Formation and stability of amylose ligand complexes formed by high pressure treatment
Highlights
► Starch gelatinization by high pressure has been investigated. ► B-type starch (potato) and A-type starch (tapioca, broad bean, pea) were considered. ► Amylose ligand complexes were formed during high pressure treatment. ► Decanoic acid and carvacrol have been selected as ligands.
Introduction
The gelatinization of starch is a well-known phenomenon frequently described in the literature. It has been extensively studied in the field of food science (Hermansson & Svegmark, 1996). Traditionally, gelatinization is achieved by heating starch in the presence of water; this method is presented as thermal gelatinization (TG) in the rest of this paper. Alternatively, gelatinization can be obtained at room temperature by hydrostatic pressure (HHP) treatment. It has been shown by a few authors that the progress of high pressure-induced starch gelatinization (HPG) of starch–water mixtures depends markedly on the botanical source of the starch, the treatment pressure, temperature and time (Bauer & Knorr, 2005).
The ability of amylose, the linear fraction of starch, to interact with certain ligands to form complexes has been known for a long time. These complexes are formed during the gelatinization of starch as described, for example, by Escher, Nuessli, and Conde-Petit (2000) or during the subsequent cooling phase in the case of TG (Kugimiya & Donovan, 1981).
Amylose forms crystalline complexes, known under the generic name of “V-amylose”, with a variety of small ligands. Different types of V-amylose, depending on the complexing molecule, can be found in the literature. The best-known and best described complex is Vh amylose, which is obtained with linear alcohols (Brisson et al., 1991, Buléon et al., 1984, Le Bail et al., 1995, Whittam et al., 1989) and monoacyl lipids (Godet et al., 1995a, Godet et al., 1993). It consists of a six-fold left-handed helix repeating at 0.80 nm, in which the complexing agent is included.
Three other crystalline types of complex with non-linear alcohol have also been highlighted. These can initially be distinguished by using the constructive amylose helix. To date, two families of V-amylose complexes have been identified, namely the V6 and V8 types, for which “6” and “8” represent the number of d-glucose units per turn. For V6 types, two trapping modes could be suggested: inclusion V6I (Vh) and inductions V6II and V6III, where I, II and III represent the varying volume between helices in the crystalline stacking. For V6I (Brisson et al., 1991), the small molecules could only be trapped in the cavity of the helix (Godet, Tran, Colonna, Buléon, & Pezolet, 1995) while for V6II and V6III, the molecules could also be trapped between the helices (Buléon et al., 1990, Helbert and Chanzy, 1994).
In this work, the specifications and properties considered for the selection of complexing molecules were the melting temperature which had to be in specific ranges (< 40 °C) and also susceptible of obtaining two different types of V-amylose.
The ability of amylose to interact with thymol and menthol can be found in the literature and the resulting crystalline structure is well known as being V6III type (Biais et al., 2005, Conde-Petit et al., 2006). Carvacrol has a similar structure to thymol and menthol but its melting temperature is significantly lower, and especially below 40 °C (3 °C against 40 to 45 °C for menthol and 49 to 51 °C for the thymol) and decanoic acid (melting point at 30 °C) is well known to form crystalline complexes in the V6I type with amylose.
The aim of this study was to investigate and to compare the changes in the physico-chemical structure and microstructure of starch–water suspensions undergoing thermal and high pressure treatment. The impact of the presence (or absence) of selected complexing molecules (decanoic acid and carvacrol) was also considered.
Section snippets
Materials
Potato starch was purchased from Sigma-Aldrich (FRANCE), broad bean (Vicia faba) and pea starches from wood food and tapioca from National-Starch (USA). Decanoic acid and carvacrol were provided by Sigma-Aldrich (France).
Thermal treatment and storage of the samples
Starch dispersions (starch, 20% w/w) were prepared with distilled water (200 ml) in a 250 ml Sovirel bottle. The mixture was stirred for 10 min with nitrogen bubbling to prevent oxidation, and then 20% of complexing molecules (starch, w/w) were added to the bottle before it was
Optical microscopy
Fig. 1 shows the granular structure of different native starches before and after high pressure treatment at 20 °C and 40 °C observed by microscopy under polarized light. As expected, the starch granules were swollen after high pressure treatment at 20 °C for the four starches tested (A2, B2, C2, D2). The starch granules lost their characteristic shape for broad bean (B2), pea (C2) and tapioca (D2) starches. However, birefringence was still observed in the granules of potato starch (A3) after
Conclusion
In this present study, thermal and high pressure treatments (500 MPa) at 20 °C and 40 °C were applied to potato, tapioca, broad bean and pea starches in excess water to provoke starch gelatinization. In addition, suspensions of broad bean starch were treated in the presence of decanoic acid or carvacrol, which were used to track the possible formation and stability of specific amylose–ligand complexes during gelatinization. The results showed that starch gelatinization was possible for broad bean,
Acknowledgments
Access to the NMR facilities of the BiBS platform of INRA Angers-Nantes is acknowledged.
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