Effects of chitosan coating on freeze-drying of blueberry enhanced by ultrasound pre-treatment in sodium bicarbonate medium

Sodium bicarbonate medium ultrasound pre-treatment can enhance the freeze-drying process of blueberries, but the quality of dried products cannot meet the actual production needs. To yield higher quality products, chitosan coating was applied in blueberry sodium bicarbonate medium ultrasound pre-treatment enhanced freeze-drying process. The improvement effect of different chitosan coating methodologies on the procedure of blueberry freeze-drying, enhanced by ultrasound pre-treatment in sodium bicarbonate medium, was investigated. These include: chitosan solution soaking alone (CH-A), chitosan medium ultrasound treatment (US-CH), first sodium bicarbonate medium ultrasound treatment then chitosan solution soaking (US-NaHCO3 + CH) and first sodium bicarbonate soaking followed by chitosan medium ultrasound treatment (NaHCO3 + US-CH). While the treatments that presoaking in sodium bicarbonate solution (NaHCO3-A), water medium ultrasound treatment (US-W) and sodium bicarbonate medium ultrasound treatment (US-NaHCO3) were used as the control groups. Results demonstrated that ultrasound treatment and sodium bicarbonate soaking have positive effect on improving the freeze-drying characteristics of blueberries, while chitosan coating has a negative effect. Chitosan coating has a significant effect on strengthening limit effect of blueberry skin on juice overflow and weakening moisture absorption capacity of dried blueberry. US-NaHCO3 + CH pretreatment yielded the best results for blueberry freeze-drying. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study found that ultrasound treatment and sodium bicarbonate soaking have a positive effect on improving the freeze-drying characteristics of blueberries, while chitosan coating has a negative impact. Chitosan coating strengthens the barrier effect of blueberry skin on juice overflow and weakens the moisture absorption capacity of dried blueberries. The best results for blueberry freeze-drying were achieved with the US-NaHCO3 + CH pretreatment.