Formation and dispersal of biofilms in dairy substrates

The formation and dispersion of biofilms in the dairy industry is a problem because it increases cross‐contamination, affecting the shelf life of the products and their safety. The objective of this study was to evaluate the influence of different dairy substrates (cows’ milk and whey protein) on the formation and dispersion of Enterococcus faecalis, Listeria monocytogenes, Staphylococcus aureus and Bacillus cereus in two biofilm systems (mono‐species and multi‐species) on stainless steel at 25 °C. The dominant behaviour of E. faecalis occurred in most of the tests on mono‐species and multi‐species biofilms. A greater dispersion of biofilm cells was observed in skimmed milk.     

Experimental study of hydrodynamics in a flat ohmic cell—impact on fouling by dairy products

This study highlights the link between hydrodynamics and fouling phenomena in a continuous rectangular ohmic cell. The hydrodynamic study was carried out using flow visualisation techniques and particle image velocimetry (PIV). The distribution of deposits in the ohmic cell was investigated by heating an aqueous solution of β-lactoglobulin-xanthan gum mixture. Experimental results show that the deposit distribution on the electrode surfaces is directly related to the flow structures in the ohmic cell.     

Microbial biofilm detection on food contact surfaces by macro-scale fluorescence imaging

Hyperspectral fluorescence imaging methods were utilized to evaluate the potential detection of pathogenic bacterial biofilm formations on five types of food contact surface materials: stainless steel, high-density polyethylene (HDPE), plastic laminate (Formica), and two variations of polished granite. The main objective of this study was to determine a minimal number of spectral fluorescence bands suitable for detecting microbial biofilms on surfaces commonly used to process and handle food. Spots of biofilm growth were produced on sample surfaces by spot-inoculations of pathogenic Escherichia coli O157:H7 and Salmonella followed by room temperature storage for 3 days. Subsequently, hyperspectral fluorescence images were acquired from 421 to 700 nm using ultraviolet-A excitation. Both E. coli O157:H7 and Salmonella biofilms emitted fluorescence predominantly in the blue to green wavelengths with emission maxima at approximately 480 nm. A single-band image at 559 nm was able to detect the biofilm spots on stainless steel. On HDPE and granite, algorithms using different two-band ratios provided better separation of the biofilm spots from background areas than any single-band images did. The biofilm spots on stainless steel, HDPE, and granite could be detected with overall detection rate of 95%. On Formica, too many false positives were present to accurately determine an effective biofilm detection rate. This may have been due to the lower cell population density that was observed for the biofilm spots grown on Formica (approximately 4.3–6.4 log cfu cm⁻²) as compared to the other surfaces. These findings can be incorporated into developing portable hand-held imaging devices for sanitation inspection of food processing surfaces.     

Effect of whey protein concentration on the fouling and cleaning of a heat transfer surface

In the studies of fouling and cleaning of heat exchange surfaces in dairy plants, whey protein deposits and heat induced whey protein gels (HIWPG) are considered as suitable model material to simulate the proteinaceous based type “A” milk fouling. Protein concentration of the fouling solution may significantly influence the formation of milk deposits on heat exchange surfaces, hence affecting the cleaning efficiency. In this study, a laboratory produced heat induced whey protein gels (HIWPG) and a pilot plant heat exchanger fouling/cleaning were used to investigate the effect of protein concentration on formation and cleaning of dairy fouling. Here, HIWPGs made from different protein concentrations were formed in capsules and then dissolved in aqueous sodium hydroxide (0.5 wt%). The dissolution rate calculation based on the UV spectrophotometer analysis. In the pilot-scale plant study, whey protein fouling deposits were formed by recirculating whey protein solutions with different concentrations through the heat exchange section in different runs, respectively. The deposit layers were then removed by recirculating aqueous sodium hydroxide (0.5 wt%) and the cleaning efficiency was monitored in the form of the recovery of heat transfer coefficient while both fluid electric conductivity and turbidity were monitored as indications of cleaning completion. It was found that increasing the protein concentration of the HIWPG significantly increased the gel hardness and the dissolution time. In addition, increasing the protein concentration significantly increased both, the amount of the fouling on the pilot-scale plant and the time required to clean the fouling deposit.     

