Potatoes are often thought of as high GI. It is known that cooking and cooling affect GI and that these effects may be mediated through the physicochemical properties of their starch. As part of a Canadian initiative to develop low GI potatoes, novel potato varieties which differed in starch composition were tested in 2 separate studies. In study 1, we determined the GI of 8 varieties and found that cooling produced a wide range of effects (0-50% reduction in GI). In study 2, four previously tested varieties were re-examined. A significant variety-x-treatment interaction (p<0.01) was observed with cooling reducing GI in some potatoes. Examination of the starch properties and their role in determining GI showed that RDS was positively associated with GI (r2= 0.85, p= 0.001) and SDS (r2=-0.60, p= 0.02) and amylose (r2=-0.99, p=0.007) negatively associated with GI. No relationship between RS and phosphorous content and GI was observed.

Potatoes are often thought of as high GI. It is known that cooking and cooling affect GI and that these effects may be mediated through the physicochemical properties of their starch. As part of a Canadian initiative to develop low GI potatoes, novel potato varieties which differed in starch composition were tested in 2 separate studies. In study 1, we determined the GI of 8 varieties and found that cooling produced a wide range of effects (0-50% reduction in GI). In study 2, four previously tested varieties were re-examined. A significant variety-x-treatment interaction (p<0.01) was observed with cooling reducing GI in some potatoes. Examination of the starch properties and their role in determining GI showed that RDS was positively associated with GI (r2= 0.85, p= 0.001) and SDS (r2=-0.60, p= 0.02) and amylose (r2=-0.99, p=0.007) negatively associated with GI. No relationship between RS and phosphorous content and GI was observed.

Compared to the overnight fasted state, a high carbohydrate (CHO) breakfast 3-4 hours before exercise enhances endurance performance. However, the optimal type or composition of the pre-exercise meal to be consumed is less clear. Glycaemic and insulinaemic responses to a meal play a key role in subsequent metabolism during exercise. The investigations described in this thesis focused on the influence of I) the composition and 2) glycaemic index (GI) of CHO breakfasts 3 hours before exercise on postprandial and exercise metabolism and endurance running capacity.

The studies described in this thesis were undertaken to examine the factors affecting adolescents cognitive function across the school morning. Specifically, the effects of breakfast consumption, breakfast glycaemic index (GI) and a mid-morning bout of exercise were examined, whilst the final experimental chapter examined their combined effects. The battery of cognitive function tests used in the present study was administered via a laptop computer and took approximately 15 min to complete. Across all experimental chapters, the visual search test (assessing visual perception), the Stroop test (assessing attention) and the Sternberg paradigm (assessing working memory) were used. Furthermore, in chapter V the Flanker task (also assessing attention) was added to the testing battery. The first experimental study (chapter IV) examined the effects of consuming a self-selected breakfast on cognitive function, compared to breakfast omission. Ninety-six adolescents (12 to 15 years old) completed two experimental trials (breakfast consumption and breakfast omission), scheduled seven days apart, in a randomised crossover design. Following breakfast consumption, accuracy on the more complex level of the visual search test was higher than following breakfast omission (p = 0.021). Similarly, accuracy on the Stroop test was better maintained across the morning following breakfast consumption when compared with breakfast omission (p = 0.022). Furthermore, responses on the Sternberg paradigm were quicker later in the morning following breakfast consumption, on the more complex levels (p = 0.012). Breakfast consumption also produced higher self-report energy and fullness, lower self-report tiredness and hunger, and higher blood glucose concentrations, compared with breakfast omission (all p < 0.001). Overall, the findings suggested that breakfast consumption enhanced adolescents cognitive function, when compared with breakfast omission. The second experimental study (chapter V) examined the effects of consuming a high GI breakfast, a low GI breakfast and breakfast omission on cognitive function. Forty-one adolescents (12 