PROTEASE OBTENTION USING BACILLUS SUBTILIS 3411 AND AMARANTH SEED MEAL MEDIUM AT DIFFERENT AERATION RATES
IMIQA (Instituto de Investigación y Desarrollo en Microbiología y Química Aplicada), Facultad de Ciencias Exactas y Naturales, UNLPam, Santa Rosa, La Pampa, Argentina.
Submitted: September 23, 1999; Returned to authors for corrections: February 04, 2000; Approved: March 07, 2001
ABSTRACT
The influence of the addition of Amaranthus cruenthus seed meal to the medium, as nutrient and growth factor, on protease production by Bacillus subtilis 3411 was studied. Tests were carried out in a rotary shaker and in mechanically stirred fermenters. The influence of aeration was also evaluated. The addition of amaranth in a concentration of 20 g/L resulted in 400% increase in protease production. Aeration up to 750 r.p.m. and 1 L/L.min had a favorable effect.
Key words: Proteases, Bacillus subtilis, amaranth, fermentation
INTRODUCTION
The bacterial proteases have found wide scale industrial application. Industries in which proteases are used include the pharmaceutical industry, the leather industry, the manufacture of protein hydrolizates, the food industry and the waste processing industry. The aim of this work was to improve the production of alcaline protease by Bacillus subtilis 3411. Using a recommended medium (1, 8, 9), the effect of amaranth seed meal at different aeration rates on the enzymatic protease levels achieved in rotary shakers and stirred fermenter was studied. Amaranth seed meal is a pseudocereal which contains a good aminoacid distribution and a high level content of several vitamins, (2, 3, 4, 7, 11). Addition of amaranth seed meal as growth factor in the culture medium can be an important procedure for optimization of the process.
Finally, using a balanced amaranth seed meal medium, the effect of aeration conditions on the protease formation was evaluated.
MATERIALS AND METHODS
Microorganism A strain of Bacillus subtilis NRRL 3411 kept in the medium Nº 1 (Table 1) as spores in peat was used. The peat, 200 mesh, was adjusted to a 12% humidity content. Five gram portions were put into tubes and sterilized at 121ºC for 3 hours. Once the sterilization process was over, the mixture was impregnated with 3 mL spore suspension obtained in medium Nº 1 (Table 1). Tubes were hermetically sealed by either a threaded cap or a plastic film cover upon cotton caps. Tubes were stored at 5ºC.
Media
Culture media are shown in Table 1. The medium used in process, Nº 3, was modified with the addition of Amaranthus cruenthus seed meal, 200 mesh. This material was used in different concentrations (g/L): 10; 20; 40; 60, 80.
Inocula
Each flask was inoculated with a peat-kept spore suspension in 5 mL sterilized distilled water, previously exposed to 10 minute, 100ºC thermal shock. (5, 13, 15).
Operating conditions
Inocula were developed in 250 mL Erlenmeyer flasks containing 50 mL of culture medium. Processes were carried out in 500 mL Erlenmeyer flasks containing 100 mL of culture medium incubated for 72 hours in a rotary shaker (250 r.p.m. and eccentricity 2.5 cm). In all these experiments culture media and containers were sterilized at 121ºC for 20 minutes. Assays in fermenter were carried out at different stirring conditions, namely: 350; 750 and 1000 r.p.m., the aeration rate was 1 L/L. Min. Fermentation studies were performed in a 5 liter New Brunswick stirred fermenter using 3 L of culture medium. A connection to monitors allowed the following measurements and control measures to be obtained, namely: pH, temperature and stirring, dissolved oxygen partial pressure, and foam control by means of an automatic addition process of an antifoam silicone agent through a peristaltic pump.
Amaranthus cruenthus seed meal was used, previously milled to 200 mesh.
Cell growth
Microbial growth was determined by optical density units (650 nm) and by dry weight. A 10 mL sample was taken and centrifuged at 5000 g for 20 minutes. Precipitate was washed with distilled water twice. Precipitate was then resuspended in water and dried at 100ºC until constant weight.
Determination of alcaline protease activity
To determine the alcaline protease activity of culture media, ANSON modified method was used (8). ANSON modified enzyme unit, uAPAM, is defined as that quantity of enzyme which produces soluble fragments in tricloroacetic acid 0.2 M equivalent to 0.5 µg tyrosine at 37ºC in 10 minutes.
Consumption of lactose
To determine lactose concentration in the culture medium, Miller's spectrophotometric method, which measures reducing sugar, was used (10).
Determining cell oxygen demand and Q02 respiratory coefficient
The oxygen demand was measured in a Warburg respirometer at 28ºC (14).
Oxygen absorption rate
The oxygen absorption rate (OAR) was measured by the sulphite method (10).
Dissolved Oxygen
The dissolved oxygen was measured with a sterilizable silver-lead galvanic probe.
RESULTS
For tests carried out in rotary shaker, cell oxygen demand was in the order of 240 mL O2/L.h for dry weight concentrations of 8.4 g/L and oxygen dissolution values were in the order of 500 mL O2/L.h
Table 2 shows results obtained in tests carried out in stirred erlenmeyers. In these experiments the influence of adding different concentrations of amaranth seed meal: 10; 20; 40; 60 and 80 g/L to a medium Nº 3, as shown in Table 1, which is used in turn as control, was considered.
