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222 IV.Resultados y discusión. Capítulo II
conditions involved in hazelnut processing might provoke the breakage of
protein bonds, as confirmed by the analyses after and before pasteurisation.
The absorbance value prior to the heat treatment was lower (0.502 ± 0.008)
than that of pasteurised milk (0.870 ± 0.005). Other authors also reported
that high heating can cause some proteins to break down in cow milk
(Douglas et al., 1981; Walstra, 2003).
Amino acid consumption by bacteria provokes the elimination of the
amino group that reacts with the OPA reagent (Heller 2001). In fact, the
longer the storage period, the lower the absorbance values (Table 3), this
concurs with the fact that bacteria need nitrogen sources for their
metabolism, despite the low storage temperature (Tamime and Robinson,
2000). Nevertheless, the observed decrease was not significant after 14
storage days (p < 0.05), which could be explained by considering that GG
will be in a stationary growth phase.
3.3.2 Sugar contents
Knowing the sugars profiles in fermented products can provide
interesting information about the fermentation process and bacterial activity
during the product shelf life. Figure 3 shows typical chromatograms of
sugar peaks obtained from non-fermented (HM) and fermented hazelnut
milk (FHM) samples after 1, 14 and 28 storage days at 4 ºC. Table 4
summarises the concentrations of the different sugar concentrations present
in fermented hazelnut milks throughout storage time (0, 1, 7, 14, 21 and 21
days).