Pasting curves of starches in gum (hydrocolloid) solutions at
low concentrations (starch 3.6%, gum 0.4%) were produced with a
Brookfield viscometer. Gums produced a variety of effects on viscosities
of starches during starch pasting (increase or decrease greatly or
slightly or no effect). A viscosity increase before the normal starch
pasting temperature was detected for normal maize starch in the presence
of carboxymethylcellulose (CMC), gellan, xanthan, guar gum, and sodium
alginate. Waxy maize, waxy rice, tapioca, regular rice, potato, and
wheat starches gave mixed responses. It appeared that interactions
between certain leached molecules, primarily amyloses, and certain gums
were responsible for the viscosity increase occurring before starch
pasting.
The pasting peak viscosity of potato starch was
greatly decreased by negatively charged gums (CMC, carageenans,
alginate, xanthan). The repelling forces between the phosphate groups on
potato starch and the negative charges on molecules of these gums were
hypothesized to be the cause. This hypothesis was supported by results
from similar systems (potato starch plus salt solution and
phosphorylated normal maize starch plus anionic gums), both of which
systems also produced lower peak viscosities. It was found, by
microscopic examination of potato starch heated to 95 °C in solutions of
ionic gums without shear, that the gums altered the granule pasting
process.
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برچسبها:
Starches; Gums; Hydrocolloids; Viscادامه مطلب
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