NEW MEASUREMENTS OF THE STICKY BEHAVIOR OF SKIM MILK POWDER

The drying of sugar-rich foodstuffs is often complicated by depositions on the walls of spray dryers, due to the stickiness of the products. This material property has been found to depend on both product temperature and moisture content and undergoes a rapid change from non-sticky behaviour to sticky behaviour with only a small change in these parameters. In this investigation, this so-called sticky point is measured for skim milk powder by measuring the cohesive force between stirred particles in a heated flask. The line separating the sticky and the non-sticky regions is given as a function of bulk temperature and moisture content. For the temperature range from 25 to 95°C investigated here, the line shows good agreement with the predicted glass transition temperature for lactose, shifted up by 23.3 K. This information can then be used in CFD simulations carried out to model the build-up of wall depositions inside spray drying chambers. As a first order approximation to estimate the behaviour of a particle impacting on a wall, sticky particles can be assumed to adhere to the wall, whereas non-sticky particles can be considered to bounce off it.     

Adhesion aspects of hydrophobic silane zeolite coatings for corrosion protection of aluminium substrate

The adhesive properties of an anti-corrosion silane–zeolite coatings on aluminium substrates have been evaluated in this work. The coated samples were obtained by dip-coating sol–gel solution. Four different composite coatings at increasing zeolite amount (60–90 wt% of zeolite) have been investigated.     

Adhesion enhancement of sol-gel coating on polycarbonate by heated impregnation treatment

The main limitation in using coated plastics for optical components, electronic applications and display systems is the softness of the substrate surfaces, which is responsible for the low impact and abrasion resistance and weak adhesion between the coating and the substrate. In this paper, we report a new strategy for surface pre-treatment of plastics using heated vacuum equipment and sol-gel materials to provide both chemical bonds and penetrated hard layer into the plastic surface to increase the overall performance of the coated plastic components. The heated vacuum treatment process involves: (1) surface cleaning and pore opening by heating and vacuum conditions, (2) impregnation of hydrolyzed hybrid precursor into polymer substrate under pressure and elevated temperature, (3) aminolysis of diffused precursor with surface to form chemical bonds and hardened surface layer, (4) formation of chemical bonds at treated surface with sol-gel hard coating. An impregnation depth of 1.5 µm was detected. Water contact angle dropped to below 40° and roughness increased after treatment. These provided better adhesion by increased wettability and contact area. Much increased nanoindentation hardness and Young's modulus after impregnation provided a gradient in mechanical properties between soft substrate and hard sol-gel coating. The hardened substrate delays the plastic deformation in substrate during pencil scratch test, thereby preventing early gouge failure. Both the better adhesion and the delayed gouge failure contributed to the increased scratch resistance from 6B to 8H after sol-gel coating.     

Effect of fluoride corrosion on the bonding strength of Ti-porcelain under static loads

The effect of fluoride corrosion on the bonding strength of Ti-porcelain under different static loads was investigated. The adhesion between the titanium and porcelain was evaluated by three-point flexure test. After being immersed in artificial saliva with pH 2.7 under 0 N, 1 N and 2 N static loads, respectively, no decrease of the bonding strength of Ti-porcelain occurred. However, the decrease of bonding strength was about 30%, 37%, and 46% after being immersed in artificial saliva with pH 2.7/F⁻ 100 ppm under 0 N, 1 N and 2 N static loads, respectively. The failure of the titanium-porcelain predominantly occurred at the titanium-oxide interface. Immersion in the artificial saliva did not affect the fracture mode of the titanium-porcelain system. The corrosion of the Ti-porcelain interface resulted in the reduction of bonding strength. The static loads enhanced the F⁻ corrosion on the Ti-porcelain interface.     

Phytate degradation by human gut isolated Bifidobacterium pseudocatenulatum ATCC27919 and its probiotic potential

The growing awareness of the relationship between diet and health has led to an increasing demand for food products that support health above and beyond providing basic nutrition. Probiotics are live organisms present in foods, which yield health benefits related to their interactions with the gastrointestinal tract. Phytases are a subgroup of phosphatases that catalyse the desphosphorylation of phytate, which reduces its negative impact on mineral bioavailability, and generates lower inositol phosphates. The aims of this investigation were to (i) study the ability of the probiotic candidate Bifidobacterium pseudocatenulatum to degrade phytate in synthetic medium, to (ii) identify the lower inositol phosphates generated, to (iii) study its survival under conditions mimicking gastrointestinal passage and finally to (iv) assess adhesion of the bacteria to Caco-2 cells. The first steps of InsP₆ degradation by B. pseudocatenulatum phytate-degrading enzyme/s were preferentially initiated at the DL-6-position and 5-position of the myo-inositol ring. It suggests that the main InsP₆ degradation pathway by B. pseudocatenulatum by sequential removal of phosphate groups was D/L-Ins(1,2,3,4,5)P₅ or D/L-Ins(1,2,3,4,6)P₅; D/L-Ins(1,2,3,4)P₄; to finally Ins(1,2,3)P₃ and D/L-Ins(1,2,4)P₃/D/L-Ins(1,3,4)P₃. This human strain also showed a notable tolerance to bile as well as a selective adhesion capacity (adhesion to control surfaces was zero), to human intestinal Caco-2 cells comparable to the commercial probiotic B. lactis. The phytate-degrading activity constitutes a novel metabolic trait which could contribute to the improvement of mineral absorption in the intestine as a nutritional probiotic feature with potential trophic effect in human gut.     

