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

Ultrasound Technology as Inactivation Method for Foodborne Pathogens: A Review

An efficient microbiological decontamination protocol is required to guarantee safe food products for the final consumer to avoid foodborne illnesses. Ultrasound and non-thermal technology combinations represent innovative methods adopted by the food industry for food preservation and safety. Ultrasound power is commonly used with a frequency between 20 and 100 kHz to obtain an “exploit cavitation effect”. Microbial inactivation via ultrasound derives from cell wall damage, the oxidation of intracellular amino acids and DNA changing material. As an inactivation method, it is evaluated alone and combined with other non-thermal technologies. The evidence shows that ultrasound is an important green technology that has a good decontamination effect and can improve the shelf-life of products. This review aims to describe the applicability of ultrasound in the food industry focusing on microbiological decontamination, reducing bacterial alterations caused by food spoilage strains and relative foodborne intoxication/infection.

Equivalent processing for pasteurization of a pineapple juice-coconut milk blend by selected nonthermal technologies

Identifying equivalent processing conditions is critical for the relevant comparison of food quality attributes. This study investigates equivalent processes for at least 5-log reduction of Escherichia coli and Listeria innocua in pineapple juice-coconut milk (PC) blends by high-pressure processing (HPP), pulsed electric fields (PEF), and ultrasound (US) either alone or combined with other preservation factors (pH, nisin, and/or heat). The two blends (pH 4 and 5) and coconut milk (pH 7) as a reference were subjected to HPP at 300-600 MPa, 20°C for 0.5-30 min; PEF at an electric field strength of 10-21 kV/cm, 40°C for 24 µs; and US at 120 µm amplitude, 25 or 45°C for 6 or 10 min. At least a 5-log reduction of E. coli was achieved at pH 4 by HPP at 400 MPa, 20°C for 1 min; PEF at 21 kV/cm, 235 Hz, 40°C for 24 µs; and US at 120 µm, 45°C for 6 min. As L. innocua showed greater resistance, a synergistic lethal effect was provided at pH 4 by HPP with 75 ppm nisin at 600 MPa, 20°C for 5 min; PEF with 50 ppm nisin at 18 kV/cm, 588 Hz, 40°C for 24 µs; and US at 45°C, 120 µm for 10 min. The total soluble solids (11.2-12.4°Bx), acidity (0.47%-0.51% citric acid), pH (3.91-4.16), and viscosity (3.55 × 10^-3 -4.0 × 10^-3  Pa s) were not significantly affected under the identified equivalent conditions. HPP was superior to PEF and US, achieving higher ascorbic acid retention and lower color difference in PC blend compared to the untreated sample.

Sodium copper chlorophyll mediated photodynamic treatment inactivates Escherichia coli via oxidative damage

Photodynamic technology (PDT) is an emerging non-thermal processing technique, however, due to a lack of edible photosensitizers, its application to the food industry is limited. To better understand sodium copper chlorophyll (SCC) feasibility as a photosensitizer, we analyzed the effects of PDT-SCC on Escherichia coli O157:H7 inactivation using different lighting times (15, 30, 45, 60, and 75 min), lighting power (30, 60, 90, 120, and 150 W), and SCC concentrations (2, 4, 6, 8, and 10 mM). We showed that bactericidal effects depended on all three parameters, but the most suitable sterilization condition for E. coli occurred at 10 mM SCC, for 60 min at 120 W. We also investigated cell morphology, reactive oxygen species (ROS) production, the activity of three oxidative response enzymes (superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX)), and ompA, ompF, uvrA, and recA expression. When compared with the control group, PDT-SCC destroyed bacterial morphology, increased ROS production, decreased antioxidant enzyme activity (SOD, CAT, and GPX), down-regulated membrane protein gene expression, including ompA and ompF, and up-regulated the DNA damage-repair related genes, uvrA and recA. Thus, bacterial rupture caused by oxidative damage could be the main mechanism underpinning PDT-SCC action.

