Inactivation of thermoduric aerobic sporeformers in milk by ultrasonication

Invited review: Role of Bacillus licheniformis in the dairy industry- friends or foes?

Bacillus licheniformis is one of the major spore-forming bacteria with great genotypic diversity in raw milk, dairy ingredients, final dairy products, and is found throughout the dairy processing continuum. Though being widely used as a probiotic strain, this species also serves as a potential risk in the dairy industry based on its roles in foodborne illness and dairy spoilage. Biofilm formation of B. licheniformis in combined with the heat resistance of its spores, make it impossible to prevent the presence of B. licheniformis in final dairy products by traditional cleaning and disinfection procedures. Despite the extensive efforts on the identification of B. licheniformis from various dairy samples, no reviews have been reported on both hazard and benefits of this spore-former. This review discusses the prevalence of B. licheniformis from raw milk to commercial dairy products, biofilm formation and spoilage potential of B. licheniformis, and its potential prevention methods. In addition, the potential benefits of B. licheniformis in the dairy industry were also summarized.

Recent developments in ultrasound approach for preservation of animal origin foods

Ultrasound is a contemporary non-thermal technology that is currently being extensively evaluated for its potential to preserve highly perishable foods, while also contributing positively to the economy and environment. There has been a rise in the demand for food products that have undergone minimal processing or have been subjected to non-thermal techniques. Livestock-derived food products, such as meat, milk, eggs, and seafood, are widely recognized for their high nutritional value. These products are notably rich in proteins and quality fats, rendering them particularly vulnerable to oxidative and microbial spoilage. Ultrasound has exhibited significant antimicrobial properties, as well as the ability to deactivate enzymes and enhance mass transfer. The present review centers on the production and classification of ultrasound, as well as its recent implementation in the context of livestock-derived food products. The commercial applications, advantages, and limitations of the subject matter are also subject to scrutiny. The review indicated that ultrasound technology can be effectively utilized in food products derived from livestock, leading to favorable outcomes in terms of prolonging the shelf life of food while preserving its nutritional, functional, and sensory attributes. It is recommended that additional research be conducted to investigate the effects of ultrasound processing on nutrient bioavailability and extraction. The implementation of hurdle technology can effectively identify and mitigate the lower inactivation of certain microorganisms or vegetative cells.

Ultrasound-Assisted Cavitation Effect on the Biofilm-Forming Ability of Common Dairy Sporeformers

Thermoduric sporeformers survive heat treatment and can form biofilm on contact food surfaces that is difficult to clean and may cause cross contamination to milk products. It was hypothesized that cavitation would influence sporeformers’ ability to attach to contact surfaces and form biofilm. Common dairy sporeformers of Geobacillus stearothermophilus, Bacillus licheniformis, and Bacillus sporothermodurans were individually inoculated in sterile skim milk at the levels of 6.0 log CFU/mL. Inoculated samples were treated by cavitation at 80% amplitudes for 10 min each. Pre and post samples were used to develop biofilms on stainless steel coupons under static conditions. Scanning electron micrograph was used to observe the developed biofilms. All the experiments were conducted in triplicate and were statistically analyzed using a t test. The average counts of spiked milk samples were 7.2, 8.0, and 7.7 logs CFU/mL, respectively, for the three sporeformers. Post-cavitation counts were reduced significantly to 3.4, 4.2, and 3.7 logs CFU/mL, respectively. Pre-cavitation biofilm counts of the three sporeformers were 5.35, 6.42, and 6.5 logs CFU/ cm2, respectively in 72 h. The three sporeformers’ biofilm showed significantly (p < 0.05) lower counts after cavitation of 4.39, 5.44, and lower counts of 4.39 logs CFU/cm2, respectively, for the three organisms. The result showed that G. stearothermophilus formed the least biofilms among others after cavitation. Although the ultrasonication treatment reduced the number of sporeformer bacteria, the survivors still retained the ability to attach to the stainless-steel food contact surfaces.

