In traditional medicine, chicken broth is regarded to have the effects of warming the body, countering body weakness and tonifying vigor, invigorating spleen and stomach, as well as strengthening tendons and bones. Chicken broth is suitable for alleviating the clinical symptoms of dystrophy, fear of cold, mental fatigue and lack of strength, menstrual irregularities, and postpartum agalactia. Originated from Ming dynasty of China, Wuji Baifeng pills have a history of more than a 100 y. These pills are made from black chickens and possess effects of nourishing blood and promoting fluid production, tranquillizing spirit, and enhancing intelligence. Combining the fact of rapid modern life rhythm and the important role of chicken broth in Chinese health preservation, chicken essence is conveniently accommodated into the fast paced modern life as an industrialized product and is prevalently consumed by Chinese in Southeast Asia. Chicken essence is mainly used to supply nutrition for patients, restore physical strength in postpartum women, improve physical quality of athletes, recover mental and physical fatigue, and enhance cognitive performance, particularly learning and memory. Besides, several lines of chicken essence products are enhanced with other traditional Chinese herbs to cater to the various needs of consumers. Because of its abundant physiological activities, chicken essence has been widely accepted by consumers, and a mature consumer market is gradually being developed. In an effort to provide useful information for consumers and further researches on chicken essence, this article summarizes the recent studies on the possible mechanisms underlying the bioactivities of chicken essence.
Active components of chicken essence
Compared with most other kinds of meat, chicken is rich in proteins, trace elements, carnosine, creatinine, and amino acids but has less fat. These ingredients can easily dissolve in and migrate to chicken soup by heating and boiling. However, due to the strictly controlled extraction processes, the ingredients proportion and their bioactivities in chicken essence are different from that in chicken broth. For example, Brand's Essence of Chicken (BEC), which has a history more than 170 y, is produced via a water extraction process from chicken meat for several hours under high-temperature, followed by centrifugation to remove fat and cholesterol, vacuum concentration to 3- to 4-fold, sterilization by high temperature and pressure before bottling. This kind of chicken essence is rich in protein, and low in sugar and fat, conveniently available and consumable, and easy for household storage. Previous studies confirmed that BEC not only contains indispensable amino acids including threonine, valine, methionine, isoleucine, leucine, phenylalanine, lysine, and tryptophan, but also contains a substantial proportion of free amino acids such as histidine and arginine (shown in Table 1) (Geissler and others 1996; Zain and Jamalulail 2003). Besides, many minerals, trace elements, vitamins, and some special nutrients such as anserine, carnosine, and taurine are also detected in BEC.
|protein (peptide)||83.0 mg/mL|
|Free amino acid||3.1 mg/mL|
|Phosphatidyl collin||0.4 mg/mL|
|Vitamin B2||1.0 mg/kg|
|Vitamin B6||0.37 mg/kg|
|Vitamin B12||0.002 mg/kg|
|Vitamin C||15 mg/kg|
Effects of chicken essence on stress and fatigue
As lifestyle changes in modern society, physical tiredness is no longer the main reason responsible for fatigue. Nowadays, fatigue mainly derives from various kinds of stresses caused by environment and living habit alterations, physical and chemical factors, as well as psychological pressure (Maghout-Juratli and others 2010). Therefore, stress-related diseases have received considerable attention, and it is important to relieve stress for the goal of health maintenance. According to theory in traditional health preservation, chicken broth can relieve fatigues. Nagai and others (1996) evaluated the effect of chicken essence on mental fatigue in 20 healthy young students. Their results indicated that, after consuming 140 mL chicken essence per day for 7 d continuously, the error rates for the 2 mental workload tests, including mental arithmetic test and short-term memory test, were decreased significantly when compared to placebo control group. Meanwhile, they also evaluated the effects of chicken essence on the performance and emotional status of subjects by determining blood cortisol level, which is a stress hormone. The results suggested that basal cortisol levels of 2 groups were similar, while their cortisol levels increased significantly before mental workload tests, indicating their high stress status. After mental workload, the recovery of mean cortisol level of subjects who consumed chicken essence was significantly faster than those consuming placebo. Besides, they also found that subjects felt more active and less fatigued during the workload when they took chicken essence regularly. They concluded that chicken essence could enhance cortisol metabolism in blood and promote mental fatigue recovery.
