For the measurement of L-malic acid in grapes, grape juice and wine using the MegaQuant? colorimeter (measurement at 505 nm). Suitable for white and red wines at all stages of the winemaking process.
INTRODUCTION:
In the wine industry, the level of L-malic acid is monitored, along with L-lactic acid, during malolactic fermentation. The assay procedure described here is specifically aimed at this industry for the measurement of L-malic acid in the latter stages of malolactic fermentation. However, the procedure is also applicable to measurement of L-malic acid in a diverse range of food and beverage matrices. The assay is simple to perform, rugged, reliable, accurate, and employs an inexpensive colorimeter.
KITS:
Kits suitable for performing 60 determinations are available from Megazyme. The kits contain the full assay method plus:
Bottle 1: Buffer (100 mL, pH 10.0) plus L-glutamate and sodium azide (0.02% w/v) as a preservative.
Stable for > 2 years at 4°C.
NOTE: This buffer contains sodium azide (0.02% w/v) as a
preservative, and thus should not be dispensed using a mouth pipette.
Bottle 2: Test tablets (60) containing diaphorase, GOT, INT, FAD and NAD+. These are supplied in a special plastic vial containing impregnated desiccant. Allow this container to warm to room temperature (preferably in the presence of a desiccant) before opening to remove tablets. This will ensure that remaining tablets will not absorb moisture and thus guarantee maximum stability. Stable for > 2 years when stored dry in a domestic freezer (-20°C).
Bottle 3: L-Malate dehydrogenase suspension (1.3 mL). Stable for > 2 years at 4°C.
Bottle 4: L-Malic acid standard solution (5 mL, 0.375 mg/mL).
Stable for
> 2 years at 4°C.
Bottle 5: Tablets (65) containing PVPP.
Stable for
> 5 years at room temperature.