Modeling the growth dependence of Streptococcus thermophilus and Lactobacillus bulgaricus as a function of temperature and pH.

The growth of the lactic acid bacteria (LAB), Streptococcus thermophilus and Lactobacillus bulgaricus, widely used for yogurt production, results in acid production and the reduction of the milk [Formula: see text]. Industrial processes can show temperature ([Formula: see text]) changes due to the large scale of the equipment. As [Formula: see text] and [Formula: see text] affect the LAB growth, this study aimed to model the dependence of S. thermophilus and L. bulgaricus as a function of temperature and pH and to estimate and internally validate their growth parameters and confidence intervals with different modeling approaches. Twenty-four datasets regarding the growth kinetics of S. thermophilus and L. bulgaricus were used for estimating the kinetic parameters for each pure culture. The classical Baranyi and Roberts (sigmoidal) primary and Rosso and coworkers (cardinal parameter) secondary models successfully described the experimental data. The one-step modeling approach showed better statistical results than the two-step approach. The values of eight growth parameters ([Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text]) for each culture estimated from the fitting with the one-step approach and the Monte-Carlo-based approach were similar. Low averaged root-mean-squared errors ([Formula: see text]) (0.125 and 0.090 log CFU/mL) and percent discrepancy factor [Formula: see text] ([Formula: see text] and [Formula: see text]) values for S. thermophilus and L. bulgaricus were obtained in the internal model validation, reinforcing the predictive ability of the model.

Water sorption isotherms on lyophilized jabuticaba (Myrciaria cauliflora) peel: potential byproduct for the production of dehydrated foods.

In this work, water sorption profiles on lyophilized jabuticaba peel were evaluated using the BET, GAB, Halsey, Henderson, Oswin and Smith isotherm models. All water sorption studies were conducted using the static gravimetric method and saturated CH3COOK, K2CO3, NaBr, SnCl2, KCl and BaCl2 solutions at 20, 30 and 35 °C. The best water sorption isotherm fits were determined with the GAB model at 20 °C, Oswin model at 30 °C and Halsey model at 35 °C. The curve profiles of the isotherm models employed were classified as type III. The results revealed that lyophilized jabuticaba peel can be safely stored at 20, 30 or 35 °C with the monitoring and control of relative humidity, equilibrium humidity and water activity. However, microbial action and undesirable enzymatic reactions may occur at 35 °C when the relative humidity is above 22%. The present results are useful for defining suitable storage and production conditions of a novel jabuticaba peel-based process for the production of dehydrated foods.

Evaluation of soil contamination by heavy metals at public cemeteries in the municipality of Lages, southern Brazil / Avaliação da contaminação de solos por metais tóxicos em cemitérios públicos do município de Lages, Sul do Brasil

ABSTRACT The burial of bodies is a potentially polluting activity. Taking this into consideration, the aim of the present study was to verify the compliance of two cemeteries with environmental legislation and to quantify the concentrations of heavy metals in soils affected by burial activities. Physicochemical characterization of the soil was performed by analyzing control samples from areas near the cemeteries. Concentrations of cadmium, lead, chromium, nickel, zinc and copper were determined using high-resolution continuum source atomic absorption spectrometry. The two cemeteries had unsatisfactory properties for the retention of metal cations, with clay percentages ranging from 15.40 to 41.40% and sand percentages ranging from 28.75 to 66.85%. The control samples presented low cation exchange capacity (12.27 to 22.73 cmolc/dm³) and high aluminum (Al3+) saturation (66.74 to 90.16%). Although neither of the two cemeteries had concentrations above the limits established for the metals analyzed by Resolution No. 420/2009 of the National Environment Council, the contaminants may be leaching to groundwater due to inadequate soil characteristics.

