The reference beverage, an oral glucose solution containing 50 g available carbohydrate, was prepared as 54.9 g Glucodin™ powder (iNova Pharmaceuticals Aust Pty Ltd., NSW, Australia) dissolved in 250 ml water (Table 1 ). The reference beverage was consumed by each participant on three separate occasions (sessions 1, 4, and 6). In addition, participants also tested three different beverage treatments which were consumed with a standardised, high GI meal. A computer-generated research randomiser program determined the randomised consumption order for each of the three meal-with-beverage treatments. Each meal and beverage treatment was consumed on one occasion, with at least 1 day in between consecutive test sessions.
The three beverage treatments were; 330 ml of soda water (Schweppes™, Asahi Beverages, VIC, Australia) that served as a placebo control, diet lemonade soft drink (Schweppes™ Zero Sugar, Asahi Beverages, VIC, Australia), and organic kombucha (The Good Brew Company Pty Ltd., VIC, Australia). The kombucha, which was made from spring water, organic oolong and green tea along with organic sugar, contained a highly complex mix of 200 probiotic species and a high concentration of polyphenols that have been previously characterised (19 (link)). The 330 ml of kombucha beverage contributed an additional 3 g of available carbohydrate (1.7 g of which was sugar) to the test meal, while the soda water and diet lemonade did not contain any sugar. The nutritional compositions of the three meal-with-beverage treatments are shown inTable 1 . The standardised meal provided 50 g available carbohydrate from microwave Jasmine rice (147.2 g, SunRice™, Ricegrowers Ltd., NSW, Australia), with an additional 2.9 g available carbohydrate provided by green peas (20 g, McCain’s™, McCain Foods Aust. Pty Ltd., VIC, Australia) and soy sauce (10 g, Kikkoman Corporation).
The test portion of microwave Jasmine rice and frozen green peas were combined together in a bowl and cooked in the microwave for 1 min on high. The soy sauce was then added to the prepared meal and immediately served to a participant with the appropriate refrigerated test beverage (soda water, diet soft drink or kombucha). The participants were required to consume all food and fluid served and were instructed to consume the test beverage with the meal (ie. alternate mouthfuls of meal and beverage).
Participants were required to consume a carbohydrate-based evening meal, excluding legumes and alcohol, on the evening prior to each test session. On the morning of each session, participants arrived following a 10–12 h overnight fast. Two capillary blood samples (≥0.5 ml blood) were collected from a warmed hand into heparin-coated tubes in the fasted state (−5 and 0 min). Participants then consumed either the reference glucose solution or one of the test meal-with-beverage treatments within 12 min. Additional capillary blood samples were collected at regular intervals (15, 30, 45, 60, 90, and 120 min) after commencement of the reference solution or test meal. Participants were required to remain seated with minimal movement throughout each 120 min test session.
Each capillary blood sample was centrifuged at 10,000xg for 45 s immediately after collection. The plasma layer was then transferred into an uncoated tube and stored at −30°C for later glucose and insulin analysis. Plasma glucose concentration was measured in duplicate using a glucose hexokinase assay (Beckman Coulter Inc.) on an automatic centrifugal spectrophotometric clinical chemistry analyser (Beckman Coulter AU480®, Beckman Instruments Inc., United States). Plasma insulin concentration was measured using an insulin sandwich type enzyme-linked immunoassay (Insulin ELISA kit, ALPCO®, Salem, NH, United States). All samples for a given participant were analysed within the same assay.
The three beverage treatments were; 330 ml of soda water (Schweppes™, Asahi Beverages, VIC, Australia) that served as a placebo control, diet lemonade soft drink (Schweppes™ Zero Sugar, Asahi Beverages, VIC, Australia), and organic kombucha (The Good Brew Company Pty Ltd., VIC, Australia). The kombucha, which was made from spring water, organic oolong and green tea along with organic sugar, contained a highly complex mix of 200 probiotic species and a high concentration of polyphenols that have been previously characterised (19 (link)). The 330 ml of kombucha beverage contributed an additional 3 g of available carbohydrate (1.7 g of which was sugar) to the test meal, while the soda water and diet lemonade did not contain any sugar. The nutritional compositions of the three meal-with-beverage treatments are shown in
The test portion of microwave Jasmine rice and frozen green peas were combined together in a bowl and cooked in the microwave for 1 min on high. The soy sauce was then added to the prepared meal and immediately served to a participant with the appropriate refrigerated test beverage (soda water, diet soft drink or kombucha). The participants were required to consume all food and fluid served and were instructed to consume the test beverage with the meal (ie. alternate mouthfuls of meal and beverage).
Participants were required to consume a carbohydrate-based evening meal, excluding legumes and alcohol, on the evening prior to each test session. On the morning of each session, participants arrived following a 10–12 h overnight fast. Two capillary blood samples (≥0.5 ml blood) were collected from a warmed hand into heparin-coated tubes in the fasted state (−5 and 0 min). Participants then consumed either the reference glucose solution or one of the test meal-with-beverage treatments within 12 min. Additional capillary blood samples were collected at regular intervals (15, 30, 45, 60, 90, and 120 min) after commencement of the reference solution or test meal. Participants were required to remain seated with minimal movement throughout each 120 min test session.
Each capillary blood sample was centrifuged at 10,000xg for 45 s immediately after collection. The plasma layer was then transferred into an uncoated tube and stored at −30°C for later glucose and insulin analysis. Plasma glucose concentration was measured in duplicate using a glucose hexokinase assay (Beckman Coulter Inc.) on an automatic centrifugal spectrophotometric clinical chemistry analyser (Beckman Coulter AU480®, Beckman Instruments Inc., United States). Plasma insulin concentration was measured using an insulin sandwich type enzyme-linked immunoassay (Insulin ELISA kit, ALPCO®, Salem, NH, United States). All samples for a given participant were analysed within the same assay.
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