Dissertation
Nonthermal processing of milk
Washington State University
Doctor of Philosophy (PhD), Washington State University
05/2008
DOI:
https://doi.org/10.7273/000005602
Abstract
Low frequency ultrasound at different intensities (24 kHz, 400 W, 120 [mu]m) plus heat (63 C) was used to inactivate Listeria innocua in milk; the most intense treatment was useful to pasteurization standards in shorter times. Inactivation kinetics did not follow a first order model; Weibullian and four parameters model better fitted survivor curves. Composition and physicochemical parameters of milk changed after sonication, but are still within reported ranges for processed milk; e.g., protein content remained at 3%. Butter fat content was shown to be an important hurdle in cell inactivation with ultrasound, as lower fat content resulted in faster and higher inactivation. Microscopy studies performed with Transmission (TEM) and Scanning Electron Microscopy (SEM) revealed that cell inactivation with ultrasound is caused by disruption of the cell membrane, pore formation and break-down of cells. With SEM fat globules showed smaller size (<1[mu]m) after sonication, producing a whiter milk color and a more homogenized and stable product matrix. Yogurt was processed with thermo-sonicated milk, showing more compact structure with minor syneresis problems; microwave energy was successfully used as a catalyst during long-term sample preparation for SEM, reducing the required time. Pulsed electric fields (PEF) was used to inactivate spores of Bacillus cereus in milk; processing conditions ranged from 0 to 240 pulses (2.5 [mu]s), 20 to 40 kV/cm; room temperature to 65 C; recirculation/refrigeration systems and nisin (10 and 50 IU/ml) were used selectively to reduce spore load in whole and skim milk. Spores showed resistance to temperature, PEF and the presence of antimicrobials. After 40 kV/cm, 65 C, 140 pulses (2.5 [mu]s) 3.5 log reduction of spores were achieved. During processing, electrode fouling was observed to generate arcing problems because of the presence of milk deposits and bubble formation; the milk layer in the electrode was composed mainly of protein, significantly reducing this milk component. Studies in strawberry flavored milk and model systems using PEF were conducted to study the stability of coloring agent Allura Red. HPLC showed the behavior of this dye, which has better stability when combined with other additives and it is present in high concentrations in model systems.
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Details
- Title
- Nonthermal processing of milk
- Creators
- Luz Daniela Bermudez
- Contributors
- Gustavo V Barbosa-Canovas (Chair) - Washington State University, Department of Biological Systems EngineeringBarry G Swanson (Committee Member)Juming Tang (Committee Member) - Washington State University, Department of Biological Systems EngineeringRalph Phillip Cavalieri (Committee Member) - Washington State University, Department of Biological Systems Engineering
- Awarding Institution
- Washington State University
- Academic Unit
- Department of Biological Systems Engineering
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Publisher
- Washington State University
- Number of pages
- 379
- Identifiers
- 99901054535401842
- Language
- English
- Resource Type
- Dissertation