The influence of ι-carrageenan on the surface activity of bovine serum
albumin (BSA) and on the
properties of BSA-stabilized oil-in-water emulsions is reported.
Surface tension data at low ionic
strength indicate a weak electrostatic protein−polysaccharide
interaction at neutral pH, which
becomes much stronger at pH 6 but disappears in 0.1 M NaCl. The
effect of the attractive BSA−ι-carrageenan interaction on the droplet-size distribution and
creaming stability of protein-stabilized
emulsions (20 vol % n-tetradecane, 1.7 wt % BSA, 5 mM) has
been investigated over a range of pH
values. At pH 6 the system behavior is interpreted in terms of
bridging flocculation leading to a
gel-like emulsion network over a certain limited polysaccharide
concentration range. This was
confirmed by small-deformation oscillatory rheological measurements on
equivalent concentrated
emulsions (40 vol %). There is a good correlation with the
rheology of the dextran sulfate plus BSA
emulsions studied previously, suggesting that the flocculation
mechanism is similar for the two
sets of systems.
Keywords: Protein−polysaccharide interaction; ι-carrageenan; bovine
serum albumin; emulsion
stability; creaming; bridging flocculation; rheology
We report on the effect of high-pressure treatment (up to 7 kbar) on the
rheology of concentrated
emulsions containing the globular protein, bovine serum albumin (BSA),
and the anionic polysaccharide dextran sulfate. Small-deformation rheological properties
have been determined for oil-in-water emulsions (40 vol % n-tetradecane, 2.7 wt % BSA,
pH 7) containing polysaccharide added
after emulsion formation. In the absence of high-pressure
treatment, a plot of complex shear modulus
G* at 1 Hz and 30 °C against polysaccharide concentration
C
P shows a maximum in G* at
C
P ≈ 0.1
wt % which is consistent with bridging flocculation caused by a net
attractive electrostatic protein−polysaccharide interaction at the emulsion droplet surface.
High-pressure treatment of BSA before
emulsification, for 30 min at a pressure in the range of 400−700 MPa,
leads to substantial changes
in the flocculation and rheological behavior of the emulsion after
polysaccharide addition but no
discernible change in the emulsion droplet-size distribution prior to
the addition. In contrast, heat
treatment of BSA at 70−80 °C before emulsification leads to an
increase in average droplet size
and to changes in emulsion rheology (following addition of
polysaccharide) that are qualitatively
different from those found with the pressure-treated systems.
These results are discussed in relation
to current knowledge about effects of high-pressure processing on
protein structure and functionality.
Keywords: High-pressure processing; protein−polysaccharide interaction;
bovine serum albumin;
dextran sulfate; emulsion rheology; bridging flocculation
Aims: To develop a rapid real‐time polymerase chain reaction (PCR) method to detect Gluconobacter and Gluconacetobacter species in electrolyte replacement drinks.
Methods and Results: Samples of electrolyte replacement drinks were artificially contaminated with Gluconobacter species and then filtered to collect cells. DNA was extracted from the filters and analysed by real‐time PCR on the ABI Prism 7000 system, using commercial detection kits for lactic and acetic acid bacteria. In addition, specific primers and Taqman® probe were designed and used for the detection of seven Gluconobacter and Gluconacetobacter species. All the assays tested demonstrated a linear range of quantification over four orders of magnitude, suggesting detection levels down to 1 CFU ml−1 in the original drink.
Conclusions: A real‐time PCR method was developed to detect low concentrations of Gluconobacter and Gluconacetobacter sp. in an electrolyte replacement drink.
Significance and Impact of the Study: Real‐time PCR methods allow a rapid, high throughput and automated procedure for the detection of food spoilage organisms. The real‐time PCR assay described is as sensitive as the conventional method that involves pre‐enrichment, enumeration on a selective agar (typically malt extract agar) and identification with a differential medium (typically Wallerstein nutrient agar). The real‐time PCR assay also provides a more rapid rate of detection, with results in less than 24 h following enrichment for Gluconobacter and Gluconacetobacter species.
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