Effects of flat sweep frequency and pulsed ultrasound on the activity, conformation and microstructure of mushroom polyphenol oxidase

The mechanisms of inactivation of polyphenol oxidase in fresh-cut Agaricus bisporus by dual-frequency ultrasound combined with electrolytic water

Fresh-cut mushrooms are gaining popularity worldwide. However, their shelf life is limited because of enzymatic browning catalyzed by polyphenol oxidase (PPO), which leads to quality loss. The effects of different treatments (dual-frequency ultrasound (DFU), electrolytic water (EW), dual-frequency ultrasound combined with electrolytic water (DFU-EW)) on the molecular structure (Fourier infrared spectroscopy, X-ray diffraction, fluorescence spectroscopy, surface hydrophobicity, etc.), thermal properties, gene expression of PPO, and storage characteristics of mushrooms were investigated. The results showed that the DFU-EW decreased the relative contents of α-helix by 6.3 % and β-turns by 11.2 %, while increasing the contents of random coil and β-sheet by13.3 % and 4.7 %, respectively, compared to the control. The XRD analysis showed that the crystallinity of PPO was 7% higher than the control, while the fluorescence spectroscopy and surface hydrophobicity of PPO decreased from 921.7 (a.u) and 1154.5 to 393.5 (a.u) and 506.5, respectively. The DFU-EW treatment changed both the secondary and tertiary structures of PPO. The TGA analysis indicated that the thermal decomposition temperature decreased from the control 351.4 ℃ to 336.9 ℃. The gene expression level of AbPPO3 and AbPPO4 lowered. A 7-day storage period showed that DFU-EW inhibited the degree of browning, maintained the firmness of mushrooms, and stabilized the relative activity of PPO at 60% on average. Taken together, the DFU-EW treatment can effectively inactivate the PPO activity in fresh-cut mushrooms, thereby extending their shelf life, and this method provides a new insight to improve the quality of fresh-cut products.

Preservation of minimally processed carrots using the combination of ultrasound and mild heat ascorbic acid

Ultrasound (US) in combination with chemical disinfectants is an efficient and cost-effective hurdle technology for disinfecting minimally processed produce (MPP). However, the demand for non-chemical disinfection methods is increasing. In addition, chemical methods have been ineffective in simultaneously improving the physiological properties and inactivating pathogens in MPP. In this study, a novel and safe method called mild heat ascorbic acid (MHAsA; 1 % AsA at 50 °C) was combined with US to process minimally processed carrots. Physiological properties and microbial inactivation efficacy were analyzed during the storage period (0-5 days). The findings indicated that US-MHAsA induced the highest levels of antioxidant enzymes (superoxide dismutase and catalase) activities and accelerated the glutathione-ascorbate cycle, resulting in lower reactive oxygen species (ROS) and malondialdehyde content compared to US and MHAsA. The efficacy of US-MHAsA in inactivating phenylalanine lyase, the initial enzyme in the lignin synthesis process, was lower than that of US. On the other hand, its ability to inactivate cinnamyl alcohol dehydrogenase, the final enzyme in the process, was better than that of both US and MHAsA. However, there were no significant differences in lignin content among the three groups. The inactivation efficacy against enzymes (polyphenol oxidase and peroxidase) involved in browning was consistent across the three treatments. Analysis of the disinfection efficacy against Escherichia coli O157:H7 and Salmonella Typhimurium revealed that US-MHAsA achieved the lowest cross-contamination incidence (10-12 %) during washing, which was significantly lower than the incidence achieved by US (75-82 %). During the period from day 0 to day 5, two pathogens on carrots in the control group increased from 6.25 to 6.64 log CFU/g, while the lowest counts were observed in the US-MHAsA group, decreasing from 4.44 to 3.74 log CFU/g. However, the counts in the US group increased from 5.22 to 6.32 log CFU/g, and the counts at day 5 were not significantly lower than the control. These findings indicate that US-MHAsA is a novel hurdle technology that effectively reduces the risk of pathogen contamination and enhances the ability of MPP to scavenge ROS.

