Effect of CO2 deastringency treatment on flesh disorders induced by mechanical damage in persimmon. Biochemical and microstructural studies
Introduction
Currently, the incidence of flesh browning is one of the main causes of postharvest loss of the ‘Rojo Brillante’ persimmon, which is the persimmon cultivar mainly cultivated in the Mediterranean region. The cause of this disorder, which appears during the commercialisation period, remains unknown. It was recently reported that the mechanically damage that fruit are submitted to during packing operations may be a decisive factor of browning manifestation (Besada, Arnal, Salvador, & Martínez-Jávega, 2010a).
As this cultivar belongs to the group of persimmon cultivars that are astringent at harvest, fruit are routinely submitted to a postharvest deastringency treatment based on the exposure of fruit to a high CO2 concentration in order to remove astringency prior to commercialisation (Salvador et al., 2007). Persimmon astringency is due to the high concentration of soluble tannins present in fruit flesh. The effectiveness of CO2 treatment to remove astringency is based on the insolubilisation of tannins by the acetaldehyde generated during anaerobic respiration intermediating, which is triggered when fruit is exposed to a high CO2 atmosphere (Matsuo and Ito, 1982, Matsuo et al., 1991). Application of treatment at 95–100% CO2 for 24 h at 20 °C has been established as optimal conditions to ensure the removal of astringency in ‘Rojo Brillante’ persimmon (Besada et al., 2010b, Salvador et al., 2007). Our former studies showed that fruit which have been previously submitted to the deastringency treatment (non astringent fruit) are susceptible to manifesting mechanical impact-induced browning, while astringent fruit are less susceptible to displaying this alteration after packing operations. Thus tannins have been suggested to be implied in the browning process (Besada, Salvador, Vázquez-Gutiérrez, Hernando, & Pérez-Munuera, 2012).
One of the main causes of browning in fruit and vegetables is the oxidation and polymerisation of phenolic compounds due to the activation of enzymes such as phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO) and peroxidase (POD). In persimmon fruit, the cause of external bruising has been poorly investigated. Lee, Kim, Kim, and Park (2005) reported no significant changes in lipid peroxidation, as expressed by malondialdehyde production, among bruised and unbruised persimmon cv. Fuyu; these authors also reported that although increased polyphenol oxidase activity appeared to be associated with the visual deterioration of bruised fruits, it could not be the only factor to influence the bruising manifestation. Similarly, our previous studies showed no significant changes in PPO and PAL activity between browned and sound flesh of ‘Rojo Brillante’ persimmon. However, POD enzyme activity has been associated with mechanical damage and browning manifestation (Khademi, Salvador, Zamani, & Besada, 2012).
Furthermore, reactive oxygen species (ROS) are produced as a normal plant cellular metabolism product. Various environmental stresses lead to excessive ROS production; such disturbances in the equilibrium between the production and scavenging of ROS bring about a sudden increase in intracellular ROS levels, which can severely damage cell structures (Gill and Tuteja, 2010, Sharma et al., 2012). Anaerobic atmospheres have been described as one of the environmental stresses that induces an oxidative burst in plants (Blokhina et al., 2001, Blokhina et al., 2003). Moreover, changes in ROS levels have been related to fruit deterioration in association with mechanical damage of fruit like apricots and pears (De Martino et al., 2006, Li et al., 2010). There is no information about the effect of CO2-deastringency treatment on the redox state of persimmon, and no studies have addressed the involvement of ROS in persimmon browning in association with mechanical damage.
This study aimed to investigate the effect of the deastringency treatment with high CO2 concentrations and the level and form (soluble/insoluble) of tannins in the mechanical-induced browning of persimmon fruit. Elucidate the implication of ROS in browning manifestation was also an objective of this research. Microstructural techniques were used to describe browning alterations.
Section snippets
Vegetal material and experimental design
Persimmon (Diospyros kaki Thunb. cv. Rojo Brillante) fruit were harvested in l’Alcúdia (E Spain) at commercial maturity stage. The harvesting date was November 8, when fruit presented an external colour index = 11 and firmness value of 44.9 N. After harvest, fruit were taken to the Instituto Valenciano de Investigaciones Agrarias (IVIA), where they were carefully selected for uniformity of size and colour, and for lack of defects.
Thirty-six lots of 20 fruits were formed and one lot of fruit was
Study of the physiological parameters related to astringency
Soluble tannin and acetaldehyde content are the main parameters relating to the astringency removal process when submitting fruit to high CO2 concentrations. Therefore, we determined them both in the fruit submitted to different CO2 treatments (0, 6, 12, 18, 24, 32 and 40 h). Besides, fruit astringency was also evaluated by a sensory panel.
The fruit not exposed to CO2 (0 h treatment) showed a soluble tannins content of 0.6% fw (Supplementary Fig. S1A), which are habitual values at harvest in the
Discussion
This work initially focused on studying the flesh browning disorder of the ‘Rojo Brillante’ persimmon. Nevertheless while this research line was underway, another flesh disorder was identified, which we named “pinkish-bruising”. Here, we attempt to collect data from the physiological, microstructural and chromatographic studies obtained in this paper, together with previous results from our laboratory, to help gain a better understanding of the flesh browning process in persimmon.
Acknowledgments
This study has been supported by the Spanish ‘Ministerio de Economía y Competitividad (Project INIA-RTA 2010-00086-00-00) and FEDER Program from the EU. We thank to ‘D.O. Kaki Ribera del Xúquer’ for his support for these studies. We thank Ph.D. Takashi Tanaka (Nagasaki University) for his support during the chromatographic analysis. Ph.D. Cristina Besada is contracted by the ‘Regional Ministry of Education of the Valencian Community’.
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