Prediction of growth of Pseudomonas fluorescens in milk during storage under fluctuating temperature

Abstract

Accurate prediction of growth of undesirable organisms (e.g., Pseudomonas fluorescens) in perishable foods (e.g., milk), held under sub-ideal storage conditions, can help ensure the quality and safety of these foods at the point of consumption. In this investigation, we inoculated sterile milk with P. fluorescens (~10(3) cfu/mL) and monitored inoculum growth behavior at constant and fluctuating storage temperatures. Three storage temperatures, 4 °C, 15 °C and 29 °C, were selected to simulate proper refrigeration conditions (4 °C) and temperature abuse, respectively. To simulate temperature fluctuation, milk held at 4 °C was subjected to temperature shifts to 15 °C or 29 °C for 4 to 6h. A modified logistic model was used to obtain the best-fit curve for the microbial growth under constant storage temperature. The specific growth rates at 4 °C, 15 °C, and 29 °C, obtained from experimental data, were 0.056 ± 0.00, 0.17 ± 0.05, and 0.46 ± 0.02 h(-1), respectively, and the lag time values were 29.5 ± 4.2, 12.7 ± 4.4, and 2.8 ± 0.3h, respectively. A model predicting bacterial growth under different temperature fluctuations was obtained using the growth parameters extracted from constant temperature experiments. Growth behavior predicted by the fluctuating temperature model and that obtained experimentally were in good agreement. Lag time exhibited a larger variation compared with specific growth rate, suggesting that it depends not only on growth temperature but also on the sample population and temperature gradient. Additionally, experimental data showed that changing the temperature during the lag phase induced an additional lag time before growth; however, no significant lag time was observed under the temperature fluctuation during the exponential phase. The results of this study provide information for precise shelf-life determination and reduction of food waste, particularly for milk and milk-containing food products.

Proteolytic and lipolytic potential of Pseudomonas spp. from goat and bovine raw milk

“…P. fluorescens represented only 1.8% of the Pseudomonas strains isolated from goat milk in this study and expressed proteolysis only at refrigeration temperature. However, their deteriorating milk activity should not be underestimated since recent studies point to the pronounced multiplication of this species in milk maintained at 4°C, increasing from 3 to 8.5 log CFU/mL in 170 hours (Lin et al 2016). Scatamburlo et al (2015) also verified the dominance of P. fluorescens in goat's milk (50% of the isolates), considering the identification through a species-specific PCR.…”

Food Quality Management Systems in the Dairy Industry: A Case Study on the Application of Predictive Microbiology in the Microbial Quality of Milk

“…The optimization of the milk production chain to reduce spoilage before the heat treatments at industry greatly relies on the knowledge of storage temperature and times at the different steps in the primary production chain [21].…”

“…The main concern of these psychrotrophic species is related to the survival capacity of their enzymes and spores to typical heat treatments applied to milk. Species as Pseudomonas fluorescens produce extracellular enzymes when bacterial population reaches or exceeds 10 6 CFU/ml in food [21]. They can contribute to casein and lipid degradation, causing product alteration during distribution and home storage [24].…”

“…The model for Pseudomonas spp. corresponded to the one developed by Lin et al [21] for P. fluorescens in UHT milk, considering storage temperature as the prediction variable:…”

Summary of the COVID-19 epidemic in China: When and how to launch an emergency response

“…The entire process presents an S-shaped development trend. A logistic growth curve model [15] is often used to describe such ecological processes [16,17]. Both the average growth rate and the maximum value of the growth curve have clear epidemiological signi cance and are of great reference value in the eld of public health.…”