Tartaric acid and its salts are important products with commercial and industrial applications in the wine and other industries.

Introduction

Tartaric acid contributes to a suitable pH and plays a crucial role in taste, as well as in the physical, biochemical and microbial stability of wine. In addition to tartaric acid existing freely, it is also found as salts (known as tartrates). Tartaric acid and its salts exist in different forms or isomers [D(‒), L(+) and DL] of natural and synthetic origin, with different properties. Centuries of extensive use established the safe properties of tartaric acid, confirmed universally in the related food laws. The demand for tartaric acid is increasing due to the growing production of organic acid-containing foods and materials, and new applications thereof in pharmaceutical industries.

Origin and effects

Producers of tartaric acid make use of different processes based on various feedstocks. These include1 (1) from grape waste and wine stone (bitartrate) (natural), and (2) from maleic acid/maleic anhydride/fumaric acid derived from petrochemicals, such as benzene and butane (chemical-synthetic). The isomer produced by chemical synthetic processes from maleic acid is DL-tartaric acid, with equal amounts of L-tartaric acid, and D-tartaric acid as by-product, separated from the mixture. The DL-form gives a much less soluble racemic product which is not suitable for inclusion in foods, because D(‒)-tartaric acid in the product is considered to be harmful to human health.1,2 Both isomers have broad industrial and scientific applications. L(+)-tartaric acid is widely used in the food, wine, pharmaceutical, agrochemical and polyester industries, while D(-)-tartaric acid is also important in pharmaceutical manufacturing.

In wine, common types of crystalline instabilities, including potassium bitartrate, calcium L-tartrate and calcium DL-tartrate, can be caused by wineries using the racemic (synthetic) forms of tartaric acid and cream of tartar (potassium hydrogen DL-tartrate) during the cold stabilisation process.

No toxic effects, including nephrotoxicity (toxicity in the kidneys), were observed in toxicological studies in which the L(+)-form was tested.3 In contrast, nephrotoxicity was reported in studies in which the DL‐form has been tested and, therefore, renal effects reported with tartrates were most likely due to the presence of the D(‒)-form of tartaric acid. According to the authors, this was due to the DL‐form being less soluble than the L(+)‐form. Tartaric acid/tartrate is fermented by colonic bacteria to short chain fatty acids, which then can be absorbed in the colon of humans, however, L(+)‐tartrate are metabolised faster than D(‒)‐tartrate, with the L(+)-form excreted more efficiently than the D(‒)-form.3

Authenticity

Since the beginning of the 21st century, natural tartaric acid [non-synthetic or L(+)-tartaric acid from a plant source] has been in direct competition with its synthetic equivalent, which mainly comes from the People’s Republic of China, where L(+)-tartaric acid and DL-tartaric acid are produced from benzene or butane. Benzene is a carcinogenic chemical. Also, the synthetic process employs a soluble metal catalyst (tungsten), increasing the likelihood of heavy metal contamination. As a result, therefore, maximum limits for heavy metals resulting from the use of any catalyst that could be present in L(+)‐tartaric acid due to its manufacturing process must be included in the EU specifications for this food additive.3 Synthetic tartaric acid is increasingly being used in various applications. Synthetic tartaric acid had about 50% market share in 2016, with global market demand projected to reach US$ 804.7 million by the end of 2027, with an estimated 4.8% CAGR (compound annual growth rate) for 2019 - 2027. Increasing consumer demand for and consumption of plant-derived or bio-based and eco-friendly alternatives in Europe and North America, however, will hamper the growth of the synthetic tartaric acid market during the forecast period. Therefore, being able to back up “natural” claims is crucial.

Verifying the botanical origin (using stable isotope analyses) of tartaric acid and that it is not of petrochemical synthetic origin (using carbon-14 analysis) is of significance. The Scientific Committee for Food (SCF) in 1990 and the Joint FAO/WHO through the Joint Expert Committee on Food Additives (JECFA 1977-1983-1990) established an acceptable daily intake (ADI) of 30 mg/kg body weight (bw) per day for L(+)‐tartaric acid (E 334) and its potassium (E 336) and sodium (E 335) salts, while the D and DL-forms of synthetic and unnatural origin are forbidden.4,5 In the EU, only the L(+)-form of tartrate is authorised and can be registered as a food additive.3 Current EU legislation does not differentiate at all between the natural and the synthetic forms or sources of tartaric acid, with the sole exception of wine legislation, stating that any L(+)-tartaric acid used must be extracted from wine products and be of agricultural origin. Canadian legislation stipulates that synthetic tartaric acid can be used as a food additive in beverages if not used as a processing aid and if the non-synthetic (natural) form is not commercially available.6 In the U.S., only tartaric acid made from grape wine can be used as an ingredient in or on processed products labelled as “organic” or “made with organic”.

Abstract

Tartaric acid exist in different forms or isomers of natural and synthetic origin, with different properties, health benefits and effects, and pharmaceutical uses. Tartaric acid isomers have broad industrial and scientific applications in the food, wine, pharmaceutical, manufacturing, agrochemical and polyester industries. Factors such as price and availability of raw materials drive the demand and supply dynamics of tartaric acid. Global demand of the synthetic product is growing due to increased availability and lower cost. Suppliers and purchasers of tartaric acid in the local wine industry must make sure that they can confirm natural claims.

References

  1. Hronská, H., Micháliková, S. & Rosenberg, M., 2017. Microbial production of specialty C4 dicarboxylic acids from maleic anhydride. Journal of Food and Nutrition Research 56(3), 219 - 231.
  2. Xuan, J. & Feng, Y., 2019. Enantiomeric tartaric acid production using cis-epoxysuccinate hydrolase: History and perspectives. Molecules 24(5), 903.
  3. Younes, M., Aquilina, G., Castle, L., Engel, K-H., Fowler, P., Fernandez, M.J.F., Fürst, P., Gürtler, R., Gundert-Remy, U., Husøy, T., Mennes, W., Shah, R., Waalkens-Berendsen, I., Wölfle, D., Boon, P., Tobback, P., Wright, M., Aguilera, J., Rincon, A.M., Tard, A. & Moldeus, P., 2020. Re-evaluation of L(+)-tartaric acid (E 334), sodium tartrates (E 335), potassium tartrates (E 336), potassium sodium tartrate (E 337) and calcium tartrate (E 354) as food additives. EFSA Journal 18(3), 6030.
  4. Technical data sheet, Distillerie Mazzari S.p.A., Italy. Natural L(+)-tartaric acid – E334, revision nr. 10 of 04/10/2012.
  5. Material technical data sheet, Caviro Distillerie, Italy. L(+)-Tartaric acid E 334, STD/01000200ENG, rev. 6, admission date 11 May 2017, pp. 1 - 5.
  6. Technical evaluation report, compiled by ICF International for the USDA National Organic Program. Tartaric acid – handling, 13 October 2011, pp. 1 of 12.

– For further information, contact Dr Francois van Jaarsveld at [email protected].