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Reduction of Streptococcus thermophilus in a whey protein isolate by low moisture extrusion cooking without loss of functional properties
Author(s) -
QUÉGUINER C.,
DUMAY E.,
CAVALIER C.,
CHEFTEL J. C.
Publication year - 1989
Publication title -
international journal of food science and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.831
H-Index - 96
eISSN - 1365-2621
pISSN - 0950-5423
DOI - 10.1111/j.1365-2621.1989.tb00686.x
Subject(s) - streptococcus thermophilus , barrel (horology) , extrusion , whey protein isolate , whey protein , chemistry , solubility , chromatography , moisture , materials science , food science , lactobacillus , organic chemistry , fermentation , composite material
Summary A whey protein isolate powder (WPI) (4–5% water) inoculated with 5x10 5 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 ( T b ) = 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 10 4.2 ‐fold (500 mm barrel, T b = 143°C) or 10 4.9 ‐fold (1000 mm barrel, T b = 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 ( T b 143°C with a barrel length = 500 mm or T b 133°C with a barrel length = 1000 mm) were identical, as judged by scanning electron microscopy and rheological evaluations.