## 4 Discussion
### Effect of 1-MCP, Storage Atmosphere, and Juice Processing
Contrary to the results observed in late-harvested McIntosh juices, the suppressive effect of 1-MCP and/or CA storage was not clearly observed in juices extracted from fruit harvested at commercial maturity. These results are unexpected, and no explanation or corresponding results were found in the literature. As compared to clear juices, cloudy juice samples from McIntosh and Honeycrisp apples had considerably higher levels of all the major esters, aldehydes, and total volatiles, which was most pronounced in Honeycrisp juices. Even though there is a lack of literature pertaining to the volatile composition of cloudy apple juices, one recent study reported higher levels of total esters in apple juice with pulp as compared to juice from concentrate [18]. The reduction of esters in clear juice samples can be explained by the hydrolysis of esters by the action of esterase that is present in the commercial enzyme preparation [26]. As mentioned in the methodology part, one of the major differences between the two juices is the absence (clear) or presence (cloudy) of ascorbic acid. The higher content of aldehydes in cloudy juices, which is processed with ascorbic acid addition, is consistent with a previous study [13] that investigated the changes in the aroma value (the ratio of volatile concentration to odor threshold) of volatile compounds due to the addition of ascorbic acid (0.2% w/v) to the apple juice. [PERSON] et al. [13] found considerably higher (4- to 5-fold) aroma value of (E)-2-hexenal and hexanal in juices treated with ascorbic acid than the control. Even though there is limited information about the exact mechanism of ascorbic acid reaction with volatile compounds, the reduced concentration of aldehydes in clear juice samples has been associated with the action of ADH during the clarification process. The lower content of aldehydes in clear juice samples was ascribed to the conversion of aldehydes to alcohols by the action of ADH during the enzymatic incubation [26; 35]. The longer incubation period (about 3 h at 25 \({}^{\circ}\)C, in our case) would give additional time for different enzymatic reactions activated via endogenous enzymes, including ADH. In our experiment, the long incubation period was not part of cloudy apple juice preparation; instead, the juice was immediately cooled and then pasteurized. This immediate cooling, which was followed by pasteurization, could slow down and inactivate the action of the indigenous enzymes such as ADH. Hence, the preservation of aldehydes in cloudy apple juice could be attributed to the inhibition of ADH activity during processing [26]. Generally, our study suggests that the content and composition of volatile aroma compounds in apple juice could be strongly influenced by the fruit quality and juice processing techniques. As each group of the volatile compound has a typical odor characteristic, the difference in their abundance associated with postharvest treatments and juice processing steps could affect the subsequent organoleptic quality of the juices. However, in future investigations, sensory evaluation is warranted to assess the consumers' perception associated with the change of volatile aroma compounds observed in this study. Conceptualization, H.P.V.R., R.A.S. and C.F.F. ; methodology, B.M.M. and M.J.; formal analysis, B.M.M. ; investigation, B.M.M. ; resources, H.P.V.R. ; data curation, H.P.V.R. ; writing--original draft preparation, B.M.M. ; writing--review and editing, H.P.V.R., R.A.S. and C.F.F. ; visualization, B.M.M. ; supervision, H.P.V.R., R.A.S. and C.F.F. ; project administration, H.P.V.R. ; funding acquisition, H.P.V.R. and C.F.F. This manuscript is based on the Doctoral thesis of B.M.M. All authors have read and agreed to the published version of the manuscript. This research was funded by the Department of Foreign Affairs, Trade and Development (DFATD) of Canada granted to [PERSON] (B.M.M.) and [PERSON] (H.P.V.R.). Authors thank [PERSON] for administrative support related to DFATD funds. The authors declare no conflict of interest.