A low-power ultrasound attenuation improves the stability of biofilm and hydrophobicity of Propionibacterium freudenreichii subsp. freudenreichii DSM 20271 and Acidipropionibacterium jensenii DSM 20535

Comparative physiological and transcriptomic analysis of sono-biochemical control over post-acidification of Lactobacillus delbrueckii subsp. bulgaricus

Thermosonication (UT) prestress treatments combining with varied fermentation patterns has been revealed as an effective method to regulate post-acidification as exerted by Lactobacillus delbrueckii subsp. bulgaricus (L. delbrueckii), but sono-biochemical controlling mechanisms remain elusive. This study employed physiological and transcriptomic analysis to explore the response mechanism of L. delbrueckii to UT-induced microstress (600 W, 33 kHz, 10 min). UT stress-induced inhibition of acidification of L. delbrueckii during (post)-fermentation was first confirmed, relying on the UT process parameters such as stress exposure duration and UT power. The significantly enhanced membrane permeability in cells treated by 600 W for 10 min than the microbes stressed by 420 W for 20 min suggested the higher dependence of UT-derived stresses on the treatment durations, relative to the ultrasonic powers. In addition, ultrasonication treatment-induced changes in cell membrane integrity enhanced and/or disrupted permeability of L. delbrueckii, resulting in an imbalance in intracellular conditions associated with corresponding alterations in metabolic behaviors and fermentation efficiencies. UT-prestressed inoculum exhibited a 21.46% decrease in the membrane potential during the lag phase compared to untreated samples, with an intracellular pH of 5.68 ± 0.12, attributed to the lower activities of H+-ATPase and lactate dehydrogenase due to UT stress pretreatments. Comparative transcriptomic analysis revealed that UT prestress influenced the genes related to glycolysis, pyruvate metabolism, fatty acid synthesis, and ABC transport. The genes encoding 3-oxoacyl-[acyl-carrier-protein] reductases I, II, and III, CoA carboxylase, lactate dehydrogenase, pyruvate oxidase, glucose-6-phosphate isomerase, and glycerol-3-phosphate dehydrogenase were downregulated, thus identifying the relevance of the UT microstresses-downregulated absorption and utilization of carbohydrates with the attenuated fatty acid production and energy metabolisms. These findings could contribute to provide a better understanding of the inactivated effects on the post-acidification of L. delbrueckii by ultrasonic pretreatments, thus providing theoretical basis for the targeted optimization of acidification inhibition efficiencies for yogurt products during chilled preservation processes.

Regulating bacterial biofilms in food and biomedicine: unraveling mechanisms and Innovating strategies

Bacterial biofilm has brought a lot of intractable problems in food and biomedicine areas. Conventional biofilm control mainly focuses on inactivation and removal of biofilm. However, with robust construction and enhanced resistance, the established biofilm is extremely difficult to eradicate. According to the mechanism of biofilm development, biofilm formation can be modulated by intervening in the key factors and regulatory systems. Therefore, regulation of biofilm formation has been proposed as an alternative way for effective biofilm control. This review aims to provide insights into the regulation of biofilm formation in food and biomedicine. The underlying mechanisms for early-stage biofilm establishment are summarized based on the key factors and correlated regulatory networks. Recent developments and applications of novel regulatory strategies such as anti/pro-biofilm agents, nanomaterials, functionalized surface materials and physical strategies are also discussed. The current review indicates that these innovative methods have contributed to effective biofilm control in a smart, safe and eco-friendly way. However, standard methodology for regulating biofilm formation in practical use is still missing. As biofilm formation in real-world systems could be far more complicated, further studies and interdisciplinary collaboration are still needed for simulation and experiments in the industry and other open systems.