It is well known that consuming tea or coffee could help focusing and consuming cocoa could relieve fatigue. Their mechanisms may be related with the activation of brain adenosine receptors by caffeine and theobromine. However, the anti-stress and anti-fatigue mechanisms of chicken essence are distinct from the previously mentioned drinks. It may relate to the activation of central histaminergic system (Lv and others 2010). It was shown in recent studies that compounds such as carnosine and anserine, which are important nutrients in chicken essence, are histamine dipeptides and antioxidants with multiple bioactivities. They are precursors in the synthesis of histamine, which can regulate central histamine and 5-hydroxytryptamine (5-HT) levels. This directly or indirectly decreased levels of stress-related substances such as cortisol during fatigue (Chen and others 2004; Yamano and others 2001), and regulated serotonin-dependent physiological activities, such as improving sleep quality, enhancing motivation, normalizing circadian rhythm, and so on. Besides, Lo and others (2005) also suggested that the anti-fatigue mechanism of chicken essence may be related with the regulation of plasma lactic acid and ammonia levels.
Effects of chicken essence on anxiety
Anxiety is a common mental disorder. Generally, it is believed that about 5% of world population suffer or experience light or moderate anxiety. Since anxiety is difficult to cure and most anti-anxiety drugs have various degrees of side effects, a combination treatment with psychotherapy and drugs as well as exercises is applied to relieve anxiety symptoms. Researchers suggested that nutritional interventions could be beneficial to both brain functions and symptoms associated with anxiety. Azhar and others (2001) investigated the effects of chicken essence combined with psychotherapy in 22 patients suffering anxiety. Results showed that chicken essence could enhance the cognitive abilities of patients, suggesting the beneficial effects of chicken essence on anxiety.
The anti-anxiety mechanism of chicken essence could be associated with regulations of histamine, 5-HT or other neurotransmitter pathways. As early as 1984, Watanabe and others (1984) successfully studied the distribution of histaminergic neuron system in the central nervous system of rats with histidine decarboxylase as a marker. Further studies showed that histaminergic neuron system was relevant to many brain functions, such as auto kinetic movement, sleep cycle, waking state, appetite control, learning, memory, and emotion, by employing pharmacological reagents, knock-out rats and positron emission tomography. Watanabe and Yanai (2001) reported that histaminergic system plays an important role in the regulation of central hyperactivity induced by food-deprived activity stress. However, we found that chicken essence had protective effects and suggested that these effects were partially correlated to carnosine, which is a histamine precursor compound abundant in chicken essence and plays important roles on central histaminergic system (Kurihara and others 2001; Lv and others. 2010). Moreover, the activity of 5-HT, another anxiety-related important neurotransmitter, was also indicated to be regulated by chicken essence. Xu and Sim (1997) found that chicken essence markedly increased the level of 5-hydroxyindoleacetic acid (5-HIAA), a main metabolite of 5-HT, in cerebrospinal fluid. This result reflected the influence of chicken essence on cerebral 5-HT metabolism. However, whether amino acids in chicken essence such as taurine, aspartate, glutamate, and glycine directly participate in regulation of 5-HIAA level still remains unknown.
