Application of ultrasound in grape mash treatment in juice processing

Optimization of thermosonication conditions for critical quality parameters of watermelon juice using response surface methodology

Topical consumer interest in natural, healthier, safer and nutritional juice, has inspired the search for innovative technologies that can minimize product degradation. In this regard, thermosonication has been proposed as a potential processing technology that can preserve and produce "fresh" products. Watermelon (Citrullus lanatus) juice is a nutrient-rich fruit juice that is desired by consumers due to its appealing color, pleasant odor, sweet taste and low-calorie content. This fruit juice is, however, highly perishable and prone to microorganisms, because of its neutral pH value and high amount of water activity. In addition, it is thermo-sensitive and therefore degrades quickly under thermal processing. This study aimed to identify the optimal thermosonication processing conditions for retaining the critical quality parameters (lycopene, β-carotene, ascorbic acid and total polyphenolic content) of watermelon juice. Response surface methodology, employing a central composite design, was used to determine the effects of temperature (18-52 °C), processing time (2-13 min) and amplitude level (24-73 μm) at a constant frequency of 25 kHz. The highest quality parameters were obtained at 25 °C, 2 min, and 24 µm at a constant frequency of 25 kHz, which resulted in lycopene of 8.10 mg/100 g, β-carotene of 0.19 mg/100 g, ascorbic acid of 3.11 mg/100 g and total polyphenolic content of 23.96 mg/GAE/g with a desirability of 0.81. The proposed model was adequate (p < 0.0001), with a satisfactory determination coefficient (R2) of less than 0.8 for all phytochemicals. Thermosonicated watermelon juice samples showed minimal changes in their phytochemical properties, when compared to fresh juices; the lycopene content showed a significant increase after thermosonication, and a significant retention of β-carotene, ascorbic acid and total polyphenolic acid was observed. According to the findings, thermosonication could be a viable method for preserving watermelon juice, with minimal quality loss and improved functional attributes.

Toward gentle chokeberry juice production by ultrasound-assisted enzymatic maceration

Sustainable processes accompanied by high extraction yields and minimized amounts of by-products are a major goal of current fruit juice production. Controlled degradation of cell wall polysaccharides, in particular pectin, may contribute to reduced emergence of side streams. Possible strategies for the optimization are the selection of enzyme preparations based on comprehensive studies of their activities, the adjustment of maceration temperature toward more gentle conditions, and the application of alternative technologies such as ultrasound (US) during maceration. The present study provides insights into the effects of ultrasound-assisted enzymatic maceration (UAEM) on pectin degradation, total anthocyanin content, thermal and storage stability, and juice yield during chokeberry juice production on pilot-plant scale. The two enzyme preparations applied predominantly possessed polygalacturonase or pectin lyase activity. Cell wall polysaccharide degradation was improved by US and resulted in a 3% increase in juice yield by UAEM using an enzyme preparation that shows mostly polygalacturonase activity. Thermostability of anthocyanins was improved in juices produced using pectin lyase and applying US and matched the stability of anthocyanins in juices produced using polygalacturonase. Storage stability of anthocyanins was improved in juice produced using polygalacturonase during UAEM. UAEM also resulted in lower yields of pomace making the production more resource-efficient. Overall, the use of polygalacturonase has promising potential to advance conventional chokeberry juice production by applying US at gentle conditions.

Effects of different maceration techniques on the colour, polyphenols and antioxidant capacity of grape juice

This study investigated the effects of different maceration techniques on the colour parameters, phenolic content and antioxidant activity of grape juice. Maceration techniques influenced colour parameters, and a* and Hue ranged from -0.77 to 0.55 and 60.90 to 104.40, respectively. The microwave and microwave and sonication combination increased the total monomeric anthocyanin, phenolic and flavonoid contents. Malvidin 3-O-glucoside increased more than twofold, and delphinidin 3-O-glucoside and cyanidin 3-O-glucoside increased one fold according to the enzymatic method in the microwave treatments. The microwave technique was the most effective technique for antioxidant capacity, but sonication, cold and thermosonication results were lower than enzymatic treatment. The microwave and microwave and sonication enhanced the polyphenols with strong antioxidant power, such as catechin from 0.87 to 37.40 and trans-resveratrol from 0.09 to 0.23 mg/100 g, by comparison with the enzymatic technique. The findings suggested these two techniques were the most effective techniques for maceration.

