Application of fixed-frequency ultrasound in the cultivation of Saccharomyces cerevisiae for rice wine fermentation.

BACKGROUND: Rice wine (RW) fermentation is limited by its long fermentation time, weak taste and unpleasant flavors such as oil and odor. In this study, a novel ultrasound technology of Saccharomyces cerevisiae was used with the aim of improving fermentation efficiency and volatile flavor quality of RW. RESULTS: The results showed that fixed-frequency ultrasonic treatment (28 kHz, 45 W L-1, 20 min) of S. cerevisiae seed culture at its logarithmic metaphase significantly increased the biomass and alcohol yield by 31.58% and 26.45%, respectively, and reduced fermentation time by nearly 2 days. Flavor analysis indicated that the flavor compounds in RW, specifically the esters and alcohols, were also increased in quantity after the ultrasonic treatment of S. cerevisiae seed liquid. Isobutyl acetate, ethyl butyrate, ethyl hexanoate and phenethyl acetate contents were increased by 78.92%, 129.19%, 7.79% and 97.84%, respectively, as compared to the control. CONCLUSION: Ultrasonic treatment of S. cerevisiae reduced fermentation time and enhanced the flavor profile of RW. This study could provide a theoretical and/or technological basis for the research and development of RW. © 2024 Society of Chemical Industry.

Isolation and genomic characterization of Vmp-1 using Vibrio mimicus as the host: A novel virulent bacteriophage capable of cross-species lysis against three Vibrio spp.

Vibrio mimicus is a zoonotic pathogen that is widely distributed in aquatic habitats/environments (marine coastal water, estuaries, etc). The development of biocontrol agents for V. mimicus is imperative for the prevention and control of aquatic animal diseases and human food-borne infections. In this study, a broad-spectrum bacteriophage Vmp-1 was isolated from dealt aquatic product in a local market by double-layer agar plate method using V. mimicus CICC21613 as the host bacteria. Results indicated that Vmp-1, which belongs to the family Podoviridae, showed good pH tolerance (pH 3.0-12.0) and thermal stability (30-50 °C). The optimal multiplicity of infection (MOI) of Vmp-1 was 0.001 for a 20-min incubation and 100-min lysis period. Vmp-1 effectively controlled V. mimicus CICC21613 in LBS model (MOI = 0.0001, 0.001, 0.01, 0.1, 1) within 8 h. The full length of the Vmp-1 genome was 43,312 bp, with average GC content of 49.5%, and a total of 44 protein-coding regions. This study provides a novel phage strain that has the highest homology with vB_VpP_HA5 (GenBank: OK585159.1, 95.96%) for the development of biocontrol agents for V. mimicus.

Changes in physicochemical, structural and functional properties, and lysinoalanine formation during the unfolding and refolding of pH-shifted black soldier fly larvae albumin.

The changes of physicochemical, structural and functional properties and the lysinoalanine (LAL) formation during the unfolding and refolding of black soldier fly larvae albumin (BSFLA) induced by acid/alkaline pH shift were explored. The results showed that acid/alkaline conditions induced unfolding of BSFLA structure, but also accompanied by the formation of some large aggregates due to the hydrophobic interactions, hydrogen bonds, and disulfide bonds. Compared with control or pH1.5 shift, pH12 shift treatment significantly increased the electrostatic repulsion, surface hydrophobicity, free sulfhydryl group, and deamidation reactions, but reduced the fluorescence intensity of BSFLA, and these change in protein conformation contributed to increase in solubility, emulsion activity, and emulsion stability. But the content of LAL in BSFLA was increased by 93.39 % by pH 12 shift treatment. In addition, pH1.5 shift modified BSFLA tended to form ß-sheet structure through unfolding and refolding, resulting in the formation of aggregates with larger particle sizes, and reducing the solubility and the LAL content by 7.93 % and 65.53 %, respectively. SDS-PAGE profile showed that pH12/1.5 shifting did not cause irreversible denaturation of protein molecules. Therefore, pH12-shift is good way to improve the functional properties of BSFLA, but the content of LAL should be reduced to make it better used in food.

