Estimating Listeria monocytogenes Growth in Ready-to-Eat Chicken Salad Using a Challenge Test for Quantitative Microbial Risk Assessment

Currently, there is a growing preference for convenience food products, such as ready-to-eat (RTE) foods, associated with long refrigerated shelf-lives, not requiring a heat treatment prior to consumption. Because Listeria monocytogenes is able to grow at refrigeration temperatures, inconsistent temperatures during production, distribution, and at consumer's household may allow for the pathogen to thrive, reaching unsafe limits. L. monocytogenes is the causative agent of listeriosis, a rare but severe human illness, with high fatality rates, transmitted almost exclusively by food consumption. With the aim of assessing the quantitative microbial risk of L. monocytogenes in RTE chicken salads, a challenge test was performed. Salads were inoculated with a three-strain mixture of cold-adapted L. monocytogenes and stored at 4, 12, and 16 °C for eight days. Results revealed that the salad was able to support L. monocytogenes’ growth, even at refrigeration temperatures. The Baranyi primary model was fitted to microbiological data to estimate the pathogen's growth kinetic parameters. Temperature effect on the maximum specific growth rate (μ_max) was modeled using a square-root-type model. Storage temperature significantly influenced μ_max of L. monocytogenes (p < 0.05). These predicted growth models for L. monocytogenes were subsequently used to develop a quantitative microbial risk assessment, estimating a median number of 0.00008726 listeriosis cases per year linked to the consumption of these RTE salads. Sensitivity analysis considering different time–temperature scenarios indicated a very low median risk per portion (<−7 log), even if the assessed RTE chicken salad was kept in abuse storage conditions.     

A Bayesian Approach for Multiple Response Surface Optimization in the Presence of Noise Variables

An approach for the multiple response robust parameter design problem based on a methodology by Peterson (2000) is presented. The approach is Bayesian, and consists of maximizing the posterior predictive probability that the process satisfies a set of constraints on the responses. In order to find a solution robust to variation in the noise variables, the predictive density is integrated not only with respect to the response variables but also with respect to the assumed distribution of the noise variables. The maximization problem involves repeated Monte Carlo integrations, and two different methods to solve it are evaluated. A Matlab code was written that rapidly finds an optimal (robust) solution in case it exists. Two examples taken from the literature are used to illustrate the proposed method.     

Diversity,civic virtues and ecological austerity

A single global culture and a unique set of world institutional arrangements, based on an ever-increasing consumption of natural resources and environmental pollution is not sustainable nor can be sustained. In this paper some key ideological and moral com­ponents of the urgently required changes towards a culture of sustainability are examined, together with the implications, difficulties and requirements for its embodiment both in individual practices and in social institutions. In particular, it is argued that the values and attitudes which promote the protection and integration of diversity—both cultural and biological—and restrain the current trends in natural resource consumption and environmental pollution are to be developed by the citizenry if global societies are to survive. In the domains of political participation, rational dialogue and civic virtue, sustainability is akin to the inherited republican ideals of liberty, equality and fraternity. Sustainability must now become an indispensable fourth moral pillar in the structuration of society and, in particular, in the coming world republican polity, which will necessarily take account of the diversity of cultures and institutions. It is shown that, otherwise, the now developing unsustainable global society would otherwise cease to exist.     

New critical region tables for Fisher's exact test

The best-known non-asymptotic method for comparing two independent proportions is Fisher's exact text. The usual critical region (CR) tables for this test contain one or more of the following defects:they distinguish between rows and columns; they distinguish between the alternatives H = p1 < p2 and H = p1 > p2; they assume that the error for the two-tailed test is twice that of the one-tailed test; they do not use the optimal version of the test; they do not give both CRs for one and two tails at the same time. All this results in the unnecessary duplication of the space required for the tables, the construction of tables of low-powered methods, or the need to manipulate two different tables (one for the one-tailed test, the other for the two-tailed test). This paper presents CR tables which have been obtained from the most powerful version of Fisher's exact test and which occupy the minimum space possible. The tables, which are valid for one- or two-tailed tests, have levels of significance of 10%, 5% and 1% and values for N (the total size of both samples) of less than or equal to 40. This article shows how to calculate the P value in a specific problem, using the tables as a means of partial checking and as a preliminary step to determining the exact P value.     