It was observed that highest values of protease were obtained when a concentration of 20 g/L was added to the medium. Higher concentrations of amaranth seed meal showed lower enzyme activity, specific production and productivity, whereas biomass concentration, yields and specific growth rate were similar.
On the basis of results obtained in rotary shaker stirred erlenmeyers flasks, using the process medium with the addition of 20 g/L amaranth seed meal, new experiments were carried out in a stirred fermenter. The influence of aeration over process productivity was studied, using different stirring conditions and an air rate of 1 L/L min (Table 3). Oxygen dissolution rates used were similar and higher than those determined by rotary shaker, 529 mL O2/L.h. Those values were for 350 r.p.m. = 562.43 mL O2/L.h; for 750 r.p.m. = 2691 mL O2/L.h and for 1000 r.p.m. = 5011 mL O2/L.h. Fig. 1 show results obtained in these series of experiments. Table 3 also shows that the highest value of enzyme production was obtained at 750 r.p.m. with a protease level in the order of 11600 uAPAM/mL of culture, a specific growth rate of 0.029 1/h, a yield of 0.43 grams of biomass for lactose gram consumed, a biomass of 7.8 g/L of culture, specific production of 1487179.5 uAPAM for biomass gram, productivity of 161111.1 uAPAM for litre of fermented culture for hour. In all processes the evolution of pH values was almost near pH 7.
DISCUSSION
The considerable increase (400%) in production of proteases in rolary shakers, should be assigned to the important contribution of amino acids and vitamins from amaranth seed meal (3).
The protease synthesized by Bacillus subtilis NRRL 3411 has a molecular weight of 27400 d and 275 amino acid residues, with a large proportion of aspartic acid, serine, glicine, alanine and valine (8). With reference to the amaranth composition, the components of the material used in our studies in g/100 g of protein were: aspartic acid, 2.8; serine, 2.3; glycine, 2.7; alanine, 1.3 and valine, 1.5. Thus, in the presence of amaranth seed meal, there will not be a limitation for these amino acids as might occur in media obtained from traditional sources. Besides, the content of vitamins (mg/100 dry weight) was thiamine, 0.07; riboflavin, 0.19; folic acid, 43.80 and ascorbic acid, 4.90 (4).
Adding amaranth seed meal in concentrations higher than 20 g/L did not produce an increase in enzyme production. This could be due either to the increase in the viscosity of the fermenting medium, limiting transference phenomena both of oxygen and metabolites, or to the fact that under such conditions, an inhibitory effect might occur due to an increase in amino acid concentration provided by amaranth.
If the results obtained in fermenters for similar oxygen dissolution rates are compared to those obtained in rotary shakers, 350 r.p.m., they will correspond, as expected, to equal rates of specific production. The highest enzyme values, obtained at 750 r.p.m., may be assigned to a greater oxygen availability in the culture medium where oxygen pressure was never below 30% of the saturation value as can be seen in Fig. 1.
However, higher agitation rates, 1000 r.p.m., increased the system's oxygen pressure but did not bring about production increase due, probably, at a high agitation rate, enzyme structure would be altered (12).
ACKNOWLEDGEMENTS
We thank the Facultad de Ciencias Exactas y Naturales, UNLPam, for finantial support.
RESUMO
Obtenção de protease usando Bacillus subtilis 3411 e meio com farinha de semente de Amaranthus em diferentes condições de aeração
Neste trabalho estudou-se a produção de proteases a partir de Bacillus subtilis 3411 cultivado em um meio no qual adicionou-se farinha de semente de Amaranthus cruentus como fonte de nutrientes e fatores de crescimento. As experiências foram realizadas em Erlenmeyers com agitador em fermentador de laboratório. Além disso, considerou-se a influência da aeração sobre a produção enzimática. A adição de amaranto em uma concentração de 20 g/L produziu um aumento de 400% no nível de proteases. A aeração das culturas teve um efeito favorável até valores de 750 r.p.m. empregando um fluxo de ar de 1 L/L. min.
