Glycoalkaloid, phenolic, and flavonoid content and antioxidative activities of conventional nonorganic and organic potato peel powders from commercial gold, red, and Russet potatoes

Highlights

• Analysis of glycoalkaloids, phenolics, and flavonoids in potato peels.

• α-Chaconine, α-solanine, caffeic, chlorogenic, and chlorogenic acid isomer content.

• Determination of antioxidative properties of peels by three methods.

• Methods can relate composition of peels to food. medical and industrial uses.

Abstract

Potato peels from the large-scale peeling of potatoes are a source of bioactive compounds. We determined the content of the glycoalkaloids α-chaconine and α-solanine, individual and total phenolics compounds, and total flavonoids extracted from three peels prepared from conventional and three from organic commercial gold, red, and Russet potatoes as well as determining their antioxidant activities using three different methods. Glycoalkaloids and individual phenolic compounds (caffeic acid, chlorogenic acid, and chlorogenic acid isomer) were determined using HPLC and LC–MS, and total phenolic and flavonoid content by colorimetry. There was a wide variation in the content of total glycoalkaloids, phenolic compounds, flavonoids, and antioxidative activities, as indicated by the following ratios for the total organic to nonorganic glycoalkaloids: gold, 3.89; Russet, 2.43; and red, 0.50. The corresponding phenolics and flavonoid ratios indicated a narrower range. The described methods could be used to determine the composition and antioxidative activities of peels derived from other potato cultivars, taking into account their methods of growth and postharvest storage, and aid in compositional, nutritional, medical, and industrial studies on potato peel, to relate their composition to their many described applications.

Introduction

The annual world production of about 1.3 billion tons of food waste that includes potato peel could be used to provide a useful and inexpensive source of high-value compounds for industrial, medical, and food uses (Matharu et al., 2016), as illustrated with the following selected examples for potato peel, the focus of this study.

Potato peels available from large-scale peeling of potatoes from the production of French fries, potato chips, and other edible potato products can serve a source for biofuel and biomanure (Arapoglou et al., 2010, Liang and McDonald, 2014, Chintagunta et al., 2016), methane (Liang and McDonald, 2015), lactic acid (Liang et al., 2015), and other high-value compounds (Matharu et al., 2016), glycoalkaloids and phenolic compounds (Wu et al., 2012, Hossain et al., 2014, Hossain et al., 2015, Silva-Beltrán et al., 2017), and as an effective biosorbent for the removal of toxic hexavalent chromium from a water effluent (Mutongo et al., 2014).

Potato peel extracts have also been investigated for their medical properties. For example, they have been reported to protect human erythrocytes against oxidative damage in vitro (Singh and Rajini, 2008), protect against carbon-tetrachloride-induced liver injury in rats (Singh et al., 2008), exhibit anti-inflammatory effects in vitro (Kenny et al., 2013), have antidiabetic effects in rodents (Singh et al., 2005, Arun et al., 2015), reduce toxicity of cholesterol oxidation products in rats (Hsieh et al., 2016), protect against atopic dermatitis (Yang et al., 2015), and exhibit antimicrobial activities in vitro (Sinha and Dua, 2016). Potato peel dressings promote wound healing in humans caused by burns (Van de Velde et al., 2011), and help in the management of necrotizing fasciitis (Manjunath et al., 2015), a subcutaneous infection with a poor prognosis (Beers, 2006).

There are also uses for potato peel byproducts in the food industry. For example, potato peel extracts retarded lipid peroxidation of irradiated meat (Kanatt et al., 2005), minced mackerel (Sabeena Farvin et al., 2012), and soybean oil (Franco et al., 2016), and improved the nutritional quality of cakes (Ben Jeddou et al., 2017).

Interest in potato glycoalkaloids arises from the fact that they are reported to exhibit both adverse effects at high concentrations that might be potentially harmful to humans and beneficial anticarcinogenic properties (Friedman, 2015). The dual biological functions of potato glycoalkaloids and controversial safe levels are discussed in detail elsewhere (Friedman, 2006, Friedman and Levin, 2016). To our knowledge, there are no recent reports on adverse effects of potato glycoalkaloids in humans. Whether potato glycoalkaloids contribute to the multiple health benefits of potatoes merits study (Visvanathan et al., 2016). Phenolic compounds in potatoes and byproducts also exhibit beneficial antioxidative and health-promoting properties (Friedman, 1997, Vinson et al., 2012, Akyol et al., 2016).

The main objective of the present study was to determine the glycoalkaloid, individual and total phenolic and total flavonoid content as well as the antioxidative effects of potato peel powders prepared from three conventional and three organic store-bought potatoes, using methods adapted from our previous studies (Friedman et al., 2003, Im et al., 2008, Kozukue et al., 2008, Choi et al., 2016). To our knowledge, this is the first such report on peels from organic potatoes.