Freeze-Thaw and Starch Gels

February 17/Bangkok, Thailand/Chemical & Chemistry -- According to a study from Bangkok, Thailand, "Frozen food products are gaining acceptance in Thai food industry, and frozen bualoy dessert is a good opportunity for marketing in domestic and for exports. One important factor affecting quality of frozen starchy foods is retrogradation of starch gels."

"Thus freeze-thaw stability of a frozen bualoy made from total waxy rice flour was studied and compared among the samples modified by 20 and 30% cross-linked tapioca starch (CTS) derivatized with phosphorylation and 0.25% propylene glycol alginate (PGA). The waxy rice flour was pregelatinized by adding boiled water before shaping as a ball, then boiled and mixed with coconut syrup. All samples were subjected to five freeze-thaw cycles over 60 days in a conventional freezer (-18 degrees C). Texture analysis firmness and stickiness of the nonfrozen gels substituted with 20% CTS (382 +/- 43, 20.5 +/- 7.1 g.f) and 30% CTS (493 +/- 37, 31.1 +/- 7.0 g.f) were significantly different as compared with the control (329 +/- 22, 14.8 +/- 3.1 g.f). Similar results were observed for the samples continuously frozen for 60 days. The effects of freeze-thaw stability to the frozen gels of the control, CTS and PGA substituted samples appeared after two cycles and exhibited a large increase in firmness and stickiness at the fourth cycle. The firmness values obtained from the control and the samples substituted with 20% and 30% CTS were 2,397 +/- 197, 2,182 +/- 203, and 2,104 +/- 200 g.f, respectively. This evidence was also observed with the samples containing PGA, but the effect was slightly less. This might account for the recrystallization of amylopectin molecules induced by freeze-thawings. With DSC, the waxy rice gels showed a significant increase in the melting enthalpy (2.39 +/- 0.23 J/g) at the fifth cycle from the nonfrozen gels (0.11 +/- 0.02 J/g)," wrote N. Vatanasuchart and colleagues, Kasetsart University.

The researchers concluded, "The sensory tests of the bualoys were correlated with textural qualities that were acceptable to the panelists when the freeze-thawing went no further than the second cycle."

Vatanasuchart and colleagues published their study in Cereal Chemistry ("Freeze-Thaw Stability of Bualoy Thai Dessert Using Waxy Rice Flour." Cereal Chemistry, 2010;87(1):73-78).

For more information, contact O. Naivikul, Kasetsart University, Dept. of Food Sci & Technol, Fac Agroind, Bangkok 10900, Thailand.

From the March 1, 2010, Prepared Foods E-dition