3.1. Dynamic rheology
The elastic or storage modulus (G0), and the viscous or loss
modulus (G00) of all samples were strain independent up to strain
values of at least 1% (not shown). Then, all the measurements were
carried out at a strain level of 0.5%, i.e. within the linear viscoelastic
region. During the three steps of the rheological measurements
(gelation, curing, and mechanical spectra), G0 was higher than G00
for all jellies (except the sample without added pectin at high fre-
quency, Fig. 3). This means that jellies showed predominantly solidlike behaviour, even at high temperatures. Consequently, G0 was
used to evaluate and compare the firmness/consistency of the
jellies structure, which is determined by the gel strength.
1a shows the increase of G0 during cooling of the jellies. This
increment represents the development and strengthening of the
jellies structure due to pectin gelation. High methoxyl (HM) pectins
form gels at low pH and high sugar concentration; this is why they
are called sugar acid gels. The gelation mechanism of HM pectins is
produced by non-covalent bonding of adjacent pectin chains,
leading to an interconnected three-dimensional network. These
bonds are produced in junction zones, which are stabilized by
hydrogen bonds and hydrophobic interactions between the
methyl-esther groups of the pectin chains. The sugar (or other cosolutes) reduces the water activity, promoting hydrophobic in-
teractions. These interactions dominate at high temperatures. The
acid releases Hþ, which neutralize the action of the ReCOO
groups, reducing the electrostatic repulsion between pectin chains,
and therefore favouring hydrogen bonding. This mechanism dominates at low temperature