Investigations in physical mechanism of ultrasound-assisted antisolvent batch crystallization of lactose monohydrate from aqueous solutions

Sonication is known to enhance crystallization of lactose from aqueous solutions. This study has attempted to reveal the mechanistic features of antisolvent crystallization of lactose monohydrate from aqueous solutions. Experiments were conducted in three protocols, viz. mechanical stirring, mechanical stirring with sonication and sonication at elevated static pressure. Mechanical stirring provided macroconvection while sonication induced microconvection in the system. Other experimental parameters were initial lactose concentration and rate of antisolvent (ethanol) addition. Kinetic parameters of crystallization were coupled with simulations of bubble dynamics. The growth rate of crystals, rate of nucleation, average size of crystal crop and total lactose yield in different protocols were related to nature of convection in the medium. Macroconvection assisted nucleation but could not give high growth rate. Microconvection comprised of microstreaming due to ultrasound and acoustic (or shock) waves due to transient cavitation. Sonication at atmospheric static pressure enhanced growth rate but reduced nucleation. However, with elimination of cavitation at elevated static pressure, sonication enhanced both nucleation and growth rate resulting in almost complete lactose recovery.     

Effect of process parameters on the recovery of lactose in an antisolvent acetone/acetone-ethanol mixture: A comparative study based on sonication medium

Recovery of lactose from the whey using sonocrystallization was studied experimentally. The effect of sonication medium and irradiation power levels was evaluated using three different ultrasonic equipments. Effects of various parameters such as sonication time, pH of the medium, antisolvent (acetone and acetone-ethanol mixture) and concentration of lactose were determined. The optimal parametric conditions were analyzed using differential scanning calorimetry, thermogravimetric analysis, particle size distribution, and zeta potential measurements. Overall, the highest lactose recovery was obtained using a mixture of acetone and ethanol as antisolvent in bath sonication as well as atomization process.     

Purification of serratiopeptidase from Serratia marcescens NRRL B 23112 using ultrasound assisted three phase partitioning

The ultrasound assisted three phase partitioning (UATPP) is a novel bioseparation method for separation and purification of biomolecules. In the present work, UATPP was investigated for the first time for purification of serratiopeptidase from Serratia marcescens NRRL B 23112. Effect of various process parameters such as ammonium sulphate saturation, t-butanol to crude extract ratio, pH, ultrasonic frequency, ultrasonic intensity, duty cycle and irradiation time were evaluated and optimized. The optimized conditions were found to be as follows: ammonium sulphate saturation 30% (w/v), pH 7.0, t-butanol to crude ratio 1:1 (v/v), ultrasound frequency 25 kHz, ultrasound intensity 0.05 W/cm², duty cycle 20% and irradiation time 5 min. The maximum purity and recovery obtained from UATPP was 9.4-fold and 96% respectively as compared to the three phase partitioning (TPP) (4.2-fold and 83%). Also the process time for UATPP was significantly reduced to 5 min from 1 h as compared to TPP. The results indicate that, UATPP is an efficient technique for the purification of serratiopeptidase with maximum purity, recovery and reduced processing time.     

The application of power ultrasound to reaction crystallization

The action of power ultrasound in controlling the supersaturation, nucleation and crystal growth during the acid-base reaction crystallization of 7-amino-3-desacetoxy cephalosporanic acid (7-ACDA) has been investigated. The experimental results show that ultrasound can mix the reaction more efficiently and uniformly than conventional agitation methods. Insonation leads to the reduction of both the induction period and metastable zone width of the crystallization, so that the process of crystallization can be more efficiently controlled than without insonation. Agglomeration is also greatly reduced. Adjusting the ultrasonic parameters can modulate the crystal size and size distribution. The mechanism of the sonoprocess has been analyzed and comments are made on the potential applicability of sonication in large-scale crystallization practice.     

