# Concentrate Apple Juice Industry: Aroma and Pomace Valuation as Food Ingredients
## 3 Results and Discussion
### Volatile Composition of Industrial Apple Aroma
Limits of the presence of 3-methyl-1-butanol and 3-methylbutyl acetate in fruit juice production have been a target of regulation [3]. The 3-methyl-1-butanol is a flavoring substance previously recognized as FEMA GRAS (Flavoring Extract Manufacturers Association's \"Generally Recognized As Safe\") with an average usual use level of 4 ppm and an average maximum use levels of 17 ppm in non-alcoholic beverages [31]. When those compounds are not present, the apple juice industry also uses other undesirable compounds at high concentrations, such as ethyl acetate (42 ppm for usual use and 67 ppm maximum for non-alcoholic beverages [31]) as negative marker for assess apple aroma quality. Industrial Apple Aroma Volatile Compounds Quality Assessment  
For the apple aroma quality assessment, five target compounds were selected, three of them contributing positively to the apple aroma, with apple odor descriptors, namely ethyl 2-methylbutanoate, hexanal, and _trans_-2-hexanal. Volatile compounds considered as undesirable to the apple aroma, e.g., 3-methyl-1-butanol and 3-methylbutyl acetate, should have been also selected [30; 32]. Because those compounds were not detected, ethyl acetate, also contributing negatively to the aroma quality when present at higher concentrations, was chosen. Another compound used to assess the aroma quality was 1-butanol, as it is present in high concentrations in apple juice aroma [3; 32] and can enhance the intensity of the overall aroma [33; 34]. Some of the volatile compounds selected have been already used as shelf life markers in apple juices [24]. However, as the shelf life of apple aroma has not yet been studied, in this study the apple aroma produced in January during the juice evaporation step, from apples harvested in 2013, was analyzed after 1, 5, 9, and 10 months of storage at room temperature (Figure 2). The compounds that present a higher concentration in the apple aroma were 1-butanol, followed by _trans_-2-hexenal, hexanal, ethyl 2-methylbutanoate, and ethyl acetate. From the five volatile compounds monitored during 10 months, a decrease was perceived after 9 months at room temperature (Figure 2a) in only two compounds. The decrease observed was 137% and 55% in the amount of ethyl acetate and butanol, respectively. The decrease observed is related to the boiling point of the compounds, as ethyl acetate has the highest volatility and lower boiling point (68 \({}^{\circ}\)C). After 9 months, ethyl acetate presented less than half of its initial concentration. At 10 months of storage, the concentration decreased four and two times for ethyl acetate and butanol, respectively. 1-Butanol, with a boiling point of 117 \({}^{\circ}\)C, presented a decrease in a lower extent than ethyl acetate. The other three compounds, the most relevant to the apple scert aroma, almost maintained their concentration during the 10 months, all having boiling points higher than 130 \({}^{\circ}\)C. Ethyl 2-methylbutanoate, hexanal, and _trans_-2-hexenal at 10 months of storage decreased 38%, 28%, and 2%, respectively. Concerning the Aroma Index, those contributions were completely distinct. Ethyl 2-methylbutanoate was the compound that presented the highest Aroma Index, with a value more than 100,000 times higher than its odor threshold, showing the highest contribution to the apple aroma, with a green apple odor descriptor [16]. Hexanal, _trans_-2-hexenal, and 1-butanol, despite the different concentrations presented, have similar Aroma Index, approximately 1000 times higher than their odor thresholds (Figure 2b). Ethyl acetate presented an Aroma Index lower than 1, decreasing after 5 months from 0.1 to 0.01, which can be inferred to have a negligible influence in apple aroma, not negatively impacting apple aroma quality [32]. These results showed that apple aroma is stable at room temperature during at least 10 months. The influence of the different raw material and technological adjustments used during the production through the year was investigated in terms of fluctuations in the apple aroma quality.