International Journal of Biological Macromolecules
Thermal and pasting properties and digestibility of blends of potato and rice starches differing in amylose content
Introduction
Starch has wide applications in the food industry, but the inherent physicochemical limitations of native starches limit its use in food processing. Modification of starch is carried out to enhance the positive attributes and to eliminate any deficiencies of native starches [1]. An alternative approach to modifying starches is to mix different individual starches to prepare blends with enhanced or targetted physicochemical and functional properties [2,3]. Starch blends made without using any chemical reagents are considered green and may satisfy consumer demands for safety, and are thus attracting more and more research and industry attention.
The properties of starch blends can display additive or nonadditive behaviours. The additive effect is the independent behaviour of each starch in mixture, i.e., the properties of mixture can be predicted based on the sum of the individual starches. In contrast, in the nonadditive effect, changes of individual starch in the blend influence each other in behaviours, that is the properties of the blend cannot be predicted simply by addition [4]. It has been reported that larger differences in the composition and structure of the individual starches tend to play a significant role in behaviours [5,6]. A-type polymorph, characteristic of cereals, is densely packed inside the granule. This structural organization limits the amount of adsorbed water resulting in greater stability and higher transition temperatures in the granules [7]. In B-type polymorph, found in tubers and roots, the double helices of amylopectin chains have more space between them. This allows higher water absorption capacity than starches with A-type pattern [7]. Additionally, the differences in relative granule sizes between individual starches, were recognized as important factors influencing gelatinisation and pasting of the blend [5]. Potato starch, from a tuber, has a B-type polymorph and relatively large granule size (10–100 μm), while rice starch from a cereal grain exhibits a typical A-type polymorph with small granule size. Moreover, rice starch has the smallest granule size among common cereal starches, ranging from 3 to 8 μm [7]. Using starches with significant differences in structure and properties may lead to a range of physicochemical properties of blend system [5]. Therefore, blending of potato and rice starches is a good model to study due to their easy availability and large differences.
The physciochemical properties of blends of potato and rice starch have been reported, focusing on the effects of starch concentration, mixing ratio and granule size [[5], [6], [7], [8], [9], [10], [11]]. At lower starch concentrations, viscosities of the blends were between those of the individual starches, while at higher concentrations, viscosities were as high as or even higher than the values of potato starch, especially for blends of potato starch with rice starch. Under such conditions, viscosity development is determined by granule rigidity rather than by swelling power [12]. Viscosities were higher for blends of waxy rice starch with the small granule size of potato starch than for those with medium or large size of potato starch. This is probably due to its higher swelling power (due to its lower amylose and higher phosphorus contents) and higher rigidity (due to its lower granule size) [6].
Chemical composition of the starches, especially the amylose content, is crucial. The ratio of amylose to amylopectin in the blend can influence pasting and gelation properties [7]. Previous research focused on the influence of amylose content on the properties of blends of starches from the same plant species [[13], [14], [15]]. Sasaki et al. [15] found that starch mixtures of wheat exhibited higher swelling power than individual starches with the same amylose content. Ortega-Ojeda et al. [14] indicated that when normal amylose potato starch was added to high amylopectin potato starch, higher moduli values of gels were obtained and could be attributed to the presence of amylose in the blends, which led to stronger network formation. This indicates that amylose is crucial for controlling rheological behaviour in blend with high amylopectin. For blends of potato starch with waxy maize starch, non-additive effect of pasting behaviour was less pronounced as waxy maize starch swelled to a greater extent than its normal amylose maize counterpant, and the difference in swelling power between potato starch with waxy maize starch was smaller [12]. The results indicated that one starch with different amylose content blended with another starch could result in different pasting behaviour in the blend. However, systematical study on the effect of amylose content in properties of two-starch blends is limited. Besides, the ratio of the two starches plays a critical role in the properties of blends and final product. Sandhu et al. [10] indicated blending of potato and rice starch in a 1:1 ratio led to optimal noodle-quality as compared to noodles prepared by using of starch with other blending ratios, in terms of their lower cooking time, higher cooked weight, transparency and slipperiness.
Obanni and BeMiller [9] concluded that in the heating process, the interaction of starch molecules from various botanical sources occurs either between leached amylose molecules from one starch and granules of the other starch or between molecules on the outer surfaces of granules of the two starches. The hypothesis is that the different amylose content in one starch may influence the behaviour of the other starch or their blends through differing level of amylose leaching during starch gelatinization, thereby leading to a range of properties in the mixed system. To elucidate the effect of amylose in a two starch mixture, potato starches (waxy and normal) and rice starches (waxy, low and high amylose) were used to make starch blends with different ratios. Amylose leaching, pasting, thermal properties and in vitro digestibility of the starch blends were determined. This study may provide a basis for applying starch mixtures to achieve diverse properties.
Section snippets
Materials
Normal potato starch (NPS) and waxy potato starch (WPS) were purchased from local supermarkets in China. Rice varieties Yangfunuo (waxy), Qiuguang (low-amylose), and Luhui (high-amylose) were bought from Jiahao Gardening Company (Suqian, China). Rice starches were isolated by the method of Sui et al. [16]. Amyloglucosidase (EC 3.2.1.3, 300 AGU mg−1) and pancreatin from porcine pancreas (EC 232.468.9, 228 USP mg−1) were supplied by Sigma Chemical Co. (St. Louis, MO). All chemicals and solvents
Apparent amylose content (AAC)
AAC of potato is classified into waxy, <5%; normal, 20–35%; and high, >40% [20]. AAC of waxy potato starch (WPS) and normal potato starch (NPS) were 0.90% and 33.2%. AAC of starches from rice varieties Yangfunuo, Qiuguang, and Luhui were 0.65%, 13.0%, and 25.2%, respectively. AAC of rice is classified as waxy (0–2% amylose), very low (5–12% amylose), low (12–20% amylose), intermediate (20–25% amylose), or high (25–33% amylose) [21]. Therefore, starches isolated from Yangfunuo, Qiuguang, and
Conclusion
Blending of potato starch with rice starch can result in properties different from those of the individual starches. Thermal behaviour of potato-WRS blend was nonadditive, but more independent gelatinization behaviour occurred between potato starch and LARS or HARS. Although pasting properties were determined in excess water, some blends exhibited nonadditive behaviour, and some mixtures of WRS and potato starches had higher peak viscosity than the individual starches. There were nonadditive
CRediT authorship contribution statement
Mengting Ma: Data curation, Formal analysis, Validation, Visualization, Writing - original draft. Yi Liu: Conceptualization, Data curation, Formal analysis, Validation. Xiaojing Chen: Methodology, Investigation. Charles Brennan: Resources, Software. Xianming Xu: Investigation, Methodology, Writing - review & editing. Zhongquan Sui: Writing - review & editing, Project administration, Supervision, Funding acquisition. Harold Corke: Writing - review & editing.
Declaration of competing interest
The authors declare that there is no conflict of interest.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (31671893, 81402366, 81773064), the National Key Research and Development Program of China (2016YFD0400206), and the Shanghai Committee of Science and Technology (19390743700, 18490741300, 18391900600).
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Authors contributed equally to the work.