Palavras-chave: Proteases, Bacillus subtilis, amaranto, fermentação
REFERENCES
1. Balatti, A.P. Producción de enzimas. Primer Simposio Interamericano sobre Biotecnología de Enzimas, México, 1984, p.89-107. [ Links ] 2. Becker, R. Amaranth Oil: Composition, processing and nutritional qualities. In: O. Paredes-López (ed). Amaranth Biology, Chemistry and Thechnology. U.S.A., 1994, p.133-140. [ Links ] 3. Bressani, R. Grain amaranth. Its chemical composition and nutritive value. Proceeding of the Fourth National Amaranth Simposium. Perspectives on Production, Processing and Marketing, Minnesota, 1990, p.23-25. [ Links ] 4. Bressani, R. Composition and Nutritional Properties of Amaranth. In: O. Paredes-López (ed). Amaranth. Biology, Chemistry and Technology. U.S.A, 1994, p.185-206. [ Links ] 5. Chiasson, P.; Zamenhof, L.P. Studies of induction mutations by heat in spores of Bacillus subtilis. J. Microbiol., Vol. 12, 1966. [ Links ] 6. Cooper, C.M.; Ferston, G.; Miller, S.A. Gas Liquid Contactor. Ind. Eng. Chem., 36 : 504-509, 1944. [ Links ] 7. Covas, G. Revista Amarantos. Novedades e Informaciones. Estación Experimental Agropecuaria Anguil, INTA, Facultad de Agronomía, UNLPam, Argentina, 19: 1-12, 1995. [ Links ] 8. Kelly, C.; Fogarty, W. Microbial alcaline enzimes. Proc. Biochem., 7: 3-9, 1976. [ Links ] 9. Massucco, A.E.; Mazza, L.A.; Balatti, A.P. Obtención de preparados enzimáticos destinados a la depilación de pieles. Biotecnología de Enzimas. Primer Simposio Interamericano sobre Biotecnología de Enzimas, México, 1981, p.271-277. [ Links ] 10. Miller, G.L. Use of dinitrosalicylic acid reagent for determination of reducing sugar. Anal. Chem., 31 : 426-428, 1959. [ Links ] 11. Ravindran, V.; Hood, R.L.; Gill, R.J.; Kneale, C.R.; Bryden, W.L. Nutritional evaluation of grain amaranth (Amaranthus hypochondriacus) in broiler diets. A.F. Sci. Technol., 63 : 323-331, 1996. [ Links ] 12. Roychoudhury S.; Parulekar S.J.; Weigand W.A. Cell Growth and a-Amylase Production Characteristics of Bacillus amyloliquefaciens. Biotechnol. Bioeng., 33 : 197-206, 1988. [ Links ] 13. Ruzal, S.; Sanchez Rivas, J. Physiological and genetic characterization of the osmotic stress response in Bacillus subtilis. Can. J. Microbiol., 40 : 140-144, 1993. [ Links ] 14. Umbreit, W.W.; Burris R.H.; Sauffer J.S. The Warburg constant volume respirometer. In: Burgues Publishing Co. Manometric and Biochemical Techniques, U.S.A., 1972, p.1-17. [ Links ] 15. Zamenhof, S. Effects of heating dry bacteria and spores on their phenotype and genotype. Proc. Natl. Acad. Sci. 46 : 101-105, 1960. [ Links ]
Tea Consumption May Improve Biomarkers of Insulin Sensitivity and Risk Factors for Diabetes
Abstract
Diabetes mellitus and its sequelae are a major and growing public health problem. The prevalence of diabetes worldwide is 194 million persons, or 5.1% of the population, and is projected to increase to 333 million, or 6.3% of the population, by 2025. Type 2 diabetes accounts for ∼90–95% of those with diabetes in the United States and other developed countries. Tea is the most widely consumed beverage in the world, second only to water. Tea contains polyphenols and other components that may reduce the risk of developing chronic diseases such as cardiovascular disease and cancer. Some evidence also shows that tea may affect glucose metabolism and insulin signaling, which, as a result, has spurred interest in the health effects of tea consumption on diabetes. Epidemiologic studies suggest some relation between tea consumption and a reduced risk of type 2 diabetes, although the mechanisms for these observations are uncertain. Findings from in vitro and animal models suggest that tea and its components may influence glucose metabolism and diabetes through several mechanisms, such as enhancing insulin sensitivity. Some human clinical studies evaluating tea and its components show improvement in glucoregulatory control and endothelial function. However, further controlled clinical trials are required to gain a better understanding of the long-term effects of tea consumption in persons with diabetes.
Introduction
Diabetes mellitus and its sequelae are a major and growing public health problem. The prevalence of diabetes worldwide is 194 million persons, or 5.1% of the population, and is projected to increase to 333 million, or 6.3% of the population, by 2025 (1,2). The number of persons with impaired glucose tolerance is estimated to increase as well. Diabetes is related to obesity, inactivity, population growth, and aging (1,3). In addition, diabetes is recognized as a group of metabolic disorders characterized by hyperglycemia and glucose intolerance as a result of insulin deficiency, impaired effectiveness of insulin action, or both (4). Type 2 diabetes accounts for ∼90–95% of those with diabetes in the United States and other developed countries. Additionally, it may account for a higher percentage in developing countries (1,5). Type 2 diabetes is frequently associated with obesity because obesity may cause insulin resistance and lead to hyperglycemia (6,7). Lifestyle strategies that include physical activity and dietary modification, such as consumption of a plant-based diet, may reduce type 2 diabetes (8). Several components of a plant-based diet may contribute to its beneficial health effects, but there has been speculation that plant polyphenols may play a role (9).