to 14 years old) completed three experimental trials, each scheduled seven days apart, in a randomised crossover design. There was a greater improvement in response times across the morning following a low GI breakfast, compared to breakfast omission on the complex level of the Stroop test (p = 0.009) and both levels of the Flanker task (p = 0.041), and compared to following a high GI breakfast on the complex level of the visual search test (p = 0.025) and all levels of the Sternberg paradigm (p = 0.013). Furthermore, accuracy was enhanced following a low GI breakfast, compared to breakfast omission on the more complex levels of the visual search test (p = 0.032), Sternberg paradigm (p = 0.051) and Flanker task (p = 0.001), and compared to following a high GI breakfast on both levels of the Stroop test (p = 0.033) and the more complex levels of the Sternberg paradigm (p = 0.002) and Flanker task (p = 0.014). Furthermore, participants exhibited a lower glycaemic response following the low GI breakfast (p < 0.001), though there was no difference in the insulinaemic response (p = 0.063), compared to following the high GI breakfast. Overall, the findings suggest that a low GI breakfast is the most beneficial for adolescents cognitive function, compared with a high GI breakfast and breakfast omission. The third experimental study (chapter VI) examined the effects of a mid-morning bout of exercise, following a self-selected breakfast, on cognitive function. Forty-five adolescents (12 to 13 years old) completed two experimental trials (exercise and resting), scheduled seven days apart, in a randomised crossover design. There was a greater improvement in response times across the morning following the mid-morning bout of exercise on all levels of the Sternberg paradigm (p = 0.010). There was also a greater improvement in response times across the morning on the visual search test following the exercise (p = 0.009), but this improved speed was combined with a greater decrease in accuracy following the exercise (p = 0.044). This suggests that following exercise, the adolescents exhibited a speed-accuracy trade-off, whereby they responded quicker, but this was to the detriment of accuracy. Overall, the findings suggest that whilst the mid-morning bout of exercise improved some components of cognitive function (e.g. response times on the Sternberg paradigm), it did not affect other components (e.g. Stroop test performance). The final experimental study (chapter VII) examined the combined effects of breakfast GI and a mid-morning bout of exercise on adolescents cognitive function. Forty-two adolescents (11 to 13 years old) were allocated to matched high GI (n = 22) and low GI (n = 20) breakfast groups. Within the matched groups, participants completed two experimental trials (exercise and resting) in a randomised, crossover design. The findings indicate that, for the complex level of the Stroop test, following the high GI breakfast there was a greater improvement in response times across the morning on the resting trial, whereas following the low GI breakfast response times improved across the morning on both the exercise and resting trials, though the magnitude of the improvement was greatest on the exercise trial (p = 0.012). On the Sternberg paradigm, response times improved across the morning following the low GI breakfast regardless of exercise, whereas following the high GI breakfast response times improved across the morning on the exercise trial, though remained similar across the morning on the resting trial (p = 0.019). Overall, the findings suggest that the effects of the mid-morning bout of exercise were dependent upon the breakfast GI and the component of cognitive function being examined and that, for the Stroop test, the beneficial effects of the low GI breakfast and mid-morning bout of exercise were additive. Overall, the results from this thesis suggest that breakfast consumption is more beneficial than breakfast omission and more specifically, that a low GI breakfast is more beneficial than both a high GI breakfast and breakfast omission, for adolescents cognitive function across the school morning. However, the effects of exercise appear to be more variable, with the effect of exercise depending upon the component of cognitive function examined and the GI of the breakfast consumed. Overall, the findings presented in this thesis suggest that the nutritional effects on adolescents cognitive function (i.e. the effects of breakfast consumption and GI) were stronger and more consistent than the exercise induced effects.

