There are so may methods available now like goni, englyst etc.
can any one help in choosing the best method for the measurement of invitro glycemic index
May be this is of use to you.
One in vitro method, based on studies by K. N. Englyst and co-workers and illustrated in FIG. 1, involved the measurement of glucose released from a test food during timed incubation at 37° C. with a mixture of digestive enzymes using a calorimetric endpoint to determine the glucose level. Englyst et al., Brit. J. Nutr., 75, 327-337 (1996). This in vitro method has more recently been modified to include a HPLC endpoint to determine the amount of glucose released. Englyst et al., Am. J. Clin. Nutr., 69, 448-454 (1999) (hereinafter referred to as the “Englyst method” or the “in vitro Englyst method”).
The Englyst method involves mincing (or otherwise crushing or breaking up) a known amount of a test food (generally to contain about 0.5 g carbohydrate). The minced samples are incubated at 37° C. for 30 minutes with mixing in 10 ml 0.05 M HCl containing pepsin (5 g/l; to effect hydrolysis of protein) and guar gum (5 g/l; to help maintain food particles in suspension throughout the analysis). After this initial incubation, the samples are buffered to pH 5.2 using 0.5 M sodium acetate. An enzyme mixture (containing specific amounts of pancreatin, amyloglucosidase, and invertase) is then added to the buffered sample and the sample placed in a shaking water bath at 37° C. (time=0). Small glass balls are included in the samples to mechanically disrupt the physical structure of the samples during the main incubation; the added guar gum helps keep the sample in suspension by stabilizing the viscosity of the samples. At exactly 20 minutes into the main incubation, an aliquot of the sample is removed and added to absolute ethanol with mixing to stop the hydrolysis; this sample is used to determine G20 (i.e., the glucose released after 20 minutes; also referred to as “rapidly available glucose” or RAG) using HPLC. The remainder of the sample is maintained in the 37° C. bath for an additional 100 minutes at which time a second aliquot of the sample is removed and added to absolute ethanol with mixing to stop the hydrolysis; this sample is used to determine G120 (i.e., the glucose released after 120 minutes) using HPLC. The remainder of the sample is then treated as illustrated in FIG. 1 by the addition of additional enzymes and then exposure to temperatures up to 100° C. to force complete hydrolysis and, thus, determine the total glucose in the sample.
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please refer this
In vitro method for glycemic index analysis
The in vitro Glycemic Index (GI) of the food materials was determined according to the methodology described by Goñi et al. (1997), with the following modifications: glucose concentration was determined using a GOD-PAD glucose kit (Laborlab, Brazil) and the color reaction was measured in a UV/VIS spectrophotometer, model DU 70 (Beckman, USA), at λ = 505 nm.
Glucose digestion rate was expressed through the percentage of glucose in each sample (mg glucose.100 mg–1 sample) at each time interval (0, 30, 60, 90, 120, 150, and 180 minutes). Hydrolysis curves were built (disregarding the value at time 0), and the area below the hydrolysis curves was calculated (AHC). The Hydrolysis Index (HI) for each sample was calculated as the ratio between the AHC of each sample and the AHC of white bread, used as reference, and expressed in percentage, as reported by Goñi et al. (1997). Finally, the GI was calculated according to Equation 1:
GI = 39.71 + (0.549 * HI)
where GI = Glycemic Index (%); and HI = Hydrolysis Index (%).
http://www.qualtech-groupe.com/wp-content/uploads/2012/10/2012-IG-engV2.pdf
@Ahila Wani
Can you please tell how many units of Amyloglucosidase need to be added for each sample as per Goni et al 1997? In paper is has been mentioned to add 60 ul, but there is no mention about the units of Amyloglucosidase needed.
Thanks.
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