Tea is the most widely consumed beverage in the world, second only to water (10). Tea contains polyphenols and other components that may reduce the risk of developing chronic diseases such as cardiovascular disease and cancer. Some evidence also shows that tea may affect glucose metabolism and insulin signaling, which as a result has spurred interest in the health effects of tea consumption on diabetes (11). Of the tea produced worldwide, 78% is black tea, which is typically consumed in North America and Europe; 20% is green, which is favored by Asian countries; and 2% is oolong, commonly consumed in China and Taiwan (12). Black, green, and oolong teas are from the plant species Camellia sinensis. Differences among the 3 tea types result from various degrees of processing and the level of fermentation. Green tea is processed to minimize fermentation, black tea is fully fermented, and oolong tea is partially fermented. Green tea contains polyphenolic compounds knowns as catechins. A typical cup of brewed green tea contains ∼30–40% catechins, which include epicatechin, epicatechin gallate, epigallocatechin, and epigallocatechin gallate. Additionally, black tea contains catechins that are converted through fermentation to theaflavins (dimers) and thearubigins (polymers). Brewed black tea contains 3–10% catechins, 2–6% theaflavins, and >20% thearubigins. A typical cup of brewed black or green tea also contains ∼45 mg or 20 mg of caffeine, respectively (13). Short-term caffeine consumption has been shown to acutely impair glucose metabolism and insulin sensitivity (14–16); however, longer-term (>4 d) caffeine intake does not alter glucose concentrations (17,18).
Epidemiologic studies: tea consumption and risk of type 2 diabetes mellitus
Several studies have examined the relation between tea consumption and risk of type 2 diabetes. For example, Salazar-Martinez et al. (19) examined the association between tea and coffee consumption and diabetes risk in 41,934 U.S. men from the Health Professionals' Follow-up Study, aged 40–75 y, and 84,276 U.S. women from the Nurses' Health Study, aged 30–55 y, who were followed for 12 y and 18 y, respectively. Diagnosis of diabetes was from self-report on biennial follow-up questionnaires; supplementary questionnaires were subsequently sent to confirm the self-report and to distinguish among type 1, type 2, and gestational diabetes. FFQ assessing beverage and caffeine intake, were obtained at multiple time points. Participants were asked how often on average during the previous year they had consumed tea [1 cup or glass (240 mL)], caffeinated coffee, and decaffeinated coffee (1 cup), different types of caffeinated sodas (1 glass, can, or bottle), and chocolate products (bar or packet). Results showed that tea consumption was not significantly associated with diabetes risk in either cohort. There was an inverse association between coffee intake and risk of type 2 diabetes and a slight inverse association between higher consumption of decaffeinated coffee (≥4 cups/d or 960 mL/d) and diabetes risk. Total caffeine intake from coffee and other sources (cola, tea, and chocolate) was associated with a lower risk of diabetes in both men and women.
In a similar prospective cohort study, van Dam et al. (20) examined the relation among tea, coffee, and caffeine and risk of type 2 diabetes, as assessed by a FFQ at multiple time points in 88,259 U.S. women aged 26–46 y from the Nurses' Health Study II, followed for 10 y. Diagnosis of type 2 diabetes was based on self-report with follow-up questionnaires for confirmation of the disease. This study showed that tea consumption was not associated with the risk of type 2 diabetes. However, consumption of ≥2 cups/d (480 mL/d) of coffee was associated with a lower risk of type 2 diabetes; this association was similar for caffeinated and decaffeinated coffee. Higher caffeine intake was associated with a lower risk of type 2 diabetes. The authors also evaluated potential independent effects of coffee and caffeine by investigating cross-categories of coffee and caffeine intake in relation to type 2 diabetes. Higher total coffee consumption was associated with lower risk of type 2 diabetes in each category of caffeine intake; however, higher caffeine intake was not associated with risk of type 2 diabetes within categories of total coffee consumption. Therefore, the risk of type 2 diabetes and coffee consumption was shown to be independent of caffeine intake.
Although these 2 prospective cohort studies showed no association of tea consumption with risk of type 2 diabetes, several studies have suggested a beneficial effect of tea consumption on diabetes risk. A recent study examined the relation between green tea and total caffeine intake and risk of type 2 diabetes among Japanese adults (21). In this retrospective cohort study, 17,413 adults aged 40–65 y completed a 5-y follow-up questionnaire on self-reported physician-diagnosed diabetes and consumption of coffee and green, black, and oolong teas. Tea intake was assessed once, at the baseline of the study, by a FFQ. The self-reported diagnosis of diabetes was compared with fasting serum glucose concentration in a subsample of participants. Adults who consumed ≥6 cups/d (1440 mL/d) of green tea lowered their risk of diabetes by 33%. No association with diabetes risk was found for oolong or black teas. Consumption of ≥3 cups/d (720 mL/d) of coffee lowered the risk of diabetes by 42%. High caffeine intake (416 mg/d) was also associated with a 33% reduction in risk of diabetes. For green tea and caffeine consumption, a lowered diabetes risk was observed primarily in women; however, for coffee consumption, a lowered diabetes risk was observed in both men and women. The authors suggested that the inverse associations seen were mostly caused by the relation between caffeine intake and diabetes risk, because green tea and coffee (∼45% for both) are major contributors to caffeine intake in Japan. However, potential independent effects of coffee, green tea, and caffeine in relation to type 2 diabetes were not evaluated. The consumption of oolong and black teas is also low in Japan, which possibly contributes to the lack of association with diabetes.
Song et al. (22) examined the association between flavonoid intake and risk of type 2 diabetes for a large cohort of U.S. middle-aged and older women (≥45 y) from the Women's Health Study. Neither the total intake of flavonoids nor the intake of most flavonoid-rich foods was associated with risk of type 2 diabetes. Interestingly, women who consumed ≥4 cups/d (960 mL/d) of tea had a 30% lower risk of developing type 2 diabetes than did those who consumed no tea.