The effect of ultrasound treatment in combination with nisin on the inactivation of Listeria innocua and Escherichia coli

Ultrasound, alone or in combination with natural antimicrobials, is a novel food processing technology of interest to replace traditional food decontamination methods, as it is milder than classical sterilisation (heat treatment) and maintains desirable sensory characteristics. However, ultrasound efficacy can be affected by food structure/composition, as well as the order in which combined treatments are applied. More specifically, treatments which target different cell components could result in enhanced inactivation if applied in the appropriate order. The microbial properties i.e. Gram positive/Gram negative can also impact the treatment efficacy. This work presents a systematic study of the combined effect of ultrasound and nisin on the inactivation of the bacteria Listeria innocua (Gram positive) and Escherichia coli (Gram negative), at a range of cavitation conditions (44, 500, 1000 kHz). The order of treatment application was varied, and the impact of system structure was also investigated by varying the concentration of Xanthan gum used to create the food model systems (0 - 0.5% w/v). Microbial inactivation kinetics were monitored, and advanced microscopy and flow cytometry techniques were utilised to quantify the impact of treatment on a cellular level. Ultrasound was shown to be effective against E. coli at 500 kHz only, with L. innocua demonstrating resistance to all frequencies studied. Enhanced inactivation of E. coli was observed for the combination of nisin and ultrasound at 500 kHz, but only when nisin was applied before ultrasound treatment. The system structure negatively impacted the inactivation efficacy. The combined effect of ultrasound and nisin on E. coli was attributed to short-lived destabilisation of the outer membrane as a result of sonication, allowing nisin to penetrate the cytoplasmic membrane and facilitate cell inactivation.

Effect of Pretreatment with Low-Frequency Ultrasound on Quality Parameters in Gulupa (Passiflora edulis Sims) Pulp

The Gulupa (Passiflora edulis f. edulis Sims) is an expression of South America’s tropics’ biodiversity, and a source of B vitamins and amino acids. It is a climacteric export fruit for which it is necessary to incorporate emerging technologies for its conservation and transport. This work investigated the effect of ultrasound on gulupa pulp and verified the stability of the characters of interest in the shelf life of 20 days. Six treatments and a control sample were used, evaluated in triplicate, and varied in frequency (30 and 40 kHz) with an exposure time of 10, 20, and 30 min. A statistical analysis of unidirectional variances and Dunnett’s test was used. It was found that the ultrasound treatments did not affect the pH or the titratable acidity. Soluble solid results presented a significant increase (p < 0.05) (from 13.4 to 14.8% w/v) in the antioxidant capacity (from 1.13 to 1.54 µmol Trolox Equivalent (TE)/g by the ABTS•+ (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) Cationic Radical Assay and from 3.3 to 3.7 µmol TE/g by the DPPH· (2,2-diphenyl-1-picrilhydrazil) Radical Scavenging Assay). During the shelf life, ascorbic acid was the parameter that varied most (p < 0.05). It decreased from 42.7 to 21.6 mg ascorbic acid/100 g of pulp in the control sample. However, a smaller decrease was observed (23.8–24.5 mg ascorbic acid/100 g of pulp) in the 40 kHz treatments. The smallest global color difference (ΔE) for the control was found in the 40 kHz treatment at 30 min through the entire shelf life (day 0 to 20). Ultrasound treatment offers a new strategy to improve and extend the shelf life of chilled gulupa pulp.

