Dynamic predictive model for the growth of Salmonella spp. in liquid whole egg and risk evaluation of egg white hydrolysates manufacturing process for spore formers: Bacillus cereus and Clostridium perfringens.

Authors

aikansh singh, University of Nebraska – Lincoln”Follow

Date of this Version

Spring 5-2010

Comments

A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of the Requirements For the Degree of Master of Science, Major: Food Science and Technology, Under the supervision of Professor Harshavardhan Thippareddi. Lincoln, Nebraska: May, 2010
Copyright (c) 2010 Aikansh Singh

Abstract

A dynamic model for the growth of Salmonella spp. in liquid whole egg under continuously varying temperature was developed and validated. A primary model (Baranyi model) was fitted to each temperature growth data and corresponding maximum growth rates were estimated. Pseudo-R² values were greater than 0.97 for primary models. The maximum growth rates obtained from each primary model were then plotted against temperature and modeled using the modified Ratkowsky model. The pseudo-R² and root mean square error were 0.99 and 0.06 h^-1, respectively for the secondary model. A dynamic model for the prediction of Salmonella spp. growth under varying temperature conditions was developed by solving a combination of primary and secondary models using fourth-order Runga-Kutta method. The developed dynamic model was validated for two sinusoidal temperature profiles, 5-15°C and 10-40°C with corresponding RMSE values of 0.28 and 0.23 log CFU/ml, respectively between predicted and observed values. The developed dynamic model can be used to predict the growth of Salmonella spp. in liquid whole egg under varying temperature conditions.

The germination and outgrowth of B. cereus and C. perfringens spores during the egg white hydrolysate (EWH) manufacturing process was evaluated. EWH was prepared by enzymatic hydrolysis of the inoculated egg white solution and maintained at optimum pH for enzymes (trypsin and chymotrypsin) for 24 h at 37°C. B. cereus population was increased by > 3.5 log CFU/ml during the EWH preparation using chymotrypsin, while minimal increase was observed during trypsin hydrolysis. C. perfringens populations were reduced during EWH preparation irrespective of the enzyme used. Hydrolysis of major egg proteins by chymotrypsin was completed within 4 h of incubation, while minimal hydrolysis of egg white proteins was observed with trypsin subsequent to 24 h incubation. New enzymes other than trypsin and chymotrypsin should be exploited for manufacturing egg white hydrolysates.

Advisor: Harshavardhan Thippareddi