Greenberg et al. (23) examined the effect of caffeine and body weight change on the relation between tea and coffee intake and diabetes risk in U.S. adults from the National Health and Nutrition Examination Survey Epidemiologic Follow-up Study. Diagnosis of diabetes was from physician-diagnosed self-report. Beverage (regular tea, herbal tea, ground coffee, ground decaffeinated coffee, instant coffee, instant decaffeinated coffee, and cola) and caffeine intake were assessed once, at baseline of the study, by a FFQ. Increased intake of regular tea and ground coffee was inversely associated with diabetes risk for adults ≤60 y of age who lost weight during the study. No association of diabetes risk was observed for herbal tea or instant coffee. When adults >60 y were included in the analysis, the inverse association between tea and diabetes risk was lost. The authors noted that this association did not appear to be caused by caffeine because regular tea consumption remained significant after the effects of caffeine were taken into account. This suggests that another tea component(s) may have contributed to diabetes risk reduction.
Data from these epidemiologic studies are limited, and the results are inconsistent. There is some evidence that tea consumption is associated with reduced risk of type 2 diabetes; however, 2 large U.S. cohort studies (the Health Professionals' Follow-up Study and the Nurses' Health Study) did not detect an association. The lack of an association may have been because of an inadequate number of persons drinking enough tea to detect a beneficial effect within the population. Several limitations exist for cohort studies examining the relation between tea consumption and type 2 diabetes. First, the majority of the cohort studies, with the exception of the study conducted in Japan, failed to provide detailed information about tea consumption, such as tea type, cup size, and preparation. Second, the diagnosis of diabetes was determined from self-report; few studies utilized serum biomarkers to verify the diagnosis. Diabetes may have been underreported, potentially affecting the relative risk and the relation between tea consumption and diabetes. Finally, retrospective self-report of dietary intake is susceptible to reporting bias. It may be doubtful that intake measured in the past accurately reflects long-term intake. As tea and its components, such as epigallocatechin gallate, become more pervasive in the food supply, it will be much more difficult to assess dietary intake.
Potential mechanisms of action
Findings from both in vitro and animal models suggest several mechanisms by which tea and its components may influence glucose metabolism and diabetes (24). Tea catechins inhibit the carbohydrate digestive enzymes α-amylase, intestinal sucrase, and α-glucosidase in the intestines of rats, which suggests that glucose production may be decreased in the gut, thus lowering glucose and insulin concentrations (25,26). Tea may also increase insulin sensitivity and insulinotropic activity (27,28). Black, green, and oolong teas were shown to enhance insulin sensitivity by increasing insulin-stimulated glucose uptake in adipocytes. Tea components, including epigallocatechin gallate, epicatechin gallate, tannins, and theaflavins, may be involved in enhancing insulin action (29). Green tea has also been shown to enhance the insulin sensitivity of normal and fructose-fed rats, improving glucose uptake by the myocytes, enhancing insulin binding to the adipocytes, and increasing the expression of intracellular glucose transporters in the myocytes (30,31). Finally, green tea and epigallocatechin gallate may prevent damage to the liver, kidney, and pancreatic β-cells (24,32).
Human studies: clinical interventions
Several human clinical interventions have examined the effects of tea consumption on biomarkers of glucoregulatory control (Table 1). Men and women from Taiwan with physician-diagnosed type 2 diabetes, taking oral glucose-lowering medications, consumed 1.5 L oolong tea or water daily along with their typical diet in a randomized crossover design for 4 wk. Subjects were instructed to consume the oolong tea 5 times/d. Food intake and physical activity were assessed by 24-h dietary recalls and pedometers. Components of oolong tea and caffeine were reported. Oolong tea lowered fasting plasma glucose and fructosamine concentrations from 229 ± 54 mg/dL (13 ± 3 mmol/L) to 162 ± 30 mg/dL (9 ± 2 mmol/L) and from 409 ± 96 μmol/L to 323 ± 56 μmol/L, respectively, whereas no changes in biomarkers were seen in the group that consumed water. The authors noted that the mechanism of the hypoglycemic effect of oolong tea is not fully understood (33). Limitations of this study included failure to control for caffeine and dietary intake.
View this table:
TABLE 1
Summary of clinical trials on the effects of tea consumption on biomarkers of glucoregulatory control
Only a limited number of studies have been conducted to evaluate the effects of black tea on glucoregulatory biomarkers. Recently, in a short-term randomized crossover trial, healthy British men and women consumed 75 g glucose in either 250 mL of water (control), 250 mL of water with caffeine (matched for the 1 g of instant black tea), or 250 mL water plus 1 g or 3 g of instant black tea. Blood samples were collected at fasting and then at 30-min intervals for 150 min after treatment ingestion. Results from only 3 treatments were reported because the 3 g of instant black tea caused emesis and tachycardia in the subjects. After consumption of the 1 g of black tea, plasma glucose was lowered at 120 min compared with the control and caffeinated treatments. Insulin concentrations were higher compared with the caffeine and the control treatments at 90 min and compared with the caffeine treatment alone at 150 min. The authors suggested that black tea can influence postprandial glycemia by inhibiting intestinal glucose transport and enhancing insulin secretion by the pancreatic β-cells. The study was well designed; it accounted for caffeine as a confounding variable. This study included young healthy adults; further research is required to gain a better understanding of both the acute and long-term effects of black tea on glucose metabolism in those with diabetes (34).
