Question 1

Brewing biotechnology: Trichoderma β-glucanase is reported to play which principal role during mashing in beer production (consider its action on cell wall β-glucans and mash rheology)?

Accepted Answer

Introduction: In brewing, exogenous enzymes are often added to improve mash handling and extract quality. Trichoderma β-glucanase targets β-glucans in malt and adjunct cell walls. This question tests whether you can distinguish β-glucanase functions from amylolytic enzymes that act on starch and dextrins. Given Data / Assumptions: Substrate of interest: β-glucans present in barley endosperm cell walls and husk fractions. Process step: mashing, where viscosity and lautering performance are critical. Comparison enzymes: amylases that act on starch and dextrins. Concept / Approach: β-glucanases hydrolyze β-1,3 and β-1,4 glucans that increase mash viscosity and impede wort run-off. By depolymerizing these gums, they stabilize the mash, reduce haze precursors, and improve filtration. In contrast, liquefaction of starch to dextrin is performed by α-amylase, and conversion of dextrins to fermentable sugars such as glucose is done by glucoamylase or by subsequent isomerization for HFCS streams. Step-by-Step Solution: Identify the substrate: β-glucans, not starch.Map enzyme to function: β-glucanase reduces viscosity and enhances lautering.Differentiate from amylases: α-amylase liquefies starch; glucoamylase saccharifies dextrins.Conclude that the principal reported role is mash stabilization and filtration improvement. Verification / Alternative check: Brewing practice shows reduced filtration time and better filter bed performance when β-glucanase is used, aligning with improved wort clarity and lower β-glucan content in the final beer. Why Other Options Are Wrong: Converts taste fractions of dextrins: dextrin hydrolysis is the role of glucoamylase, not β-glucanase. Converts starch to dextrin: this is the role of α-amylase during liquefaction. All of the above: incorrect because β-glucanase does not perform the amylolytic functions described. Common Pitfalls: Assuming all carbohydrate-active enzymes act on starch or dextrins. Confusing viscosity reduction from β-glucan breakdown with saccharification yield improvements from amylases. Final Answer: Stabilizes mashing by degrading β-glucans and improving wort filtration

Question 2

Industrial enzymes for sweeteners: Which enzyme mainly performs the conversion step that turns glucose syrups into high fructose corn syrup (HFCS) in starch processing?

Accepted Answer

Introduction: High fructose corn syrup production involves a cascade of enzymatic steps: liquefaction, saccharification, and isomerization. This question checks whether you know which specific enzyme is mainly responsible for the glucose to fructose conversion that defines HFCS. Given Data / Assumptions: Feedstock: starch from corn or other cereals. Process: liquefaction to dextrins, saccharification to glucose, then isomerization to fructose. Target: fructose enrichment characteristic of HFCS. Concept / Approach: α-amylase hydrolyzes internal α-1,4 bonds to liquefy starch into shorter dextrins. Glucoamylase hydrolyzes α-1,4 (and some α-1,6) bonds from non-reducing ends to produce glucose. The pivotal step that differentiates HFCS is the isomerization of glucose to fructose, catalyzed by glucose isomerase (also called gluco-isomerase or xylose isomerase variants for immobilized systems). Step-by-Step Solution: Liquefaction: starch --(α-amylase)--> dextrins.Saccharification: dextrins --(glucoamylase)--> glucose syrup.Isomerization: glucose syrup --(glucose isomerase)--> fructose-rich syrup (HFCS).Therefore, the enzyme mainly responsible for the HFCS conversion step is glucose isomerase. Verification / Alternative check: Industrial HFCS specifications (HFCS-42, HFCS-55) are achieved by controlling glucose isomerase reaction conditions and subsequent chromatographic enrichment if needed. Why Other Options Are Wrong: α-amylase: necessary for liquefaction but does not create fructose. Glucoamylase: produces glucose but does not isomerize it to fructose. All of these: incorrect because only glucose isomerase performs the defining step to fructose. Common Pitfalls: Confusing saccharification with isomerization. Assuming any carbohydrate hydrolase can generate fructose directly. Final Answer: Glucose isomerase (gluco-isomerase)

Question 3

Dairy enzyme specificity: Chymosin (rennin) specifically cleaves κ-casein at which peptide bond during cheese making?