Sono-activation of food enzymes: From principles to practice

Over the last decade, sono-activation of enzymes as an emerging research area has received considerable attention from food researchers. This kind of relatively new application of ultrasound has demonstrated promising potential in facilitating the modern food industry by broadening the application of various food enzymes, improving relevant industrial unit operation and productivity, as well as increasing the yield of target products. This review aims to provide insight into the fundamental principles and possible industrialization strategies of the sono-activation of food enzymes to facilitate its commercialization. This review first provides an overview of ultrasound application in the activation of food protease, carbohydrase, and lipase. Then, the recent development on ultrasound activation of food enzymes is discussed on aspects including mechanisms, influencing factors, modification effects, and its applications in real food systems for free and immobilized enzymes. Despite the far fewer studies on sono-activation of immobilized enzymes compared with those on free enzymes, we endeavored to summarize the relevant aspects in three stages: ultrasound pretreatment of free enzyme/carrier, assistance in immobilization process, and modification of the already immobilized enzyme. Lastly, challenges for the scalability of ultrasound in these target areas are discussed and future research prospects are proposed.

High power ultrasound treatment of crushed grapes: Beyond the extraction phenomena

The treatment of white and red crushed grapes by high power ultrasounds (US) represents an emerging technology in winemaking. In 2019, it was officially recognized by OIV through the resolution n°616-2019, and it was also approved by European Union in January 2022. The US effect on extraction mechanisms was widely studied, but more researches are needed to better understand the ultrasound effect on some specific classes of grape compounds. This research aimed to highlight at laboratory scale some specific effects of ultrasounds on some key compounds of white and red grapes. The samples were sonicated at different frequency (20-30 kHz), time (1-10 min), and power (30-90%) technological conditions used in maceration, to obtain valuable information on potential technological transferability. Valuable results were obtained regarding the release of thiols from their precursors, and the reactivity changes of unstable proteins of white wines. The experimental trails on red grape varieties allowed a maintenance of free anthocyanins and no degradative effects were highlighted. Significant and valuable effects were determined also on the tannin polymerization, with an astringency decrease.

The sonication treatment of crushed grapes showed several chemical effects that contribute to decreasing the winemaking inputs and preserving the wine quality. The process conditions must be managed related to grape variety and ripeness for a precision winemaking.

The impact of ultrasound-assisted thawing on the bioactive components in juices obtained from blue honeysuckle (Lonicera caerulea L.)

Ultrasound (US) assisted thawing of blue honeysuckle berry was utilized in order to reduce the losses of bioactive components (ascorbic acid, anthocyanins, phenolic acids, iridoids, proanthocyanins) and increase the extraction efficiency during juice processing. It was analysed whether it was more beneficial to apply US (alone or with enzymatic treatment) to the frozen state, until reaching the cryoscopic temperature or thawed state. Both the US and enzymatic treatment significantly increased the extraction efficiency, extract content, acidity and the content of iridoids and chlorogenic acid in juices, especially if the US was applied to 50 °C. It was probably due to a higher extractivity by the greater damage of the tissue and detexturation. Enzymatic treatment due to long heating contributed to a higher degradation of anthocyanins, ascorbic acid and proanthocyanidins, which are more heat-sensitive. The results of the study mainly indicated the possibility of including ultrasound-assisted thawing in the fruit processing before pressing the juices. This may replace costly enzymatic treatment.

Effects of ultrasound on the enzymatic degradation of pectin

Ultrasound-assisted enzymatic maceration (UAEM) has gained considerable interest in the fruit juice industry, owing to its potential to increase juice yield and content of polyphenols while simultaneously saving time and energy. In this study, the effects of UAEM (ultrasonic probe, 20 kHz, 21 W*cm^-2 and 33 W*cm^-2) on pectin degradation in a continuous circulation system were investigated over 60 and 90 min. Main pectinolytic enzymes activities of (polygalacturonase, pectin lyase and pectin methylesterase) of a commercial enzyme preparation were examined for individual synergistic effects with US. Pectin hydrolysis by UAEM differed significantly compared to treatment with ultrasound or enzymes alone regarding the profile of degradation products compared to treatment with ultrasound or enzymes alone. Ultrasound fragmented pectin to less branched oligomers of medium molecular weight (Mp approx. 150 kDa), which were further degraded by pectinolytic activities. The low molecular weight fraction (<30 kDa), which is known to be beneficial for juice-quality by adding nutritional value and stabilizing polyphenols, was enriched in small oligomers of homogalacturonan-derived, rhamnogalacturonan I-derived, and rhamnogalacturonan II-derived residues. Synergistic effects of ultrasound application enhanced the effective activities of polygalacturonase and pectin lyase and even prolonged their performance over 90 min, whereas the effective activity of pectin methylesterase was not affected. Final marker concentrations determined by each enzyme assay revealed a considerable higher total process output after UAEM treatment at reduced temperature (30 °C) comparable to the output after conventional batch maceration at 50 °C. The obtained results demonstrate the high potential of UAEM to produce high-quality juice by controlling pectin degradation while reducing process temperature and equally highlight the matrix and enzyme specific effects of a simultaneous US treatment.