Human studies evaluating the effects of green tea consumption on glucoregulatory biomarkers are inconsistent. Fukino et al. (35) conducted a randomized controlled trial examining the effects of green tea extract supplementation on glucose metabolism and insulin sensitivity. Overweight Japanese men and women with borderline diabetes (not taking oral glucose-lowering medications) consumed green tea extract containing 544 mg polyphenols and 102 mg caffeine dissolved in hot water daily for 8 wk along with their usual diet. The subjects were asked to consume the treatment with meals and snacks. Food intake was assessed by 24-h dietary recalls at baseline, 4 wk, and 8 wk. The results showed that daily supplementation with the green tea extract lowered hemoglobin A1C, although very small changes were observed. No significant changes were reported in fasting glucose concentrations, insulin concentrations, or homeostasis model assessment of insulin resistance values. The study limitations included not controlling for caffeine or dietary intake and exclusion of a washout period. Ryu et al. (36) examined the effects of green tea consumption on insulin resistance in a randomized crossover design. South Korean men and women with physician-diagnosed type 2 diabetes consumed either 900 mL water with 9 g of green tea or water without tea for 4 wk along with their typical diet. No significant changes were observed in fasting glucose concentrations, insulin concentrations, or homeostasis model assessment of insulin resistance values. The previous studies failed to detect effects on glucose and insulin concentrations in fasting samples. This observation raises the question of whether biomarkers should be evaluated after tea consumption because dietary polyphenols are so rapidly metabolized. For example, after consumption of green tea, catechin concentrations in human plasma have been shown to reach their peak within 1.5 to 2 h and to decline to undetectable levels after 24 h (37). Measuring the effects of tea after a 12-h fast may produce inconsistent results.
Diabetes causes both microvascular (retinopathy, nephropathy, and neuropathy) and macrovascular (myocardial infarction and stroke) complications (7). Black tea may help to reverse some vascular complications, such as endothelial dysfunction. In 1 study, U.S. adults with coronary artery disease were randomly assigned to consume black tea or water in a crossover design. Short-term and long-term effects of tea consumption on brachial artery flow-mediated dilation were measured after 2 h and 4 wk, respectively. Both short-term and long-term tea consumption improved endothelium-dependent flow-mediated dilation of the brachial artery. Adults with diabetes were included as participants in the study; thus, black tea consumption may improve endothelial function in persons with diabetes (38).
Few clinical trials have examined the effects of tea consumption on biomarkers of glucoregulatory control in persons with diabetes. The majority of the clinical trials, with the exception of the study from Britain, failed to control for caffeine consumption. Additionally, the studies did not control for dietary intake; other dietary components may have influenced study outcomes. Tea components were reported in only 1 clinical study; future clinical trials should further describe tea and its components. Clinical trials should be appropriately designed to control for caffeine intake and other confounding variables such as diet and lifestyle. Additional controlled clinical trials are also required to confirm the health effects of tea and its components, including the dose of polyphenols and the duration of consumption, on glucose metabolism in persons with diabetes.
Because of the increased consumption of tea and rising global rates of diabetes, it is important to clearly establish tea's association with diabetes risk. Epidemiologic evidence suggests some relation between caffeine and tea consumption and reduced risk of type 2 diabetes. Further well-designed epidemiological studies should provide more detailed information about tea consumption, such as type, cup size, and preparation. Findings from in vitro and animal models suggest that tea and its components may influence glucose metabolism and diabetes through several mechanisms, such as enhancing insulin sensitivity. Some human clinical studies evaluating tea and its components show improvement in glucoregulatory control and endothelial function. However, further controlled clinical trials are required to gain a better understanding of the long-term effects of tea consumption in persons with diabetes.
Footnotes
·Published in a supplement to The Journal of Nutrition. Presented at the conference “Fourth International Scientific Symposium on Tea and Human Health,” held in Washington, DC at the U.S. Department of Agriculture on September 18, 2007. The conference was organized by the Tea Council of the U.S.A., and was cosponsored by the American Cancer Society, the American College of Nutrition, the American Medical Women's Association, the American Society for Nutrition, and the Linus Pauling Institute. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the Tea Council of the U.S.A. or the cosponsoring organizations. Supplement coordinators for the supplement publication were Lenore Arab, University of California, Los Angeles, CA and Jeffrey Blumberg, Tufts University, Boston, MA. Supplement coordinator disclosure: L. Arab and J. Blumberg received honorarium and travel support from the Tea Council of the U.S.A. for cochairing the Fourth International Scientific Symposium on Tea and Human Health and for editorial services provided for this supplement publication; they also serve as members of the Scientific Advisory Panel of the Tea Council of the U.S.A.
LITERATURE CITED
1. 1.↵
International Diabetes Federation. Diabetes atlas. Brussels: International Diabetes Federation. 2008 [cited 2008 Jan 20]. Available from: http://www.idf.org.
