Use of Bioactive Compounds to Improve Human Health
Managing The Challenge Of Bitter And Astringent Flavors
Gustavo Duarte and Patricia Rayas-Duarte
Robert M Kerr Food & Agricultural Products Center
Oklahoma State University, Stillwater, OK 74075
There is no doubt we are experiencing a change in paradigm of the cultural trends in the food industry. The Gen X’ers, Boomers and Matures generation are growing in awareness of the link between health and diet. These well-informed consumers prefer innovative products with health benefits, including products containing bioactive compounds. Experimental data suggests that biologically active compounds protect from a number of age, genetic and stress related diseases and disorders. Examples include protection against oxidative stresses on cell membranes and coronary diseases, as well as display of antioxidant functions not yet related to specific diseases, and wide spectrum of tumor blocking activities [1-2]. Bioactive compounds are naturally produced by plants for natural protection against predators and disease. These compounds are generally bitter and astringent to the human tasting senses. The challenge for food scientists is to formulate new products with ingredients known to contribute to the well being of humans and avoid/minimize the bitter and astringent notes. In addition, formulators have to protect bioactive compounds during food processing. Micro-encapsulation is a technology that holds promise to mask bitter taste and off-odors, preserve integrity of nutrients, and deliver bioactives.
The nature of bitter taste
All animals including humans have a keen sense for detecting bitter taste. This has protected us from potentially toxic substances, especially at young age. The taste reception in all vertebrates except hagfish are in the taste buds . The taste buds are bundles of about 100 cells present on the tongue, soft palate epiglottis, pharynx and larynx in humans and other mammals . As a result of evolution and adaptation mechanisms, there is a single receptor with low affinity for sucrose (millimolar range) and a family of multiple receptors with higher affinity for bitter compounds (micromolar range) in our taste buds. This translates into animals well-equipped with sensitivity to detect bitter compounds in foods.
A better understanding of the bitter taste reception in biological and physiological terms continues to unfold. A large family of putative mammalian bitter taste receptors, apparently as high as 40 to 80 receptors, appear to be organized in the genome in clusters and are genetically linked to loci that influence bitter perception in humans and mice [5-6]. This new evidence reveals that some fungiform taste buds cells expressing T2Rs may be capable of recognizing multiple bitter tastants. This supports the observations that humans are not always capable of distinguishing diverse among bitter compounds, but easily recognize bitter taste .
The case of caffeine
Some alkaloids such as caffeine are naturally present in more than 60 plant species, including beans, leaves and fruits of many plants [7-8]. Caffeine is a moderately bitter purine alkaloid and its major source is seeds of Coffea sp. plants. The caffeine content in raw Arabica and Robusta coffee varieties ranges from 0.8-2.5% and as high as 4%, respectively . Caffeine is also found in tea leaves (Camellia sinensis), whose content varies from 2.5 to 5.5% caffeine in dry leaves depending on origin, age and processing. Two other alkaloids (the methylxanthines theobromine and theophylline) present in much lower content, gives tea its flavor signature . Other products such as yerba maté and cocoa beans also contain caffeine (0.5-1.5% and 0.2%, respectively).
Caffeine continues to be one of the most popular products for use as an energy stimulant, and as an antioxidant. The demand for Caffeine has risen to the extent that Caffeine manufacturers are producing Caffeine synthetically to keep up with its demand. Caffeine is being used in bakery products, nutrient bars, smoothies, cereal, powders, sports nutrition supplements, confection products and more. But it is a bitter compound.The challenge is how to mask the bitter taste of this bioactive ingredient and permit its use in everyday staples.
The major effect of caffeine in animals (psychostimulant) is believed to be due to its antagonistic effect of the adenosine receptors which in turn affect the release of a number of neurotransmitters, such as noradrenaline, acetylcholine, dopamine and the gamma-aminobutyric acid (GABA)/benzodiazepine system . The exact compounds and mechanism for the cardiovascular effect of caffeine in animals is still not clear [11-12].
The case of tea
Flavonoid-rich extracts and pure chemical constituents of green tea demonstrated antioxidant protection in vitro and in vivo [13-15]. Inhibition of carcinogenesis in rodent cancer models have been demonstrated by green tea extract, green tea polyphenols and epigallocatechin gallate. The cancer chemopreventive activity of these compounds/extracts has been found in tissue from colon, duodenum, esophagus, to mention some. Bioavailability studies as well as controlled prospective human intervention trials of the bioactive compounds in green tea will solve the riddle of the conditions conducive to an improvement of the uptake of these compounds .The benefits of green tea extract are known. Formulators have struggled with ways to incorporate this bioactive into finished goods because of its bitter taste. Recent developments  indicate that it is possible to come up with a bitter-free green tea extract which is suitable for bakery applications.
The case of sulphur-containing compounds
The bioactive components in brassica vegetables (broccoli, cabbage, cauliflower, brussel sprouts, kale, etc.) are glucosinolates. The sulphur-containing glucosinolates are broken down by cooking and in the gut into a number of products including isothiocyanates and indole compounds, which are associated with cancer protecting properties . This is an active research area that will elucidate the biochemical mechanisms as well as the risk-benefits from these compounds.
Plants of the genus Allium (garlic, onions, chives and leeks) contain sulphur-substituted cysteine sulphoxides, which among other compounds have shown health promoting effects . An example is the relation of garlic and the prevention of cardiovascular diseases and some forms of cancer [19-20]. The anticancer effects have been attributed to the induction of Phase II detoxification mechanisms. There is evidence that a number of sulphur compounds may specifically inhibit the bacterial conversion of nitrate to nitrite in the stomach .
Challenges of the Trade Solved with Microencapsulated Ingredients
Food scientists and developers face a number of challenges in protecting bioactive compound(s) during processing. For example, with microencapsulation technology it is possible to control the release of bioactive compounds to protect them from heating, aseptically packaging, freezing, pH, storage, shelf life, etc. Control release will also prevent the detection of bitterness or lasting off flavors in human taste bud receptors, which in turn will directly improve the palatability of products containing bioactive compounds with bitter flavors. Microencapsulation of biologically active compounds such as caffeine, green tea extract, other botanicals, proteins, amino acids, vitamins, minerals and others has been a very effective tool in masking bitter taste, and in protecting and delivering the intended dosage in complex processing and food matrices, thus rendering them usable across a wide cross-section of applications.
Advances in microencapsulation technology have allowed the production of a variety of bioactive compounds not available before to the food industry. This has been made possible through very specific approaches to protect molecules to survive target area/environment and be released at the appropriate time/environment. Sensitive material is then delivered, minimizing losses normally found in non-micro-encapsulated products. Micro-encapsulation is an effective tool for masking bitter taste and astringent off-flavors and delivering sensitive and labile bioactive compounds.
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