A new decontamination method for Bacillus subtilisin pasteurized milk: Thermosonication treatment

Thermosonication (TS) is a novel and viable technique employed to replace conventional thermal processing. TS treatment combined with pasteurization was used to kill the residual heat-resistant Bacillus in pasteurized milk and extend the shelf life of pasteurized milk and compared with High Temperture Shoort Time (HTST) pasteurization to study its decontamination effect on Bacillus subtilis and the quality of treated milk. The results showed that after 40 kHz, 240 W, 25 min ultrasonic treatment and 50 °C heating decontamination treatment, the number of B. subtilis in the medium and milk medium decreased by 4.17 log CFU/mL and 4.09 log CFU/mL respectively. The results of cell membrane permeability showed that the leakage of DNA and protein in the HTST-TS group increased by 52.3 % and 34 %, respectively, when compared to that in the HTST group. In addition, transmission electron microscopy (TEM) analysis showed that the bacterial cell membrane of the HTST-TS group swelled up, the cell wall was ruptured, and the cell content was accumulated in the cells. The results showed that HTST-TS treatment significantly inhibited the activities of ATPase (47 %), succinate dehydrogenase (SDH) (68.6 %), and malate dehydrogenase (MDH) (54.4 %). The physical and chemical sensory evaluation of milk treated with HTST-TS showed that HTST-TS treatment could improve the L* value (2.24 %), zeta potential (64.19 %), and colloidal particle size (14.49 %) of milk but had no significant effect on oral sensitivity. In conclusion, this study provides new insights, which may be helpful in implementing this new combined decontamination method in the dairy industry to improve the quality of pasteurized milk and extend the its shelf life.

Current progress of emerging technologies in human and animals' milk processing: Retention of immune-active components and microbial safety

Human milk and commercial dairy products play a vital role in humans, as they can provide almost all essential nutrients and immune-active components for the development of children. However, how to retain more native immune-active components of milk during processing remains a big question for the dairy industry. Nonthermal technologies for milk processing are gaining increasing interest in both academic and industrial fields, as it is known that thermal processing may negatively affect the quality of milk products. Thermosensitive components, such as lactoferrin, immunoglobulins (Igs), growth factors, and hormones, are highly important for the healthy development of newborns. In addition to product quality, thermal processing also causes environmental problems, such as high energy consumption and greenhouse gas (GHG) emissions. This review summarizes the recent advances of UV-C, ultrasonication (US), high-pressure processing (HPP), and other emerging technologies for milk processing from the perspective of immune-active components retention and microbial safety, focusing on human, bovine, goat, camel, sheep, and donkey milk. Also, the detailed application, including the instrumental design, technical parameters, and obtained results, are discussed. Finally, future prospects and current limitations of nonthermal techniques as applied in milk processing are discussed. This review thereby describes the current state-of-the-art in nonthermal milk processing techniques and will inspire the development of such techniques for in-practice applications in milk processing.

Degradation mechanism and toxicity assessment of chlorpyrifos in milk by combined ultrasound and ultraviolet treatment

The aim of this study was to compare the degradation kinetics of chlorpyrifos by treatment with ultrasound (US), ultraviolet radiation (UV) and a combination of both (US/UV), to evaluate the toxicity of the degradation products and the effect of the treatments on milk quality. US/UV markedly accelerated the degradation of chlorpyrifos. The half-life of chlorpyrifos by US/UV was 6.4 min, which was greatly shortened compared to the treatment with US or UV alone. Five degradation products were identified by GC-MS, and a degradation pathway for chlorpyrifos was proposed, based on density functional theory calculations. According to the luminescent bacteria test and predictions from a structure/activity relationship model, the toxicity of the degradation products was lower than that of chlorpyrifos. In addition, US/UV treatment had little effect on the quality of the treated milk. Therefore, US/UV can be used as a potential non-thermal processing method to degrade pesticide residues in milk.

Non-thermal Processing Technologies for Dairy Products: Their Effect on Safety and Quality Characteristics

Thermal treatment has always been the processing method of choice for food treatment in order to make it safe for consumption and to extend its shelf life. Over the past years non-thermal processing technologies are gaining momentum and they have been utilized especially as technological advancements have made upscaling and continuous treatment possible. Additionally, non-thermal treatments are usually environmentally friendly and energy-efficient, hence sustainable. On the other hand, challenges exist; initial cost of some non-thermal processes is high, the microbial inactivation needs to be continuously assessed and verified, application to both to solid and liquid foods is not always available, some organoleptic characteristics might be affected. The combination of thermal and non-thermal processing methods that will produce safe foods with minimal effect on nutrients and quality characteristics, while improving the environmental/energy fingerprint might be more plausible.

