RESIDENCE TIME DISTRIBUTION STUDIES IN CONTINUOUS THERMAL-PROCESSING OF LIQUID FOODS - A REVIEW

This paper presents a review on residence time distribution (RTD) stud ies in continuous thermal processing of liquid foods. The theoretical basis of the Danckwerts analysis is summarized, as well as the most im portant flow models, with special emphasis on tubular systems. Methods for experimental determination, modelling and estimation of RTD are c ritically described. While main design objectives in continuous therma l processes may be guaranteed by a proper minimum residence or holding time, process optimization requires the knowledge of the residence ti me distribution. Both concepts are reviewed and discussed. A significa nt scatter was noticed among published results and the need for a syst ematic work is clear It was concluded that future research should focu s on studies at pasteurization/sterilization temperatures, as well as ori studies conducted with real food products or model food systems wi th non-Newtonian flow behaviour. Furthermore, information relating RTD to processing conditions would be a useful tool for process optimizat ion. (C) 1998 Elsevier Science Limited. All rights resented.