Modelling the growth of lactic acid bacteria at different temperatures

ABSTRACT Mathematical models are widely used to predict the shelf life of foods. Lactic acid bacteria (LAB), particularly Lactobacillus plantarum, Weissella viridescens and Lactobacillus sakei, are the main spoilage bacteria of refrigerated, vacuum-packed meat products, stored in modified atmosphere, and their growth determines the shelf life length of these products. The objective of this study was to model the growth of L. plantarum, W. viridescens and L. sakei under different isothermal cultivation conditions and establish secondary models to describe the effect of temperature on the growth parameters of these bacteria. The LAB growth was evaluated in culture medium at temperatures of 4, 8, 12, 16, 20 and 30 ºC. The fit of Baranyi and Roberts (BAR) and Gompertz (GO) primary models to the growth curves of LAB was compared by statistical indices, in which the BAR model showed slightly better fits to the experimental data. The BAR growth parameters were used to establish the secondary models, µmax and Nmax were established for the three LAB. The power model described the influence of temperature on the parameter λ for L. plantarum, and other bacteria showed no lag phase. The growth of LAB was strongly influenced by storage temperature and the obtained models allow predicting the growth of these bacteria within the temperature range from 4 to 30 ºC.

Modeling the Growth of Byssochlamys fulva on Solidified Apple Juice at Different Temperatures

The aim of this study was to establish primary and secondary models to describe the growth kinetics of Byssochlamys fulva on solidified apple juice at different temperatures. B. fulva was inoculated on solidified apple juice at 10, 15, 20, 25 and 30 °C. Linear-with-breakpoint, Baranyi and Roberts, and Huang primary models (without upper asymptote) were fitted to the data, and they showed good ability to describe the growth kinetics. B. fulva showed longer adaptation time on apple juice than on culture medium, but growth rates were similar as reported in the literature. The dependence of µmax and λ parameters on temperature was described with Square Root and Arrhenius-Davey secondary models, respectively. These models were important to establish process/storage conditions and apple juice shelf life.

Survey of molds, yeast and Alicyclobacillus spp. from a concentrated apple juice productive process

Bacteria and molds may spoil and/or contaminate apple juice either by direct microbial action or indirectly by the uptake of metabolites as off-flavours and toxins. Some of these microorganisms and/or metabolites may remain in the food even after extensive procedures. This study aim to identify the presence of molds (including heat resistant species) and Alicyclobacillus spp., during concentrated apple juice processing. Molds were isolated at different steps and then identified by their macroscopic and microscopic characteristics after cultivation on standard media at 5, 25 and 37ºC, during 7 days. Among the 19 isolated found, 63% were identified as Penicillium with 50% belonging to the P. expansum specie. With regards to heat resistant molds, the species Neosartorya fischeri, Byssochlamys fulva and also the genus Eupenicillium sp., Talaromyces sp. and Eurotium sp. were isolated. The thermoacidophilic spore-forming bacteria were identified as A. acidoterrestris by a further investigation based on 16S rRNA sequence similarity. The large contamination found indicates the need for methods to eliminate or prevent the presence of these microorganisms in the processing plants in order to avoid both spoilage of apple juice and toxin production.

Behaviour of Neosartorya fischeri Ascospores in pineapple juice

For heat-resistance derterminations, a Neosartorya fischeri ascospore suspension, obtained at three different conditions of temperature (20, 30 and 35ºC) and age (1, 2 and 3 months), was heat treated in pineapple juice with three different ratio conditions. The 1/k (min) values obtained were statistically analysed through the software Statisitca 6.0. At 80ºC, when there was a level change in the ratio factor from a lower (10) to a higher one (38), the thermal resistance (1/k) increased in approximately 41 per cent. The increase of the ascospore production age and temperature caused an increase on the thermal resistance approximately equal to 28 per cent and 14 per cent, respectively. Throufh the results, it could be concluded that N. fischeri presented lower thermal resistance for heating mediums with lower ratio values, or rather, the increase of the soluble solids concentration caused an increase of its thermal resistance. It was also observed that the ascospore production age and temperature increased significantly the thermal resistance of this mould in pineapple juice.

Avaliação da resistência térmica de Byssochlamys nivea E de Neosartorya fischeri em suco de abacaxi / Thermal resistance evaluation of Byssochllamys nivea E in pineapple juice

Estudou-se a resistência térmica de ascósporos dos fungos termorresistentes Byssochlamys nivea e Neosartorya fischeri, usando suco de abacaxi (pH 3,5 e 12ºBrix) como meio de aquecimento. Determinou-se a resistência térmica em Tempo de Destruição Térmica (TDT) nas temperaturas de 85,90 e 92 ºC. O maior valor de 1/k encontrado foi de 45 minutos para ascósporos de B. nivea a 85 ºC. Nessas mesmas condições, o valor de 1/k para N. fischeri foi de 30 minutos. Os resultados indicaram maior resist~encia térmica de ascósporos de B. nivea em comparação com ascósporos de N. fischeri em suco de abacaxi.

Factors affecting the thermal activation of Neosartorya fischeri in pineapple and papaya nectars

In this research factors that influence the activation of Neosartorya fischeri ascospores (heating medium, temperature of production and age of the ascospores) were studied. The heating medium used was pineapple and papaya nectars at different ratios (°Brix/acidity). Lower activation times were observed for the N. fischeri ascospores in pineapple and papaya nectars under the conditions of temperature and production age of 25°C for 1 month and using ratios of the heating medium of 10 for pineapple nectar and 26 for papaya nectar. In these cases, the activation time was 5 minutes for the pineapple nectar and 10 minutes for the papaya nectar at 85°C. For the ascospores produced at 35°C over three months, heated in pineapple nectar at a ratio of 38 and in papaya nectar at a ratio of 66, the longest activation times of 15 and 20 minutes, respectively, were observed. The statistical analysis showed that the factors which had the most influence in the activation time of the ascospores were the ratio and the production temperature of ascospores.

Nesta pesquisa, foram estudados fatores que influenciam a ativação de ascósporos do fungo termorresistente Neosartorya fischeri (meio de aquecimento, a temperatura de produção e idade dos ascósporos). Os meios de aquecimento utilizados foram sucos de abacaxi e de mamão, em diferentes ratios (°Brix/acidez) e a temperatura de ativação foi 85°C. Pôde-se observar que o fungo N. fischeri apresentou seus menores tempos de ativação quando presentes no suco de abacaxi e no mamão, nas condições de temperatura e de idade de produção de 25°C por 1 mês e o ratio do meio de aquecimento de 10 para suco de abacaxi e de 26 para suco de mamão. Nestes ensaios, o tempo de ativação foi de 5 minutos para suco de abacaxi e 10 minutos para o suco de mamão a 85°C. Ascósporos produzidos a 35°C, durante 3 meses e aquecidos em suco de abacaxi com ratio 38 e em suco de mamão com ratio 66 apresentaram os maiores tempos de ativação sendo estes de 15 a 20 minutos, respectivamente. Através de uma análise estatística, verificou-se que os fatores que mais influenciaram no tempo de ativação dos ascósporos foram o ratio e a temperatura de produção dos ascósporos.