Facile synthesis of mesoporous ZSM-5 aided by sonication and its application for VOCs capture

Application of ultrasound power to the mother liquor is popular pretreatment for zeolite synthesis which offers a simple way of accelerating crystallization process and finetuning the properties of nanocrystalline zeolites. In this work, sonication-aided synthesis of mesoporous ZSM-5 at low temperature and ambient pressure was systematically studied, in an attempt to reach efficient and benign synthesis of zeolites with hierarchical pore structure, which has wide applications as catalysts and sorbents. The effects of sonication duration, power density, sonication temperature and seeding on the crystallization of ZSM-5 were investigated. The obtained samples were characterized by XRD, SEM, BET and VOCs capture. High quality mesoporous ZSM-5 can be obtained by a facile 5 d synthesis at 363 K, much faster than conventional hydrothermal synthesis. The reduced synthesis time was mainly attributed to the enhanced crystallization kinetics caused by the fragmentation of seeds and nuclei, while sonication radiation had little impact on the nucleation process. Compared with control sample, mesoporous ZSM-5 prepared by sonochemical method had higher surface area and mesoporosity which demonstrated improved adsorption performance for the capture of isopropanol.     

Ultrasonic processing of dairy systems in large scale reactors

High intensity low frequency ultrasound was used to process dairy ingredients to improve functional properties. Based on a number of lab-scale experiments, several experimental parameters were optimised for processing large volumes of whey and casein-based dairy systems in pilot scale ultrasonic reactors. A continuous sonication process at 20 kHz capable of delivering up to 4 kW of power with a flow-through reactor design was used to treat dairy ingredients at flow rates ranging from 200 to 6000 mL/min. Dairy ingredients treated by ultrasound included reconstituted whey protein concentrate (WPC), whey protein and milk protein retentates and calcium caseinate. The sonication of solutions with a contact time of less than 1 min and up to 2.4 min led to a significant reduction in the viscosity of materials containing 18% to 54% (w/w) solids. The viscosity of aqueous dairy ingredients treated with ultrasound was reduced by between 6% and 50% depending greatly on the composition, processing history, acoustic power and contact time. A notable improvement in the gel strength of sonicated and heat coagulated dairy systems was also observed. When sonication was combined with a pre-heat treatment of 80 °C for 1 min or 85 °C for 30 s, the heat stability of the dairy ingredients containing whey proteins was significantly improved. The effect of sonication was attributed mainly to physical forces generated through acoustic cavitation as supported by particle size reduction in response to sonication. As a result, the gelling properties and heat stability aspects of sonicated dairy ingredients were maintained after spray drying and reconstitution. Overall, the sonication procedure for processing dairy systems may be used to improve process efficiency, improve throughput and develop value added ingredients with the potential to deliver economical benefits to the dairy industry.     

Ultrasound-assisted alkali removal of proteins from wastewater generated during oil bodies extraction

In this study, an ultrasonic-assisted alkaline method was used to remove proteins from wastewater generated during oil-body extraction, and the effects of different ultrasonic power settings (0, 150, 300, and 450 W) on protein recovery were investigated. The recoveries of the ultrasonically treated samples were higher than those of the samples without ultrasonic treatment, and the protein recoveries increased with increasing power, with a protein recovery of 50.10 % ± 0.19 % when the ultrasonic power was 450 W. Amino acid analysis showed that the amino acids comprising the recovered samples were consistent, regardless of the ultrasonic power used, but significant differences in the contents of amino acids were observed. No significant changes were observed in the protein electrophoretic profile using dodecyl polyacrylamide gel, indicating that sonication did not change the primary structures of the recovered samples. Fourier transform infrared and fluorescence spectroscopy revealed that the molecular structures of the samples changed after sonication, and the fluorescence intensity increased gradually with increasing sonication power. The contents of α-helices and random coils obtained at an ultrasonic power of 450 W decreased to 13.44 % and 14.31 %, respectively, whereas the β-sheet content generally increased. The denaturation temperatures of the proteins were determined using differential scanning calorimetry, and ultrasound treatment reduced the denaturation temperatures of the samples, which was associated with the structural and conformational changes caused by their chemical bonding. The solubility of the recovered protein increased with increasing ultrasound power, and a high solubility was essential in good emulsification. The emulsification of the samples was improved well. In conclusion, ultrasound treatment changed the structure and thus improved the functional properties of the protein.     

