posted on 2013-04-26, 08:10authored byDeirdre C. Walsh O'Grady, Brendan T. O'Kennedy, Richard J. Fitzgerald, C.N. Lane
The application of high pressure as an alternative to heat treatment in the acid-set gelling
of milk proteins was studied using a “simulated yogurt milk” (SYM) system, containing
phosphocasein and whey protein isolate (WPI) in a ratio of 4:1. Gels were made by acidification of
SYM with glucono-δ-lactone (GDL) at 40 oC to pH 4.6 and their properties measured by dynamic
rheology using a Bohlin CVO rheometer. Gelation was studied in heat – (90 oC × 10 min) or pressure
– (700 MPa × 20 min) treated SYM or SYM containing heat – (78 oC × 30 min) or pressure –
(0–700MPa × 20 min) treated WPI. For a constant time (20 min) and temperature (25 oC), the extent
of whey protein denaturation was dependent on the applied pressure. Although pressures of
≤400 MPa caused as much as 57% denaturation, they did not support acid-set gelation when pressure-
treated WPI was incorporated into SYM. Pressurisation ofWPI at 600 and 700 MPa, which resulted
in 86.5 and 91.4% denaturation, respectively, resulted in the formation of cohesive gels when
SYM was acidified with GDL. The acid-induced gelation profiles of SYMpressurised at 700 MPa ×
20 min and SYM containing WPI pressurised under the same conditions were different, suggesting
that the kinetics of aggregation were different, presumably due to the disruption of caseinmicelles in
the SYMsystem during the pressurisation step. Gels prepared from SYMcontaining pressure-treated
WPI were weaker, i.e., they had lower values for G’ throughout acidification, than those prepared
from SYMcontaining heat-treated WPI. The gelation properties of heated SYM containing native or
pressurisedWPI were similar, indicating that the combination of pressurisation ofWPI followed by
heating SYMdoes not have an additive effect in relation to acid-induced gelation. Heating was more
efficient at producing casein/whey protein interaction products that were suitable for the formation of
gels on acidification.