2.2.4. Determination of protein-precipitable phenolics
2.2.4.1. Determination of tannins (phenolics) in tannin–protein complex.
The precipitable protein phenolics as tannins was quantified by the
method described by Makkar (2003). Briefly, to a 2 ml of BSA solution
(containing 1 mg BSA/ml acetate buffer), suitable aliquots of PFJP were
taken in a test tube and mixed well before incubating at 4 °C overnight.
The contents were centrifuged at 3000 g for about 10 min and the
precipitatewas dissolved in 1.5 ml of 1% SDS solution. An aliquot of this
solutionwas mixedwith 3 ml of SDS-triethanolamine solution and 1 ml
ferric chloride (0.01M) and the absorbance at 510 nm (Model: UV–
VIS1700 Shimadzu, Japan) was recorded after 15–30 min. The amount
of tannins phenolics was calculated as tannic acid equivalent from the
calibration curve using standard tannic acid solution (0.5 mg/ml).
2.2.4.2. Determination of protein precipitable phenolics as percentage of
total phenolics. The protein precipitable phenolics as a percentage of
total phenolics was quantified by the method described by Makkar
(2003). Briefly, different aliquots of the PFJP was made up to 1 ml with
1 ml 1% SDS, and 3 ml SDS-triethanolaminewas added followed by 1 ml
of ferric chloride (0.01 M) and the absorbance at 510 nm (Model: UV–
VIS1700 Shimadzu, Japan) was recorded. The amount of total phenolics
was calculated as tannic acid equivalent fromthe calibration curve using
standard tannic acid solution (0.5 mg/ml). Protein precipitable phenolics
as percentage of total phenolics was calculated by following the
equation:
Protein precipitable phenolics ð%Þ = ðTannins phenolics = Total phenolicsÞ
× 100:
2.2.5. Determination of condensed tannins (proanthocyanidins)
The condensed tanninswere quantified by the method described by
Makkar (2003). Briefly, Aliquots of 25 or 50 μl PFJP made into 2.0ml
with 50% (v/v)methanolwasmixedwith 3.0 ml of Butanol–HCl reagent
followed by 0.1 ml ferric chloride reagent and kept in boilingwater bath
for 60 min. The absorbance was recorded at 550 nm (Model: UV–
VIS1700 Shimadzu, Japan) after cooling the tubes at room temperature
with suitable blank. The percent condensed tannins were calculated as
per extinction coefficient method: E1%, 1 cm, 550 nm of leucocyanidin 460.