No. 1 to 8 youtiao samples were randomly purchased from eight
different locations including food factories, popular chain restaurants,
school cafeterias, and representative supermarkets in
Shanghai, China, from the years 2012 to 2014. We collected 3e5
batches of samples from each location for analysis. Samples from
each batch were mixed prior to analysis. No. 9 and 10 samples were
prepared in the laboratory. Origins and frying oils of the samples
are shown in Table 1.
The ingredients for lab-made youtiao included 500 g of wheat
flour, 8.5 g of salt, 9.5 g of sodium bicarbonate, 8.6 g of aluminum
potassium sulfate, and 270 ml of deionized water. Solutions of salt,
sodium bicarbonate, and aluminum potassium sulfate in deionized
water were added to the flour. All ingredients were kneaded for
5e6 min to form a soft elastic structure and smooth skin. Then the
dough was conditioned at 20 C for 4e6 h. After conditioning, the
dough was rolled out and cut into pieces of 8 cm length and 2.5 cm
width. Every two pieces were stacked, pressed on the center with a
wooden rod, stretched to 25 cm long from both ends, and then
deep-fried at 180 C for 130 s.