A new synbiotic dairy food containing lactobionic acid and Lactobacillus casei

As well as its beneficial health properties, the incorporation of the prebiotic lactobionic acid (LBA) in fermented dairy products can provide a technological advantage due to its gelling capacities. This study aimed to develop a new functional dairy product containing LBA synthesised within the process itself by the bacterium Pseudomonas taetrolens. A probiotic Lactobacillus casei strain was introduced through a sequential fermentation system. After incubation, in the case of the most effective experimental procedure, a synbiotic fermented milk with 30 g/L of prebiotic LBA was obtained, together with an active L. casei population of 10⁹ cfu/mL and <1% lactose content.     

On-line local thermal pulse analysis sensor to monitor fouling and cleaning: Application to dairy product pasteurisation with an ohmic cell jet heater

In the process industry, fouling is considered as a complex (sometimes partially known and identified) phenomenon. In this paper, a fouling sensor (FS) based on local differential thermal analysis is scrutinized and we report the comparison of two operating modes, steady (STR) and periodic (PTR) thermal regimes. Moreover, the development of alternating technologies like direct Joule effect (ohmic) heating to pasteurise and sterilise liquid food products in a continuous process is of great scientific and industrial interest. Heat treatment by direct Joule effect exhibits numerous advantages because rapid heating kinetics or homogeneous heat treatment is required. However, fouling of electrode surfaces in this kind of apparatus is much more problematic than in conventional heat exchangers. In the present study, a new continuous ohmic heating apparatus (Emmepiemme®, Piacenza, Italy) in which an alternating electrical current is applied directly to a jet falling between two stainless steel electrodes is investigated during pasteurisation of a dairy product. Conventional fouling measurements (pressure drop, heat transfer or electrical parameters) cannot be used in such a heater. Fouling and cleaning phases are monitored with fouling sensor and fouling quantified.     

Synergistic effect between Helichrysum italicum essential oil and cold nitrogen plasma against Staphylococcus aureus biofilms on different food‐contact surfaces

Staphylococcus aureus is the most common pathogen in human, and the most diseases produced by S. aureus are associated with biofilms. Helichrysum italicum essential oil (EO), as a natural and safe spice, was employed to disperse S. aureus biofilm by cold nitrogen plasma (CNP) assist. After S. aureus biofilm formation on food container surfaces, they were exposed to CNP and then treated with Helichrysum italicumEO for biofilm dispersion. The population of S. aureus biofilm was approximately reduced by 2 logs after individual treatment of 0.5 mg mL^?1 Helichrysum italicumEO or 400 W CNP. Interestingly, the combined treatment of Helichrysum italicumEO (0.5 mg mL^?1, 40 min) and CNP (400 W, 1 min) reduced the S. aureus viable count in biofilm below 2 logs CFU per cm² after 1‐day storage. Therefore, the synergetic treatment holds great promise to improve the current treatment systems of bacterial contamination on different food‐contact surfaces.     

Computational analysis of fouling by low energy surfaces

Fouling is a cost increasing problem for a variety of industries including aerospace, chemical, petroleum, and food. There have been studies on mitigation of fouling some of which recommend use of lower surface free energy materials, manufactured by different techniques, as an alternative to conventional materials. Although modeling of fouling for a given surface has been an area of interest; there is a lack in the models about correlating the surface free energy with deposit amount computationally. In this study, computational model, including the effect of surface energy and operational parameters, was proposed and validated to estimate amount of foulants deposits and rate of deposition. Towards this purpose, four coated surfaces (Microlube/PTFE, TM117P, AMC148, and CNT) were compared with stainless steel (SS316 as control) for flow rates of 3 and 10 g/s and inlet milk temperatures of 40 and 60 °C. The percent error for the decrease in outlet milk temperatures between the experimental data and computed results was between 2% and 18% except for CNT (29.2%). The calculations of deposit amount for each test case and the surfaces tested were in good agreement with the experiments, i.e., average percent difference values between measured and calculated values were from 11.1% to 38.1% (except CNT) with overall average of 21.5%.     