Spineless cactus use management on microbiological quality, performance, and nutritional disorders in sheep

The physically effective neutral detergent fiber content alone has not been able to explain the appearance of diarrhea in ruminants fed diets with large volumes of spineless cactus, so the proliferation of enterobacteria in spineless cactus may be associated with cases of diarrhea in sheep. In the in vitro test, used two varieties of spineless cactus, both of which were chopped to particles of 4 and 2 cm². For the in vivo test, 15 lambs were allocated to three treatment groups, namely, spineless cactus crushed and immediately supplied to the animals; spineless cactus crushed 8 h before supply; and silage of spineless cactus. The variables evaluated were dry matter intake, weight gain, fecal score, hemogram, and fecal colony count. In the in vitro test, higher Enterobacteriaceae and lactic acid bacteria counts were found both at 12 h and 24 h when the spineless cactus was crushed to 2 cm² in both varieties. The sheep fed the spineless cactus crushed 8 h prior to supply showed the highest Enterobacteriaceae count in the feces (8.48 CFU/g), compared to animals fed silage of spineless cactus (4.95 CFU/g). It can thus be concluded that the management of spineless cactus influences the development of total and fecal coliforms, especially when it is chopped to 2 cm² and exposed to the environment for periods longer than 7 h, and that the bacterial population can be controlled by administering the spineless cactus in the form of silage.

Thermosonication as an alternative method for processing, extending the shelf life, and conserving the quality of pulque: A non-dairy Mexican fermented beverage

The aim of this study was to evaluate thermosonication as an alternative method for the pasteurization of pulque in order to improve its shelf life and retain its quality parameters. Thermosonication was carried out at 50 °C using amplitudes of 75% (for 6 and for 9 min), 85% (for 4 and for 6 min), and 95% (for 3 and for 5 min). These were the optimal conditions found for processing pulque by thermosonication. Physicochemical (acidity, color, alcohol content, and sensory analysis) and microbiological (lactic acid bacteria and yeasts) parameters were determined during 30 days for storage at 4 ± 1 °C. Conventional pasteurization (63 °C, 30 min) and raw pulque were used as controls. According to the results, the shelf life of pulque was extended up to 24 days storage at 4 °C. After this time, the quality of beverage decreased, due that the microbial load increases. Thermosonication treatments at 75% and 85% showed a higher content of LAB (6.58-6.77 log CFU/mL) and yeasts (7.08-7.27 log CFU/mL) than conventional pasteurization (3.64 log CFU/mL of LAB and 3.97 log CFU/mL of yeasts) at 24 days of storage. Raw pulque demonstrated up to 7.77 log CFU/mL of yeasts and 7.51 log CFU/mL of LAB. Pulque processed by thermosonication exhibited greater lightness, sensory acceptance, a maximal acidity of 0.83 g/lactic acid, and an alcohol content of 4.48-4.95% v/v. The thermosonication process preserves sensory and physicochemical properties better than conventional pasteurization. Lactic acid bacteria such as Lactobacillus kefiri, Lactobacillus acidophilus, and Lactobacillus hilgardii and yeasts such as Saccharomyces cereviasiae were identified in thermosonicated pulque.

Nondestructive monitoring, kinetics and antimicrobial properties of ultrasound technology applied for surface decontamination of bacterial foodborne pathogen in pork

In this study, electronic nose (E-nose) and Hyperspectral Imaging (HSI) was employed for nondestructive monitoring of ultrasound efficiency (20KHZ) in the inactivation of Salmonella Typhimurium, and Escherichia coli in inoculated pork samples treated for 10, 20 and 30 min. Weibull, and Log-linear model fitted well (R2 ≥ 0.9) for both Salmonella Typhimurium, and Escherichia coli inactivation kinetics. The study also revealed that ultrasound has antimicrobial effects on the pathogens. For qualitative analysis, unsupervised (PCA) and supervised (LDA) chemometric algorithms were applied. PCA was used for successful sample clustering and LDA approach was used to construct statistical models for the classification of ultrasound treated and untreated samples. LDA showed classification accuracies of 99.26%,99.63%,99.70%, 99.43% for E-nose - S. Typhimurium, E-nose -E. coli, HSI - S. Typhimurium and HSI -E. coli respectively. PLSR quantitative models showed robust models for S. Typhimurium- (E-nose Rp2 = 0.9375, RMSEP = 0.2107 log CFU/g and RPD = 9.7240 and (HSI Rp2 = 0.9687 RMSEP = 0.1985 log CFU/g and RPD = 10.3217) and E. coli -(E-nose -Rp2 = 0.9531, RMSEP = 0.2057 log CFU/g and RPD = 9.9604) and (HIS- Rp2 = 0.9687, RMSEP = 0.2014 log CFU/g and RPD = 10.1731). This novel study shows the overall effectiveness of applying E-nose and HSI for in-situ and nondestructive detection, discrimination and quantification of bacterial foodborne pathogens during the application of food processing technologies like ultrasound for pathogen inactivation.

