Probabilistic representation of the exposure of consumers to Clostridium botulinum neurotoxin in a minimally processed potato product

We have examined the potential of a well-specified, minimally processed potato product as a vehicle for the exposure of consumers to Clostridium botulinum neurotoxin. The product is a relatively simple combination of raw potato flakes, flour, starch and other minor ingredients and has an extended lifetime under refrigeration conditions. A combination of information and data, from a variety of sources that includes the manufacturer, has shown that the product is particularly safe with respect to non-proteolytic C. botulinum hazards. The model concentrates on a simple end point, the toxicity of an individual retail unit of the product at the point of consumer preparation, which is related to an individual risk. The probabilistic analysis was built using Bayesian Belief Network (BBN) techniques.     

PCR assay for differentiating between Group I (proteolytic) and Group II (nonproteolytic) strains of Clostridium botulinum

Groups I (proteolytic) and II (nonproteolytic) C. botulinum are genetically and physiologically distinct groups of organisms, with both groups being involved with human botulism. Due to differences in spore heat resistance and growth characteristics, the two groups possess different types of human health risks through foods, drink, and the environment. The epidemiology of human botulism due to Groups I and II C. botulinum is poorly understood, largely due to insufficient characterization of disease isolates, and warrants thorough outbreak investigation with a particular attention to discrimination between the different physiological groups of C. botulinum. In this study, a PCR assay was developed to discriminate between Group I and Group II C. botulinum. The assay is based on the fldB associated with phenylalanine metabolism in proteolytic clostridia, and employs an internal amplification control targeted to conservative regions of 16S rrn in Groups I and II C. botulinum. The assay correctly identified all 36 Group I and 24 Group II C. botulinum strains, possessing a 100% exclusivity and inclusivity. The assay provides a substantial improvement in discriminating between the Groups I and II C. botulinum, which traditionally is based on a time-consuming and error-prone culture method. Differentiation between the physiological groups of C. botulinum is an essential step in investigation of human botulism outbreaks, and should be considered as a diagnostic corner-stone in order to improve our epidemiological understanding of human botulism.     

Growth and toxigenesis of C. botulinum type E in fishes packaged under modified atmospheres

Modified atmosphere packaging of fresh fish is used to market high quality products in some European countries. The potential risk of C. botulinum growth in these extended shelf-life foods is still a concern; especially since toxigenesis may precede organoleptic spoilage. This paper will present toxigenic data from rockfish, salmon and sole muscle tissues which were inoculated with a pool of non-proteolytic C. botulinum type E at seven levels (10⁻² −10⁴ spores/sample), and stored under vacuum and 100% CO₂, at incubation temperatures between 30 and 4°C, for up to 60 days. Factorial experimental design allowed predictive formulae to be developed able to describe the lag time prior to C. botulinum toxigenesis and the probability of one spore to initiate toxigenesis based upon the storage conditions. Accurate characterization of the microbial ecology of C. botulinum in modified atmosphere-packaged fish, will support safe exploitation of these packaging systems in the market place, and identify critical control points for potential product or process abuses.     

Inhibition of Non-proteolytic Clostridium botulinum with Lactic Acid Bacteria in Extended Shelf-Life Cook-Chill Soups

The possibility of protecting cook-chill foods with microbial cultures against the risk of botulism was demonstrated. Three commercial soups were incubated with Clostridium botulinum 17B (10³ spores/g) and protective cultures (PCs) during 10-15 days at 10°C. The PCs populations were enumerated on M17, MRS and maltose tryptic soy agar, C. botulinum—on sorbitol tryptic soy agar, botulinal toxin was detected by the immunoassay, bacteriocins—by well diffusion assay. C. botulinum did not grow in two soups with low pH (5.2-5.5) and was unaffected by the PCs. In seafood chowder (pH 6.2) C. botulinum populations reached 10⁸ cfu/g. The co-incubation with the PCs, nisin-producing Lactococcus lactis (10⁷ cfu/g) or pediocin-producing Pediococcus pentosaceus (3×10⁸ cfu/g) singularly and as a mixture, prevented toxigenesis as well as reduced the product pH to 4.8-5.0 and C. botulinum populations to undetectable levels. Color, mouth-feel, texture, flavor and the overall acceptability of seafood chowder was not affected by the presence of the PCs.     

