Determining Phenolic Compound Content in Apple Peel with HPLC–MS/MS

A study published in Food & Function (1) investigated whether edible peels from autochthonous and commercial apple cultivars could also be used as a natural matrix of phenolic bioactive compounds for different industrial applications. Researchers analyzed polyphenols using high performance liquid chromatography coupled with tandem mass spectrometry (HPLC–MS/MS) following a method previously developed by the researchers (2).

Diabetes mellitus, a chronic disease, develops when pancreatic islet β-cells fail to produce insulin or when the body becomes resistant to insulin, leading to deficient action in sensitive tissues (3). It contributes to high blood glucose levels, which induce a rise in reactive oxygen species (ROS) and inflammation, leading to long-term damage of hyperglycaemia-sensitive cells in various organs and tissues (4). The World Health Organization (WHO) classifies hyperglycaemic disorders into diabetes mellitus type 1, type 2, and gestational diabetes, with type 2 diabetes accounting for 90% of all diabetes cases; type 2 diabetes occurs because of excess body weight, sedentary behavior, and dietary changes (5).

One of the most common components in plant-derived foods is polyphenols (6)—phenolic compounds with a survival and antioxidant function as secondary metabolites in plants (7). These phenolic compounds may help in the prevention of metabolic and non-communicable diseases such as type 2 diabetes because of their antiradical and anti-inflammatory properties. These properties are associated with specific antidiabetic properties such as enzyme inhibitory properties, anti-glycation activity, improvement of beta cell function and insulin resistance, as well as regulation of carbohydrate metabolism, among others (8).

The fruit and vegetable processing industries generate increasing amounts of waste, with 25–30% of peels discarded (9). The United Nations Food and Agriculture Organization (FAO) estimate that 1.3 billion tons of food are lost or wasted globally each year (10). Phenolic compounds from this huge volume of plant residue product may be extracted and transformed into health-promoting ingredients. These compounds could support the development of innovative products, including nutraceuticals and food supplements, as well as cosmetics or medicinal products (11), potentially providing a wide variety of phytochemicals as hypoglycaemic drugs to prevent type 2 diabetes (12,13). 

Researchers collected six different varieties of fresh apples (Pinova and Verde Doncella as commercial samples; Esperiega de Ademuz, Manzana Helada, Amarilla de Octubre, and Borau 01 as indigenous apple varieties) for experimentation in Huesca, Aragon (Spain). They determined that all six varieties were rich sources of phenolic compounds (particularly flavonols, anthocyanins, flavan-3-ols, dihydrochalcones, and cinnamic acids). The samples showed antidiabetic and antioxidant properties without altering cell viability at physiological concentrations. Bioassays showed that the indigenous local apple variety known as Amarilla de Octubre showed the highest phenolic content and the lowest IC₅₀ value in the bioassays, which suggests its hypothetical use in nutraceutical or pharmaceutical product development for type 2 diabetes prevention or treatment, as well as for certain phytochemical extraction (1).

Woman peeling apple. © familylifestyle - stock.adobe.com

References

1. Cano-Lou, J.; Millán-Laleona, A.; Candrea, R.; et al. Apple Peels as an Edible Source of Phenolic Bioactive Compounds with Antidiabetic and Antiglycation Properties. Food Funct. 2025,DOI: 10.1039/d4fo05241b

2. Mustafa, A. M.; Angeloni, S.; Abouelenein, D.; et al. A New HPLC-MS/MS Method for the Simultaneous Determination of 36 Polyphenols in Blueberry, Strawberry and Their Commercial Products and Determination of Antioxidant Activity. Food Chem. 2022, 367, 130743. DOI: 10.1016/j.foodchem.2021.130743

3. Zheng, Y.; Ley, S. H.; Hu, F. B. Global Aetiology and Epidemiology of Type 2 Diabetes Mellitus and Its Complications. Nat. Rev. Endocrinol. 2018,14 (2), 88–98. DOI: 10.1038/nrendo.2017.151

4. Rendra, E.; Riabov, V.; Mossel, D. M.; et al. Reactive Oxygen Species (ROS) in Macrophage Activation and Function in Diabetes. Immunobiology 2019, 224 (2), 242–253. DOI: 10.1016/j.imbio.2018.11.010

5. Health topics: Diabetes. World Health Organization website.https://www.who.int/health-topics/diabetes#tab=tab_1 (accessed 2024-10-15).

6. Guasch-Ferré, M.; Merino, J.; Sun, Q.; Fitó, M.; Salas-Salvadó, J. Dietary Polyphenols, Mediterranean Diet, Prediabetes, and Type 2 Diabetes: A Narrative Review of the Evidence. Oxid. Med. Cell Longev. 2017, 6723931. DOI: 10.1155/2017/6723931

7. Manach, C.; Scalbert, A.; Morand, C.; Rémésy, C.; Jiménez, L. Polyphenols: Food Sources and Bioavailability. Am. J. Clin. Nutr. 2004, 79 (5), 727–747. DOI: 10.1093/ajcn/79.5.727

8. de Paulo Farias, D.; de Araújo, F. F.; Neri-Numa, I. A.; Pastore, G. M. Antidiabetic Potential of Dietary Polyphenols: A Mechanistic Review. Food Res. Int. 2021, 145, 110383. DOI: 10.1016/j.foodres.2021.110383

9. Nirmal, N. P.; Khanashyam, A. C.; Mundanat, A. S.; et al. Valorization of Fruit Waste for Bioactive Compounds and Their Applications in the Food Industry. Foods 2023, 12 (3), 556. DOI: 10.3390/foods12030556

10. Gustavsson, J.; Cederberg, C.; Sonesson, U.; van Otterdijk, R.; Meybeck, A. Global Food Losses and Food Waste - Extent, Causes and Prevention Save Food! Congress, 2011. https://www.researchgate.net/publication/285683189_Global_Food_Losses_and_Food_Waste-_Extent_Causes_and_Prevention (accessed 2025-03-12).

11. De la Peña-Armada, R.; Mateos-Aparicio, I. Sustainable Approaches Using Green Technologies for Apple By-Product Valorisation as A New Perspective into the History of the Apple. Molecules 2022, 27 (20), 6937. DOI: 10.3390/molecules27206937

12. Dinda, B.; Dinda, M.; Roy, A.; Dinda, S. Dietary Plant Flavonoids in Prevention of Obesity and Diabetes. Adv. Protein Chem. Struct. Biol. 2020, 120, 159–235. DOI: 10.1016/bs.apcsb.2019.08.006

13. Weaver, C. M. Bioactive Foods and Ingredients for Health. Adv. Nutr. 2014, 5 (3), 306S-311S. DOI: 10.3945/an.113.005124