## 3 Results and Discussion
### Hierarchical Cluster Analysis (HCA) and Volatile Profiles Development
#### 3.3.7 Changes in the Concentration Profiles of Sulfur-Derived Compounds, Phenols, Acids and Others  
Sulfur compounds, phenols, acids, and naphthalene also contribute to the overall aroma. The sulfur compounds dimethyl sulfide and dimethyl sulfoxide that have been classed as heat-derived sulfur compounds [38; 39] were detected in the samples, of which the dimethyl sulfide has been identified in fresh NCS sample accounting for 11.96% of the volatile flavor components [6]. In the dehydration process, it experienced a 10-fold increase with the content from S-0 to S-240 (5.11 to 50.49 \(\upmu\)g/g), which could originate from the Strecker degradation of the cysteine and methionine that existed in the system [27; 40], acting as an off-odor generator due to the extremely low sensory threshold values. Meanwhile, dimethyl sulfoxide decreased from S-0 to S-150, and then increased slightly from S-180 to the final product (0.94 \(\upmu\)g/g).  
Five (5) phenols were identified, of which butylated-hydroxy-toluene presented in S-0 to S-210 and disappeared in the final product. Throughout the process, 2,4-di-tert-butylphenol, which has previously identified in sugarcane juice, grape berries, and pomelo juice [13; 41; 42], was the only phenol detected, and had its highest concentration in S-0 but then showed an overall decreasing trend (S-0 to S-240, 6.70 to 2.65 \(\upmu\)g/g). Then, 2-methoxy-4-vinylphenol, a woody odor phenol identified in the fresh NCS [6], was also identified from S-30 to S-240 and showed an increasing trend (from 1.05 to 5.92 \(\upmu\)g/g). Spicy odor scented eugenol was only identified in S-30. In addition to the aroma supplementary characteristics, these phenols also contribute to the antimicrobial properties [43].  
Three types of acids that were detected in sample S-30 to S-240, while were absent in the initial juice, indicating that no microbial or chemical degradation occurred prior to the dehydration process [44; 45]. Among the detected acids, acetic acid, which provides an acidic odor, was detected in S-60 and progressively decreased in the other samples. Further, 2-propenoic acid was the other dominant acid identified and experienced an increasing trend from S60 to S-180 (0.14 to 6.06 \(\upmu\)g/g), followed by a decreasing trend towards the end (S-240, 2.54 \(\upmu\)g/g). The acid concentration in the NCS produced in this study was much lower than the values reported in previous studies [6; 10; 16; 33]. This could be attributed to the relatively lower temperature used, no microbial or chemical degradation in the initial sugarcane juice, and reduced amounts of fine fibres by membrane filtration.  
Six (6) naphthalene compounds, including 1,2,3,4-tetrahydro-1,6,8-trimethyl-naphth-lene, 2-(2-butenyl)-1,3,5-trimethyl-benzene, 1,2,3,4-tetrahydro-1,1,6-trimethyl-naphthalene, 2,2',5,5'-tetramethyl-1,1'-biphenyl/, (E)-1,2,3-trimethyl-4-propyl-naphthalene, and methoxyphenyl-loxime, that have not been reported as the aroma profiles in NCS, were identified in this study, and the first three of them are only developed at the very end of the process. The concentration of the other three fluctuated through the process, in which (E)-1,2,3-trimethyl-4-propenyl-naphthalene was the only compound detected in initial sugarcane juice S-0.