Abstract：Liquid smoke was prepared by dry distillation (anaerobic pyrolysis) of red willow twigs. The effects of dry distillation temperature, dry distillation time and wood thickness on the yield, phenol content and carbonyl compound content of liquid smoke were investigated by the combined use of one-factor-at-a-time method and response surface methodology (RSM). Based on the obtained results, the optimal combination of processing parameters was determined. Further, the effect of retorting temperature on the color of the liquid smoke prepared with the optimized processing conditions was evaluated along with the effect of adsorption-based refining on its physicochemical properties. Dry distillation at 402.22 ℃ for 75.66 min and a wood thickness of 0.627 cm were found to be the optimal conditions. Under these conditions, the yield of liquid smoke was 33.082%. The contents of phenolics and carbonyl compounds in the obtained product were 10.066 mg/mL and 14.35 g/100 mL, respectively. The experimental values were consistent with the predicted ones. The lightness value (L*) of liquid smoke declined with increasing retorting temperature, and so did the yellowness value (b*), chromaticity value and hue. However, the opposite trend was observed for the redness value (a*) (P < 0.05). As retorting temperature rose, the liquid smoke changed from yellowish to brown, and the lowest total color difference (ΔE) was observed at a retorting temperature of 380 ℃. The bright color of the product prepared under this condition was the closest to that of a commercial one. Refining by adsorption onto macroporous resin and walnut shells had no impact on the pH value of liquid smoke despite reducing the contents of benzo(a)pyrene, phenolics and carbonyl compounds in liquid smoke and its yield (P < 0.05). The content of benzo(a)pyrene in the liquid smoke prepared in this study was far below the Chinese national standard limit (0.5 μg/kg).
2021, Vol. 35 
