Power ultrasound decontamination of wastewater from fresh-cut lettuce washing for potential water recycling

Multimode ultrasonic-assisted decontamination of fruits and vegetables: A review

Fruits and vegetables (F&V) are a significant part of our diet consumption. Microbial and pesticide residues are the predominant safety hazards of F&V consumption. Ordinary water washing has a very limited effect on removing microorganisms and pesticide residues and requires high water usage. Ultrasound, as an environmentally friendly technology, shows excellent potential for reducing microbial contamination and pesticide residue. This paper summarizes the research on ultrasound application in F&V washing, including the removal of microbial and pesticide residues and the comprehensive effect on their physicochemical characteristics. Furthermore, multimode ultrasonic-assisted techniques like multi-frequency and sequential ultrasound, combined with novel and conventional methods, can enhance the ultrasound-based effect and be more effective and sustainable in preventing F&V from microbial contamination. Overall, this work explicitly establishes the background on the potential for ultrasound cleaning and disinfection in the food industry as a green, effective, and ultimate method of preventing foodborne illnesses.

Cactus polysaccharides enhance preservative effects of ultrasound treatment on fresh-cut potatoes

The shelf life of fresh-cut fruits and vegetables is affected by microbial growth, enzymatic browning, and loss of flavor. Although ultrasound (US) treatment is often used in the preservation of fresh-cut fruits and vegetables, it has limited antibacterial and preservative effects. Here, we used cactus polysaccharides (CP) to enhance the preservative effect of ultrasound treatment and extended the shelf life of fresh-cut potatoes. The results showed that combined treatment (CP + US) exerted better antimicrobial and anti-browning effects than individual treatments (either US or CP alone). In addition, CP + US has no adverse effect on texture and quality properties, as well as reduced the mobility of internal water. Combination treatment not only significantly decreased the activities of polyphenol oxidase and peroxidase (P < 0.05), but also maintained a high level of phenylalanine ammonia lyase activity and total phenol content during storage. It also maintained the integrity of cell membrane and reduced its permeability by inhibiting the peroxidation of membrane lipids. In addition, CP + US treatment significantly inhibited the activity of antioxidant enzymes and maintained a high DPPH scavenging ability. GC-IMS technology was used to evaluate the flavor of fresh-cut potatoes. The results showed that CP + US treatment reduced the production of a peculiar smell during storage and maintained a good flavor by inhibiting the production of aldehydes. Taken together, these results indicate that the effective preservation method of CP + US treatment can be utilized to increase the shelf life of fresh-cut potatoes.

Effect of ultrasound and chlorine dioxide on Salmonella Typhimurium and Escherichia coli inactivation in poultry chiller tank water

This study evaluated the application of ultrasound alone or combined with chlorine dioxide (ClO₂) for Salmonella Typhimurium and Escherichia coli inactivation in poultry processing chiller tank water. A Full Factorial Design (FFD) 2² was conducted for each microorganism to evaluate the effect of ultrasound exposure time (x₁: 1 to 9 min; fixed: 37 kHz; 330 W; 25 °C) using a bath, and ClO₂ concentration (x₂: 1 to 17 mg L^-1) on microorganism count expressed in log CFU mL^-1 in distilled water. Variable x₂ had a negative effect on Salmonella Typhimurium (-5.09) and Escherichia coli (-2.00) count, improving the inactivation; while a x₁ increase present no inactivation improvement, explaining the use of x₁ lower level (1 min) and x₂ higher level (17 mg L^-1). The best condition for microorganism inactivation based on FFD was evaluated in chiller tank water (with organic matter) at 25, 16, and 4 °C; x₁ was kept (1 min), however x₂ was adjusted to obtain the same residual free chlorine (2.38 mg L^-1) considering the ClO₂ consumption by organic matter, achieving the value of 30 mg L^-1. An inactivation of 49% and 31% were observed for Salmonella Typhimurium and Escherichia coli. When ultrasound was replaced by a simple agitation in the presence of ClO₂, there was no inactivation for both microorganisms. Moreover, at poultry carcass pre-chilling (16 °C) and chilling (4 °C) conditions, the synergism of ultrasound combined with ClO₂ was more pronounced, with microorganisms' reductions up to 100%.

