以商业橘皮果胶为原料，在无水甲醇环境中采用盐酸催化甲酯化反应制备高甲氧基果胶。通过对反应时间、反应温度、料液比以及盐酸添加量的调节，可以制备得到酯化度在90%以上的高甲氧基果胶。分子质量分布结果表明，随着反应温度升高、反应时间延长和盐酸浓度增加，产物的酯化度逐渐提高，但数均分子质量逐渐降低。在料液比1∶50，盐酸添加量0.1 mol/L，温度60℃下反应12 h，产物酯化度达到91.20%，但数均分子质量降低为15.00 kDa。基于极高酯化度果胶所具有的双亲性(甲氧基为疏水基团而羟基为亲水基团)和分子链短的特点，进一步研究了极高酯化度果胶的乳化性质。用高能量法(高速剪切)分别制备了油滴体积分数为10%、20%和30%的纳米乳液，并考察了7 d内乳状液的稳定性、粒径和Zeta-电位变化。结果显示采用极高酯化度果胶可制备得到粒径为3 500 nm的乳状液(油滴体积分数10%～30%)，并具有较好的稳定性。

Methoxylation of commercial citrus pectin in anhydrous methanol catalyzed by HCl was conducted. Reaction conditions including reaction time, temperature, solid-to-liquid ratio (SLR) and HCl concentration were investigated and optimized. High methoxyl pectins with various degree of methoxylation (DM) of >90% were obtained. Results of molecular weight distribution showed that DM was improved with the increase of reaction temperature, reaction time and acid concentration, but the number-average molecular weight was decreased. Particularly, HMP with DM of (91.20±0.13)% was obtained under SLR 1∶50 (w/v) at 60 ℃ with 0.1 mol/L HCl for 12 h, and the Mw was decreased to 15.00 kDa. Furthermore, extremely high DM emulsification properties were studied due to its amphiphilic property (by hydrophobic methoxyl groups and hydrophilic hydroxyl groups) and short molecular length. Nano-emulsions with φ (oil)= 10%-30% were prepared by high energy method (high speed shearing) and their 7-day stability, Zeta-potential and particle size were characterized. Emulsion of 3 500 nm with good stability was produced by high methoxyl pectin with DM of 91.20%.