Multi-frequency power ultrasound (MFPU) pretreatment of crayfish (Procambarus clarkii): Effect on the enzymatic hydrolysis process and subsequent Maillard reaction

Crayfish, as a new consumer trend, has become one of the most popular freshwater aquatic foods in China, and its processed product output has been increasing year by year. In this study, the effect of multi-frequency power ultrasound (MFPU) pretreatment in various working modes including mono-, dual- and tri-frequency on the enzymatic hydrolysis and Maillard reaction of crayfish was investigated. Additionally, the underlying mechanism was also explored. Results showed that the degree of hydrolysis (DH) of crayfish was 23.89 %, while it increased to 40.78 % after MFPU pretreatment at 20/40 kHz dual-frequency, indicating that MFPU pretreatment significantly (p < 0.05) enhanced the enzymatic hydrolysis of crayfish. The crayfish protein after MFPU pretreatment exhibited a decrease in α-helix and increase in β-fold content, and the occurrence in the unfolding of the protein structure and alteration of tertiary structure. According to scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses, the MFPU pretreatment resulted in the fragmentation of crayfish protein. During the analyses of subsequent Maillard reaction, the composition and quantity of volatiles detected by the electronic nose and GC-MS indicated that MFPU pretreatment enhanced flavor of the Maillard reaction products. In conclusion, MFPU pretreatment is a promising technology for improving the degree of hydrolysis of crayfish protein and enhancing the flavor of Maillard reaction products.

7-(Diethylamino) coumarin-3-carboxylic acid as a novel antibrowning agent: Activity and mechanism

Browning caused by polyphenol oxidase (PPO) and microorganisms significantly impacts the nutritional quality of fruits and vegetables. This study identified 7-(Diethylamino) coumarin-3-carboxylic acid (7-DCCA) as an effective inhibitor of both PPO and bacteria. Enzyme assays revealed that 7-DCCA competitively inhibits PPO activity with an IC50 value of 0.275 ± 0.002 mM. Fluorescence and molecular simulation methods demonstrated that 7-DCCA forms a complex with PPO through hydrogen bonding and hydrophobic interactions, altering the enzyme's structure and reducing its activity. Thermogravimetric and differential scanning calorimetry (DSC) assays showed that 7-DCCA stabilizes PPO, delaying its thermal decomposition. Antibacterial tests proved that 7-DCCA inhibits Staphylococcus aureus and Escherichia coli by disrupting cell membranes. Additionally, 7-DCCA suppressed PPO and peroxidase activities, delaying phenolic oxidation and preventing browning in fruits and vegetables. Cytotoxicity assays confirmed its safety, with over 85 % cell viability at concentrations up to 0.1 mM. Stability experiments verified that 7-DCCA had greatly light and thermal stability. This study highlighted 7-DCCA as a promising antibrowning agent with potential application in food preservation.

In Vitro Inhibitory Mechanism of Polyphenol Extracts from Multi-Frequency Power Ultrasound-Pretreated Rose Flower Against α-Glucosidase

This paper explored the in vitro inhibitory mechanism of polyphenol-rich rose extracts (REs) from an edible rose flower against α-glucosidase using multispectral and molecular docking techniques. Results showed that REs had an inhibitory effect on α-Glu activity (IC50 of 1.96 μg/mL); specifically, the samples pretreated by tri-frequency ultrasound (20/40/60 kHz) exhibited a significantly (p < 0.05) stronger inhibitory effect on α-Glu activity with an IC50 of 1.33 μg/mL. The Lineweaver-Burk assay indicated that REs were mixed-type inhibitors and could statically quench the endogenous fluorescence of α-Glu. REs increased the chance of polypeptide chain misfolding by altering the microenvironment around tryptophan and tyrosine residues and disrupting the natural conformation of the enzyme. Molecular docking results showed that polyhydroxy phenolics had a high fit to the active site of α-Glu, so REs with high polymerization and numerous phenolic hydroxyl groups had a stronger inhibitory effect. Therefore, this study provides new insights into polyphenol-rich REs as potential α-glucosidase inhibitors.

