Ultrasound Processing Alone or in Combination with Other Chemical or Physical Treatments as a Safety and Quality Preservation Strategy of Fresh and Processed Fruits and Vegetables: A Review

Transcriptomic analysis reveals differential gene expression patterns of Lacticaseibacillus casei ATCC 393 in response to ultrasound stress

In recent years, there has been a growing interest in modulating the performance of probiotic, mainly Lactic Acid Bacteria (LAB), in the field of probiotic food. Attenuation, induced by sub-lethal stresses, delays the probiotic metabolism, and induces a metabolic shift as survival strategy. In this paper, RNA sequencing was used to uncover the transcriptional regulation in Lacticaseibacillus casei ATCC 393 after ultrasound-induced attenuation. Six (T) and 8 (ST) min of sonication induced a significant differential expression of 742 and 409 genes, respectively. We identified 198 up-regulated and 321 down-regulated genes in T, and similarly 321 up-regulated and 249 down-regulated in ST. These results revealed a strong defensive response at 6 min, followed by adaptation at 8 min. Ultrasound attenuation modified the expression of genes related to a series of crucial biomolecular processes including membrane transport, carbohydrate and purine metabolism, phage-related genes, and translation. Specifically, genes encoding PTS transporters and genes involved in the glycolytic pathway and pyruvate metabolism were up-regulated, indicating an increased need for energy supply, as also suggested by an increase in the transcription of purine biosynthetic genes. Instead, protein translation, a high-energy process, was inhibited with the down-regulation of ribosomal protein biosynthetic genes. Moreover, phage-related genes were down-regulated suggesting a tight transcriptional control on DNA structure. The observed phenomena highlight the cell need of ATP to cope with the multiple ultrasound stresses and the activation of processes to stabilize and preserve the DNA structure. Our work demonstrates that ultrasound has remarkable effects on the tested strain and elucidates the involvement of different pathways in its defensive stress-response and in the modification of its phenotype.

Probiotic-loaded edible films made from proteins, polysaccharides, and prebiotics as a quality factor for minimally processed fruits and vegetables: A review

Minimally processed fruits and vegetables (MPFVs) are gaining popularity in households because of their freshness, convenience, and rapid consumption, all of which align with today's busy lifestyles. However, their exposure of large surface areas during peeling and slicing can result in contamination by foodborne pathogens and spoilage bacteria, posing potential food safety concerns. In addition, enzymatic browning of MPFVs can significantly reduce their consumer appeal. Therefore, it is necessary to adopt certain methods to protect MPFVs. Recent studies have shown that utilizing biopolymer-based edible films containing probiotics is a promising approach to preserving MPFVs. These active food packaging films exhibit barrier function, antioxidant function, and antimicrobial function while protecting the viability of probiotics, which is essential to maintain the nutritional value and quality of MPFVs. This paper reviews microbial contamination in MPFVs and the preparation of probiotic-loaded edible films with common polysaccharides (alginate, gellan gum, and starch), proteins (zein, gelatin, and whey protein isolate), prebiotics (oligofructose, inulin, and fructooligosaccharides). It also explores the potential application of probiotic-loaded biopolymer films/coatings on MPFVs, and finally examines the practical application requirements from a consumer perspective.

Effect of chitosan coating, carbon dots and ultrasound treatment on microorganisms and physicochemical quality of fresh-cut lettuce

The effect of chitosan (CH) coating, carbon dots (CDs) and ultrasound (US) treatment on microorganisms and the physicochemical quality of fresh-cut (FC) lettuce was investigated. FC lettuces were treated by US and dipped into CD/CH coating, then packed and stored for 15 d at 4°C. Results presented that CD/CH coating exhibited a superior effect on the depressing growth of aerobic plate count, mould and yeast, the decrease of respiratory rate, the inhibition of peroxidase and polyphenol oxidase activities, the maintenance of ascorbic acid and chlorophyll contents, the reduction of mass loss, the restriction of water distribution in US-treated FC lettuce. This exhibited that CD/CH coating effectively kept the microbial and physicochemical quality of FC lettuce.

Effectiveness of a Phage Cocktail as a Potential Biocontrol Agent against Saprophytic Bacteria in Ready-To-Eat Plant-Based Food

This study aimed to evaluate the effectiveness of the phage cocktail to improve the microbiological quality of five different mixed-leaf salads: rucola, mixed-leaf salad with carrot, mixed-leaf salad with beetroot, washed and unwashed spinach, during storage in refrigerated conditions. Enterobacterales rods constituted a significant group of bacteria in the tested products. Selected bacteria were tested for antibiotic resistance profiles and then used to search for specific bacteriophages. Forty-three phages targeting bacteria dominant in mixed-leaf salads were isolated from sewage. Their titer was determined, and lytic activity was assessed using the Bioscreen C Pro automated growth analyzer. Two methods of phage cocktail application including spraying, and an absorption pad were effective for rucola, mixed leaf salad with carrot, and mixed leaf salad with beetroot. The maximum reduction level after 48 h of incubation reached 99.9% compared to the control sample. In washed and unwashed spinach, attempts to reduce the number of microorganisms did not bring the desired effect. The decrease in bacteria count in the lettuce mixes depended on the composition of the autochthonous saprophytic bacteria species. Both phage cocktail application methods effectively improved the microbiological quality of minimally processed products. Whole-spectral phage cocktail application may constitute an alternative food microbiological quality improvement method without affecting food properties.

Ultrasonic washing as an abiotic elicitor to induce the accumulation of phenolics of fresh-cut red cabbages: Effects on storage quality and microbial safety

Ultrasonic washing has been proved to be an abiotic elicitor to induce the accumulation of phenolics in some fruit and vegetables. However, the feasibility of ultrasonic washing on the accumulation of phenolics in fresh-cut red cabbages has not yet been reported. Therefore, the effects of ultrasonic washing on the phenolics and related phenolic metabolism enzymes of fresh-cut red cabbages, as well as quality and microbial safety during cold storage, were investigated. Firstly, the single-factor tests were used to optimize the ultrasonic processing parameters, including frequency mode, frequency amplitude, power density, frequency cycle time, and ultrasonic washing. Then the activities of the enzymes related to phenolic metabolisms after optimal ultrasound treatment were investigated, including phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), and peroxidase (POD). Additionally, the quality and microbial safety of fresh-cut red cabbages stored at 4°C under the optimal ultrasound treatment were evaluated. The results showed that the content of soluble phenolics (SPs) in fresh-cut red cabbages increased significantly during storage under the optimal conditions (28 ± 2 kHz, 60 W/L, 400 ms, and 20 min) compared with the control (P < 0.05). The PAL activity was activated and the PPO and POD activities were inhibited after ultrasonic washing, which contributed to the increase in the content of SPs. Meanwhile, the storage quality and microbial safety of fresh-cut red cabbages were improved. Ultrasonic washing reduced the weight loss and respiration rate and improved the color and texture characteristics. Additionally, the fresh-cut red cabbages after ultrasonic washing showed more retention of ascorbic acid (AA), total soluble proteins (TSPs), total soluble sugars (TSSs), and total soluble solids (SSs) compared with the control. Finally, ultrasonic washing effectively inhibited the growth of bacteria, molds and yeasts, which is beneficial to the extension of the shelf-life of fresh-cut red cabbages. Therefore, ultrasonic washing can be used as a tool to increase the content of SPs in fresh-cut red cabbages while retaining quality attributes and microbial safety.

Conventional and non-conventional disinfection methods to prevent microbial contamination in minimally processed fruits and vegetables

Pandemic COVID-19 warned the importance of preparing the immune system to prevent diseases. Therefore, consuming fresh fruits and vegetables is essential for a healthy and balanced diet due to their diverse compositions of vitamins, minerals, fiber, and bioactive compounds. However, these fresh products grew close to manure and irrigation water and are harvested with equipment or by hand, representing a high risk of microbial, physical, and chemical contamination. The handling of fruits and vegetables exposed them to various wet surfaces of equipment and utensils, an ideal environment for biofilm formation and a potential risk for microbial contamination and foodborne illnesses. In this sense, this review presents an overview of the main problems associated with microbial contamination and the several chemicals, physical, and biological disinfection methods concerning their ability to avoid food contamination. This work has discussed using chemical products such as chlorine compounds, peroxyacetic acid, and quaternary ammonium compounds. Moreover, newer techniques including ozone, electrolyzed water, ultraviolet light, ultrasound, high hydrostatic pressure, cold plasma technology, and microbial surfactants have also been illustrated here. Finally, future trends in disinfection with a sustainable approach such as combined methods were also described. Therefore, the fruit and vegetable industries can be informed about their main microbial risks to establish optimal and efficient procedures to ensure food safety.