Relationships between saliva and food bolus properties from model dairy products

During food consumption, complex oral processing occurs to transform the food into a bolus, ready to be swallowed. The objective of this study was to relate food, saliva and bolus properties, by using model dairy products, to better understand the role of saliva in bolus formation. Un-stimulated and stimulated saliva was collected from 5 subjects and biochemical and enzymatic properties were measured. Food bolus was then obtained from 8 different dairy products, varying in composition and ranging from liquid to gelled samples. The rate of saliva incorporation, pH, spreading ability and bolus rheological properties were determined. Some correlations seemed to exist between lysozyme activity and bolus properties. Subject and food product had a significant effect on almost all bolus properties. The rheology of bolus was highly correlated with food product texture. Even though preliminary, this approach could be used to better understand stimulus release and perception during food consumption.     

Feasibility of using electrodialysis with bipolar membranes to deacidify acid whey

A nonreagent method for the regulation of the pH of acid whey was investigated at a laboratory scale. Acid whey and concentrated acid whey were subjected to electrodialysis with bipolar membranes in order to raise the pH value to 6.5. Demineralised whey underwent identical processing. The deacidification rate as per tonne of a dry matter was similar for acid whey and concentrated acid whey treatment at 70% and 90% degrees of demineralisation. We estimated the energy consumption of electrodialysis. The preliminary demineralisation of whey significantly increased the energy efficiency of whey pH correction. Additionally, we observed substantial fouling on the diluate side of bipolar membranes after whey treatment.     

Microbial,physico‐chemical and sensory characteristics of mango juice‐enriched probiotic dairy drinks

This study aimed to determine whether mango juice can improve the viability of probiotics in a fermented dairy‐based beverage whilst maintaining its quality characteristics. Formulations containing Lactobacillus acidophilus La‐5 culture, whole cow's milk and varying concentrations of mango juice (0%, 10%, 20%, 30% and 40% (w/w)) were produced and stored for five weeks at 4 °C. Results showed that probiotic viability was enhanced with the addition of 10% mango juice. Additionally, this formulation improved probiotics tolerance when exposed to in vitro gastrointestinal digestion. According to the sensory analysis, beverage sensory scores improved as levels of mango juice increased from 20% to 40%.     

内蒙古传统风味民族乳食品简介

本文根据作者多年的实际考查并参阅了有关文献,系统地综述了内蒙古地区蒙古族各种传统乳制品的生产历史、制作工艺、贮存和食用方法及其成分,同时对这些传统的民族乳制品将来的进一步开发提出了合理的指导性建议。文中论述的蒙古族传统乳制品有奶茶、奶皮子、稀奶油和奶油、黄油、酸奶子、奶干、奶豆腐、酸乳清、牛奶酒和马奶酒。     

Efficacy testing of teat dip solutions used as disinfectants for the dairy industry: Antimicrobial properties

The production of raw milk containing a limited number of bacterial contaminants, which retains its quality during storage, is the major task of the dairy industry. This can only be achieved with adequate regular cleaning and disinfection of the udder, milking equipment, the dairy parlour and animal housing areas. Studies were conducted to assess the efficacy of a range of dairy disinfectants on bacterial species isolated from cow udders as well as reference microbial strains (ATCC). Testing included the assessment of bacterial growth inhibition, biofilm inhibition or bacterial susceptibility to disinfection treatment. Findings show that Lir Analytical chemical disinfectants proved highly successful at inactivating a range of Gram‐positive (Bacillus, Enterococcus, Aeromonas) and Gram‐negative (Escherichia coli, Pseudomonas, Micrococcus) organisms, with up to 99.9% inactivation achieved. Additionally, test chemicals provided significant levels (P < 0.05) of biofilm inhibition for a number of test species. Furthermore, it was found that bacterial isolates from cow udders proved more sensitive to the test chemicals than their reference counterparts.     

