What is behind the difference in glycemic index in different kinds of rice

[Wesley_Clark]

Supposedly basmati has a lower GI than jasmine or white rice. I could understand how brown rice would have a lower GI than white rice but what accounts for the fact that basmati has a GI about 20-40 points lower than jasmine?

[cookiecuttercc]

iirc, there is an enzyme (Amylase (spelling?)), the presence of which in rice makes it easier/harder for your body to break down the carbohydrates.

in addition the levels of arsenic in rice (which is a natural byproduct of rice cultivation and vary depending on rice variety) affect your body’s ability to breakdown the carbohydrates.

[DSeid]

No idea about arsenic in rice varying per variety (rather than location) and if that has anything to do with glycemic index but that big deal is the level of what is called “resistant starch” (as oppposed to the fiber content that you understand relevant to brown rice.

That’s where its amylose content comes in (not amylase which is an enzyme that breaks down carbohydrates; amylose is not an enzyme). Amylose is a form of startch that is slow to break down and basamti has a fair amount of it.

Amylose starch, which is more difficult to digest and absorb, is both smaller, containing only 100 to 10,000 glucose units, and less heavily branched compared to amylopectin. This linear shape allows amylose to pack more tightly into the less accessible regions of starch granules where it’s more difficult to digest.[4] A high ratio of amylose in starch granules also makes it more difficult to gelatinize (it gelatinizes at a higher temperature), making digestion by amylase enzyme even more difficult. In general, foods that contain more amylopectin (higher glycemic index), such as jasmine rice, short grain sticky rice (also known as glutinous or sushi rice) as well as some varieties of potatoes, such as Russet Burbank, are much easier to digest and absorb than foods containing more amylose (lower glycemic index), such as basmati rice, most long grain rice (except for jasmine), pasta, most wheat, corn, oat and barley products, most potatoes and bananas.

Resistant starch escapes digestion and absorption yet is fermentable by certain bacteria common to the large intestine, such as Bifidobacterium, Clostridium and Bacteriodes species. These bacteria contain efficient starch-degrading enzymes and most can break down both amylopectin and amylose starch.[5]

Cold potatos and green bananas are very high sources of resistant startch btw.

[misling]

@DSeid

Cold potatos and green bananas are very high sources of resistant startch btw.

Just curious, why would a cold potato be more resistant than a hot potato? If both were cooked, I mean. I could see a raw potato being more resistant.

[DSeid]

Well there are several different sorts of resistant and slowly digested starches …

Some are resistant to digestion because the starch is physically protected inside cell walls, as in some whole grains and seeds especially if only partly milled.

Some are resistant because the starch is packed together tightly radially in the granules and are somewhat dehydrated. This is the amylose of basamti rice, for example. Also the green banana and raw potato. The tight packing limits the ability of enzymes like amylase to get to it effectively and break it down.

Then there is retrograded starch as in cooled cooked potatoes. Cooking has gotten the starch to come out of the granules, hydrate, and uncoil and upon cooling down it forms a new, double helical, structure that is pretty stable and which packs tightly into crystals, again more difficult for the enzymes to get to.