Bacteriostatic effects of high-intensity ultrasonic treatment on Bacillus subtilis vegetative cells

The bacteriostatic effects of high-intensity ultrasonic treatment (HIU) on Bacillus subtilis vegetative cells were evaluated, and the related mechanisms were explored using quantitative proteomics. The bacteriostatic effect of HIU on B. subtilis was proportional to the ultrasound treatment time and power, and the number of cultivable B. subtilis cells was decreased by approximately one log (at 270 W for 15 min) or half log (at 90 W for 25 min or 360 W for 5 min). Scanning electron microscopy images and gel electrophoresis results showed that HIU caused the destruction of the cell structure and intracellular protein leakage. In addition, HIU treatment at 270 W for 15 min resulted in the greatest decrease (84.22%) in intracellular adenosine triphosphate (ATP) content. The quantitative proteomic analysis showed that B. subtilis resisted the stress of HIU treatment by regulating the key proteins in physiological activities related to membrane transport (ATP-binding cassette [ABC] transporter), signal transduction (the two-component system), and energy metabolism (the tricarboxylic acid [TCA] cycle). HIU-induced physical damage, stress, and metabolic disorders were the main causes of the bacteriostatic effects on B. subtilis. These findings provide a foundation for the subsequent optimization and potential applications of HIU inactivation of B. subtilis.

Recovery potential of cavitation-induced injured cells of common spore-forming bacteria in skim milk exposed to ultrasonication

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Ultrasonication is a new technique that could lower bacterial counts in milk.

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Ultrasonication treatment may cause injury to the bacterial cells.

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Holding the cavitated milk helps the bacteria to recover and return to normalcy.

The presence of spore-forming microorganisms and their adhesion to contact surfaces in dairy plants is a major concern because dairy products are prone to cross-contamination. Spore formers and their spores can survive milk processing treatments due to their heat resistance. One source of these spore formers is bacterial biofilms, which grow and accumulate on most surfaces in dairy industrial plants, such as pipes, heat exchangers, pasteurized plates, and storage tanks. Their endospores form biofilms by attaching to these surfaces and germinating when conditions become more favorable. The cross-contamination of dairy products by bacterial biofilms may lead to reduced shelf life and spoilage. To minimize the problem caused by thermoduric bacteria, the dairy industry adopts several approaches. Pasteurization is an irreplaceable technique for milk processing. Unfortunately, some bacteria and endospores are resistant to heat treatment, which can grow and cause spoilage of dairy products. Thus, alternative approaches that could help to reduce microbial counts are needed. In our previous study, we demonstrated the effectiveness of ultrasonication to inactivate spore formers and reduce the overall microbial counts in milk. In the current study, we investigated the recovery of cavitation-induced injured cells during the storage of ultrasonicated skim milk. Three common spore formers—Geobacillus stearothermophilus (ATCC 15952), Bacillus licheniformis (ATCC 6634), and Bacillus sporothermodurans (DSM 10599)—were selected to conduct challenge studies by inoculating skim milk samples and exposing them to ultrasonication (10 min each at 80% amplitude). This treatment was done in an ice bath to control the resultant temperature increase. The ultrasonicated skim milk samples were then held for 1, 2, 4, or 12 h in the refrigerator (4°C) to study the recovery of cells following cavitation-induced injury. Ultrasonication resulted in cell injury, as demonstrated by scanning electron microscopy. The injured cells can potentially recover under appropriate conditions during the storage of ultrasonicated milk and could affect the microbiological quality of milk and products manufactured with such milk. The respective bacterial counts for the 3 organisms in the spiked skim milk, on average, were approximately 6.0 log cfu/mL; immediately after ultrasonication, these counts decreased to 3.50 ± 0.02, 4.38 ± 0.02, and 3.75 ± 0.05 log cfu/mL for G. stearothermophilus, B. licheniformis, and B. sporothermodurans, respectively. During 12 h of subsequent incubation at 4°C, their counts increased to 4.17 ± 0.05, 5.25 ± 0.1, and 5.69 ± 0.06 log cfu/mL, respectively. All experiments were done in triplicate for all 3 bacteria. To conclude, slow recovery of injured cells of spore-forming bacteria is possible in ultrasonicated milk during storage under refrigeration conditions.