Germination and growth from spores: variability and uncertainty in the assessment of food borne hazards

We have developed a model for the variability of spore lag times and shown that variability has an important role in the quantitative assessment of risks associated with spore forming bacteria in food. The model includes two sequential independent delay times that contribute to the lag time for a single spore. We have shown that a population of variable spores also has a variable lag time, and we have emphasised the significance of this variability in quantitative representations of population dynamics for small populations. We have made a Bayesian estimate for the extent of the variability in spore lag times and made a comparison with direct microscopic observations of individual spores of nonproteolytic Clostridium botulinum. We conclude that Bayesian inference is a practical method for quantifying variability and hence a significant element in the development of quantitative risk assessments for hazards associated with spore forming bacteria.     

The effect of growth temperature on the phospholipid and fatty acyl compositions of non-proteolytic Clostridium botulinum

A non-proteolytic strain of Clostridium botulinum (NCIB 4270) was found to have a complex lipid composition, comprising five major phosphorus-containing lipids: phosphatidylethanolamine (PE), phosphatidylglycerol (PG), diphosphatidylglycerol (DPG), phosphatidylserine (PS) and a glycophospholipid of unknown structure (GPL), in order of abundance. Changing the growth temperature did not alter the lipid composition either qualitatively or quantitatively. The main fatty acyl components of the lipids are 14:0, 16:0 and 16:1. When the growth temperature was lowered from 37 to 8°C, there was an increase in 14:0 from 16.4 to 37.5%, an increase in 16:1 from 10.5 to 22.5%, and a decrease in the proportion of 16:0 from 40.3 to 19.1%. There was also a decrease in the proportion of cyclopropane fatty acids (15:0cyc and 17:0cyc) from 7.3 to 0.5%, and in the equivalent chain length of the total fatty acids from 15.9 to 15.3 as the temperature was lowered. The same temperature-dependent changes occurred in the five major lipid classes examined. Despite reports of the presence of plasmalogenic forms of phospholipids (i.e. those lipids which have the acyl chain in the sn-1 position replaced by an alk-1-enyl group) in some Clostridium spp., none were detected in C. botulinum NCIB 4270 using either commercially available spray reagents or by gas-liquid chromatographic analysis of the products or acid methanolysis of total lipid extracts. It is concluded that non-proteolytic C. botulinum lacks plasmalogens, typical of other clostridia, in its membranes and instead modulates its fatty acid composition in response to temperature changes in a manner that is typical of other (non-clostridial) bacteria.     

Models and mechanisms for bacteriocin action and application

There is considerable research on bacteriocin genetics, purification, and properties. Less is known about the mechanism(s) by which bacteriocins kill pathogens, the physical chemistry of the bacteriocin/pathogen interaction, and of the variables which influence bacteriocins' efficacy in foods. Such knowledge is prerequisite to the wider applications of bacteriocins and to increasing their efficacy by genetic engineering. Mechanistic studies using spores as bacteriocin targets are relatively few. Empirical challenge studies in a variety of foods have had mixed results. Working with well defined model foods, we have determined that increasing protein or phospholipid concentrations decrease nisin 's effectiveness against Clostridium botulinum growth from spore inocula. Nisin is also less effective at abuse compared to refrigerated temperatures. This may be a general characteristic of bacteriocins since increasing temperature decreases many bacteriocins' inhibition of Listeria monocytogenes in foods. L. monocytogenes vegetative cells provide a better target for bacteriocin action than do C. botulinum spores. Bacteriocins dissipate proton motive force (PMF) in L. monocytogenes, C. sporogenes and vegetative cells of other sensitive species. The cytoplasmic membrane is generally considered to be the site at which bacteriocins act. We have adopted fluorescence spectroscopy to characterize the interaction of bacteriocins with liposomes comprised of lipids extracted from L. monocytogenes membranes. The regulatory status of bacteriocins, various models for bacteriocin action, and future prospects for their application are also discussed.     