Glucose is the primary fuel for the brain and also important for exercising muscle. The purpose of the thesis was to investigate the effects of the glycaemic index (GI) of mixed meals on appetite, cognitive performances and metabolic responses during intermittent exercise in recreationally active adults. Study one investigated whether a low GI (LGI) breakfast (GI = 42.5) could suppress appetite and reduce energy intake (EI) of 12 recreationally active females (28.2 ± 8.0 years) more than a high GI (HGI) breakfast (GI = 73.5). Area under the curve of the appetite score (AS AUC) following LGI breakfast was significantly greater than the HGI trial during the 60-min postprandial (pp) period (2568 ± 1027 vs. 2198 ± 821 mm∙min, p = 0.025). The HGI breakfast facilitated a stronger appetite suppressing effect up to eight hours post breakfast than the LGI trial (18834 ± 3906 vs. 21278 ± 3610 mm∙min, p = 0.028). The EI on the LGI trial day was significantly higher than on the pre-trial day (2,215 ± 576 vs. 1,748 ± 464 kcal, corrected p = 0.008). Fourteen recreationally active males (34.5 ± 8.9 years) in study two consumed the LGI (GI = 41.3) and HGI (GI = 74.3) breakfasts in the laboratory and then prescribed LGI and HGI meals in the free living environment. In line with study one, the AS AUC was significantly smaller following HGI than LGI breakfast over the 60-min pp period (2,989 ± 1,390 vs. 3,758 ± 1,290 mm∙min, p = 0.027). The HGI meals (GI = 76.9) suppressed appetite more than the LGI meals (GI = 39.6) over 12 hours on the trial day (35,454 ± 9,730 vs. 41,244 ± 8,829 mm∙min, p = 0.009) although energy balance was not different between trials. Study three investigated whether following a LGI breakfast (GI = 42.2) providing 1 g CHO kg-1 BM could result in a better vigilance and attention than a HGI breakfast (GI = 72.4), and reduced lunch EI in 16 recreationally active males (24.4 ± 3.6 years). A significant trial x time effect in the interference time of the Stroop Colour Word Task (SCWT) (p = 0.039) showed that the LGI breakfast maintained the attentional performance up to 90-min pp. Both high pre-task glucose concentration ([Glucose]) at 15-min pp and low pre-task [Glucose] at 105-min pp in the HGI trial were associated with unfavourable outcomes in vigilance in the Rapid Information Processing Task (RIPT). The LGI pre-task [Glucose] returning back to fasting level at 60-min pp was associated positively with the response time. The pre-lunch AS was a significant predictor of the lunch EI per fat free mass which explained 21% and 26% of variance in the LGI and HGI trials respectively. No significant difference was found in the ad libitum lunch EI between trials. Sixteen recreationally active males (27.8 ± 7.7 years) in study four consumed a LGI (GI = 42) and a HGI breakfast (GI = 72.8) providing 1.2 g CHO kg-1 BM consumed 60 minutes prior to intermittent running on two separate mornings. Better attentional performance at 150-min pp was found following LGI than HGI breakfast. The significant trial x time interaction in the SCWT (p = 0.045) showed the shortest interference time performed after the last exercise session in the LGI trial. The amounts of CHO and fat being oxidized were comparable between trials during three sessions of 16-min intermittent running with an average intensity of 65% V̇O2max. In conclusion, the pre-meal appetite sensation is more predictive of the subsequent meal EI than the pre-meal [Glucose]. The meal strategy for weight management in recreationally active adults may focus on greater appetite suppression by selecting HGI foods whilst maintaining healthy eating guidelines. Recreationally active males performing sports requiring high levels of vigilance and selective attention with low physical activity levels can benefit up to 60–90 min pp from the LGI breakfast. Their attentional performance can benefit from the LGI breakfast with moderate to high intermittent intensities in the late exercise period at 150–min pp. Recreationally active adults should consider the timing of meal consumption in relation to performing intermittent exercise, in order to maximize the advantages from the LGI or HGI breakfasts for cognitive performance or appetite suppression. They may be more liberal in pre-exercise food choices if substrate oxidation during intermittent running is only of their concern.