Effects of ultrasonic irradiation on crystallization kinetics,morphological and structural properties of zeolite FAU

In this work, NaX zeolite was synthesized and the effect of ultrasound irradiation on reaction kinetics, morphological and structural properties was investigated. Ultrasound was applied, by using a plate transducer (91.8 kHz), for the first time during the crystallization of zeolite NaX, at high temperature, varying the irradiation moment and its duration. Furthermore, ultrasound was applied after the crystallization by a horn-type transducer (20–24 kHz) at low temperature. The effects of irradiated volume (100–300 mL), sonication time (2–10 min) and ultrasound power (10–200 W) were studied with a power intensity up to 100 W/cm². It was found that the application of ultrasound during the first hour of crystallization resulted in 20% reduction of reaction time compared to a standard crystallization. Ultrasound can also reduce the agglomeration degree of the final powder by combining high power and long sonication time. After 5 min sonication time at 0.3 W/mL, the tapped density of the powder was increased by 10%, from 0.37 to 0.41 g/mL. Finally, by scanning electron microscopy (SEM) it was demonstrated that ultrasound can disrupt the agglomerates without affecting the morphology of individual crystals.     

Ultrasound-assisted crystallization of high purity of 2,4-dinitrotoluene from spent acid

The high purity crystal of 2,4-dinitrotoluene (DNT) could be successfully recovered from spent acid in a short period through diluting method assisted with ultrasonic irradiation. The sonication tests were carried out to elucidate the influence of various ultrasonic powers on the performance of crystallization of 2,4-DNT. It is remarkable that under the supersaturated condition ultrasonic irradiation could significantly accelerate the crystal formation, in which the purity of 2,4-DNT reaches to approximate 98.9 wt%. Based on the particle size distribution of crystals, it is proposed that the enhancement on recovery rate of 2,4-DNT crystals by ultrasound is mainly ascribed to the elevation of mass transfer rate for crystal growth. According to the spectra examined by field emission scanning electron microscope (FESEM), the above hypothesis is further verified by the appearance of smoother surface of crystals. Furthermore, the results of metallurgical microscope measurements show that ultrasound has also an abrasive effect on 2,4-DNT crystals under high ultrasonic power inputs.     

Lysozyme crystallization in hydrogel media under ultrasound irradiation

Sonocrystallization implies the application of ultrasound radiation to control the nucleation and crystal growth depending on the actuation time and intensity. Its application allows to induce nucleation at lower supersaturations than required under standard conditions. Although extended in inorganic and organic crystallization, it has been scarcely explored in protein crystallization. Now, that industrial protein crystallization is gaining momentum, the interest on new ways to control protein nucleation and crystal growth is advancing. In this work we present the development of a novel ultrasound bioreactor to study its influence on protein crystallization in agarose gel. Gel media minimize convention currents and sedimentation, favoring a more homogeneous and stable conditions to study the effect of an externally generated low energy ultrasonic irradiation on protein crystallization avoiding other undesired effects such as temperature increase, introduction of surfaces which induce nucleation, destructive cavitation phenomena, etc. In-depth statistical analysis of the results has shown that the impact of ultrasound in gel media on crystal size populations are statistically significant and reproducible.     

