Answer:
Mr. M kindly answered this question:

  Glucose is mainly made from starch such as cornstarch. The basic process is “liquefaction, conversion to the monomer sugar which is glucose, purification, concentration, crystallization (if necessary), and drying”. The procedure is as follows:

  Starch is broken up by the enzyme called a-amylase under high temperature (~ 100 C°), so that it becomes a sticky paste.

  When glucoamylase is added to the pasty starch, 95% of it becomes glucose.

  Then it is cooled down and crystallized, forming a syrup and powder. The syrup is removed and the powder part is taken out and dried. This is the way to make highly purified glucose in industry.


  Why does the enzyme work at such a high temperature as 100 C°? I learned in school that enzymes are deactivated at high temperatures.

  Regarding the heat resistance of enzymes, it is difficult to answer because there are so many factors that affect the stability of enzymes, for example, temperature, pH, and the existence of substrate. The enzyme for starch liquefaction is employed under this specific condition, 30% starch, pH 6.0 ~ 6.5, and a small amount of Ca²⁺ ion. In this case, it is expected that around 50% of the enzyme is deactivated in 15 min at 105 C°. There are many kinds of industrial enzymes with slightly different properties. We can tell whether a technician is skillful or not by how he/she treats these enzymes.

  As for the reason why a temperature greater than 100 C° is applied, different types of starch have different temperatures at which the starch becomes starch glue. For example, potato starch becomes glue at around 70 C°, however, cornstarch requires 105 C° to 107 C° to become glue completely because cornstarch possesses some parts where it is difficult for this process to occur. This does not mean that enzymes do not work at high temperature. Many years of experience have shown that these methods are most effective.

  Industrial production of enzymes is different from the method that we learned in school. Sometimes people come to visit my company and ask us how to make starch syrup. I give them a manual, however, the manual is different from the one applied in industry.


Acknowledgement
We thank to Mr. M, Kato Brothers Honey Co.,Ltd, and Terry for their kind suggestions.
 

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