Enzymes Flashcards
What is the reaction product of b-amylase with starch?
Maltose with the OH on the reducing end in b form (can you draw it)?
Why are maltogenic α-amylases better against staling?
Staling occurs because of re-association of the short chains in amylopectin over storage (after gelatinization), which causes recrystallization. These enzymes preferentially hydrolyze the short chains in amylopectin, which delays recrystallization.
Why may camel rennet be considered better than calf rennet for cheese making?
Cheese making requires a destabilization of k-casein to effect curd formation, which is achieved by the selective cleavage of the bond between Phe105-Met106. Camel rennet has higher specific activity towards this bond, but exhibits less unspecific peptide bond hydrolysis, which would cause bitterness
What is chill haze in beer and what enzymes could be used to prevent chill-haze in beer and why?
Chill-haze in beer is due to interactions between proteins and polyphenols.
Proteases may be employed to cleave proteins (with care to not overdose them, as this would decrease formation of beer foam) or polyphenol oxidases could be used to remove the polyphenols.
Which enzyme can be used to analyze for proper blanching conditions and why?
Peroxidase can be used for this purpose as it is typically more heat stable than other enzymes in the system. If peroxidase activity has stopped, then it can be assumed that the other enzymes are also not active any more.
Name 3 cases where cell-wall degrading enzymes are used industrially?
Pectinases to clarify fruit juice
Xylanases to ensure proper hydration of gluten and good bread volume
b-Glucanases in beer brewing to prevent permanent haze
Compare the reactions occurring in rennet-coagulated vs acid-coagulated dairy products
Acid Coagulation
As the pH is lowered, the negative charges on the hairy layers of kappa casein become neutralized, and shrink until the point where electrostatic and steric repulsion is sufficiently suppressed to allow for protein aggregation.
Rennet Coagulation
Chymosin, a peptidase, cleaves kappa-casein between Met105-Phe106. This causes the hydrophilic C terminus to be released, while the remaining para-kappa casein is very hydrophobic and unable to prevent calcium-mediated precipitation of the other caseins.
What does Kappa-Casein do in milk in respect to the other proteins present.
In milk, the majority of proteins are caseins, and they are mostly found in casein micelles, colloidal particles that contain caseins, calcium phosphate, as well as traces of magnesium and citric acid. All caseins except for kappa-casein would precipitate at the high calcium phosphate concentration, but the hairy layer of kappa-casein prevents this
