Effect of ultrasonic far-infrared synergistic drying on the characteristics and qualities of wolfberry (Lycium barbarum L.)

Application of ultrasonic-enhanced active seed crystals in the removal of sodium oxalate from alumina refinery waste liquor

When organic matter, especially sodium oxalate (Na2C2O4), accumulates to a certain extent, it will seriously affect the alumina production process in the refinery and therefore urgently needs to be removed. This work attempts to illuminate the benefits of ultrasonic intensification of the crystallization process of Na2C2O4, taking the alumina refinery waste liquor, i.e., flat plate washing liquor, as a case study. The effects of different operating parameters (seed crystal addition amount, caustic soda concentration, reaction time, ultrasonic power) on the crystallization behavior and yield are discussed, and it is found that ultrasonic can increase the Na2C2O4 removal rate to 70.4%. The addition of ultrasonic promotes the morphological evolution of Na2C2O4 and is of great significance to the optimization of the components of the precipitated Na2C2O4. Specifically, the proportion of Na2C2O4 in the crystallized product reaches 64% with conventional conditions, while it reaches 77% with ultrasonic conditions. Therefore, ultrasonic can greatly reduce the alkali loss caused by the crystallization process of Na2C2O4 in flat plate washing liquor, which has great economic benefits.

Enhancing peach slices radio frequency vacuum drying by combining ultrasound and ultra-high pressure as pretreatments: Effect on drying characteristics, physicochemical quality, texture and sensory evaluation

To maximally maintain fruits and vegetables quality after harvest, this study used ultrasonic (US) and ultra-high pressure (UHP) techniques as pretreatments for radio frequency vacuum (RFV) drying of peach slices, and investigated the effects of different pretreatments (US, UHP, UHP-US, and US-UHP) on drying characteristics, physicochemical qualities, texture properties, and sensory evaluation of peach slices. Results showed that the drying rate was increased by 15.79 ∼ 54.39 % and the contents of pectin, hemicellulose, total phenolic, total flavonoid, phenolic acids, individual sugar annd antioxidant of the samples were significantly increased after US combined with UHP pretreatment (P < 0.05). US-UHP + RFV dried peach slices obtained brighter color, better texture attributes of hardness, cohesiveness, chewiness, springiness, and resilience. The dehydrated samples pretreated by UHP-US had the best overall acceptance, appearance, and crispness with lower off-odor and sourness compared to the dehydrated peach slices with US and UHP pretreatment. Notably, the highest cellulose and organic acids were found in dehydrated peach slices by control, followed by samples US, and samples with UHP pretreatment. The microstructure showed that the internal organization of peach slices appeared as uniform and regular honeycomb porous structure after US-UHP pretreatment. The findings may provide theoretical reference for the development of energy-efficient and high-quality drying technology for fruits and vegetables.

Drying kinetics prediction and quality effect of ultrasonic synergy vacuum far-infrared drying of Codonopsis pilosula

By using ultrasonic synergy vacuum far-infrared drying (US-VFID), the effects of different conditions on the drying kinetics, functional properties, and microstructure of Codonopsis pilosula slices were studied. The sparrow search algorithm (SSA) was used to optimize the back-propagation (BP) neural network to predict the moisture ratio during drying. With the increase of ultrasonic frequency, power and radiation temperature, the drying time of C. pilosula was shortened. The drying time of US-VFID was 25% shorter than VFID, when radiation temperature was 50°C, ultrasonic power was 48 W, and frequency was 28 kHz. The SSA-BP neural network, the average absolute error prediction was 0.0067. Compared with hot air drying (HAD), the total phenolic content and antioxidant activity of C. pilosula by US-VFID were increased by 29.47% and 8.67%, respectively, and a reduction in color contrast of 16.19%. The dilation and generation of microcapillary of C. pilosula were more obvious. The study revealed US-VFID could be used for the selection and process control of agro-processing methods for C. pilosula products.

Evaluation of the Effect of Ultrasonic Pretreatment on the Drying Kinetics and Quality Characteristics of Codonopsis pilosula Slices Based on the Grey Correlation Method

Ultrasonic (US) maltreatment was performed before the vacuum far-infrared drying (VFID) of Codonopsis pilosula (CP) slices to investigate the effects of different US parameters on the drying characteristics and nutrients of CP slices. The grey correlation method with relative correlation degree (r_i) as the evaluation measure was used to construct a model for the evaluation of the pretreatment quality of CP and to determine the optimal pretreatment conditions. The results showed that with the increase in US frequency and power, the drying rate increased. Under the conditions of US power of 180 W, frequency of 60 kHz and a pre-treatment time of 30 min, the drying time reduced by 28.6%. The contents of polysaccharide and syringin in dried CP slices pretreated by US increased by 14.7% and 62.0%, respectively, compared to the non-pre-treated samples, while the total flavonoid content decreased by 10.0%. In terms of colour, pretreatment had a certain protective effect on the red colour of dried products. The highest relative correlation (0.574) and the best overall quality of performance were observed at 180 W, 60 kHz and 30 min. Overall, US technology is suitable for the pretreatment processing of CP, which is of great significance to the drying of CP.