Effect of thermosonication on quality attributes of hog plum (Spondias mombin L.) juice

The use of thermosonication (TS) technique to preserve the qualities of fruit juice as an alternative to conventional pasteurization has attracted research interest in recent times. In the present study, freshly prepared hog plum juice (control), and the juice samples subjected to pasteurization (90 °C for 60 s) and thermosonication (40 kHz, 400 W at 40, 50 and 60 °C each for 5, 10, 20 and 30 min) were each analyzed for physicochemical, bioactive, microbial and sensory properties. After treatment, no significant changes in pH, total soluble solids and titratable acidity were observed. Notably, TS at 40 and 50 °C significantly (p < 0.05) improved color parameters, cloudiness and browning index. Furthermore, thermosonication increased ascorbic acid (11.40-18.55%), total phenolic content (17.98-18.35%), carotenoids (2.19-4.30%), flavonoids (10-16%) and antioxidant activity (32.52-48.5%) relative to the control. Both treatments significantly reduced the microbial count to non-detectable level after processing, while sensory attributes slightly improved. However, TS treatment at 60 °C decreased most of the quality parameters. Results showed that TS can improve quality, safety and economic potential of hog plum juice as a feasible alternative to pasteurization.

Effects of Blueberry and Black Carrot Extracts Addition on Antioxidant Properties and Protein-Precipitating Capacity of Ultrasound-Treated Cider

The results presented in this study highlight the level of total phenolic content (TPC), total flavonoid content (TFC) and protein-precipitating capacity (PPC) correlated with the antioxidant capacity of new cider varieties enriched with valuable bio compounds by the addition of blueberry and black carrot extracts. The cider variants were treated with ultrasound (constant frequency of 20 kHz) at 20%, 30% and 40% amplitude (A) for two, five or seven minutes. TPC determination was performed by Folin–Ciocâlteu method and TFC was determined by an aluminum chloride colorimetric method. The antioxidant capacity was determined by ferric-reducing antioxidant power assay (FRAP), ABTS (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) assay and DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity. The results showed that the antioxidant performance indicators (FRAP, ABTS and DPPH) were positively correlated with the TPC and TFC of the ultrasound-treated cider variants, suggesting that the content of these bio compounds may be improved by the treatments applied. The highest mean values for TPC and TFC were found in the cider variant enriched with black carrot extract (0.3%, v/v), subsequently ultrasound-treated (A20%, five minutes) Conclusively, the extracts used in this study could improve the antioxidant capacity of the cider, especially in case of variants ultrasound-treated.

Rapid and Enhanced Liquefaction of Pulp from Mango (Mangifera indica L.) cv. Totapuri Using Ultrasound-Assisted Enzyme Pretreatment

The effect of ultrasound and enzyme pretreatment (with pectinase, amylase, and cellulase) on the physicochemical properties (yield, viscosity, total soluble solids, and total phenolics) of mango juice was evaluated through a set of six experiments. Ultrasonication treatment alone showed no influence on juice yield (54.6 ± 1.1%). However, the combined uses of ultrasonication with a pectinase or the enzyme mixture significantly increased the yield (94.1 ± 1.4% and 80.0 ± 2.1%, respectively) and decreased the enzyme pretreatment time (from 2 h to 1 h). Pectinase treatment assisted by ultrasonication was more effective with regard to juice yield, viscosity reduction, and the clarity of the juice than the enzyme mixture treatment with ultrasonication. Ultrasonication alone significantly increased the amount of total phenolics (65.5 ± 1.0 mg/100 mL) and showed a slight reduction of viscosity and improvement of clarity compared to the control.

