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 mu g/g), alkanes (11.69-70.01 mu g/g), and terpenes (5.89-47.93 mu g/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.

Automated summary

This study employed steam blanching, high-humidity hot air impingement blanching, and vacuum-steam pulsed blanching to significantly improve the efficiency and quality of dried peony flowers. Blanching pretreatment led to reductions in drying time, energy consumption, browning degree, and shrinkage ratio, while enhancing the retention levels of bioactive compounds in the dried samples.