Many people are curious, why do sweet potatoes baked on the roadside have a more attractive aroma and sweet taste than sweet potatoes steamed in a steamer at home? Just in March this year, a research team actually studied the effects of different cooking methods on the flavor and chemical composition of sweet potatoes.
What substances have changed between roasted sweet potatoes and steamed sweet potatoes?
The researchers prepared a total of 12 yellow sweet potatoes and randomly divided them into four groups. One group served as a control group and was not treated. The other three groups were steamed in a pot for 40 minutes, boiled for 30 minutes, and baked in an oven at 200°C for 90 minutes.
The researchers also invited 10 volunteers to evaluate the sweet potatoes. Roasted sweet potatoes, steamed sweet potatoes, and boiled sweet potatoes all differ in appearance, texture, flavor, and chemical composition. Roasted sweet potatoes have a sweeter taste and richer aroma, while steamed sweet potatoes and boiled sweet potatoes have a moister taste but a relatively weak aroma.
Why are baked sweet potatoes sweeter? This is directly related to the sweetness of the soluble sugar content. Roasting increased the soluble sugar content of sweet potatoes from 9.12% to 36.65%. A total of five sugars (galactose, glucose, fructose, sucrose, and maltose) were detected in all samples. Specifically, roasted sweet potatoes contain 200 times more maltose, which may be why roasted sweet potatoes are sweeter.
Why does it smell better? Using gas chromatography-mass spectrometry, it was shown that the aroma of roasted sweet potatoes is more fragrant because of the large amounts of furans and terpenes produced during the roasting process. In the study, five furans were identified, including furfural, 2-furanmethanol, 2-acetylfuran, 2-pentylfuran, and 2-methyl-benzofuran. However, only small amounts of furans were detected in raw, steamed and boiled sweet potato samples.
What do these five furan compounds smell like?
Furfural: Has an almond aroma.
2-Furanmethanol: has a woody or burnt caramel smell.
2-Acetylfuran: smells similar to coffee or baked goods.
2-Amylfuran: It has a fruity and green leafy smell, and on some occasions, the smell is described as close to tomatoes or fruits.
2-Methyl-benzofuran: The odor of this compound is variable and generally has a more complex aroma that may include spice, woody, or phenolic-like notes.
How to produce so many kinds of furans depends on the Maillard reaction, which is inseparable from cooking. The Maillard reaction is a non-enzymatic, heat-induced chemical reaction that occurs primarily between reducing sugars and amino acids. This reaction was first described in 1902 by French chemist Louis-Camille Maillard.
The Maillard reaction is a very complex multi-step reaction, including various intermediate products and final products. Initially, reducing sugars and amino acids (or proteins) are heated or catalyzed to form stable or unstable sugar amines. These sugar amines then undergo a series of reactions such as rearrangement, redox, and polymerization, ultimately generating a variety of complex molecules, including glycation end products.
Some classic delicacies produced through the Maillard reaction include roasted meats, baked breads and pastries, coffee and chocolate, among others.
In addition to Maillard caramelization is also important
The standard for a good roasted sweet potato is that it must ooze dark red sugar juice. In addition to the Maillard reaction, the reason why roasted sweet potatoes are delicious is also inseparable from the caramelization reaction.
Caramelization differs from the Maillard reaction in that it does not involve amino acids or proteins. It is a heat-induced chemical reaction that involves the breakdown and reorganization of sugars when heated. This process is usually carried out at temperatures between 160°C and 210°C, depending on the type of sugar and environmental conditions.
Caramelization is a complex multi-step reaction involving the following main stages: Sugar molecules first undergo a dehydration reaction to generate some low molecular weight compounds. These low molecular weight compounds may undergo structural rearrangements. As the reaction proceeds, the resulting low molecular weight compounds polymerize to form larger, more complex molecules. Ultimately, these compounds form many different types of caramel, with varying colors and flavors.
Like the Maillard reaction, caramelization is a highly complex and variable reaction that produces a wide variety of compounds, including polycyclic compounds, carbonyl compounds, and various organic acids.
In life, we can often experience the effects of caramelization in caramel candies, baked goods, grilled and fried foods, as well as various desserts and specialty drinks. Whether it’s hard caramel, crème brûlée, roasted meats or specialty coffees, caramelization is one of the key factors that give food its attractive color and delicious taste.
Is steamed or baked sweet potatoes healthier?
When it comes to healthy ways to eat sweet potatoes, both roasted and steamed sweet potatoes have their own merits. From a nutritional perspective, studies have proven that cooking sweet potatoes has advantages in retaining carotenoids. Carotenoids are powerful antioxidants, especially beta-carotene, which not only provides abundant vitamin A, but also plays a significant role in maintaining vision, strengthening the immune system, and promoting skin health.
From a glycemic index (GI) perspective, there is a significant difference in sugar content between baked and steamed sweet potatoes. The glycemic index is a measure of the impact of carbohydrates in food on blood sugar levels. The lower the number, the smaller the impact on blood sugar.
Steamed sweet potatoes have a lower glycemic index (GI of 44), while roasted sweet potatoes have a higher glycemic index (GI of 94), meaning they break down into sugar quickly and may cause a temporary spike in blood sugar levels.
However, the differences between baked and steamed sweet potatoes were not significant in terms of protein and fat content. So if those two nutrients are your concern, both cooking methods are acceptable.
Of course, eating sweet potatoes is not just for nutritional intake, taste and personal preference are also important considerations. Roasted sweet potatoes generally have a richer flavor and better texture, which is why most people prefer roasted sweet potatoes to steamed sweet potatoes.