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Effect of ultra-high-pressure homogenization and pH on buttermilk.

S. Touhami



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Effect of ultra-high-pressure homogenization and pH on buttermilk.
S. Touhami*, A. Doyen, G. Brisson. Department of Food Sciences, Dairy Research Center (STELA), Institute of Nutrition and Functional Foods (INAF), Universit� Laval Quebec, QC, Canada.

Buttermilk (BM) is defined as the by-product of butter making. BM is of a particular interest due to the composition of the milk fat globule membrane (MFGM) rich in phospholipids (PL). While interesting for their nutritional and emulsifying properties, the presence of PL impairs the techno-functional properties of BM in dairy applications. Treatments to improve BM functionality are necessary to allow its valorization in dairy products. Consequently, this project aims to test the combination of ultra-high-pressure homogenization (UHPH) and pH modification on BM. Raw and pasteurized BMs, initially at pH 6.7, were produced, adjusted at pH 8.5 and 10.5, before application of UHPH at 100, 200, and 300 MPa. Changes in particle sizes were followed by laser diffraction. Protein profiles were determined by SDS-PAGE on BM and their corresponding supernatants recovered after centrifugation (70000xg/60 min) of the casein micelles, MFGM, and protein aggregates. Structural changes induced by UHPH were also monitored by TEM. For the non-homogenized BM, laser diffraction measurements showed an increase in particle mean diameter while increasing pH from pH 6.7 to 10.5, for raw BM it increased from 0.324 � 0.044 μm to 0.700 � 0.084 μm, and from 0.198 � 0.017 μm to 0.302 � 0.049 μm for pasteurized BM suggesting more severe changes in casein micelle structure and protein aggregation in raw BM. In fact, the supernatant protein profiles of the non-homogenized BM showed an increase in casein band intensity as the pH increase, indicating casein micelle dissociation, while no casein micelle dissociation was observed for the control BM. Moreover, for the BM treated at 300 MPa, the amount of soluble caseins recovered in the supernatant was markedly higher compared with the non-homogenized BM. These latest changes were more intense in pasteurized BM than raw BM. This result demonstrated that a 300 MPa UHPH treatment at pH 10.5 induced a drastic disruption of the casein micelles as confirmed by TEM. This study indicated that combination of UHPH and pH can be used to modify BM constituents, especially the casein micelles and open the door for new applications for the valorization of BM in dairy products.

Keywords: ultra-high-pressure homogenization, milk fat globule membrane, casein micelle.