Exploitation of Ultrasound Technique for Enhancement of Microbial Metabolites Production

Microbial metabolites have significant impacts on our lives from providing valuable compounds for nutrition to agriculture and healthcare. Ever-growing demand for these natural compounds has led to the need for smart and efficient production techniques. Ultrasound is a multi-applicable technology widely exploited in a range of industries such as chemical, medical, biotechnological, pharmaceutical, and food processes. Depending on the type of ultrasound employed, it can be used to either monitor or drive fermentation processes. Ultrasonication can improve bioproduct productivity via intensifying the performance of living organisms. Controlled ultrasonication can influence the metabolites' biosynthesis efficiency and growth rates by improvement of cell permeability as well as mass transfer and nutrient uptake rates through cell membranes. This review contains a summarized description about suitable microbial metabolites and the applications of ultrasound technique for enhancement of the production of these metabolites as well as the associated downstream processing.

Effect of dielectric barrier discharge plasma, ultra-sonication, and thermal processing on the rheological and functional properties of sugarcane juice

The present work was designed to study the impact of dielectric barrier discharge (DBD) plasma, ultrasound (US), and thermal treatment on the functional, rheological, and microbial analysis of sugarcane juice. The results showed that plasma and US treatment did not significantly affect the pH and color of the juice. Total soluble solids (°Brix) value increased from 16.30 ± 0.10 for untreated to 20.50 ± 0.15 during plasma treatment at 45 V for 2 min and 16.65 ± 0.27 during US treatment (40 kHz, power 240 W, and time 40 min). The maximum increase of 25% in total phenolic contents (TPC) and 21% in total flavonoid contents (TFC) was observed in a plasma-treated sample at 40 and 45 V (for 2 min) respectively, whereas 18% in TPC and 16% TFC was observed in the US-treated sample (40 kHz, power 240 W, and time 30 min) as compared to control sample. Plasma treatment increased the antioxidant activities (Ferric reducing antioxidant power (FRAP) assay and 2,2-Diphenyl-1-picrylhydrazyl (DPPH) activity) toward maximum at 40 V and only 6% of vitamin C was degraded than others. Similarly, plasma treatment significantly reduced particle size, which further led to decreased significantly (P < 0.05) the apparent viscosity of sugarcane juice with a rise in shear rate and drove to a speedy breakdown on initial shearing. A significant reduction was observed in the microbial load among all treatments as compared to the control. Significant reductions of 3.6 and 0.50 log CFU/mL were observed in the total aerobic mesophilic and yeast and mold counts after DBD plasma treatment at 45 V for 2 min, respectively. Thus, we can conclude that novel technology like plasma treatment can be effectively used at an industrial scale for the preservation and processing of sugarcane juice. PRACTICAL APPLICATION: Nowadays, novel processing techniques are employed to improve the nutritional quality and stability of juices. The consequences of the present research showed that DBD plasma treatment could improve the TPC, TFC, antioxidant activities, vitamin C, and rheological properties while reducing the activity of the microbial load better than the US and thermal treatment. The verdicts described that novel processing methods can enhance the quality of sugarcane juice at an industrial scale.

