Application of blanching pretreatment in herbaceous peony (Paeonia lactiflora Pall.) flower processing : Improved drying efficiency, enriched volatile profile and increased phytochemical content

Although various techniques have been developed to dry herbaceous peony (Paeonia lactiflora Pall.) flowers, the dried products usually have a low retention level of bioactive compounds, which limits the valorization of peony-derived products. This work is the first to employ steam blanching (SB), high-humidity hot air impingement blanching (HHAIB), and vacuum-steam pulsed blanching (VSPB) before drying to improve the drying efficiency and quality of dried peony flowers. Results showed blanching pretreatment led to significant (p < 0.05) reductions in drying time by 7.02–40.35% and energy consumption by 6.86–39.96%, respectively. The final dried samples also exhibited reductions in browning degree by 30.93–62.89% and shrinkage ratio by 30.05–68.83%, respectively. Based on blanching pretreatment, the retention levels of bioactive compounds in dried samples were significantly (p < 0.05) improved. The dried samples blanched with VSPB possessed the highest contents of gallic acid (76.76 ± 1.75 mg/100 g DW), catechins (0.327 ± 0.010 mg/100 g DW), paeoniflorin (51.00 ± 1.41 mg/100 g DW), total phenolic (85.41 ± 1.81 mg GAE/100 g DW), flavonoid (11.00 ± 0.26 mg RE/100 g DW), and sugar (22.86 ± 0.13 g/100 g DW), thus causing superior antioxidant capacity. Furthermore, a total of 28 volatiles were identified, with alcohols (8.58–166.10 μg/g), alkanes (11.69–70.01 μg/g), and terpenes (5.89–47.93 μg/g) being the dominant contributors to the flavor of dried samples. This work provides insight for researchers to develop dried peony flowers with high added value using an energy-efficient strategy in the future.