Ae. Hagerman et al., MECHANISMS OF PROTEIN PRECIPITATION FOR 2 TANNINS, PENTAGALLOYL GLUCOSE AND EPICATECHIN(16)(4-]8) CATECHIN (PROCYANIDIN), Journal of agricultural and food chemistry, 46(7), 1998, pp. 2590-2595
The precipitates that form when purified pentagalloylglucose or a puri
fied procyanidin [epicatechin(16) (4-->8) catechin; EC16-C] are mixed
with bovine serum albumin were quantitatively analyzed. EC16-C isa mor
e efficient protein precipitating agent than pentagalloylglucose on a
molar or a mass basis. EC16-C precipitates protein independently of te
mperature and presence of organic solvent. Precipitation by pentagallo
ylglucose increases as temperature is increased and decreases when alc
ohols are present. When tannin is in excess, up to 40 mol of pentagall
oylglucose is bound per male of protein precipitated, but only 20 mol
of EC16-C is bound per mole of protein precipitated. The data support
different models of precipitation for the two types of tannin: pentaga
lloylglucose, which is very nonpolar, precipitates by forming a hydrop
hobic coat around the protein, whereas the much more polar EC16-C form
s hydrogen-bonded cross-limbs between protein molecules.