CHLOROGENIC ACID CONTENT OF FRESH AND PROCESSED POTATOES DETERMINED BY ULTRAVIOLET SPECTROPHOTOMETRY

Chlorogenic acid is reported to be involved in preharvest defenses of the potato plant against fungi and insects, in postharvest browning, and in after-cooking blackening, all of which affect quality and safety. As part of a program of potato improvement, HPLC and ultraviolet spectroscopy were evaluated to measure the chlorogenic content of commercial and experimental potatoes, of parts of the potato plant, and of processed potato products. HPLC analysis appears to be less satisfactory because chlorogenic acid undergoes a time- and light-dependent change in the methanolic and ethanolic extracts of potatoes used. The decrease of the chlorogenic acid peak on chromatograms was accompanied by a corresponding increase of a new peak. Use of ultraviolet spectrophotometry to estimate chlorogenic acid by contrast appears to be reproducible. Recoveries of spiked samples measured by UV were higher than those measured by HPLC. Thus, our results suggest that the UV method may have advantages over HPLC. Seven varieties of potatoes contained from 10 to 19 mg of chlorogenic acid/100 g of fresh weight. The experimental potato plant NDA 1725 contained 754 mg/100 g of fresh weight for sprouts, 224 mg/100 g for leaves, 26 mg/100 g for roots, and 17 mg/l00 g for tubers. The relative concentrations paralleled those of the glycoalkaloids alpha-chaconine and alpha-solanine. Oven-baked potatoes contained 0% of the original amount of chlorogenic acid, boiled potatoes 35%, and microwaved potatoes 55%. Commercially processed french-fried potatoes, mashed potato flakes, and potato skins contained no chlorogenic acid. The absence of chlorogenic acid was confirmed by ultraviolet spectrophotometry and thin-layer chromatography. The significance of these findings for plant physiology, food quality, and food safety is discussed.