3.1 Physicochemical and thermal characterization
In order to confirm previous results obtained from Santos et al. (2021)
[26], results of UV-vis spectroscopy analysis of annatto extract, CA
nanofibers, and CA@A nanofibers are presented in Figure 1. The annatto
extract spectrum revealed a strong absorption band at 410, which can be
attributed to bixin and norbixin [29,30,31]; according to Calogero
et al. (2015) [30], these two substances exhibit absorption bands
above 400 nm due to an electronic-dipole transition oriented along the
axis of the molecule. For carotenoids such as bixin and norbixin, the
p/p* transition is relevant; in this conjugated system, the p-electrons
are highly delocalized and the excited state is of comparatively low
energy. As a result, relatively little energy is required to cause the
transition, which corresponds to absorption in the visible region and
can be attributed to the peak obtained in the spectrum. No peaks
attributed to other annatto compounds were observed. This result agrees
with previous work demonstrating that annatto seed extraction with low
polarity solvents produces highly concentrated extracts mainly comprised
of cis-bixin (70–80%) along with lesser quantities of other
carotenoids as trans-bixin, cis-norbixin, and trans-norbixin
[30,31,32,33,34,35,36]. The UV spectrum of CA@A nanofiber samples
revealed a low-intensity absorption band centered at 410 nm, confirming
the presence of annatto extract.