Influence of ultrasound on the microbiological, physicochemical properties, and sensory quality of different varieties of pumpkin juice

This study has investigated the effect of ultrasound (US) as an emerging non-thermal sterilization technique on microbial growth and quality changes in three freshly squeezed pumpkin juices (Cucurbita maxima Duchesne, Cucurbita moschata Duchesne, and Cucurbita pepo L.).The three pumpkin juices were ultrasonicated at different ultrasonic power (0-400 W), time (0-20 min), and temperature (0-30 °C), and the total colony counts of the treated pumpkin juices were less than 5 log CFU/mL, which complied with the food safety and consumption standards. Based on these results, we further investigated the effects of different ultrasonic power (25 kHz, 10 min, 20 °C, 0-400 W) on the physicochemical properties and sensory quality of the three pumpkin juices. The physicochemical properties (color, sugar content, organic acid content, soluble solids, and carotenoids) of treated pumpkin juice were retained or improved to some extent. The antioxidant capacity was also increased by 9.09%, 10.25%, and 16.9% compared to the untreated group. During sonication, the particle size of all samples decreased significantly, the microstructure broke down significantly, and the sensory qualities of pumpkin juice were well preserved after sonication.

Egg White Protein-Proanthocyanin Complexes Stabilized Emulsions: Investigation of Physical Stability, Digestion Kinetics, and Free Fatty Acid Release Dynamics

Egg white proteins pose notable limitations in emulsion applications due to their inadequate wettability and interfacial instability. Polyphenol-driven alterations in proteins serve as an effective strategy for optimizing their properties. Herein, covalent and non-covalent complexes of egg white proteins-proanthocyanins were synthesized. The analysis of structural alterations, amino acid side chains and wettability was performed. The superior wettability (80.00° ± 2.23°) and rigid structure (2.95 GPa) of covalent complexes established favorable conditions for their utilization in emulsions. Furthermore, stability evaluation, digestion kinetics, free fatty acid (FFA) release kinetics, and correlation analysis were explored to unravel the impact of covalent and non-covalent modification on emulsion stability, dynamic digestion process, and interlinkages. Emulsion stabilized by covalent complex exhibited exceptional stabilization properties, and FFA release kinetics followed both first-order and Korsmeyer-Peppas models. This study offers valuable insights into the application of complexes of proteins-polyphenols in emulsion systems and introduces an innovative approach for analyzing the dynamics of the emulsion digestion process.

Epsilon-poly-l-lysine alleviates brown blotch disease of postharvest Agaricus bisporus mushrooms by directly inhibiting Pseudomonas tolaasii and inducing mushroom disease resistance

The natural antimicrobial peptide, epsilon-poly-l-lysine (ε-PL), is widely acknowledged as a food preservative. However, its potential in managing bacterial brown blotch disease in postharvest edible mushrooms and the associated mechanism remain unexplored. In this study, concentrations of ε-PL ≥ 150 mg L-1 demonstrated significant inhibition effects, restraining over 80% of growth and killed over 99% of Pseudomonas tolaasii (P. tolaasii). This inhibition effect occurred in a concentration-dependent manner. The in vivo findings revealed that treatment with 150 mg L-1 ε-PL effectively inhibited P. tolaasii-caused brown blotch disease in Agaricus bisporus (A. bisporus) mushrooms. Plausible mechanisms underlying ε-PL's action against P. tolaasii in A. bisporus involve: (i) damaging the cell morphology and membrane integrity, and increasing uptake of propidium iodide and leakage of cellular components of P. tolaasii; (ii) interaction with intracellular proteins and DNA of P. tolaasii; (iii) inhibition of P. tolaasii-induced activation of polyphenol oxidase, elevation of antioxidative enzyme activities, stimulation of phenylpropanoid biosynthetic enzyme activities and metabolite production, and augmentation of pathogenesis-related protein contents in A. bisporus mushrooms. These findings suggest promising prospects for the application of ε-PL in controlling bacterial brown blotch disease in A. bisporus.

