High and low molecular weight dextran polysaccharide formation in the three juice treatments is
shown in Fig. 3. In the untreated juice, dextran formation was slow in the first 7 h, then accelerated between 7
and 14 h. A slowdown then occurred up to 31 h, and
then a second acceleration phase (this may just be
characteristic of the microbial load). In contrast, in the
pre-heated juice, no dextran was formed in the first 14 h,
because the heat would have destroyed or vastly
reduced the numbers of most of the Leuconostoc bacteria initially present in the juice. The large formation of
dextran between 14 and 23 h could be because of reinnoculation in the incubator from the non-sterile
experimental conditions. A further explanation is that
the heat treatment just reduced the number of viable
Leuconostoc bacteria to a level where lag phase growth
occurred, and it took 14 h for the bacteria to recuperate
and produce dextran, especially in exponential phase
growth. After 23 h no significant dextran was formed
which was likely because the very low pH stopped Leuconostoc growth and/or the activity of dextransucrase.
As expected, in the biocide control juice, there was no
formation of dextran over 71 h. Ravelo et al. (1995)
applied the disinfectant IFOPOLTM to stored billeted
cane and observed that the formation of polysaccharides, as well as total oligosaccharides, was
greatly reduced.
Changes in sucrose, glucose, and fructose concentrations, on a
Brix basis, are illustrated in Fig. 4. Degra-
dation of sucrose in the factory can occur via a variety
of mechanisms. It can be hydrolysed into glucose and
fructose by either acid (acid inversion of sucrose) or by
naturally-occurring cane invertase enzymes (sucrose
inversion). Another mechanism of sucrose loss is by its
utilization by microbes. High infections and stagnant
zones occur often in the cane factory, particularly in the
milling station, and these act as ‘open fermentors’. Leuconostoc bacteria are able to utilize the glucose in the
sucrose molecule to form dextran (a glucose poly-
saccharide). Yeast, particularly Saccharomyces, often
found at factories (Chen & Chou, 1993), can convert
sucrose into ethanol and carbon dioxide, especially
under anaerobic conditions, often found in cane storage
piles and at the factory. Yeasts, and other microbes, are
also known to secrete periplasmic invertase enzymes
(Hanko & Rohrer, 2000).In the untreated juice, sucrose degraded rapidly
(Fig. 4a), particularly over the first 14 h (29.0% sucrose
loss), which is further shown by the concomitant, sharp
increase in glucose and fructose concentrations (Fig. 4b
and c). Although, after 39 h, sucrose loss decelerated, by
71 h very little sucrose, glucose, and fructose remained,
because the solids had been transformed by microbes
(see
Brix results). In comparison, the sucrose in the
biocide-treated juice was only slightly degraded in the
juice (1.7% after 14 h). This slight degree may be
because the biocide is unable to stop the enzymic and acid inversion of sucrose. In the juice preheated before
deterioration, only 0.4% sucrose was measurably lost
during the first 14 h. This strongly suggests that the
heating treatment denatured the invertase enzymes, as
well as markedly reducing the levels of microbes
(including thermophilic bacteria), and that at ambient
temperatures, acid sucrose inversion contributes very
little to sucrose loss in the factory. Glucose and fructose
similarly increased slightly on sucrose inversion and
G/F ratios stayed constant (Table 1).
Using the combination of untreated, biocide-treated,
and heat-treated juices after 14 h deterioration, it was
possible to calculate the contributions of the different
sucrose loss mechanisms. The untreated juice was taken
as equivalent to total deterioration, biocide-treated juice
as equivalent to enzymic and chemical deterioration,
and the pre-heated juice as chemical (acid) deterioration
only. It was calculated that 93.0% of deterioration was
microbial, 5.7% enzymic, and 1.3% was chemical. As
microbiological deterioration is such a major source of
loss, the need to use biocide agents, or other aseptic
conditions at the factory is highlighted.
Dextran formation on deterioration of the untreated
juice was also indicated by the change in G/F ratios
(Table 1). Low G/F ratios indicate a relative increase in
fructose to glucose, which occurs when dextran is
formed because Leuconostoc bacteria utilize glucose to
form dextran, leaving fructose from the sucrose molecule as a by-product.
