GI20 Glycemic Index Analyser
The CSIRO, Division of Food and Animal Nutrition, Adelaide, South Australia, has developed two automated instruments for predicting Glycemic Index and Resistant Starch. These novel instruments provide a means of rapidly and reliably predicting the Glycemic Index (GI) and Resistant Starch (RS) content of foods. These instruments are capable of processing large numbers of samples for a fraction of the cost and time required using in vivo methods which typically cost A$5000 per panel1.
The instruments have undergone extensive validation against the in vivo method in order to verify their predictive accuracy. Numerous commercial foods spanning a broad range of GI and RS values and food groups have been tested to date. The foods were selected on the basis that they are representative of everyday starchy foods eaten in Australia that would qualify for GI and RS testing, span the spectrum of values, and were commercially processed and shelf-stable products. Cereal foods predominate, which reflects the fact that cereals are the main carbohydrate and energy source for most humans. Predicted GI and RS values obtained with the CSIRO concept instrument are comparable to those yielded by accepted in vivo testing procedures.
The sensitivity and precision of the automated procedure compares favourably to in vivo methods. For GI, repeatability and reproducibility coefficients of variation (CVs) are about 3% and 6%, respectively. Comparable precision estimates are also obtained for RS. Analytical precision of the in vitro methods is independent of the magnitude of the predicted GI and RS values.
In summary, the instrument is substantially faster and simpler than in vivo testing, does not require specialised clinical skills and facilities, and mitigates the present invasive process. Hands-on time for predicting GI and RS using the instrument is minimal.
The in-vitro glycemic index and resistant starch predictors are new fully automated concept instruments capable of rapidly and reliably predicting the GI and RS content of foods.
The methodological basis of the instrumentation is a quantitative assay system that essentially simulates the digestion of food as occurs in the gastrointestinal tract of humans.
Foods in a form in which they are normally consumed are tested (usually in duplicate) and minimal sample preparation is required. The reaction system involves a series of incubations, at physiological pH and temperature that essentially mimic the buccal, gastric and pancreatic phases of digestion.
Protein, fat and starch are sequentially digested using a cocktail of hydrolytic enzymes. Total glucose released at designated stages of the digestion process is quantified and the predicted GI and (or) RS calculated. The reaction cycles and digestion conditions are programmed in a PC and the entire operation of the instrument is fully computer controlled.
Predicted GI and RS values generated with the prototype instrumentation are comparable to those produced by standardised GI testing methodology (Standards Australia, 2007) and the gold standard human ileostomy model, respectively. Statistical analyses of the data derived using the prototype instruments demonstrates close agreement with the corresponding results obtained using the very best testing methods in humans.
NutriScan GI20 Glycemic Index Analyser
Next Instruments has been chosen by CSIRO to commercialise their GI and RS analyser technology. The first product in the NutriScan range is the GI20 Glycemic Index Analyser.
The NutriScan GI20 is an automated, 20 sample capacity, analyser that simulates the digestion of a small quantity of food as it passes through the human gut. The food samples are weighed, mascerated using a kitchen chopping device and placed into sample cups that contain a stirrer bar and are placed in a heating block to maintain the temperature at 37C. Three enzyme mixtures are added to each sample cup in a specific sequence along with buffers. As the samples are digested, the GI20 measures the amount of glucose released from the food samples at 15, 30, 60, 120, 240 and 300 minutes during the digestion process.
The glucose is measured using a Glucose Analyser based on the following reaction:
β−D-glucose + O2 + H2O >>>GOD >>>> D-glucono-1,5-lactone + H2O2
GOD = Glucose Oxidase
An oxygen electrode placed in the reaction cell measures the consumption of O2 which is proportional to the amount of glucose that is oxidised by the glucose oxidase reagent.
The glucose concentration of the digests are plotted over the 5 hours. The total amount of glucose released is then used to calculate the GI of the original sample.
Figure 1 and 2 show pictures GI20 Glycemic Index Analyser.
Figure 1.GI20 Analyser
Figure 2. Picture of the sample cups
The systems consists of a X,Y,Z sample dispensing system, two syringe pumps, 4 peristaltic pumps, a 20 well heating block, a 20 position stirrer block, Glucose Analyser, enzyme delivery system and a PC controller.
