86 Part I: Principles
elimination at C-4 from this compound and decar-
boxylation to give rise to 3-deoxypentosone, which
is further degraded to furfural. Under aerobic condi-
tions, xylosone is produced by simple decarboxyla-
tion of diketogulonic acid and is later converted to
reductones. In the presence of amino acids, ascorbic
acid, DHAA, and their oxidation products furfural,
reductones, and 3-deoxypentosone may contribute
to the browning of foods by means of a Maillard-
type reaction (Fennema 1976, Belitz and Grosch
1997). Formation of Maillard-type products has
been detected in both model systems and foods con-
taining ascorbic acid (Kacem et al. 1987; Ziderman
et al. 1989; Loschner et al. 1990, 1991; Mölnar-Perl
and Friedman 1990; Yin and Brunk 1991; Davies
and Wedzicha 1992, 1994; Pischetsrieder et al.Figure 4.10.Pathways of ascorbic acid degradation (solid line, anaerobic route; dashed line, aerobic route).