Residue aspects of disinfectants used in the food industry

Disinfectants are frequently used in the food industry against harmful (micro-)organisms on equipment (surfaces, pipelines etc.) which can come into contact with food. In The Netherlands, such uses of disinfectants are only allowed when registered according to the provisions of our national Pesticide Law. In most cases, (registered) uses require an operating procedure consisting of 3 consecutive steps: cleaning, disinfection and rinsing the equipment with clean water, thus avoiding contamination of food as much as possible. However, in some cases traces of the used compound(s) in food are inevitable. Therefore, Maximum Residue Limits (MRLs) for the disinfectants involved are established in food in the Netherlands. As remaining residues must be safe when ingested by the public, intake must be well below the Acceptable Daily Intake (ADI) for the respective chemicals. Also, sensitive and easy-to-operate methods of residue analysis, capable of detecting low levels of the compounds in food, must be available for enforcement purposes. In the Netherlands, experience with the existing legislation was gained over the past 25 years, resulting in the establishment of some 15–20 MRLs for residues of disinfectants in food.Harmonisation of the use of disinfectants (and other biocides) in the EU will be achieved in a draft ‘Biocide Directive’ in which the residue aspects of disinfectants are also covered, in a more-or-less comparable way as has been layed down in the Dutch legislation.Recent developments include the use of disinfectants in food as such, to reduce micro-organisms and to prolong the shelf-life of food products. Although in some surrounding countries this technique may already have become common practice. The Netherlands is reluctant to register those uses, and restricts it to cases where there is an inevitable technical need for disinfection, to minimize the exposure of the consumer to residues of (potentially) dangerous chemicals.     

Tables for Testing the Equality of Two Proportions when Prior Information on their Common Value May be Available

In testing the equality of two proportions, one may define a rejection point T? such that if the test statistic T (in this paper, the ordinary Pearsonian chi-squared) exceeds T? then the hypothesis may safely be rejected, whatever the common value p of the two proportions may be; and similarly define an acceptance point A? such that if T ≦ T? then one may safely accept. These points may be refined if prior information is available, for example that p must lie in the central interval (c, 1 – c) or one of the extremal intervals (v, w) and (1 – w, 1 – v). Smallsample tables are provided both for the unrestricted case and for situations where one has such prior information.     

Resistance to the Brownian movement of red blood cells on flat horizontal surfaces

The movements of red blood cells (RBC), suspended in plasma, on plastic, glass, rhodium metal plate, siliconized glass, and siliconized rhodium were recorded on cinéfilm and analyzed. Values for the drag coefficient were calculated, using Einstein's theory of Brownian movement, and compared with the theoretical Stokes' hydrodynamic drag. The difference between the computed and Stokes' values gave the frictional coefficient or resistance resulting from the interaction of the cells, with the test surface. Of the three uncoated test surfaces, plastic was found to have the least interaction with the RBC. The frictional coefficient for plastic was found to be 1.75×10⁻⁷ N s m⁻¹ compared with a value of 2.82×10⁻⁷ N s m⁻¹ for rhodium metal, which had the largest interaction. Upon siliconization of the test surfaces, the interaction decreased by 40%. Reduction in the pH of the suspending plasma increased the interaction between the cells and the uncoated test surfaces, but the pH effect of diminished when the surfaces were siliconized.     

On the Assessment of the Performance of Multiple Test Procedures

Based on the concept of the multiple level of significance two criteria for assessing the performance of multiple tests are proposed: The simultaneous power is defined as the probability of rejecting all false null hypotheses. The probability of a correct decision is defined as the probability of correctly rejecting all false null hypotheses and accepting all true ones. Both criteria are discussed for nonstagewise and stagewise procedures in case of independent test statistics. For the example of 5 independently and normally distributed test statistics the values of the two criteria are calcutated under reasonably simple alternatives.     

