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Q: Several people have complained to me that their idlis are turning red after cooking.
Working women prepare the batter and keep it in fridge for several days as daily preparation is not possible for them. These women are facing this problem as fresh batter doesn't turn cooked idlis rust-red.
I too noticed that if the batter is kept in the fridge for more than 10 days, the idlis are turning rust-red. Some women told me their idlis have turned red even when cooked within five days of preparing the batter (consisting of black gram, parboiled rice rava or idli rava which is commercially available, iodine-fortified salt and chlorinated water and some, it seems, added methi seed powder to it). This, I think, depends on the temperature in the fridge. The high temperatures speed up the reaction and also fermentation of the batter.
Why is this happening? What is the chemical reaction occurring? People are worried about consuming them. I wanted to help them in finding an answer. Therefore, I approached a food technologist for the answers to these Qs.
And this is the answer given by Dr. Ajit Singh Bhatnagar, Food Technologist, Central Food Technological Research Institute...
Madam, given the background that you have provided about this idli batter being kept for 10 days in fridge resulting in reddish brown idlis on steaming, I can predict of Maillard Browning reaction *taking place during steaming of idlis. Maillard browning reaction involves precursors like reducing sugars and free alpha-amino acid. This is a chemical action resulting in brown coloration. The reducing sugars present in rice and the alpha-amino acids present in urad dal may on prolonged storage facilitate this reaction which on steaming gets accentuated due to oxidation by heat. Hope this helps.
The reactive carbonyl group of the sugar reacts with the nucleophilic amino group of the amino acid, and forms a complex mixture of poorly characterized molecules responsible for a range of aromas and flavors. This process is accelerated in an alkaline environment, as the amino groups (RNH3+ → RNH2) are deprotonated and, hence, have an increased nucleophilicity. The type of the amino acid determines the resulting flavor. This reaction is the basis for many of the flavoring industry's recipes. At high temperatures, a potential carcinogen called acrylamide can be formed.
In the process, hundreds of different flavor compounds are created. These compounds, in turn, break down to form yet more new flavor compounds, and so on. Each type of food has a very distinctive set of flavor compounds that are formed during the Maillard reaction. It is these same compounds that flavor scientists have used over the years to make artificial flavors.
The Maillard reaction also occurs in the human body. It is a step in the formation of advanced glycation endproducts (AGEs).
Although the Maillard reaction has been studied most extensively in foods, it has also shown a correlation in numerous different diseases in the human body, in particular degenerative eye diseases. In general, these diseases are due to the accumulation of AGEs on nucleic acids, proteins, and lipids. Though AGEs have numerous origins, they can form from the oxidation and dehydration of Amadori adducts, which themselves are products of nonenzymatic Maillard reactions. Apart from ocular diseases, whose correlation with Maillard chemistry has been more recently studied, the formation of AGEs has also proven to contribute to a wide range of human diseases that include diabetic complications, pulmonary fibrosis, and neurodegeneration. The positron emission tomography imaging agent fluorodeoxyglucose has been shown to undergo the Maillard reaction to form fluorodeoxyglycosylamine.
Q: Is it safe to consume food products that turn brown because of Maillard reaction?
Dr. Bhatnagar says ...
"There are no adverse effects as such during short term consumption. However, if prolonged consumption of maillard reaction products may lead to certain ailments like tissue inflammation. The final reaction product of maillard browning is acrylamide which has been linked to tumors/cancer. That's why repetitively deep fried products are not advisable on long term basis. Once in a while is ok. The thing is these maillard browning reaction products are basically free radicals and hence are reactive oxygen species which need to countered with natural antioxidants **. Stored Idli batter kept for more than 5 days should be avoided however there is no immediate harm in consuming it once in a while. Now, the fresh idli batter is also available easily so I don't see any need to store idli batter for 10 days. The condition of storage also matters. If at all we need to store the idli batter then it must be stored at 1–2 degree Celsius."
**Like the antioxidants you get in fruits and vegetables.
Maillard reaction produces flavour and aroma during cooking process; and it is used almost everywhere from the baking industry to our day to day life to make food tasty. It is often called nonenzymatic browning reaction since it takes place in the absence of enzyme. When foods are being processed or cooked at high temperature, chemical reaction between amino acids and reducing sugars leads to the formation of Maillard reaction products (MRPs). Depending on the way the food is being processed, both beneficial and toxic MRPs can be produced. Therefore, there is a need to understand the different types of MRPs and their positive or negative health effects.
Maillard reaction products have both positive and negative impacts on health. Diverse MRPs act as antioxidants, bactericidal, antiallergenic, antibrowning, prooxidants, and carcinogens. Most of these properties depend on processing of food. High temperature heating makes some food nutritious, whereas some of the foods lose their nutritional value. Many strategies are employed in the food industries to reduce the production of MRPs. For example, acrylamide has been classified as a probable carcinogen to humans by the International Agency for Research on Cancer. During food preparation at high temperature, acrylamides are formed in many types of foods via Maillard reaction. To reduce the amount of acrylamide, asparaginase has been successfully used in laboratory for potatoes and cereals . It has also been reported that injection of CO2 during extrusion process helps to reduce the level of acrylamide.
More information can be obtained here: https://www.hindawi.com/journals/ijfs/2015/526762/