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Taurine - valuable component of goat milk
Abstract
Among many other valuable properties and components, goat milk has a relatively high content of free amino acids. Of the latter, particular attention should be paid to the non-protein amino acid taurine, which has a 20-fold higher level than in cow's milk and is almost equal to that in human milk. Therefore both goat milk and goat-milk products can be an excellent source of this amino acid. The paper presents the general characteristics and properties of taurine, its biosysnthesis paths and its role in the human body. The presence of taurine in milk and dairy products (including goat milk and cheese), methods of its analysis and changes in taurine induced by heat treatment of milk have been described.
A previous study showed that addition of β-cyclodextrin to goat milk made a difference to its flavour, but in an undescribed way. Cyclodextrins (CDs, comprising α- β- and γ-CD) may be able to bind the free branched chain fatty acids in goat milk responsible for the largely undesirable ‘goaty’ flavour. The primary aim was to test the effect of CDs on this flavour in goat milk and its products with a view to marketing goat milk products with reduced flavour intensity. A secondary aim was to test the effect of β-CD on skatole flavour, a characteristic flavour of milk from pasturefed ruminants. Study design and methods: The present study evaluates addition of mainly β-CD to goat milk, cow milk and their products to reduce undesirable flavours. The methods applied were mainly ranking and hedonic assessment in sensory experiments. The tests done were with CDs added to buffers and milks, some of which were flavour-enhanced with 4-methyloctanoic acid as a representative goaty fatty acid, or with skatole. Goat milk yoghurts were also tested. Free fatty acid concentrations, which may be affected by CD binding, were measured after separating cream and skim milk. The methods applied were standard dairy procedures: titration of free fatty acids in milk fat and the copper-salt method for measuring fatty acids in skim milk. A fungal lipase was added to milks to accelerate fat hydrolysis (lipolysis). This was done to increase the concentration of free fatty acids for several experimental purposes. Some minor experiments studies were also done, for example the comparative effect of lipases on goat milk and cow milk, and the lipolytic activity at different temperatures over different times. Results: The results of skatole experiments were inconclusive. The odour of 4-methyloctanoic acid was reduced in acidic buffers by addition of α- and β-CD, particularly the former. Alpha and β-CD were both effective in goaty flavour reduction in goat milk. γ-CD was not effective. In all this work differences were statistically significant to varying levels. Goaty flavour was reduced by addition of β-CD to goat milk yoghurt, but only when added before fermentation (P < 0.001), not after (P = 0.09). The liking scores for goat milk yoghurts for both plain and flavoured yoghurts increased with β-CD treatment (both P < 0.001 for 59 panellists). The chemistry experiments revealed a reduction of free fatty acid concentration in the fat phase when β-CD treatment was added to full cream cow milk. However, analysis of skim milk did not show a corresponding increase in concentration. Further experiments are required to reveal the fate of the ‘missing’ fatty acids. Conclusion: Overall it was shown that under certain conditions, CDs were effective in reducing goaty flavour in milk and yoghurts. Whereas CDs are approved for addition to foods in many countries – including the bellwether U.S.A. – formal approval by Food Standards Australia New Zealand has not yet been finalized. When it is, the way should be clear to market a range of more consumer-acceptable goat milk products in New Zealand as a primary market. In short, this research has significant commercial relevance.
Taurine (2-aminoethylsulphonic acid), a non-protein amino acid, is present in most animal tissues. Its highest concentrations are found in skeletal muscles, heart, brain, and retina. Although this compound can be synthesized from other sulfonic amino acids such as methionine and cysteine, the endogenous production is insufficient for the human organism, so taurine has to be delivered with food. Animal products such as fish, meat, and milk are good sources of taurine. Taurine exhibits antioxidative properties, regulates intracellular Ca2+ concentration, acts as a neuromediator and neuromodulator, is responsible for osmoregulation, is involved in cholic acid production, and modulates inflammatory reactions. The amino acid seems to be an important trophic factor in the retina, nervous system, and kidneys. The protective action of taurine on heart muscle and the antagonistic effects of this amino acid and angiotensin II arouse great interest. The role of taurine in glucose metabolism regulation is also extensively studied. However, the detailed mechanisms of taurine's action are still unknown. Lowered tissue taurine concentrations are characteristic of many pathological states, including diabetes. In many studies, also in clinical trials, it has been reported that supplementation with taurine reverses or at least attenuates pathological changes. Therefore, it seems likely that taurine might be used in the treatment of cardiomyopathy, myotony, hypercholesterolemia, or diabetes. However, future thorough studies are required.