Effect of Ultrasonic Pretreatment on the Far-Infrared Drying Process and Quality Characteristics of Licorice

In this paper, the effects of different ultrasonic pretreatment processes on the far-infrared drying characteristics, quality indexes, and microstructure of licorice are evaluated. The results showed that ultrasonic pretreatment, combined with far-infrared drying, significantly reduced the drying time and moisture content of licorice compared with those of the control group. The highest total flavonoid content was obtained at an ultrasound power of 80 W. The total phenolic content (0.686 mg gallic acid equivalent/g) was higher than that in the control group, the increase was 19.4%, and its content was the highest at the sonication frequency of 20 kHz. The antioxidant capacity tended to increase and then decrease with the increase in sonication time, sonication power, and sonication frequency, and was the highest at 30 min of sonication. The soluble sugar content (31.490 mg glucose equivalent/g) was the highest at 30 kHz and 30 min. Observation of the microstructure revealed that the surface structure of the ultrasonic pretreated licorice slices changed significantly, forming more micropore channels, which facilitated the mass heat transfer during the drying process. In conclusion, ultrasonic pretreatment can significantly improve the quality of licorice tablets and significantly reduce the time required for subsequent drying. The combination of pretreatment parameters of 60 W ultrasonic power and 40 kHz ultrasonic frequency for 30 min was found to be an optimal combination of pretreatment parameters; therefore, this study may provide a technical reference for the industrialization of licorice drying.

Ultrasound applications in drying of fruits from a sustainable development goals perspective

This review focuses on the many contributions of ultrasound technologies for fruit drying toward the United Nations Sustainable Development Goals (SDG). Along this review, several aspects attained from the application of ultrasound technologies are correlated with the SDGs. The main ultrasonic technologies applied for fruit drying, such as ultrasonic bath, probe ultrasound, air-borne ultrasound air-drying, and ultrasound-assisted contact air-drying, are presented. An in-depth discussion on ultrasound contributions, its advantages, disadvantages, and limitations are made. The effects of ultrasound on water diffusivity in several fruits are presented by correlating this effect with drying time and cost of energy. Ultrasound-assisted fruit drying, like other food processing technologies, directly impacts Zero Hunger, but ultrasound technologies contribute to much more than delivering long shelf-life food. This technology can be used to produce healthy foods and provide well-being, which will be discussed by correlating the effects of ultrasound-assisted air-drying with the concentration of nutritional compounds. Ultrasound-assisted fruit drying reduces wastewater toxicity and energy consumption and improves productivity, potentially improving workplaces and salaries. A walk through the technology is presented from Zero Hunger to No Poverty.

Improving Drying Characteristics and Physicochemical Quality of Angelica sinensis by Novel Tray Rotation Microwave Vacuum Drying

In order to improve the shortcomings of uneven heating of traditional microwave drying and to maximally maintain food quality after harvest, a rotary microwave vacuum drying equipment was fabricated and used for drying experiments on Angelica sinensis to explore the effects of drying temperature, slice thickness, and vacuum degree on drying characteristics, physicochemical quality, and microstructure of dried Angelica sinensis products. The results showed that microwave vacuum drying can significantly shorten the drying time and improved the drying efficiency. Six different mathematical models were investigated and the Midilli model was the best-fitted model for all samples (R2 = 0.99903, Pearson’s r = 0.99952), and drying methods had various effects on different indexes and were confirmed by Pearson’s correlation analysis and principal component analysis. The optimal process parameters for microwave vacuum drying of Angelica sinensis were determined by entropy weight-coefficient of variation method as 45 °C, 4 mm, −0.70 kPa. Under this condition, well preserved of ferulic acid, senkyunolide I, senkyunolide H, ligustilide, total phenols and antioxidant activity, bright color (L* = 77.97 ± 1.89, ΔE = 6.77 ± 2.01), complete internal organizational structure and more regular cell arrangement were obtained in the samples. This study will provide a theoretical reference for the excavation of the potential value and the development of industrial processing of Angelica sinensis.

Study on Ultrasonic Far-Infrared Radiation Drying and Quality Characteristics of Wolfberry (Lycium barbarum L.) under Different Pretreatments

In order to explore the effects of different pretreatment methods on the ultrasonic far-infrared synergistic drying characteristics and quality of wolfberry, the bioactive components (polysaccharide, total phenol, total flavonoids, and antioxidants), the quality characteristics (rehydration ratio, color, vitamin C content, and betaine content), and the microstructure of the dried products were used as evaluation indices to test wolfberry treated by five different pretreatments (hot blanching; candied pretreatment; NaOH solution treatment; NaCl solution treatment; and Na₂CO₃ solution treatment). The results showed that hot blanching pretreatment improved the drying rate and shortened the drying time, and that the vitamin C content of dried products pretreated by hot blanching (92.56 mg/100 g) was higher than that of dried products pretreated by other methods. All five pretreatment methods increased the contents of the total phenols, vitamin C, and betaine of wolfberry. Wolfberry treated by candied pretreatment had lower color differences and higher contents of polysaccharide (0.83 g/g), total phenol (9.26 mg/g), and total flavonoids (2.61 mg/g) than wolfberry treated by the other pretreatment methods. Wolfberry pretreated by NaCl solution had the strongest antioxidant capacity (65.01%). Wolfberry pretreated by Na₂CO₃ solution had the highest betaine content (3.24%). The observation of the microstructure of the dried products revealed that hot blanching caused the most damage to wolfberry, while the candied pretreatment was less destructive to the tissue cells of wolfberry. On the whole, the dried wolfberry products obtained by the candied pretreatment were of a better quality than products obtained by the other pretreatment methods.