Guar gum and glycemia

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Guar gum and glycemia

Hi All,

The below excerpts from the available pdf for the Medline citation appear to

indicate that guar gum is superior to insoluble and other soluble fiber and

highly

effective for reducing the glycemic response to different

carbohydrates-containing

foods. It seemed that the effectiveness was much greater on a percent basis for

the

pasta versus the bread for guar gum reducing the glycemic response.

Brennan CS.

Dietary fibre, glycaemic response, and diabetes.

Mol Nutr Food Res. 2005 Jun;49(6):560-70.

PMID: 15926145

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve & db=pubmed & dopt=Abstra\

ct & list_uids=15926145 & query_hl=77

.... 9 The physiological role of dietary fibre:

effect on the carbohydrate metabolism

DF has been shown to affect the rate and extent of starch

degradation.In particular,soluble DF has been shown to

reduce the rate of starch digestion and alter the rate of glu-

cose absorption [8,47 ].Research has concentrated on the

use of guar gum in food systems as a postprandial glucose

modifying ingredient [27 ].Similarly cellular components

of cereal grains,such as oat b -glucan gum,have been shown

to have nutritional benefits [48 –50 ].

The viscosity-altering behaviour of these soluble DFs

within the small intestine must account for some of these

effects,however,the DFs also appear to alter the structure

of the foods and hence the accessibility of the starch gran-

ules to the amylase enzymes [27,51 ].For instance,a range

of DFs (insoluble and soluble)have been used in the pro-

duction of pasta and bread.In vitro starch degradation of

these products has shown that the addition of DF has an

effect in reducing the amount of glucose produced follow-

ing digestion with amylase [51 –53 ].This reduction in glu-

cose can not be explained just on the basis of the DF exert-

ing a dilution factor on the starch component of the food.

Determination of residual starch following digestion indi-

cates that soluble fiber (such as inulin)additions to pasta

(Fig.2)significantly reduces the amount of starch digested

over a 300 min period.In many cases the magnitude of this

response is a direct function of dose.

Table 2. Predicted GI values of cereal foods following addition of soluble and

insoluble DFs

--------------------------

-------------Dietary fibre added

Type-----Amount Bread PGI Pasta PGI

-----------------------------

Control 0.0 94.4±1.6 45.2±3.6

Guar Gum 2.5 90.5±1.7 28.3±5.6

5.0 82.5±6.3 25.6±1.3

Locust bean gum 2.5 81.9±6.9 36.1±0.1

5 85.4±8.2 34.3±0.7

Pea fibre 2.5 92.0±3.2 44.5±2.5

5 88.5±1.4 40.3±2.4

This reduction in reducing sugar release following diges-

tion,and the extent of starch degradation results in a reduc-

tion in the predicted glycaemic index (PGI)of such foods.

Table 2 illustrates the potential use of DF ingredients in

manipulating the PGI of common foods.As can be seen

from these values,the soluble DFs (guar and locust bean

gum)appear to decrease the PGI value of these carbohy-

drate-rich foods to a larger extent than the insoluble DF

(pea fibre).What is of interest is the difference in the

degree of PGI reduction between food products using the

same DF source.Thus,a 2.5 and 5%addition of guar gum

to bread reduces the PGI value by 4 and 13%,respectively,

whereas a 2.5 and 5%addition of guar gum to pasta elicits a

37 and 43%reduction in PGI,respectively.This indicates

that the response of DFs in reducing the GI of foods may be

process/product dependent.

Scanning electron microscopy (SEM)images of pasta and

bread samples before and after digestion clearly illustrate

the possible influence DF additions have in altering food

structure,and subsequently the influence that food structure

has on the digestibility of starch.For instance,Fig.3 illus-

trates the effect of a 10%guar inclusion on bread structure

before (Fig.3b)and after (Fig.3d)a 300 min in vitro diges-

tion process.Note that the control bread sample before

digestion (Fig.3a)shows a porous structure in which indi-

vidual starch granules are embedded in a glutinous protein

matrix,whereas the sample with added guar (Fig.3b)is

less defined,with protein,DF,and starch in a dense contin-

uous network.This may be a result of the gelation charac-

teristics of the soluble fibre used in this experiment.It is

interesting to observe that this dense continuous network is

still retained in the added fibre bread sample,even after 300

min ingestion (Fig.3d),with starch granules seemingly

engulfed in a gelatinous matrix.However,the control bread

sample (Fig.3c)shows evidence of enzymic digestion,

with the majority of its structure degraded.

The striking effect of the DF on food structure and starch

digestibility may in part be related to the theory on

,thermodynamic incompatibility ’of biopolymers as pro-

posed by Tolstoguzov [54,55 ].The thermodynamic incom-

patibility theory describes the basis by which biopolymers

show a preference to be surrounded by their own type in

mixed solutions.For instance,Tolstoguzov [54,55 ]notes

that amylopectin is incompatible with guar gum.Thus,if

guar gum is added to a starch-rich matrix,it can lead to

phase separation,and an encapsulation of the starchy phase

by the guar gum-enriched phase.This encapsulation may

then lead to impaired starch gelatinisation and hence degra-

dation (as observed in Fig.2 and 3).

The in vitro results shown above are in agreement with

those of other in vitro [36 ]and in vivo experiments on the

GI of foods. ...

Al Pater, PhD; email: old542000@...

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