Taurine (Tau) is a sulfonated amino acid which is not incorporated into polypeptide structures and whose importance in the
growth of newborns and young children has been well established. It is the most abundant free amino acid in goat's milk, where
it occurs in higher amounts than in other kinds of milk. Tau and other free amino acids were analysed by high-performance
liquid chromatography in Apulian Cacioricotta goat's cheese. Tau was present in both fresh and ripened cheese, providing a
new reason for enhancing the value of this typical local dairy product.
A simple and rapid method has been developed for the determination of taurine in foods by HPLC with an on-column fluorescence derivatization technique. Taurine was extracted from foods with water, and the crude extract was deproteinized with Carrez solution, followed by purification on a Bond Elut SCX cartridge column. Taurine was chromatographed on a polymer column with a mobile phase of acetonitrile and alkaline borate buffer solution containing o-phthaladehyde and 2-mercaptoethanol as derivatizing reagents. The average recoveries were greater than 90% for taurine added to various kinds of foods, such as milk products, shellfish, chicken egg and honey. Application of the method to the foods resulted in the detection of taurine in egg (1.26±0.15 mg/100 g) and honey (0.34±0.08 mg/100 g), in which taurine had not previously been found.
A method based on formation of the fluorescamine derivative of taurine and HPLC was developed for analysis of taurine in milk. Taurine in milk ranged from 2.4 to 12.0 mg/L. The degradation of taurine in taurine-fortified milk and in a buffered taurine and lactose solution (pH 6.7) was determined by heating at 80, 100, and 120°C. First-order reaction kinetics were observed for taurine losses in milk and buffered solution. Activation energies were 20.5 and 21.0 kcal/mol for milk and buffered solution, respectively. The taurine loss in milk seems to proceed through browning with the same degradation rate as lysine.
Fresh beef steaks were sprayed on the surface with vitamin C (500 ppm), taurine (50 mM), rosemary (1000 ppm) and vitamin E (100 ppm), the three latter in combination with 500 ppm of Vitamin C, packaged in modified atmosphere (70% O2+20% CO2+10% N2) and stored at 1±1 °C for 29 days. Metmyoglobin formation, lipid oxidation (TBARS), instrumental colour (CIE a∗), psychrotrophic bacterial counts (PCA) and sensory discolouration and odour were determined. Results demonstrated that surface application of antioxidant combinations resulted in an effective delay of oxidative deterioration of fresh beef steaks. Shelf life was extended beyond that of control, according to evaluation of sensory attributes. Both combinations of vitamin C with either rosemary or taurine significantly (P<0.01) extended the shelf life of fresh beef steaks by about 10 days. Rosemary was the most effective in delaying oxidation processes. The combination of vitamins E and C was significantly (P<0.01) less effective than those combinations in delaying meat oxidation.
Taurine is a sulfonated beta amino acid derived from methionine and cysteine metabolism. It is present in high concentrations in most tissues and in particular in proinflammatory cells such as polymorphonuclear phagocytes. Initial investigation into the multifaceted properties of this non-toxic physiologic amino acid revealed a link between retinal dysfunction and dietary deficiency. Since then a role for this amino acid has been found in membrane stabilization, bile salt formation, antioxidation, calcium homeostasis, growth modulation, and osmoregulation. Our own group has demonstrated a key role for taurine in modulation of apoptosis in a variety of cell types. This review summarizes our current knowledge of taurine in nutrition, host proinflammatory cell homeostasis, therapeutic applications, and its potential immunoregulatory properties. It is our belief that taurine, similar to arginine and glutamine, is now more than worthy of critical clinical analysis.