Comparison between hydrodynamic and ultrasound cavitation on the inactivation of lipoxygenase and physicochemical properties of soy milk

The effects of hydrodynamic cavitation (HC) and ultrasound cavitation (UC) on the lipoxygenase activity and physicochemical properties of soy milk were evaluated. The results revealed that both ultrasound cavitation and hydrodynamic cavitation significantly inactivated the lipoxygenase activity. After the exposure to ultrasound cavitation at 522.5 W/L and 70 °C for 12 min, the lipoxygenase activity was inactivated by 96.47 %. Meanwhile, HC treatment with the cavitation number of 0.0133 for 240 min led to the loss of 79.31 % of lipoxygenase activity. An artificial neural network was used to model and visualize the effects of different parameters after ultrasound cavitation treatment on the inactivation efficiency of soy milk. Turbiscan test results showed that hydrodynamic and ultrasound cavitation decreased the instability index and particle size of soy milk. Moreover, the total free amino acid content was significantly increased after hydrodynamic and ultrasound cavitation treatment. Gas chromatography-mass spectrometry showed that the total content of beany flavor compounds decreased after acoustic cavitation and HC treatment. Acoustic cavitation and HC affected the tertiary and secondary structure of soy milk, which was related to the inactivation of lipoxygenase. We aim to explore a potential and effective way of the application in soy milk processing by comparing the ultrasound equipped with heat treatment and hydrodymic cavitation.

Ultrasound-Assisted Enzymatic Protein Hydrolysis in Food Processing: Mechanism and Parameters

Ultrasound has been widely used as a green and efficient non-thermal processing technique to assist with enzymatic hydrolysis. Compared with traditional enzymatic hydrolysis, ultrasonic-pretreatment-assisted enzymatic hydrolysis can significantly improve the efficiency of enzymatic hydrolysis and enhance the biological activity of substrates. At present, this technology is mainly used for the extraction of bioactive substances and the degradation of biological macromolecules. This review is focused on the mechanism of enzymatic hydrolysis assisted by ultrasonic pretreatment, including the effects of ultrasonic pretreatment on the enzyme structure, substrate structure, enzymatic hydrolysis kinetics, and thermodynamics and the effects of the ultrasonic conditions on the enzymatic hydrolysis results. The development status of ultrasonic devices and the application of ultrasonic-assisted enzymatic hydrolysis in the food industry are briefly described in this study. In the future, more attention should be paid to research on ultrasound-assisted enzymatic hydrolysis devices to promote the expansion of production and improve production efficiency.

From polyphenol to o-quinone: Occurrence, significance, and intervention strategies in foods and health implications

Polyphenol oxidation is a chemical process impairing food freshness and other desirable qualities, which has become a serious problem in fruit and vegetable processing industry. It is crucial to understand the mechanisms involved in these detrimental alterations. o-Quinones are primarily generated by polyphenols with di/tri-phenolic groups through enzymatic oxidation and/or auto-oxidation. They are highly reactive species, which not only readily suffer the attack by nucleophiles but also powerfully oxidize other molecules presenting lower redox potentials via electron transfer reactions. These reactions and subsequent complicated reactions are capable of initiating quality losses in foods, such as browning, aroma loss, and nutritional decline. To attenuate these adverse influences, a variety of technologies have emerged to restrain polyphenol oxidation via governing different factors, especially polyphenol oxidases and oxygen. Despite tremendous efforts devoted, to date, the loss of food quality caused by quinones has remained a great challenge in the food processing industry. Furthermore, o-quinones are responsible for the chemopreventive effects and/or toxicity of the parent catechols on human health, the mechanisms by which are quite complex. Herein, this review focuses on the generation and reactivity of o-quinones, attempting to clarify mechanisms involved in the quality deterioration of foods and health implications for humans. Potential innovative inhibitors and technologies are also presented to intervene in o-quinone formation and subsequent reactions. In future, the feasibility of these inhibitory strategies should be evaluated, and further exploration on biological targets of o-quinones is of great necessity.

Applications of ultrasonication on food enzyme inactivation- recent review report (2017-2022)

Ultrasound processing has been widely applied in food sector for various applications such as decontamination and structural and functional components modifications in food. Enzymes are proteinaceous in nature and are widely used due to its catalytic activity. To mitigate the undesirable effects caused by the enzymes various technologies have been utilized to inactive the enzymes and improve the enzyme efficiency. Ultrasound is an emerging technology that produces acoustic waves which causes rapid formation and collapse of bubbles. It has the capacity to break the hydrogen bonds and interact with the polypeptide chains due to Vander Waals forces leading to the alteration of the secondary and tertiary structure of the enzymes thereby leading to loss in their biological activity. US effectively inactivates various dairy-related enzymes, including alkaline phosphatase (ALP), lactoperoxidase (LPO), and γ-glutamyl transpeptidase (GGTP) with increased US intensity and time without affecting the natural dairy flavors. The review also demonstrates that inactivation of enzymes presents in fruit and vegetables such as polyphenol oxidase (PPO), polygalacturonase (PG), Pectin methyl esterase (PME), and peroxidase. The presence of the enzymes causes detrimental effects causes off-flavors, off-colors, cloudiness, reduction in viscosity of juices, therefore the formation of high-energy free molecules during sonication affects the catalytic function of enzymes and thereby causing inactivation. Therefore this manuscript elucidates the recent advances made in the inactivation of common, enzymes infruits, vegetables and dairy products by the application of ultrasound and also explains the enzyme inactivation kinetics associated. Further this manuscript also discusses the ultrasound with other combined technologies, mechanisms, and its effects on the enzyme inactivation.

Chalcone derivatives as xanthine oxidase inhibitors: synthesis, binding mode investigation, biological evaluation, and ADMET prediction

Xanthine oxidase (XO) is a crucial target for the treatment of hyperuricemia and gout. A series of derivatives based on natural 3,4-dihydroxychalcone, obtained from Carthamus tinctorious and Licorice, were designed and synthesized. Nine derivatives (9a-e, 10b,c, and 15a,b) exhibited apparent XO inhibitory activity in vitro (IC₅₀ values varied from 0.121 to 7.086 μM), 15b presented the most potent inhibitory activity (IC₅₀ = 0.121 µM), which was 27.47-fold higher than that of allopurinol (IC₅₀ = 3.324 µM). The SAR analysis indicated that introducing hydroxyl groups at 3'/4'/5'-position on ring A was more beneficial to the inhibition of XO than at 2'/6'-position; the removal of 3‑hydroxyl group on ring B could weaken the inhibitory potency of hydroxychalcones on XO, but it was beneficial to the XO inhibitory potency of methoxychalcones. Molecule modeling studies afforded insights into the binding mode of 15b with XO and supported the findings of SAR analysis. Additionally, kinetics studies demonstrated that 15b presented a reversible and competitive XO inhibitor, which spontaneously combined with XO through hydrophobic force, and finally changed the secondary conformation of XO. Furthermore, the acute hyperuricemia model was employed to investigate the hypouricemic effect of 15b, which could effectively reduce the serum uric acid levels of rats at an oral dose of 10 mg/kg. ADMET prediction suggested that compound 15b possessed good pharmacokinetic properties. Briefly, compound 15b emerges as an interesting XO inhibitor for the treatment of hyperuricemia and gout with beneficial effects on serum uric acid levels regulating. Meanwhile, the XO inhibitors with chalcone skeleton will deserve further attention and discussion.

