Effect of thermal processing on the nutritional quality and bioactive potential of sweet chestnuts (Castanea sativa Mill.) grown in Slovakia

Sweet chestnuts (Castanea sativa Mill.) belong to species with a rich nutritional composition. However, their composition can be significantly changed by thermal processing. This study determined the effects of boiling, roasting, microwaving, and steaming on the mineral profile (K, Ca, Mg, P), total polyphenolic content (TPC), DPPH antioxidant activity, and vitamin C levels in chestnuts grown in Slovakia. Although mineral contents varied with thermal processing, no statistically significant differences were found between treatments. Raw chestnuts had a TPC of 2.35 mg GAE/g DW, which increased to 3.65 mg GAE/g DW with microwaving, while boiling caused the greatest reduction (0.91 mg GAE/g DW). The antioxidant activity in raw chestnuts was 4.59 µmol TE/g DW. Following heat treatment, the antioxidant activity values ranked in descending order: steamed > boiled > roasted > microwaved chestnuts. Raw samples had the highest levels of vitamin C (1.341 g/kg DW). Steaming successfully retained it (1.199 g/kg DW), while roasting caused the largest loss (0.779 g/kg DW). Different thermal treatments distinctively impacted chestnut chemical composition. Microwaving and steaming have been shown to be favourable methods for preserving or enhancing the content of bioactive compounds and antioxidant properties. We can conclude that microwave heating is beneficial for TPC but not for antioxidant activity and vitamin C, while steaming is excellent for preserving antioxidant activity and vitamin C. These findings are crucial for optimising processing to preserve the nutritional quality of chestnuts.