Rapid Pasteurization of Apple Juice Using a New Ultrasonic Reactor

A new ultrasonic reactor was used to rapidly inactivate Escherichia coli and Staphylococcus aureus in apple juice. It was found that high pulp content made ultrasound less lethal to S. aureus, while it had no significant effect on E. coli. When the pulp free apple juice was ultrasonically processed, the 5-log reduction time was 35 s for E. coli at 60 °C and 30 s for S. aureus at 62 °C. Ultrasound treatment had no significant effect on antioxidant activity determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, but it significantly increased the total phenolic content. The treatment also resulted in more stable juice with higher uniformity. During 28 d of storage at 4 °C, the total plate count in apple juice ultrasonically treated at 60 °C for 35 s remained around 1.00 log CFU/mL, whereas it was nearly zero for a stronger ultrasound treatment at 62 °C for 30 s. These values were much lower than those in the untreated one, which increased from 3.65 log CFU/mL to 8.36 log CFU/mL during the storage. At the end of the storage, the control and thermally treated apple juice lost almost 70% of antioxidant activity, whereas the ultrasonically treated juice only lost 20-40%.

Stimulation of biosurfactant production by Lactobacillus plantarum using ultrasound

Due to their nonpathogenic status, biosurfactants produced by Lactobacillus strains have been shown to have potential applicability in several industrial sectors, particularly food and pharmaceutical industries. However, products with high efficiency are needed to fulfill the demand for these biosurfactants. Therefore, the present study investigated kinetic parameters, biomass and biosurfactant production of Lactobacillus plantarum ATCC 8014 applying standard MRS and modified MRS (supplemented standard MRS by nitrogen and carbon sources) culture medium under various ultrasonic frequencies of 20, 25, 35, 45, 130 and 950 kHz to obtain more efficient conditions. The optimum conditions were found when using the modified MRS treated by the frequency of 25 kHz (the power of 7.4 W) for 30 min, which led to a significant effect on the growth rate (µ_max, h^-1) rather than control. Furthermore, this condition caused the highest population (10.07 ± 0.1 log CFU/mL) and biomass concentration (4.33 ± 0.06 g/L), and lowest surface tension (39.26 ± 0.5 mN/m), leading to higher biosurfactant production. Hence, given the results of the present study, it can be established that controlled ultrasound exposure and supplementation of culture media using the main growth factors can intensify the microbial activity and the productivity of biological processes.

Effects of Ultrasound Processing on Physicochemical Parameters, Antioxidants, and Color Quality of Bayberry Juice

Effects of ultrasound on physicochemical parameters, ascorbic acid, anthocyanins, polymeric color (PC), 5-hydroxymethylfurfural (HMF), browning degree (BD), color, and superoxide dismutase (SOD) activity of bayberry juice were investigated. Treatments were carried out at amplitude levels from 20 to 100% of total input power (600 W) at 20 kHz for 2–10 min. The results showed that no notable differences in pH, total soluble solids, titratable acidity, and yellowness b∗ values were found in ultrasound-treated samples. The HMF, PC, BD, and L∗ values of bayberry juice obviously increased with enhancing ultrasonic intensity and treatment time. The ascorbic acid exhibited no notable changes after ultrasound treatment at lower intensity levels for short time, while anthocyanins showed an increasing tendency. With increasing ultrasonic intensity and time, antioxidants gradually decreased. Furthermore, the SOD activity apparently increased at short-time treatment and then decreased with ultrasound processing extension.

Three Pillars of Novel Nonthermal Food Technologies: Food Safety, Quality, and Environment

This review gives an overview of the impact of novel nonthermal food technologies on food safety, on quality, and on the environment. It confirms that research in this field is mainly focused on analyzing microbial and/or chemical aspects of food safety. However, recent research shows that in spite of various food safety benefits, some negative (quality oriented) features occur. Finally, this paper shows the necessity of analyzing the environmental dimension of using these technologies.

