| MadSci Network: Biochemistry |
Hi Patrick,
The answer to your question is sort of tricky, because diastase is not an enzyme in the sense that you are using. As a biochemist and a home-brewer, I have always had a soft spot for diastase, as this was the name given to the first enzyme ever discovered. In 1833, French scientist Anselme Payen isolated an activity from a malt solution that converted starches to glucose. He named the factor responsible for the activity 'diastase', from the greek term for separation (separating the individual glucose monomers from the starch polymer). Due to the structure of the name that Payen chose, enzymes have been named with the suffix '-ase' ever since. Payen was also the first person to isolate cellulose (which he also named) and started the practice of using the '-ose' suffix for saccharides (glucose, maltose, etc.).
Today, the term diastase is used to refer to a broad group of enzymes that catalyze the hydrolysis of starches into glucose, and includes alpha, beta and gamma amylases, limit dextrinase and various alpha glucosidases (e.g., maltase). So, that is why I say that diastase is not really an enzyme; depending on the organism from which the activity is isolated, it can be a mixture of any of these enzymes. Because of this, it is usually safer to refer to diastatic power (abbreviated as DP) rather than to diastase activity.
In malt, alpha and beta amylase are responsible for more than 99% of the DP, so considerations of the optimal pH and pH range for diastase will be reflections of the pH requirements for these two enzymes. I located a very nice paper by AM Osman, published in the Journal of the Institute and Guild of Brewing, that determines the optimal pH values for alpha and beta amylase (and other enzymes that contribute to the DP), as well as the pH for optimal DP, in malt. Osman found the optimal pH for alpha amylase to be 4.5, the optimal pH for beta amylase to be 5.5, and the pH for optimal DP to be between the optimal pH values for all of the enzymes that contribute to the DP, at about 5.0 to 5.5. The high value of this last pH range relative to the average of the optimal alpha and beta amylase pH values reflects the key role played by beta amylase in producing maltose -- the primary substrate for fermentation in wort -- from starch in malt.
So, there you have it, the spleandor of diastase. For more detail about this topic, I have included the reference for Osman's paper, and a link to the PDF version of the paper, below. This paper, and the references cited, should be of considerable use to you (e.g., it describes alpha amylase, beta amylase and DP activity assays).
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