One of the key contributors to the exponentially growing obesity pandemic is the increased consumption of sugar-sweetened beverages such as soft drinks, energy drinks and fruit juices (Malik et al., 2010). In this experiment, a spectrophotometer was used to determine the glucose concentrations of both Coke and Gatorade. The results determined that both drinks contained less glucose than those indicated in the nutrition label. This was due to the fact that the majority of the sugar content in both drinks is in the form of sucrose, which unless hydrolysed can’t be measured by a spectrophotometer.
Introduction
Obesity is a major public health issue in Australia with statistics showing that in 2017-2018, just under one third (31.7%) of Australian’s 18 years or older were classified as obese and another 35.6% were classified as overweight (Australian Bureau of Statistics, 2019). One of the main factors linked to the rise of obesity worldwide is the consumption of sugar-sweetened drinks such as Gatorade and Coke. This is said as from 1965-2002 caloric intake from sugar-sweetened beverages increased by 4 times going from 50 calories to 200 calories per capita (Duffey & Popkin, 2012), following that of the upward trend in obesity levels. Although an increase in consumption of sugar-sweetened beverages (SSB) doesn’t only increase an individual's chances of obesity, with increased consumption of SSBs being linked to chronic health issues such as diabetes, cardiovascular disease, and fatty liver disease.
Therefore, with not only sugar-sweetened beverage consumption rising but obesity levels too, it is becoming more important to educate consumers as to what they are in fact consuming. The recommended treatment for patients who suffer from obesity is to increase physical activity and lower caloric intake. Research indicates people often don't compensate for the extra energy they consume from sugary drinks, resulting in an increased total energy intake, this has the possibility of health issues like diabetes mellitus with sugar-sweetened drinks being proven to stimulate appetite and in turn suppress satiety (Imamura et al., 2016). Therefore, by determining the glucose concentration in these two drinks, the consumer will know exactly what they are consuming, and in turn, will be able to use this information to improve not only their health but the health of others around them.
Methods
The spectrophotometer was set to a 340nm wavelength in order to measure the glucose concentration. A stock 20mM glucose was then used to prepare 1mL glucose standards at the following concentrations: 1-4 and 6mM in microcentrifuge tubes, which were then labelled appropriately. 35​µL of each prepared solution was then​ transferred to 9 cuvettes and 665​µL of H​2​O was added. These were then tested at 0 and 18 minutes in order to determine absorbance. Refer to the lab manual for more detail (Pearson, 2019, 44-49).
Although the hydrolysis of sucrose occurs at varied rates in different pHs and temperatures. This was shown by the sucrose absorption data from the lab, with sucrose hydrolysing best at a lower pH and a higher temperature. These results were able to show that the sample treated at a pH of 2.5 and a temperature of 90​°​C had the highest concentration with 1.95 g/100ml. Therefore Coke would have a higher measured concentration of glucose thanGatorade as Coke has a pH of 2.5 whilst Gatorade has a pH of around 3 (​Seow & Thong, 2005)​. Although the concentrations measured in the lab for both drinks were still lower than that of the label values, this is most likely because the glucose concentration would have been determined by the amount present after the drink has been fully broken down, which would take longer than 18 minutes.
When the sugar content of Gatorade is analysed deeper it can be seen that out of the 6 grams 5.5g are in the form of sucrose, while 0.5g is in the form of maltodextrin (Gatorade Australia, 2019). Maltodextrin is a polysaccharide that’s used as a food additive. It is formed by several D-glucose units that are connected by alpha(1,4) linkages in chains of varied lengths. Maltodextrin is easily digestible and is absorbed as quickly as that of glucose. This explains the glucose present in the Gatorade sample despite the fact that it not only has an unfavourable pH for sucrose hydrolysis but also no glucose content stated on the label. Therefore the glucose measured by the spectrophotometer in the lab was mostly from the hydrolysis of maltodextrin as well as 0.454g of glucose resulting from sucrose hydrolysis.
The results may also have been varied from the labeled glucose content due to human error. Although this is unlikely as the results were more than 6 times less than the concentrations reported on the label, with Coke said to have 10.6g/100mL (Coca-Cola Australia, 2019) and Gatorade having 6g/100mL (Gatorade Australia, 2019). If human error were to be the reason for these differences, there are a few possibilities for this error, the first being the improper taring of the spectrophotometer with the water cuvette. This would have caused all the results to be off as the spectrophotometer would not have been set at 0. The second possibility is that the sample solution concentrations may have been incorrectly prepared. This would occur if the pipette provided is faulty in any way. ​The last way human error could have caused faulty results is through the incorrect use/reading of the spectrophotometer. This can occur due to the cuvette being put in the wrong way or the lid not being closed properly. The absorbance could also be read wrong if the person taking the results doesnt understand the measurement, or records it incorrectly.
Although the results differed from what was expected, they were able to provide insight into that of the contents of the drinks. It is suggested that further study should be completed in this area, with obesity levels continuing to rise exponentially each year. Future research should be completed using an array of different techniques and approaches, in order to understand the full scope of the epidemic. This being said spectrophotometry should continue to be used, both in universities and professional labs as it gives insight into what exactly is contained in our food.
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Erin Hendrex (s5143319) Chemistry of Biological Systems II https://doi.org/10.1111/j.1834-7819.2005.tb00357.x