Preparation of housefly (Musca domestica) larvae protein hydrolysates: Influence of dual-sweeping-frequency ultrasound-assisted enzymatic hydrolysis on yield, antioxidative activity, functional and structural attributes.

Dual-sweeping-frequency ultrasound (DSFU) was utilized in the preparation of polypeptides from housefly (Musca domestica) larvae protein (HLP). Results indicated that ultrasonication (20 ± 2/28 ± 2 kHz, 42 W/L, 25 min) significantly increased peptide yield and DPPH scavenging capacity by 8.25 % and 14.83 %, respectively. Solubility, foaming and emulsification properties of polypeptides were improved by 19.89 %, 33.33 % and 38.74 % over the control; along with notable reduction in particle size and increase in zeta potential. Tertiary structural changes of the sonicated hydrolysates were illustrated by UV and fluorescence spectra. FTIR showed that ultrasonication increased α-helix, ß-turn, and random coil by 38.23 %, 46.35 % and 16.36 %, respectively, but decreased ß-sheet by 48.03 %, indicating partial unfolding in HLP hydrolysate conformation and reduction in intermolecular interactions. The research results demonstrated that dual-sweeping-frequency ultrasonication has a great prospect in industry application for the purpose of improving enzymolysis efficiency and product quality for housefly larvae protein hydrolysates production.

Enhancing the growth of thermophilic Bacillus licheniformis YYC4 by low-intensity fixed-frequency continuous ultrasound.

The effect of low-intensity fixed-frequency continuous ultrasound (LIFFCU) on the growth of Bacillus licheniformis YYC4 was investigated. The changes in morphology and activity of the organism, contributing to the growth were also explored. Compared with the control, a significant increase (48.95%) in the biomass of B. licheniformis YYC4 (at the logarithmic metaphase) was observed following the LIFFCU (28 kHz, 1.5 h and 120 W (equivalent to power density of 40 W/L)) treatment. SEM images showed that ultrasonication caused sonoporation, resulting in increased membrane permeability, evidenced by increase in cellular membrane potential, electrical conductivity of the culture, extracellular protein and nucleic acid, and intracellular Ca2+ content. Furthermore, LIFFCU action remarkably increased the extracellular protease activity, volatile components of the culture medium, microbial metabolic activity, and spore germination of the strain. Therefore, LIFFCU could be used to efficiently promote the growth of targeted microorganisms.

Mono-frequency ultrasonic-assisted thawing of frozen goose meat: Influence on thawing efficiency, product quality and microstructure.

This study aimed to investigate the influences of mono-ultrasound assisted thawing on the thawing efficiency, product quality and conformational characteristics of frozen goose meat. The thawing time, thawing loss, muscle quality, and microstructure of frozen goose meat were studied. The results displayed that ultrasonic-assisted thawing effectively reduced the thawing time by 45.37-57.58% compared with non-sonicated group, and significantly decreased the thawing loss. For the quality properties of goose meat tissue, ultrasound-assisted thawing with single-frequency of 50 kHz indicated a lower protein turbidity; meanwhile, hardness values were also significantly increased, and displayed a higher springiness, gumminess and chewiness of goose meat tissue. The microstructure analysis exhibited that the conformation of goose myofibrillar protein (MP) was modified following ultrasonic-assisted thawing, and became closer and more irregular. Therefore, ultrasound-assisted thawing treatments at 50 kHz mono-frequency (temperature 25℃) have a high potential application value in the thawing research of frozen goose meat, and lay a theoretical foundation for use in the meat process industries.

Synergistic effects of pH shift and heat treatment on solubility, physicochemical and structural properties, and lysinoalanine formation in silkworm pupa protein isolates.