High and low molecular weight dextran polysaccharide formation in the three juice treatments isshown in Fig. 3. In the untreated juice, dextran formation was slow in the first 7 h, then accelerated between 7and 14 h. A slowdown then occurred up to 31 h, andthen a second acceleration phase (this may just becharacteristic of the microbial load). In contrast, in thepre-heated juice, no dextran was formed in the first 14 h,because the heat would have destroyed or vastlyreduced the numbers of most of the Leuconostoc bacteria initially present in the juice. The large formation ofdextran between 14 and 23 h could be because of reinnoculation in the incubator from the non-sterileexperimental conditions. A further explanation is thatthe heat treatment just reduced the number of viableLeuconostoc bacteria to a level where lag phase growthoccurred, and it took 14 h for the bacteria to recuperateand produce dextran, especially in exponential phasegrowth. After 23 h no significant dextran was formedwhich was likely because the very low pH stopped Leuconostoc growth and/or the activity of dextransucrase.As expected, in the biocide control juice, there was noformation of dextran over 71 h. Ravelo et al. (1995)applied the disinfectant IFOPOLTM to stored billetedcane and observed that the formation of polysaccharides, as well as total oligosaccharides, wasgreatly reduced.Changes in sucrose, glucose, and fructose concentrations, on a Brix basis, are illustrated in Fig. 4. Degra-
dation of sucrose in the factory can occur via a variety
of mechanisms. It can be hydrolysed into glucose and
fructose by either acid (acid inversion of sucrose) or by
naturally-occurring cane invertase enzymes (sucrose
inversion). Another mechanism of sucrose loss is by its
utilization by microbes. High infections and stagnant
zones occur often in the cane factory, particularly in the
milling station, and these act as ‘open fermentors’. Leuconostoc bacteria are able to utilize the glucose in the
sucrose molecule to form dextran (a glucose poly-
saccharide). Yeast, particularly Saccharomyces, often
found at factories (Chen & Chou, 1993), can convert
sucrose into ethanol and carbon dioxide, especially
under anaerobic conditions, often found in cane storage
piles and at the factory. Yeasts, and other microbes, are
also known to secrete periplasmic invertase enzymes
(Hanko & Rohrer, 2000).In the untreated juice, sucrose degraded rapidly
(Fig. 4a), particularly over the first 14 h (29.0% sucrose
loss), which is further shown by the concomitant, sharp
increase in glucose and fructose concentrations (Fig. 4b
and c). Although, after 39 h, sucrose loss decelerated, by
71 h very little sucrose, glucose, and fructose remained,
because the solids had been transformed by microbes
(see
Brix results). In comparison, the sucrose in the
biocide-treated juice was only slightly degraded in the
juice (1.7% after 14 h). This slight degree may be
because the biocide is unable to stop the enzymic and acid inversion of sucrose. In the juice preheated before
deterioration, only 0.4% sucrose was measurably lost
during the first 14 h. This strongly suggests that the
heating treatment denatured the invertase enzymes, as
well as markedly reducing the levels of microbes
(including thermophilic bacteria), and that at ambient
temperatures, acid sucrose inversion contributes very
little to sucrose loss in the factory. Glucose and fructose
similarly increased slightly on sucrose inversion and
G/F ratios stayed constant (Table 1).
Using the combination of untreated, biocide-treated,
and heat-treated juices after 14 h deterioration, it was
possible to calculate the contributions of the different
sucrose loss mechanisms. The untreated juice was taken
as equivalent to total deterioration, biocide-treated juice
as equivalent to enzymic and chemical deterioration,
and the pre-heated juice as chemical (acid) deterioration
only. It was calculated that 93.0% of deterioration was
microbial, 5.7% enzymic, and 1.3% was chemical. As
microbiological deterioration is such a major source of
loss, the need to use biocide agents, or other aseptic
conditions at the factory is highlighted.
Dextran formation on deterioration of the untreated
juice was also indicated by the change in G/F ratios
(Table 1). Low G/F ratios indicate a relative increase in
fructose to glucose, which occurs when dextran is
formed because Leuconostoc bacteria utilize glucose to
form dextran, leaving fructose from the sucrose molecule as a by-product.
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