Effect of ultrasound, heating and enzymatic pre-treatment on bioactive compounds in juice from Berberis amurensis Rupr

The aim of the study was to assess the influence of ultrasound (frequency 20 kHz, amplitude 70%, power 140 W for 10 min), heating (80 °C, 5 min) and enzymatic pre-treatment of mash (50 °C, Rohapect 10L at a dose of 0.23 g/1000 g, maceration time 60 min) on the yield, the content of phenolic compounds (including anthocyanins), ascorbic acid, and the antioxidative capacity of Berberis amurensis juice. Additionally, the polyphenols profile of this raw material and juices was identified. 25 phenolic compounds were identified in the fruit and 24 in juices. The content of phenolics in the fruit was 636 mg/100 g. Chlorogenic acid, 4-hydroxybenzoate and quercetin-3-O-glicoside were predominant. The content of anthocyanins in the fruit was 217 mg/100 g f.w., where peonidin-3-O-glucoside (98%) was predominant. The content of ascorbic acid amounted to 16.60 mg/100 g. The yield of the barberry juice pressing process ranged from 56% to 60% - there were no differences between the mash treatment methods. The enzymatic and thermal treatment of the mash resulted in the highest content of phenolic compounds in the juice. The sonication resulted in the highest content of anthocyanins, including peonidin-3-O-glucoside, as the main anthocyanin. The thermal treatment of the mash resulted in a lower loss of ascorbic acid than the other methods. The juice from the mash subjected to pectinolysis or heat treatment exhibited the highest antioxidative capacity.

An Overview of Effects Induced by Pasteurization and High-Power Ultrasound Treatment on the Quality of Red Grape Juice

In juice processing, ultrasound treatment has been tested as a potential alternative to conventional thermal methods to inactivate microorganisms and to enhance the nutritional status of juice. In this study, the impact of pasteurization and high-power ultrasound treatment on the quality of red grape juice was investigated in terms of the content of bioactive compounds such as phenolic compounds and l-ascorbic acid as well as regarding the microbiological and physicochemical properties. The grape juice was subjected to pasteurization (80 °C, 2 min) as well as to ultrasound treatment with an amplitude of 50 and 70% for 5 and 10 min. The results indicated the same level of total phenolic content for pasteurized and sonicated samples for 10 min with an amplitude of 70%, while the highest level of l-ascorbic acid was recorded for sonicated samples with an amplitude of 70% for 10 min. pH of sonicated samples decreased with amplitude and treatment time while total soluble solids and titratable acidity increased with amplitude and time. Moreover, the results indicated the usefulness of juice sonication to enhance the inactivation of microorganisms. Thus, the high-power ultrasound treatment might represent a viable technique to replace the conventional thermal treatment in grape juice processing.

Influence of Combined Effect of Ultra-Sonication and High-Voltage Cold Plasma Treatment on Quality Parameters of Carrot Juice

Influence of the combined effect of ultra-sonication (US) and high-voltage cold plasma treatment (HVCP) on the quality parameters of fresh carrot juice has been studied. During the treatment of ultra-sonication, carrot juice was subjected to a 0.5 inch probe for 3 min by adjusting the pulse duration 5 s on and off at 20 kHz frequency, amplitude level 80%. The ultrasound intensity was measured by using a thermocouple and was 46 Wcm⁻². The temperature was maintained at 10 °C by an automatic control unit. During the treatment of HVCP, carrot juice was then subjected to dielectric barrier discharge (DBD) plasma discharge at 70 kV voltage for 4 min. Significant increases were observed when HVCP treated carrot juice was tested against total carotenoids, lycopene, and lutein when compared to the control treatments. Moreover, this increase was raised to its highest in all pigments, chlorogenic acid, sugar contents, and mineral profile, as the results of ultra-sonication when combined with high voltage atmospheric cold plasma (US-HVCP). Whereas, a significant decreased was observed in Mg, total plate count, yeast, and mold after US-HVCP treatment. Furthermore, results indicated that the combined effect of US-HVCP treatment has improved the quality and led to a higher concentration of lycopene, lutein, chlorogenic acid, and mineral compounds (Na, K, and P). Therefore, the findings of the current study suggested that US-HVCP treatment is a novel combined technique that could provide better quality and more stability during the processing of carrot juice with better physicochemical properties and bio-available nutrients, so this novel processing technique could serve as an alternative to traditional processes.