Evaluation of SICAN performance for biofouling mitigation in the food industry

Biological fouling in food industry leads to an increase in maintenance costs, decreases operational efficiencies and promotes food contamination leading to economic losses and the dissemination of foodborne pathogens. In order to maintain production efficiency and hygienic standards, cleaning in place (CIP) procedures are required. However, the existence of critical zones shielded from the main flow carrying the CIP disinfectants requires new strategies for reducing biofilm buildup and/or easy to clean surfaces. In this work, a Diamond-Like Carbon (DLC) coating modified by incorporation of silicon (a-C:H:Si or SICAN), was evaluated regarding bacterial adhesion, biofilm formation and cleanability. Assays included the natural flora present in industrial water (from a salad washing line) and Escherichia coli, one of the most persistent foodborne microorganisms.Results show that bacterial adhesion and biofilm formation on SICAN and stainless steel were similar, thus surface modification was not able to prevent biological fouling development. However, it was verified that after performing a cleaning protocol with chlorine, reduction of bacterial counts was much higher in SICAN (about 3.3 Log reduction) when compared to stainless steel (1.7 Log reduction). Although full biofilm recovery was observed on both surfaces 18 h after treatment, an operational window was identified for which processes with cleaning intervals of about 6 h could potentially use SICAN surfaces on critical areas (such as dead zones, crevices, corners, joints) and therefore operate at a much higher hygienic level than the one attained with stainless steel.     

Viability and surface properties of spores subjected to a cleaning-in-place procedure: Consequences on their ability to contaminate surfaces of equipment

This study was designed to evaluate how conditions encountered by spores during cleaning-in-place (CIP) procedures affected their surface properties, their viability and ability to contaminate materials. Spores from five Bacillus cereus strains were treated with NaOH at high temperature. Results revealed that high temperatures (exceeding 60 °C) and NaOH concentrations (over 0.5%) were required to significantly decrease spore viability (3–5 log decrease). In these conditions, modifications were also clearly observed by microscopy to various surface structures of spores (appendages, exosporium, and especially to the hair-like nap) but also to their coat. Therefore, the ability of culturable spores to adhere decreased for the majority of strains tested. We then demonstrated that spores in suspension in NaOH could adhere to surfaces of a CIP rig and that the contamination level was controlled by flow pattern. Consequently, re-adhesion along the processing line might occur during CIP procedures and this phenomenon must be taken into account when defining cleaning strategies.     

On the dynamics of localization and fragmentation—III. Effect of cladding with a polymer

In this series of papers, we investigate the mechanics and physics of necking and fragmentation in ductile materials. The behavior of ductile metals at strain rates of about 4,000–15,000 per second is considered. The expanding ring experiment is used as the vehicle for examining the material behavior in this range of strain rates. In Part I, the details of the experiment and the experimental observations on Al 6061-O were reported. Statistics of necking and fragmentation were evaluated and the process was modeled through the idea of the Mott release waves both from necking and fragmentation. Finally, it was shown that the strain in the ring never exceeded the necking strain in regions that strained uniformly. In Part II, we addressed the issues of strain hardening, ductility, geometry and size. Specifically, we examined different materials—Al 1100-H14, and Cu 101—and concluded that geometric constraint influences the strain at onset of localization significantly. The time taken for the localization to propagate across the cross-section and begin to unload its neighborhood was shown to control the amount of strain that can be experienced by the material; this also influences the statistics of localization and fragmentation. In the present paper, Part III, we examine the influence of compliant polymeric claddings on the localization and fragmentation response of metallic materials. Thin aluminum rings were coated with a layer of polyurea, with the thickness being an important parameter in the study. The onset of necking localization is shown not to be influenced by the coating; however, the propagation of unloading or release waves is shown to be significantly impeded by the cladding and therefore, further straining and fragmentation of the rings is affected. This result is of great importance in determining the impact resistance of elastomer-clad metallic structures. In future contributions as part of this sequel, we will explore the effect the development of localization and fragmentation in tubes and sheets where the geometric constraint can be varied over an even larger range.     

The effect of post surface silanization and luting agents on the push-out bond strengths of adhesively inserted fiber reinforced posts

The effect of silane treatment on the push-out bond strengths of three different luting agents to fiber-reinforced composite (FRC) posts after thermocycling was evaluated.Sixty single-rooted human maxillary central incisors were sectioned below the cemento-enamel junction, and the roots were endodontically treated. RelyX Fiber Posts (size #2) were inserted using etch-and-rinse, self-etch, and self-adhesive luting agents (cementing agents). For half of the specimen in each group, the fiber posts were treated with a silane coupling agent. Bonded specimens were cut (2-mm-thick sections) and push-out tests were performed (crosshead speed, 0.5 mm/min). Failure modes were evaluated using a stereomicroscope at original magnification ×40.For each luting agent the use of silane did not result in any statistically significant difference at any level of the root compared to those of the control groups except for Variolink II and RelyX Unicem luting agents in apical root section (p<0.05; one-way ANOVA). The post hoc analysis showed that regardless of the pre-treatment procedures, Variolink II achieved significantly higher bond strengths than Panavia F 2.0 and RelyX Unicem in all root sections (p<0.05).The use of a silane coupling agent had no influence on bond strengths depending on the luting agent used, whereas the type of luting agent (etch-and-rinse, self-etch, and self-adhesive) appeared to be a significant influence on the push-out bond strength values independent of the pre-treatment used. Therefore, pre-treatment of fiber posts with a silane coupling agent does not seem to be mandatory, which saves time in the clinical situation.