The Effect of Salt and Temperature on the Growth of Fresco Culture

The effect of environmental factors, including temperature and water activity, has a considerable impact on the growth dynamics of each microbial species, and it is complicated in the case of mixed cultures. Therefore, the aim of this study was to describe and analyze the growth dynamics of Fresco culture (consisting of 3 different bacterial species) using predictive microbiology tools. The growth parameters from primary fitting were modelled against temperature using two different secondary models. The intensity of Fresco culture growth in milk was significantly affected by incubation temperature described by Gibson’s model, from which the optimal temperature for growth of 38.6 °C in milk was calculated. This cardinal temperature was verified with the Topt = 38.3 °C calculated by the CTMI model (cardinal temperature model with inflection), providing other cardinal temperatures, i.e., minimal Tmin = 4.0 °C and maximal Tmax = 49.6 °C for Fresco culture growth. The specific growth rate of the culture under optimal temperature was 1.56 h−1. The addition of 1% w/v salt stimulated the culture growth dynamics under temperatures down to 33 °C but not the rate of milk acidification. The prediction data were validated and can be used in dairy practice during manufacture of fermented dairy products.

Modeling the Recovery of Heat-Treated Bacillus licheniformis Ad978 and Bacillus weihenstephanensis KBAB4 Spores at Suboptimal Temperature and pH Using Growth Limits

ABSTRACTThe apparent heat resistance of spores ofBacillus weihenstephanensisandBacillus licheniformiswas measured and expressed as the time to first decimal reduction (δ value) at a given recovery temperature and pH. Spores ofB. weihenstephanensiswere produced at 30°C and 12°C, and spores ofB. licheniformiswere produced at 45°C and 20°C.B. weihenstephanensisspores were then heat treated at 85°C, 90°C, and 95°C, andB. licheniformisspores were heat treated at 95°C, 100°C, and 105°C. Heat-treated spores were grown on nutrient agar at a range of temperatures (4°C to 40°C forB. weihenstephanensisand 15°C to 60°C forB. licheniformis) or a range of pHs (between pH 4.5 and pH 9.5 for both strains). The recovery temperature had a slight effect on the apparent heat resistance, except very near recovery boundaries. In contrast, a decrease in the recovery pH had a progressive impact on apparent heat resistance. A model describing the heat resistance and the ability to recover according to the sporulation temperature, temperature of treatment, and recovery temperature and pH was proposed. This model derived from secondary mathematical models for growth prediction. Previously published cardinal temperature and pH values were used as input parameters. The fitting of the model with apparent heat resistance data obtained for a wide range of spore treatment and recovery conditions was highly satisfactory.

New record of Phytophthora root and stem rot of Lavandula angustifolia

<em>Phytophthora cinnamomi</em> was isolated from rotted root and stem parts of lavender as well as from soil taken from containers with diseased plants. Additionally <em>Botrytis cinerea, Fusarium</em> spp. and <em>Sclerotinia sclerotiorum</em> were often isolated from diseased tissues. <em>P. cinnamomi</em> colonised leaves and stem parts of 4 lavender species in laboratory trials and caused stem rot of plants in greenhouse experiments. Cardinal temperature for <em>in vitro</em> growth were about 7,5 and 32°C with optimum 25-27,5°C. The species colonised stem tissues at temperature ranged from 10° to 32°C.

Investigation on Temperature Stability of Scale Factor for an Optical Voltage Sensor Based on Pockels Effect

The temperature stability of scale factor (SF) has been analyzed and tested systematically for an optical voltage sensor (OVS) based on Pockels effect in this paper. The cardinal temperature sensitive parameters in sensor head and their impacts on SF are brought out by theoretical analysis and simulation method. Corresponding experiments are arranged to verify the validity of theoretical analysis. A real-time temperature compensation system is fabricated to reduce the error of SF in temperature fluctuation environment and its effectiveness is certified by experiment.

Evaluation of temperature effect on growth rate of Lactobacillus rhamnosus GG in milk using secondary models

The application of secondary temperature models on growth rates of Lactobacillus rhamnosus GG, the much studied probiotic bacterium, is investigated. Growth parameters resulting from a primary fitting were modelled against temperature using the following models: Hinshelwood model (H), Ratkowsky extended model (RTK2), Zwietering model (ZWT), and cardinal temperature model with inflection (CTMI). As experienced by other authors, the RTK2, ZWT, and CTMI models provided the best statistical indices related to fitting the experimental data. Moreover, with the biological background, the following cardinal temperatures of L. rhamnosus GG resulted from the study by the model application: t min = 2.7°C, t opt = 44.4°C, t max = 52.0°C. The growth rate of the strain under study at optimal temperature was 0.88 log10(CFU mL−1 h−1).

Improving the CROPGRO-Tomato Model for Predicting Growth and Yield Response to Temperature

Parameterizing crop models for more accurate response to climate factors such as temperature is important considering potential temperature increases associated with climate change, particularly for tomato (Lycopersicon esculentum Mill.), which is a heat-sensitive crop. The objective of this work was to update the cardinal temperature parameters of the CROPGRO-Tomato model affecting the simulation of crop development, daily dry matter (DM) production, fruit set, and DM partitioning of field-grown tomato from transplanting to harvest. The main adaptation relied on new literature values for cardinal temperature parameters that affect tomato crop phenology, fruit set, and fruit growth. The new cardinal temperature values are considered reliable because they come from recent published experiments conducted in controlled-temperature environments. Use of the new cardinal temperatures in the CROPGRO-Tomato model affected the rate of crop development compared with prior default parameters; thus, we found it necessary to recalibrate genetic coefficients that affect life cycle phases and growth simulated by the model. The model was recalibrated and evaluated with 10 growth analyses data sets collected in field experiments conducted at three locations in Florida (Bradenton, Quincy, and Gainesville) from 1991 to 2007. Use of modified parameters sufficiently improved model performance to provide accurate prediction of crop and fruit DM accumulation throughout the season. Overall, the average root mean square error (RMSE) over all experiments was reduced 44% for leaf area index, 71% for fruit number, and 36% for both aboveground biomass and fruit dry weight simulations with the modified parameters compared with the default. The Willmott d index was higher and was always above 0.92. The CROPGRO-Tomato model with these modified cardinal temperature parameters will predict more accurately tomato growth and yield response to temperature and thus be useful in model applications.

Effect of temperature and lactic acid bacteria on the surface growth of Geotrichum candidum

The surface growth of Geotrichum candidum isolated from ewes&rsquo; lump cheese was studied on pure agar medium and that inoculated with Lactobacillus rhamnosus GG and L. paracasei subsp. paracasei CCM 1753. The colony growth rates of fungus calculated from the growth curves were modelled in relation to temperature by the cardinal temperature model with inflection (CTMI). The following cardinal values resulted from the secondary model: T_min = &ndash;3&deg;C, T_opt = 27.6&deg;C, and T_max = 35.4&deg;C and optimal colony growth rate &micro;_opt = 5.34 mm/day. A quantitative study also showed that the simultaneous growth of L. rhamnosus GG and L. paracasei subsp. paracasei CCM 1753 had either no or only a slight effect on the fungal growth rates, respectively. These results pointed out that other intrinsic or extrinsic factors should be applied for the protection of fresh cheeses against the undesirable growth of G. candidum.