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A Technical Guide for Wine Producers
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RECENT ARTICLES | WYNBOER HOME
Talking Biotech
For many wine lovers (the author included), the mere possibility that their "'89 Cabernet" might not be so wholesome after all, borders on sacrilege. (There is of course also the issue of quantity which should be included in this discussion, but we will conveniently ignore that for the moment). Fact of the matter is, we simply don't know.
Reassuring though, is that every possible effort is being made to ensure that your "'89 Cabernet" is indeed as healthy as it tastes (or for some vintages maybe even healthier than the taste).
The first contribution comes from Dalene de Beer, a PhD student at the Department of Food Science, Stellenbosch University, who - in conjunction with Dr Marena Manley (Senior lecturer, Department of Food Science, Stellenbosch University) and Drs Lizette Joubert and Johann Marais (Specialist researchers, Division Post Harvest and Wine technology, ARC Infruitec-Nietvoorbij) - conducts research to try and manipulate the antioxidant capacity of Pinotage wines.
Manipulating antioxidant capacity of Pinotage wines
During recent years, natural phenolic phytochemicals have received considerable attention, mainly due to the implied health benefits associated with these molecules. A strong line of evidence suggests that most of these beneficial properties can be attributed to their strong antioxidant activity. Following suit, the South African wine industry is giving high priority to the enhancement of mainly red wine antioxidant capacity by the manipulation of phenolic contents. Given the complex sensorial aspects of most wines, care must be taken not to disturb the delicate balance between nutritional benefit and sensorial quality. Not an easy feat considering that some phenolics are known to contribute to bitterness and astringency in wine!
Continuing on the antioxidant theme, a more fundamental approach is being followed by Dr Philip Young (who contributed the following section) in the laboratory of Prof Melané Vivier at the Institute for Wine Biotechnology, Stellenbosch University. Their research focuses on manipulating a central pathway, the carotenoid biosynthetic pathway in grapevine.
"Golden grapes"?
Medical research is proving what mothers have known for years: that eating carrots (or any carotenoid-rich food) is good for you! Carotenoids obtained from our diet are converted to Vitamin A that is subsequently utilised for a variety of biological functions in our bodies. These functions are so crucial that in under-developed countries a Vitamin A deficiency is thought to be responsible for blindness, and even death, in more than 500 000 children a year.
Similarly in plants, carotenoids have a variety of important functions. Carotenoids are intrinsically involved in the photosynthetic process by serving as accessory light-harvesting pigments, dissipate excess light energy, and are precursors of the so-called stress hormone, abscisic acid. Due to their nutritional value, as well as their role in both photo-protection and abscisic acid formation, the carotenoid biosynthetic pathway has been identified as a promising target for genetic manipulation of crop plants. The carotenoid biosynthetic pathway of a number of plant species has successfully been manipulated, and includes tomato, canola, and the much-publicised "Golden Rice". From an oenological perspective, carotenoids are important for the formation of the flavour and aroma compounds, b-damascenone and vitispirane that contributes to the unique character of certain cultivars such as Semillon, Chardonnay, Shiraz and Cabernet Sauvignon.
In the final section of the column, we explore a very interesting similarity between humans and grapevine (and presumably in many other plants for that matter). This work started off in the laboratory of Prof Chris Gehring at the University of the Western Cape and is currently continued by Dr Ndiko Ludidi in the laboratory of Prof Johan Burger. Dr Ludidi contributed this final section.
Don't shoot the (secondary) messenger, we all need it!
In the human body, important secondary messenger molecules known as cGMP, are synthesized by enzymes called guanylyl cyclases. cGMP regulates various processes in the body, including vasodilation, kidney function, smooth muscle activity and light perception in the retina of the eye. Guanylyl cyclases in turn, act as receptors for natriuretic peptides. In plants, the role of cGMP is only starting to be established, but evidence exists that they are required for a whole range of functions, including developmental processes mediated by hormones, fungal and bacterial disease resistance, as well as tolerance to drought and osmotic stress. Recent evidence shows that anthocyanin biosynthesis in plants also requires cGMP, a discovery that is of great interest to the wine industry, considering that anthocyanins form an integral part of the polyphenolics found in wine. The health benefits of these plant polyphenolics are well established.
We have recently discovered a natriuretic peptide and a guanylyl cyclase in Arabidopsis thaliana, a plant used as a genetic model to study plant biology. The natriuretic peptide appears to regulate salt and water homeostasis in plants and also stimulates the production of cGMP. We are currently investigating the role of both the natriuretic peptide and the guanylyl cyclase in A. thaliana and grapevine. Specific attention is given to the regulation of the expression of the genes (when they are "switched on") and discovering plant processes controlled by these molecules. We expect that a number of plant processes regulated by cGMP (including anthocyanin biosynthesis in grapevine) would be the target of these two proteins, since natriuretic peptides lead to the production of cGMP and guanylyl cyclases synthesize cGMP.
These contributions illustrate but a few of the exciting projects that are currently running in order to try and elucidate the many health related wine issues. There are of course many more factors to consider and the scenario is infinitely more complex than those described here. What remains clear, however, is that the results obtained in any study should be interpreted objectively and responsibly to ensure that the main beneficiary is always the consumer.
Albert Joubert IWBT, (021) 808-2188, e-mail iwbt10@sun.ac.za.
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