Emphasis on using the glycaemic index (GI) in addition to carbohydrate exchange lists has led to a greater variety of foods from which to choose for the diabetic population. Breakfast is regarded as the most important meal of the day and the glycaemic response to lunch can be improved by decreasing the GI of breakfast. However, most conventional breakfast cereals and bread exhibit a high GI. Dried beans have a low GI and various processes such as cooking and canning increase GI values, but still in the low GI range. In recent years, extrusion cooking has become one of the popular new processes developed by the food industry. Extrusion provides a convenient alternative for the ingestion of dry beans in the diet. Muffins are eaten by many South Africans and may be an ideal alternative for breakfast cereals and bread, especially if the GI of the muffins is low. The aim of this study was to determine the GI of a muffin baked with extruded bean flour and compare it to the GI of a muffin baked with whole wheat flour. Subjects and methodology: The study cohort consisted of ten healthy males and ten healthy females. Subjects randomly consumed test meals of glucose (the reference), bean muffins and whole wheat muffins on different days. Each test meal provided 509 available carbohydrate as analysed by the Englyst method. Results: The GI of the muffin baked with extruded bean flour (mean 53.0%, Confidence intervals (CI): 41.7; 64.2) was not significantly different from that of the whole wheat muffin (mean 55.5%, CI: 41.8; 69.2) but still in the low to intermediate GI category. Conclusion: Extrusion of dried beans results in a fine flour with relatively no intact starch which may explain the very low resistant starch content (1.6I100g) of the muffins. The small particle size of the fine flour could further have contributed to the higher than expected GI of the bean muffin because the size of the particle is inversely related to glycaemic response. Muffins baked with extruded dried bean meal are nevertheless regarded as an excellent choice for breakfast and as part of the prudent diet. Beans have additional health benefits and are included in the South African Food Based Dietary Guidelines. / Thesis (M.Sc. (Dietetics))--North-West University, Potchefstroom Campus, 2004.

Emphasis on using the glycaemic index (GI) in addition to carbohydrate exchange lists has led to a greater variety of foods from which to choose for the diabetic population. Breakfast is regarded as the most important meal of the day and the glycaemic response to lunch can be improved by decreasing the GI of breakfast. However, most conventional breakfast cereals and bread exhibit a high GI. Dried beans have a low GI and various processes such as cooking and canning increase GI values, but still in the low GI range. In recent years, extrusion cooking has become one of the popular new processes developed by the food industry. Extrusion provides a convenient alternative for the ingestion of dry beans in the diet. Muffins are eaten by many South Africans and may be an ideal alternative for breakfast cereals and bread, especially if the GI of the muffins is low. The aim of this study was to determine the GI of a muffin baked with extruded bean flour and compare it to the GI of a muffin baked with whole wheat flour. Subjects and methodology: The study cohort consisted of ten healthy males and ten healthy females. Subjects randomly consumed test meals of glucose (the reference), bean muffins and whole wheat muffins on different days. Each test meal provided 509 available carbohydrate as analysed by the Englyst method. Results: The GI of the muffin baked with extruded bean flour (mean 53.0%, Confidence intervals (CI): 41.7; 64.2) was not significantly different from that of the whole wheat muffin (mean 55.5%, CI: 41.8; 69.2) but still in the low to intermediate GI category. Conclusion: Extrusion of dried beans results in a fine flour with relatively no intact starch which may explain the very low resistant starch content (1.6I100g) of the muffins. The small particle size of the fine flour could further have contributed to the higher than expected GI of the bean muffin because the size of the particle is inversely related to glycaemic response. Muffins baked with extruded dried bean meal are nevertheless regarded as an excellent choice for breakfast and as part of the prudent diet. Beans have additional health benefits and are included in the South African Food Based Dietary Guidelines. / Thesis (M.Sc. (Dietetics))--North-West University, Potchefstroom Campus, 2004.

