Sea
buckthorn (Hippophaë rhamnoides L.) berries contain versatile
combination of chemical compounds having health promoting features such
water-soluble vitamins (C, B1, and B2), fat-soluble vitamins (A, K, and E),
fatty acids, flavonoids, and plant sterols. However, the sour, bitter and
astringent taste characteristics limit its regular consumption. The main
chemical factors related to the sourness of sea buckthorn are the high
concentrations of malic and quinic acids. Additionally, strong sourness
intensifies the perception of astringency. Currently, malolactic fermentation
is used commonly to decrease acidity in wines, as in this microbial process
dicarboxylic malic acid is converted into carbon dioxide and monocarboxylic
lactic acid. Therefore, in this study, we investigated potential to use Lactobacillus
plantarum as a novel malolactic fermentation organism in sea buckthorn
juice for decreasing concentrations of malic and quinic acids, ultimately
leading to a juice with less sour and astringent traits.

Juices was
extracted from Estonian sea buckthorn (subspecies mongolica) berries
with hydraulic pressing, and the juice diluted to 1:1 with distilled water.
Diluted juices were pasteurized in 85 °C for 5 min. Fermentations were
performed with four different strains of Lactobacillus plantarum. An
over-night growth of un-adapted cells was collected, washed, and inoculated
(~10⁸ CFU/ml) to the juice samples with no additional nutrients. Samples
were fermented in 30 °C for 72 hours.

Conversion
of malic acid (initial level of 11 g/L) into lactic acid was most effective
with strain DSM 10492 (100 %), followed by DSM 100813 (31.4 %) and DSM 20174
(28.7 %). Additionally, a small but significant decrease in quinic acid content
was measured from samples fermented with DSM 10492. No significant changes were
detected in the concentrations of glucose, ethyl-glucose, fructose,
L-quebrachitol, and methyl-myo-inositol after pasteurization or
fermentation. This work shows that malolactic fermentation with L. plantarum
could be used to decrease acidity of sea buckthorn juice without affecting its
sugar content.