The effects and mechanism of phycocyanin removal from water by high-frequency ultrasound treatment

The effects and mechanism of phycocyanin removal from water by high-frequency ultrasound treatment were studied. The efficiency of sonication treatment in removing proteins derived from algal cells was investigated, and the factors influencing the process, including the effects of coagulation, were also studied. In addition, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), the three-dimensional fluorescence spectrum, and mass spectrum were used to illustrate the removal mechanism. The results indicated that phycocyanin can be degraded to the point where it is barely detectable in water samples after 180 min of high-frequency sonication. While the total nitrogen (TN) concentration remained consistent during the entire sonication process (240 min), about 78.9% of the dissolved organic nitrogen (DON) was oxidized into inorganic nitrogen. The sonication effect was greatly influenced by the ultrasound frequency, with 200 kHz having the highest removal performance due to the large production of hydroxyl (HO) radicals. Coagulation was adversely influenced by sonication in the first 60 min due to the cross-linking reaction between protein molecules caused by the sonication. The influence of sonication weakened with sonication time due to the further degradation of the proteins by ultrasound. The variation of the TN, DON, and inorganic nitrogen indicated that the main mechanism occurring during the high-frequency sonication of the phycocyanin was the direct oxidation of the radicals, which was totally different from of the mechanism occurring during ultrasound with low frequency.     

Optimization of salt concentration in PEG-based crystallization solutions

Although polyethylene glycol (PEG) is the most widely used precipitant in protein crystallization, the concentration of co-existing salt in the solution has not been well discussed. To determine the optimum salt concentration range, several kinds of protein were crystallized in a 30% PEG 4000 solution at various NaCl concentrations with various pH levels. It was found that, if crystallization occurred, the lowest effective salt concentration depended on the pH of the protein solution and the pI of the protein molecule; that is, higher salt concentrations were required for crystal growth if the difference between pH and pI was increasing. The linear relationship between the charge density of the protein and the ionic strength of the crystallization solution was further verified. These results suggested that the lowest effective concentration of salt in a crystallization solution can be predicted before performing a crystallization experiment. Our results can be a tip for tuning crystallization conditions by the vapor-diffusion method.     

Intensified recovery of valuable products from whey by use of ultrasound in processing steps – A review

The current review focuses on the analysis of different aspects related to intensified recovery of possible valuable products from cheese whey using ultrasound. Ultrasound can be used for process intensification in processing steps such as pre-treatment, ultrafiltration, spray drying and crystallization. The combination of low-frequency, high intensity ultrasound with the pre-heat treatment minimizes the thickening or gelling of protein containing whey solutions. These characteristics of whey after the ultrasound assisted pretreatment helps in improving the efficacy of ultrafiltration used for separation and also helps in preventing the blockage of orifice of spray dryer atomizing device. Further, the heat stability of whey proteins is increased. In the subsequent processing step, use of ultrasound assisted atomization helps to reduce the treatment times as well as yield better quality whey protein concentrate (WPC) powder. After the removal of proteins from the whey, lactose is a major constituent remaining in the solution which can be efficiently recovered by sonocrystallization based on the use of anti-solvent as ethanol. The scale-up parameters to be considered during designing the process for large scale applications are also discussed along with analysis of various reactor designs. Overall, it appears that use of ultrasound can give significant process intensification benefits that can be harnessed even at commercial scale applications.     

High intensity ultrasound treatment of protein isolate extracted from dephenolized sunflower meal: Effect on physicochemical and functional properties

The influence of high intensity ultrasound (HIUS) on physicochemical and functional properties of sunflower protein isolates was investigated. Protein solutions (10% w/v) were treated with ultrasound probe (20 kHz) and ultrasound bath (40 kHz) for 5, 10, 20 and 30 min. Thermal stability of protein isolates was reduced as indicated by differential scanning calorimetry. Minimum thermal stability was observed at 20 min of sonication and increased further with increase in treatment time indicating aggregation at prolonged sonication. SDS-PAGE profile of proteins showed a significant reduction in molecular weight. Further, surface hydrophobicity and sulfhydryl content increased after HIUS treatment indicating partial unfolding of proteins and reduction in the intermolecular interactions. The particle size analysis showed that HIUS treatment reduced the particle size. Less turbid solution were observed largely due to reduction in particle size. HIUS decreased the available lysine content in protein isolates. Solubility, emulsifying capacity, emulsion stability, foaming capacity, foam stability and oil binding capacity were improved significantly, while as, water binding capacity was decreased. The effect of HIUS on physicochemical and functional properties of sunflower protein isolates was more pronounced in probe sonication rather than bath sonication. Protein isolates with improved functional properties can be obtained using high intensity ultrasound technology.     

