Lab Cat

2 Mar 2007

Physicochemical Properties of Starch

Filed under: Chemistry, Food, Research — Cat @ 2:47 pm

One of my research interests is the behavior of corn starch gels. Corn starch has interesting properties as shown by these couple of videos:

Previously, I discussed the general chemistry of starch and corn starch is similarly made up of amylose and amylopectin arranged in starch granules. Corn starch undergoes gelation, gelatinization and retrogradation on heating, cooling and storage. As corn starch is also widely used by the food industry especially as a gelling agent, thickener or bulking agent its physicochemical behavior is important. One of my undergraduate research projects has been to study the texture and rheology of corn starch gels. So I was excited to come across this article [1].

According to The Dictionary of Food Ingredients [2], cornstarch is:

The starch made from the endosperm of corn [[3]], containing amylose and amylopectin starch molecules. When starch is heated in water it forms a viscous, opaque paste. The paste forms semisolid gels upon cooling and has the ability to form strong adhesive films when spread and dried. Cornstarch is not freeze-thaw stable and is used widely except when clarity or the lack of gel formation is required. It exists as fine or course powders. The coarse starch is sometimes termed pearl starch. It is used in sauces, puddings. pie fillings. and salad dressings. the typical usage level is 1 to 5 percent. It is also termed common, regular or unmodified cornstarch.

For any of cooks reading – you often use cornstarch [3] to make a gravy.

The objective of this research paper was:

to characterize the corn varieties grown in India on the basis of the physicochemical, thermal, pasting and gel textural properties of their starch. This will be useful in selecting the appropriate variety for end use suitability.

Thus, this article was a characterization of different corn starches. The researchers measured many properties including amylose content, swelling power, solubility, water binding capacity, thermal properties – to obtain gelatinization temperature, pasting properties, and texture. All these properties of starch can be used to determine what is the best use of the particular starch.

I was interested in the techniques they used as that is directly applicable to the research in my lab. I was especially interested in their texture measurements. Once they had a gelled starch:

…the gel was compressed at a speed of 0.5 mm/s to a distance of 10 mm with a cylindrical plunger (diameter = 5 mm). The compression was repeated twice to generate a force–time curve from which hardness (height of first peak) and springiness (ratio between recovered height after the first compression and the original gel height) was determined. The negative area of the curve during retraction of the probe was termed adhesiveness. Cohesiveness was calculated as the ratio between the area under the second peak and the area under the first peak. Gumminess was determined by multiplying hardness and cohesiveness. Chewiness was derived from gumminess and springiness and was obtained by multiplying these two.

This type of analysis is a texture profile analysis (TPA).

Some definitions:
Hardness:
• Force required to deform the product to given distance, i.e., force to compress between molars, bite through with incisors, compress between tongue and palate.
• Determined as maximum force required to compress gel 10 mm in first compression
Adhesiveness:
• Force required to remove the material that adheres to a specific surface (e.g., lips, palate, teeth).
• Determined from the negative area after the probe was removed after the first compression
Cohesiveness:
• Degree to which the sample deforms before rupturing when biting with molars.
• Determined as the ratio of the areas under the second to first compressions
Springiness:
• The resilience rate at which the sample returns to the original shape after partial compression.
• Determined as the ratio of the max force for the second compression to hardness.
Gumminess:
• Energy required to disintegrate a semi-solid food to a state ready for swallowing.
• Determined as hardness x cohesiveness
Chewiness:
• Number of chews (at 1 chew/sec) needed to masticate the sample to a consistency suitable for swallowing.
• Determined as gumminess multiplied by springiness.

Until I read this article I had only been measuring hardness. Now I could tweak my texture analyzer method and I would be able to put numbers on other texture properties of the starch.

A typical texture graph looks like this:

Starch Texture

I carried out a series of experiments with different starch gels. Comparing the controls (5% starch solutions heated in a microwave to >85 oC showed that the methods are consistent.

Starch Results

The researchers found that the different corn varieties produced starches with different physicochemical properties. In particular, they showed that the African Tall had a lower amylose content and also had the weakest (hardness was lowest) gel.

I am more interested in the effects of adding food additives on gel strength (hardness) and other properties. This is shown clearly in the next picture where the control gel is compared to one with added ingredients (I’m not say what is in my experimental gel yet (other than starch) as I still need to formally write this up for publication):

Corn Starch Gels


[1] Link will only work if you have access to Food Chemistry.

