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Folate content in commercial wine is associated with the yeast that is used to produce the wine

21 October 2015

Bioengineering is an important strategy used in the fortification of foods. In their recent study Liu et al from the University of British Columbia bioengineered a yeast, commonly used in wine production, to synthesise more folate and add to health benefits of wine consumption. Their aim was also to improve the stability of folate during storage and after opening the wine, which has been recognised as a limiting factor in folate biofortification.

Researchers engineered their own strain of yeast to oversynthesise folate during fermentation of Chardonnay and Pinot Noir grape juice. This was done by replacing an endogenous promoter with the highly active PGK1 promoter. In consequence, there was more mRNA for the manipulated gene. Manipulation of the gene FOL2 led to the highest increase in folate level in wines when comparing with other folate biosynthesis genes. 2-fold increase in folate levels in white wine and 5-fold increase in red wine was observed.

To demonstrate the losses of natural folate in wine the researchers stored commercially available wines for 5 days. At the beginning of the study the folate content in beverages varied between 11-88 µg/L in white wines and 16-90 µg/L in red wines. For comparison, previously reported values for beer were between 30-180 µg/L. After 5 days of storage of wines at 4˚C the folate content fell dramatically. The most significant drop of 72 % was in wines that had initially the lowest levels of folate, comparing to 18 % in wines with higher content at start. The authors noted that the presence of potential stabilizers such as phenol and sulphite present in wine did not improve the folate stability. Liu et al demonstrated on the other hand that the addition of sodium ascorbate has potential for protecting folate from thermal oxidation and thus reduction in folate losses.

The total folate content in wine used in this study was determined using microbiological assay with chloramphenicol-resistant Lactobacillus casei as the test microorganism. The total phenolic content expressed as mg gallic acid equivalents was determined by the Folin-Ciocalteu method and sulphite levels using Megazyme kit.

‘The same strategy could be applied to produce folate enhanced bakery products through bioengineering of baker‘s yeast’ Liu et al concluded.

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