Effect of pectin concentration on emulsifying properties of black soldier fly (Hermetia illucens) larvae albumin modified by pH-shifting and ultrasonication.

The effect of pectin concentration on the structural and emulsifying properties of black soldier fly larvae albumin (BSFLA) modified by pH-shifting (pH12) and ultrasound (US) was studied. The results (intrinsic fluorescence, surface hydrophobicity, Fourier transform infrared spectrum, and disulfide bonds) showed that modified BSFLA samples, especially pH12-US, were more likely to bind to pectin through hydrogen bonding, electrostatic interactions, and hydrophobic interactions due to the unfolding of BSFLA, the collapse of disulfide bonds and exposure of hydrophobic groups. Thus, a BSFLA-pectin complex with smaller particle size, more negative charges, and a relatively loose structure was formed. The emulsifying activity (EAI) and stability index (ESI) of pH12-US modified BSFLA were significantly enhanced by the addition of pectin, reaching the highest values (associated with 174.41 % and 643.22 % increase, respectively) at pectin concentration of 1.0 %. Furthermore, the interface modulus of the emulsion prepared by the modified BSFLA was mainly viscous, and had higher apparent viscosity, smaller particle size and droplet size, contributing to higher EAI and ESI. The study findings suggest the addition of pectin to pH12-US treated BSFLA could be used in industry to prepare BSFLA-pectin emulsion with exceptional/desirable properties.

Inhibition of cross-linked lysinoalanine formation in pH12.5-shifted silkworm pupa protein, and functionality thereof: Effect of ultrasonication and glycation.

We added three different carbohydrates (Xylose/Xyl, Maltose/Mal, and Sodium alginate/Sal) to pH12.5-shifted silkworm pupa protein isolates (SPPI), and examined the influence of multi-frequency ultrasound (US) on them, with reference to lysinoalanine (LAL) formation, changes in conformational characteristics and functionality. Results showed that, the LAL content of the glycoconjugates - SPPI-Xyl, SPPI-Mal, and SPPI-Sal decreased by 1.47, 1.39, and 1.54 times, respectively, compared with the control. Notably, ultrasonication further reduced the LAL content by 45.85 % and brought SPPI-Xyl highest graft degree (57.14 %). SPPI-Xyl and SPPI-Mal were polymerized by different non-covalent bonds, and SPPI-Sal were polymerized through ionic, hydrogen, and disulfide (covalent/non-covalent) bonds. Significant increase in turbidity, Maillard reaction products and the formation of new hydroxyl groups was detected in grafted SPPI (p < 0.05). US and glycation altered the structure and surface topography of SPPI, in which sugars with high molecular weight were more likely to aggregate with SPPI into enormous nanoparticles with high steric hindrance. Compared to control, the solubility at pH 7.0, emulsifying capacity and stability, and foaming capacity of SPPI-US-Xyl were respectively increased by 244.33 %, 86.5 %, 414.67 %, and 31.58 %. Thus, combined US and xylose-glycation could be an effective approach for minimizing LAL content and optimizing functionality of SPPI.

Effect of carbonyl-amino condensation, non-covalent cross-linking and conformational changes induced by ultrasound-assisted Maillard reaction on lysinoalanine formation in silkworm pupa protein.

