Spectrophotometry is the simple and economically feasible way to estimate the starch content.

If you look for something simple, yes I think previous answer is right.

Dear Md. Asaduzzaman,

The popular method for starch estimation is the method of Englyst et al. (1992), and then subjecting your final  aliquot to spectrophotometry. I hope it helps and try to get the full version of the article from the author.

Dear Tilahun Abera,

I went through the abstract of that article and it seemed like the method is eventually involving DNS method for estimating reducing sugar. But I am searching for something apart from this one.

I want to know whether the color resulting from the soluble starch-iodine complex is stable and measurable for generating standard curve and be used to estimate unknown soluble starch content.  

I will suggest that you freeze dry the soluble starch solution and follow the AOAC method for starch assay using Megazyme Kit. 

Specific gravity? You have the rice with an analysis, you have water.

Iodine shows blue if the starch is  not converted to sugar. Having used Iodine in a microbrewery it is binary test in the field. In the mash tun samples tested there are a lot of particulates; of grain. The liquid stays brown while particles still containing starch turn blue. It does not seem you could get consistent measurements.

My suggestion:

Rice cooking : Analyze the starch in both solid and liquid phase    by Megazyme Assay kit.

More information:

-www.megazyme.com

-Effect of processing conditions and cooking methods on resistant starch, dietary fiber and glycemic index of rice,2013,Darandakumbura et al, Tropical Agricultural Research

,vol.24(2):163-174

Dear Race Vanderdecken,

I was wondering the same problem with suspended colored particles that would eventually settle down. It will definitely affect the consistency of absorbances.

May be useful:

1.A qualitative starch-iodine method for measuring alpha-amylase and glucoamylase activities.

by Zhizhuang Xiao, Reginald Storms and Adrian Tsang.

2.The mechanism of starch-iodine reaction

    I Critical investigation of  actual viewpoints .

by J.Hollo and J.SzejTLI.

3. Note on limitation of the starch-iodine blue test for milled rice amylose.

by Bienvenido O.Juliano, Artemio V. Cartano and Amanda J. Vidal.

The spectrum of a starch -iodine complex depends on the length of the starch chains (intensity and lambda max), so I would not use this assay to quantify starch. But indeed (unfortunately as it is much more time-consuming) total starch degradation then reducing sugar assay, as indeed in the  Megazyme kit.

Md. Asaduzzaman, 

We centrifuge before doing spectrometry on beer. Same could apply here?

Race Vanderdecken,

The starch liquor, separated from the cooked rice, contains insoluble particles which are clearly visible as those settle down with time. Hence, it is possible that the liquor is centrifuged before the starch-iodine reaction takes place to facilitate soluble starch estimation.  

I do not think there would be a linear relationship between absorbance and starch concentration. I would advise to achieve a mlld acidic hydrolysis of starch into dextrose and then to determine glucose concentration using iodometry. 

A modified AOAC method 17th edition, 925.50 may be used. All starches are converted into reducing sugar, which is determined by Lane and Eyon method. Then a factor of 0.9 is used to convert it into Starch.