Effects of Roasting on Bioactive Components and Volatile Compounds of Prunus tangutica Kernels

Abstract

Prunus tangutica is an underused wild nut of the Chinese highlands. Its kernels are rich in polyphenols and flavonoids but also contain amygdalin, so debittering must precede roasting, and how the two steps act together is not known. This study determined the effects of debittering and of roasting temperature and time on the bioactive components, antioxidant capacity and volatile profile of P. tangutica kernels from Diebu, Gansu Province, roasted at 100–180 °C for 10–30 min. Debittering markedly reduced polyphenols (from 0.21–0.36 to 0.09–0.27 mg GAE/g) and flavonoids (from 0.57–1.87 to 0.10–0.63 mg RE/g). Both declined as temperature and time increased, whereas antioxidant capacity rose under intense roasting. FRAP peaked at 180 °C/20 min in non-debittered samples and DPPH radical-scavenging activity at 180 °C/30 min in debittered samples, suggesting that Maillard reaction products may partially offset the loss of native antioxidants. Roasting strongly promoted pyrazine formation (2,5-dimethylpyrazine rose from 28.77 to 3909.28 µg/kg) but also increased benzaldehyde and benzyl cyanide, the thermal degradation products of amygdalin, at 180 °C/30 min. Of the conditions tested, 160 °C/30 min was the most suitable for debittered kernels, and 120 °C/30 min was the most suitable for non-debittered kernels; no condition is proposed for the direct consumption of non-debittered kernels, because residual cyanogenic compounds were not quantified.