Modified stainless steel surfaces targeted to reduce fouling – Evaluation of fouling by milk components

Several stainless steel based surfaces with different properties were evaluated according to their fouling behaviour for different dairy products under different conditions. Surface properties were obtained by the following modification techniques: , and TiC ion implantation; diamond-like carbon (DLC) sputtering; DLC, DLC–Si–O and SiO_x, plasma enhanced chemical vapor Deposition (PECVD); autocatalytic Ni–P–PTFE and silica coating. Aqueous solutions that simulate milk (SMUF – simulated milk ultrafiltrate for the mineral components, β-lactoglobulin for the protein components and FMF – fouling model fluid for complex milk systems) were used to study the fouling behaviour during pasteurisation. Bacteriological deposition studies were also performed with two heat resistant strains of Bacillus. The experiments were carried out at laboratory scale for the evaluation of calcium phosphate and protein deposition, and at pilot scale for adhesion of bacteria and deposits from complex milk systems.

In all cases, the fouling behaviour was affected by the surface material, although in different ways for the deposition or the cleaning phases. For the non-microbiological deposits (calcium phosphate, whey protein and FMF milk-based product), the Ni–P–PTFE surface was the most promising one, since it generally promoted less deposit build up and, in all cases, was the easiest to clean. On the other hand, for bacterial adhesion, the most suitable surface was the ion implanted (TiC) surface, which also showed less spores after the cleaning process.     

Effectiveness of ozone,heat and chlorine for destroying common food spoilage bacteria in synthetic media and biofilms†

Ozone, chlorine and heat applications were compared for killing effectiveness against food spoilage bacteria in synthetic broth. Fresh 24‐h bacterial cultures of Pseudomonas fluorescens (ATCC 948), Pseudomonas fragi (ATCC 4973), Pseudomonas putida (ATCC 795), Enterobacter aerogenes (ATCC 35028), Enterobacter cloacae (ATCC 35030) and Bacillus licheniformis (ATCC 14580) were exposed to ozone (0.6 ppm for 1 min and 10 min), chlorine (100 ppm for 2 min) or heat (77 ± 1°C for 5 min). One‐minute ozonation had little effect against the bacteria. There were significant differences (P < 0.05) among 10‐min ozonation, chlorine or heat inactivation of all bacteria exceptB. licheniformis. Ten‐minute ozonation caused the highest bacterial population reduction, with a mean reduction over all species of 7.3 log units followed by heat (5.4 log reduction) and chlorine (3.07 log reduction). Clean, passivated, sterile stainless steel (SS) metal coupons [2.54 × 2.54 cm², American Society for Testing Materials (ASTM) number 304] were incubated in ultra‐high temperature (UHT) sterile milk inoculated with P. fluorescens (ATCC 948), P. fragi (ATCC 4973) and P. putida (ATCC 795) for 24–72 h. After biofilm formation, the SS metal coupons were rinsed with phosphate‐buffered saline (1 min) and exposed to ozone (0.6 ppm for 10 min) and chlorine (100 ppm for 2 min). Results indicated that both ozone and chlorine significantly reduced the biofilm bacteria adhered to the SS metal coupons as compared to the control (P < 0.05). However, there was no significant difference (P > 0.05) between ozone and chlorine inactivation of the bacteria with the exception of P. putida. Ozone killed P. putida more effectively than chlorine.     

An imaging-based analysis of lipid deposits on contact lens surfaces

Purpose

To evaluate whether LipidTOX could stain lipid deposits on contact lens (CL) surfaces and compare lipid deposition patterns on various CL surfaces using an imaging method.

Study on the dissolution of heat-induced ovalbumin gel in alkaline solutions relevant to the removal of fouling deposits

Heat-induced whey protein concentrate gels (HIWPCG) have previously been used to simulate milk fouling and cleaning processes. The related research has generated considerable knowledge, which is of practical interest. In the current study, heat-induced ovalbumin gels (HIOVAG) have been employed to investigate the dissolution process (related to chemical cleaning process). Both HIOVAG and HIWPCG are sensitive to NaOH solution, which is a common cleaning fluid in food industry. In contrast to the HIWPCG behavior, HIOVAG dissolution presents no optimal NaOH concentration where the rate of dissolution is highest. The dissolution temperature was found to positively influence the dissolution process of HIOVAG, i.e. the dissolution rate increased with increasing dissolution temperature. In addition, ovalbumin (OVA) concentration in HIOVAG was found to be another important factor influencing the dissolution process. However, the stirring speed (convection) and heating time had no effect in the range tested, indicating that the process was internally limited.     

