Ultrasound-assisted extraction of pectins from grape pomace using citric acid: A response surface methodology approach

•Pectin was obtained from grape pomace by power ultrasound and citric acid.•Pectins were extracted at different temperature, time and pH.•Extraction yield, molecular weight and degree of esterification of pectins were evaluated.•Pectin extraction process was optimized by response surface methodology.•Maximum extraction yield of pectin was achieved at 75 °C for 60 min and pH 2.0.

An ultrasound-assisted procedure for the extraction of pectins from grape pomace with citric acid as the extracting agent was established. A Box–Behnken design (BBD) was employed to optimize the extraction temperature (X1: 35–75 °C), extraction time (X2: 20–60 min) and pH (X3: 1.0–2.0) to obtain a high yield of pectins with high average molecular weight (MW) and degree of esterification (DE) from grape pomace. Analysis of variance showed that the contribution of a quadratic model was significant for the pectin extraction yield and for pectin MW whereas the DE of pectins was more influenced by a linear model. An optimization study using response surface methodology was performed and 3D response surfaces were plotted from the mathematical model. According to the RSM model, the highest pectin yield (∼32.3%) can be achieved when the UAE process is carried out at 75 °C for 60 min using a citric acid solution of pH 2.0. These pectic polysaccharides, composed mainly by galacturonic acid units (<97% of total sugars), have an average MW of 163.9 kDa and a DE of 55.2%. Close agreement between experimental and predicted values was found. These results suggest that ultrasound-assisted extraction could be a good option for the extraction of functional pectins with citric acid from grape pomace at industrial level.