Antioxidant Capacity, Anthocyanins and Total Phenolics in Purple- and Red-Fleshed Potato (Solanum tuberosum L.) Genotypes

American Journal of Potato Research, Jul/Aug 2005 by Reyes, L F, Miller, J C Jr, Cisneros-Zevallos, L

ABSTRACT

Purple- and red-fleshed potatoes (Solanum tuberosum L.) were evaluated for their total anthocyanin (ACY), total phenolic (PHEN), and antioxidant capacity. The ACY and PHEN compounds were distributed throughout the tubers; however, a higher concentration was found at the stem-end than the bud-end. Although ACY and PHEN concentrations in potato peel were 0.9-to 1.6-fold higher than in potato flesh, overall contribution of the peel to ACY and PHEN contents of a potato slice was ~20%. These observations differ from the widespread idea that phytonutrients are mostly accumulated in the peel of tubers. The ACY and PHEN contents of different purple- and red-fleshed potato genotypes ranged from 11 to 174 mg cyanidin-3-glucoside/100 g fresh weight and from 76 to 181 mg chlorogenic acid/100 g fresh weight, respectively, and were genotype and location dependent. High positive correlations between antioxidant capacity and ACY and PHEN suggest that these compounds are mainly responsible for the antioxidant capacity. These results provide useful and important information for potato breeders and researchers in order to increase the antioxidant capacity and functional value of purple- and red-fleshed potatoes for the food and nutraceutical industries.

RESUMEN

Papas (Solanum tuberosum L.) de pulpa morada y roja, se evaluaron para determinar su contenido total de antocianina (ACY), compuestos fenólicos totales (PHEN) y capacidad antioxidante. Los compuestos ACY y PHEN estuvieron distribuidos por todo el tubércule; sin embargo, se encontró una mayor concentración en el extremo cerca del tallo que en el extreme distal. Aunque las concentraciones en Ia piel del tubércule fueron de 0.9 a 1.6 veces más que en Ia pulpa, el aporte total del ACY y PHEN de la piel de una rodaja de papa fue de aproximadamente 20%. Estas observaciones difleren de la idea generalizada de que los fitonutrientes se acumulan mayormente en la piel de los tubércules. El contenido de ACY y PHEN de los tubérculos de los diferentes genotipo de papa de pulpa morada y roja estuvo entre los limites de 11 a 174 mg de cianidina-3-glucósido/100 g de peso fresco y de 76 a 180 mg de ácido clorogénico/100 g de peso fresco respectivamente dependiendo del lugar y genotipo. La alta correlación positiva entre la capacidad antioxidante y ACY y PHEN sugiere que estos compuestos son principalmente responsables de la capacidad antioxidante. Estos resultados proporcionan información muy importante y útil a los mejoradores e investigadores para incrementar la capacidad antioxidante y el valor funcional de las papas de pulpa morada y roja para el consume y las industrias nutraceúticas.

ADDITIONAL KEY WORDS: antioxidants, distribution, flesh, peel

INTRODUCTION

Purple- and red-fleshed potatoes provide a natural source of phenolic compounds (Reyes et al. 2004; Reyes and Cisneros-Zevallos 2003). Phenolic compounds have been associated with health promotion due to their antioxidant activity (Espín et al. 2000; Velioglu et al. 1998; Simon 1997). The functional properties of purple- and red-fleshed potatoes as natural colorants and antioxidants (Reyes et al. 2004; Reyes and Cisneros-Zevallos 2003; Brown et al. 2000) and the increased concern regarding the toxicological safety of their synthetic counterparts (Bridle and Timberlake 1997; Francis 1989), indicate that potatoes have a potential use for the food and nutraceutical industries. However, there is a need for the selection of genotypes to meet high antioxidant yield requirements.

Previous work on potatoes has shown a longitudinal concentration gradient of ACY and/or PHEN in different cultivars (Lewis et al. 1999; Al-Saikhan et al. 1995). For example, Lewis et al. (1999) observed that, as tubers reached maturity, the concentration of ACY at the stem-end was always higher than at the bud-end. In addition, the observed differences were more marked in smaller than in larger tubers. These observations initiated concern about the adequacy of sampling procedures used when evaluating ACY and PHEN content of purple- and red-fleshed tubers. There has been extensive work on the characterization of specific phenolic compounds present in purpleand red-fleshed potatoes, but much less information is available regarding their antioxidant capacity, limiting the potential interest of breeders and the food and nutraceutical industries. Phenolic acids such as chlorogenic, caffeic, protocatechuic, and p-coumaric acid, among several others, have been identified in purple- and red-fleshed potatoes (Lewis et al. 1998; Rodríguez-Saona et al. 1998). Small amounts of rutin, quercetin, myricetin, kaempferol, naringenin, and some other flavonoids have also been detected (Lewis et al. 1998). The main ACY pigments in purple-fleshed potatoes have been identified as petunidin- and malvidin-3-rutinoside-5-glucosides acylated with p-coumaric or ferulic acid (Fossen and Andersen 2000; Lewis et al. 1998), whereas those in red-fleshed potatoes have been identified as pelargonidin- and peonidin-3-rutinoside-5-glucosides acylated with p-coumaric or ferulic acid (Sachse 1973; Lewis et al. 1998; Naito et al. 1998; Rodríguez-Saona et al. 1998). The p-coumaric acid acylated derivatives from petunidin, malvidin, pelargonidin, and peonidin are referred to as petanin, malvanin, pelanin, and peonanin, respectively.