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 (Tg) was determined. Pomace was obtained from commercial Granny Smith apples and dried in a rotary drier at different air temperatures (Tdr = 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, Tdr affected both the degree of methoxylation (DM) and the molecular weight (Mw) of extracted pectin. Mw was estimated by applying the Mark Houwink – Sakurada equation, through determination of intrinsic viscosity of pectin solutions. Mw reduced withTdr from approximately 122,000 (60°C) to 57,000 (105°C). Pectin color, as Hunter ΔE, was also affected by Tdr. A lighter color was obtained at 80°C. The higher gelpoint value (Tg= 80°C) was obtained with pectin from pomace dried at 80°C. Gelpoint was shown to be more sensitive to Tdr than other quality parameters: while DM had the same value both at 80 and 105°C, minimumTg occurred at the higher temperature. Tg was also very sensitive to pH.