Effect of milk bactofugation on the counts and diversity of thermoduric bacteria

The objective of this work was to determine the effect of milk bactofugation on the counts and microbial diversity of mesophilic (MT), psychrotrophic (PT), and thermophilic (TT) thermoduric bacteria and its potential as a technological method to remove spoilage microorganisms resistant to pasteurization. Different batches of raw milk from 69 dairy farms divided into sets in 3 bulk tanks (A, B, C) were evaluated at different times during the technological process. As the raw milk was preheated (∼55°C) immediately before bactofugation (10,000 × g), the effect of bactofugation was estimated by comparing the counts in raw, preheated, and bactofuged milk. This centrifugation was sufficient to reduce the isolation of 88% of the MT in preheated milk. For PT, it was possible to verify a reduction of 72.5% in batch C. The TT were not recovered at higher detection limits (<5 cfu/mL). For diversity, 310 isolates were identified using a molecular approach; 15 species of contaminating thermoduric bacteria were identified from raw and preheated milk, and only 6 species were recovered in bactofuged milk. Only MT were recovered from the bactofuged milk, mainly the species Lysinibacillus fusiformis (61.7%) and Bacillus licheniformis (12.3%). Both species are known to be endospore-forming psychrotrophs and have proteolytic or lipolytic activity. The bactofugation of raw milk reduced the number of isolates of B. licheniformis, Bacillus toyonensis, Micrococcus aloeverae, and Aestuariimicrobium kwangyangense by 33, 43, 86, and 92%, respectively, and reduced the isolates of Macrococcus caseolyticus, Lysinibacillus varians, Carnobacterium divergens, Microbacterium hominis, Kocuria indica, Micrococcus yunnanensis, Gordonia paraffinivorans, Bacillus invictae, and Kocuria kristinae to undetectable levels. The results of this study indicate that bactofugation can be applied by the dairy industry to reduce pasteurization-resistant microorganisms in combination with prophylactic measures to prevent the contamination of raw milk by spores and vegetative forms of bacteria.

Thermosonication-induced structural changes and solution properties of mung bean protein

Mung bean protein is considered a highly nutritive food ingredient, but its solution properties are not well defined. In this study, suspensions of mung bean protein isolate (MPI, 10%, w/v) were subjected to high intensity ultrasound (20 kHz, 30% amplitude) at varied durations (5, 10, 20, and 30 min) with controlled temperatures (30, 50, and 70 °C) to determine the effects of thermosonication treatment on physical properties of the protein solution. Results showed that thermosonication treatment significantly reduced the particle size and free sulfhydryl content of MPI in a time-dependent manner. Ultrasound increased surface hydrophobicity, and the exposure of nonpolar groups led to the formation of soluble aggregates. Changes in secondary structure of MPI were minimal at 30 and 50 °C but were significant at 70 °C. The dissociation of native components followed by reaggregation into soluble particles following ultrasound treatment at 70 °C resulted in remarkable improvements of protein solubility (>2 fold), clarity, and stability of the MPI suspensions. The findings indicated that thermosonication could be a promising technology for the processing of mung bean protein beverage.

Comparative assessment of high-intensity ultrasound and hydrodynamic cavitation processing on physico-chemical properties and microbial inactivation of peanut milk

Ultra-sonication (US) at varying intensities (200 W, 300 W and 400 W) and hydrodynamic cavitation (HC) at increasing pressures (6 bar, 8 bar and 10 bar) on freshly extracted peanut milk as non-thermal processing of milk for enhanced quality. The effects of US and HC was investigated on physico-chemical properties of peanut milk, microbial inactivation (total plate count and yeasts and molds), microstructure by optical microscopy and particle size, ζ-potential, sedimentation index, rheology and color measurements. The high temperature short time (HTST) treated milk samples have shown 1.53 and 2 log reduction in TPC, yeast and molds respectively with highest protein hydrolysis of 15.7%. Among the non-thermal treatments HC has shown highest log reduction of TPC at around 1.2 for sample treated at 10 bar pressure, whereas the US treatment was most effective for yeast and mold at 400 W with log reduction of 0.9. A non-Newtonian flow behaviour was observed for all peanut milk samples. Viscosity determined by Herschel-Bulkley equation decreased significantly (p > 0.05) after both cavitation treatments. The US was found to be superior to HC and HTST with improved separation index and colour attributes. Therefore, the US and HC appear to be a remarkable non-thermal processing methods for peanut milk and or any dairy or non-dairy beverages.