Ultrasound assisted acid catalyzed lactose hydrolysis: Understanding into effect of operating parameters and scale up studies

The current work deals with the value addition of lactose by transforming into hydrolyzed lactose syrup containing glucose and galactose in major proportion using the novel approach of ultrasound assisted acid catalyzed lactose hydrolysis. The hydrolysis of lactose was performed in ultrasonic bath (33 kHz) at 50% duty cycle at different temperatures as 65 °C and 70 °C and two different hydrochloric acid (HCl) concentrations as 2.5 N and 3 N. It was observed that acid concentration, temperature and ultrasonic treatment were the major factors in deciding the time required to achieve ∼90% hydrolysis. The ultrasonic assisted approach resulted in reduction in the reaction time and the extent of intensification was established to be dependent on the temperature, acid concentration and time of ultrasonic exposure. It was observed that the maximum process intensification obtained by introduction of ultrasound in the lactose hydrolysis process performed at 70 °C and 3 N HCl was reduction in the required time for ∼90% hydrolysis from 4 h (without the presence of ultrasound) to 3 h. The scale-up study was also performed using an ultrasonic bath with longitudinal horn (36 kHz as operating frequency) at 50% duty cycle, optimized temperature of 70 °C and acid concentration of 3 N. It was observed that the reaction was faster in the presence of ultrasound and stirring by axial impeller at rpm of 225 ± 25. The time required to complete ∼90% of hydrolysis remained almost the same as observed for small scale study on ultrasonic bath (33 kHz) at 50% duty cycle. The use of recovered lactose from whey samples instead of pure lactose did not result in any significant changes in the progress of hydrolysis, confirming the efficacy of the selected approach. Overall, the work has presented a novel ultrasound assisted approach for intensified lactose hydrolysis.     

Effect of ultrasonic irradiation on production of fermented milk with Lactobacillus delbrueckii

Milk fermentation with Lactobacillus delbrueckii under ultrasonic irradiation was carried out in a 450 cm³ bioreactor with a polyethylene film bottom. Ultrasonic irradiation increased the hydrolysis of lactose in milk but decreased the cell viability. However, the viable cell count increased again when the ultrasound was stopped, because ultrasound did not destroy the ability for cell propagation. When the sonication power was 17.2 kW m^-2 and the sonication period was 3 h, 4.9 × 10⁸ cfu cm^-3 of the viable cell count and 55% lactose hydrolysis were attained. In contrast, the viable cell count was 2 × 10⁹ cfu cm^-3 and 35.6% lactose was hydrolysed in control fermentation.     

Ultrasound-assisted extraction of xyloglucan from apple pomace

Ultrasound-assisted extraction was evaluated as a simpler and more effective alternative to conventional extraction method for the isolation of xyloglucan from apple pomace. The apple pomace samples were extracted under indirect sonication in an ultrasound cleaning bath. The ultrasound extraction was compared with the conventional method, on the productions of xyloglucan. It was found that the ultrasound-assisted extraction of xyloglucan was about three times faster than the traditional extraction method. Response surface methodology was employed to study the effect of liquid:solid ratio, KOH concentration and ultrasound-assisted extraction time on the yield of xyloglucan from apple pomace. Regression analysis was performed on the data obtained. The most relevant variable was the quadratic of liquid:solid ratio. The coefficient determination (R²) was good for the second-order model. The optimum combination was determined as a liquid:solid ratio of 34.4:1 (v/w), a KOH concentration of 3.3 M and an ultrasound-assisted extraction time of 2.5 h.     

