title: The influence of ultra-pasteurization by indirect heating versus direct steam injection on skim and 2% fat milks.
abstract: Fluid milk is traditionally pasteurized by high temperature, short time (HTST) pasteurization, which requires heating to at least 72°C for 15 s. Ultra-pasteurization (UP) extends milk shelf life and is defined as heating to at least 138°C for 2 s. The UP process can be done by indirect heating (IND) or by direct steam injection (DSI). The influence of these 2 UP methods on milk flavor has not been widely investigated. The objective of this study was to compare the effect of HTST, IND-UP, and DSI-UP on sensory perception of fluid milk. Raw skim and standardized 2% milks were pasteurized at 140°C for 2.3 s by IND or DSI or by HTST (78°C, 15 s) and homogenized at 20.7 MPa. The processed milks were stored in light-shielded opaque high-density polyethylene containers at 4°C and examined by descriptive analysis and microbial analysis on d 3, 7, and 14. Furosine and serum protein denaturation analyses were performed on d 0 and 14 as an indicator of heat treatment. Last, consumer acceptance testing was conducted at d 10, with adults (n = 250) and children (ages 8 to13 y, n = 100) who were self-reported consumers of skim or 2% milk; consumers only received samples for either skim or 2% milk. The entire experiment was repeated in triplicate. Milks treated by HTST had lower cooked flavor than either UP milk. Milks heated by DSI-UP were characterized by sulfur or eggy and cooked flavors, whereas IND-UP milks had higher sweet aromatic and sweet taste compared with DSI-UP milk. Aromatic flavor intensities of all milks decreased across 14 d of storage. Furosine concentrations and serum protein denaturation were highest for the IND treatments, followed by DSI and HTST. Furosine content in both skim and 2% milk increased with time, but the increase was faster in IND-UP skim milk. Adult and child consumers preferred HTST milk over either UP milk, regardless of fat content. Ultra-pasteurization by IND or DSI did not affect consumer acceptance at 10 d postprocessing, but traditional HTST milks were preferred by consumers of all ages.
authors.affiliation: Department of Food, Bioprocessing and Nutrition Sciences, Southeast Dairy Foods Research Center, North Carolina State University, Raleigh 27695.
authors.forename: A P
authors.initials: AP
authors.lastname: Lee
authors.affiliation: Department of Food Science, Northeast Dairy Research Center, Cornell University, Ithaca, NY 14850.
authors.forename: D M
authors.initials: DM
authors.lastname: Barbano
authors.affiliation: Department of Food, Bioprocessing and Nutrition Sciences, Southeast Dairy Foods Research Center, North Carolina State University, Raleigh 27695. Electronic address: mdrake@ncsu.edu.
authors.forename: M A
authors.initials: MA
authors.lastname: Drake
mesh_terms: D000818:Animals; D005511:Food Handling; D006361:Heating; D006358:Hot Temperature; D008892:Milk; D061352:Pasteurization; D013227:Steam
chemical_list: D013227:Steam
keywords: consumer acceptance; direct steam injection; flavor; fluid milk; ultra-pasteurization