Effects of chicken essence on glucose and lipid metabolisms
Fatigue not only affects central neurotransmitters and subsequently results in mental lassitude, but also induces bad appetite, which may be related with energy metabolism disorder. To maintain normal physiological functions, it is necessary to obtain energy from dietary glucoses and lipids. Stress was found to affect energy metabolism, limit energy uptakes of tissues and organs, disturb physiological functions, and lead to fatigue (Roberts and Sindhu 2009). Taketani and others (1998) reported that 2 dynamic hormones, cortisol and dehydroepiandrosterone (DHEA), had dual-direction regulation on glucose and lipid metabolisms, and at the same time controlled the occurrence of fatigue. Previously, our laboratory observed that blood cortisol level was significantly increased in 55 healthy adults who worked all night (Kurihara and others 2003), while Nagai and others (1996) confirmed that chicken essence reduced cortisol level after stress load. Recently, we found that restraint stress significantly reduced blood insulin level and decreased hepatic glycogen synthesis in mice. In addition, we also found that restraint stress could increase the levels of blood ketone bodies, and decrease the clearance of blood glucose in mice loaded with sucrose (Kurihara and others 2006). Restraint stress was also demonstrated to inhibit the activity of lipoprotein lipase in fat tissue, and reduce the clearance of blood neutral fat in mice loaded with Intralipid (He and others 2009a). However, chicken essence was indicated to increase lipoprotein lipase activity in fat tissues, and improve blood lipid metabolism in stressed mice. Apart from lipid metabolism, chicken essence was also observed to increase insulin level, promote hepatic glycogen synthesis and blood glucose utilization in stressed mice (Kurihara and others 2006). These indicated that chicken essence could protect stress-mediated dysfunction in glucose and lipid metabolism, suggesting its benefits against fatigue.
Effects of chicken essence on energy metabolism
In the study of the effects of chicken essence on resting metabolism rate, Ikeda and others (2001) found that resting energy expenditure (REE) values after consuming chicken essence tablets were significantly higher than those consumed skim milk protein tablets (control trial). The increased thermogenic effects were continued at least for 1 h and then gradually decreased towards the baseline. The REE values during control treatment did not show such an augmented response. Geissler and others (1989) tested the thermic response after chicken essence consumption in 2 sets of 20 young healthy male and female subjects. Results showed that metabolic rate was significantly increased by 10% to 12% after consuming 70 mL of chicken essence for 2 h. They also confirmed that the effects of chicken essence on metabolism rate were greater than that of chicken broth. In another experiment, they found that consuming 70 mL of chicken essence with 30 to 40 kcal calories and a mixture of foods with 250 to 300 kcal had equal effects on metabolism. The response was greater than expected from the total energy and protein content of chicken essence, which may be due to the particular amino acid composition, other specific components and/or a cephalic response to taste. Tsi and others (2003) found that the combined thermogenic effect of capsaicin, green tea extract, and chicken essence could translate to a positive clinical effect by reducing approximately 460 g of body fat, following 2 wk of supplementation.
Effect of chicken essence on hyperglycemia
According to traditional health preserving experiences, people believe that frequent consumption of chicken essence by diabetics is beneficial to their health. Yamano and others (2001) observed the effects of chicken essence and its active component carnosine on 2-deoxy-D-glucose (2DG)-induced hyperglycemia by intracranial injection in rats. They found that the elevated blood glucose level induced by 2DG was notably decreased after consuming 5% chicken essence for 7 consecutive days. They also confirmed that carnosine, administrated intraperitoneally, intracerebroventricularly, or intragastrically, was effective to 2DG-induced hyperglycemia in rats. Moreover, they demonstrated that the anti-hyperglycemic effect of carnosine was related to the elevation of blood insulin level and reduction of glucagon level. In this experiment, Yamano and others (2001) also noticed that intravenous injection of certain doses of carnosine could inhibit the activity of sympathetic efferent nerves, which innervate the adrenal gland and liver, and reinforce the activity of parasympathetic efferent nerves, which innervate the pancreas. At the same time, certain doses of histamine were also found inhibiting 2DG-induced hyperglycemia in rat. Their experimental results showed that the inhibition of 2DG-induced hyperglycemia in rat by intracerebroventricular injection of histamine or carnosine could be counteracted by thioperamide, which is histamine H3 receptor antagonist. The researchers suggested that carnosine, which act as precursor of histamine and is abundant in mammalian skeletal muscles, may act on the autonomic nervous system via H3 receptors and thereby reducing blood glucose levels. However, further confirmations on the mechanism of action and conduction pathway are still needed.
