Polyglycerol polyricinoleate and lecithin stabilized water in oil nanoemulsions for sugaring Beijing roast duck: Preparation, stability mechanisms and color improvement

Traditional Beijing roast duck often suffers from uneven color and high sugar content after roasting. Water-in-oil (W/O) nanoemulsion is a promising alternative to replace high concentration of sugar solution used in sugaring process according to similarity-intermiscibility theory. Herein, 3% of xylose was embedded in the aqueous phase of W/O emulsion to replace 15% maltose solution. W/O emulsions with different ratios of lecithin (LEC) and polyglycerol polyricinoleate (PGPR) were constructed by high-speed homogenization and high-pressure homogenization. Distribution and penetration extent of solutions and emulsions through the duck skin, as well as the color uniformity of Beijing roast duck were analyzed. Emulsions with LEC:PGPR ratios of 1:3 and 2:2 had better stability. Stable interfacial film and spatial structure were important factors influencing emulsion stabilization. The stable W/O emulsions could more uniformly distribute onto the surface of duck skin and longitudinally penetrate through the skin than solutions.

Effects of W/O Nanoemulsion on Improving the Color Tone of Beijing Roast Duck

Traditional Beijing roast duck is often brushed with a high concentration of maltose solution (15% w/v) and shows ununiform color after roasting. A novel W/O nanoemulsion was applied to improve the color tone of Beijing roast ducks and, meanwhile, reduced the amount of sugar. For the W/O emulsion, 3% (w/v) xylose solution as the aqueous phase, soybean oil as the oil phase, and polyglycerol polyricinoleate (PGPR) and whey protein isolate (WPI) as co-emulsifiers were fabricated by high-pressure homogenization. Particle size measurement by Zetasizer and stability analysis by Turbiscan stability analyzer showed that WPI as co-emulsifier and internal aqueous phase at pH 9 decreased the droplet size and improved the emulsion stability. In addition, by color difference evaluation, the W/O nanoemulsion improved the Maillard reaction degree and color tone of Beijing roast duck. The molecular structure and key composition of pigments on the surface of Beijing roast duck skins were also identified and characterized by UV-vis spectroscopy and UHPLC-MS. This study creatively offers theoretical guidance for increasing applications of W/O-nanoemulsion-based Maillard reaction in the roast food industry, especially for the development of reduced-sugar Beijing roast duck with uniform and desired color satisfying consumers' acceptance and marketability.

[Atmospheric Pollutant Emission Characteristics from the Cooking Process of Traditional Beijing Roast Duck]

As one of the characteristics of traditional food in Beijing, there is a significant difference between roast duck and other foods in the cooking process, in that fruit trees are used as fuel in the former. However, system research about the emission characteristics of this food source has not been done domestically. In order to grasp such food source emission characteristics and provide technical basis for pollution control, we selected the representative roast duck restaurant in Beijing and studied the emission characteristics of atmospheric pollutants in the cooking process of roast duck. The results showed that the emission concentrations of cooking fumes, particulate matter, volatile organic compounds (VOCs), and aldehyde and ketone compounds were (0.74±0.45), (15.32±7.93), (7.60±3.41), and (1.22±0.59) mg·m^-3, respectively. The emission concentration of particulate matter was much higher than that of cooking fumes. The VOC component composition was very complex, containing alkanes, alkenes, aromatic hydrocarbons, and oxygen VOCs, such as aldehydes, ketones, alcohols, ester compounds, and halogenated hydrocarbons, with the highest concentrations of 3-methylfuran, ethanol, and methyl acetate. The main components of aldehyde and ketone compounds were acetaldehyde, formaldehyde, and acrolein, of which C1-C3 compounds were 72.27%.