806 Sweeteners from Starch: Product

806 Sweeteners from Starch: Production, Properties and Uses
removing components that could otherwise participate in a Maillard reaction with the
reducing sugars, it also substantially reduces the ash level and improves the fl avor.
Ion exchange resins are synthetic organic polymers containing functional groups
that exchange mobile ions in a reversible reaction based on affi nities. A cation
exchange resin in the hydrogen ion form will exchange hydrogen ions for equally
charged cations and become converted into a salt. Cation exchange resins in corn
syrup manufacturing are typically strong acid exchangers with a sulfonic acid functional
group. The anion exchange resins employed contain tertiary amino groups and
act as weak bases. 25
Typical ion exchange processes consist of ‘ trains ’of three cation and three anion
beds arranged in pairs. The fi rst pair takes the heaviest load, while the second pair
acts as the polishing unit and the third pair undergoes regeneration. As the resins
become exhausted, ions start to leak through the primary units. At a predetermined
level of exhaustion, the primary units are taken offl ine and the secondary units are
moved to the primary position. The units that were in regeneration are put online as
the secondary units and the exhausted primary units are regenerated ( Figure 21.6 ). 26
Following the carbon columns or the demineralizers, the pH of the fi ltrate is
adjusted and the liquor is evaporated. The solids level of the fi ltrate prior to the
evaporators is about 30% dry solids (DS). Typical evaporators are multiple-effect,
falling-fi lm evaporators in which the temperature is increased under precisely controlled
conditions that prevent formation of unwanted fl avors or color in the syrup.
As shown in Figure 21.7 , the fl ow is generally countercurrent, i.e. the hottest portion
of the evaporation contains the syrup of lowest solids. 11 After evaporation, the syrup
is pumped to large storage tanks where it is held under agitation and analyzed prior
to shipment.
Acid – Enzyme Processes
As in the case of acid-catalyzed hydrolysis, the starch molecule is hydrolyzed to the
desired starting DE in a converter, but further conversion is carried out with enzymes
until the fi nal DE or carbohydrate profi le is reached. This is done by adding the
appropriate enzymes to the acid-converted slurry and allowing them to react in a
holding vessel called an ‘ enzyme tank. ’ Several enzymes may be used to achieve the
desired carbohydrate profi le.
The alpha-amylases (EC3.2.1.1) used are bacterial or fungal enzymes that hydrolyze
alpha-1,4 linkages in both amylose and amylopectin, eventually producing dextrose
and maltose. The reaction is initially rapid, then relatively slow 27 (see Chapter 7).
The beta-amylases (EC3.2.1.2) used are enzymes of barley and yeast that act on
the non-reducing ends of starch molecules and produce maltose in the beta form
from the starch polymers. These enzymes are used to produce high-maltose syrups.
Although beta-amylase converts linear chains completely to maltose, the enzyme cannot
cleave branch points and the yield of maltose from amylopectin 11 (see Chapter 7)
is only 55% of the molecule.
Glucoamylases (EC3.2.1.3) are fungal enzymes which hydrolyze maltose to produce
glucose (dextrose). These enzymes catalyze hydrolysis of alpha-1,3, alpha-1,6 and betal,6
linkages. Their primary reaction is on the 1,4-linked α -D-glucopyranosyl units of
II. Production Methods 807
non-reducing ends, releasing β-D-glucopyranose (see Chapter 7). When branch points
are reached, the enzyme will cleave the 1,6 bonds, but at a much slower rate. 28
Pullulanase (EC3.2.1.41) and isoamylase (EC3.2.1.68) are so-called debranching
enzymes because they catalyze the hydrolysis of the 1,6 linkages without effect on
the 1,4 linkages 29 (see Chapter 7). These enzymes are particularly useful in the production
of extremely high maltose syrups with maltose levels of 50 to 90%. 30 Table
21.3provides an overview of commercial enzymes used in the corn refi ning process
today and typical operating requirements.
Proper pH and temperature control is critical during batch enzyme conversion processes,
which usually last about 48 hours. In such processes, a number of enzyme tanks
are fi lled sequentially from the converter at the adjusted temperature for treatment
(140 – 150 ° F) and then dosed with the necessary enzymes. Progress of the reaction
Cation Cation Anion Anion Cation Anion
Separate bed syrup demineralization
A
Primary
Syrup
supply
A and B: Service
C: Stand-by
A: Sweeten-off 1
B: Sweeten-on 1
A: Sweeten-off 1
B: Sweeten-on 2
A: Sweeten-off 2
B and C: Service
Secondary Stand-by
Product
B C
Syrup
supply
Sweeten-off
Water
Sweeten-on
Water
recovery
Product
Syrup
supply
Sweeten-off
Water
Sweeten-on
Product Sweet water
Syrup
supply
Syrup
supply
Sweeten-off
Sweet water
Primary
Water
Secondary
P