Plasma-activated liquids for mitigating biofilms on food and food contact surfaces

Plasma-activated liquids (PALs) are emerging and promising alternatives to traditional decontamination technologies and have evolved as a new technology for applications in food, agriculture, and medicine. Contamination caused by foodborne pathogens and their biofilms has posed challenges and concerns to the food industry in terms of safety and quality. The nature of the food and the food processing environment are major factors that contribute to the growth of various microorganisms, followed by the biofilm characteristics that ensure their survival in severe environmental conditions and against traditional chemical disinfectants. PALs show an efficient impact against microorganisms and their biofilms, with various reactive species (short- and long-lived ones), physiochemical properties, and plasma processing factors playing a crucial role in mitigating biofilms. Moreover, there is potential to improve and optimize disinfection strategies using a combination of PALs with other technologies for the inactivation of biofilms. The overarching aim of this study is to build a better understanding of the parameters that govern the liquid chemistry generated in a liquid exposed to plasma and how these translate into biological effects on biofilms. This review provides a current understanding of PALs-mediated mechanisms of action on biofilms; however, the precise inactivation mechanism is still not clear and is an important part of the research. Implementation of PALs in the food industry could help overcome the disinfection hurdles and can enhance biofilm inactivation efficacy. Future perspectives in this field to expand existing state of the art to seek breakthroughs for scale-up and implementation of PALs technology in the food industry are also discussed.     

Investigating the effect of starting mode on food fat gel layer formation on cold surfaces

In a previous study, Huang et al. (2012) employed a spinning disc apparatus to study deposition of fats on cooled stainless steel surfaces using model solutions of tripalmitin in non-crystallising paraffin. The apparatus was modified to give more accurate estimation of the test surface temperature, allowing the surface temperature and shear stress to be manipulated independently. The effect of different starting modes, simulating various situations which arise in pipelines, was studied. When fouling is induced by a step change in the test surface temperature, the presence of a subcooled surface promotes the rapid formation, initially, of a gel layer, followed by a period of linear fouling, and eventually falling rate fouling behaviour. When fouling is driven by a change in concentration the initial gel formation step is absent. The linear fouling regime was relatively insensitive to temperature, shear stress and starting mode for the conditions studied here. In the falling rate regime, the rate was determined by the deposit/solution interface temperature, following normal growth kinetics. At low tripalmitin concentrations, of 2.5 wt.%, sigmoidal growth behaviour was observed, which is attributed to the wall shear stress being initially high enough to disrupt the gel. As time proceeded, the gel increased in strength and was able to grow as before.     

Survival of Streptococcus pyogenes on foods and food contact surfaces

Streptococcus pyogenes causes septic sore throat in millions of Americans each year and may be transmitted from food handlers to food contact surfaces, foods, and consumers. This study examined the individual survival of six S. pyogenes strains on food contact surfaces (plastic and ceramic plates, plastic cups, and stainless steel utensils) held at 21 degrees C for 2 h and on tomatoes stored aerobically at 21 degrees C for 2 h and at 5 degrees C for 24 h. Survival of a cocktail of the six S. pyogenes strains was also evaluated on vacuum-packaged ready-to-eat meats and cheeses held at 21 degrees C for 8 h and at 5 degrees C for 24 h. Populations generally did not change on tomatoes, cheeses, or beef bologna; however, there were small (0.1 to 0.7 log CFU) but statistically significant decreases (P < 0.05) in average S. pyogenes populations on turkey luncheon meat and beef summer sausage stored for 8 h at 21degrees C and on beef summer sausage stored for 24 h at 5 degrees C. On food contact surfaces, average populations either decreased slightly (P > or = 0.05) or remained constant, with the exception of three strains that significantly decreased in number on ceramic plates (P < 0.05; average decreases, 0.3 log CFU). Results of this study suggest the importance of preventing the contamination of foods and food contact surfaces with S. pyogenes by infected workers.