Optimization of microwave-assisted extraction of pectin from pineapple peel

Abstract

Pineapple peel has the potential to become one of the sources for pectin production due to its high pectin content in its dietary fibre composition. Pectin has been widely used in food industry as food thickener, stabilizer, emulsifier and gelling agent. The conventional extraction process with long operating hours at high temperature has been identified to cause thermal degradation of pectin molecules. Microwave technology application in pectin extraction is able to expedite the extraction process and produce higher yield. Therefore, this study was conducted to optimize the microwave-assisted extraction (MAE) process of pineapple peel pectin. The extracted pectin from optimal condition was subjected to physical characterization and chemical and physicochemical properties evaluation and it was also compared to the commercial pectin. Preliminary studies on the best solvent for pectin extraction from pineapple peel showed that hot solvent sulphuric acid resulted in higher recovery in pectin yield. The optimization of MAE of pectin from pineapple peel was performed using Box-behnken design under the response surface method. The optimum operating conditions obtained were pH 1.52 of solvent, 1:10 (w/v) of solid to liquid ratio and 600 W of microwave power with 2.43 ± 0.03 % (w/w) of pectin yield and 54.61 ± 0.21 % (w/w) of anhydrouronic acid (AUA) content. Under these optimal conditions, the degree of esterification (DE) of pectin was 63.93 ± 0.30 % (w/w). The flow behaviour of pineapple peel pectin solutions at low concentration exhibited the Newtonian behaviour whilst at higher concentration it exhibited the pseudo-plastic behaviour. The elevation of temperature caused the pectin solution viscosity to decrease. The emulsifying activity of extracted pectin was 45 % and the emulsion prepared from pineapple peel pectin has high stability at 4 °C with 93.75 % and 88.24 % at 25 °C, after 30 days of storage. The Fourier transform infrared spectrum showed that the extracted pineapple peel pectin contained the same functional groups that exist in the commercial pectin. Through this study, it can be proven that extraction by using MAE could provide higher quantity and better quality of pectin from pineapple peel. Moreover, pectin produced using pineapple peel has comparable DE value, flow behaviour of pectin solution and emulsifying properties, to the commercial pectin. Hence, pineapple peel can be a potential source for pectin production with some extended studies in sample pre-treatment and pectin purification process.