Tools and Techniques for the Assessment of Ecotoxicological Impacts of Contaminants in the Terrestrial Environment

Until recently, only a small number of standardized (mainly acute) tests with earthworms and plants were available for terrestrial risk assessment. However, during the last years various new methods (especially with chronic endpoints such as reproduction) were developed and standardized. Moreover, beyond structural aspects (e.g., the effect on individuals), the question of influences of chemicals on ecological soil functions like litter decomposition has been raised. Later, biological test methods were used in the area of Soil Quality Assessment, where an often unknown and complex contamination of a site-specific field soil has to be evaluated. Due to the variety of soils to be tested, the existing methods had to be adapted. This article briefly summarizes basic principles of method standardization before providing an overview of existing standardized tests for the compartment soil (mainly from Europe), focusing on zoological, plant, and functional methods. After presenting the main features of already standardized tests (in particular those used in soil quality assessment so far) the development of new tests for specific purposes, ideas for a battery of tests and a new, community-based approach assessing the biological quality of field soils are discussed.     

Molecular mechanism for the initial process of visual excitation. IV. Energy surfaces of visual pigments and photoisomerization mechanism

Using the twisted conformations of the chromophores for visual pigments and intermediates which were theoretically determined in the previous paper, energy surfaces of the pigment at −190‡ C were obtained as functions of the torsional anglesθ _9–10 andθ _11–12 or of the torsional anglesθ _9–10 andθ _13–14. In these calculations, the existence of specific reaction paths between rhodopsin (R) and bathorhodopsin (B), between isorhodopsin I (I) and bathorhodopsin, and between isorhodopsin II (I′) and bathorhodopsin were assumed. It was shown that the total energy surfaces of the excited states had minimaC ₁ atθ _9–10 ∼ −10‡ andθ _11–12 ∼ −80‡,C ₂ atθ _9–10 ∼ −85‡ andθ _11–12 ∼ −5‡, andC ₃ atθ _9–10 ∼ 0‡ andθ _13–14 ∼ −90‡. These minima are considered to correspond to the thermally barrierless common states as denoted by Rosenfeld et al. Using the total energy surfaces in the ground and excited states, the molecular mechanism of the photoisomerization reaction was suggested. Quantum yields for the photoconversions among R, I, I′ and B were related to the rates of vibrational relaxations, radiationless transitions and thermal excitations. Some discussion was made of the temperature effect on the quantum yield. Similar calculations of the energy surfaces were also made at other temperatures where lumirhodopsin or metarhodopsin I is stable. Relative energy levels of the pigments and the intermediates were discussed.     

Heterogeneity in the efficacy of dental chemical disinfectants on water-derived biofilms in vitro

Abstract

Conditions in dental unit waterlines are favourable for biofilm growth and contamination of dental unit water. The aim of this study was to assess the effect of several chemical disinfectants on bacteria in a biofilm model. Water-derived biofilms were grown in a static biofilm model (Amsterdam Active Attachment model), using two growth media. Biofilms were challenged with Alpron/Bilpron, Anoxyl, Citrisil, Dentosept, Green & Clean, ICX and Oxygenal in shock dose and maintenance doses. The concentration and the composition of the chemical disinfectants influenced the number of culturable bacteria in the biofilms. The application of a single shock dose followed by a low dose of the same chemical disinfectants resulted in the greatest suppression of viable bacteria in the biofilms. Exposure to Citrisil and ICX consistently resulted in failure to control the biofilms, while Alpron/Bilpron had a substantial and relevant effect on the number of bacteria in the biofilms.     

Effect of substrate on the responsive behaviour of functionalised surfaces: insights from molecular simulation

Abstract

Responsive surfaces have been suggested to enhance longevity and antifouling performance of materials in many applications from industrial coatings to tissue engineering and drug delivery. We present a molecular dynamics study investigating de-swelling and swelling of some of the most commonly used responsive materials – PEG-functionalised silica and polymer surfaces – as a function of hydration and temperature. We show that PEG chains grafted onto the hard silica substrates exhibit a dehydration-induced collapse that is far more pronounced compared to chains grafted onto the soft polyester surface. The difference between the hard and soft substrates is particularly notable at low coverage densities where the chains are sufficiently separated from one another. We also show that inter-molecular hydrogen bonding responsible for the conformational state of the tethered chains in water can be temperature controlled. It can be suggested that the hard substrates with the intermediate-to-high coverage densities of low molecular weight hydrophilic grafts may be more appropriate for anti-fouling applications due to their ability to trap greater amount of water molecules. Soft substrates may be detrimental for the efficient response of the functionalised surfaces to changes in hydration and enhancement of the surface hardness must be considered when designing responsive surfaces for solution-based applications, such as antimicrobial coatings for industry and biomedicine.     