Steps towards a consumer-driven ‘concept innovation machine’ for food and drink

Innovation is often left to insight and serendipity. A lot of what researchers call innovation is actually a process by which one can make the individual consumer or practitioner more ‘creative’. Although it is important to work with the creative individual in hopes of coming up with the better ‘idea’ and new product/service opportunity, an equally valid albeit novel and counterintuitive approach systematizes creativity in a ‘research-driven machine’. This paper presents an approach to the systematization, based upon the point of view that creativity and innovation comprise the recombination of components into new blends. Given this point of view, to then spur innovation requires a systematic database that the user can access, with tools to help manipulate that database. The paper shows how such a database can be constructed and then used to create a novel product. The approach provides a general framework for the sensory professional to become more involved in the early stages of product development, where the focus is on the conceptual aspects of food features rather than on their physical manifestations in actual products.     

Comparing the antimicrobial effectiveness of NaCl and KCl with a view to salt/sodium replacement

A study using a small range of pathogenic bacterial species (Aeromonas hydrophila, Enterobacter sakazakii, Shigella flexneri, Yersinia enterocolitica and 3 strains of Staphylococcus aureus) has shown that potassium chloride has an equivalent antimicrobial effect on these organisms when calculated on a molar basis. Combined NaCl and KCl experiments were carried out and data was analysed using a modification to the Lambert and Lambert [Lambert, R.J.W., and Lambert, R., 2003. A model for the efficacy of combined inhibitors. Journal of Applied Microbiology 95, 734–743.] model for combined inhibitors and showed that in combination KCl is a direct 1:1 molar replacement for the antimicrobial effect of common salt. If this is a general finding then, where salt is used to help preserve a product, partial or complete replacement by KCl is possible.     

桑葚、蓝莓和红薯复配物的自由基清除能力研究

以桑葚、蓝莓和红薯为原料,采用两种体外抗氧化活性测定方法(DPPH和ABTS)评价单一农产品提取物的抗氧化活性,以及两两农产品提取物按照一定比例混合后的抗氧化活性。运用等辐射分析法作图,对比不同比例混合的农产品提取物的抗氧化相互作用。结果表明:DPPH试验中,单个农产品提取物抗氧化活性由强至弱为蓝莓>桑葚>红薯,混合后抗氧化协同效果最好的组合为桑葚∶红薯=15∶5(体积比)。ABTS试验中,抗氧化活性由强至弱为桑葚>蓝莓>红薯,混合后协同效果最好的组合为桑葚∶红薯=9∶11(体积比)。农产品混合后,水溶性-脂溶性组合的抗氧化协同效果最好。     

The antimicrobial efficacy of plant essential oil combinations and interactions with food ingredients

The objective of this study was to evaluate the efficacy of plant essential oils (EOs) in combination and to investigate the effect of food ingredients on their efficacy. The EOs assessed in combination included basil, lemon balm, marjoram, oregano, rosemary, sage and thyme. Combinations of EOs were initially screened against Bacillus cereus, Escherichia coli, Listeria monocytogenes and Pseudomonas aeruginosa using the spot-on-agar test. The influence of varying concentrations of EO combinations on efficacy was also monitored using E. coli. These preliminary studies showed promising results for oregano in combination with basil, thyme or marjoram. The checkerboard method was then used to quantify the efficacy of oregano, marjoram or thyme in combination with the remainder of selected EOs. Fractional inhibitory concentrations (FIC) were calculated and interpreted as synergy, addition, indifference or antagonism. All the oregano combinations showed additive efficacy against B. cereus, and oregano combined with marjoram, thyme or basil also had an additive effect against E. coli and P. aeruginosa. The mixtures of marjoram or thyme also displayed additive effects in combination with basil, rosemary or sage against L. monocytogenes. The effect of food ingredients and pH on the antimicrobial efficacy of oregano and thyme was assessed by monitoring the lag phase and the maximum specific growth rate of L. monocytogenes grown in model media. The model media included potato starch (0, 1, 5 or 10%), beef extract (1.5, 3, 6 or 12%), sunflower oil (0, 1, 5 or 10%) and TSB at pH levels of 4, 5, 6 or 7. The antimicrobial efficacy of EOs was found to be a function of ingredient manipulation. Starch and oils concentrations of 5% and 10% had a negative impact on the EO efficacy. On the contrary, the EOs were more effective at high concentrations of protein, and at pH 5, by comparison with pH 6 or 7. This study suggests that combinations of EOs could minimize application concentrations and consequently reduce any adverse sensory impact in food. However, their application for microbial control might be affected by food composition, therefore, careful selection of EOs appropriate to the sensory and compositional status of the food system is required. This work shows that EOs might be more effective against food-borne pathogens and spoilage bacteria when applied to ready to use foods containing a high protein level at acidic pH, as well as lower levels of fats or carbohydrates.     