In addition, our laboratory has proven that carnosine can accelerate blood glucose elimination rate, improve glycogen synthase gene expression, and enhance the ability of glycogen synthesis in restraint stressed mice (Yang and others 2010). The mechanism can be related to the improvement of glucocorticoid level and the activation of glycogen synthase kinase by carnosine, which then lead to dephosphorylation of glycogen synthase. It is well known that the sympathetic-adrenal medullary system will be activated as a response to stress. Large amounts of catecholamine and excitatory amino acids will then be released, which in turn hyper-activate the hypothalamic-pituitary-adrenal axis (HPA axis) and elevate blood corticosteroid level (Tsigos and Chrousos 2002). The augmentation of glucocorticoid release not only promotes glycogen degradation and gluconeogenesis, but also inhibits transportation and utilization of glucose in peripheral tissues. Blood glucose is then promptly increased under this condition. Administration of carnosine can lower blood glucose level in restraint stressed mice. It can also improve stress-induced decrease of blood glucose utilization. At the same time, carnosine improved stress-induced energy insufficiency as seen by significantly dropped plasma corticosterone level, promoted glycogen synthesis, lowered glucocorticoid contents, and increased glucose storage in restraint stressed mice. Glycogen synthase is an important rate-limiting enzyme for the synthesis of liver and muscle glycogen. Glycogen synthase-2 is mainly found in liver and regulates the synthesis of liver glycogen. Through the regulation of cAMP and Ca2+, glucocorticoid causes phosphorylation of glycogen synthase by activating glycogen synthase kinase, which lowers glycogen synthase activity (Bollen and others 1998; Exton 1987).
Effects of chicken essence on immune function
In the study of effects of chicken essence on immunity, Man and others (2005) showed that chicken essence could increase the activity of serum immunoglobulin in normal and stressed animals. Candlish (1998) demonstrated that chicken essence has a stimulatory effect on human circulating neutrophils. They concluded that these effects may be due to the alcohol soluble micromolecules, of which carnosine is present in, and alcohol precipitated macromolecules. Their study also indicated that the macrophage-like cell line U937 could be activated by chicken essence in vitro. Recently, our laboratory investigated the effects of chicken essence on immune function in mice loaded with restraint stress and the results showed that chicken essence inhibited spleen lymphocytes apoptosis to maintain immune cell number and protect immune functions (Li and others 2010). We further found that carnosine, which showed similar immune effects with chicken essence on function, was the active substance in chicken essence (unpublished data).
Influenza is an acute infectious disease caused by RNA viruses of the Orthomyxoviridae family (the influenza viruses). Influenza virus infections often occur in the elderly population and individuals presenting fatigue or stress, who have weakened immunity (Dushoff and others 2006). Previous studies demonstrated that fatigue could induce oxidative stress in immune cells and result in immune dysfunction (Piche and others 2008). Fatigue was also demonstrated to affect nasal ciliary motility and increase the probability of microorganism infections. Besides, stress has been shown to affect the number and cytotoxicity of nature killer (NK) cells and induce significant changes in immune response of host towards viral or bacterial pathogens (He and others 2011). Recently, we have conducted a study to investigate anti-influenza virus effect of chicken essence in mice loaded with restraint stress. Results showed that chicken essence could prevent influenza infection by modulating immune functions, although it could not directly treat influenza as a drug (Wang and others 2011).
