High-pressure homogenisation of raw bovine milk. Effects on fat globule size distribution and microbial inactivation |
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| Affiliation: | 1. AZTI, Food Research Division, Parque Tecnológico de Bizkaia, Astondo bidea, Edificio 609, 48160 Derio, Bizkaia, Spain;2. Basque Culinary Center, University of Mondragón, Paseo Juan Avelino Barriola, 101, 20009, Donostia-San Sebastián, Gipuzkoa, Spain;1. Faculty of Science and Engineering, Queensland University of Technology, 2 George Street, QLD 4001, Australia;2. Department of Animal Science, Faculty of Agriculture, University of Peradeniya, Sri Lanka;3. Pharmacy Discipline, School of Clinical Sciences, Faculty of Health, Queensland University of Technology, 2 George Street, QLD 4001, Australia;4. Institute of Health and Biomedical Innovations, Queensland University of Technology, 2 George Street, QLD 4001, Australia;5. School of Agriculture and Food Sciences, The University of Queensland, St Lucia, QLD 4072, Australia;6. Department of Animal Science, Faculty of Animal Science and Export Agriculture, Uva Wellassa University, Badulla, Sri Lanka;1. Institute of Food Science and Nutrition, University of Sargodha, Sargodha, Pakistan;2. School of Chemistry, The University of Melbourne, Parkville, Victoria 3010, Australia;3. Food Science Research Institute, National Agricultural Research Centre, Islamabad, Pakistan;4. The ARC Dairy Innovation Hub, The University of Melbourne, Parkville, Victoria 3010, Australia;5. Department of Chemical Engineering, The University of Melbourne, Parkville, Victoria 3010, Australia;6. Department of Food Sciences, Cholistan University of Veterinary & Animal Sciences, Bahawalpur, Pakistan |
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| Abstract: | Whole raw milk was processed using a 15 L h?1 homogeniser with a high-pressure (HP) valve immediately followed by a cooling heat exchanger. The influence of homogenisation pressure (100–300 MPa) and milk inlet temperature Tin (4°C, 14°C or 24°C) on milk temperature T2 at the HP valve outlet, on fat globule size distribution and on the reduction of the endogenous flora were investigated. The Tin values of 4–24°C led to milk temperatures of 14–33°C before the HP valve, mainly because of compression heating. High Tin and/or homogenisation pressure decreased the fat globule size. At 200 MPa, the d4.3 diameter of fat globules decreased from 3.8±0.2 (control milk) to 0.80±0.08 μm, 0.65±0.10 or 0.37±0.07 μm at Tin=4, 14°C or 24°C, respectively. A second homogenisation pass at 200 MPa (Tin=4°C, 14°C or 24°C) further decreased d4.3 diameters to about 0.2 μm and narrowed the size distribution. At all Tin tested, an homogenisation pressure of 300 MPa induced clusters of fat globules, easily dissociated with SDS, and probably formed by sharing protein constituents adsorbed at the fat globule surface. The total endogenous flora of raw milk was reduced by more than 1 log cycle, provided homogenisation pressure was ?200 MPa at Tin=24°C (T2～60°C), 250 MPa at Tin=14°C (T2～62°C), or 300 MPa at Tin=4°C (T2～65°C). At all Tin tested, a second pass through the HP valve (200 MPa) doubled the inactivation ratio of the total flora. Microbial patterns of raw milk were also affected; Gram-negative bacteria were less resistant than Gram-positive bacteria. |
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