Tri-frequency ultrasound as pretreatment to infrared drying of carrots: impact on enzyme inactivation, color changes, nutrition quality parameters and microstructures

Abstract

The effects of tri-frequency ultrasound as pretreatment on the peroxidase (POD) inactivation and infrared drying attributes of carrots were studied in the temperature range of 60–80 °C. Thermosonication (TS) treatment reduced 65.21, 73.33 and 81.43% POD activity after 5 min for the temperatures at 60, 70 and 80 °C, respectively, which were all higher than hot water (HW) blanching treated samples. The first-order kinetics fitted well for the POD inactivation curves. Similar retention ranges of vitamin C (VC) were observed after TS (88.41–82.51%) and HW (91.91–88.75%) treatments at the studied range of temperatures. Compared to HW treated samples, drying times of thermosonicated carrot slices were shortened by 13.6, 15 and 15.8% for blanching temperatures at 60, 70 and 80 °C, respectively. The aid of ultrasound showed a positive effect on the rehydration ration (RR) of samples. Sonicated dried samples exhibited higher hardness compared with thermal dried samples. No significant variation (p > 0.05) in the total color difference (ΔE) was attained for dried carrot slices pretreated by TS and HW processes.

Multi-frequency power ultrasound as a novel approach improves intermediate-wave infrared drying process and quality attributes of pineapple slices

“…The increase in a* and b* values depicts that a certain extent of non-enzymatic browning (Maillard reaction) took place due to sample exposure to hot air [40] . US and US-OD improved the brightness of samples compared to the control and aligns with the findings of Rani & Tripathy [47] and Guo et al [27] . However, untreated samples had a higher a* value (redness) than US and US-OD groups but smaller than US-ET samples.…”

“…It is worth noticing that TFU treatment of US samples had water uptake similar to that of DFU in ethanol. Guo et al [27] , Xu et al [25] , and Zhou et al [31] have also demonstrated the positive effect of multi-frequency ultrasound on the rehydration of agro-products. Generally, ultrasound was found to improve the reconstitution of dried samples due to the rupture of cell walls [40] , [49] , [58] .…”

“…Likewise, Xu et al [25] reported for strawberry slices that DFU (20/40 kHz) decreased 50% of the drying time while time reduction at the mono-frequency modes of 20 kHz and 40 kHz were 15.25% and 32.2%, respectively. Besides, TFU (20/28/40 kHz) reduced the infrared drying times of carrots by 15–25% [27] .…”

“…In addition, DR curves were in the order: US-ET > US > US-OD > Control, and aligns well with the observation aforementioned for MR and drying time. Zhou et al [31] , Xu et al [25] , and Guo et al [27] have recently found that multi-frequency ultrasound enhances drying kinetics and reduces the drying time of scallion (54.5%), strawberry (40.68–50%), and carrot slices (13.6–15.8%), respectively.…”

“…Hence, recently, the combination of two or more frequencies (multi-frequency ultrasound) has gained momentum. This strategy aims to improve sound resonance, increase the number and the radius of cavitation bubbles, uniformize bubble dispersion, and intensify their implosion strength [25] , [26] , [27] . Under such high sonochemical energy, violent microjets and shock waves resulting from cavitation maximize cell distortion and improve moisture diffusion during the subsequent drying process compared to the single frequency mode.…”