Effects of chicken essence on lactation
According to the theory of traditional Chinese medicine, the reasons for postpartum hypogalactia include “Xu” (deficiency) and “Shi” (excess). “Xu” means blood deficiency, spleen, and stomach dysfunction, fluid exhaustion, loss of blood, and so on. It may cause lactation failure and result in postpartum hypogalactia. “Shi” means stagnations of meridian and blood. It may cause galactostasis and result in postpartum hypogalactia. Therefore, puerperal with “Xu” should be treated by tonification, while those with “Shi” should be treated by dredging. In reality, hypogalactia in puerperals are mostly caused by “Xu” and tonification is needed during the first few days of postpartum. Li and Li (1997) showed that chicken essence consumption could promote post-partum lactation and increase the production of milk. Besides, Chao and others (2004) examined the effects of chicken essence on lactation in 30 lactating women and found that chicken essence significantly elevated the contents of lactoferrin and epidermal growth factor (EFG), which are important for infants growth and contribute to the improvement of their immunity.
Effects of chicken essence on anemia
Chicken essence is widely used as a traditional remedy for several ailments, including anemia. A series of experiments was carried out in anemic rats by Geissler and others (1996) and results demonstrated that chicken essence could improve hemoglobin levels and indicated that the effects were mediated by increased appetite and enhanced availability of dietary iron. On one hand, chicken essence could increase appetite through stimulating the secretion of gastric juice. The increased appetite resulted in more consumption and thus the absorption of more nutrients from diet, which would be required for the synthesis of hemoglobin. On the other hand, many nutrients such as vitamins and amino acids can stimulate the absorption and usage of iron from food. It is generally recognized that iron obtained from food is non-heme iron, which cannot be utilized until it is dissolved and reduced. Earlier researches demonstrated that various factors, such as vitamin C and citric acid, could affect the dissolution and reduction processes of non-heme iron obtain from food. Carnosine and anserine, which are abundant in chicken essence, were also indicated to affect the absorption of iron through their anti-oxidative and metal chelating effects. However, the role of chicken essence in prevention of anemia needs to be further elucidated.
Effects of chicken essence on hypertension
In recent years, studies have proven that the angiotensin converting enzyme (ACE) inhibitory peptide obtained from protease hydrolyzed chicken protein is safe, easily absorbed into the body and inhibits the activity of ACE in human body. Zhang and others (2007) proved that among the chicken-originated bioactive peptides, ACE inhibitory peptide was one of the antihypertensive peptides, which has strong application prospect as a functional component in food. Saiga and others (2003) extracted 3 peptides from chicken extract which possess hypotensive activity by inhibiting ACE. These peptides were found to have a common sequence, Gly-X-X-Gly-X-X-Gly-X-X, among which Gly-Phe-Hyp-Gly-Thr-Hyp-Gly-Leu-Hyp-Gly-Phe showed the strongest ACE inhibitory activity. Matsumura and others (2001) used deoxycorticosterone acetate salt (DOCA-salt) induced hypertension model after unilateral nephrectomy in Sprague–Dawley rats to investigate the effect of chicken essence towards hypertension. It turned out that administration of freeze-dried chicken essence powder, which is equivalent to 0.175 to 0.35 mL chicken essence, once a day for 5 wk could notably lower DOCA-salt induced hypertension in rats. Moreover, chicken essence improved cardiac histology alteration caused by DOCA-salt. Physiological examination revealed that chicken essence can alleviate the thickened aortic wall and increased aortic wall area induced by DOCA-salt. Chicken essence could also alleviate renal damages induced by DOCA-salt, like glomerular fibrous necrosis, renal artery thickening, and tubular expansion. Matsumura and others also noticed that chicken essence could inhibit the increase of urine protein induced by DOCA-salt. Ririe and others (2000) proved that carnosine is beneficial to vascular endothelium-independent vasodilation of aorta in rats. It is believed that the generation of oxygen radicals is increased in hypertension animals, while oxidative stress is closely related to hypertension. Thus, we can infer that the anti-oxidant and free radical clearing carnosine could alleviate hypertension and organic pathologic histology alterations. Slim (2001) also confirmed that chicken essence could relieve overload myocardial hypertrophy, hypertension, atherosclerosis, and so on. When comparing the anti-myocardial hypertrophic effects of chicken essence with extracts from pork, the cardiovascular improving effects of chicken essence is well worth attention. Chicken meat extract also showed stimulating activity on the production of NO by macrophage. This may be related to its effect on improving cardiovascular functions. Taken together, from a nutritional point of view, long-term consumption of chicken essence may have certain preventive and curing effects on hypertension.