Recent advances in ultrasound application as a novel technique in analysis, processing and quality control of fruits, juices and dairy products industries: A review

Recently, ultrasound has been widely used in the researches in the food science and technology. Among the food materials, fruits, juices and dairy products are strongly sensitive to ultrasound-based techniques. In this review paper, applications of ultrasound in terms of high and low-power modes in processing, instrumentation and control of the industrial operations are studied in the fruit, juice and dairy sectors of the food science and technology by emphasizing the principles of these techniques and their physicochemical effects on the products. Also, a comprehensive analysis of these methods and important factors influencing their performance are presented, along with the advantages and the drawbacks of each ultrasound-assisted techniques. The solutions for better productivity of this technique would be presented and future trend of this technology would be outlined. By studying the latest researches and advances in the field of ultrasound applications, it has been confirmed that this technique can be helpful in accelerating processes, reducing energy requirements, increasing productivity, and producing better quality food materials in the fields of fruits, juices and dairy products. Notwithstanding, in order to solve the challenges ahead, and for potential applications of ultrasound technology, further researches need to be expanded in the areas mentioned. Also, with the advancement of technology, more advanced equipment, ultrasound transducers and instrumentations would be introduced that needs to be applied in this regard, to solve the current challenges.

Ultrasonic Effects on the Quality of Mulberry Juice

This study was conducted to investigate the effects of ultrasonic treatments on the extraction yield and the quality of mulberry juice. The mulberry mash was treated with ultrasound at different incubation times from 30 to 120 min and different temperatures from 30 to 75 °C. The determination of the juice yield, total phenolic content, total anthocyanin content, antioxidant capacity, l-ascorbic acid content, total soluble solids, and the titratable acidity of the juice were carried out. Overall, applying ultrasound at 45 °C for 60 min resulted in the highest juice yield and antioxidant contents for the mulberry juice. The ultrasonic treatment increased the extraction yield (29.6%), the total soluble solid (8.7%), the titratable acidity (39.3%), the l-ascorbic acid content (94.3%), total phenolic content (174.1%), total anthocyanin content (156.9%) and the antioxidant capacity (40.7%) of the mulberry juice as compared to pressing only. A strong positive correlation between the total phenolic content and the antioxidant capacity indicated that phenolic compounds were the main antioxidants in the beverage.

Comparison of Enzymatic and Ultrasonic Extraction of Albumin from Defatted Pumpkin (Cucurbita pepo) Seed Powder

In this study, ultrasound- and enzyme-assisted extractions of albumin (water-soluble protein group) from defatted pumpkin (Cucurbita pepo) seed powder were compared. Both advanced extraction techniques strongly increased the albumin yield in comparison with conventional extraction. The extraction rate was two times faster in the ultrasonic extraction than in the enzymatic extraction. However, the maximum albumin yield was 16% higher when using enzymatic extraction. Functional properties of the pumpkin seed albumin concentrates obtained using the enzymatic, ultrasonic and conventional methods were then evaluated. Use of hydrolase for degradation of cell wall of the plant material did not change the functional properties of the albumin concentrate in comparison with the conventional extraction. The ultrasonic extraction enhanced water-holding, oil-holding and emulsifying capacities of the pumpkin seed albumin concentrate, but slightly reduced the foaming capacity, and emulsion and foam stability.

Microbial pectinases: an ecofriendly tool of nature for industries

Pectinases are the growing enzymes of biotechnological sector, showing gradual increase in their market. They hold a leading position among the commercially produced industrial enzymes. These enzymes are ecofriendly tool of nature that are being used extensively in various industries like wine industry; food industry; paper industry for bleaching of pulp and waste paper recycling; in the processing of fruit–vegetables, tea–coffee, animal feed; extraction of vegetable oil and scouring of plant fibres. Moreover, enzymatic catalysis is preferred over other chemical methods, since it is more specific, less aggressive and saves energy. This is the review which covers the information available on the applicability potential of this group of enzymes in various sectors.

Effect of ultrasound on survival and growth of Escherichia coli in cactus pear juice during storage

The aim of this study was to investigate the effectiveness of ultrasound as a conservation method for the inactivation of Escherichia coli inoculated into cactus pear juices (green and purple). Total soluble solids, pH, titratable acidity, and the kinetics of E. coli in cactus pear juices treated by ultrasound (60%, 70%, 80% and 90% amplitude levels for 1, 3 and 5min) were evaluated over 5 days. Total inactivation was observed in both fruit juices after 5min of ultrasound treatment at most amplitude levels (with the exception of 60% and 80%). After one and two days of storage, the recovery of bacteria counts was observed in all cactus pear juices. Ultrasound treatment at 90% amplitude for 5min resulted in non-detectable levels of E. coli in cactus pear juice for 2 days. The parameters of pH, titratable acidity and soluble solids were unaffected.