The inhibition of cross-linked lysinoalanine (LAL) formation in silkworm pupa protein isolates (SPPI) by Maillard reaction (using varying xylose concentration) and ultrasound treatment was studied. Results showed that sonicated SPPI was effectively grafted with high concentration of xylose (5 %), resulting in the lowest LAL content, which was 48.75 % and 30.64 % lower than the control and ultrasound-treated samples, respectively. Chemical bond analysis showed that the combined treatment destroyed the ionic bonds, intrachain (g-g-t), and interchain (g-g-g) disulfide bonds, but stimulated the polymerization of hydrogen and hydrophobic bonds between SPPI and xylose, and as well enhanced the net negative charge between SPPI/Xylose complexes. The particles of the complexes were more loose, dispersed and rough, and had a stronger hydrophilic microenvironment, accompanied by alterations in microscopic, secondary and tertiary structures. Ultrasound treatment induced the breakdown of the oxidative cross-linking in SPPI, and promoted the sulfhydryl group-dehydroalanine binding and the carbonyl-amino condensation of the protein and xylose, and thus inhibited the formation of cross-linked LAL. Furthermore, the physicochemical and structural parameters were highly interrelated with cross-linked LAL content (|r| > 0.9). The outcomes provided a novel avenue and theoretical basis for minimizing LAL formation in SPPI and improving the nutrition and safety of SPPI.

Hexagonal plate ultrasound pretreatment on the correlation between soy protein isolate structure and cholesterol-lowering activity of peptides, and protein's enzymolysis kinetics, thermodynamics.

In this study, a hexagonal plate ultrasound (HPU) pretreatment technology was employed to modify soy protein isolate (SPI) and enhance the hypocholesterolemic activity of enzymatic digests from SPI. Results demonstrated that under the condition of ultrasound power density of 40 W/L, the hypocholesterolemic activity of enzymatic digests from HPU-pretreated SPI (HPU-SPI) increased by 88.40 % compared to control group after gastrointestinal digestion. The sulfhydryl content of HPU-SPI increased by a maximum of 45.32 % compared to control group. Fourier transform infrared and scanning electron microscopy revealed that HPU pretreatment partially unfolded the SPI conformation, reduced the intermolecular interactions, and exposed the internal hydrophobic regions. Pearson correlation analysis showed that sulfhydryl groups (r = 0.860), disulfide bonds (r = -0.875) and random coil (r = 0.917) were strongly correlated with the cholesterol-lowering activity of soy protein hydrolysate (SPH), following a simulated gastrointestinal digestion. Finally, the effects of HPU pretreatment on enzymolysis kinetics and thermodynamics of the SPI enzymatic process showed that HPU pretreatment significantly reduced the Mie's constant, activation energy, activation enthalpy, activation entropy and Gibbs free energy. Overall, the study outcome suggested that HPU pretreatment could positively influence the hypocholesterolemic peptide activity, and thus, may be beneficial to the pharmaceutical/food industry.

Stereo-hindrance effect and oxidation cross-linking induced by ultrasound-assisted sodium alginate-glycation inhibit lysinoalanine formation in silkworm pupa protein.

Silkworm pupa protein isolate (SPPI) is rich in amino acids, making it chemically reactive, degradable, and easy to form lysinoalanine (LAL). We investigated how conformational cross-linking, induced by ultrasound-assisted sodium alginate, could inhibit the formation of LAL during the preparation of SPPI. Glycoconjugated SPPI (using 1 % sodium alginate under ultrasonication) showed the lowest LAL content i.e., 7.403 µg·mg-1, representing a 49.58 % decrease, with reference to the control. The ionic, hydrogen, and covalent bonds in the glycoconjugate increased by 171.79 %, 8.48 %, and 35.56 %, respectively. Glycation decreased arginine by 28.92 % and caused the oxidation of tyrosine, methionine and proline to form carbonyl groups. Some precursor amino acids, including lysine, serine, cysteine and threonine were not degraded during the combined treatment. The macromolecular aggregation caused by structural modifications strengthened the steric resistance of LAL cross-linking. The study outcomes provide a novel approach and theoretical basis for inhibition of LAL formation in SPPI.

Comparative analysis of the nutritional composition and volatile compounds in male and female adults, nymphs, and molts of Eupolyphaga sinensis Walker.

