Evaluation of acetylation and cross-linking on functional properties of acorn starch

Starch is the most widely used natural polysaccharide in the food industry, which plays a significant role in the consistency, texture and nutritional value of food products. Although natural starch from various plant sources has unique properties, with the advancement of food technology and the development of new methods of food processing, the structure of starch changes which can lead to the loss of some of its desirable properties in foods. In order to improve the functional properties of starch, its structure can be modified through modification. The aim of this study was to evaluate the effect of acetylation and cross-linking on functional properties of acorn starch in comparison to commercial wheat starch.

In this research, the acorn fruit was collected from mature trees located in Baghmalek in Khuzestan province, and its starch was extracted. To compare with a high-consumption starch, commercial wheat starch was used as a reference. The chemical composition of wheat and acorn starches was measured using standard AACC methods, amylose was measured based on the formation of a blue complex with iodine reagents and reading of absorbance at 615 nm. Modification of starches by cross-linking methods at 0.1%, and percentage of acetylation and degree of substitution with 6% acetic anhydride was measured accurately using the titration method, and the swelling factor was determined. Syneresis was measured during days 1, 2, 3, 4, 7. Statistical analysis was performed using SPSS software and comparisons of the meanings by Duncan test at 5% probability level.

The results showed a significant difference in the amount of amylose in natural starch of wheat and acorn. Fat, moisture and protein content of two starches showed a significant difference but there was no difference in ash. The protein and moisture content of acorn starch was higher and its fat was less than wheat starch. The percentage of acetylation and degree of substitution were significantly different in two studied starch. Cross-linking reduces the factor of swelling and acetylation caused increased swelling factor in the two examined starches. The highest swelling factor was indicated in acetylated wheat starch and the lowest swelling factor was indicated in cross-linking acorn starch. Syneresis was the highest in cross-linked wheat starch and the lowest in acetylated wheat starch.

The results of this study showed cross-linking could be caused to decrease and increase the swelling factor and syneresis in modified starches compared to natural starches in both studied starch respectively. On the other hand, acetylation of starch caused decreasing and increasing the syneresis and swelling factor in modified starch respectively compared to natural starches of wheat and acorn. Therefore, the degree of cross-linking is an important factor in creating the desired properties. The Cross-linked starch of acorn in food products can be used to improve the crispness of crispy crackers and biscuits, as well as acetylated starch could be used as the thickening agent in soups, sauces, stews, bakery products, dairy products, and baby food. Also, due to the low amylose content of acorn starch and suitable functional properties it is suggested that application of acorn starch as an alternative starch in food industry evaluated in future studies.