Impact of ultrasound processing on alternative protein systems: Protein extraction, nutritional effects and associated challenges

Proteins from alternative sources including terrestrial and aquatic plants, microbes and insects are being increasingly explored to combat the dietary, environmental and ethical challenges linked primarily to conventional sources of protein, mainly meat and dairy proteins. Ultrasound (US) technologies have emerged as a clean, green and efficient methods for the extraction of proteins from alternative sources compared to conventional methods. However, the application of US can also lead to modifications of the proteins extracted from alternative sources, including changes in their nutritional quality (protein content, amino acid composition, protein digestibility, anti-nutritional factors) and allergenicity, as well as damage of the compounds associated with an increased degradation resulting from extreme US processing conditions. This work aims to summarise the main advances in US equipment currently available to date, including the main US parameters and their effects on the extraction of protein from alternative sources, as well as the studies available on the effects of US processing on the nutritional value, allergenicity and degradation damage of these alternative protein ingredients. The main research gaps identified in this work and future challenges associated to the widespread application of US and their scale-up to industry operations are also covered in detail.

Reduction of oil uptake in vacuum fried Pleurotus eryngii chips via ultrasound assisted pretreatment

The reduction of oil uptake in vacuum-fried Pleurotus eryngii chips by ultrasound assisted pretreatment was investigated regarding the pore structure changes. Pore structure of P. eryngii chips with four pretreatments, such as blanching, blanching + osmosis, blanching + ultrasound and blanching + ultrasound assisted osmosis was determined by mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). In addition, the quality parameters of vacuum-fried P. eryngii chips such as hardness, rehydration ratio, reducing sugar, protein and oil content were also measured. The results showed that the oil absorption of vacuum fried P. eryngii chips was affected by the porous structure. The oil content of vacuum fried P. eryngii chips was significantly and positively correlated with the pores with diameters above 50, 5–50, and 0.5–5 μm in the samples both before and after vacuum frying, while negatively correlated with the pores with diameters below 0.5 μm. Ultrasound pretreatment changed the microporous structure of P. eryngii chips, effectively hindering the oil absorption of samples. In particular, ultrasound assisted osmosis pretreatment induced the formation of more micropores. It was concluded that blanching + ultrasound assisted osmosis pretreatment is a promising method to reduce oil absorption and improve the quality of vacuum fried foods.

Ultrasonic treatment decreases Lyophyllum decastes fruiting body browning and affects energy metabolism

Lyophyllum decastes is a common mushroom that is prone to browning during prolonged storage. In this study, the effects of ultrasonic treatment on metabolic gene expression, enzyme activity, and metabolic compounds related to L. decastes browning were investigated. Treatment of the fruiting body at 35 kHz and 300 W for 10 min reduced the browning index of L. decastes by 21.0 % and increased the L* value by 11.1 %. Ultrasonic treatment of the fruiting body resulted in higher levels of total phenols, flavonoids, and 9 kinds of amino acid with catalase (CAT) and peroxidase (POD) activities maintained at high levels. Higher cytochrome c oxidase (CCO), succinate dehydrogenase (SDH), phosphofructokinase (PFK), and pyruvate kinase (PK) activities may be ascribed to increased antioxidant capacity. Moreover, ultrasonication retained higher adenosine triphosphate (ATP) concentrations with an increased energy charge, while there were lower levels of adenosine diphosphate (ADP) and reduced and oxidized nicotinamide adenine dinucleotide (NADH and NAD⁺), respectively. Meanwhile, lower lignin contents were observed, along with retarded polyphenol oxidase (PPO) and lipoxygenase (LOX) activities. Lower PPO activity reduced the fruiting body enzymatic browning rate through decreased expression of LdPpo1, LdPpo2, and LdPpo3 during storage at 4 °C for 16 days. This activity may be used to determine the effectiveness of ultrasonication.