Neither thermosonication nor cold sonication is better than pasteurization for milk shelf life

High-power, low-frequency ultrasound has been suggested as a novel processing technique with the potential to extend milk shelf life via inactivation of bacteria and spores that survive standard pasteurization. The primary objective of this research was to determine whether short-duration (≤60 s) sonication treatment, in conjunction with pasteurization, can increase shelf life while producing no adverse aroma effect. Skim milk was inoculated with Paenibacillus amylolyticus, a spore-forming, thermotolerant and psychrophilic milk contamination bacterium. Milk was sonicated under 6 selected amplitude and time conditions, except for control. Both cold sonicated (C-S) and thermosonicated (T-S) milk and milk treatments were pasteurized; however, T-S milk was sonicated after pasteurization (72.5 ± 0.3°C; mean ± SD), whereas C-S milk was sonicated at 12.5 ± 5°C (mean ± SD) before pasteurization. Milk was refrigerated up to 50 d and total aerobic counts were enumerated on pasteurized control, C-S, and T-S milk weekly. Neither C-S nor T-S treatments reduced total aerobic counts to an equivalent level as pasteurization alone. Counts in pasteurized controls and C-S milk did not exceed 3.00 log cfu/mL for up to 50 d; counts in T-S milk exceeded 5.00 cfu/mL by d 36. Aroma qualities (cooked, lacks freshness, and rubbery) of 2 T-S treatment intensities [170 µm peak-to-peak (p-p) for 60s and 200 µm_p-p for 10 s] and pasteurized controls were evaluated by a trained descriptive sensory panel. No significant differences were observed in cooked or lacks freshness aromas among samples. Only the milk treated with 170 µm_p-p for 60 s had significantly higher rubbery aroma on d 1 compared with milk treated with 200 µm_p-p for 10 s. Although the sensory effects of T-S on milk may not limit the commercial feasibility of cold sonication or thermosonication, conditions that differ from those used in the present study should be considered in the future. Neither C-S nor T-S were appropriate techniques for reducing bacterial count in fluid milk beyond standard pasteurization and, in fact, increased counts of spore-forming spoilage bacteria.

Low frequency ultrasound inactivation of thermophilic bacilli (Geobacillus spp. and Anoxybacillus flavithermus) in the presence of sodium hydroxide and hydrogen peroxide

The vegetative cells and spores of Geobacillus spp. and Anoxybacillus flavithermus were subjected to 20 kHz ultrasound with a power ∼8 W. Ultrasonication had considerable effect on vegetative cells (5-log reduction in Geobacillus spp. and 1.6-log reduction in A.flavithermus). TEM imaging of the ultrasonicated vegetative cells showed an extensive damage both internally and externally. However, spores showed high resistance towards ultrasound treatment in the absence of NaOH and H₂O₂, although the outer layers such as the exosporium and the outer coat layer were disrupted, resulting in the reduced resistance of spores towards sonication. The combination of 0.12 M NaOH and 10 min ultrasonication inactivated 6 log spores of Geobacillus spp. A 7 log spore reduction of A.flavithermus was achieved by combining 0.17 M NaOH with 10 min ultrasonication. Ultrasonication combined with 1% H₂O₂ inactivated ∼7 log Geobacillus spp. spores in 6 min and ∼7 log A.flavithermus spores in 3 min. These ultrasound treatments in the presence of NaOH and H₂O₂ are synergistic as they showed a greater spore reduction when compared to NaOH combined with high temperature (85 °C), where only 1 and 3 log reduction was achieved in Geobacillus spp. and A.flavithermus spores, respectively.

