# Effects of Glyoxylic Acid on Metabolism and Ripening of 'Rocha' Pears Treated with 1-MCP
## 4 Discussion  
The suppression of ripening traits by 1-MCP negatively impacts essential fruit ripening quality attributes such as texture, sugar content, acidity, and aroma, directly affecting consumer acceptance [29; 30]. Previous studies in 'D'Anjou' pears have shown that organic acids like GLA can modulate fruit's metabolism, although their capacity to reverse 1-MCP-induced ripening inhibition remains largely unexplored, especially in other cultivars [7; 31]. In this study, we hypothesized that GLA could influence metabolic pathways of 'Rocha' pears, particularly those related to ripening, under 1-MCP treatment. Multivariate data analysis revealed that GLA promoted changes in the fruit, as evident in the PLS-DA clustering patterns that distinguished GLA-treated samples from CTRL samples, thereby showing GLA's ability to disrupt some usual effects of 1-MCP. However, GLA did not significantly promote a different pattern compared to 1-MCP-treated fruits (CTRL) in key ripening indicators such as ethylene production, fruit softening, or color changes. Instead, GLA-treated pears exhibited increased CO\({}_{2}\) production and specific VOCs, namely, esters, aldehydes, terpen, and alcohols (Table 1). GLA promoted higher emissions of ethyl, butyl, and hexyl acetates, which are esters strongly related to ripening, as well as limonene [32; 33]. However, since these results were not accompanied by an increase in ethylene production, and combined with other ripening results, they suggest that GLA affected other metabolic pathways unrelated to ethylene-driven ripening. It is known that GLA plays a key role in amino acid metabolism, which serves as a precursor for various VOCs, including the formation of aldehydes, alcohols, and esters, contributing to fruits' aroma [20]. Since GLA can influence amino acid metabolism, it is plausible that these VOC changes resulted from alterations in precursor availability, shifting metabolic fluxes toward stress- or defense-related pathways rather than ripening-associated volatile synthesis [7; 20]. For example, studies in apples and tomatoes have shown that alterations in amino acid pathways lead to modifications in volatile production, particularly affecting aldehydes and alcohols [34; 35]. In kiwifruit, shifts in amino acid metabolism have been linked to increased ester formation [36]. Additionally, as GLA is an intermediate of the glyoxylate cycle, which is connected to lipid metabolism, it may indirectly affect metabolic pathways involved in aldehyde and ester biosynthesis. In fact, higher levels of the aldehydes hexanal and (E)-2-hexenal were observed in GLA-treated pears. These compounds contribute to the green aroma present in fruits and vegetables, and they are commonly associated with plant defense mechanisms and lipid oxidation [37; 38]. Notably, the alcohols ethanol, butanol, and hexanol--volatile compounds strongly associated with fermentation and oxidative stress [39]--were also present in higher amounts in the GLA-treated fruits. The higher ethanol concentration suggests that GLA may have influenced fermentation-related pathways, possibly by shifting carbon fluxes toward anaerobic metabolic routes [7]. Based on these results, GLA-treated pears exhibited increased emissions of VOCs linked to oxidative stress, suggesting that GLA may have triggered stress-related metabolic pathways rather than those directly involved in ripening. This aligns with higher respiration rates and possible ROS accumulation, leading to lipid oxidation and the release of stress-associated volatiles. Notably, the 1-MCP-treated CTRL group exhibited a natural ripening progression, as evidenced by the distance of CTRL at T15 from T0 and T7. This suggests that these pears underwent some physiological and metabolic alterations even under the exclusive effect of 1-MCP, as evidenced mainly by a loss of firmness and increased ethylene production over time, indicating that 1-MCP's effect was not entirely restrictive during this phase of the study.