Nisin adsorption on hydrophilic and hydrophobic surfaces: evidence of its interactions and antibacterial activity

Study of peptides adsorption on surfaces remains a current challenge in literature. A complementary approach, combining X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) was used to investigate the antimicrobial peptide nisin adsorption on hydrophilic and hydrophobic surfaces. The native low density polyethylene was used as hydrophobic support and it was grafted with acrylic acid to render it hydrophilic. XPS permitted to confirm nisin adsorption and to determine its amount on the surfaces. ToF‐SIMS permitted to identify the adsorbed bacteriocin type and to observe its distribution and orientation behavior on both types of surfaces. Nisin was more oriented by its hydrophobic side to the hydrophobic substrate and by its hydrophilic side to the outer layers of the adsorbed peptide, in contrast to what was observed on the hydrophilic substrate. A correlation was found between XPS and ToF‐SIMS results, the types of interactions on both surfaces and the observed antibacterial activity. Such interfacial studies are crucial for better understanding the peptides interactions and adsorption on surfaces and must be considered when setting up antimicrobial surfaces. Copyright © 2013 European Peptide Society and John Wiley & Sons, Ltd.     

The physico-chemical characterization of casein-modified surfaces and their influence on the adhesion of spores from a Geobacillus species

To gain a better understanding of the factors influencing spore adhesion in dairy manufacturing plants, casein-modified glass surfaces were prepared and characterized and their effect on the adhesion kinetics of spores from a Geobacillus sp., isolated from a dairy manufacturing plant (DMP) was assessed using a flow chamber. Surfaces were produced by initially silanizing glass using (3-glycidyloxypropyl) trimethoxysilane (GPS) or (3-aminopropyl) triethoxysilane to form epoxy-functionalized (G-GPS) or amino-functionalized glass (G-NH₂) substrata. Casein was grafted to the G-GPS directly by its primary amino groups (G-GPS-casein) or to G-NH₂ by employing glutaraldehyde as a linking agent (G-NH₂-glutar-casein). The surfaces were characterised using streaming potential measurements, contact angle goniometry, infrared spectroscopy and scanning electron microscopy. The attachment rate of spores suspended in 0.1 M KCl at pH 6.8, was highest on the positively charged (+14 mV) G-NH₂ surface (333 spores cm^?2 s^?1) compared to the negatively charged glass (?22 mV), G-GPS (?20 mV) or G-GPS-casein (?21 mV) surfaces (162, 17 or 6 spores cm^?2 s^?1 respectively). Whilst there was a clear decrease in attachment rate to negatively charged casein-modified surfaces compared to the positively charged amine surface, there was no clear relationship between surface hydrophobicity and spore attachment rate.     

Identification of microbes from the surfaces of food-processing lines based on the flow cytometric evaluation of cellular metabolic activity combined with cell sorting

In this study the design of a flow cytometry-based procedure to facilitate the detection of adherent bacteria from food-processing surfaces was evaluated. The measurement of the cellular redox potential (CRP) of microbial cells was combined with cell sorting for the identification of microorganisms. The procedure enhanced live/dead cell discrimination owing to the measurement of the cell physiology. The microbial contamination of the surface of a stainless steel conveyor used to process button mushrooms was evaluated in three independent experiments. The flow cytometry procedure provided a step towards monitoring of contamination and enabled the assessment of microbial food safety hazards by the discrimination of active, mid-active and non-active bacterial sub-populations based on determination of their cellular vitality and subsequently single cell sorting to isolate microbial strains from discriminated sub-populations. There was a significant correlation (r = 0.97; p < 0.05) between the bacterial cell count estimated by the pour plate method and flow cytometry, despite there being differences in the absolute number of cells detected. The combined approach of flow cytometric CRP measurement and cell sorting allowed an in situ analysis of microbial cell vitality and the identification of species from defined sub-populations, although the identified microbes were limited to culturable cells.     