Reference:
Sandhu & Singh (2007) Some properties of corn starches II: Physicochemical, gelatinization, retrogradation, pasting and gel textural properties. Food Chemistry; 101, (4), 2007, Pages 1499-1507

[2] This is a great book for anyone interested in what and why are those ingredients in the food label. I have the third edition, but the fourth is available from Amazon

Reference
Igoe & Hui (1999) Dictionary of Food Ingredients

[3] Another of those England and America being separated by having the same language moments. Corn is England is maize. However, corn starch is corn flour. You know, just to confuse.

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21 Comments »

  1. Did you see the article on nutrition in this past Sunday’s NY TIMES magazine?

    Comment by biosparite — 8 Mar 2007 @ 6:41 pm

  2. I’ve seen some interesting things regarding starches…

    Do you know of Chitosan at all??? Not sure as it’s not exactly a foodstuff.

    I’ve heard of someone using modified starches as catalyst supports… after pretreatment. Also as a novel chromatographic medium.

    Either way it’s one interesting renewable material!

    Nice site ;)

    Mark

    Comment by Mark C R UK — 8 Mar 2007 @ 6:53 pm

  3. Biosparite -I’ll check that out.

    Mark – all I know about chitosan is that is it from insect shells right? Now I’m going to have to look that up.

    Starch is amazing; especially considering it is just glucose molecules joined together.

    Comment by Cat — 9 Mar 2007 @ 9:01 am

  4. Trouble comes from it’s stability…

    Those glycosidic bonds aren’t very acid tolerant…

    But hey – that’s what makes starch and ligno-celluloses of interest in the whole biofuels area…

    I just find it amazing how so many different areas of science can converge!
    (I’m talking to a food scientist!! ;) )

    Comment by Mark C R UK — 9 Mar 2007 @ 11:07 am

  5. Cat, I love that second video using corn startch to demonstrate a non-Newtonian fluid and I think I actually posted on it awhile back. As you said, amazing stuff for just a polymer of sugar molecules!

    Comment by Abel Pharmboy — 12 Mar 2007 @ 3:27 pm

  6. Abel

    Yes, I think I saw that video at your site first. I thought it fitted well with this post.

    Comment by Cat — 12 Mar 2007 @ 7:52 pm

  7. [...] of lipids and emulsifiers on the rheological behavior of corn starch gels (IFT [...]

    Pingback by It is times like this... « Lab Cat — 28 Mar 2007 @ 12:05 pm

  8. Dear Sir/Madam,

    i would like to ask you the following question:

    What are the characteristics of the rice starch in particular in relation to the adhesion of the B.cereus spores on it?

    Comment by Maria — 5 Apr 2007 @ 10:34 am

  9. Maria

    Sorry, I don’t have a clue!

    Comment by Cat — 5 Apr 2007 @ 10:38 am

  10. dear sir/madam,
    could you tell me the propertirs of corn starch and the methods to determine those properties
    thank you!

    Comment by chamila — 28 Jun 2007 @ 3:20 am

  11. pls,i want to know the various functional properties of cereal starches, and how to go about determining them.

    Comment by michael — 7 Dec 2007 @ 10:29 am

  12. Sir

    Can u tell me what exactly imparts adhesive properties to starch molecules?

    Comment by Shantanu — 20 Dec 2007 @ 4:14 am

  13. hello there, i’m just wondering if the cornstarch gel capable of sagging after the freeze-thaw cycle? i know syneresis occurs but what about the percentage sag?

    Comment by Anon — 21 Feb 2008 @ 12:12 pm

  14. hello, i’m interested in what you menssion here. what if you descrube corn starch application in textile factories and type of corn that they use ,and the properties of the corn

    Comment by abubeker — 6 Mar 2008 @ 5:59 am

  15. sir/madam
    pls i would like to know the physiochemical propwerties of cassava starch

    Comment by iwuoha nwamaka — 22 Sep 2008 @ 4:04 pm

  16. sir…. i would like 2 know how to isolate starch from black gram ( vigna munga)… it will help in my project if u provide any link…thnk u sir

    Comment by nevil — 29 Jul 2009 @ 11:59 pm

    • You’ll need to see how you isolate starch from other foods and adapt the method.

      Comment by Cat — 30 Jul 2009 @ 8:05 am

  17. Does anyone know of info on the chemical makeup of cornstarch pudding (water, constarch, sugar, & salt, brought to a boil etc.)?

    Comment by tom arnall — 13 Aug 2009 @ 9:26 pm

  18. excellent post.

    http://www.christy.com

    Comment by chris — 5 Jan 2010 @ 9:22 am

  19. waooooooooo amazing

    Comment by shabana — 30 Sep 2010 @ 7:31 am

  20. sir..
    pls i would like to now the physicochemical properties of maize starch. also simple methods for the dterminations

    Comment by asma — 12 Apr 2011 @ 6:45 am


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