Antioxidants and Flavor Masking
Many antioxidants tend to have strong flavors, ranging from acid to astringent and bitter. Antioxidants in well-known products--such as green tea, coffee, chocolate, citrus, fruits and berries, vegetables, and beverages, such as beer and wine--add bitter or acrid notes of flavor to the product. Taste preference has been linked to age, background and culture.
Culture and Bitter Preferences
It is known infants adore sweet tastes, and older children go for “extreme” sourness. However, they all tend to dislike bitter tastes. At a later age, people start to appreciate bitter-tasting vegetables and beverages. This explains why virtually no child likes the taste of beer, when offered the opportunity to take a sip, nor wine nor coffee, while most adults are known to generally like these beverages.
Besides age-related differences in taste and preference, cultural differences can also be striking. For instance, Central American, pre-Columbian cultures were reported to drink extremely bitter beverages from the fruit of the cocoa tree (Theobroma cacao). Currently, northern European cultures, such as the Belgians, Brits and Dutch, have a taste for bitter beers and ales. A Belgian beer type, Poperings Hommelbier, is typically named after its main bitter ingredient, hops, known in the local Flemish dialect as hommel (the botanical name Humulus lupulus).
In the tropics (e.g., in Suriname), various extremely bitter vegetables are grown, such as bitawiri (literally meaning bitter leaves--Cestrum latifolium) and bitter gourd (Momordica charantia). Bitter gourd is also grown in India, South East Asia, China, Africa and the Caribbean, and it is known as one of the bitterest vegetables consumed by humans.
Dietary Sources of Antioxidants
Some of the main dietary phytochemicals that possess antioxidant properties can be found in four chemical groups. They are the carotenoids (examples include beta-carotene, lycopene, lutein, zeaxanthin); glucosinolate derivatives (compounds in this group include isothiocyanates, thiocyanates, indoles, nitrils); polyphenolics (chlorogenic acid found in coffee, resveratrol in red wine and flavonoids fall into this chemical group); and vitamins C (ascorbic acid) and E (alpha-tocopherol).
Beta-carotene, a precursor of vitamin A, acts as a direct “quencher” of singlet oxygen. Other well-known dietary carotenoids are lycopene, lutein and zeaxanthin. Lycopene is abundant in tomatoes (accountable for its bright red color), but will have a higher activity, when consumed in a mashed or ground product, such as tomato purée, ketchup or a sauce. Furthermore, adding vegetable oil will probably enhance its bioavailability even more, due to its fat-soluble nature. Lutein and zeaxanthin, present in leafy green vegetables and eggs, amongst other things, play an important role in preventing AMD eye disease.
Glucosinolates are found abundantly in crucifer species, such as cabbages, kales, cauliflower, Brussels sprouts and broccoli. Glucosinolate derivatives are formed when the plant cells are cut during preparation, provided cooking time is kept short.
Polyphenolic antioxidants, such as tannins present in tea, cacao and red wine, are known to possess a strong astringent effect in the mouth. They bind to proteins present in one’s mouth, causing a dry mouthfeel. Tannins in tea and cacao are predominantly catechins. In red wine, one can find tannins from two sources: the skins and seeds of the grapes, which are dissolved during maceration, and from the wooden casks in which the wine is matured. Hops used for brewing beer contains several bitter substances, including antioxidant polyphenolic compounds, such as phenolic acids, condensed tannins and flavonoids (quercetin glycosides and rutin). Typically, hops is used for its antiseptic qualities, but also to counterbalance the sweet taste of the malt used for beer production.
The following is a list of important flavonoid antioxidant subgroups, along with an example of specific phytochemical(s) in that group, as well as primary natural sources.
* Flavones (e.g., tangeritin [found in citrus]).
* Flavonols (e.g., quercetin [found in apple, grape, mate]).
* Flavonol glycosides (e.g., rutin [found in buckwheat, black tea, hops]).
* Flavonols (e.g., dihydroquercetin [found in larch wood]).
* Flavanones (e.g., naringenin [found in citrus]).
* Flavanone glycosides (e.g., narirutin and naringin [found in citrus]).
* Anthocyanins (e.g., natural red/blue pigments [found in berries, red cabbage]).
* Flavanols (e.g., catechin derivatives, [found in green tea, cocoa]).
* Chalcones (e.g., xanthohumol [found in hops, beer]).
* Isoflavones (e.g., genistein, daidzein and glycitein [found in soy, tofu]).
Traditional Taste Masking
Though adults are known to like bitter tastes more than children, only a few go for the extreme; the rest tend to prefer a slightly softer bitterness. With beer and wine, there is a tendency among consumer groups for sweeter varieties. This also explains why milk chocolate is more popular than dark chocolate, and why many people drink their coffee with milk and sugar. Chocolate’s bitter ingredient is cacao. Cacao is a natural substance, produced from the fruit of Theobroma cacao, and it is rich in polyphenols, especially flavanols and proanthocyanidin oligomers. In practice, many cacao products contain considerable amounts of milk and sugar. The milk proteins bind to the polyphenolics present in the cacao.
