## 3 Results and Discussion
### Retention of Phenolic Compounds during Spray Drying  
A HPLC system equipped with a DAD was employed to analyse the major phenolics in the mandarin juices and the spray-dried powders from both Afourer and Richard Special cultivars in order to investigate the effect of sample types on the retention of individual phenolic compound. The method validation parameters, including the repeatability, intermediate precision, regression coefficient, LOD, and LOQ, are shown in Table S2.  
Table 3 shows the concentrations of major phenolics in the juice and powder samples. It has been widely reported that mandarin fruits have an abundant flavanone profile that is dominated by hesperidin [37], and this was confirmed by the results that were obtained for the Richard Special cultivar in the current study (15 to 180.5 ug/100 mg DW). Sinapic acid was present as the predominant phenolic compound with the concentration ranging from 406.9 to 913 ug/mg DW in both mandarin juice samples and powders of the Afourer cultivar. Some other flavonoids, such as naringin, rutin, and eriocitrin, which have been identified as major flavonoids in mandarin fruits by previous researchers, were not detected in our samples [3]. This could probably be explained by the diversity of mandarin varieties, as the literature indicated that the phenolic profile could be genetically controlled [37]. Additionally, the effect of environmental factors, including climate, soil properties, humidity, and light, could also be responsible for the diverse phenolic profile for mandarins [3].  
With regards to the retention of phenolic compounds, sinapic acid decreased significantly (\(p<0.05\)) in all samples, except RS3, after drying. This decline could be attributed to the degradation of phenolic compounds. The hesperidin had an opposite trend, showing a dramatic increase in the spray-dried samples, especially for the RS1 sample, giving a retention value of 594.6%. The results showed that thermal processing did not affect the stability of hesperidin, in agreement with a previous study that was conducted by [PERSON] et al. [38]. They reported no significant loss of hesperidin under heat treatment at 90 \({}^{\circ}\)C for 240 min. The increase of phenolic acids, for example, \(p\)-hydroxybenzoic acid for RS1 (retention of 225%), ocularic acid for all Richard Special samples (retention of 254-287%), and vanillic acid for all samples, except RS1 (retention of 101-199%), was associated with the release of phenolic aglycones from their glycosidically bound precursors, due to the disruption of cell membranes under thermal treatment [39]. This was supported by the findings of a previous study [37], that the concentrations of the bound-form phenolic acids in citrus _reticulata Blanco_ were considerably higher than their free counterparts, especially for chlorogenic acids, which has a bound form concentration that is 5.6 times higher than that in the free fraction (264.93 \(\upmu\)g/g DW vs. 46.68 \(\upmu\)g/g DW).  
When comparing the total five phenolics concentrations in all samples, the spray-dried whole fruit powders (A3 and RS3) showed the highest value (1023 \(\upmu\)g/100 mg DW, and 314 \(\upmu\)g/100 mg DW, respectively), followed by the powders that were prepared from the flavedo-removed mandarin (A2 and RS2, 808.6 and 179 \(\upmu\)g/100 mg DW, respectively). The powders that are prepared from the peel-removed fruit juice (A1 and RS1, 653 and 146 \(\upmu\)g/100 mg DW, respectively) have the lowest total phenolic contents. These findings reaffirmed that the preparation of spray-dried powders from whole mandarin fruit juices has an advantage, as they retain higher phenolic contents.