Microalgae based wastewater treatment coupled to the production of high value agricultural products: Current needs and challenges

One of the main social and economic challenges of the 21st century will be to overcome the worlds' water deficit expected by the end of this decade. Microalgae based wastewater treatment has been suggested as a strategy to recover nutrients from wastewater while simultaneously producing clean water. Consortia of microalgae and bacteria are responsible for recovering nutrients from wastewater. A better understanding of how environmental and operational conditions affect the composition of the microalgae-bacteria consortia would allow to maximise nutrient recoveries and biomass productivities. Most of the studies reported to date showed promising results, although up-scaling of these processes to reactors larger than 100 m² is needed to better predict their industrial relevance. The main advantage of microalgae based wastewater treatment is that valuable biomass with unlimited applications is produced as a co-product. The aim of the current paper was to review microalgae based wastewater treatment processes focusing on strategies that allow increasing both biomass productivities and nutrient recoveries. Moreover, the benefits of microalgae based agricultural products were also discussed.

Synergistic effects and antityrosinase mechanism of four plant polyphenols from Morus and Hulless Barley

Sanggenone C, oxyresveratrol, catechin and l-epicatechin exist in Morus and Hulless Barley as natural polyphenols with antityrosinase activity. Little research on their synergistic and structure-function relationships of them has been reported in recent years. In this paper, the inhibition mechanisms of these four plant polyphenols were investigated by enzyme kinetics, HPLC, fluorescence spectra, and molecular docking methods. The results showed that oxyresveratrol (IC₅₀ = 1.096 ± 0.048 μg/mL), sanggenone C (IC₅₀ = 13.360 ± 1.029 μg/mL), l-epicatechin (IC₅₀ = 55.730 ± 1.762 μg/mL), and catechin (IC₅₀ = 148.500 ± 3.355 μg/mL) exhibited tyrosinase inhibition activity. When sangenone C (14 μg/mL) was mixed with l-epicatechin (56 μg/mL) at 4:1 (40 μL + 10 μL), the highest tyrosinase inhibition was achieved. Molecular docking showed that the number and position of phenolic hydroxyls of polyphenols were the key for tyrosinase inhibition activity. This study provided new ideas for the application of these four plant polyphenols from Hulless Barley and Morus as tyrosinase inhibitors in food preservation.

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.

A review of recent advances in the decontamination of mycotoxin and inactivation of fungi by ultrasound

Innovative technologies for the pasteurization of food products have increased due to the global demand for higher-quality food products. In this regard, the current article aimed to provide an overview regarding the latest research on US application in the decontamination of fungi in food products and highlight the parameters influencing the effectiveness of this method. Therefore, the related article with inactivation of fungi and mycotoxins by ultrasound among last four years (2018-2021) by using terms such as 'mycotoxin,' 'inactivation,' 'ultrasound,' 'decontamination' among some international databases such as PubMed, Web of Science, Embase and Google Scholar" was retrieved. Ultrasound (US) is considered a non-thermal decontamination method for food products. In US, the release of energy due to the acoustic phenomenon destroys microorganisms. This technology is advantageous as it is inexpensive, eco-friendly, and does not negatively affect food products' food structure and organoleptic properties. The influence of the US on food structure and organoleptic properties dramatically depends on the intensity and energy density applied In addition, it can preserve higher levels of ascorbic acid, lycopene, and chlorophyll in sonicated food products. The treatment conditions, including frequency, intensity, duration, temperature, and processing pressure, influence the effectiveness of decontamination. However, US displays synergistic or antagonistic effects on bacteria, yeasts, molds, and mycotoxins when combined with other types of decontamination methods such as chemical and thermal approaches. Thus, further research is needed to clarify these effects. Overall, the application of US methods in the food industry for decreasing the microbial content of food products during processing has been applied. However, the use of US with other techniques needs to be studied further.

