3.2 Color of walnut butter
Color was usually an unappreciated physical parameter (Jose Moyano et
al., 2010). However, the study by Gambaro showed that color could
influence the preferences of consumers (Gambaro et al., 2014). In the
color analysis, L* represented lightness and darkness (black and white),
a* represented red-green, and b* represented yellow-blue. Table 1
represented the color difference results of different walnut butter.
There were significant differences (p<0.05 ) in the L*,
a*, and b* between the FLWB and commercial walnut butter. MCT-WB had
slightly higher L* than SS1 and SS2. The L*, a* and b* of DG-WB and
CLA-WB were lower than those of commercial walnut butter. As a result,
the color of the sauces showed different degrees of yellow color for
commercial walnut butter and FLWB. The b* of FLWB was significantly
lower than the commercial walnut butter. The oil in traditional walnut
butter was mainly derived from the walnut oil in the walnut kernels, and
its color was mainly influenced by the beta-carotene contained in the
walnut oil (Misawa, 2009). The carotenoid content in walnuts ranged from
0.08-0.49 mg/kg (Ozrenk et al., 2012), which was resulting in a higher
yellow value of walnut oil (MartÃnez et al., 2008).
As a result, walnut oil had a more
yellow color due to its highest carotenoid content, while other oils
appear lighter yellow or even colorless. Walnuts could lose the
carotenoids after the extraction of walnut oil, which caused that the
defatted walnut meal lost the original color of walnuts and took on a
grayish-yellow color. This could also affect the color of walnut butter
which could appeared light-yellow or grayish-yellow. It may also be the
reason why commercial walnut butter containing walnut oil is more
yellowish than walnut butter prepared with FL. Tables 2S also showed
differences in the color of the four oils. There is a correlation
between the prepared walnut butter and FL, which may account for the
differences in the color of the walnut butter.