Application of ultrasound-assisted thermal processing for preservation and quality retention of liquid foods.
A continuously working pilot plant-scale prototype was used to evaluate the effects of continuous-flow ultrasound-temperature treatment for bacterial decontamination of model suspensions and various liquid food systems such as milk, fruit, and vegetable juices. Escherichia coli K12 DH 5 alpha and Lactobacillus acidophilus were used as test microorganisms. In addition, treated juices were investigated for damage caused by heat or ultrasound-induced degradation of sensory and nutritional properties after treatment and storage. Changes in color and destruction of heat-labile and slightly oxidizable L-ascorbic acid content were monitored as an index to measure processing effects. Results were assessed with respect to the total energy requirement and compared with those using a conventional, indirect heating method having similar processing conditions. For the bacteriological process evaluation, the temperature- and time-dependent process lethality was used as the basis; for the quality- and energy-related investigations, the degree of bacterial inactivation was used. At identical degrees of bacterial inactivation, the ultrasound-assisted thermal treatments required a lower processing temperature than treatment with conventional thermal processing. However, according to energy balances, the total energy consumption was not reduced compared to conventional heating. Indications for a positive influence on shelf life, with improvements in surface color stability (lightness) and L-ascorbic acid retention, were found among quality parameters of treated orange juice.
D001628:Beverages / Q000382:microbiology / Q000592:standards*; D003611:Dairy Products / Q000382:microbiology; D004926:Escherichia coli / Q000254:growth & development; D005511:Food Handling / Q000379:methods*; D005516:Food Microbiology; D005519:Food Preservation / Q000379:methods*; D005638:Fruit / Q000382:microbiology; D006358:Hot Temperature; D007779:Lactobacillus acidophilus / Q000254:growth & development; D010865:Pilot Projects; D011786:Quality Control; D014465:Ultrasonics