Ultrasound Attenuation Improves Some Surface Properties of the Probiotic Strain Lacticaseibacillus casei ATCC 393

Ultrasound attenuation has been recently proposed as a tool to modulate probiotic metabolism. The study aimed to characterize the response of the probiotic Lacticaseibacillus casei ATCC 393 to sonication. Two ultrasound treatments were tested (57 W, duty cycle 50%, 6 or 8 min). Attenuation was assessed as a pH decrease in MRS broth after 6 and 24 h of incubation at 37 °C. Cultivability was evaluated by plate count immediately after sonication and by growth index on overnight cultures. Surface changes were determined by auto-aggregation, hydrophobicity, biofilm production tests, and by membrane damages. The 6 min treatment induced a temporary attenuation, while a prolongated exposure to sonic waves caused major attenuation effects (ΔpH 0.97 after 24 h). Both sonication treatments affected probiotic cultivability with a significant (p < 0.05) reduction of plate counts and an alteration of the growth index. Although auto-aggregation was negatively affected upon sonication, the hydrophobicity and biofilm production were improved with no significant differences (p > 0.05) between the sonicated samples. Moreover, sonicated L. casei ATCC 393 resulted in increased membrane permeability. These results suggest that ultrasound technology can be successfully used to modulate the L. casei ATCC 393 fermentative metabolism and to improve its surface properties.

Ultrasound can increase biofilm formation by Lactiplantibacillus plantarum and Bifidobacterium spp

The main goal of this research was to study the effect of an Ultrasound (US) treatment on biofilm formation of Lactiplantibacillus plantarum (strains c19 and DSM 1055), Bifidobacterium animalis subsp. lactis DSM 10140, Bifidobacterium longum subsp. longum DSM 20219, and Bifidobacterium longum subsp. infantis DSM 20088. From a methodological point of view, each microorganism was treated through six US treatments, different for the power (10, 30, or 50% of the net power, 130 W), the duration (2, 6, or 10 min) and the application of pulses (0 or 10 s). After the treatment, a biofilm of the strains was let to form on glass slides and the concentration of sessile cells was analyzed for 16 days. Biofilms formed by untreated microorganisms were used as controls. As a first result, it was found that US significantly increased the concentration of sessile cells of B. longum subsp. infantis, while for some other strains US treatment could not affect the formation of biofilm while improving its stability, as found for L. plantarum DSM1055 after 16 days. The variable mainly involved in this positive effect of US was the duration of the treatment, as biofilm formation and stability were improved only for 2 min-treatments; on the other hand, the effect of power and pulses were strain-dependent. In conclusion, the results suggest practical implication of a US pre-treatment for various fields (improvement of adhesion of microorganisms useful in food or in the gut, biomedical and environmental industries), although further investigations are required to elucidate the mode of action.

Application of ultrasound and microencapsulation on Limosilactobacillus reuteri DSM 17938 as a metabolic attenuation strategy for tomato juice probiotication

Counteracting probiotic-induced physicochemical and sensory changes is a challenge in the development of probiotic beverages. The aim of the study is to apply ultrasound and microencapsulation for the attenuation of Limosilactobacillus reuteri DSM 17938 to avoid change in a probiotic tomato juice. Preliminarily, six ultrasound treatments were applied. Probiotic survival in acid environment (pH 2.5) and bile salts (1.5 g/l) after ultrasound treatment was also studied. The probiotic was inoculated in tomato juice in four forms: free cells (PRO-TJ), sonicated-free cells (US-TJ), untreated-microencapsulated (PRO-MC-TJ) and sonicated-microencapsulated cells (US-MC-TJ). Probiotic viability and pH were monitored during 28 days of storage at 4 and 20 °C. Sensory analysis was performed for PRO-TJ and US-MC-TJ sample (4 °C). Ultrasound (57 W for 6 min) did not affect cell survival and transitorily modulated probiotic acidifying capacity; it reduced probiotic survival in acidic environment but increased probiotic survival in bile salts solution. Ultrasound was effective in maintain pH value of tomato juice but only at 4 °C. Instead, microencapsulation with sodium-alginate leads to a more stable probiotic juice, particularly at 20 °C. Finally, probiotication slightly modified some sensory attributes of the juice. This study shows the potential of ultrasound and microencapsulation as attenuation strategies and highlights the need for process optimization to increase ultrasound efficacy.

