Causes of starch browning, why starch browning?
In the starch-based processing industry, most requests starch to be pure and white. However, some people have been unable to effectively solve the problem of browning of starch and excessive impurities due to factors such as poor production process and irregular operation. Products such as fan powder and skin processed with browning and excessive starch have poor color and low grade, which naturally affects economic benefits. Therefore, it is necessary to understand the causes of starch browning and excessive impurities in the products, find the cause of starch browning, and take corresponding measures to solve this problem.
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What is starch browning?
Starch browning refers to the process of changing the normal color of starch from white to brown or near brown, yellow, gray, black, etc., during the extraction and storage process. Browning is a common discoloration phenomenon in food processing, including beneficial browning and unhelpful browning. Beneficial browning is the use of browning properties to make it discoloration in favor of video value, such as bread, pastry, coffee and other foods produced during the baking process, the yellowing of the caramel and the resulting aroma. Unhelpful browning refers to the reduction of the aesthetic value of the product and the value of the product itself after browning. For example, after fruit, lotus root incision or wounding, browning occurs quickly, which not only affects the appearance but also reduces the nutritional value, and is serious. Browning can be a sign that products are unpalatable. The browning during the processing of potato starch is unhelpful browning, and finding a solution to this problem is key.
So what is the causes of starch browning in starch processing?
1. Phenolase browning
Starch browning of sweet potato and potato is due to the inclusion of polyphenol oxidase in the root tissue, also known as tyrosinase or catechol oxidase, phenolase. When the potato pieces are cut or pulverized, a large amount of phenolic substances such as tyrosine are directly exposed to the air, and under the action of oxygen, the zymogen is activated into an active enzyme, which adheres to the surface of the starch granules to make the starch brown.
Under the action of polyphenol oxidase, tyrosine is easily oxidized to terpenoids. Once the ruthenium molecule appears, it will polymerize quickly. When the amount of polymerization reaches 16 or more, it will become a brown substance, and the browning will be faster under high temperature conditions. In starch processing, enzymatic browning is inhibited mainly by inhibiting the activity of the polyphenol oxidase to kill the enzyme.
2. Phenol iron reaction
Sweet potatoes and potatoes contain phenolic substances, and phenols are prone to browning when they are in contact with iron. The powder slag and starch have a long contact time with the iron, and the dark purple color is mostly phenol iron reaction. When producing starch, it is necessary to avoid contact with iron, or to shorten the contact time as much as possible, and to control the ferric ions generated by iron due to oxidation and the like when the starch is in contact with the iron.
3. Tannin organic matter
Sweet potato, potato and cassava contain tannin organic matter. When the potato are broken, the tannins in the slurry will become black after contact with the iron equipment for a long time. The tannin can be removed by washing.
4. Processing the color contained in the raw material
Purple potato contains a large amount of anthocyanins, and the potato is yellowish after crushing. In the process of processing starch, the starch slurry is not clean enough, so that some pigment remains in the starch, making the starch whiteness worse. The high starch content sweet potato variety with red skin white heart not only has improved yield, but also has good starch whiteness.
5. Maillard reaction
Also known as the ammonium carbamate reaction is a complex reaction that occurs when a sugar and an amino acid are heated, and the reaction then forms a brown so-called "melanoid".
6. Ascorbic acid browning
Potato contains vitamin C, which is oxidized to brown when exposed to air. Opportunities to contact with air should be minimized during starch production. And vitamin C is soluble in water, and the starch removes most of the vitamin C by washing it several times, thereby reducing the browning caused thereby.
7. Hydrogen cyanide reacts with iron
Cassava contains a large amount of hydrocyanic acid. When the potato pieces are broken, hydrocyanic acid is released and dissolved in the washing water to react with iron to form ferrocyanide, which is light blue.
Starch slurry in the process of standing precipitation, if the temperature is high and the precipitation time is long, the soluble sugar in the slurry will be fermented and the pH will be lowered. When it reaches 4.3 to reach the isoelectric point of the protein, the protein will precipitate, and the soluble sugar will be dissolved. The pectin forms a gel and is mixed with the starch granules, causing difficulty in separation and reduction in starch whiteness and extraction rate.
All in all, from above you can see that to solve starch browning, professional technical process is very important, good quality starch processing equipments can guarantee produced starch good quality, pure white.