Physicochemical changes and microbial inactivation after high-intensity ultrasound processing of prebiotic whey beverage applying different ultrasonic power levels

In this work, we investigated the effects of the ultrasonic power (0, 200, 400 and 600 W) on non-thermal processing of an inulin-enriched whey beverage. We studied the effects of high-intensity ultrasound (HIUS) on microbial inactivation (aerobic mesophilic heterotrophic bacteria (AMHB), total and thermotolerant coliforms and yeasts and molds), zeta potential, microstructure (optical microscopy, particle size distribution), rheology, kinetic stability and color. The non-thermal processing applying 600 W of ultrasonic power was comparable to high-temperature short-time (HTST) treatment (75 °C for 15 s) concerning the inactivation of AMHB and yeasts and molds (2 vs 2 log and 0.2 vs 0.4 log, respectively), although HIUS has reached a lower output temperature (53 ± 3 °C). The HIUS was better than HTST to improve beverage kinetic stability, avoiding phase separation, which was mainly attributed to the decrease of particles size, denaturation of whey proteins and gelation of polysaccharides (inulin and gellan gum). Thus, non-thermal processing by HIUS seems to be an interesting technology for prebiotic dairy beverages production.

Application of nisin-assisted thermosonication processing for preservation and quality retention of fresh apple juice

The effects of thermosonication (TS) and 100 ppm nisin-assisted TS (TS + nisin) on the inactivation of naturally occurring microorganisms, retention of nutritional quality and extension of shelf life of fresh apple juice were evaluated, with nisin and mild heat (nisin + MH) treatments as control. Fresh apple juice was addressed by nisin + MH, TS and TS + nisin at 37, 42, 47, and 52 °C for 5-40 min. After processing, microbial growth was evaluated during storage at 8 °C at every 5 days. Temperature played a vital role in the inactivation of aerobic bacteria and yeasts and molds by TS and TS + nisin, higher temperature up to 52 °C could cause a considerable inactivation of microbial cells in apple juice. As apple juice was subjected to TS and TS + nisin at 52 °C for 30 min, retention of original quality including 89% ascorbic acid, non-visible color change, no significant alteration in BD, pH, TA and TSS values of fresh apple juice, and extension shelf life to 15 d at 8 °C were obtained. Nisin exhibit additional inactivation effect of aerobic bacteria in apple juice while not obviously effect on yeast and molds. These results indicated a potential application of TS and TS + nisin (100 ppm) to produce fresh-like quality apple juice and/or to extend its shelf life.

Comparison of adhesion characteristics of common dairy sporeformers and their spores on unmodified and modified stainless steel contact surfaces

The attachment of aerobic spore-forming bacteria and their spores to the surfaces of dairy processing equipment leads to biofilm formation. Although sporeformers may differ in the degree of attachment, various surface modifications are being studied in order to develop a surface that is least vulnerable to attachment. This study was conducted to compare the extent of adhesion of spores and vegetative cells of the thermotolerant sporeformer Bacillus licheniformis and the high-heat-resistant sporeformers Geobacillus stearothermophilus and Bacillus sporothermodurans on both native and modified stainless steel surfaces. We studied the effect of contact surface and cell surface properties (including surface energy, surface hydrophobicity, cell surface hydrophobicity, and zeta potential) on the adhesion tendency of both types of sporeformers and their spores. Attachment to native and modified (Ni-P-polytetrafluoroethylene, Ni-P-PTFE) stainless steel surfaces was determined by allowing interaction between the respective contact surface and vegetative cells or spores for 1 h at ambient temperature. The hydrophobicity of vegetative cells and spores of aerobic spore-forming bacteria was determined using the hexadecane assay, and zeta potential was determined using the Zeta sizer Nano series instrument (Malvern Panalytical, Malvern, UK). The results indicated a higher adhesion tendency of spores over vegetative cells for both thermotolerant and high-heat-resistant sporeformers. On comparing the sporeformers, B. sporothermodurans demonstrated the highest adhesion tendency followed by G. stearothermophilus; B. licheniformis exhibited minimal attachment on both surfaces. The tendency to adhere varied with cell surface properties, decreasing with lower cell surface hydrophobicity and higher cell surface charge. On the other hand, modifying contact surface properties for higher surface hydrophobicity and lower surface energy decreased attachment.

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.