Strategic thermosonication-mediated modulation of lactic acid bacteria acidification kinetics for enhanced (post)-fermentation performance

This study explored the feasibility of thermosonication (TS)-prestressed inoculum with different fermentation patterns for regulating microbial (post)-fermentation acidification kinetics. Through a Box-Behnken design, stimulative (20 min, 400 W, 33 kHz, 25 °C) and inhibitive (10 min, 600 W, 33 kHz, 20 °C) effects on the acidification capability of Lactobacillus plantarum A3 were achieved without observing greatly activated/inactivated strains growth, further confirmed by lactose fermentation performed by Streptococcus thermophilus and Lactobacillus bulgaricus. Lactic acid was the major contributing factor responsible for TS-induced acidification modifications corresponding to the potential fluctuations of CoA biosynthesis, fatty acid degradation and chain elongation pathways to TS prestress. Microscopy observations and quantitative extracellular substance assays showed palpable stress disturbance on microbes, but causing insignificant effects on product characteristics. This investigation demonstrated the potential of controlled sonication prestress strategies to achieve dual engineering effects on microbial metabolic behavior, for alleviating post-acidification problem or enhancing process efficiencies.

Effect of low-level ultrasound treatment on the production of L-leucine by Corynebacterium glutamicum in fed-batch culture

Various process intensification methods were proposed to improve the yield, quality, and safety of fermented products. Here, we report the enhancement of L-leucine production by Corynebacterium glutamicum CP using ultrasound-assisted fed-batch fermentation. Response surface methodology was employed to optimize the sonication conditions. At an ultrasonic power density of 94 W/L, frequency of 25 kHz, interval of 31 min, and duration of 37 s, C. glutamicum CP produced 52.89 g/L of L-leucine in 44 h, representing a 21.6% increase compared with the control. The production performance of L-leucine was also improved under ultrasonic treatment. Moreover, the effects of ultrasound treatment on the fermentation performance of L-leucine were studied in terms of cell morphology, cell membrane permeability, and enzyme activity. The results indicate that ultrasonication is an efficient method for the intensification of L-leucine production by C. glutamicum CP.

Propionic acid bacteria in the food industry: An update on essential traits and detection methods

Propionic acid bacteria (PAB) is an umbrella term for a group of bacteria with the ability to produce propionic acid. In the past, due to this common feature and other phenotypic similarities, genetically heterogeneous bacteria were considered as a single genus, Propionibacterium. Members of this genus ranged from "dairy propionibacteria," which are widely known for their role in eye and flavor formation in cheese production, to "cutaneous propionibacteria," which are primarily associated with human skin. In 2016, the introduction of two new genera based on genotypic data facilitated a clear separation of cutaneous (Cutibacterium spp.) from dairy PAB (Propionibacterium spp., Acidipropionibacterium spp.). In light of these taxonomic changes, but with particular emphasis on dairy PAB, this review describes the current state of knowledge about metabolic pathways and other characteristics such as antibiotic resistance and virulence factors. In addition, the relevance of dairy PAB for the food industry and cheese production in particular is highlighted. Furthermore, methods for cultivation, detection, and enumeration are reviewed, incorporating the current taxonomy as well as the potential for routine applications.