Exploring thermosonication as non-chemical disinfection technology for strawberries

The scope of this work was to study the efficacy of the combination of sonication at 35 or 130 kHz with three temperature treatments: 20, 50 and 55 ºC, on the population of artificially inoculated Listeria innocua in strawberries, and on their overall quality. Prior in vitro results showed that temperature was the main factor in decreasing L. innocua population: a maximum of 3.8 log reductions was obtained with sonication at 130 kHz and 55 ºC for 15 min Treatments combining—or not—sonication at 130 kHz with mild temperatures (50 and 55 ºC) for 5 or 10 min were able to decrease about 3 log units of artificially inoculated L. innocua in strawberries and about 2 log units of total aerobic mesophilic and yeasts and molds populations naturally occurring in strawberries. Thermosonication treatments did not exert a detrimental impact on fruit quality, except for those at the higher temperatures and times, which caused a change in color to more purplish and a little softening of the strawberries, which were proposed to be assessed for further processing other than fresh commercialization. Overall, the impact of sonication in fresh strawberries needs to be further investigated to find the adequate conditions to enhance the effects of temperature itself.

Effective pretreatment technologies for fresh foods aimed for use in central kitchen processing

The central kitchen concept is a new trend in the food industry, where centralized preparation and processing of fresh foods and the distribution of finished or semi-finished products to catering chains or related units take place. Fresh foods processed by a central kitchen mainly include fruit and vegetables, meat, aquatic products, and edible fungi; these foods have high water activities and thermal sensitivities and must be processed with care. Appropriate pretreatments are generally required for these food materials; typical pretreatment processes include cleaning, enzyme inactivation, and disinfection, as well as packaging and coating. To improve the working efficiency of a central kitchen, novel efficient pretreatment technologies are needed. This article systematically reviews various high-efficiency pretreatment technologies for fresh foods. These include ultrasonic cleaning technologies, physical-field enzyme inactivation technologies, non-thermal disinfection technologies, and modified-atmosphere packagings and coatings. Mechanisms, applications, influencing factors, and advantages and disadvantages of these technologies, which can be used in a central kitchen, are outlined and discussed. Possible solutions to problems related to central-kitchen food processing are addressed, including low cleaning efficiency and automation feasibility, high nutrition loss, high energy consumption, and short shelf life of products. These should lead us to the next step of fresh food processing for a highly demanding modern society. © 2020 Society of Chemical Industry.

The effect of ultrasonic on reducing anti-browning minimum effective concentration of purslane extract on fresh-cut potato slices during storage

Enzymatic browning is one of the major difficulties for the preservation and commercial value of fresh-cut products. To research more healthy and inexpensive anti-browning methods, we investigated the effect of ultrasonic coupling purslane extract on the browning resistance of fresh-cut potato during 8d storage at 4 °C. Firstly, the optimal ultrasonic time (10 min) was obtained. Then, the results showed that the combined application with lower purslane extract concentration (0.02%, w/w) could achieve a better anti-browning effect than the optimal concentration of alone purslane extract (0.05%, w/w). The combined application not only significantly inhibited the key enzyme activities of polyphenol oxidase (PPO) and peroxidase (POD), but also effectively reduced the damage to cell membrane, maintained its integrity and permeability. Meanwhile, it also improved antioxidant capacity during storage. Overall, the ultrasonic cavitation combined with purslane extract would be a promising method for fresh-cut industry.

Microbiological Reduction Strategies of Irrigation Water for Fresh Produce

ABSTRACT

Irrigation water can be a source of pathogenic contamination of fresh produce. Controlling the quality of the water used during primary production is important to ensure food safety and protect human health. Several measures to control the microbiological quality of irrigation water are available for growers, including preventative and mitigation strategies. However, clear guidance for growers on which strategies could be used to reduce microbiological contamination is needed. This study evaluates pathogenic microorganisms of concern in fresh produce and water, the microbiological criteria of water intended for agricultural purposes, and the preventative and mitigative microbial reduction strategies. This article provides suggestions for control measures that growers can take during primary production to reduce foodborne pathogenic contamination coming from irrigation water. Results show that controlling the water source, regime, and timing of irrigation may help to reduce the potential exposure of fresh produce to contamination. Moreover, mitigation strategies like electrolysis, ozone, UV, and photocatalysts hold promise either as a single treatment, with pretreatments that remove suspended material, or as combined treatments with another chemical or physical treatment(s). Based on the literature data, a decision tree was developed for growers, which describes preventative and mitigation strategies for irrigation-water disinfection based on the fecal coliform load of the irrigation water and the water turbidity. It helps guide growers when trying to evaluate possible control measures given the quality of the irrigation water available. Overall, the strategies available to control irrigation water used for fresh produce should be evaluated on a case-by-case basis because one strategy or technology does not apply to all scenarios.