Efficacy of six grain protectants applied alone or in combination against three species of coleoptera

Laboratory experiments were carried out to establish whether there were synergistic or antagonistic interactions in combination treatments of certain grain protectants. Six protectants were applied alone, or in combination, against Rhyzopertha dominica (F.) in stored maize and wheat, and Sitophilus oryzae (L.) and Tribolium castaneum (Herbst) in stored wheat. There were four organophosphorus (OP) insecticides (fenitrothion, chlorpyrifos-methyl, pirimiphos-methyl and methacrifos), one juvenile hormone analogue (methoprene) and one synergised pyrethroid (deltamethrin+piperonyl butoxide); and combination treatments consisted of either methoprene or synergised deltamethrin plus an OP insecticide. Based on the levels of control of adult progeny and periods of protection, there were no interactions between protectants. The results show that there is no need to alter field application rates to compensate for antagonism or to take advantage of synergism. They also support the view that application rates for combination treatments can be estimated from experiments on individual protectants using target species or strains.     

紫薯蛋白-葡萄糖美拉德产物制备及其与花色苷相互作用研究

通过干法美拉德反应制备紫薯蛋白-葡萄糖美拉德产物,并分析其与花色苷相互作用。采用聚丙烯酰胺凝胶电泳(SDS-PAGE)测定产物的分子质量,运用傅里叶红外变换光谱(FIRT)、差示扫描量热(DSC)和荧光光谱等多种方法对产物进行结构表征。结果表明:美拉德反应主要产物分子量为25 kDa;相较于紫薯蛋白花色苷复合物,美拉德产物的红外吸收强度普遍较低,尤其体现于酰胺I带处的红外吸收,美拉德产物变性峰温度(76℃)较高,变性焓值(366.7 J/g)较低;美拉德产物的最大荧光发射波长为340 nm,花色苷猝灭美拉德产物荧光为动静态联合猝灭,静态猝灭为主导;花色苷与美拉德产物之间的相互作用力属于强作用力,包括范德华力和氢键。花色苷与紫薯蛋白-葡萄糖美拉德产物相互作用结合位点靠近色氨酸残基。     

Determination of convective heat transfer coefficient and specific energy consumption of potato using an ingenious self tracking solar dryer

In the present work, an attempt has been made to experimentally determine the heat transfer properties of potato in terms of convective heat transfer coefficient, specific energy consumption and specific heating rate. Drying experiments with potato cylinders have been performed in an in-house fabricated laboratory scale natural convection indirect solar dryer with self tracking mechanism. The convective heat transfer coefficient of cylindrical potato samples was evaluated by considering the combined effects of heat capacities of food product as well as radiative heat transfer from drying chamber to the food product. This study revealed that the convective heat transfer coefficient for potato cylinders was varying from 11.73 to 16.23 W/m² °C with an experimental error of 7.86 %. The specific energy consumption was decreasing exponentially with drying time, and the average value was estimated to be 3,491 kJ/kg. It was also observed that the specific heating rate for potato cylinders decrease with dimensionless moisture content.     