Increase of acidification of synthetic brines by ultrasound-treated Lactiplantibacillus plantarum strains isolated from olives

This paper focused on the evaluation of Ultrasound effect on the growth patterns (3-6% of salt and 45 °C), acidification (pH-decrease), interactions with microorganisms, and membrane permeability of nine strains of Lactiplantibacillus plantarum. Ultrasound treatment was applied at 20% of net power by modulating duration (2-10 min) and pulses (2-10 s). Viable count (7.15-8.16 log CFU/mL) was never affected by Ultrasound, while the treatment increased the extent of pH decrease of at least three strains (109, 162 and c19). L. plantarum c19 was the best performer, as a low intensity treatment was able to increase its acidification, without affecting its growth. The effects could be attributed to an increased permeability of the cellular membrane, as suggested by the increase of released intracellular components. Other factors should be further assessed (e.g. possible changes in the metabolism) and the performances of Ultrasound-treated strains in real brines.

Surface properties associated with the production of polysaccharides in the food bacteria Propionibacterium freudenreichii

This study explores the production of polysaccharides (PS) in the strain Pf2289 of the food species Propionibacterium freudenreichii. Pf2289 presents characteristics atypical of the species: a molar-shaped morphotype upon plating, and cells strongly aggregative in liquid medium. When plating Pf2289, another morphotype was observed with a 4% frequency of appearance: round-shaped colonies, typical of the species. A clone was isolated, designated Pf456. No reversibility of Pf456 towards the molar-shaped morphotype was observed. Pf2289 was shown to produce a surface polysaccharide (PS) bound to the cell wall, mainly during the stationary growth phase. Meanwhile, Pf456 had lost the ability to produce the PS. AFM images of Pf2289 showed that entangled filaments spread over the whole surface of the bacteria, whereas Pf456 exhibited a smooth surface. Adhesion force maps, performed with concanavalin-A grafted probes, revealed twice as much adhesion of Pf2289 to concanavalin-A compared to Pf456. Furthermore, the length of PS molecules surrounding Pf2289 measured at least 7 μm, whereas it only reached 1 μm in Pf456. Finally, the presence of PS had a strong impact on adhesion properties: Pf2289 did not adhere to hydrophobic surfaces, whereas Pf456 showed strong adhesion.

Ultrasonic Modulation of the Technological and Functional Properties of Yeast Strains

This research was aimed at studying the effects of low intensity ultrasound (US) on some technological and functional properties of eight strains of Saccharomyces cerevisiae; namely, growth patterns (growth at 2–5% of NaCl or at 37 °C), autoaggregation and tolerance to simulated gastrointestinal conditions were evaluated. A US treatment was applied at 20% of net power (130 W) by a modulating duration (2–10 min) and pulses (2–10 s). The viable count (4.81–6.33 log CFU/mL) was not affected by US, while in terms of technological traits the effect was strain specific; in particular, for some strains a positive effect of US was found with a significant growth enhancement (growth index > 120%). The treatment was also able to increase the autoaggregation of some strains, thus suggesting that US could represent a promising way to treat and select nonconventional functional yeasts for food applications.

Ultrasound-Attenuated Microorganisms Inoculated in Vegetable Beverages: Effect of Strains, Temperature, Ultrasound and Storage Conditions on the Performances of the Treatment

Four microorganisms (Lactobacillus acidophilus LA5, Bifidobacterium animalis subsp. lactis DSM 10140 and Lactiplantibacillus plantarum c16 and c19) were attenuated through ultrasound (US) treatments (40% of power for 2, 4 and 6 min; and 60% for 2 min; pulses were set at 2 s) inoculated in rice–oats–almond–soy-based beverages and stored at 4 °C for eight days. All strains were able to survive throughout the storage independently by the food matrix. Concerning the effect on acidification, the results were analyzed through multifactorial analysis of variance (MANOVA) and the key-findings of this were: (i) The treatment with 40% of power for 6 min was the most efficient at delaying acidification; (ii) Lb. acidophilus LA5 showed the best capacity to delay acidification; (iii) in the soy-based beverage a lower acidification was found. In a second step, L. plantarum c16 and c19 were attenuated, inoculated in rice beverage, stored under a thermal abuse (for 4 and 24 h) and then at 4, 15 and 20 °C. The results showed that only when US were combined with refrigeration temperatures were they efficient at delaying acidification. Thus, a perspective for attenuation could be the optimization of the treatment to design an effective way to counteract acidification also under a thermal abuse.