Thesis (MTech (Food Technology))--Cape Peninsula University of Technology, 2013. / Acha starch was isolated and purified from clean and milled acha grain. Functional, thermal and physicochemical properties of acha starch were analysed using appropriate methods. Wheat starch was used as the reference standard. Acha bread from acha grain was baked and the consumer sensory acceptability was evaluated and white wheat bread was used as the reference standard. The effect of baking, boiling, steaming and microwaving on the starch and glycemic properties of the acha starch was evaluated. With regard to thermal properties, gelatinisation temperature of acha and iburu starches typifies that of waxy starch. Acha starch has similar retrogradation temperature profiles as that of wheat. There were however significant differences in some of the functional properties (pasting and turbidity) and physico-chemical properties (in vitro starch digestibility), but no significant difference in the texture profile analysis (TPA) and water binding capacity (WBC). WBC of both acha varieties was higher than that for wheat starch. Due to its high break down viscosity, white acha starch can be included in foods that are subjected to high temperature processing. This indicates that both acha starch varieties can be used for hot and cold desserts as well as for soft jelly like sweets and confectionery toppings. A prescreening exercise using carboxymethyl cellulose (CMC), Xanthan gum, yeast and acha starch as the variables was successful in concluding a recipe which rendered acha bread with the optimum specific loaf volume for both white and black acha bread. The optimum recipe consisted 8.0 % acha starch, 2.0 % xanthan gum, 2.0 % CMC and 1.0 % yeast. The majority of the consumer panellists found the crust colour, taste and aroma to be moderately desirable. This implies that most consumers find acha bread to have the potential to be marketed as wheat free bread. The different processing methods baking, boiling, microwaving and steaming, affected the black and white acha starch hydrolysis. The amount of starch hydrolysed for the different processing methods was in the following order: baking > boiling > microwaving > steaming. It can thus be concluded that different processing methods affects the micro structure and physical properties of the acha and wheat samples which thus influence their starch hydrolysis. The equilibrium percentage of starch hydrolysed after 180 min incubation was affected differently for the various starches, black acha, white acha and wheat starch by the different processing methods and times. In the case of baking black acha starch and wheat bread were affected similarly. However, this was not the case for microwaving, steaming and boiling, where both acha starch varieties and wheat starch were affected in the same way. The rate of starch hydrolysis for both acha varieties and wheat grain for the different processing methods, steaming, boiling, microwaving and baking was affected to the same degree respectively.

The glycaemic index (GI) is a measurement used to classify foods according to their potential for raising blood glucose levels. The GI of a foodstuff is generally measured by determining the increment in blood glucose concentration after the consumption of a test meal over a set period of time and comparing it with an isoglucosidic control meal (normally white bread or glucose) and expressed as a percentage within a group of individuals (in vivo). Rapid analysis methods (in vitro) are being developed and evaluated worldwide, and in many cases the values obtained have correlated well with the GI values determined by in vivo methods. The criticism against rapid analysis methods is that the methods do not provide numerical GI values. Proposed labelling legislation in South Africa recommends that suppliers should only indicate if the product has a high, intermediate or low GI. The purpose of this study was to investigate existing rapid assessment methods for the prediction of GI, and develop such a method for South Africa to be used by food producers as a screening tool during product development in line with the newly proposed national labelling requirements. The preliminary studies on the developed rapid assessment method indicated good repeatability (CV 0.78%), reproducibility and precision (CV 3.5%). Further comparative trials indicated that the in vitro method accurately predicts the GI category of Almera potatoes (Solanum Tuberosum L. cultivar Almera) and Gero fat free litchi and raspberry flavoured yoghurt, in line with results found from in vivo analysis. Significant inter-laboratory variability of in vivo analysis of GI values obtained for the Almera potato cultivar was found, and the need for future alignment of methodology and sample preparation is recommended./p> / Dissertation (MSc)--University of Pretoria, 2010. / Food Science / unrestricted