For the same reason, traditional English tea is served with milk (added to it as a standard procedure), meant to soften the extreme bitter and astringent taste caused by its high tannin content. Indian tea, also known as chai, contains a number of oriental spices: cinnamon, cardamom, ginger, clove and black pepper. All contain several sharp-tasting antioxidants. No wonder chai is traditionally prepared with milk and sugar, like black tea, cocoa and coffee. Another important Asian spice is ginger, which contains phenolic compounds, such as gingerol, accountable for fresh ginger’s spicy taste. Once again, besides its use as a cooking ingredient, fresh ginger is often conserved in syrup and consumed fully saturated with sugar.
Lemonade is a very popular drink on hot days and is also a useful provider of vitamin C. Originating from the Mediterranean, lemonade’s basic recipe is lemon juice, with water and sugar added. In the Northern Hemisphere, highly important sources of vitamin C are a large variety of berries, which are harvested after summer and conserved in marmalades or juices. Examples include elderberries, blackberries, cowberries or lingonberries, cranberries, red and black currants, bilberries or blueberries. Besides containing high amounts of vitamin C, all are packed with polyphenolic compounds, accountable for their astringent, bitter and acid tastes. To soften these strong tastes, a considerable amount of sugar is added, when preparing juices or marmalades of these fruits.
Current Antioxidant Taste Challenges
A common trait of all the above is that beverages and foodstuffs with a high antioxidant content, mostly made up by polyphenolic compounds, are traditionally prepared with either sugar or milk, or a combination of both. Chemically, this makes perfect sense. Sugar is known to mask acid and bitter tastes, and milk proteins are accountable for chemical binding to astringent polyphenolic compounds, such as tannins.
A well-known antioxidant present in citrus and vegetables is, of course, ascorbic acid, or vitamin C. In its pure form, the substance shows strong acid flavor characteristics. For this reason, producers of vitamin C supplements often use sweet carbohydrates to make it palatable. Another option is to use mineral ascorbates, such as calcium ascorbate, potassium ascorbate or sodium ascorbate. They are not acidic, but one should keep in mind that mineral intakes would also increase.
The encapsulation of ingredients with dairy-derived coatings is one example of modern applications of taste masking that include the use of dairy. Wolfberries (Lycium barbarum and Lycium chinense), also known as goji berries, form part of the Solanaceae group and are, therefore, related to tomato and potato. They are produced in large amounts in China and contain high levels of natural antoxidants, including several carotenoids and phenolic compounds. Modern formulas with goji berries include yogurt and chocolate coatings.
Being a famous member of the same family, tomato (Solanum lycopersicum) contains high levels of carotenoids, especially lycopene, the typical tomato antioxidant. The Japanese food-innovating concern, Kagome, produces dairy products fortified with lycopene.
In many beverages, including various soft drinks, gum Arabic is frequently used as a stabilizer. In many modern table wines, the advantage of gum Arabic, in addition to providing roundness and body, is that it also softens bitterness and astringency. Gum Arabic is a mixture of arabinogalactan olygosaccharides, polysaccharides and glycoproteins, which are accountable for its effects of stabilizing, emulsion, adsorption and encapsulation. Formerly, gum Arabic was used in winemaking, to prevent tartaric acid from precipitating in the bottle, but modern storage techniques before bottling (particularly cooling below 5° C) ensure most of the tartaric acid precipitates in the vat itself, instead of in the bottle. Still, during the past few years, more and more bulk wines contain considerable amounts of gum Arabic (up to 1.5ml/l), which softens and masks harsh tannins and provides the wine with a smooth, creamy mouthfeel. For high-quality wines, however, the downside of adding gum Arabic is that they will lose some flavor and aromas. At the same time, high-quality wines do not really need gum Arabic, in order to obtain a smooth, creamy mouthfeel. This is achieved by another glycoprotein complex, mannoproteins, which are formed by autolysis of yeast cells, occurring during traditional time- and labor-consuming storage in an aging vat (a procedure referred to by winemakers as storage sur lie). A huge advantage of mannoproteins, in comparison with gum Arabic, is that mannoproteins do not interfere negatively with the wines’ aromas and fragrances.
Suppliers Step up with Masking Flavors
There are programs in place for masking the off-notes of antioxidants in the ingredients industry, particularly in the flavors segment. For example, one flavor house is using its branded “masking technology” as a bitterness masker to hide the bad aftertaste of green tea catechins. The flavor-masking range is not specifically aimed at antioxidants, but covers a whole range of “plus” ingredients--that is, nutritional ingredients, added for health, that usually bring off-tastes.
Another international flavor supplier markets a masking flavorings range, as part of its portfolio. These flavors have been effective in overcoming bitter, burning, astringent, chalky, salty, metallic tastes and a host of other off-flavors and off-notes. Lastly, a recent study, conducted by Polish and Spanish researchers and published in Food Quality and Preference, found the common hydrocolloid carboxymethylcellulose (CMC) could work to mask the bitterness of polyphenols. The researchers assessed the efficacy of guar gum, xanthan gum, gum Arabic and CMC on masking the bitter flavor of the polyphenolic extracts of black chokeberry, green tea and walnut.
With a better understanding of how to subdue less desirable taste contributions of healthful components, R&D can more easily formulate foods and beverages with enhanced nutritional and sensory properties. pf