The NutriScan GI20 Analyser is designed to provide an estimate of the GI of food samples by simulating the digestion of food as it passes through the human gut. However in humans, blood glucose is controlled by the pancreas which release insulin into the blood stream if the glucose concentration is too high. As well the stomach and intestines are continually passing the food through the gut and as such the digest is changing. As such, the In Vivo methodology monitors the blood glucose as it rises and falls over a two hours period. Figure 3 shows a typical plot for the In Vivo methodology. In the In Vivo methodology the area under this curve is called the Glycemic Response. The Glycemic Index is calculated from the following equation:
Glycemic Index = Glycemic Response/Available carbohydrates in the Sample
GI is a relative fiure where pure glucose has a GI of 100. All other foods will have a GI less than 100, with high GI above 76, moderate GI between 58 -76 and low GI below 58.
Figure 3. Typical blood Glycemic response curves for different foods.
In the In Vitro methodology there is no insulin to drop the glucose levels and as such, the glucose concentrations rise and then level off as all the available sugars are converted into glucose, as shown in figure 4. The GI20 calculates the total amount of glucose released or the end point concentration of glucose in the samples. As such, the GI20 does not measure GI but provides an estimate of the Glycemic Load of the samples and this is used to predict the Glycemic Index of the food sample.
Figure 4. In Vitro Glycemic Response Curves
Figure 5 shows the plot of several food samples analysed by the automated In Vitro methodology vs the In Vivo methodology.
Figure 5. Correlation Plot of the In Vivo vs In Vitro methods.
The most significant advantages of In Vitro method over the In Vivo method are the reduced cost per test and the improved precision of the analysis. The following table shows the comparison the In Vitro method vs the In Vivo method.
The NutriScan analyser is an Artificial Gut that can be used simulate the digestion of food, grains, animal feed, drugs etc, in a sample cup rather than having to perform human or animal trials. The first application that is available is the Glycemic Index(GI) prediction of foods. The second application will be the Resistant Starch(RS) prediction of foods. However there has already been enquiries by potential customers as whether the NutriScan could be used for other applications such as lipid profiles, protein profiles and beta-glucan digestion.
The answer to these questions is definitely yes. The GI20 comes with a specific cocktail of enzymes and has been tested over many years to establish the validity of the In Vitro method as compared with the In Vivo method. However the system could be used with a HPLC system, a UV Visible spectrophotometer or a Mass Spectrometer and a different enzyme cocktail and program to simulate other digestion based applications.
The following are potential applications and organisations that may use a NutriScan automated digestion analyser, ie, an Artificial Gut.
1) Food Companies: The GI20 is specifically designed to provide food manufacturers with a rapid means of testing foods for Glycemic Index. Their use of such an instrument will be mainly in the product development cycle where formulating the product may take several years and many tests.
GI is becoming a marketing tool to attract customers that are more conscience of the nutritional value of food. High GI foods tend to give the consumer a quick sugar rush but does not satiate the consumer for very long and thus leads them to want more food. A low GI food will release the glucose more slowly and the consumer will be less likely to want to eat again for several hours.
Diabetics also need to know the GI of the foods they consume as it will effect their blood glucose levels. Labelling for GI on foods will be of benefit to diabetics.
2) Human Nutrition Research: Private and public institutions that are involved in human nutrition are a potential market for this technology. Just like the CSIRO, research institutions could use this technology to assess the GI and in the future Resistant Starch(RS) of grains, fruit, nuts and other agricultural products as well as processed and natural foods. Screening large numbers of samples for low GI and RS traits is an excellent application for the NutriScan system because it can process up to 20 samples simultaneously and at a relatively low cost per test.
3) Animal Nutrition Research: Research institutions that are involved in the studies of animal nutrition is a potential for the NutriScan as an artificial gut rather than a GI analyser. In this case, the potential is for the base NutriScan system but supplied with other enzyme protocols and possibly a different detection systems.
4) Food Testing Laboratories: Consulting laboratories that offer routine testing for food manufacturers are a potential customer. In the same way these laboratories analyse customers samples for protein, fat and moisture, the NutriScan analyser would provide them with a means of measuring GI and RS for customers.
5) Pharmaceutical Manufacturers: Pharmaceutical companies could use the NutriScan Artificial Gut as a very useful tool to study the progressive breakdown of drugs as they pass through the digestion system. The Artificial Gut would be used in conjunction with a HPLC, Capillary Electrophoresis or Mass Spectrometer.
The NutriScan GI20 Analyser is a fully automated apparatus designed to simulate the digestion of foods in order to monitor the release of glucose from food samples. The system consists of the following components:
Enzymes are supplied in disposable cartridges for 5, 10 or 20 tests. Buffers are supplied is 500ml containers.
Automated In-Vitro Digestion System
Measures the Glycaemic Index
Resistant Starch Analysis