Compositional analyses of ice cream samples performed in the
1st day of storage revealed that the targeted total solids and
fat levels were achieved (Table 1). As expected, pH and lactic acid
contents of regular and probiotic ice cream samples were significantly
different (P < 0.05) while similar lactic acid contents and
pH values were determined in all probiotic ice creams (P > 0.05).
Regular ice cream sample had a mean pH value of 6.90 ± 0.01 and
lactic acid percentage of 0.14 ± 0.01. There were significant differences
in viscosities among all mixes, including probiotic ice cream
mixes, and viscosity increased by addition of oligofructose or inulin
to mix (P < 0.05) (Table 1). High apparent viscosity in the
probiotic ice cream mix containing oligofructose or inulin can be
explained by the interactions of the dietary fiber and liquid components
of the probiotic ice cream mix. Ice cream mixes containing
carbohydrate-based fat replacers exhibit a viscous behavior because
of the capability for imbibing water, which would increase
the viscosity of the system (Schmidt and others 1993). The highest
mean apparent viscosity of 3905 MPa.s (P < 0.05) was obtained
in the probiotic mixes containing inulin (Table 1). Similar to our
findings, significantly higher apparent viscosity was obtained by
replacing 100% of the 42 DE corn syrup with inulin in a reduced
fat ice cream mix (Schaller-Povolny and Smith 2001). The authors
reported that higher apparent viscosity resulted from the higher
molecular weight of inulin and that a potential interaction between
the inulin and milk proteins could also be present in the system.
Higher molecular weight of inulin may be related to higher apparent
viscosity of the ice cream mix with inulin in our study. Inulin,
being highly hygroscopic, would bind water and form a gellike
network that, in addition to other components (like corn syrup
or emulsifier–stabilizer mixture), would modify the rheology of the
mix. Similar results in relation to the effect of inulin on viscosity
were also reported by El-Nagar and others (2002) and Akın (2005)
for yog-ice cream and probiotic-fermented ice cream, respectively.