ABSTRAC: Female adult Eupolyphaga sinensis Walker (FAESW) has traditionally been a food source in Southeast Asian countries such as China and India, due to its rich nutritional content. However, the nutritional value of male adults (MAESW) and its molts (MESW) has hardly been reported. Therefore, this study aims to explore the potential application of MAESW and MESW in food by investigating and comparing their nutritional composition (i.e., protein, amino acids, fatty acids, and essential elements) with traditional sources of nutrition. The protein content of MAESW and MESW was 66.10 ± 0.49% and 59.86 ± 6.07%, respectively, and the highest energy content (462.26 ± 1.28 kcal/100 g) was observed for MAESW. Eight essential amino acids were determined, of which the males and MESW were found to have higher contents than those of FAESW (p < 0.05). Oleic and linoleic acid contents were higher in the adults than nymphs. Moreover, MESW was predominant in calcium (6770.84 mg/kg), whereas MAESW was rich in iron (556.12 mg/kg). Likened to chicken, the protein, amino acid, fatty acid, and mineral contents of ESW were higher. The volatiles of ESW were related to hexaldehyde, benzaldehyde, acetic acid, and butyric acid. This study provides a better understanding of the chemical composition of ESWs during their growth cycle and helps optimize information on edible insects, promoting their use as a potential food source for humans. PRACTICAL APPLICATION: As a kind of edible insect, the utilization of adult male Eupolyphaga sinensis Walker (ESW) and its molt is very low at present. Therefore, this study examined the nutrients and volatile substances of ESW (at different growth stages) and molt, which provided a theoretical basis for the subsequent development and utilization of ESW.

Effect of dual-frequency thermosonication, food matrix, and germinants on Alicyclobacillus acidoterrestris spore germination.

The off-odors associated with spoilage of acidic beverages are linked to the germination and growth of Alicyclobacillus acidoterrestris (AAT) spores. As a consequence, we determined the influence of nutrients, non-nutrient germinants, dual-frequency thermosonication (DFTS), and food matrix on spore germination. AAT spores in orange juice (OJ), supplemented by L-alanine (L-ala), had the highest germination rate and lowest DPA content at 10 h of incubation. The formation of microscopic pores in cell membranes during DFTS caused irreversible damage in AAT spores in citrate buffer solution (CBS); however, it stimulated AAT spore germination in CBS containing L-ala. Hence, the germination potential was established in the order: L-ala > Calcium dipicolinate > asparagine, glucose, fructose, and potassium ion mixture (AGFK) > L-valine. The conductivity analysis indicated that membrane damage could be a key factor contributing to the artificial germination in CBS. AFM images revealed that after 2 h of adding L-ala, the protein content increased with increased germinated cells. TEM showed that membrane poration and coat detachment were the main pre-germination morphological changes detected after DFTS treatment. This study provides evidence that germination stimulated with DFTS might be an effective strategy for reducing A. acidoterrestris spores in fruit juices.

An overview of factors affecting the quality of beef meatballs: Processing and preservation.

Beef meatball (BM) is a traditional delicious snack with rich nutrition and unique flavor, making it a preferred choice for most consumers. However, the quality of BM is easily affected by many factors, such as the processing, storage, and preservation, which limit the competitive positioning with respect to its market. Therefore, it is essential to pay attention to each step during the processing of BMs. Based on previous studies, this systematic review focuses on the effect of key processing factors (including raw materials and ingredients, beating, cooking methods, storage, and preservation) on the quality of BMs. Additionally, this study assessed the effect of each process factor on the physicochemical, sensory, nutritional, and safety attributes of BMs. Finally, the existing review will be beneficial in examining/describing the factors impacting the quality of BMs during processing, which would provide theoretical reference and scientific basis for the standardization and industrialization of BMs.

Mixed-Strain Fermentation Conditions Screening of Polypeptides from Rapeseed Meal and the Microbial Diversity Analysis by High-Throughput Sequencing.

