Stress-relaxation properties of French fries as a function of moisture content, oil content, frying temperature, and testing temperature

Abstract

There is insufficient information on the effect of temperature, moisture content (MC), and oil concentration on the mechanical properties of fried potatoes. The static mechanical testing capabilities of a dynamic mechanical analyzer (DMA) were utilized to measure the stress relaxation function of fried potatoes as a function of frying time, temperature, and testing temperature. The French fries were prepared in oil heated at 177°C, 184°C, and 191°C, and their MC and oil content (OC) values were measured as a function of frying time. The samples loaded in DMA were subjected to 2% strain, and the stress relaxation was performed for 600 s. The DMA furnace temperature was set at 37°C, 60°C, and 90°C. A two-element generalized Maxwell model was fitted into the DMA data. French Fries lost more than 70% of their moisture and absorbed more than 80% of their final OC during the first 180 s of frying. During the same interval (up to 180 s), the relaxation modulus parameters (G₀ , G₁ , and G₂ ) did not change significantly and then increased linearly. These parameters also did not change considerably for MC above 2 g/g solids. At lower MC values, G₁ and G₂ increased as the MC was reduced, but the elastic modulus G₀ stayed almost constant, independent of the MC.

Keywords: French fries; frying; strain; stress relaxation; viscoelastic properties.