Monitoring sugar levels in potatoes is a critical process for growers, as it helps minimize losses resulting from factors that impact the color of processed products. Simply put, when chips or fries are produced, elevated glucose levels can lead to a darker color, which is undesirable.
Sucrose, the primary free sugar in immature potatoes, serves as the main source of carbons and energy for starch synthesis and growth. As potatoes mature, a portion of the carbon from sucrose undergoes complete oxidation to CO2, H2O, and energy. Invertase, an enzyme produced by yeast, catalyzes the hydrolysis of sucrose, forming invert sugar.
If a protein inhibitor prevents invertase from breaking down sucrose during growth, the invertase reaction becomes active in storage, generating undesirable reducing sugars from the available sucrose pool. Consequently, high levels of sucrose are present in potatoes at harvest.
When raw potatoes are sliced and fried at high temperatures, excess reducing sugars react with abundant free amino acids in the potato cells, resulting in the formation of brown to black pigmented chips.
Increased Levels of Reducing Sugars
What causes increased levels of reducing sugars? Several factors influence the sugar content of potatoes, including variety, growing season, vine kill, harvest, and storage. Additional factors encompass storage duration, ventilation, transport, and handling.
Many researchers attribute storage temperature as a major contributor to the issue. Numerous studies indicate that colder storage temperatures can lead to increased reducing sugars. Even a slight temperature variation can have a significant impact. Recommended storage temperatures may vary depending on the potato variety and intended end use.
Monitoring Sugar Levels
ZP offers our SenseItAll (SIA) glucose measuring system. Generally, glucose levels below 0.1% are deemed acceptable for french fry processing quality, while levels of 0.2% and below are ideal for quality dehydrated potato products, such as potato chips.
When sampling potatoes, it’s critical to select from two sample sets, picking a random 5 or 6 potatoes from each sample.