Effects of ultrasound and gamma irradiation on quality maintenance of fresh Lentinula edodes during cold storage

Microbial infection, senescence and water losses result in serious quality deterioration of postharvest mushrooms. The aim of this study was to investigate the impact of ultrasound treatment (US), gamma irradiation treatment (GI) and their combination on quality maintenance of fresh Lentinula edodes during storage. The results showed that US + GI was the most effective approach to maintaining the quality of mushrooms. US + GI reduced natural microflora present on L. edodes, such as total number of colonies, molds, yeasts, Pseudomonas and Enterobacteriaceae. Furthermore, US + GI stimulated phenylalanine ammonia lyase, maintained the highest level of total phenolic content (733.63 mg GAE/kg on Day 4), and postponed the occurrence of reduced ascorbic acid (33.7% retention relative to the control), which contributed to strengthening the antioxidant capacity. Additionally, US + GI retarded water mobility and loss. In brief, the US + GI in this study is an effective hurdle technology for preserving the quality of fresh L. edodes during storage.

Sonolytic-ozonation technology for sanitizing microbial contaminants and pesticide residues from spinach (Spinacia oleracea L.) leaves, at household level

Increasing foodborne illnesses linked with the consumption of contaminated food pose serious health risks. Fresh fruits and vegetables can potentially be contaminated (microbes/chemicals) throughout the supply chain. Various chemical and thermal approaches have been used in the past to decontaminate fresh produce, which have had a negative impact on commodities and health hazardous. Henceforth, this conducted study was aim to test an ecofriendly/green decontamination technique, for impact on food safety and quality of spinach. Freshly harvested spinach leaves were treated with a combined application of ozone and ultrasound (O₃+US) for different times (5, 10, and 15 min) in an aqueous medium. Different food safety (microbes and pesticide residues) and quality (VC content, TSS, TA, and weight loss) parameters were studied in comparison with tap washed samples. Total plate count method was used to evaluate microbial contamination and pesticide residues were determined by HPLC. There was gradual decrease in contaminants with increase in O₃+US treatment time. Sonolytic-ozonation 10 and 15 min treatments were found optimal in reduction of microbial counts (TPC, E. coli, Salmonella, and Listeria) and pesticide residues (10 min 94.04% and 15 min 99.77% residue reduction). However, chlorophyll degradation was observed in 15 min treated sample under 1-week household storage. There was no significant detrimental impact on quality parameters of spinach during 1 week of storage under refrigerated conditions. So, it was concluded that O₃+US treatment for 10 min can be employed for microbial and chemical decontamination in spinach leaves at household level without any negative effect on its quality up to 1 week under refrigerator storage (5 ± 2 ^○C).

Antibacterial mechanism of ultrasound against Escherichia coli: Alterations in membrane microstructures and properties

This study was aimed at providing new insights on the response of bacterial cell membranes to ultrasound exposure. Escherichia coli (E. coli) O157:H7 cells were exposed to different ultrasound treatments (power intensities of 64, 191, 372, and 573 W/cm², frequency of 20 kHz, pulsed mode of 2 sec: 2 sec) and the dynamic changes in cell viability within 27 min were assessed. With an increase in ultrasonic intensity and prolonged duration, a 0.76-3.52 log CFU/mL reduction in E. coli populations was attained. The alterations in the sensitivity of ultrasound-treated cells to antimicrobial compounds were evaluated by exposure to thyme essential oil nanoemulsion (TEON). The treatment reduced the E. coli population by 2.16-7.10 log CFU/mL, indicating the effects of ultrasonic field on facilitating the antibacterial efficacy of TEON. Ultrasonic-treated E. coli cells also displayed remarkable morphological and ultrastructural damages with destroyed membrane integrity and misshaped cell structures, which was observed by electron microscopy analysis. Significant increase in outer and inner membrane permeability, along with the cytoplasmic leakage and membrane depolarization were assessed utilizing spectrophotometry. For the first time, significant reduction in the membrane fluidity in response to ultrasound exposure were investigated. Additional efforts in exploring the effect of ultrasonic field on some bacterial membrane compositions were performed with infrared spectroscopy. In this study, multiple lines of evidence effectively served to elucidate the alterations on cellular membrane structure and property during exposure to sonication that could extend our understanding of the antimicrobial molecular mechanisms of ultrasound.

Impact of ultrasonic treatment on rice starch and grain functional properties: A review

As a green, nonthermal, and innovative technology, ultrasonication generates acoustic cavitation in an aqueous medium, developing physical forces that affect the starch chemistry and rice grain characteristics. This review describes the current information on the effect of ultrasonication on the morphological, textural, and physicochemical properties of rice starch and grain. In a biphasic system, ultrasonication introduced fissures and cracks, which facilitated higher uptake of water and altered the rice starch characteristics impacting textural properties. In wholegrain rice, ultrasonic treatment stimulated the production of health-related metabolites, facilitated the higher uptake of micronutrient fortificants, and enhanced the palatability by softening the rice texture. This review provides insights into the future direction on the utilization of ultrasonication for the applications towards the improvement of rice functional properties.

