Antioxidant capacity, biochemical composition, and mineral composition of leaves in two apple species (Malus domestica Borkh. and M. kirghisorum Al. Fed. & Fed.).

Background: Apple leaves are a rich source of bioactive compounds such as phenolics, flavonoids, and essential minerals, which exhibit significant antioxidant and therapeutic properties. This study focuses on comparing the biochemical composition, antioxidant capacity, and mineral contents of Malus domestica Borkh. cultivars and M. kirghisorum Al. Fed. & Fed. genotypes. The goal is to identify potential health-promoting compounds and establish a basis for utilizing apple leaves as a sustainable resource in the food, pharmaceutical, and cosmetic industries.

Results: The study revealed significant biochemical and nutritional variation among the genotypes. Total antioxidant capacity ranged from 36.00 in 'A12' to 59.50% in 'Starking Delicious'. Total phenolic content varied between 70.42 in 'A28' and 147.45 mg GAE/100 g in 'Granny Smith', while total flavonoid content ranged from 15.43 in 'A28' to 38.66 mg QE/100 g in 'A16', demonstrating considerable variability in bioactive compound composition. Correlation matrix analysis identified several significant relationships. Total phenolics and total flavonoids showed a positive correlation (r = 0.52**), while calcium strongly correlated with magnesium (r = 0.79**), potassium (r = 0.52**), and phosphorus (r = 0.52**), underscoring their physiological interconnections. Multiple regression analysis clarified key traits. Total phenolic content was positively influenced by total flavonoids (β = 0.52, p < 0.00). Calcium was strongly associated with magnesium (β = 0.52, p < 0.00) and sodium (β = 0.46, p < 0.00), reflecting their synergistic roles in cellular and metabolic functions. Principal component analysis revealed that the first three components explained 57.80% of the total variation. PC1 (30.56% variance) was predominantly associated with calcium, potassium, phosphorus, and magnesium. PC2 (14.16%) highlighted the relationship between manganese and total antioxidant capacity, while PC3 (13.08%) reflected the influence of lead, total phenolics, and total flavonoids. Heat map analysis indicated that the calcium, phosphorus, sulfur, phenolic compounds, and antioxidant activities in subgroup A1 suggest that the genotypes may be beneficial for health. Additionally, the accumulation of heavy metals such as lead, nickel, and aluminum in subgroup B1 could pose a health risk; however, the genotypes 'A18', 'A21', 'A21-1', and 'A22' possess the capacity to reduce this accumulation.

Conclusions: The results highlight the nutritional and therapeutic potential of apple leaves as a natural source of antioxidants and essential minerals. In particular, the genotypes 'A21-1' and 'A16' stand out due to their high content of bioactive compounds and nutrients, offering promising prospects for further research and applications. These findings contribute to the conservation of wild apple genetic resources and their potential for industrial use.

Clinical Trial Number: Not applicable.