Effect of novel ultrasound based processing on the nutrition quality of different fruit and vegetable juices

Increasing consumer awareness regarding the health benefits of different nutrients in food have led to the requirement of assessing the effect of food processing approaches on the quality attributes. The present work focuses on understanding the effects of novel approaches based on the use of ultrasound and ultraviolet irradiations on the nutritional quality of different fruit and vegetable juices (orange, sweet lime, carrot and spinach juices) and its comparison with the conventional thermal pasteurization operated at 80°C for 10 min. The ultrasound sterilization parameters were maintained at ultrasound frequency of 20 kHz and power of 100 W with treatment time as 15 min. For the case of ultraviolet irradiations, 2 UVC lamps (254 nm) of 8 W were placed in parallel on either sides of the reactor. The treated juices were analyzed for total phenol content, antioxidant activity, vitamin C, carbohydrates etc. It has been established that ultrasound processed juice retained most of the nutrient components to higher extent in comparison to all the other techniques used in the work. Combination of ultrasound and ultraviolet irradiations used to achieve an effective decontamination of juices (recommended 5 log reduction of microorganisms) also retained nutrients to a higher level in comparison to the thermal method; however some losses were observed as compared to the use of only ultrasound which could be attributed to inefficient heat exchange in the combined approach. A scale up attempt was also made for treatment of spinach juice using ultrasonic reactors and analysis for quality attributes confirmed that the juice satisfied the criteria of required nutrient contents for 18 days shelf life trial in refrigerated storage conditions. The present work has clearly established the usefulness of ultrasound based treatment in maintaining the nutritional quality of beverages while giving enhanced shelf life as compared to the conventional approaches.

Shelf life, physicochemical, microbiological and antioxidant properties of purple cactus pear (Opuntia ficus indica) juice after thermoultrasound treatment

The objective of this study was to evaluate changes in color, betalain content, browning index, viscosity, physical stability, microbiological growth, antioxidant content and antioxidant activity of purple cactus pear juice during storage after thermoultrasonication at 80% amplitude level for 15 and 25 min in comparison with pasteurized juice. Thermoultrasound treatment for 25 min increased color stability and viscosity compared to treatment for 15 min (6.83 and 6.72 MPa, respectively), but this last parameter was significantly lower (p<0.05) compared to the control and pasteurized juices (22.47 and 26.32 MPa, respectively). Experimental treatment reduced significantly (p<0.05) sediment solids in juices. Total plate counts decreased from the first day of storage exhibiting values of 1.38 and 1.43 logCFU/mL, for 15 and 25 min treatment, respectively. Compared to the control, both treatments reduced enterobacteria counts (1.54 logCFU/mL), and compared to pasteurized juice decreased pectinmethylesterase activity (3.76 and 3.82 UPE/mL), maintained high values of ascorbic acid (252.05 and 257.18 mg AA/L) and antioxidant activity (by ABTS: 124.8 and 115.6 mg VCEAC/100 mL; and DPPH: 3114.2 and 2757.1 μmol TE/L). During storage thermoultrasonicated juices had a minimum increase in pectinmethylesterase activity (from day 14), and exhibited similar total plate counts to pasteurized juice. An increase of phenolic content was observed after 14 days of storage, particularly for treatment at 80%, 25 min, and an increase in antioxidant activity (ABTS, DPPH) by the end of storage.

Inactivation, aggregation, secondary and tertiary structural changes of germin-like protein in Satsuma mandarine with high polyphenol oxidase activity induced by ultrasonic processing

The inhibition of Polyphenol oxidase (PPO) in plants has been widely researched for their important roles in browning reaction. A newly found germin-like protein (GLP) with high PPO activity in Satsuma mandarine was inactivated by low-frequency high-intensity ultrasonic (20 kHz) processing. The effects of ultrasound on PPO activity and structure of GLP were investigated using dynamic light scattering (DLS) analysis, transmission electron microscopy (TEM), circular dichroism (CD) spectral measurement and fluorescence spectral measurement. The lowest PPO activity achieved was 27.4% following ultrasonication for 30 min at 400 W. DLS analysis showed ultrasound caused both aggregation and dissociation of GLP particles. TEM images also demonstrated protein aggregation phenomena. CD spectra exhibited a certain number of loss in α-helix structure content. Fluorescence spectra showed remarkable increase in fluorescence intensity with tiny blue-shift following ultrasonication. In conclusion, ultrasound applied in this study induced structural changes of GLP and eventually inactivated PPO activity.