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IV. Resultados y discusión. Capítulo II 229
Previous studies have also shown there are stability problems in
vegetable milks mainly due to the low content in proteins, which act as
emulsifiers in water-oil emulsions (Walstra et al., 1983). These problems
are usually overcome by adding hydrocolloids, such as xanthan gum, which
in this case lead to a gel formation by increasing the hydrogen bonds when
the solvent properties of the aqueous phase change due to a modification of
the pH (Song, Kin and Chang, 2006). The gel structure is dynamic,
increasing the bond formation over time and giving rise the phenomenon of
syneresis.
Table 5 shows the colour parameters of non-fermented and fermented
products at different storage times. The fermentation process modified the
optical properties of hazelnut milk, increasing both lightness and chrome
and decreasing the hue (p < 0.05). Moreover, the milk was whiter in
fermented samples, which was considered positive, since consumers
associate this type of products with the colour white.
Nevertheless, very few differences were observed between the colour
parameters of the fermented samples cold stored for different times; these
ranged over an interval of less than one unit. The total colour difference
between fermented and non-fermented hazelnut milks (E) was low and
undetectable by the human eye since, according to Francis (1983), values
lower than 3 units cannot be easily detected.