Effect of Pomace Drying on Apple Pectin

Abstract

The effect of temperature used for drying apple pomace on apple pectin characteristics, including chemical composition, color and gelpoint temperature ( T g) was determined. Pomace was obtained from commercial Granny Smith apples and dried in a rotary drier at different air temperatures ( T dr = 60, 70, 80 and 105 °C). Pectin was extracted from dried pomace in nitric acid solution (pH = 2.5) at 80 °C. Major minerals in apple pectin were Ca>Na>Mg. Galacturonic acid content (% AGA=60.6±1.8) was practically unaffected by drying temperature. Conversely, T dr affected both the degree of methoxylation (DM) and the molecular weight ( M w ) of extracted pectin. M w was estimated by applying the Mark Houwink – Sakurada equation, through determination of intrinsic viscosity of pectin solutions. M w reduced with T dr from approximately 122,000 (60°C) to 57,000 (105°C). Pectin color, as Hunter ΔE, was also affected by T dr. A lighter color was obtained at 80°C. The higher gelpoint value ( T g= 80°C) was obtained with pectin from pomace dried at 80°C. Gelpoint was shown to be more sensitive to T dr than other quality parameters: while DM had the same value both at 80 and 105°C, minimum T g occurred at the higher temperature. T g was also very sensitive to pH.