Multi-frequency power ultrasound as a novel approach improves intermediate-wave infrared drying process and quality attributes of pineapple slices

This study evaluated the effect of mono-frequency ultrasound (MFU, 20 kHz), dual-frequency ultrasound (DFU, 20/40 kHz), and tri-frequency ultrasound (TFU, 20/40/60 kHz) on mass transfer, drying kinetics, and quality properties of infrared-dried pineapple slices. Pretreatments were conducted in distilled water (US), 35 °Brix sucrose solution (US-OD), and 75% (v/v) ethanol solution (US-ET). Results indicated that ultrasound pretreatments modified the microstructure of slices and shortened drying times. Compared to the control group, ultrasound application reduced drying time by 19.01-28.8% for US, 15.33-24.41% for US-OD, and 38.88-42.76% for US-ET. Tri-frequency ultrasound provoked the largest reductions, which exhibited time reductions of 6.36-11.20% and better product quality compared to MFU. Pretreatments increased color changes and loss of bioactive compounds compared to the control but improved the flavor profile and enzyme inactivation. Among pretreated sample groups, US-OD slices had lower browning and rehydration abilities, higher hardness values, and better retention of nutrients and bioactive compounds. Therefore, the combination of TFU and osmotic dehydration could simultaneously improve ultrasound efficacy, reduce drying time, and produce quality products.

Environmentally Friendly Techniques for the Recovery of Polyphenols from Food By-Products and Their Impact on Polyphenol Oxidase: A Critical Review

Even though food by-products have many negative financial and environmental impacts, they contain a considerable quantity of precious bioactive compounds such as polyphenols. The recovery of these compounds from food wastes could diminish their adverse effects in different aspects. For doing this, various nonthermal and conventional methods are used. Since conventional extraction methods may cause plenty of problems, due to their heat production and extreme need for energy and solvent, many novel technologies such as microwave, ultrasound, cold plasma, pulsed electric field, pressurized liquid, and ohmic heating technology have been regarded as alternatives assisting the extraction process. This paper highlights the competence of mild technologies in the recovery of polyphenols from food by-products, the effect of these technologies on polyphenol oxidase, and the application of the recovered polyphenols in the food industry.

The promoted hydrolysis effect of cellulase with ultrasound treatment is reflected on the sonicated rather than native brown rice

Brown rice is nutritionally superior to polished white rice, as it maintains a large content of external bran that involves a series of bioactive compounds. However, the presence of bran also restricts water diffusion and results in adverse quality of brown rice. In this work, ultrasound conditions were optimized for cellulase to improve its hydrolysis effect on rice bran, and combinations of enzymatic and ultrasound treatment in different manners were conducted on brown rice, to improve the textural attributes. The results showed significant improvements in the catalytic activity and efficiency of cellulase after ultrasonication at the optimal intensity of 1.67 W cm-3 and duration of 30 min, with the conformational variation of cellulase observed from the fluorescence spectra and circular dichroism (CD). Despite the enhanced activity of ultrasonicated cellulase, it leaded to a similar rice surface morphology and a comparable amount of released glucose, and equivalent textural parameters of brown rice treated by native cellulase. However, for the pre-sonicated brown rice, the ultrasonicated cellulase showed a significantly higher hydrolysis capacity than the untreated enzyme, suggesting the important influence of ruptured bran surface on amplifying the hydrolysis effect of cellulase. Compared to the successive ultrasound stimulation on both cellulase and brown rice, ultrasound-assisted cellulase treatment on brown rice produced less glucose from rice bran, but induced similar textural properties of brown rice, possibly resulting from the simultaneously promoting effect of ultrasonication on cellulase and water diffusion. Ultimately, this study highlighted that the mild rice surface rupture is a crucial factor to display the promoted hydrolysis effect of ultrasonicated cellulase on brown rice. Ultrasound-assisted cellulase treatment potentially provides an effective strategy to improve the edible quality of brown rice.