For the specific assay of L-malic acid (L-malate) in beverages and food products.
INTRODUCTION:
As a component of the citric acid cycle, L-malic acid (L-malate)
is found in all living organisms. Its quantitative determination is
especially important in the manufacture of wine, beer, bread, fruit
and vegetable products, as well as in cosmetics and pharmaceuticals.
It is one of the most important fruit acids, and has the highest
concentration of all acids in wine. In the wine industry, the level of
L-malic acid is monitored, along with L-lactic acid, during malolactic
fermentation. L-Malic acid finds many applications as a food
preservative (E296) and flavour enhancing compound, such as in the
manufacture of low calorie drinks.
This booklet describes a manual spectrophotometric and a microplate
method for the quantitative determination of L-malic acid. However,
an alternative method tailored towards the small winery is also
available from Megazyme that is based on the use of an inexpensive
colorimeter, the MegaQuantTM meter (see product D-LMALMQ).
A third kit for L-malic acid has been optimised for auto-analyser
applications (see product K-LMALAF).
KITS:
Kits suitable for performing 58 / 116 assays in manual format (or 580 /
1160 assays in microplate format) are available from Megazyme. The kits
contain the full assay method plus:
58 Determinations Kit (cat. no. K-LMALR)
Bottle 1: Buffer (6 mL, pH 10.0) plus L-glutamate and sodium
azide (0.02% w/v) as a preservative.
Stable for > 2 years at 4°C.
Bottle 2: NAD+ plus PVP.
Stable for > 5 years at -20°C.
Bottle 3: Glutamate-oxaloacetate transaminase suspension
(1.25 mL).
Stable for > 2 years at 4°C.
Bottle 4: L-Malate dehydrogenase suspension
(1.25 mL).
Stable for > 2 years at 4°C.
Bottle 5: L-Malic acid standard solution (5 mL, 0.15 mg/mL).
Stable for > 2 years at 4°C.
116 Determinations Kit (cat. no. K-LMALL)
Bottle 1: Buffer (12 mL, pH 10.0) plus L-glutamate and sodium
azide (0.02% w/v) as a preservative.
Stable for > 2 years at 4°C.
Bottle 2: (x2) NAD+ plus PVP.
Stable for > 5 years at -20°C.
Bottle 3: Glutamate-oxaloacetate transaminase suspension
(2.5 mL).
Stable for > 2 years at 4°C.
Bottle 4: L-Malate dehydrogenase suspension (2.5 mL).
Stable for > 2 years at 4°C.
Bottle 5: L-Malic acid standard solution (5 mL, 0.15 mg/mL).
Stable for > 2 years at 4°C.