2. 2.↵
Boyle JP, Honeycutt AA, Narayan KM, Hoerger TJ, Geiss LS, Chen H, Thompson TJ. Projection of diabetes burden through 2050: impact of changing demography and disease prevalence in the U.S. Diabetes Care. 2001;24:1936–40.
3. 3.↵
Wild S, Roglic G, Green A, Sicree R, King H. Global prevalence of diabetes: estimates for the year 2000 and projections for 2030. Diabetes Care. 2004;27:1047–53.
4. 4.↵
Reaven GM. Pathophysiology of insulin resistance in human disease. Physiol Rev. 1995;75:473–86.
5. 5.↵
Cowie CC, Rust KF, Byrd-Holt DD, Eberhardt MS, Flegal KM, Engelgau MM, Saydah SH, Williams DE, Geiss LS, Gregg EW. Prevalence of diabetes and impaired fasting glucose in adults in the U.S. population: National Health and Nutrition Examination Survey 1999–2002. Diabetes Care. 2006;29:1263–8.
6. 6.↵
American Diabetes Association. Diagnosis and classification of diabetes mellitus. Diabetes Care. 2006;29: Suppl 1:S43–8.
7. 7.↵
American Diabetes Association. Standards of medical care in diabetes–2007. Diabetes Care. 2007;30: Suppl 1:S4–41.
8. 8.↵
Biesalski HK. Diabetes preventive components in the Mediterranean diet. Eur J Nutr. 2004;43 Suppl 1:I/26–30.
9. 9.↵
Willett WC. The Mediterranean diet: science and practice. Public Health Nutr. 2006;9:105–10.
10. 10.↵
Higdon JV, Frei B. Tea catechins and polyphenols: health effects, metabolism, and antioxidant functions. Crit Rev Food Sci Nutr. 2003;43:89–143.
11. 11.↵
Khan N, Mukhtar H. Tea polyphenols for health promotion. Life Sci. 2007;81:519–33.
12. 12.↵
Yang CS, Landau JM. Effects of tea consumption on nutrition and health. J Nutr. 2000;130:2409–12.
13. 13.↵
Balentine DA, Wiseman SA, Bouwens LC. The chemistry of tea flavonoids. Crit Rev Food Sci Nutr. 1997;37:693–704.
14. 14.↵
Greer F, Hudson R, Ross R, Graham T. Caffeine ingestion decreases glucose disposal during a hyperinsulinemic-euglycemic clamp in sedentary humans. Diabetes. 2001;50:2349–54.
15. 15.
Keijzers GB, De Galan BE, Tack CJ, Smits P. Caffeine can decrease insulin sensitivity in humans. Diabetes Care. 2002;25:364–9.
16. 16.↵
Lane JD, Feinglos MN, Surwit RS. Caffeine increases ambulatory glucose and postprandial responses in coffee drinkers with type 2 diabetes. Diabetes Care. 2008;31:221–2.
17. 17.↵
Astrup A, Breum L, Toubro S, Hein P, Quaade F. The effect and safety of an ephedrine/caffeine compound compared to ephedrine, caffeine and placebo in obese subjects on an energy restricted diet. A double blind trial. Int J Obes Relat Metab Disord. 1992;16:269–77.
18. 18.↵
van Dam RM, Pasman WJ, Verhoef P. Effects of coffee consumption on fasting blood glucose and insulin concentrations: randomized controlled trials in healthy volunteers. Diabetes Care. 2004;27:2990–2.
19. 19.↵
Salazar-Martinez E, Willett WC, Ascherio A, Manson JE, Leitzmann MF, Stampfer MJ, Hu FB. Coffee consumption and risk for type 2 diabetes mellitus. Ann Intern Med. 2004;140:1–8.
20. 20.↵
van Dam RM, Willett WC, Manson JE, Hu FB. Coffee, caffeine, and risk of type 2 diabetes: a prospective cohort study in younger and middle-aged U.S. women. Diabetes Care. 2006;29:398–403.
21. 21.↵
Iso H, Date C, Wakai K, Fukui M, Tamakoshi A. The relationship between green tea and total caffeine intake and risk for self-reported type 2 diabetes among Japanese adults. Ann Intern Med. 2006;144:554–62.
22. 22.↵
Song Y, Manson JE, Buring JE, Sesso HD, Liu S. Associations of dietary flavonoids with risk of type 2 diabetes, and markers of insulin resistance and systemic inflammation in women: a prospective study and cross-sectional analysis. J Am Coll Nutr. 2005;24:376–84.
23. 23.↵
Greenberg JA, Axen KV, Schnoll R, Boozer CN. Coffee, tea and diabetes: the role of weight loss and caffeine. Int J Obes (Lond). 2005;29:1121–9.
24. 24.↵
Kao YH, Chang HH, Lee MJ, Chen CL. Tea, obesity, and diabetes. Mol Nutr Food Res. 2006;50:188–210.
25. 25.↵
Kobayashi Y, Suzuki M, Satsu H, Arai S, Hara Y, Suzuki K, Miyamoto Y, Shimizu M. Green tea polyphenols inhibit the sodium-dependent glucose transporter of intestinal epithelial cells by a competitive mechanism. J Agric Food Chem. 2000;48:5618–23.