Intensification of leaching process by dual-frequency ultrasound

Ultrasound is gaining importance in metal extraction process. In the previous laboratory scale investigation the authors have established the positive influence of ultrasound on copper recovery from oxide ores of Malanjkhand, Madhya Pradesh, India in an ammonical media. The process parameters in a conventional agitation method were optimized and a maximum recovery of ≈32% in 20 min was obtained without sonication. The recovery was increased to ≈78% by the application of ultrasound over the same period with several advantages like decrease in leaching time and the reagent consumption. In the present study the leaching process is intensified by studying the metal recovery variation at different ultrasonic frequencies (20, 40, 43 and 720 kHz) and intensities (up to 8 W cm⁻²) with sonication time. The results show that sinusoidal ultrasound even at larger intensity has some limitations with single frequency. However, simultaneous application of dual frequency 20 and 40 kHz ultrasound enhanced extraction rates along with increased yield. While conventional single frequency exposure at either one of the two frequencies at the same acoustic power level did not yield similar results, application of two wave sources, as used in the study revealed that it is possible to save energy through lowering of time of operation process.     

Polymer-mediated and ultrasound-assisted crystallization of ropivacaine: Crystal growth and morphology modulation

The objective of this research was to modify the crystal shape and size of poorly water-soluble drug ropivacaine, and to reveal the effects of polymeric additive and ultrasound on crystal nucleation and growth. Ropivacaine often grow as needle-like crystals extended along the a-axis and the shape was hardly controllable by altering solvent types and operating conditions for the crystallization process. We found that ropivacaine crystallized as block-like crystals when polyvinylpyrrolidone (PVP) was used. The control over crystal morphology by the additive was related to crystallization temperature, solute concentration, additive concentration, and molecular weight. SEM and AFM analyses were performed providing insights into crystal growth pattern and cavities on the surface induced by the polymeric additive. In ultrasound-assisted crystallization, the impacts of ultrasonic time, ultrasonic power, and additive concentration were investigated. The particles precipitated at extended ultrasonic time exhibited plate-like crystals with shorter aspect ratio. Combined use of polymeric additive and ultrasound led to rice-shaped crystals, which the average particle size was further decreased. The induction time measurement and single crystal growth experiments were carried out. The results suggested that PVP worked as strong nucleation and growth inhibitor. Molecular dynamics simulation was performed to explore the action mechanism of the polymer. The interaction energies between PVP and crystal faces were calculated, and mobility of the additive with different chain length in crystal-solution system was evaluated by mean square displacement. Based on the study, a possible mechanism for the morphological evolution of ropivacaine crystals assisted by PVP and ultrasound was proposed.     

Alkaline and ultrasound assisted alkaline pretreatment for intensification of delignification process from sustainable raw-material

Alkaline and ultrasound-assisted alkaline pretreatment under mild operating conditions have been investigated for intensification of delignification. The effect of NaOH concentration, biomass loading, temperature, ultrasonic power and duty cycle on the delignification has been studied. Most favorable conditions for only alkaline pretreatment were alkali concentration of 1.75 N, solid loading of 0.8% (w/v), temperature of 353 K and pretreatment time of 6 h and under these conditions, 40.2% delignification was obtained. In case of ultrasound-assisted alkaline approach, most favorable conditions obtained were alkali concentration of 1 N, paper loading of 0.5% (w/v), sonication power of 100 W, duty cycle of 80% and pretreatment time of 70 min and the delignification obtained in ultrasound-assisted alkaline approach under these conditions was 80%. The material samples were characterized by FTIR, SEM, XRD and TGA technique. The lignin was recovered from solution by precipitation method and was characterized by FTIR, GPC and TGA technique.