A comparison of different methods used for the quantitative evaluation of biomass of freshwater phytoplankton

Although in a strict sense the term phytoplankton biomass only refers to living algal material, in aquatic ecology the term has been associated with a variety of biological and biochemical procedures used to quantify the particulate matter suspended in natural waters. Relative merits of different biomass characteristics have been studied in three Dutch freshwater lakes with great differences in absolute biomass. Parallel determinations have been made of seston dry weight and supplementary elementary and caloric analyses of seston, of chlorophyll-a concentration and supplementary paper chromatographic analyses of pigment extracts, of particle concentration and particle size distribution as studied with an electronic particle counter, and of phytoplankton cell volume as calculated from the results of microscopic enumeration and sizing of algae. In this way an attempt was made to create a detailed picture of the nature of the seston of the three freshwater lakes.Different analytical techniques give strikingly different information, the accuracy of any method is largely dependent on the circumstances present, and different biomass characteristics therefore are only of value in limited spheres. It is suggested to distinguish between total seston characteristics (e.g. seston dry weight, particulate organic carbon, total particle volume) and strictly algological biomass characteristics (e.g. chlorophyll-a concentration, phytoplankton cell volume). The pattern of growth of phytoplankton populations shown by e.g. chlorophyll-a concentration may differ markedly from that indicated by e.g. total particle volume or seston dry weight. Also, to more or less extent the wax and wane of phytoplankton populations may go undetected among the total seston. Apparently, there is no one method of estimating biomass and no conversion factor that may serve for general purposes. In general, unambiguous information on the nature of the seston of natural waters may only be obtained by estimating total seston characteristics and algological biomass characteristics simultaneously. Depending on the objective of the investigation supplementary component analyses should be carried out to guarantee the correct interpretation of the results.     

Studies on the growth-stimulatory activity of pigeon milk-comparison and synergistic effects with serum

Pigeon milk, a nutritive secretion from the crop of breeding pigeons, was tested (on v/v basis) for growth factor activity either separately or in combination with other growth supplements. Synthesis of DNA in confluent monolayers of quiescent Chinese hamster ovary cells was enhanced by the homogenates of pigeon milk in the presence of both fetal bovine serum and bovine serum albumin, although the response with fetal bovine serum was greater than that with bovine serum albumin. The in vitro growth stimulation by pigeon milk was also reflected in the increase in cell number. Specific activity of pigeon milk growth factor, measured against both Chinese hamster ovary cells and mouse embryo fibroblasts, was found to be higher than that of fetal calf serum, fetal bovine serum, and goat, horse, pig and human serum. The growth-stimulatory property of pigeon milk did not change in the first 5 days of its secretion.Abbreviations BSA bovine serum albumin - CHO Chinese hamster ovary cells - DMEM Dulbecco's modified minimum essential medium - DNA deoxyribonucleic acid - EDTA ethylenediaminetetraacetic acid - EGF epidermal growth factor - FBS fetal bovine serum - FCS fetal calf serum - GF growth factor - GS goat serum - NIH/3T3 mouse embryo fibroblasts - PBS phosphate-buffered saline - PDGF platelet-derived growth factor - PM pigeon milk     