HIGHLIGHTS

Escherichia coli inactivation using a hybrid ultrasonic-electrocoagulation reactor

In the current study, a new hybrid ultrasonic-electrocoagulation reactor (U-E reactor) has been used to inactivate Escherichia coli in water. The new hybrid reactor consists of an ultrasonic bath fitted with four perforated aluminium electrodes. These perforated electrodes are designed to act as baffle-plates to enhance the water-mixing process. The electrodes eliminate the need for external mixing devices, which in turn, enhances the cost-effectiveness of the unit. Initially, the ability of the electrocoagulation to inactivate E. coli was optimised for different operating parameters such as electrolysing time (T_e), electrodes spacing (ES) and current density (CD). The ultrasonic field was then applied over different time periods (T_u), during the course of the electrolysing process. Statistical analyses have been conducted to assess the relative effect of each operating parameter on the inactivation of E. coli. An economic study has also been conducted to assess the operating costs of the U-E reactor. The results revealed that the new U-E reactor inactivated 100% of the E. coli within 11 min of electrolysis at ES of 5 mm, CD of 1.5 mA/cm², and an operation cost of 0.212 US $/m³. It was been established that the relative effect of operating parameters on E.coli inactivation followed the order: T_e>T_u>CD>ES.

Evaluation of the ultrasound effect on treated municipal wastewater

In this research, ultrasound (US; 26 kHz) application was evaluated as tertiary treatment of treated municipal wastewater coming from conventional activated sludge (AS) and constructed wetland (CW) systems. The degree of disinfection was evaluated through the total (TC) and faecal (FC) coliforms and by somatic coliphages (SCs) determinations. The experiments were carried out without temperature control at times of 200, 400 and 600 s and with temperature control (298.1 K) at 600, 1200 and 1800 s. Changes in the concentrations of C, N and P were also studied. The results shown that treatment without temperature control allowed 100% inactivation for TC, FC and SC at 600 s, while maximum with temperature was achieved at 1800 s. Temperature was an important factor influencing pathogens inactivation. In both cases, microorganism concentrations complied with different international guidelines for the reuse of treated wastewater. At 1800 s sonication concentrations of biochemical oxygen demand, chemical oxygen demand and total phosphorus were reduced 39.5, 39.4, 50.0 and 37.3% TN in the AS-treated water and 24.0, 49.8, 20.2 and 7.7% in the CW-treated water, respectively. In both cases, the formation of H⋅ and OH⋅ radicals is most likely related to the observed pollutants removal. While energy consumption of ultrasound was higher than other advanced treatments such as electrocoagulation, its implementation allows the simultaneous removal of pathogens and organic pollutants without the generation of toxic by-products. In conclusion, ultrasound can be implemented as tertiary treatment of municipal wastewater for the removal of biological and organic pollution, according to reuse guidelines in terms of pathogens presence.

Effect of power ultrasound on crystallization characteristics of magnesium ammonium phosphate

Magnesium ammonium phosphate (MAP) crystallization could be utilized for the recovery of phosphorus from wastewater. However, the effectiveness of the recovery is largely determined by the crystallization process, which is very hard to be directly observed. As a result, a specific ultrasonic device was designed to investigate the crystallization characteristics of MAP under various ultrasonic conditions. The results demonstrated that the metastable zone width (MZW) narrowed along with the rising of the ultrasonic power. Similarly, for the 6mM MAP solution, with the ultrasonic power gradually enhanced from 0W to 400W, the induction time was shortened from 340s to 38s. Meanwhile, the crystallization rate was accelerated till the power reached 350W, and then remained a constant value. It can be observed from the scanning electron microscopy (SEM), the MAP crystal became bigger in size as well as the crystal size distribution (CSD) became broad and uneven, with the increase of ultrasonic power. The results indicate that the crystallization process enhanced by power ultrasound could be used as an effective method to eliminate and recover the phosphorus from wastewater.