Ultrasound assisted process intensification of uricase and alkaline protease enzyme co-production in Bacillus licheniformis

Low energy ultrasound irradiation was used to enhance co-production of enzymes uricase and alkaline protease using Bacillus licheniformis NRRL 14209. Production of uricase and alkaline protease was evaluated for different ultrasound parameters such as ultrasound power, time of irradiation, duty cycle and growth stage of organisms at which irradiation is carried out. Maximum uricase production of 0.825 U/mL and alkaline protease of 0.646 U/mL have been obtained when fermentation broth was irradiated at 6 h of growth stage with 60 W power for 15 min of duration having 40% of duty cycle. The enzyme yield was found to be enhanced by a factor of 1.9-3.8 and 1.2-2.2 for uricase and alkaline protease respectively. Nevertheless, intracellular uricase was also observed in a fermentation broth after ultrasonic process intensification. The results indicate the effectiveness of low frequency ultrasound in improving enzyme yields with a vision of commercial applicability of the process.

Combined Effect of Ultrasound and Mild Temperatures on the Inactivation of E. coli in Fresh Carrot Juice and Changes on its Physicochemical Characteristics

The combination of ultrasound and mild temperatures to process fruits and vegetables juices is a novel approach that is showing promising results for microbial inactivation and preservation of bioactive compounds and sensory attributes. This study centers on investigating the inactivation of Escherichia coli (ATCC 11755) in carrot juice as a result of the combined effect of ultrasound (24 kHz frequency, 120 μm, and 400 W) with temperature (50, 54, and 58 °C) and processing time (0 to 10 min). In addition, the possible changes in physicochemical properties and the retention of bioactive compounds after processing were analyzed. Microbial inactivation with ultrasound treatment at 50 °C resulted in 3.5 log reduction after 10 min, whereas at 54 °C almost 5 log reduction was attained in the same period of time; meanwhile, for treatment at 58 °C, no viable cells were detected (>5 log reduction) after 2 min. There was no significant difference (P > 0.05) on pH (6.80 to 6.82), °Brix (8.0 to 8.5), titratable acidity (0.29% to 0.30%), total carotenoid (1774 to 1835 μg/100 mL), phenolic compounds (20.19 to 20.63 μg/mL), ascorbic acid (4.8 mg/100 mL), and color parameters between fresh and ultrasound treated samples at the studied temperatures. To predict the inactivation patterns, observed values were tested using 3 different general models: first-order, Weibull distribution, and biphasic. The Weibull and biphasic models show good correlation for inactivation under all processing conditions. Results show ultrasound in combination with mild temperature could be effectively used to process fresh carrot juice providing a safe product without affecting physicochemical characteristics.

PRACTICAL APPLICATIONS

The combination of ultrasound and mild temperatures is effective in reducing microbial load in carrot juice to safe levels. This combination would be beneficial in the industrial processing of carrot juice without altering the quality attributes or bioactive compounds.

Applications of ultrasound in processing of liquid foods: A review

Ultrasonic processing of a variety of liquids, drinks and beverages has generated much interest with published literature papers increasing within this area in recent years. Benefits include enhanced emulsification with improved homogenization and fat globule size reduction being recorded. In dairy systems increased creaming rates are observed on sonication in a process known as fractionation. Whilst fruit juices exhibit retention or enhancement of quality parameters whilst increasing levels of bioactive compounds. Sterilization of liquids is a large feature of ultrasonic treatment with microbial activity of a range of fruit juices being monitored over time as increased stability and reduced spoilage is observed. Progress has also been made towards scale up of ultrasonic processes with several examples of batch and continuous processes being studied with reduced processing times and temperatures being quoted as a result of ultrasonic treatment. This short review covers the effect of sonication on liquids and beverages with a specific focus towards dairy and fruit juices and covers emulsification, fractionation, sterilization and some pilot scale initiatives.