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IV. Resultados y discusión. Capítulo I 87
2.4.4. Optical properties
Colour coordinates were measured from the infinite reflection spectrum
in a spectrocolorimeter (CM-3600 d, MINOLTA Co; Osaka, Japan). CIE
L * a * b * coordinates were obtained using illuminant D65/10º observer. Colour
of samples was characterised as to Lightness (L * ), Chrome (C * ab), hue (h * ab)
and Whiteness Index (WI) as defined in Eq. (3) to (5). Colour difference
(E) between treated and untreated samples was also calculated by using
Eq. (6).
* *2 *2
C ab a b
(3)
*
* *
h ab arctan b a
(4)
* 2 *2 * 2
100
L a
WI 100
b
(5)
* 2 * 2 *
L
a
b
2
E
(6)
2.4.5. Protein denaturation
The protein denaturation degree in each sample was analysed by
Differential Scanning Calorimetry in DSC 220 calorimeter (CU-SSC5200,
Seiko Instruments; USA). Prior to the analyses, samples were freeze-dried
(ioalfa-6 free-dryer, TELSTAR; Terrassa, Spain) and afterwards rehydrated
with 70 g/100 mL of water. 25 mg of rehydrated samples were introduced in
hermetic aluminium capsules (P/N SSC000C008, Seiko Instruments, USA).
An empty capsule was used as reference. Sample heating was carried out
from 25 ºC to 120 ºC at 5 ºC/min. From the obtained thermograms (heat flux
vs. temperature), the peak temperature and enthalpy for protein denaturation
were obtained.