Abstract:
The glycaemic index (GI) is a relative ranking of carbohydrate foods that reflects the change in blood sugar following consumption. Chronic consumption of high GI foods is associated with many adverse impacts on human health. The GI is a somewhat abstract concept and the purpose of this thesis was to develop a tool to help primary and secondary school students to understand and visualise the glycaemic index in order to support informed healthful food choices. The overall experimental approach was based on an in vitro simulated digestion with an amylase catalysed hydrolysis of carbohydrate-rich food including a variety of starches, maltodextrin, cellulose and rice, followed by a quantification of the concentration of released glucose. Glucose analysis included two colourimetric methods, a method with dinitrosalicylic acid (DNS) and urinalysis test strips which were quantified using image analysis in RGB colour space.
Initial experiments demonstrated that the amount of glucose released (as measured using DNS) from the simulated digestion followed the expected trends of GI for the different starches. Specifically, a higher amylose content of a starch decreased the amount of glucose released; maltodextrin had the highest glucose release whilst cellulose was close to the zero. This was followed by experiments with six varieties of rice that had GI values that ranged from 48 to 95. Various parameters of the simulated digestion were explored including grinding time, reaction time and the influence of cooking time. The glucose release was followed over time from 0.5 to 240 minutes. Both the average glucose released between 120 and 240 minutes and the integrated area under the whole time period had a strong linear correlation (R² ≈ 0.77) with the reported GI values for the different rice varieties.
A series of experiments were then performed to refine the tool to enable its use in a school setting without hazardous or specialist chemicals. We demonstrated that urinalysis test strips could be used for glucose analysis in place of dinitrosalicylic acid. In addition, it was found that an acetate-acetic acid buffer system that can be prepared with baking soda and vinegar could be used with commercial amylase to achieve the required simulated digestion and could be combined with the urinalysis test strips reagent to enable colorimetric evaluation of comparative GI values. The two methods for visualisation of GI were presented to a group of practicing primary and secondary
school science teachers and science education leaders for critical evaluation. Focus groups were employed to enable the collection of qualitative evidence during this process. The educators identified that the proposed tools could be used to contribute to learning that was contextualised in exploration of food and nutrition, and addressed objectives in the New Zealand Curriculum. They identified key health and safety issues associated with the tool and recommended improved documentation of these issues. Further issues of concern to the expert panel were the cost and accessibility of the required consumables and accessibility of key background knowledge, particularly for non-science specialist primary school teachers. Participants identified that to advance the tool from this development trial into potential use would require documentation inclusive of background knowledge, pedagogical approaches, links to the New Zealand Curriculum, detailed instructions for teachers inclusive of all relevant health and safety information, costs and accessibility, as well as differentiated student learning resources.