Postharvest senescent dark spot development mechanism of Musa acuminata (“Khai” banana) peel associated with chlorophyll degradation and stomata cell death

Abstract

The occurrence of the postharvest physiological disorder of dark spots on the peel of the ripened “Khai” banana has led to a reduction in its commercial value. The objective of the present study was to investigate the development mechanisms of senescence dark spots of the “Khai” (Musa AA group) banana peel in relation to chlorophyll degradation and stomata cell death. Freshly harvested bananas (commercial mature green stage) were let to ripened at 25 ± 2°C (90%–95% RH). Peel color, senescent spots, DNA degradation, chlorophyll content, chlorophyll‐degrading enzyme activities were assessed. The senescent dark spots developed on the ripened bananas right after 6 days of storage, which coincided with remarkably increased DNA degradation, and a rapid decreased of hue angle value and total chlorophyll content which indicated the chlorophyll degradation. The activities of chlorophyllase, chlorophyll‐degrading peroxidase and pheophytinase increased gradually to the highest point where the chlorophyll content drastically reduced and the appearance of the dark spots was first recorded after 6 days of storage. These dark spots were observed to be surrounded with a bright luminescent ring of hypermodified fluorescent chlorophyll catabolites (FCCs), the product of chlorophyll breakdown. Additionally, the scanning electron microscope (SEM) revealed that the dark spots were found to have originated from the collapsed cells around the stomata of the ripened banana peel whereby the chlorophyll was entirely diminished. Practical applications This research revealed the senescent dark spot development mechanisms of the “Khai” banana peel. The dark spot development symptom on the banana peel surface was caused by the senescence and cell death of the relevant stomata, further associated with chlorophyll degradation. Therefore, any further research into minimizing the dark spot symptom must focus on preventing or delaying stomata senescence and cell death.

Polyvinyl alcohol based functional coating incorporated with Sonneratia ovata extract: Preparation, characterization, and banana preservation

“…The breakdown of chlorophyll which is accountable for the green color of the peel produced xanthophyll and other pigments identified by the appearance of yellow color. During the banana ripening and over‐ripening stage, the senescence dark spots begin to appear and develop more and more on the banana peel surface due to the polyphenol oxidation to produce quinine and polymerization of small molecules to produce macromolecules 13,52 . Eventually, the banana peel turns brown along with a change in taste and aroma in the banana pulp as spoilage signals.…”

“…During the banana ripening and over-ripening stage, the senescence dark spots begin to appear and develop more and more on the banana peel surface due to the polyphenol oxidation to produce quinine and polymerization of small molecules to produce macromolecules. 13,52 Eventually, the banana peel turns brown along with a change in taste and aroma in the banana pulp as spoilage signals. Based on the evaluation of performance of blend coating film prepared from solution, PAD-0.6SO solution was chosen for coating on bananas due to its plasticity and even distribution of SO on the surface with sufficient antimicrobial and antioxidant ability.…”

“…This finding makes a main contribution to fruit deterioration. 12,13 In the present work, the respiration of bananas with and without coating are evaluated by the release of CO 2 (mgCO 2 kg À1 h À1 ). Table 3 shows the amount of CO 2 produced in the first days of bananas with uncoating, PAD coating, and PAD-0.6SO at 298.70 ± 7.57, 341.46 ± 22.40, and 349.19 ± 14.89 mgCO 2 kg À1 h À1 , respectively.…”

“…11 The presence of oxygen-rich environments surrounding the peel can incentivize oxidative polymerization of phenolic compounds and thereby facilitates the growth of dark spots in the vicinity of the stomata on the ripped banana peel surface. 12,13 Recently, coatings are considered an effective method for the purpose of delaying banana ripening, dehydration, and spoilage as they act as a barrier layer to prevent direct contact between the fruit skin and the surrounding atmosphere. 14 Coating-based barrier can hinder oxygen and carbon dioxide transportation from external environment and thus reduce respiration rate.…”

“…However, banana is highly perishable with a short shelf life by virtue of biological and physical deterioration after harvest 11 . The presence of oxygen‐rich environments surrounding the peel can incentivize oxidative polymerization of phenolic compounds and thereby facilitates the growth of dark spots in the vicinity of the stomata on the ripped banana peel surface 12,13 . Recently, coatings are considered an effective method for the purpose of delaying banana ripening, dehydration, and spoilage as they act as a barrier layer to prevent direct contact between the fruit skin and the surrounding atmosphere 14 .…”