Effect of pomace drying on apple pectin

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 v Smith apples and dried in a rotary drier at different air temperatures (T-dr = 60, 70, 80 and 105 degreesC). Pectin was extracted from dried pomace in nitric acid solution (pH = 2.5) at 80 degreesC. 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 degreesC) to 57,000 (105 degreesC). pectin color, as Hunter DeltaE, was also affected by T-dr. A lighter color was obtained at 80 degreesC. the higher gelpoint value (Tg = 80 'C) was obtained with pectin from pomace dried at 80 degreesC. 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 degreesC, minimum T-g occurred at the higher temperature. T-g was also very sensitive to pH.