Conventional fermentation of rapeseed meal has disadvantages such as sterilization requirement, high energy consumption and low efficiency, as well as poor action of single bacteria. To overcome these drawbacks, mixed-strain fermentation of unsterilized rapeseed meal was investigated. Mixed-fermentation of unsterilized rapeseed meal (ratio of solid-liquid 1:1.2 g/mL) using Bacillus subtilis, Pediococcus acidilactici and Candida tropicalis (at 40 °C, for 3 days, with inoculation amount of 15% (w/w)) substantially increased the polypeptide content in rapeseed meal by 814.5% and decreased the glucosinolate content by 46.20%. The relationship between microbial diversity and physicochemical indicators showed that the improvement in polypeptide content was mainly caused by C. tropicalis (on the first day of fermentation) and B. subtilis (on the second day). Compared to raw rapeseed meal, the microbial diversity following the fermentation was significantly reduced, indicating that mixed-strain fermentation can inhibit the growth of miscellaneous bacteria. The study findings suggest that mixed-strain fermentation could be used to considerably increase the polypeptide content of unsterilized rapeseed meal, increasing the potential of rapeseed meal.

Ultrasonic-assisted extraction of bioactive chlorogenic acid from heilong48 soybean variety: Parametric optimization and evaluation of physicochemical and bioactive properties.

Chlorogenic acid (CA), especially that found in soybeans, is a rich bioactive compound but has received very little attention in research settings in past decades. Ultrasonic-assisted extraction (UAE) could be an efficient method to increase CA release from soybeans. Hence, this study aimed to optimize UAE parameters for CA extraction from heilong48 soybean (HS) variety and evaluate the physicochemical and bioactive properties of the soybean. Optimization of ultrasound parameters with a Box-Behnken design found a frequency of 20.0 kHz, a power density of 30.0 W/L), a temperature of 37.9°C, and a time of 28.0 min to be the best conditions, which gave a CA yield of 5.007 ± 0.033 mg/g and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity of 93.197 ± 0.213 µmol of AA eq/g dry sample; these were higher than those of a non-ultrasound-treated (raw) HS sample (CA yield of 1.627 ± 0.528 mg/g and DPPH radical scavenging activity of 10.760 ± 0.207 µmol of AA eq/g dry sample). A satisfactory model was obtained. Scanning electron microscopy results confirmed the structural changes of the HS variety caused by the optimized UAE parameters. High total polyphenol contents (TPCs; 4.726 ± 0.002 mg GAE/g) and total phenolic acids (1.883 ± 0.005 mg GAE/g) and low total flavonoid contents (0.040 ± 0.008 mg RE/g) were obtained. A positive linear correlation between antioxidant activity and TPC was established. A protein-phenolic interaction in the HS variety was observed. The results established that polyphenols should be considered a significant component of the HS variety. Likewise, the HS variety could be used for CA extraction.

Influence of Low-Intensity Ultrasound on ε-Polylysine Production: Intracellular ATP and Key Biosynthesis Enzymes during Streptomyces albulus Fermentation.

The effect of low-intensity sonication treatment on cell growth, ε-polylysine (ε-PL) yield and its biological mechanism were investigated, using a 3-L-jar fermenter coupled with an in situ ultrasonic slot with a Streptomyces albulus strain SAR 14-116. Under ultrasonic conditions (28 kHz, 0.37 W cm-2, 60 min), a high biomass of SAR 14-116 and concentration of ε-PL were realized (i.e., they increased by 14.92% and 28.45%, respectively) when compared with a control. Besides this, ultrasonication increased the mycelia viability and intracellular ATP as well as activities of key enzymes involved in the ε-PL biosynthesis pathway, resulting in an improvement in the production of ε-PL. Data on qRT-PCR revealed that ultrasonication also affected the gene expression of key enzymes in the ε-PL biosynthesis pathway, including ε-PL synthetase (PLS). These outcomes provided the basis for understanding the effects of ultrasound-assisted fermentation on the stimulation of metabolite production and fermentation procedure in a fermenter.

Recent Insight on Edible Insect Protein: Extraction, Functional Properties, Allergenicity, Bioactivity, and Applications.