Investigation revealed that stress-induced physical and mental fatigue is related to the increment of lipid peroxidation (LPO) (Kennedy and others 2005). For example, LPO amount in urine of tired people is in inverse proportion with flicker fusion threshold (the index that evaluates brain functions) and in direct proportion to lactic acid concentration in blood. We also discovered that working overnight caused brain fatigue and lowered calculation ability, and was associated with increased blood LPO. Ou and others (2001) suggested that the Eastern concept of yin and yang constraints parallels the Western concept of the balance of peroxidation and anti-oxidation. Abidin and others (2004) also confirmed this phenomenon. When people are continuously depressed, certain degree of brain ischemia and production of reactive oxygen species may occur. When peroxidized lipids, product of oxidative damage, are accumulated in cerebral cortex, physical and mental faculties may be affected adversely. In addition, we found that physical and mental pressure in mice was induced by restraint stress. At the same time, the oxygen radical absorbance capacity was significantly decreased (He and others 2009b; Kurihara and others 2009). It can be seen that stress load not only causes fatigue but also induces endogenous oxidative stress. In the past few years, studies found that small molecule compounds like carnosine and anserine could enhance the anti-oxidative capacity of body, tissues and cells. Kurihara and others (2009) indicated that carnosine could improve the internal oxidative stress induced by fatigue. Zhou and others (2006) indicated that the hydrolysates, obtained from hydrolysis of chicken protein by alkaline protease, possess notable clearing activity of hydroxyl and superoxide free radicals. Lai and Guo (1999) indicated that carnosine extracted from chicken meat has LPO inhibiting effects. The anti-oxidant activity of carnosine is related with the reductive and metal chelating characteristic (Kohen and others 1988). Carnosine can form non-reactive adducts with various free radicals such as lipid peroxyl radicals and hydroxyl radicals, thus demonstrating a strong free radicals capture ability (Salim-Hanna and others 1991). Carnosine also possesses non-enzymatic glycating activity (Hipkiss and Chana 1998). As carnosine can competitively react with aldehydes and ketones, it can lower the content of active carbonyls, inhibit protein cross-linking and relieve the damaging effects of free radical to biomacromelecules. We have confirmed that, although in vitro anti-oxidant activity of carnosine is not obvious, oral administration of carnosine shows apparent anti-oxidant and anti-stress effects (unpublished data). However, the mechanisms of action still need further investigation in the future.
Besides, Wu and others (2011) had reported the effect of chicken essence on the adaptation of circadian clocks to experimental jet lag in rats. They found that chicken essence markedly facilitated the re-entrainment of all examined clock genes (Bmal1, Cry1, Per1, and Per2) in the pineal gland, reduced from 7 d to only 3 to 5 d. In the liver clock, chicken essence was also indicated to shorten the resetting of Bmal1 and Per2 by nearly 2 d. However, the resetting rate of locomotor activity rhythm was not affected by chicken essence, suggesting that it might be unable to affect behavioral rhythm.
Moreover, chicken essence is a traditional functional food, which is rich in diversified nutrients, flavor, and it can enhance appetite and help digestion. Its function is being paid attention in clinical nutrition. The clinical results of Wang (2006) confirmed that chicken essence used in the process of enteral nutrition therapy could improve patients’ health. Another research indicated that chicken essence can effectively protect intestinal functions and reduce the occurrence of complications during enteral nutrition therapy (Wang 2007). In addition, chicken essence also has other physiologic functions such as improving physical fitness in athletes and enhancing responsiveness of the brain.