Food Science and Technology Department


Date of this Version



A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Food Science and Technology, Under the supervision of Professor Harshavardhan Thippareddi. Lincoln, Nebraska: May, 2012

Copyright (c) 2012 Maria A. Calle


Beef prime rib is a delicacy cooked at low temperatures for long period and extended hot holding prior to consumption. Due to the potential survival and outgrowth of foodborne pathogens, this process may pose a public health risk. Considering an increase in the availability of non-intact beef, the microbial safety of the preparation of prime rib from intact and mechanically tenderized beef was evaluated.

In the first study, lethality of the prime rib (from intact and non-intact, blade tenderized beef) cooking process to Salmonella spp. was evaluated. Boneless beef rib eye was surface inoculated with a five-strain cocktail of Salmonella spp. to obtain ca. 5.9 log CFU/g. The inoculated blade tenderized subprimals were passed with the fat side facing the blades to prepare non-intact beef rib eye. The subprimals were seared for 15 min at 260°C, cooked at 121°C to internal temperatures of either 37.8 or 48.9°C and held at 60°C for up to 8 h. The searing of blade tenderized rib eye resulted in 0.63 log CFU/g reduction in Salmonella spp. and cooking to internal temperatures of 37.8 and 48.9°C resulted in 2.86 and 3.58 log CFU/g reduction in Salmonella spp., respectively. Subsequent holding of the blade tenderized prime rib at an oven temperature of 60°C for 8 h resulted in an increase of 1.99 log CFU/g in Salmonella spp. population. Thermal processing of intact rib eye resulted in 5.22 and 5.54 log CFU/g reduction of Salmonella spp. population after cooking to 37.8 and 48.9°C respectively. Subsequent holding at 60°C during 8 h resulted in an increase in Salmonella spp. population of 1.07 and 0.44 log CFU/g, respectively.

In the second study, the growth of C. perfringens during hot holding and cooling was evaluated. Ground rib eye was dispensed in 5-g pouches, inoculated to obtain 2.5 spores/g of C. perfringens, and vacuum-packaged. C. perfringens spores were heat activated and the pouches with the inoculated meat were held at 43 or 49°C. Hot holding of inoculated rib eye resulted in germination and outgrowth of C. perfringens spores by 6.5 and 6.05 log CFU/g. Abusive cooling of cooked prime rib from 57.2 to 5°C within 6, 9, 12, and 15 h resulted in C. perfringens spore germination and outgrowth by 0.2, 0.4, 0.8, and 2.2 log CFU/g respectively.

Use of non-intact rib eye can pose an enhanced risk of foodborne illness when prime rib is cooked to low end point temperatures, held for extended periods of times at these low temperatures, and cooled at slow rates.

Advisor: Harshavardhan Thippareddi