灌浆期遮光对水稻籽粒生长和Q酶活性的影响

以“协优9308”和“秀水110”为材料,设计了不遮光、全程遮光和阶段遮光等处理,用Richards方程对不同处理的籽粒灌浆动态进行分析,研究了弱光胁迫对籽粒生长的影响及其与垩白度和直链淀粉含量的关系。结果表明：全程遮光和阶段遮光处理的最终粒质量和最大灌浆速率（GR_max）均随着遮光强度的增加降低,处理间的差异几乎都达显著水平(P<0.05);全程遮光处理对平均灌浆速率、相对起始势以及实灌时间无规律性影响,而阶段遮光处理的平均速率随着遮光强度增加而降低,相对起始势和实际灌浆时间则随之增强,除个别外,处理间的差异均达显著水平(P<0.05);全程遮光处理的Q酶活性、结实率、千粒质量以及直链淀粉含量均随着遮光强度的增大而减少,垩白度则随着遮光强度的增大而增加,且差异在多数处理间达显著水平（P<0.05）,但阶段遮光处理对这些指标的影响无规律性;品种间比较,阶段遮光对“协优9308”的结实率、千粒质量、垩白度和直链淀粉含量的影响不大,但对“秀水110”影响较大,总体上看“协优9308”的耐阴性强于“秀水110”。     

番茄煤霉病生防融合子基因组RAPD分析鉴定

RAPD分子标记以其快速、简便等优点,克服了传统的标记手段和形态分类学的缺点,在亲本和杂交种的鉴别以及在基因克隆与分离和遗传图谱的建立等研究中都起着重要的作用。以番茄煤霉病生防菌株木霉菌T-23和链霉菌A的融合子为实验材料,比较和研究了真菌融合子基因组DNA的提取。并用20个随机引物对亲本及其融合子进行RAPD分析。结果表明,SDS-CTAB法提取的基因组DNAOD260/OD280为1.909,DNA浓度约为42.0 ng/μL,可以满足分子生物学实验的需要;融合子是双亲融合的产物,但从双亲获得的遗传信息不等,融合子在DNA水平上更接近链霉菌。     

An ellipsometry study on the effect of aluminium chloride and ferric chloride formulations on mucin layers adsorbed at hydrophobic surfaces

Ellipsometry was used to investigate the effect of polyaluminium chloride (PAC) formulations of different degrees of hydrolysation on an adsorbed mucin film. The results were compared to the effect of aluminium chloride (AlCl₃) and ferric chloride. A compaction of the mucin film took place upon addition of the formulations and this occurred to different extents and at different concentrations for the different formulations. The compaction of PAC of a low degree of hydrolysis behaved similarly to AlCl₃. PAC of a high degree of hydrolysis showed a greater compaction effect than the other aluminium formulations. The initial compaction concentration was found to be 0.001 mM which is less than previously found for aluminium–mucin complex formation in bulk. The reversibility of the compaction was also investigated. The compaction of the mucin film was found to be partly reversible for AlCl₃ and PAC of low degree of hydrolysis. No reversibility was observed for the formulations of PAC of high hydrolysis grade or for ferric chloride. The results are consistent with previously observed effects of PAC of a low degree of hydrolysis on bacterial surfaces where a compaction of surface polymers was indicated by the reduced range of repulsive steric interactions.     

Influence of substrate and relative humidity on the efficacy of three entomopathogenic fungi for the hide beetle,Dermestes maculatus (Coleoptera,Dermestidae)

Dermestes maculatus De Geer (Coleoptera: Dermestidae) is a carrion feeder that is also a pest of poultry houses, museums, silkworm culture, and many stored foods. The Hypocreales, Beauveria bassiana (Balsamo) Vuillemin, Metarhizium anisopliae (Metschnikoff), and Isaria fumosorosea Wize, were tested for efficacy against D. maculatus larvae on concrete, plastic, leather, and wood surfaces. Only wood had a significant negative effect on efficacy, and B. bassiana was the most efficacious species. The conidia of all three species lost viability quickly on wood with various responses on the other surfaces. When beetle larvae were exposed to deposited B. bassiana and incubated at 43, 56, 75, or 82% relative humidity, mortality was greatest at the lowest humidity suggesting enhancement of fungal infection by desiccation stress. The results indicate that entomopathogenic Hypocreales, especially B. bassiana, may be useful for control of hide beetles when applied at a low dose to surfaces that do not impact the viability of conidia.