26. 26.↵
Shimizu M, Kobayashi Y, Suzuki M, Satsu H, Miyamoto Y. Regulation of intestinal glucose transport by tea catechins. Biofactors. 2000;13:61–5.
27. 27.↵
Kao YH, Hiipakka RA, Liao S. Modulation of endocrine systems and food intake by green tea epigallocatechin gallate. Endocrinology. 2000;141:980–7.
28. 28.↵
Waltner-Law ME, Wang XL, Law BK, Hall RK, Nawano M, Granner DK. Epigallocatechin gallate, a constituent of green tea, represses hepatic glucose production. J Biol Chem. 2002;277:34933–40.
29. 29.↵
Anderson RA, Polansky MM. Tea enhances insulin activity. J Agric Food Chem. 2002;50:7182–6.
30. 30.↵
Wu LY, Juan CC, Ho LT, Hsu YP, Hwang LS. Effect of green tea supplementation on insulin sensitivity in Sprague-Dawley rats. J Agric Food Chem. 2004;52:643–8.
31. 31.↵
Wu LY, Juan CC, Hwang LS, Hsu YP, Ho PH, Ho LT. Green tea supplementation ameliorates insulin resistance and increases glucose transporter IV content in a fructose-fed rat model. Eur J Nutr. 2004;43:116–24.
32. 32.↵
Crespy V, Williamson G. A review of the health effects of green tea catechins in in vivo animal models. J Nutr. 2004;134:3431S–40S.
33. 33.↵
Hosoda K, Wang MF, Liao ML, Chuang CK, Iha M, Clevidence B, Yamamoto S. Antihyperglycemic effect of oolong tea in type 2 diabetes. Diabetes Care. 2003;26:1714–8.
34. 34.↵
Bryans JA, Judd PA, Ellis PR. The effect of consuming instant black tea on postprandial plasma glucose and insulin concentrations in healthy humans. J Am Coll Nutr. 2007;26:471–7.
35. 35.↵
Fukino Y, Ikeda A, Maruyama K, Aoki N, Okubo T, Iso H. Randomized controlled trial for an effect of green tea-extract powder supplementation on glucose abnormalities. Eur J Clin Nutr. 2007 Jun 6 [Epub ahead of print].
36. 36.↵
Ryu OH, Lee J, Lee KW, Kim HY, Seo JA, Kim SG, Kim NH, Baik SH, Choi DS, Choi KM. Effects of green tea consumption on inflammation, insulin resistance and pulse wave velocity in type 2 diabetes patients. Diabetes Res Clin Pract. 2006;71:356–8.
37. 37.↵
Henning SM, Niu Y, Lee NH, Thames GD, Minutti RR, Wang H, Go VL, Heber D. Bioavailability and antioxidant activity of tea flavanols after consumption of green tea, black tea, or a green tea extract supplement. Am J Clin Nutr. 2004;80:1558–64.
38. 38.↵
Duffy SJ, Keaney JF Jr, Holbrook M, Gokce N, Swerdloff PL, Frei B, Vita JA. Short- and long-term black tea consumption reverses endothelial dysfunction in patients with coronary artery disease. Circulation. 2001;104:151–6.
39. 39.↵
Arab L, Blumberg JB. Introduction to the Proceedings of the Fourth International Scientific Symposium on Tea and Human Health. J Nutr. 2008;138:1526S–8S.
40. 40.
Henning SM, Choo JJ, Heber D. Nongallated compared with gallated flavan-3-ols in green and black tea are more bioavailable. J Nutr. 2008;138:1529S–34S.
41. 41.
Auger C, Mullen W, Hara Y, Crozier A. Bioavailability of polyphenon E flavan-3-ols in humans with an ileostomy. J Nutr. 2008;138:1535S–42S.
42. 42.
Song WO, Chun OK. Tea is the major source of flavan-3-ol and flavonol in the U.S. diet. J Nutr. 2008;138:1543S–7S.
43. 43.
Kuriyama S. The relation between green tea consumption and cardiovascular disease as evidenced by epidemiological studies. J Nutr. 2008;138:1548S–53S.
44. 44.
Grassi D, Aggio A, Onori L, Croce G, Tiberti S, Ferri C, Ferri L, Desideri G. Tea, flavonoids, and NO-mediated vascular reactivity. J Nutr. 2008;138:1554S–60S.
45. 45.
Arts ICW. A review of the epidemiological evidence on tea, flavonoids, and lung cancer. J Nutr. 2008;138:1561S–6S.
46. 46.
Hakim IA, Chow HHS, Harris RB. Green tea consumption is associated with decreased DNA damage among GSTM1 positive smokers regardless of their hOGG1 genotype. J Nutr. 2008;138:1567S–71S.
47. 47.
Kelly SP, Gomez-Ramirez M, Montesi JL, Foxe JJ. L-Theanine and caffeine in combination affect human cognition as evidenced by oscillatory alpha-band activity and attention task performance. J Nutr. 2008;138:1572S–7S.
48. 48.↵
Mandel SA, Amit T, Kalfon L, Reznichenko L, Youdim MBH. Targeting multiple neurodegenerative diseases etiologies with multimodal-acting green tea catechins. J Nutr. 2008;138:1578S–83S.
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