Collinearity diagnostic applied in ridge estimation through the variance inflation factor

The variance inflation factor (VIF) is used to detect the presence of linear relationships between two or more independent variables (i.e. collinearity) in the multiple linear regression model. However, the traditionally used VIF definitions encounter some problems when extended to the case of the ridge estimation (RE). This paper presents an extension of the VIF in RE by providing two alternative VIF expressions that overcome these problems in the general case. Some characteristics of these expressions are also presented and compared with the traditional expression. The results are illustrated with an economic example in the case of three independent variables and with a Monte Carlo simulation for the general case.     

Modelling university image: The teaching staff viewpoint

This study proposes a methodology for identification of the main dimensions determining university image and understanding the relative weight of each of these dimensions. This is important for university governance in order to improve the service provided and to develop and maintain a distinctive position giving a competitive advantage. The conclusions and implications deriving from these results suggest actions designed to improve the image of the university.     

Patterns of Attachment and Emotional Competence in Middle Childhood

The study investigated the relationship between patterns of attachment and emotional competence at the beginning of middle childhood in a sample of 122 seven‐year‐olds. A new battery of tasks was developed in order to assess two facets of emotional competence (emotion recognition and knowledge of regulation strategies). Attachment was related to the choice of emotion regulation strategies in hypothetical situations; secure children produced the highest frequency of cognitive engagement strategies (e.g., reappraisal), and disorganized children the lowest. Insecure children produced more behavioral engagement strategies and fewer behavioral diversion ones. There was a minor effect of attachment on emotion recognition, with disorganized children scoring lower in the discrimination of facial expression. Consistent sex differences were also apparent in the direction of a female advantage in emotional competence: Girls scored higher in emotion recognition than boys, and in the regulation knowledge task, they produced fewer helpless answers and more cognitive engagement strategies.     

CLASH OF CAREER AND FAMILY: FERTILITY DECISIONS AFTER JOB DISPLACEMENT

In this paper we investigate how career considerations may affect fertility decisions in the presence of a temporary employment shock. We compare the birth rates of women displaced by a plant closure with those of women unaffected by job loss after establishing the pre‐displacement comparability of these groups. Our results reveal that job displacement reduces average fertility by 5%–10%, and that these effects are largely explained by the response of women in more skilled occupations. We offer an explanation of our results based on career interruptions of women.     

Variable Weighting via Multidimensional IRT Models in Composite Indicators Construction

One of the most controversial steps in Composite Indicators (CIs) construction is the selection of one (possibly) best weighting technique. In this paper, we introduce a new endogenous weighting methodology developed in an extended Item Response Theory (IRT) framework. As weighting is much more thorough when carried out by accounting for the dimensionality of a dataset rather than by ignoring it, we suggest to assign weights on the basis of the discrimination parameters estimated through a multidimensional two-parameter logistic IRT model. Specifically, the procedure is developed through two consecutive steps. The first applies a hierarchical clustering algorithm to ascertain the number of dimensions measured by the data. The second estimates the discrimination parameters under the multidimensional two-parameter logistic model selected at the first step. The discrimination parameters can then be used to compare and weight the items that refer to the same dimension. Besides, in order to make such discrimination indices comparable across dimensions, the distribution of the latent trait is standardised for each dimension. The potentialities of this novel weighting technique are illustrated through an application to educational data, which refer to a national standardised test developed and collected by the Italian National Institute for the Evaluation of the Education System.     

Book reviews

A classic republished

Sex and Sex Worship. By O.A. Wall. London: Kegan Paul, 2006, 607 pages. Cloth, $255.

Senior sex: Exploring the sex lives of older adults

Sexuality, Sexual Health, and Ageing. By Merryn Gott. New York, NY: Open University Press, 2005,149 pages. Paper, $36.95.

The social construction of erotophobia

The Politics of Lust. By John Ince. Amherst, NY: Prometheus Books, 2005, 335 pages. Paper, $16.00.