## 3 Results and Discussion  
Figure 1 shows the appearance of youtiao with traditional deep-frying, by electrostatic frying and by vacuum frying, with and without potassium aluminum sulfate. Figure 1A,C indicate that there is no significant difference in appearance between deep-frying (Figure 1A) and electrostatic frying (Figure 1C). The youtiao have darker appearance without potassium aluminum sulfate addition after frying (Figure 1B,D) compared to the control (Figure 1A) and when fried in the electrostatic fryer (Figure 1C). In cross section,  
Figure 1: Appearance of fried bread youtiao by traditional frying, electrostatic frying, and vacuum frying. **(A)** Control: traditional frying + sodium aluminum sulfate. **(B)** Traditional frying without adding sodium aluminum sulfate. **(C)** Electrostatic frying + sodium aluminum sulfate. **(D)** Electrostatic frying without adding sodium aluminum sulfate. **(E)** Vacuum frying + sodium aluminum sulfate without dough stretching before frying. **(F)** Vacuum frying without adding sodium aluminum sulfate without dough stretching before frying. **(G)** Cross section: traditional frying + sodium aluminum sulfate. **(H)** Cross section: traditional frying without adding sodium aluminum sulfate. **(I)** Cross section: electrostatic frying + sodium aluminum sulfate. **(J)** Cross section: electrostatic frying without adding sodium aluminum sulfate. **(K)** Cross section: vacuum frying + sodium aluminum sulfate. **(L)** Cross section: vacuum frying without adding sodium aluminum sulfate. the deep-fried youtiao (Figure 1G,H) seems to have risen more than when electrostatically fried (Figure 1I,J). Vacuum-fried youtiao did not hold its structure during centrifugation to remove oil and broke into pieces. The appearance of the vacuum-fried youtiao (Figure 1E,F) at 120 \({}^{\circ}\)C is subjectively lighter than that fried by the traditional (Figure 1A) and electrostatic (Figure 1C) methods. The results show that youtiao fried at a lower temperature (120 \({}^{\circ}\)C) for 4 min would not incur as strong Maillard reaction as deep-fried (Figure 1A) and the electrostatic (Figure 1C) method at 180 \({}^{\circ}\)C for 4 min. The dough that was not stretched before vacuum frying showed rising in its width but not in its length (Figure 1E) when compared with the control (Figure 1A). The appearance of vacuum fried youtiao showed no difference (Figure 1E,K) whether or not potassium aluminum sulfate was added (Figure 1F,L). Therefore, vacuum frying should be used when products are expected to be lighter in color. The results show that potassium aluminum sulfate might react with sodium bicarbonate at temperatures higher than 120 \({}^{\circ}\)C (Figure 1). Table 1 shows that the pH of youtiao with potassium aluminum sulfate frying in vacuum fryer is lower than without potassium aluminum sulfate addition (\(p<0.05\)). Potassium aluminum sulfate is a slow acting acidulant; it may react with sodium bicarbonate at 180 \({}^{\circ}\)C and release carbon dioxide to raise the crumb after the youtiao crust forming. The youtiao samples without potassium aluminum sulfate addition, the pH of youtiao is higher than that of potassium aluminum sulfate is added. Therefore, more Maillard reaction might occur with deep-frying (Figure 1B) and electrostatic frying (Figure 1D) at a higher pH than with the addition of potassium aluminum sulfate (Figure 1A,C). Moreover, the appearance of the youtiao crust of samples B and D in Figure 1 is darker than that of Sample A and C. The Maillard reaction associated with the decreased solution pH when comparing trials, including acetic acid, formic acid, glyoxal, and pyruvatehyde (S  
Figure 2 shows the fat content of youtiao when fried by different methods. The control group (deep-frying) with potassium aluminum sulfate had an oil content of 13.36% while the youtiao fried by the vacuum frying methods had a higher oil content (20.73%) (Figure 2). [PERSON] et al.