The particle diameter of oil droplets of 10% menhaden oil-inwater
emulsion stabilised by 0.5% and 1.0% gelatin modified without
and with oxidised tannic acid is shown in Table 2. The particle
size of emulsion stabilised by 0.5% and 1.0% control gelatin was
2.24 ± 0.19 and 0.33 ± 0.02 lm, respectively, whereas that of emulsion
stabilised by gelatin modified with oxidised tannic acid was
2.65 ± 0.09 and 0.37 ± 0.02 lm, respectively. Droplet size of the
emulsion decreased markedly when the higher concentration of
gelatin either with or without modification was used. A sufficient
amount of proteins at the oil–water interface is required to cover
oil droplet completely. This result was in agreement with Surh,
Decker, and McClements (2005) who found that an increase in fish
gelatin concentration from 0.5% to 4.0% protein could increase the
fraction of small droplets and decrease the fraction of large particles.
When the protein amount is limited, there is no longer suffi-
cient protein to fully stabilise the droplet interface, and therefore
larger particles may be formed as a result of coalescence or bridging
flocculation. The increase in protein concentration enhanced
protein adsorption and surface coverage of oil droplets, which
effectively inhibited droplet aggregation or coalescence (Sun &
Gunasekaran, 2009). The larger particle size was observed in the
emulsion stabilised by gelatin modified with oxidised tannic acid
when compared with that found in the emulsion stabilised by
the control gelatin. The decreased surface hydrophobicity might
not favour the migration of gelatin modified by oxidised tannic
acid to the oil droplets, which were lipophilic. Thus, the amount
of modified gelatin occupied at oil droplet might be slightly lower.
This led to the lower emulsifying property of modified gelatin.