The effect of starch isolation method on physical and functional properties of Portuguese nut starches. II. Q. rotundifolia Lam. and Q. suber Lam. acorns starches

摘要

A new starch was isolated from fruits of two acorn species, Quercus rotundifolia and Quercus suber byalkaline (A3S) and enzymatic (ENZ) methods and physical and functional properties were studied. Theisolation method induced changes in most of those properties in the isolated starches, mainly in resistantstarch content, syneresis, pasting, thermal and rheological properties. Isolated acorn starches presentedhigh amylose content (53e59%) and resistant starch content (30.8e41.4%). Acorn starches showedlimited and similar solubility values and swelling power values, showing a gradual increase from 60 C to90 C. The pasting temperatures ranged from 67.5 to 72.0 C and pastes did not present breakdown,which is suggestive of a high paste stability of acorn starches during heating. At ambient temperature theturbidity and syneresis values were low, but when held at freezing temperatures the syneresis significantlyincreased. Thermal analysis revealed that the acorn starches easily undergo transition phenomenaas shown by the low To and enthalpy values (4.1e4.3 J/g), these effects were more evident in starchesisolated by ENZ method. Pastes are more elastic than viscous and form strong gels after cooling. Q. suberstarch was shown to be more sensitive to the effect of isolation method. Generally, starch isolated byenzymatic method presented less interesting functional properties, since this isolation procedure greateraffected the raw structure of starches