PREDICTION OF FREEZING TIMES FOR FOODS AS INFLUENCED BY PRODUCT PROPERTIES

This investigation utilizes a computer simulation technique to predict the freezing times and temperature history curves for food products. The input information consists of the product properties for temperatures above the initial freezing point, freezing medium conditions and the initial product temperature. It has been established that food products with lower initial freezing points, higher initial water contents and higher initial product densities will have longer freezing times. The prediction of freezing time is most sensitive to the accuracy of the measurement of the product density and the initial freezing point if the freezing point is above ?0.5°C. The influence of the accuracy of unfrozen product thermal conductivity data on the freezing time is not important in the range of 0.45 to 0.55 W/m°K investigated. The combined influence of inaccuracy in measuring these product properties on the freezing time prediction will be significant even if the influence of an individual product property is small.     

Evaluation of culture media for selective enumeration of probiotic strains of lactobacilli and bifidobacteria in combination with yoghurt or cheese starters

A series of culture media were evaluated for selective enumeration of 10 commercial probiotic cultures. The media M17 and MRS 5.2 were most suitable to enumerate the yoghurt starters Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus, respectively. For the enumeration of probiotic Lb. acidophilus cultures, the MRS-clindamycin medium was found to be most optimal. Selective recovery results of the tested Bifidobacterium sp. were not uniform but indicated strain-to-strain variations depending on whether NPLN or MRS-LP were used. For the enumeration of probiotic cultures of Lb. rhamnosus and Lb. paracasei, LC medium (for yoghurt products) and MRS-AC medium (for cheese products) are recommended. In conclusion, our data indicate that the choice of culture medium and methodology for selective enumeration of commercial probiotic strains in combination with starters depends strongly on the product matrix, the target group and the taxonomic diversity of the bacterial background flora in the product.     

紫色马铃薯颗粒全粉加工关键工艺参数优化

为获得高品质紫色马铃薯颗粒全粉,以"黑美人"马铃薯为原料,通过单因素和正交试验对关键工艺参数进行优化,得出最佳工艺参数组合为:漂烫时间25 min,蒸煮温度95℃,蒸煮时间35 min,干燥温度120℃。该工艺条件下生产紫色马铃薯颗粒全粉,产品得率为22.87%,水分6.96%,蛋白质10.23%,淀粉68.9%,维生素C23.64 mg/100 g,灰分4.06%,花青素346.06 mg/100 g,花青素保持率83.72%,碘蓝值6.6786。所得颗粒全粉色泽均匀,游离淀粉含量低,花青素保持率高,感官品质良好。     

Contribution to the morphology and ecology of Sitophilus zeamais Motsch. in Yugoslavia

After we established the existence of Sitophilus zeamais in Yugoslavia in 1968, we examined the various morphological characters given in the literature in which this species differs from S. oryzae. In an experiment S. zeamais has infested maize in the field, but was unable to survive the winter in the field in Zagreb in any stage of development. It is quite possible that some might survive some winters in the warmer southern parts of the country. When each species was placed separately on samples of wheat, more progeny were obtained from S. zeamais than from S. oryzae. Sitophilus zeamais is more resistant to starvation than S. oryzae. Differences in the suitability of individual maize hybrids for the development of S. zeamais were found. Differences in preference for individual maize hybrids and wheat for oviposition have been determined.     

EXTRUSION COOKING OF SWEET POTATO ROOTS1

An extruded product was prepared using a mixture of sweet potato roots (SP), high protein wheat flour (WF), oil and water. The mixture was extruded in a Wenger X-5 extruder. The best physical characteristics of the extruded product were obtained using drum dried baked sweet potato powder (DDSPP) and WF in the ratio of 3:1, oil content of 4.0% and an initial moisture content of 12.32%. This combination yielded a 4.33 fold expansion of the product. Physical measurements on the extruded product were: diameter, bulk density, expansion, and percent rehydration. The carotenoid content of the extruded product did not change considerably from that of DDSPP. The use of DDSPP: WF ratio of 3:1 represented 89.86% utilization of raw SP roots on a fresh weight basis.