Food Biochemistry and Food Processing (2 edition)

(Wang) #1

BLBS102-c04 BLBS102-Simpson March 21, 2012 11:59 Trim: 276mm X 219mm Printer Name: Yet to Come


4 Browning Reactions 71

degradation. Contribution from sugar-amine reactions is negligi-
ble, as evident from the constant total sugar content of degraded
samples. The presence of amino acids and possibly other amino
compounds enhance browning (Roig et al. 1999).
Both oxidative and nonoxidative degradation pathways are
operative during storage of citrus juices. Since large quantities
of DHAA are present in citrus juices, it can be speculated that the
oxidative pathway must be dominant (Lee and Nagy 1996, Ro-
jas and Gerschenson 1997a). A significant relationship between
DHAA and browning of citrus juice has been found (Kurata
et al. 1973, Sawamura et al. 1991, Sawamura et al. 1994). The
rate of non-oxidative loss of ascorbic acid is often one-tenth or
up to one-thousandth the rate of loss under aerobic conditions
(Lee and Nagy 1996). In aseptically packed orange juice, the
aerobic reaction dominates first and it is fairly rapid, while the
anaerobic reaction dominates later and it is quite slow (Nagy and
Smoot 1977, Tannenbaum 1976). A good prediction of ascor-
bic acid degradation and the evolution of the browning index of
orange juice stored under anaerobic conditions at 20–45◦Cmay
be performed by employing the Weibull model (Manso et al.
2001).
Furfural, which is formed during anaerobic degradation of
ascorbic acid, has a significant relationship to browning (Lee
and Nagy 1988); its formation has been suggested as an ade-
quate index for predicting storage temperature abuse in orange
juice concentrates and as a quality deterioration indicator in
single-strength juice (Lee and Nagy 1996). However, furfural is
a very reactive aldehyde that forms and decomposes simultane-
ously; therefore, it would be more difficult to use as an index for
predicting quality changes in citrus products (Fennema 1976).
In general, ascorbic acid would be a better early indicator of
quality.

Control of Ascorbic Acid Browning

Sulfites (Wedzicha and Mcweeny 1974, Wedzicha and Imeson
1977), thiols compounds (Naim et al. 1997), maltilol (Koseki
et al. 2001), sugars, and sorbitol (Rojas and Gerschenson 1997b)
may be effective in suppressing ascorbic acid browning. Doses
to apply these compounds highly depend on factors such as con-
centration of inhibitors and temperatures.l-Cysteine and sodium
sulfite may suppress or accelerate ascorbic acid browning as a
function of their concentration (Sawamura et al. 2000). Glucose,
sucrose, and sorbitol protectl-ascorbic acid from destruction
at low temperatures (23◦C, 33◦C, and 45◦C), while at higher
temperatures (70◦C, 80◦C, and 90◦C), compounds with active
carbonyls promoted ascorbic acid destruction. Sodium bisulfite
was only significant in producing inhibition at lower temper-
ature ranges (23◦C, 33◦C, and 45◦C; Rojas and Gerschenson
1997b).
Although the stability of ascorbic acid generally increases as
the temperature of the food is lowered, certain investigations
have indicated that there may be an accelerated loss on freezing
or frozen storage. However, in general, the largest losses for
noncitrus foods will occur during heating (Fennema 1976).

The rapid removal of oxygen from the packages is an im-
portant factor in sustaining a higher concentration of ascorbic
acid and lower browning of citrus juices over long-term storage.
The extent of browning may be reduced by packing in oxygen
scavenging film (Zerdin et al. 2003).
Modified-atmosphere packages (Howard and Hernandez-
Brenes 1998), microwave heating (Villamiel et al. 1998, Howard
et al. 1999), ultrasound-assisted thermal processing (Zenker et al.
2003), pulsed electric field processing (Min et al. 2003), and
carbon dioxide-assisted high-pressure processing (Boff et al.
2003) are some examples of technological processes that allow
ascorbic acid retention and consequently prevent undesirable
browning.

Lipid Browning

Protein-Oxidized Fatty Acid Reactions

The organoleptic and nutritional characteristics of several foods
are affected by lipids, which can participate in chemical modifi-
cations during processing and storage. Lipid oxidation occurs in
oils and lard, and also in foods with low amounts of lipids, such
as products of vegetable origin. This reaction occurs in both un-
processed and processed foods, and although in some cases it is
desirable, such as in the production of typical cheeses or fried-
food aromas (Nawar 1985), in general, it can lead to undesirable
odors and flavors (Nawar 1996). Quality properties such as ap-
pearance, texture, consistency, taste, flavor, and aroma can be
adversely affected (Erikson 1987). Moreover, toxic compound
formation and loss of nutritional quality can also be observed
(Frankel 1980, Gardner 1989, Kubow 1990, 1992).
Although the lipids can be oxidized by both enzymatic and
nonenzymatic reactions, the latter is the main involved reaction.
This reaction arises from free radical or reactive oxygen species
(ROS) generated during food processing and storage (Stadtman
and Levine 2003), hydroperoxides being the initial products. As
these compounds are quite unstable, a network of dendritic reac-
tions, with different reaction pathways and a diversity of prod-
ucts, can take place (Gardner 1989). The enzymatic oxidation of
lipids occurs sequentially. Lipolytic enzymes can act on lipids
to produce polyunsaturated fatty acids that are then oxidized by
either lipoxygenase or cyclooxygenase to form hydroperoxides
or endoperoxides, respectively. Later, these compounds suffer a
series of reactions to produce, among other compounds, long-
chain fatty acids responsible for important characteristics and
functions (Gardner 1995).
Via polymerization, brown-colored oxypolymers can be pro-
duced subsequently from the lipid oxidation derivatives (Khayat
and Schwall 1983). However, interaction with nucleophiles such
as the free amino group of amino acids, peptides, or proteins can
also take place, because of the electrophilic character of free
radicals produced during lipid oxidation, including hydroper-
oxides, peroxyl and alkoxyl radicals, carbonyl compounds and
epoxides. As a result of this, end products different from those
formed during oxidation of pure lipids can be also produced
(Gillat and Rossell 1992, Schaich 2008). Both lipid oxidation
Free download pdf