Starch gel and paste undergo syneresis, which is the release of water during cooling, storage, and freeze-thawing, resulting in changes in texture and sensory perception in refrigerated and frozen food products. Therefore, the assessment of syneresis is essential for determining the quality of these food products. Chemical modification of starch has been shown to enhance the stability of refrigerated and frozen foods by interfering with the alignment of amylose and amylopectin through steric hindrance from the functional groups introduced.
One primary method for reducing syneresis and preserving the textural changes in refrigerated and frozen food products is acetylation of waxy maize, tapioca, and potato starch. Hydroxypropylation, on the other hand, enhances the ability of starch to withstand freeze-thaw cycling by increasing its water-binding capacity or preventing starch chain alignment via the introduced hydroxypropyl groups.
Studies have shown that modified treatments improve the freeze-thaw stability of starch. For instance, waxy barley treated with hydroxypropylation followed by cross-linking has demonstrated improved stability, with six to seven freeze-thaw cycles compared to the one to two cycles of native waxy barley starch. Additionally, a combined modified treatment of rice starch with 1% STMP and 4% STPP provides the highest freeze-thaw stability compared to those modified using 1% STMP or 4% STPP alone. This is attributed to the branching of phosphate groups, which affects the dramatic high peak and final viscosities of the starch paste.
Inhibiting the interaction of amylose chains through substitution of starch side chains with a succinate group has been shown to lead to weaker gel formation. This results in a reduction in the formation of junction zones, thus weakening the gel. Increasing the spatial hindrance of OSA-modified potato starch with an increase in DS reportedly weakens the association between starch chains, leading to an increase in water retention capacity under refrigerated conditions, hence improving the freeze-thaw stability.
In conclusion, modifying starch is a vital aspect of enhancing the stability and quality of refrigerated and frozen food products. This modification, through acetylation, hydroxypropylation, or substitution of starch side chains, can improve the water retention capacity and prevent starch chain alignment, ultimately leading to improved freeze-thaw stability.