Aplicação do ultrassom no processamento de frutas e hortaliças

Resumo Este trabalho objetivou apresentar aspectos relacionados à utilização do ultrassom no processamento de frutas e hortaliças, como o funcionamento do método, os efeitos no alimento, as aplicações, os aspectos sensoriais e a percepção dos consumidores. As mudanças dos hábitos alimentares e a busca do bem-estar refletem no aumento da procura por alimentos naturais, como as frutas e as hortaliças. Estes alimentos podem sofrer alterações microbiológicas ao longo da cadeia produtiva, sendo necessária a aplicação de boas práticas agrícolas e de manipulação, e processos tecnológicos de conservação para a garantia da qualidade do produto. O ultrassom é uma tecnologia emergente aplicada no processamento de frutas e hortaliças que está relacionada a melhorias na qualidade e preservação. O princípio básico do ultrassom é a cavitação acústica, que envolve o crescimento e colapso de bolhas durante períodos de rarefação e compressão, causando alterações químicas, físicas e mecânicas no alimento. Essas alterações estão relacionadas à inativação de micro-organismos e de enzimas, à remoção de resíduos e às melhorias na qualidade físico-química, e à acessibilidade de compostos bioativos. Além disso, a aplicação deste método pode ter boa aceitabilidade pelos consumidores, que procuram alimentos mais naturais e submetidos a processos que não causem impacto ambiental.

Optimisation of Protein Recovery from Arthrospira platensis by Ultrasound-Assisted Isoelectric Solubilisation/Precipitation

A response surface methodology was used to optimise the solubilisation and precipitation of proteins from the cyanobacterium Arthrospira platensis. Two separate experiments were designed and conducted in a sequential manner. Protein solubilisation was affected by pH, extraction time, and biomass to solvent ratio (p < 0.001). Although spray-drying and the osmotic shock suffered when resuspending the dried biomass into distilled water led to a certain degree of cell wall disruption, the amount of protein that could be solubilised without an additional disruption step was in the range 30–60%. Sequential extractions improved protein solubilisation by less than 5%. For this reason, a pre-treatment based on sonication (400 W, 24 kHz, 2 min) had to be used, allowing the solubilisation of 96.2% of total proteins. Protein precipitation was affected by both pH and extraction time (p < 0.001). The optimised precipitation conditions, which were pH 3.89 over 45 min, led to a protein recovery of 75.2%. The protein content of the extract was close to 80%, which could be further increased by using different purification steps. The proteins extracted could be used in the food industry as technofunctional ingredients or as a source of bioactive hydrolysates and peptides for functional foods and nutraceuticals.

Ultrasound improves the decontamination effect of thyme essential oil nanoemulsions against Escherichia coli O157: H7 on cherry tomatoes

Development of novel and effective decontamination technologies to ensure the microbiological safety of fresh produce has gained considerable attention, mainly driven by numerous outbreaks. This work presented the first approach regarding to the application of the previously reported hurdle technologies on the sanitization of artificially contaminated cherry tomatoes. Thyme (Thymus daenensis) essential oil nanoemulsion (TEON, 8.28 nm in diameter with a narrow size distribution) was formulated via ultrasonic nanoemulsification, showing remarkably improved antimicrobial activity against Escherichia coli (E. coli) O157:H7, compared to the coarse emulsion. The antimicrobial effect of ultrasound (US), thyme essential oil nanoemulsion (TEON) and the combination of both treatments was assessed against E. coli O157:H7. The remarkable synergistic effects of the combined treatments were achieved, which decontaminated the E. coli populations by 4.49-6.72 log CFU/g on the surface of cherry tomatoes, and led to a reduction of 4.48-6.94 log CFU/sample of the total inactivation. TEON combined with US were effective in reducing the presence of bacteria in wastewater, which averted the potential detrimental effect of cross-contamination resulted from washing wastewater in fresh produce industry. Moreover, the treatments did not noticeably alter the surface color and firmness of cherry tomatoes. Therefore, ultrasound combined with TEON is a promising and feasible alternative for the reduction of microbiological contaminants, as well as retaining the quality characteristics of cherry tomatoes.