## 3 Results and Discussion
### Volatile Compounds Formation and Their Precursors  
As observed from the overall compositional profiles of the intermediates during dehydration of membrane-clarified sugarcane juice (Figure 4), S-0 had a relatively high content of volatile compounds, among which aldehydes, alcohols, hydrocarbons, and esters are the four major components that form the typical aroma present in fresh cane juice. As shown in Figure 4 Stage1, aldehydes and alcohols present in sugarcane juice are mainly long chain fatty aldehydes and alcohols. Meanwhile, from S-30 to S-180 (Figure 4 Stage 2), there is a significant loss of these endogenous volatiles, which could be due to the evaporation caused by the increased temperature and vacuum applied to the system. The development of the aroma compounds present in NCS mainly occurred at the post dehydration stages from S-210 to S-240 (Figure 4 Stage 3), during which the temperature was 106-108 \({}^{\circ}\)C and pH was \(\sim\)5.50. Aldehydes, ketones, oxygen heterocyclic compounds, typically furrans, and nitrogen heterocyclic, typically pyrazines, were found to predominate, which are associated with both caramelization and Maillard reactions. Sugars are the dominate components in sugarcane juice, and represent a source for caramelization, while the chemistry underlying the Maillard reaction is a complex reaction between the carbonyl group of reducing sugars and amine group of free amino acid, peptides, and proteins [46]. A reasonable number of proteins and free amino acids (FAA) are present in juice which could provide reactants with sufficient basicity for the reaction to occur. Partial least squares regression (PLSR) analysis was used to determine the correlation between each volatile species and each of the FAA and sugars (Supplementary Section S2.1 and Figure S2a). PLSR analysis confirmed that volatiles including aldehydes, sulphur compounds, acids, oxygen, and nitrogen heterocyclic compounds formation were also positively associated with glucose and fructose, while negatively associated with sucrose, indicating that sucrose was not directly involved in the formation of volatile compounds. However, as sucrose (\(\sim\)19.78%) is the dominant sugar in sugarcane juice, is readily inverted to glucose and fructose under acidic conditions (6.8 to 5.5) and high temperature (85 to 108 \({}^{\circ}\)C). This is shown with the increased glucose and fructose concentrations found at the end of the dehydration process (S-0 to S-240, 7.8 to 67.9 and 11.8 to 36.4 mg/kg.\({}^{\circ}\)Bx, respectively). A possible reaction pathway of the inversion of sucrose to mono sugars i.e., glucose and fructose, and their further participation in the caramelization and Maillard reaction are shown in Figure 5a,b. The mono sugars could cyclize at the relatively high temperature to produce aromatics and furans, and produce acids, aldehydes, alcohols and other compounds through oxidation and reduction [47]. Furfural, 2-furanmethanol, 2-furanmethanol acetate, methyl salicate, acetic acid, and 2-propenoic acid that developed in the post dehydration process could be caramelization products, while ethanol and ethyl acetate were identified in fresh sugarcane juice indicated the caramelization occurred under the higher temperature in the membrane filtration process (Figure 5a). The participation of glucose and fructose in the Maillard reaction was initiated by the condensation of their carbonyl groups with amino groups from amino acids/peptides/proteins, and Schiff bases were formed in this step, which then undergo Amadori and Heyns rearrangements respectively. The Amadori product and Heyns products undergone enolization, deamination process, forming deoxy-dicarbonyl sugar derivatives [48]. As the pH of the current reaction system was \(<\)7, only 1,2-enaminol process occurred for the Amadori product, forming the 3-deoxyglucose, while for Heyns products, both 3-deoxyfructosome and 4-deoxyfructosome were formed.