Reduction of Streptococcus thermophilus in a whey protein isolate by low moisture extrusion cooking without loss of functional properties |
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Authors: | C QUÉGUINER E DUMAY C CAVALIER J C CHEFTEL |
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Affiliation: | Laboratoire de Biochimie et Technologie Alimentaires, Centre de Génie et Technologie Alimentaires, Universitédes Sciences et Techniques, 34095 Montpellier, France. |
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Abstract: | A whey protein isolate powder (WPI) (4–5% water) inoculated with 5x105 viable Streptococcus thermophilus per g, was continuously processed in a twin screw extruder under the following conditions (barrel length = 500 or 1000 mm; screw profile = forward transport and compression elements; moisture content during extrusion = 4–5%; feed rate = 10 kg h-1; barrel temperature ( Tb ) = 80–204°C; speed of screw rotation = 50 r.p.m.). The minimum residence time determined by pulse injection of erythrosin was 20–25 s (500 mm barrel) or 35–40 s (1000 mm barrel). Reduction values of viable Streptococcus thermophilus of 104.2-fold (500 mm barrel, Tb = 143°C) or 104.9-fold (1000 mm barrel, Tb = 133°C) were obtained without any modification of protein solubility or gelling properties. WPI extruded at the highest barrel temperatures (182–204°C) underwent limited browning and reduction of protein solubility. Gel permeation and hydrophobic interaction chromatography of the soluble constituents did not show any aggregates of β-lactoglobulin or α-lactalbumin. Gels prepared from control or extruded WPI ( Tb 143°C with a barrel length = 500 mm or Tb 133°C with a barrel length = 1000 mm) were identical, as judged by scanning electron microscopy and rheological evaluations. |
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Keywords: | β-Lactoglobulin gelling properties lactic acid bacteria low moisture heating power pasteurization |
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