54F-1 |
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D. BERMUDEZ-AGUIRRE, Biological Systems Engineering, Washington State University, 213 LJ Smith Hall, Pullman, WA 99164, T. Mobbs, K. Versteeg, Food Science Australia, 671 Sneydes Road, Werribee, Vic, 3030, Australia, and G. V. Barbosa-Cánovas, Dept. of Biological Systems Engineering, Washington State Univ., 220 L.J. Smith Hall, PO Box 646120, Pullman, WA 99164-6120. Heat can cause undesirable effects in food during conventional pasteurization. Ultrasound is being tested as an alternative preservation technique for liquid foods. The objective of this work was to study the inactivation of Listeria innocua and the total count plate in raw whole milk under different conditions of thermo-ultrasonic treatment. Five systems were evaluated at constant temperature (63º C). Five different levels of amplitude of ultrasonic wave were studied (0, 30, 60, 90 and 100%) in an ultrasonic processor Hielscher® UP400S (400 W, 24 kHz) with a 22 mm probe. Treatment time was 30 minutes for all the samples. Results showed that thermal treatment and ultrasound at 30% amplitude have similar inactivation. Both had 4 log reductions after 30 minutes of treatment for Listeria innocua. Meanwhile, with higher amplitudes (60, 90, and 100%) more than 5 log reductions were achieved in the first 10 minutes of treatment. This shows that with high amplitude, cavitation is more intense, generating higher cell destruction. Higher log reductions can be reached with lower treatments times. For total count plate, similar reductions were achieved with thermal treatment than with ultrasonic treatments, at all amplitudes. Storage life was evaluated for all thermo and thermoultrasonicated samples and compared with raw milk. Results showed that ultrasonicated milk has a similar storage life compared with thermal treated milk. Samples presented a lower microbial count for 14 days. Studies in skimmed milk are suggested to increase the level of inactivation, because fat milk can protect the microbial cells. Ultrasound represents a viable option for pasteurization of milk, although key physicochemical properties should be evaluated in order to assure the total quality of the product.
Session 54F, Nonthermal Processing: General I
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |