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

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)