# Effects of Glyoxylic Acid on Metabolism and Ripening of 'Rocha' Pears Treated with 1-MCP
## 4 Discussion
Several studies have shown that the extent of 1-MCP's effect varies primarilybased on the cultivar, the timing of postharvest treatment application, storage conditions, and the fruit's developmental stage at analysis/treatment [6; 10]. For instance, a study by [PERSON] et al. [7], which used the 'D'Anjou' cultivar, found that GLA treatment accelerated the ripening response, leading to increased ethylene production and reduced firmness compared to 1-MCP-treated fruits. Additionally, over time, fruits synthesize new ethylene receptors that are not bound by 1-MCP [33], allowing ethylene perception to resume, and gradually restoring normal ripening processes. In our study, the 1-MCP-treated pears eventually began to ripen, suggesting that ethylene perception was restored over time due to receptor renewal. This loss of 1-MCP's effect could explain why GLA was unable to entirely counteract its impact; by the time GLA was applied, the fruit was already regaining its ripening ability. This raises the possibility that the physiological status of the pears at the time of GLA application influenced the outcome, potentially interfering with GLA's expected effects [34]. In this study, GLA caused no significant impact on ethylene production compared to the CTRL. This finding aligns with the lower ACC concentrations measured in GLA-treated fruits. Since ACC is the direct precursor of ethylene, its lower levels in GLA-treated fruit suggest that either ACS enzyme activity (the enzyme responsible for producing ACC) was inhibited or ACC was rapidly metabolized by the ACO enzyme into ethylene [40; 41]. In fact, ACO activity showed no significant differences between the conditions, and the ethylene levels in both CTRL and GLA-treated pears were similar. So, the limiting factor was ACS enzyme activity. This suggests that the basal ACS activity caused by 1-MCP was not significantly stimulated by GLA, which explains the low ACC values and thereby limits higher ethylene biosynthesis compared to the CTRL. This demonstrates the central role of ethylene in regulating the ripening process of 'Rocha' pears. Sugars play a crucial role in the ripening process and influence consumer preferences. The primary sugars that vary in pears during ripening are sucrose, glucose, and fructose [42; 43]. Numerous studies have shown a positive relationship between ethylene and sucrose production, particularly through the activation of enzymes that convert starch into simpler sugars [35; 44]. Hence, the significant increase in ethylene production observed in both conditions during the time of analysis supports the measured pattern of sucrose (Figure 5). The rise in sucrose levels in the CTRL samples suggests starch degradation, which aligns with the observed loss of firmness [21]. Additionally, further breakdown of sucrose into simpler sugars, such as fructose and glucose, did not occur, as indicated by the lack of increase in these sugars shown in Table 1. The slight decrease in sucrose observed in GLA-treated pears, combined with the higher respiration measured in these pears, suggests its utilization as a substrate for respiration and consequent higher CO\({}_{2}\) production [45]. Despite the lack of ethylene stimulation, GLA-treated pears exhibited a significant increase in respiration rates, reinforcing that GLA activates alternative metabolic pathways. Elevated respiration without softening or ethylene production suggests that GLA-induced metabolic changes are more related to stress responses or energy metabolism than to ripening itself. Similar patterns were observed in citrus fruits, where exogenous organic acids altered respiration without promoting ripening-associated changes [39].