Analysis of protein amino acids, non-protein amino acids and metabolites, dietary protein, glucose, fructose, sucrose, phenolic, and flavonoid content and antioxidative properties of potato tubers, peels, and cortexes (pulps)

Authors: CHOI, SUK-HYUN - Seowon University, Korea; KOZUKUE, NOBUYUKI - Seowon University, Korea; KIM, HYUN-JEONG - Keimyung University; Friedman, Mendel

Submitted to: Journal of Food Composition and Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/24/2016
Publication Date: 5/25/2016
Citation: Choi, S., Kozukue, N., Kim, H., Friedman, M. 2016. Analysis of protein amino acids, non-protein amino acids and metabolites, dietary protein, glucose, fructose, sucrose, phenolic, and flavonoid content and antioxidative properties of potato tubers, peels, and cortexes (pulps). Journal of Food Composition and Analysis. 50(1):77-87. doi:10.1016/j.jfca.2016.05.011.

Interpretive Summary: To our knowledge, this is the first report on the analysis of the composition of whole potato tubers, peels, and pulps of commercial potatoes in a single study. The described methodology could serve as a model for future studies designed to elucidate the role of whole potatoes, potato peels, and pulps in nutrition, health-promoting properties, and in food safety, and industrial uses. The data on the protein and free amino acid content of the 16 freeze-dried powders evaluated in this study suggest that those with the highest protein content might contribute to dietary protein and highlight the need to evaluate their nutritional quality. The observed range in asparagine content of the whole potatoes, but not of the peels or cortexes, implies that potatoes cultivars with a low asparagine content are expected to result in low acrylamide content after frying or baking. The observed content of the bioactive phenolic compounds and flavonoids suggests that consumers could choose those cultivars with a high content of phenolic compounds and presumably high antioxidative properties. The high-phenolic peels, considered as a waste byproduct of potato processing, merit further study for their health-promoting properties and industrial uses.

Technical Abstract: The composition and antioxidative activity of whole potato tubers from five Korean cultivars, three peels from one cultivar, and eight pulps (cortexes) after peeling from six different cultivars were evaluated. The following characteristics were determined: the dimensions and water content of whole tubers; protein content consisting of protein and free amino acids by an automated Kjeldahl N assay; free nonprotein amino acids and metabolites by ion-exchange chromatography (HPLC); individual sugars (fructose, glucose, and sucrose) by HPLC; phenolic compounds by HPLC and LC/MS; total phenolics and flavonoids by colorimetry; and antioxidative properties by ABTS, DPPH, and FRAP assays. The results demonstrate differences and similarities in the content of nutritional and bioactive compounds and in their bioactivities from whole potatoes, peels, and pulps. The present study reports for the first time the analysis of multiple potato nutrients (free amino acids, proteins, carbohydrates) and bioactive components (nonprotein amino acids, metabolites, phenolic compounds, flavonoids) as well the antioxidative properties of potato tubers, peels, and pulps derived from the same tubers. The described methods are expected to facilitate the analysis of commercial and newly-developed whole potato cultivars, peels, and pulps and relate their composition to their reported nutritional, health-promoting, and industrial properties.