RESUMO O sepultamento de corpos é uma atividade potencialmente poluidora. Este trabalho teve como objetivo verificar a adequação das áreas de dois cemitérios públicos à legislação ambiental e à atividade cemiterial e quantificar a concentração de metais pesados nos solos que estão sob influência desses empreendimentos. Realizou-se a caracterização físico-química do solo, com a análise de amostras testemunha de solo de cada cemitério. Também foram determinadas as concentrações dos metais pesados: cádmio, chumbo, cromo, níquel, zinco e cobre, por meio de espectrometria de absorção atômica de alta resolução com fonte contínua. As áreas dos cemitérios apresentam condições insatisfatórias para a retenção de íons catiônicos metálicos, com percentuais de argila variando entre 15,40 e 41,40% e de areia entre 28,75 e 66,85%. Os solos testemunha apresentaram reduzida capacidade de troca de cátions entre 12,27 e 22,73 cmolc/dm³) e elevada saturação por alumínio entre 66,74 e 90,16%. Apesar de nenhum dos cemitérios apresentar concentrações dos metais analisados acima dos limites de prevenção estabelecidos pela Resolução nº 420/2009 do Conselho Nacional do Meio Ambiente, em função das características dos solos, os contaminantes podem estar sendo lixiviados para os recursos hídricos subjacentes.

Modeling Salmonella spp. inactivation in chicken meat subjected to isothermal and non-isothermal temperature profiles.

Salmonella genus has foodborne pathogen species commonly involved in many outbreaks related to the consumption of chicken meat. Many studies have aimed to model bacterial inactivation as a function of the temperature. Due to the large heterogeneity of the results, a unified description of Salmonella spp. inactivation behavior is hard to establish. In the current study, by evaluating the root mean square errors, mean absolute deviation, and Akaike and Bayesian information criteria, the double Weibull model was considered the most accurate primary model to fit 61 datasets of Salmonella inactivation in chicken meat. Results can be interpreted as if the bacterial population is divided into two subpopulations consisting of one more resistant (2.3% of the total population) and one more sensitive to thermal stress (97.7% of the total population). The thermal sensitivity of the bacteria depends on the fat content of the chicken meat. From an adapted version of the Bigelow secondary model including both temperature and fat content, 90% of the Salmonella population can be inactivated after heating at 60 °C of chicken breast, thigh muscles, wings, and skin during approximately 2.5, 5.0, 9.5, and 57.4 min, respectively. The resulting model was applied to four different non-isothermal temperature profiles regarding Salmonella growth in chicken meat. Model performance for the non-isothermal profiles was evaluated by the acceptable prediction zone concept. Results showed that >80% of the predictions fell in the acceptable prediction zone when the temperature changes smoothly at temperature rates lower than 20 °C/min. Results obtained can be used in risk assessment models regarding contamination with Salmonella spp. in chicken parts with different fat contents.

Use of modified Richards model to predict isothermal and non-isothermal microbial growth

Abstract Mathematical models are often used to predict microbial growth in food products. An important class of these models involves the adaptation of classical sigmoid functions, such as the Gompertz and logistic functions. This study aimed to validate the use of the modified Richards model in various situations, which have not previously been tested. The model was obtained through solving a system of two differential equations and could be applied to both isothermal and non-isothermal environments. To test and validate this model, we used published datasets containing data for the growth of Pseudomonas spp. in fish products. The results obtained after fitting the model showed that it could be effectively used to describe and predict the Pseudomonas growth curves under various temperature regimens. However, the influence of the shape parameter on the growth curve is an issue that needs further evaluation.

Use of modified Richards model to predict isothermal and non-isothermal microbial growth.

Mathematical models are often used to predict microbial growth in food products. An important class of these models involves the adaptation of classical sigmoid functions, such as the Gompertz and logistic functions. This study aimed to validate the use of the modified Richards model in various situations, which have not previously been tested. The model was obtained through solving a system of two differential equations and could be applied to both isothermal and non-isothermal environments. To test and validate this model, we used published datasets containing data for the growth of Pseudomonas spp. in fish products. The results obtained after fitting the model showed that it could be effectively used to describe and predict the Pseudomonas growth curves under various temperature regimens. However, the influence of the shape parameter on the growth curve is an issue that needs further evaluation.