Difference between Purple and White Onions
In kitchen seasonings and salad accompaniments, the difference between purple-skinned onions and white-skinned onions often piques the curiosity of culinary enthusiasts. This article delves into a four-dimensional comparison to give you a comprehensive understanding of the characteristic differences between these two common edible plants.
Core Difference Comparison of Onion Varieties
Epidermis Color and Morphological Features
The most distinctive feature of purple onions is their violet outer skin, with bulbs generally in a flattened spherical shape, about 5-8 centimeters in diameter. White onions have an ivory white epidermis and are closer to a standard spherical shape, reaching up to 10 centimeters in diameter. This color difference is due to the varying anthocyanin content, with the purple variety containing 3-5 times more than the white variety.
Cell Structure and Water Content
Electron microscopy data shows that the cell wall thickness of purple onions is about 0.8 micrometers, with a flesh layer of only 4-6 layers, maintaining a water content of 86%-88%. White onions have a thinner cell wall of only 0.5 micrometers but have up to 8-10 layers of flesh, with a water content of up to 92% or more. This structural difference directly affects the storage period, with white onions having a shelf life 7-10 days shorter than that of purple onions when refrigerated.
Analysis of Flavor Compound Composition
Purple onions have a sulfur compound concentration of 3.2mg/g, producing a stronger pungent sensation. White onions, due to their high sugar content of up to 6.8% (compared to 4.2% in purple onions), present a sweet taste. Cooking experiments show that purple onions retain 75% of their flavor compounds after high-temperature stir-frying, while white onions retain only 52%, which is directly related to the tightness of their cell structure.
Planting Conditions and Yield Comparison
Purple onions are more adaptable, with yields of up to 4500 kilograms per mu in soils with a pH of 5.6-6.8. White onions require strict control within a pH range of 6.2-6.8 and yield about 2800 kilograms per mu. Recent data shows that purple onions account for 63% of the global onion planting area, while white onions account for only 17%.
Through systematic comparison, it is evident that there are significant differences between the two types of onions in terms of nutritional content, culinary characteristics, and planting requirements. It is recommended that for home cooking, one should choose based on the needs of the dish: white onions are best for salads, and purple onions are recommended for high-temperature stir-frying. Understanding these differences helps in more scientific ingredient matching and storage management.