Recent nano-, micro- and macrotechnological applications of ultrasonication in food-based systems

There is a neoteric and rising demand for nutritional and functional foods which behooves food processors to adopt processing techniques with optimal conservation of bioactive components in foods and with minimal pernicious impacts on the environment. Ultrasonication, a mechanochemical technique has proven to be an efficacious panacea to these concerns. In this review, an analytic exploration of recent researches and designs regarding ultrasound methodology and equipment on diverse food systems, technological scales, procedural parameters and outcomes of such experimentations optimally scrutinized. The relative effects of ultrasonication on food formulations, components and attributes such as nanoemulsions, nanocapsules, proteins, micronutrients, sensory and mechanical characteristics are evaluatively delineated. In food systems where ultrasonication was employed, it was found to have a remarkable effect on one or more quality parameters. This review is a supplementation to the pedagogical awareness to scholars on the suitability of ultrasonication for research procedures, and a call to industrial food brands on the adoption of this technique for the development of foods with optimally sustained nutrient profiles.

Two Nonthermal Technologies for Food Safety and Quality-Ultrasound and High Pressure Homogenization: Effects on Microorganisms, Advances, and Possibilities: A Review

Some nonthermal technologies have gained special interest as alternative approaches to thermal treatments. High pressure homogenization (HPH) and ultrasound (US) are two of the most promising approaches. They rely upon two different modes of action, although they share some mechanisms or ways of actions (mechanic burden against cells, cavitation and micronization, primary targets being the cell wall and the membrane, temperature and pressure playing important roles for their antimicrobial potential, and their effect on cells can be either positive or negative). HPH is generally used in milk and dairy products to break lipid micelles, whereas US is used for mixing and/or to obtain active compounds of food. HPH and US have been tested on pathogens and spoilers with different effects; thus, the main goal of this article is to describe how US and HPH act on biological systems, with a focus on antimicrobial activity, mode of action, positive effects, and equipment. The article is composed of three main parts: (i) an overview of US and HPH, with a focus on some results covered by other reviews (mode of action toward microorganisms and effect on enzymes) and some new data (positive effect and modulation of metabolism); (ii) a tentative approach for a comparative resistance of microorganisms; and (iii) future perspectives.

Red-Brown Pigmentation of Acidipropionibacterium jensenii Is Tied to Haemolytic Activity and cyl-Like Gene Cluster

The novel Acidipropionibacterium genus encompasses species of industrial importance but also those associated with food spoilage. In particular, Acidipropionibacterium acidipropionici, Acidipropionibacterium thoenii, and Acidipropionibacterium jensenii play an important role in food fermentation, as biopreservatives, or as potential probiotics. Notably, A. jensenii and A. thoenii can cause brown spot defects in Swiss-type cheeses, which have been tied to the rhamnolipid pigment granadaene. In the pathogenic bacterium Streptococcus agalactiae, production of granadaene depends on the presence of a cyl gene cluster, an important virulence factor linked with haemolytic activity. Here, we show that the production of granadaene in pigmented Acidipropionibacterium, including A. jensenii, A. thoenii, and Acidipropionibacterium virtanenii, is tied to haemolytic activity and the presence of a cyl-like gene cluster. Furthermore, we propose a PCR-based test, which allows pinpointing acidipropionibacteria with the cyl-like gene cluster. Finally, we present the first two whole genome sequence analyses of the A. jensenii strains as well as testing phenotypic characteristics important for industrial applications. In conclusion, the present study sheds light on potential risks associated with the presence of pigmented Acidipropionibacterium strains in food fermentation. In addition, the results presented here provide ground for development of a quick and simple diagnostic test instrumental in avoiding potential negative effects of Acidipropionibacterium strains with haemolytic activity on food quality.