Evaluation of modified stainless steel surfaces targeted to reduce biofilm formation by common milk sporeformers

The development of bacterial biofilms on stainless steel (SS) surfaces poses a great threat to the quality of milk and other dairy products as the biofilm-embedded bacteria can survive thermal processing. Established biofilms offer cleaning challenges because they are resistant to most of the regular cleaning protocols. Sporeforming thermoduric organisms entrapped within biofilm matrix can also form heat-resistant spores, and may result in a long-term persistent contamination. The main objective of this study was to evaluate the efficacy of different nonfouling coatings [AMC 18 (Advanced Materials Components Express, Lemont, PA), Dursan (SilcoTek Corporation, Bellefonte, PA), Ni-P-polytetrafluoroethylene (PTFE, Avtec Finishing Systems, New Hope, MN), and Lectrofluor 641 (General Magnaplate Corporation, Linden, NJ)] on SS plate heat exchanger surfaces, to resist the formation of bacterial biofilms. It was hypothesized that modified SS surfaces would promote a lesser amount of deposit buildup and bacterial adhesion as compared with the native SS surface. Vegetative cells of aerobic sporeformers, Geobacillus stearothermophilus (ATCC 15952), Bacillus licheniformis (ATCC 6634), and Bacillus sporothermodurans (DSM 10599), were used to study biofilm development on the modified and native SS surfaces. The adherence of these organisms, though influenced by surface energy and hydrophobicity, exhibited no apparent relation with surface roughness. The Ni-P-PTFE coating exhibited the least bacterial attachment and milk solid deposition, and hence, was the most resistant to biofilm formation. Scanning electron microscopy, which was used to visualize the extent of biofilm formation on modified and native SS surfaces, also revealed lower bacterial attachment on the Ni-P-PTFE as compared with the native SS surface. This study thus provides evidence of reduced biofilm formation on the modified SS surfaces.

Determining the Effects of High Intensity Ultrasound on the Reduction of Microbes in Milk and Orange Juice Using Response Surface Methodology

This study investigated the effects of high intensity ultrasound (temperature, amplitude, and time) on the inactivation of indigenous bacteria in pasteurized milk, Bacillus atrophaeus spores inoculated into sterile milk, and Saccharomyces cerevisiae inoculated into sterile orange juice using response surface methodology. The variables investigated were sonication temperature (range from 0 to 84°C), amplitude (range from 0 to 216 μm), and time (range from 0.17 to 5 min) on the response, log microbe reduction. Data were analyzed by statistical analysis system software and three models were developed, each for bacteria, spore, and yeast reduction. Regression analysis identified sonication temperature and amplitude to be significant variables on microbe reduction. Optimization of the inactivation of microbes was found to be at 84.8°C, 216 μm amplitude, and 5.8 min. In addition, the predicted log reductions of microbes at common processing conditions (72°C for 20 sec) using 216 μm amplitude were computed. The experimental responses for bacteria, spore, and yeast reductions fell within the predicted levels, confirming the accuracy of the models.

The Prevalence and Control of Bacillus and Related Spore-Forming Bacteria in the Dairy Industry

Milk produced in udder cells is sterile but due to its high nutrient content, it can be a good growth substrate for contaminating bacteria. The quality of milk is monitored via somatic cell counts and total bacterial counts, with prescribed regulatory limits to ensure quality and safety. Bacterial contaminants can cause disease, or spoilage of milk and its secondary products. Aerobic spore-forming bacteria, such as those from the genera Sporosarcina, Paenisporosarcina, Brevibacillus, Paenibacillus, Geobacillus and Bacillus, are a particular concern in this regard as they are able to survive industrial pasteurization and form biofilms within pipes and stainless steel equipment. These single or multiple-species biofilms become a reservoir of spoilage microorganisms and a cycle of contamination can be initiated. Indeed, previous studies have highlighted that these microorganisms are highly prevalent in dead ends, corners, cracks, crevices, gaskets, valves and the joints of stainless steel equipment used in the dairy manufacturing plants. Hence, adequate monitoring and control measures are essential to prevent spoilage and ensure consumer safety. Common controlling approaches include specific cleaning-in-place processes, chemical and biological biocides and other novel methods. In this review, we highlight the problems caused by these microorganisms, and discuss issues relating to their prevalence, monitoring thereof and control with respect to the dairy industry.