# Concentrate Apple Juice Industry: Aroma and Pomace Valuation as Food Ingredients
## 3 Results and Discussion
### Volatile Composition of Industrial Apple Aroma
After this validation, SPME was used. Figure 1: The compounds identified in the apple aroma are plotted in a logarithmic scale against its own contribution to the aroma; values higher than 1 can contribute to aroma, values higher than 1000 present an odor intensity in the suprathreshold area (blue line). The GC peak area obtained by Headspace–Solid Phase Microextraction Gas Chromatography Combined with Quadrupole Mass Spectrometry (HS–SPME/GC–qMS) was divided by the odor threshold given by the (**a**) Relative Aroma Index (the compounds corresponding to each bar are presented in Table 1 in the same sequence); (**b**) the concentration calculated by Simultaneous Distillation Extraction (SDE)/GC–qMS divided by the odor threshold given by the Aroma Index. Ethyl-2-MBT: ethyl-2-methylbutanoate. The compounds that most contribute to the scent of apple aroma were aldehydes and esters (Figure 1a,b), namely the ethyl-2-methylbutanoate, which presents a green apple odor descriptor with a very low odor threshold (0.006 ppb) [16]. Its Aroma Index is 2 \(\times\) 10\({}^{6}\), meaning aroma intensity more than 12, within the saturation zone [26; 27; 28]. The esters, hexyl acetate and 2-methylbutyl acetate also exhibited an Aroma Index (Figure 1b) and Relative Aroma Index (Figure 1a) within the same magnitude, 4 and 3, respectively. The other four esters (ethyl butanoate, butyl acetate, ethyl hexanoate, and hexyl 2-methylbutanoate) also seem to contribute greatly to the fruity, green, and apple aroma to this concentrate apple juice coproduct. The aldehydes can also have impact in apple aroma, namely hexanal and _trans_-2-hexanal, both with a magnitude of 3, which means an aroma intensity greater than 6 [26; 27; 28]. As a coproduct of the concentrate juice industrial process, the apple aroma has a high potential of valuation due to the presence of apple aroma key compounds present in higher concentration, allowing the use of a small amount of this industrial apple aroma (e.g., 0.1% incorporation will contribute with a distinct apple odor) to aromatize different food stuffs as a natural apple aroma. This apple aroma is usually used to reconstitute the apple juice from the concentrated juice that is derived from most apple aroma compounds. In addition, apple aroma maintains the volatile profile of the single strength apple juice [3]. The apple aroma recovered from the industrial concentrate juice process has been used as food flavoring; usually there are key compounds that are used to give the price of this product. It is important to create simple and rapid methodologies to assess the quality of the aroma. In the food industry, the most common compounds used are the presence of three positive compounds: ethyl-2-methylbutanoate, hexanal, and _trans_-2-hexanal. These three compounds were described as important contributors to apple juice aroma by [PERSON] et al. [29] more than 50 years ago, and they are still used. However, the balance with some negative odor compounds are also requested to assess quality in the food industry, namely the presence of ethanol, 2-methyl-1-butanol, 3-methyl-1-butanol, isobutanol, and phenylethanol, where these compounds were classified as undesirable for apple by [PERSON] and [PERSON] [30] almost 30 years ago. In addition, the presence of the 3-methylbuthylacetate is also considered undesirable for apple aroma, since is thought to arise from fermentation. The 3-methyl-1-butanol was found in all apple juices and aromas from different countries, within a total of 30 samples from Poland, Germany, Turkey, Romania, and China, and also 3-methylbutyl acetate was present in almost one half of the samples [3]. In our samples, only 2-methyl-1-butanol was present; however, it is considered to be a genuine apple constituent [23]. In order to assess aroma quality, some limits are regulated in juices and food matrices, and their limits should be taken into account in the aromas used as flavorings.