The principle aims of this work were two fold; firstly to identify the current dietary intakes (specifically dietary glycaemic carbohydrate (CHO)) and physical activity (PA) and cardiorespiratory fitness (CRF) levels of a UK, postpubertal, adolescent population (n = 105) and assess the relationship between these factors, adiposity and cardiometabolic health. Diet and health relationships were assessed whilst accounting for energy misreporting and controlling for levels of PA and CRF. The effect of excluding dietary misreporters on the associations between glycaemic CHO and health was assessed whilst comparing an established technique (the Goldberg equation) to a novel approach (the ratio of energy intake (EI) to energy expenditure (EE)), which utilised RT3 accelerometry data (EI:EE(RT3)). Associations of PA and metabolic risk factors were also assessed whilst comparing two child specific PA thresholds for the assessment of PA subcomponents. Secondly, the impact of a flexible, ad libitum, low GI dietary intervention on cardiometabolic health was examined in an „at risk‟, overweight, postpubertal, adolescent population. Glycaemic index (GI) but not glycaemic load (GL) was shown to be associated significantly with anthropometric measures (body mass index (BMI), waist circumference (WC)) and adiposity (body fat percentage (BF%)) in this general group of post-pubertal adolescents from Bedfordshire. When adjusting for dietary intake, CRF was also associated with adiposity but PA was not. The prevalence of misreporting varied depending on the method used to assess the validity of dietary intakes; between 23% and 31% increasing to 62.1% (in overweight) of adolescents under reported energy intakes and up to 11.1% over reported. The novel application of a triaxial accelerometer to measure EE resulted in more under and over reporters being identified than when compared to the widely used Goldberg equation. Increased dietary GI was associated with increased odds of having a high WC; however, associations between GL and other risk factors were less clear; no associations with risk were observed. Excluding dietary misreporters from analysis had important implications for these associations. Only after removal of misreporters by EI:EE(RT3) was a borderline significant positive association between GL and blood glucose (BG) revealed using multiple analysis of covariance (MANCOVA), that was not present in prior analyses. Increased GI (moderate vs low GI intake) was significantly associated with reduced high density lipoprotein cholesterol (HDL) and increased triglyceride (TG) levels (borderline significant) after removal of misreporters. In addition, using different PA thresholds to assess PA intensity resulted in different relationships between PA subcomponents and metabolic risk factors. Regardless of the threshold used, evidence suggested that limiting sedentary (SED) behaviour and engaging in moderate to vigorous PA (MVPA) is beneficial for blood pressure (BP) in this adolescent population. Additionally, irrespective of the threshold utilised, higher levels of vigorous PA (VPA) were associated with reduced odds of having a high clustered risk score and the associations observed between CRF and risk factors were stronger than those observed with PA. Despite a lack of significant improvement in individual metabolic risk factors as a result of the low GI (LGI) dietary intervention, there was a significant reduction in clustered risk score for the LGI group at week 12. A borderline significant improvement in glycated haemoglobin (HbA1c) was also observed as a result of the LGI intervention compared to those in the control group. Conversely, there appeared to be an unfavourable effect of the LGI diet on fasting insulin levels and thus the diet‟s impact on health overall is unclear. The small sample size of this randomised controlled trial (RCT) means that caution is required when interpreting the results. These data suggest that future research in this age group should target improvements in CRF and a lower dietary GI to reduce adiposity. Controlling for dietary misreporting appears to have a significant impact on associations of glycaemic CHO and cardiometabolic health and should be an important consideration of future research. The low GI intervention may be an effective approach for reducing glycaemic CHO, whilst maintaining a healthy macronutrient intake, in comparison to more restricted dietary regimens published in the literature. However, the impact of this regime needs to be confirmed utilising a larger sample of adolescents. This may provide a useful approach for future research aiming to assess the impact of reduced GI and GL.