Accepted Answer

Introduction: Cheese manufacturing relies on precise proteolysis to destabilize casein micelles. Chymosin, historically called rennin, is highly specific for a single bond in κ-casein that triggers curd formation. This question evaluates recognition of that signature cleavage site. Given Data / Assumptions: Substrate: κ-casein on the micelle surface. Outcome: micelle destabilization and curd formation. Need: exact peptide bond identity. Concept / Approach: Chymosin cleaves the peptide bond between Phe105 and Met106 in κ-casein, generating para-κ-casein and the glycomacropeptide. This removes steric and electrostatic stabilization, allowing casein aggregation in the presence of calcium ions. Step-by-Step Solution: Identify the protein and site: κ-casein Phe105–Met106.Describe the result: release of glycomacropeptide into whey.Explain the functional consequence: curd formation from aggregated casein micelles. Verification / Alternative check: Cheese process analytics show glycomacropeptide in whey as a marker of chymosin action, validating the specific cleavage site. Why Other Options Are Wrong: Alanine–Glycine, Glutamic acid–Alanine, Alanine–Phenylalanine: these are not the known κ-casein cleavage by chymosin and would not reproduce the characteristic micelle destabilization kinetics. Common Pitfalls: Confusing general chymotrypsin aromatic preferences with the unique κ-casein site of chymosin. Assuming multiple bonds are equivalently cleaved during renneting. Final Answer: Phenylalanine–Methionine (Phe105–Met106) in κ-casein

Question 4

Starch processing: During the liquefaction step, starch is converted to dextrins primarily by which enzyme?

Accepted Answer

Introduction: Industrial starch conversion proceeds through liquefaction and saccharification. This question focuses on the liquefaction step that reduces viscosity by depolymerizing starch into shorter dextrins. Given Data / Assumptions: Feed: gelatinized starch slurry. Goal: rapid viscosity reduction and dextrin formation. Operating conditions: elevated temperature suitable for thermostable amylases. Concept / Approach: α-amylase cleaves internal α-1,4 glycosidic bonds in amylose and amylopectin, generating dextrins and lowering viscosity. Cellulase acts on cellulose, and pectinase acts on pectins; neither targets starch polymers. Step-by-Step Solution: Gelatinize starch to expose α-1,4 linkages.Apply α-amylase to hydrolyze internal bonds, forming dextrins.Monitor viscosity drop as an indicator of liquefaction progress. Verification / Alternative check: Process control via dextrose equivalent and viscosity confirms that α-amylase action accomplishes liquefaction before saccharification by glucoamylase. Why Other Options Are Wrong: Cellulase: targets β-1,4 glucans in cellulose, not starch. Pectinase: targets pectic substances, not starch. All of these: cannot be correct because only α-amylase performs starch liquefaction. Common Pitfalls: Equating any carbohydrate hydrolase with starch hydrolysis. Confusing liquefaction with saccharification stages. Final Answer: α-amylase

Question 5

Wine and juice processing: Enzyme preparations used to reduce grape bitterness commonly contain which glycosidases?

Accepted Answer

Introduction: Bitterness and astringency in grape products are influenced by glycosidically bound phenolics and aroma precursors. Targeted glycosidases can modify these compounds to improve sensory attributes. This question asks which enzymes are typically included in such preparations. Given Data / Assumptions: Matrix: grape must or wine. Compounds: glycosides of terpenes and phenolics. Goal: reduce bitterness and enhance desirable aroma release. Concept / Approach: α-L-rhamnosidase and β-D-glucosidase act sequentially or in combination to cleave disaccharide moieties on glycosides, freeing aglycones that can be less bitter and more aroma active. β-galactosidase is used for lactose hydrolysis and some glycan modifications but is not the principal choice for grape bitterness reduction. Step-by-Step Solution: Identify common grape glycosides: rhamnose–glucose linked to volatile aglycones.Apply α-L-rhamnosidase to remove terminal rhamnose.Apply β-D-glucosidase to release the aglycone from glucose.Result: modified phenolic profile with reduced bitterness and enhanced aroma. Verification / Alternative check: Analytical profiling shows increased free terpenes after combined rhamnosidase and glucosidase treatment, correlating with sensory improvements. Why Other Options Are Wrong: α-L-rhamnosidase or β-D-glucosidase alone: each can help, but together they address the common disaccharide linkages. β-galactosidase: not the standard enzyme for this specific oenological objective. Common Pitfalls: Assuming pectinases alone solve bitterness; they mainly improve clarification. Using single-enzyme treatments when the glycoside structures require two steps. Final Answer: Both (a) and (b)

Enzymes and Application Questions