG) pectin in the cell wall of loquat fruit was identified using monoclonal antibodies. An oligogalacturonide (OG) probe was used to label the egg-box structure formed by Ca2+ cross-linking with low-methylesterified HG. An exogenous injection was used to verify the role of egg-box structures in the firmness increase in loquat fruit. RESULTS: The JIM5 antibody revealed that low-methylesterified HG accumulated in the tricellular junctions and middle lamella of loquat fruit that had severe lignification symptoms. The pectin methylesterase (PME) activity increased during the early stages of storage at 0 °C, and the calcium-pectate content and flesh firmness constantly increased during storage. The OG probe demonstrated the accumulation of egg-box structures at the cellular level. The exogenous injection of PME and Ca2+ into the loquat flesh led to an increase in firmness with more low-methylesterified HG and egg-box structure signals. CONCLUSION: PME-mediated demethylesterification generated large amounts of low-methylesterified HG in the cell wall. This low-methylesterified HG further cross-linked with Ca2+ to form egg-box structures. The pectin-involved complexations then contributed to the increased firmness in loquat fruit. Overall, besides being involved in fruit softening, pectin could also be involved in strengthening the mechanical properties of postharvest fruit. This study provides new ideas for obtaining a better texture of postharvest loquat fruits based on pectin regulation.

Quantitative visualization of pectin distribution maps of peach fruits.

Pectin content is an important quality index of fruits, as pectin content undergoes significant changes during the peach ripening process. The commonly used carbazole colorimetry method measures only the total content value of each kind of pectin for each pulp sample and cannot provide distribution maps of the pectin contents for the whole fruit pulp. This work used the hyperspectral imaging technique to quantitatively visualize the distribution maps of pectin contents inside peach pulp at the pixel level. The protopectin contents were well predicted, with the best residual predictive deviation of 2.264, whereas the predictions of the water-soluble pectin and the total pectin contents were not satisfied. On the basis of the best predictive model, the distribution maps of the protopectin contents were quantitatively visualized. A histogram of an example protopectin distribution revealed the existence of a wide range of protopectin contents in peach pulp. Our results show that hyperspectral imaging holds promise as a powerful alternative to the carbazole colorimetry method for measuring the spatial variations in the protopectin distribution inside peach pulp. The distribution maps could be used as a maturity indicator to understand and evaluate the ripening process of peach fruit in depth.