Due to the recent increase in the human population and the associated shortage of protein resources, it is necessary to find new, sustainable, and natural protein resources from invertebrates (such as insects) and underutilized plants. In most cases, compared to plants (e.g., grains and legumes) and animals (e.g., fish, beef, chicken, lamb, and pork), insect proteins are high in quality in terms of their nutritional value, total protein content, and essential amino acid composition. This review evaluates the recent state of insects as an alternative protein source from production to application; more specifically, it introduces in detail the latest advances in the protein extraction process. As an alternative source of protein in food formulations, the functional characteristics of edible insect protein are comprehensively presented, and the risk of allergy associated with insect protein is also discussed. The biological activity of protein hydrolyzates from different species of insects (Bombyx mori, Hermetia illucens, Acheta domesticus, Tenebrio molitor) are also reviewed, and the hydrolysates (bioactive peptides) are found to have either antihypertensive, antioxidant, antidiabetic, and antimicrobial activity. Finally, the use of edible insect protein in various food applications is presented.

Effect of ultrasonication on the metabolome and transcriptome profile changes in the fermentation of Ganoderma lucidum.

Development of an efficient liquid fermentation method is helpful for food and pharmaceutical applications. This study investigated the effect of ultrasonication on the liquid fermentation of Ganoderma lucidum, a popular edible and medical fungi. Significant changes at both metabolic and transcriptional levels in mycelia were induced by ultrasound treatment. Compared with the control, 857 differential metabolites were identified (578 up- and 279 down-regulated metabolites), with more metabolites biosynthesis after sonication; 569 differentially expressed genes (DEGs) (267 up- and 302 down-) and 932 DEGs (378 up- and 554 down-) were identified in ultrasound-treated samples with recovery time of 0.5 and 3 h, respectively. Furthermore, 334 DEGs were continuously induced within the recovery time of 3 h, indicating the lasting influence of sonication on mycelia. The DEGs and differential metabolites were mainly involved in pathways of carbohydrate, energy metabolism, amino acids, terpenoids biosynthesis and metabolism and membrane transport, suggesting that ultrasound induced multifaceted effects on primary and secondary metabolism. Ultrasonication enhanced the triterpenoids production of G. lucidum (34.96 %) by up-regulating the expression of terpenoids synthase genes. This study shows that the application of ultrasound in liquid fermentation of G. lucidum is an efficient approach to produce more metabolites.

Inhibition Effect of Ultrasound on the Formation of Lysinoalanine in Rapeseed Protein Isolates during pH Shift Treatment.

pH shift is an effective technique for modifying functional properties of food proteins. However, it can increase lysinoalanine (LAL) content under alkali conditions, thus limiting the use of proteins. This study investigated the inhibition effect of ultrasonic parameters on LAL formation in rapeseed protein isolates (RPI) during pH shift treatment (pH-ST). Results showed that the content of LAL decreased by 49.5% and 74.1%, following the use of ultrasound (28 kHz, 40 W/L, 40 °C, and 30 min) under alkali and acidic treatment, respectively. Structural analysis showed that after ultrasonic irradiation, increased sulfhydryl groups and amino acids reduced the dehydroalanine and, thus, decreased LAL content. Particle size, secondary structure, and microstructure (SEM, AFM) analyses showed relative dispersion in protein distribution, reducing intermolecular or intramolecular cross-linking, thereby lowering the LAL content. Thus, ultrasonic-aided pH-ST may be an operational technique toward minimizing LAL formation in RPI.

Proteolysis efficiency and structural traits of corn gluten meal: Impact of different frequency modes of a low-power density ultrasound.

The influence of varying frequency modes of a low-power density ultrasound (LPDU) on the enzymolysis efficacy and structural property of corn gluten meal (CGM) was investigated. Sonication pretreatment (of CGM) with sequential and simultaneous duple-frequency modes enhanced notably the relative enzymolysis efficiency, compared to other LPDU frequency modes. With a sequential duple-frequency of 20/40 kHz showing the most significant effect, the maximum value of enzymolysis efficiency and protein dissolution rate were 15.99% and 61.69%, respectively. Changes in the surface hydrophobicity, secondary structure and microstructure revealed alterations of conformation of CGM by ultrasound-induced effect. Furthermore, the molecular weight distribution CGM hydrolysates primarily distributed in 200-500 Da following ultrasonication. Sonication efficaciously enhanced the susceptibility of CGM to alcalase proteolysis. Thus, the use of various LPDU frequency modes in pretreating target proteins (CGM) may be considered as a practical approach to improve protein-enzyme reactions (proteolysis).

