# Differentiation of Fresh and Processed Fruit Juices Using Volatile Composition
## 3 Discussion
Our study showed that the volatile profile of processed juices is more complex than that of fresh juices. This result is in accordance with a previous work carried out by [PERSON] and colleagues [49], in which fresh apple juice was compared with commercial apple juice. These authors highlighted that the differentiation criteria between fresh and commercial juices based on individual compounds implied a difficult characterization process, which is not helpful in establishing a quality index. Consequently, the most appropriate and useful method is to compare groups of VOCs (in our study: esters, alcohols, carbonyl compounds, terpenoids, volatile phenols, acids, and furanic compounds). In general, fresh juices were mainly characterized by the presence of esters and terpenoids, while furanic compounds (Maillard products) were important contributors to the profile of processed juices. Our findings are in accordancewith a previous report concerning pomegranate juices [56]. Moreover, storage time and temperature can also change juice aroma profiles due to Maillard, strecker, and acid catalyzed hydration reactions. The formation of methional from methionine is probably the most significant example of Strecker degradation in orange juice [51]. Methional concentration in processed orange juice is higher than fresh juice (Table 1). Moreover, esters as stated above represent an important contribution to fruit juice odor, and the level of total esters in aqueous essence has been used as a quality index [51]. Nevertheless, their concentration in processed juice was lower than fresh juice, since during processing many esters rapidly hydrolyzed by hydrolase enzymes. The presence of ethanol in the investigated fruit juices is indicative of the fermentation process caused by microorganisms as a consequence of inefficient sterilization of raw materials or later contamination. A previous study reported that high ethanol contents were observed mainly in juices without preservatives, particularly freshly-squeezed juices. Octanal and decanal, the most dominant compounds, of the carbonyl group found, in orange juice unlike other juices, have been considered to be important contributors to the orange flavor and standard of orange peel oil [57]. An important point to highlight is that the production of excessive volatile phenols is regarded as spoilage. In our study, 4-ethyl phenol, in particular, was only detected in processed juices, suggesting a possible microbial contamination (e.g., _Brettanomyces_ sp). It has been reported [58] that this phenol may provide woody, smoky, leather, and animal off-odors. In the same sense, [PERSON] and colleagues [59] reported that another family of compounds, which may contribute to undesirable smells or odors, is acidic compounds such as octanoic and hexanoic acids. The data obtained in the current study represent an added value to the existing knowledge, as well as provide a useful platform to improve the organoleptic characteristics of the processed juices, and consequently contribute to their economic valorization and improve their acceptance by consumers.