Abstract
Refrigerated storage is widely applied in order to maintain peach quality but it can also induce chilling injuries (CIs) such as flesh browning and bleeding, and mealiness. Peach fruit from three cultivars (‘Red Haven’, RH, ‘Regina di Londa’, RL, and ‘Flaminia’, FL) were stored for 4 weeks under low temperatures (0.5 and 5.5°C). GC-MS was employed to study changes in both metabolome and volatilome induced by cold storage in the mesocarp. CIs were assessed both at the end of each week of storage and after subsequent shelf-life (SL) at 20°C. Flesh browning and mealiness appeared to be more related to 5.5°C storage, while flesh bleeding revealed high incidence following 0.5°C storage. Compared to RL and FL, RH showed a marked lower incidence of CIs. Multivariate statistical analyses indicate that RH peaches indeed differ from RL and FL in particular when considering data from samples collected at the end of the cold storage. Common and divergent responses have been identified in terms of metabolic responses to the applied low temperatures. In all three cultivars raffinose, glucose-6P, fucose, xylose, sorbitol, GABA, epicatechin, catechin, and putrescine markedly increased during cold storage, while citramalic, glucuronic, mucic and shikimic acids decreased. Among volatile organic compounds (VOCs), aldehydes and alcohols generally accumulated more under low temperature conditions while esters and lactones evolved during subsequent SL. The main cultivar differences developed after cold storage during SL although some common responses (e.g., an increased production of ethyl acetate) were observed. The lower levels of flesh browning and bleeding displayed by RH peaches were related to compounds with antioxidant activity, or acting as osmotic protectants and membrane stabilizer. Indeed, RH showed higher levels of amino acids and urea, together with a marked increase in putrescine, sorbitol, maltitol, myoinositol and sucrose detected during storage and SL.
Highlights
When kept at room temperature peach fruit undergo a rapid postharvest loss of firmness, weight loss and decay (Ramina et al, 2008)
Firmness loss was reduced in samples stored at 0.5◦C in all varieties, whereas less pronounced effects were observed at 5.5◦C, both under and after storage (SL), with RH showing a better firmness retention if compared to FL and RL (Figure 1)
In RL and FL the different behavior between the two low temperature conditions is evident when comparing fruit evaluated immediately after storage, with higher chilling injuries (CIs) incidence detected in samples kept at 5.5◦C (Figure 2, solid lines)
Summary
When kept at room temperature peach fruit undergo a rapid postharvest loss of firmness, weight loss and decay (Ramina et al, 2008). One of the problems caused in peaches by cold storage is the onset of chilling injuries (CIs), manifested as loss of flavor and the ability to ripen, increased incidence of decay, internal browning, flesh breakdown, lack of juiciness (mealiness/woolliness), and reddish flesh discolouration (reddening/bleeding) (Crisosto and Mitchell, 2002; Lurie and Crisosto, 2005). Between 2.2 and 7.6◦C (the so-called “killing zone”) these symptoms develop faster and more severely than at 0◦C or below but above the freezing point (Crisosto and Valero, 2008). The onset of peach fruit disorders under the “killing zone” temperature appears to be linked with the low levels of ethylene biosynthesis only partly inducing ripening-related genes (Fernández-Trujillo et al, 1998; Walsh et al, 2001; Zhou et al, 2001; Pons et al, 2015; Wang et al, 2017). The specific temperature requirement to maintain fruit quality may vary in relation to the genetic background resulting in different metabolic reactions that impact on both the organoleptic properties (aroma compounds, primary and secondary metabolites) (Oms-Oliu et al, 2013; Johanningsmeier et al, 2016) and the incidence of the storage physiological disorders (Dagar et al, 2013; Pons et al, 2015)
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