The application of silkworm pupa protein isolates (SPPI) in food industry was limited because SPPI's solubility is poor and it contains a potential harmful component of lysinoalanine (LAL) which formed during protein extraction. In this study, combined treatments of pH shift and heating were performed to improve the solubility of SPPI and to reduce the content of LAL. The experimental results showed that the promoting effect on SPPI's solubility by alkaline pH shift + heat treatment was greater than that by acidic pH shift + heat. And an 8.62 times increase of solubility was observed after pH 12.5 + 80 â„ƒ treatment compared to the control SPPI sample which was extracted at pH 9.0 without pH shift treatment. Very strong positive correlation was found between alkali dosage and SPPI solubility (Pearson's correlation coefficient r = 0.938). SPPI with pH 12.5 shift treatment showed the highest thermal stability. Alkaline pH shift combined with heat treatment altered the micromorphology of SPPI and destroyed the disulfide bonds between macromolecular subunits (72 and 95 kDa), resulting in reduced particle size and increased zeta potential and free sulfhydryl content of the isolates. The fluorescence spectra analysis showed red shifts phenomena with pH increasing and fluorescence intensity increase with temperature increasing, implying the alterations in the tertiary structure of protein. Compared to the control SPPI sample, the amount of LAL reduced by 47.40 %, 50.36 % and 52.39 % using pH 12.5 + 70 â„ƒ, pH 12.5 + 80 â„ƒ and pH 12.5 + 90 â„ƒ treatment, respectively. These findings provide fundamental information for the development and application of SPPI in food industry.

Fermentation of Saccharomyces cerevisiae in a 7.5 L ultrasound-enhanced fermenter: Effect of sonication conditions on ethanol production, intracellular Ca2+ concentration and key regulating enzyme activity in glycolysis.

In this study, the effect of sonication on the fermentation process of a single-celled fungus was examined. During the experiment, Saccharomyces cerevisiae (S. cerevisiae) was used as the starting strain for ethanol fermentation (batch fermentation) in a 7.5 L automated fermentation tank. The fermentation tank connected with a six-frequency ultrasonic equipment. Non-sonication treatment was set up as the control. Sonication treatment with power density of 280 W/L and 48 h of treatment time were set up as trial groups for investigating the influence of different ultrasound frequency including 20, 23, 25, 28, 33 and 40 kHz on the changes in dry cell-weight, glucose consumption rate, and ethanol yield. The results showed that the dry cell-weight, glucose consumption rate, and ethanol content reached the best results under the ultrasonic condition of 28 kHz ultrasound frequency in comparison with other ultrasound frequency. The dry cell-weight and ethanol content of the 28 kHz ultrasonic treatment group increased by 17.30% and 30.79%, respectively in comparison with the control group The residual sugar content dropped to a lower level within 24 h, which was consistent with the change in ethanol production. Besides, the results found that the glucose consumption rate increased compared to the control. It indicated that ultrasound accelerated glucose consumption contributed to increase the rate of ethanol output. In order to explore the mechanism of sonication enhanced the content of ethanol output by S. cerevisiae, the morphology, permeability of S. cerevisiae and key enzyme activities of ethanol synthesis were investigated before and after sonication treatment. The results showed that after sonication treatment, the extracellular nucleic acid protein content and intracellular Ca2+ concentration increased significantly. The morphology of S. cerevisiae was observed by SEM and found that the surface of the strain had wrinkles and depressions after ultrasonic treatment. furthermore after sonication treatment, the activities of three key enzymes which catalyze three irreversible reactions in glycolysis metabolism, namely, hexokinase, phosphofructokinase and pyruvate kinase increased by 59.02%, 109.05% and 87.27%, respectively. In a word, low-intensity ultrasound enhance the rate of ethanol output by S. cerevisiae might due to enhancing the growth and cell permeability of strains, and increasing the activities of three key enzymes of ethanol biosynthesis.

Lysinoalanine formation and conformational characteristics of rice dreg protein isolates by multi-frequency countercurrent S-type sonochemical action.

The influences of multi-frequency countercurrent S-type ultrasound (MFSU), with various frequency modes, on lysinoalanine (LAL) formation and conformational characteristics of rice dreg protein isolates (RDPI) were investigated. The ultrasonic operating mode with dual-frequency combination (20/40 kHz) indicated lower LAL content and higher protein dissolution rate of RDPI compared with that of other ultrasound operating modes. Under the dual-frequency ultrasound mode of 20/40 kHz, acoustic power density of 60 W/L, time of 20 min, and temperature of 35 °C, the relative reduction rate of LAL of RDPI reached the highest with its value of 26.95%, and the protein dissolution rate was 71.87%. The changes in chemical interactions between protein molecules indicated that hydrophobic interactions and disulfide bonds played a considerable role in the formation of LAL of RDPI, especially the reduction of g-g-g and g-g-t disulfide bond. Alterations in microstructure showed that ultrasonication loosened the protein structure and created more uniform protein fragments of RDPI. In conclusion, using MFSU in treating RDPI was an efficacious avenue for minimizing LAL content and modifying the conformational characteristics of RDPI.

Effect of dual-frequency ultrasound on the formation of lysinoalanine and structural characterization of rice dreg protein isolates.

The effect of dual-frequency ultrasound treatment with different working modes on the lysinoalanine (LAL) formation and structural characterization of rice dreg protein isolates (RDPI) was studied during alkaline exaction processing. Ultrasonic notably decreased the LAL amount of RDPI and enhanced the protein dissolution rate. The LAL content of RDPI, especially sequential dual frequency 20/40 kHz, decreased by 12.02% (P < 0.05), compared to non-sonicated samples. Herein, the protein dissolution rate was higher. The changes in sulfhydryl groups was positively correlated with the LAL formation. The amino acids (AA) such as threonine (Thr), lysine (Lys), and arginine (Arg) were reduced, resulting in a decrease in LAL content following sonication. Besides, ultrasonication altered protein secondary structure by reducing random coil and ß-sheet contents, while α-helix and ß-turn contents increased. Alterations in the surface hydrophobicity, particle size, particle size distribution, and microstructure indicated more irregular fragment with microparticles of RDPI by sonochemical treatment. Thus, ultrasound treatment may be a new and efficacious process for controlling the LAL generation in prepared-protein food(s) during alkali extraction.

Improvement in enzymolysis efficiency and changes in conformational attributes of corn gluten meal by dual-frequency slit ultrasonication action.

The influences of dual-frequency slit ultrasound (DFSU) pretreatment with various working parameters on the enzymolysis efficiency and conformational characteristics of corn gluten meal (CGM) were studied. Results indicated that under the conditions of ultrasonic power density of 80 W/L, time of 30 min, ultrasonic intermittent ratio of 5:2 s/s, temperature of 30 °C, and substrate concentration of 50 g/L, the relative enzymolysis efficiency (REE) of CGM reached a maximum of 21.05%, and the protein dissolution rate was 68.50%. In addition, ultrasonication had considerable impact on the conformation of CGM and consequently improved the susceptibility to alcalase proteolysis. Changes in free sulfhydryl (SHF) and disulfide bonds (SS) groups indicated spatial conformation of CGM was altered following sonication (sonochemical) treatment. Fourier Transform Infrared Spectrum (FITR) analysis showed a reduction in α-helix and ß-turn content; and an increase in ß-sheet and random coil content of CGM. Alterations in the particle size, particle size distribution, microstructure and surface roughness (Ra, Rq) indicated generation of smaller and more uniform protein fragments of CGM by sonochemical pretreatment. The proposed mechanism of sonicated CGM was elaborated. Our findings suggest that using DFSU in pretreating CGM may be an efficacious approach to enhance proteolysis.

Preparation of allicin-whey protein isolate conjugates: Allicin extraction by water, conjugates' ultrasound-assisted binding and its stability, solubility and emulsibility analysis.

The instability of allicin makes it easily decomposed into various organic sulfur compounds, resulting in significant decrease in biological activity. In this study, allicin was firstly extracted with water, then bound with whey protein isolates (WPI) which were pretreated by ultrasound to form conjugates, and the stability, water solubility and emulsibility of conjugates were as well investigated. The research results showed that there were no significant differences in the extraction yields of allicin from water, 40% and 80% ethanol. Appropriate frequency (20/40 kHz), power (50 W/L) and time (20 min) of ultrasonic pretreatments significantly increased (P < 0.05) the sulfhydryl groups content of WPI by 35.05% over control, causing improvement in binding ability of protein to allicin. The binding process of allicin-WPI displayed good fit with Elovich kinetic model (R2 = 0.9781). The mass retention rate of the conjugates (in 60% combination rate) with ultrasonic pretreating kept at 95.97% after 14 days of storage at 25 °C, whereas allicin's mass retention rate was only 61.79% at same storage condition. The water solubility of the prepared conjugates was significantly higher than allicin. And with optimal condition ultrasonic pretreatment of WPI, the conjugates showed the highest emulsifying capacity and emulsion stability (49.56 m2/g, 10.06 min). In conclusion, the ultrasonically pretreated allicin-WPI conjugates exhibited better stability, water solubility and emulsifying properties compared to allicin, this expands the application field of allicin.