NMR Characterization of Ten Apple Cultivars from the Piedmont Region.

Giacomo Di Matteo,Luisa Mannina,Mattia Spano,Cinzia Ingallina,Alessandra Baldi,Maria Daglia,Cristina Esposito,Anatoly P Sobolev,Cristina Santarcangelo

doi:10.3390/foods10020289

Abstract

The metabolite profile of ten traditional apple cultivars grown in the Piedmont region (Italy) was studied by means of nuclear magnetic resonance spectroscopy, identifying an overall number of 36 compounds. A more complete assignment of the proton nuclear magnetic resonance (1H NMR) resonances from hydroalcoholic and organic apple extracts with respect to literature data was reported, identifying fructose tautomeric forms, galacturonic acid, γ-aminobutyric acid (GABA), p-coumaroyl moiety, phosphatidylcholine, and digalactosyldiacylglycerol. The chemical profile of each apple cultivar was defined by thorough quantitative NMR analysis of four sugars (fructose, glucose, sucrose, and xylose), nine organic acids (acetic, citric, formic, citramalic, lactic, malic, quinic, and galacturonic acids), six amino acids (alanine, asparagine, aspartate, GABA, isoleucine, and valine), rhamnitol, p-coumaroyl derivative, phloretin/phloridzin and choline, as well as β-sitosterol, fatty acid chains, phosphatidylcholine, and digalactosyldiacylglycerol. Finally, the application of PCA analysis allowed us to highlight possible differences/similarities. The Magnana cultivar showed the highest content of sugars, GABA, valine, isoleucine, and alanine. The Runsé cultivar was characterized by high amounts of organic acids, whereas the Gamba Fina cultivar showed a high content of chlorogenic acid. A significant amount of quinic acid was detected in the Carla cultivar. The knowledge of apple chemical profiles can be useful for industries interested in specific compounds for obtaining ingredients of food supplements and functional foods and for promoting apple valorization and preservation.

Highlights

1 H-1 H TOCSY experiment allowed us to identify the correlation with the CH-4 proton (4.00 ppm), whereas the 1 H-13 C Heteronuclear Multiple Bond Correlation (HMBC) experiment showed the correlation of the CH-3 proton with the C-2 carbon at 105.5 ppm, typical of ketoses
The studies only agree on the fact that fructose seemed to be the most abundant in all apple cultivars, whereas the relative content of glucose and sucrose was highly variable
The presented results show that every local variety has its own chemical profile responsible for the sensorial, nutritional, and health-related properties, and they may be used as sources of specific substances that are utilized as ingredients of health products, such as food supplements, functional foods, and cosmetics

Summary

Introduction

From a nutritional point of view, apples are a low-fat (less than 1%) and low-protein food (less than 1%) [2], whereas sugars represent about 10% of total apple weight, with fructose being the most abundant sugar (6%). Micronutrients, such as minerals (mainly potassium, phosphorus, calcium, and magnesium), vitamins (mainly vitamin C), and secondary metabolites (such as phenolic compounds [3,4]) are present. Piedmont represents today the third largest Italian producer, contributing 225.281 tons of apples to the national production and with an increase of +13% with respect to 2019.

Methods

Results

Discussion

Conclusion