Formation and stability of amylose ligand complexes formed by high pressure treatment

https://doi.org/10.1016/j.ifset.2012.10.006Get rights and content

Abstract

Starch can be gelatinized during high pressure processing in the presence of water, but to a greater or lesser extent. Starch gelatinization is often accompanied by the formation of amylose complexes, in particular when a thermal treatment is used. Four different starches were considered in this study: potato, broad bean (Vicia faba), pea and tapioca. A comparison between high pressure-induced starch gelatinization (HPG) and conventional thermal gelatinization (TG) was made. In the case of broad bean starch, selected complexing molecules were considered for both thermal and high pressure treatments. Cross polarization/magic angle spinning (CP/MAS) 13C NMR, X-ray diffraction and thermal analysis were used to monitor physico-chemical changes in the structure and microstructure of starch preparations. Decanoic acid and carvacrol were selected as complexing agents to track the formation of amylose ligand complexes. It was observed that B-type starch (potato) was more resistant to pressure than the A-type starches (tapioca, broad bean and pea) considered in this study. The results showed that amylose ligand complexes were formed during high pressure treatment (20 min at 500 MPa at temperatures of 20 °C and 40 °C). Decanoic acid induced the complexing of amylose in the V6I type whatever the treatment used. On the other hand, the complexation of carvacrol appeared to depend on the temperature used during the high pressure treatment. It is assumed that carvacrol forms amorphous complexes with amylose during high pressure treatment. The amylose complexes were characterized by 13C CP/MAS NMR confirming the results obtained by X-ray analysis.

Industrial relevance

Development of innovative assembly of amylose + molecules of interest (i.e. antioxidant) using a mild processing (40 °C) instead of 90 °C. At 90 °C, some molecules are damaged or oxidized.

The use of high pressure permits the production of larger amount of compounds than using conventional thermal treatment. The main reason is that there is no need to solubilise the molecule of interest.

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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