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Comparison of pressure treatment and heat treatment of skim milk with added starch on subsequent acid gelation of milk
- Oh, H.E., Wong, M., Pinder, D.N., Anema, S.G.
- Lebensmittel-Wissenschaft + [i.e. und] Technologie 2011 v.44 no.4 pp. 1189-1198
- gelation, glutinous rice, heat treatment, potato starch, pressure treatment, rice starch, skim milk, starch, storage modulus
- Skim milk with added starch (waxy rice starch or potato starch at levels of 0â1.5Â g/100Â g) was either pressure-treated (500Â MPa, 20Â Â°C, 30Â min) or heat-treated (80Â Â°C, 30Â min) and subsequently acidified (using glucono-Î´-lactone) to form acid milk gels. In the second part of the study, the pH of the skim milk samples was adjusted from the natural condition (pH 6.64) to pH 6.5, 6.6 or 6.9 before the pressure or heat treatment and re-adjusted back to pH 6.64 after the respective treatment. The rheological properties of the samples during acidification and of the final acid gels were studied. The storage modulus, Gâ², of the final acid milk gels increased as more waxy rice starch was added to milk before pressure or heat treatment. However, acid milk gels made from pressure-treated milk with added potato starch did not show significant changes in the Gâ² of the final acid gels whereas those made from the heat-treated counterparts showed a marked increase in the final Gâ² as the potato starch level increased. Waxy rice starch was gelatinised in milk by both pressure treatment and heat treatment whereas potato starch was gelatinised by heat treatment only. Increasing the pH of milk before pressure or heat treatment increased the final Gâ² of the acid milk gel produced on subsequent acidification of the milk and the final Gâ² was increased further by the addition of waxy rice starch before the pressure or heat treatment.