Reduction of acidity in northern region berry juices

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Applied biochemistry and microbiology report, 2/2003
Northern region berries may be used for wide variety of product alternatives as well as serving as a supply of many nutritionally valuable components. However, there are only rare, fragmentary and inconsistent scientific data available on the chemical composition of northern region berries. Therefore, comprehensive information was gathered on organic acid and soluble sugar concentrations of juices of six wild berries (bilberry, lingonberry, cranberry, cloudberry, red raspberry, black crowberry) and five cultivated berries (black currant, white currant, red currant, gooseberry (red), strawberry) all grown in Finland. The main acids of the berry juices were invariably citric and malic acid even though their concentrations varied widely from one berry variety to another (2.9 - 16.2 g/l and 3.3 - 24.7 g/l, respectively). In addition, juices of lingonberry, cranberry, cloudberry and black crowberry contained benzoic acid (0.1 - 0.7 g/l). The main sugars of the investigated berry juices were fructose (18.0 - 57.2 g/l) and glucose (22.2 - 50.0 g/l). Most of the berries contained also sucrose (0.2 - 5.1 g/l). The data enable direct comparison of northern region berries and underline the wide variation in their organic acid and soluble sugar content, which offers possibilities for the production of numerous sensory profiles. Accordingly, the selection of the right berry for individual purposes is enhanced. Due to their acid and sugar composition, fermentation of northern region berry juices into wines faces challenges that are not normally met when using grape juices. In berry juices the fermentations should maintain or alleviate the often rich berry aroma under conditions where the content of organic acids is high and that of fermentable sugars low. Prior to fermentation the juices have to be diluted and sugar has to be added. This causes significant weakening of the aroma and body of the wine. To reduce the acidic mouthfeel of grape wines malolactic fermentation (MLF) is widely used. However, it is not known whether MLF is applicable to modifying the acid composition of berry juices. Therefore, acid conversion by MLF by Oenococcus oeni was studied to improve the usability of northern region berry juices. During MLF at low pH values (pH < 4.5), malic acid was always degraded first to completion without consumption of sugars or citric acid. After the exhaustion of malic acid the degradation of both citric acid and glucose were initiated simultaneously. Thus, it is concluded that by MLF, selective conversion of malic acid to lactic acid can be achieved without loss of sugar, also in berry juices. Sequential utilization of substrates by MLF thus enables a multitude of compositional changes in acidic juices. Control of duration of the fermentation is essential when acid reduction without loss of sugar should occur. The most problematic compound with reference to winemaking from lingonberry is benzoic acid, which contributes to the acidity of the berry. As a microbicidal compound, benzoic acid also prevents fermentation of lingonberry juice. Thus, the known pH-dependent ability of Saccharomyces cerevisiae yeast to uptake benzoic acid from solutions was applied. By suspending 15 - 20 % (w/w) of the yeast for 10 min in undiluted lingonberry juice, the benzoic acid concentration was reduced by 75 - 91 %, titratable acids by about 14 % and pH increased by 0.1 units. The resulting undiluted juice was successfully fermented with a new yeast inoculum. Thus, yeast may be used as a selective absorbent to remove a certain fermentation-hindering component from the juice. These results offer new insights into berry juice fermentation. Accordingly, MLF represents a new, promising means for acidity reduction of northern region berry juices and berry wines without a significant loss of their natural sugar content. Also, the benzoic acid uptake by the yeast was proven to be effective. By these new methods, the critical inhibitors of the further processing of the juices can be eliminated and thus it is possible to facilitate the development of various berry products of northern regions.
northern region berries, organic acids, soluble sugars, acid reduction, malolactic fermentation, Oenococcus oeni, yeast uptake, alcoholic fermentation, berry wine, sensory quality
Other note
  • Viljakainen, S., Visti, A. and Laakso, S., 2002. Concentrations of organic acids and soluble sugars in juices from Nordic berries. Acta Agriculturæ Scandinavica B 52, pages 101-109. [article1.pdf] © 2002 Taylor & Francis. By permission.
  • Viljakainen, S. and Laakso, S., 2000. The use of malolactic Oenococcus oeni (ATCC 39401) for deacidification of media containing glucose, malic acid and citric acid. European Food Research and Technology 211, pages 438-442. [article2.pdf] © 2000 Springer-Verlag. By permission.
  • Viljakainen, S. and Laakso, S., 2002. Acidity reduction in northern region berry juices by the malolactic bacterium Oenococcus oeni. European Food Research and Technology 214, pages 412-417. [article3.pdf] © 2002 Springer-Verlag. By permission.
  • Viljakainen, S., Visti, A. and Laakso, S., 2003. Malolactic and alcoholic fermentations in black currant juice. Die Wein-Wissenschaft, in press. [article4.pdf] © 2003 by authors and © 2003 Fachverlag. By permission.
  • Visti, A., Viljakainen, S. and Laakso, S., 2003. Preparation of fermentable lingonberry juice through removal of benzoic acid by Saccharomyces cerevisiae yeast. Food Research International 36, in press. [article5.pdf] © 2003 Elsevier Science. By permission.
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