Modification of structural, physicochemical and digestive properties of normal maize starch by thermal treatment

doi:10.1016/j.foodchem.2019.125733

Food Chemistry

Volume 309, 30 March 2020, 125733

https://doi.org/10.1016/j.foodchem.2019.125733 Get rights and content

Highlights

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Dry-heat treatment brought a significant effect on starch structure.
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Dry-heat treatment effectively destroyed the crystalline structure of starch.
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Dry-heat treatment decreased T_o, T_p and T_c values.
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Dry-heat treatment facilitated the aggregation of starch granules.
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Dry-heat treatment improved the solubility of starch.

Abstract

Thermal treatment is an effective technique to modify the physiochemical properties of starch. However, investigation on the effect of repeated dry-heat treatment (RDHT) on the starch properties is limited. In this work, RDHT and continuous dry-heat treatment (CDHT) were conducted on normal maize starch. Both treatments increased pore no on the granule surface and facilitated the granule aggregation. The solubility and swelling power of normal maize starch were improved. The levels of slowly digestible starch (SDS) and resistant starch (RS) + SDS were increased. The structural characteristics, including crystallinity and short-range order, were impaired. The peak viscosity and thermal properties (T_o, T_p, T_c and ΔH) of starch paste were decreased. When comparing of CDHT samples with the same treating time, RDHT samples showed a lower crystallinity, a weaker thermal stability, a higher paste viscosity and a lower resistance to amylase. These results were useful for industrial application of thermal treatment on starch.

Introduction

Maize starch is an ingredient widely used in food product formulations, especially in cooked and baked products (Zhang, Gu, Zhu, & Hong, 2018). However, native maize starch has some deficiencies in applications, including low viscosity, poor thermal stability, high syneresis rate and easy to retrogradation (Niu, Han, Cao, Liu, & Kong, 2018). In order to improve the physicochemical properties of maize starch, modification has been investigated. Physical modification techniques are desirable as no chemical pollution is involved and are generally recognized as safe. There are some commonly used physical techniques, including annealing, pre-gelatinization, dry-heat treatment and heat-moisture treatment. Dry-heat treatment (DHT) has been highlighted due to safety and simple practice. It exposes starch to the heat at 120–200 °C under dry condition with moisture content below 10%. The treatment can modify the physical properties of starch without gelatinization (Chi et al., 2019, Ru et al., 2015). Continuous and repeated dry-heat treatments (CDHT) have been recognized as an effectively physical technique for starch modification (Dutta, Mahanta, & Singh, 2015).

In vitro digestibility test can simulate the digestion process of food in human body to estimate the glycemic index (GI) of food. It has been verified that low GI foods have benefits in the prevention and control of obesity, diabetes, cardiovascular diseases and other chronic diseases. The content of slowly digestible starch (SDS) is negatively correlated with GI, while the content of rapidly digestible starch (RDS) is positively correlated with GI (Englyst, Vinoy, Englyst, & Lang, 2003). Pasta with the addion of resistant starch (RS) can reduce GI (Cecilia, Perez, & Edel, 2013). The GI values of sweet potato increase after cooking or baking (Allen, Corbitt, Maloney, Butt, & Truong, 2012). Therefore, changing the SDS and RS levels in starch by physical modification will be beneficial to control the GI.

As normal maize starch is an important starch resource for food production formulation, improvement of physical properties for better application in foods is always the persuit for researchers in this field. It is of great interest to investigate the impact of repeated dry-heat treatment (RDHT) on the structure characteristics and in vitro digestibility of starches. Relevant information available in this field is very limited. Therefore, in this work, normal maize starch was subject to CDHT and RDHT. The structure characteristics, in vitro digestive properties and other properties were measured. The results would be useful for starch processing and further application in food industry.

Section snippets

Materials

Normal maize starch was obtained from Linyi Hengyuan Co., Ltd (Shandong, China). It was normal maize starch with amylose of 27.46%. The content of starch, protein, fat and ash were determined by AACC 76-13, 46-30, 30-25 and 08-01 (AACC, 2000). They were 98.36%, 0.22%, 0.45% and 0.17%, respectively. Chemical reagents used in this work were of analytical grade.

Starch modification

The normal maize starch was dried in an oven at 40 °C for 12 h to keep the moisture content below 10%. The dry starch (200 g) were added

Morphology

SEM images of native and dry-heat-treated normal maize starch granules are showed in Fig. 1. Even though the native starch granules presented as varied shapes, their surfaces appeared to be compact and smooth. Compared with native starch granules, DHT could cause pores on the granule surface. Furthermore, agglomeration in normal maize starch was observed after DHT of only one cycle and the extent of aggregation was increased with extended duration or increased cycles (Fig. 1). The development

Conclusions

In this study, CDHT and RDHT showed apparent effects on the microstructure, crystallinity, viscosity, thermal properties and in vitro digestibility of normal maize starch. Compared with CDHT, RDHT had a greater capacity to decrease crystallinity, thermal stability, weaken short range order, and impair paste stability of normal maize starch. The cooling treatment during RDHT programme played an important role in the differences observed. In the future work, it is required to analyse the possible

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper

Acknowledgements

We appreciated the financial support of research and innovation team construction plan of Henan University of Animal Husbandry and Economy (2018KYTD17).

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Modification of structural, physicochemical and digestive properties of normal maize starch by thermal treatment

Highlights

Abstract

Introduction

Section snippets

Materials

Starch modification

Morphology

Conclusions

Declaration of Competing Interest

Acknowledgements

Food Hydrocolloids

Food Hydrocolloids

International Journal of Biological Macromolecules

Journal of Cereal Science

Food Research International

International Journal of Biological Macromolecules

Carbohydrate Polymers

Food Chemistry

LWT-Food Science and Technology

Food Hydrocolloids

Carbohydrate Polymers

International Journal of Biological Macromolecules

International Journal of Biological Macromolecules

Food Research International

Carbohydrate Polymers

Carbohydrate Polymers

Carbohydrate Polymers

Food Research International