Encapsulation and retention profile of thymol in the preformed “empty” V-type starch inclusion complex

Abstract

Starch, especially its amylose component can form inclusion complex (IC) with various small molecules, such as flavor and aroma compounds. Complexation of flavor compounds using starch matrices is driven by the hydrophobic interaction and the successful complexation may increase the retention of flavor compounds. In the present study, thymol (2-isopropyl-5-methylphenol) at two different concentrations was introduced into three types of V-type crystalline starches that have different inner helical cavity size, namely V6h, V7, and V8, and the formed ICs were characterized by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The encapsulation efficiency (EE), loading efficiency (LE), and retention profile were determined by gas chromatography-mass spectrometry (GC-MS). The results indicated that when preparing ICs using V6h high amylose maize starch (HAMS) at a starch/thymol mass ratio of 2:1, the helical cavity of V6h helices was expanded and resulted in the formation of V7 crystals. Such circumstance could be owing to the cyclic structure of thymol and caused the minor phase transition at T2 of around 110°C observed in DSC. While in other conditions, the complexation with thymol did not alter the structure of starch. The EE and LE results suggested that V6h-type HAMS exhibits higher capability to encapsulate thymol compared to V7 and V8 HAMS. All ICs demonstrated potent flavor retention ability and retained more than 70% of thymol after 8 h treatment. This study suggested that preformed “empty” V-type starch could act as a potential matrix to encapsulate thymol, and this encapsulation technology should enable targeted applications of thymol for food processing and formulation applications.