Fruit maturity and antioxidant activity affecting superficial scald development in ‘Abate Fétel’ pears

From Firenze University Press Journal: Advances in Horticultural Science

A. Bonora, Department of Agricultural and Food Science, University of Bologna

A. Venturoli, Department of Agricultural and Food Science, University of Bologna

M. Venturi, Department of Agricultural and Food Science, University of Bologna

A. Boini, Department of Agricultural and Food Science, University of Bologna

Luca Corelli Grappadelli, Department of Agricultural and Food Science, University of Bologna

Superficial scald (SS) is one of the main physiological storage disorders of European pears (Pyrus communis L.). SS is a skin disorder that appears as brown or black patches on the fruit. SS is considered a chilling injury which induces a damage and death within the surface layers of cells in localized regions (Lurie and Watkins, 2012). During SS development necrosis of the hypodermal cortical tissue seems to be induced by oxida­tion products of the sesquiterpene (E, E)­α­farnesene (Bain and Mercer, 1963; Rowan et al., 2001). α­farnesene, accumulates at a relatively high level in the fruit peel during low­temperature storage (Whitaker et al., 2009; Yazdani et al., 2011; Lu et al., 2013; Calvo et al., 2015). The observation that SS could be inhibited by certain antioxidant treatments and low oxygen in the storage rooms atmosphere has provided evidence that development of the disorder was associated with oxidative processes (Huelin and Coggiola, 1970; Whitaker, 2004; Vanoli et al., 2015). Thus, the conjugated trienols (CTols) that result from the oxidation of α­farnesene are assumed to play a causal role in the occurrence of SS (Whitaker, 2007; Giné Bordonaba et al., 2013). Nevertheless, it is gen­erally accepted that the accumulation of both α­far­nesene and CTols may be mediated by ethylene which is effectively correlated with SS development (Bai et al., 2009; Lu et al., 2013; Xie et al., 2014; Yazdani et al., 2011). Therefore, it has been suggest­ed that α­farnesene oxidations is a direct conse­quence of free radical reactions occurring during chilling injury and α­farnesene is not always required for the induction of SS but rather in aggravating the symptoms in fruit already compromised by oxidative stress (Rao et al., 1998; Rupasinghe et al., 2000). In this context, it has been suggested that superficial scald mainly results from an imbalance between the fruit capacity to generate antioxidants and the reac­tive oxygen species (ROS) produced during cold stress (Ahn et al., 2007; Guerra et al., 2012; Ju and Bramlage, 2019). Nevertheless, the antioxidant sys­tem in fruit includes an enzymatic and a non­enzy­matic component that play an important role modu­lating oxidative damage to cell walls (Ahn et al., 2007; Lurie and Watkins, 2012; Li et al., 2016). Furthermore, non­enzymatic antioxidants can pre­vent oxidation­linked damages responsible for super­ficial scald through biosynthesis of phenolics that are involved in protective redox­linked pathways under cold stress (Larrigaudière et al., 2016; Sarkar et al., 2018). The nonenzymatic scavengers of reactive oxy­gen species include low molecular mass antioxidants with high­reducing potentials, such as ascorbic acid (AA) and glutathione (GSH). Ascorbic acid acts as an antioxidant compound since it can protect fruit mem­branes from lipid peroxidation (Shewfelt and Del Rosario, 2000) and acts against reactive O2 species in concert with α­tocopherol (Jimenez et al., 1997). Nevertheless, AA tends to decrease during storage and processing of fruit and vegetables (Haffner et al., 1997). A relationship was found between AA content and the susceptibility to browning during experimen­tal storage under various brown core­inducing condi­tions (Pintó et al., 2001). In pears the antioxidant capacity is well explained by phenolics content (Galvis Sánchez et al., 2003). Several studies have demonstrated that these compounds are associated with resistance to SS development in apples and pears (Ju et al., 1996; Zhao et al., 2016). Phenolic compounds are particularly sensitive to storage fac­tors such as controlled atmosphere (Amiot et al., 1993). Variability of phenolics in plant tissues depends on many pre­harvest factors, such fruit maturity and environmental conditions, including temperature, UV light, and nutrition (Markham et al., 1998; Rivero et al., 2001; Rühmann et al., 2002). Casero et al. (2004) used the partial least squares regressions (PLS), a multivariate technique, and found correlations between fruit quality attributes, such as fruit acidity and firmness, and storage disor­ders with nutrients such as calcium, potassium and phosphorus, both in the leaf and fruit. Moreover, PCA biplots were helpful in showing the segregation between SS classes and their associations with the various physicochemical attributes (Cronje et al., 2015). In pear, pulp firmness is one of the most rele­vant quality parameters (Saquet, 2019). Softer fruit had rounder cells separated by larger intercellular spaces than firmer fruit. On the other hand, firmer fruit have smaller cells with less interspace which means denser tissues and longer storage than soft fruit (Johnston et al., 2002). Moreover, the DA­meter, a handheld device that measures chlorophyll concentration several millimetres into the flesh of fruit providing the index of absorbance difference (IAD) (Ziosi et al., 2008), can discriminate the ripening stage of climacteric fruit for postharvest tailored cold storage (Bonora et al., 2013; Gagliardi et al., 2014; Sadar and Zanella, 2019). Fruit ripeness is also well predicted by starch degradation using a multivariate statistical approach (Zude­Sasse et al., 2002). Conversely, in ‘Abate Fétel’ pear fruit the starch index is not always employed even if some studies have reported the use of this procedure to predict pear storability and postharvest issues (Kingston, 1992; Le Lezec and Belouin, 1994; Agar et al., 1999; Calvo et al., 2011). In pears starch pattern degrada­tion can be influenced by environmental and man­agement factors such as temperatures, harvest date and deficit irrigation affecting the kinetics of starch accumulation and degradation (Watkins et al., 1982; Kramer, 1983; Lopez et al., 2013; Lindo­García et al., 2019). Total sugar content is an internal fruit quality trait that is crucial for consumer acceptance (Osorio and Fernie, 2014). Total soluble solids in ‘Abate Fétel’ and ‘Forelle’ pear are mainly fructose, glucose and sucrose (Mesa et al., 2016), and they increase in con­centration after storage since starch is converted via hydrolysis into sugars over time (Visser et al., 1968; Crouch and Huysamer, 2011; Rizzolo et al., 2015). Additionally, sorbitol accumulates in the fruit still attached to the tree (Mesa et al., 2016), acting as cry­oprotectant in cellular structures during cold storage by preventing dehydration of membranes and pro­teins through an osmotic adjustment process (Busatto et al., 2018). Therefore, the aim of this work was to research relations between antioxidant activi­ty, phenolic content, and SS development on ‘Abate Fétel’ pears. Furthermore, preharvest maturity and non­destructive postharvest quality parameters, as well as antioxidant activity and phenolic content, influencing the occurrence of superficial scald using multivariate analysis and regression trees were inves­tigated to develop new reliable hypotheses of their effects in SS development, without compromising consumer acceptance and nutritive value.

DOI: https://doi.org/10.36253/ahsc-13902

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