Ultrasonication has potential application in the dairy industry for extending milk shelf life by killing bacteria and spores that survive pasteurization. However, ultrasound treatment may result in off-aromas or undesirable milk quality consequences, which increase as treatment time and intensity increase. The primary objective of this research was to determine whether short treatments of acoustic energy, in conjunction with pasteurization, increase refrigerated shelf life while producing no adverse aroma effect. Shelf life was determined by performing total aerobic counts (TAC) on skim milk that had been inoculated with Paenibacillus amylolyticus, a spore-forming, thermotolerant and psychrophilic milk contamination bacterium. Pasteurized control milk was plated against thermosonicated (TS) milk and cold sonicated (CS) milk. Both treatments were pasteurized; however TS milk was sonicated after pasteurization while CS milk was sonicated before pasteurization. CS delivered significantly more acoustic energy to milk compared to TS under the same amplitude and treatment duration. TAC for almost all TS and CS treatments were higher than TAC for pasteurized control through 50 d refrigerated storage. Aroma quality of two TS treatment intensities (20 J/mL and 80 J/mL) and pasteurized controls were also evaluated by a trained descriptive sensory panel. No differences in cooked or lacks freshness aroma attributes were noted. The 80 J/mL TS sample had significantly higher rubbery aroma on day 1 after treatment compared to 20 J/mL sample but the aroma dissipated by day 8 or 22. Under the conditions evaluated in the present study, neither TS nor CS were more effective at reducing bacteria in milk than standard pasteurization conditions. Neither TS nor CS extended the shelf life of milk beyond standard pasteurization.
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