Modification of rapeseed protein by ultrasound-assisted pH shift treatment: Ultrasonic mode and frequency screening, changes in protein solubility and structural characteristics.

We investigated the effect of ultrasound-assisted pH shift treatment on the micro-particle, molecular, and spatial structure of rapeseed protein isolates (RPI). Various ultrasonic frequency modes (fixed, and sweep) was used. Protein characterization by the indexes: particle size, zeta potential, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), scanning electron microscopy (SEM), free sulfhydryl (SH), surface hydrophobicity (Ho), Fourier transform infrared Spectrum (FTIR) and fluorescence intensity was studied to elucidate the changes in solubility and structural attributes of RPI. The results showed that ultrasonic frequency and working modes substantially altered the structure, and modified the solubility of RPI. Ultra + pH mode at fixed frequency of 20 kHz had the best effect on the solubility of RPI. Under the condition of ultra + pH mode, 20 kHz at pH 12.5, solubility, compared to control, increased from 8.90% to 66.84%; and the change in molecular structure of RPI was characterized by smaller particles (from 330.90 to 115.77 nm), high zeta potential (from -17.95 to -14.43 mV, p < 0.05), and increased free sulfhydryl (from 11.63 to 24.50 µmol/g) compared to control. Likewise, surface hydrophobicity increased (from 2053.9 to 2649.4, p < 0.05), whilst ɑ-helix and random coil decreased (p < 0.05), compared to control. The fluorescence spectroscopy and FTIR spectroscopy showed that the secondary and tertiary structure of the RPI were altered. These observations revealed that changes in RPI structure was the direct factor affecting solubility. In conclusion, ultrasound assisted pH shift treatment was proven to be an effective method for the modification of protein, with promising application in food industry.

Effect of multi-frequency countercurrent ultrasound treatment on extraction optimization, functional and structural properties of protein isolates from Walnut (Juglans regia L.) meal.

This study evaluated the effects of ultrasound treatment on walnut meal protein (WMP) extraction and techno-functional properties. The Box-Behnken Design (BBD) was adopted for the optimization of the traditional and ultrasound-assisted extraction (UAE) processes. Standard protocols were used to assay the techno-functional characteristics. The extraction models' statistical results exhibited adequacy with the least desirability index of 95.8%. The UAE enhanced the WMP extraction yield, purity, and chemical score by 30.15%, 16.27%, and 9.74%, respectively, while reducing the extraction time by 25% over the control. The emulsion and foam stabilities and bulk density increased by 34.5%, 39.8%, and 6.1%, respectively, over the control. The α-helix decreased while ß-sheet, ß-turns and random coil secondary structure components increased significantly (p < .05) by 95.76%, 101.3%, 105.1%, and 85.7% correspondingly. The dual-frequency combination (20/40 kHz/kHz) was the best frequency mode. WMP could serve as a functional additive in manufactured foods as texture and flavor enhancer. PRACTICAL APPLICATIONS: Walnut meal protein (WMP) has a well-balanced amino acid profile and its economic use could be practically increased as a food ingredient by ultrasound-assisted extraction. By this technique, WMP could be employed for the development of enhanced food ingredients rather than being discarded as animal feed. This study showed a positive effect of ultrasonic-assisted alkaline pretreatment on WMP extraction, functionality and structure characteristics. In addition to process improvement, ultrasound is energy efficient and environmentally friendly. Therefore, the applicability of this technique to improve the functionality of plant proteins from industrial by-products to be included in food products is promising.