Physicochemical properties of quinoa flour as affected by starch interactions

Highlights

• Chemical composition of whole grain quinoa flour of 7 varieties analyzed.

• Physicochemical properties of quinoa flour related to isolated starch properties.

• PCA and Pearson correlation employed to reveal starch interactions.

• Starch and non-starch components interact and contribute to flour properties.

Abstract

There has been growing interest in whole grain quinoa flour for new product development due to the unique nutritional benefits. The quality of quinoa flour is much determined by the properties of its major component starch as well as non-starch components. In this study, composition and physicochemical properties of whole grain flour from 7 quinoa samples have been analyzed. Flour properties have been correlated to the flour composition and the properties of isolated quinoa starches through chemometrics. Great variations in chemical composition, swelling power, water soluble index, enzyme susceptibility, pasting, gel texture, and thermal properties of the flour have been observed. Correlation analysis showed that thermal properties and enzyme susceptibility of quinoa flour are highly influenced by the starch. Interactions of starch with non-starch components, including lipids, protein, dietary fibre, phenolics, and minerals, greatly impacted the flour properties. For example, peak gelatinization temperature of the flour is positively correlated to that of the starch (r = 0.948, p < 0.01) and negatively correlated to the lipid content (r = −0.951, p < 0.01). Understanding the roles of starch and other components in physicochemical properties of quinoa flour provides a basis for better utilization of this specialty crop.

Introduction

Quinoa (Chenopodium quinoa Willd.) is a pseudo-cereal that been cultivated in the Andes of South America as an important food item for several thousand years (Abugoch, 2009). In recent years, quinoa has attracted increasing attention not only in South America but also worldwide, because of its great adaptability to different growing conditions, its multiple uses, as well as the well-balanced nutritional values (Abderrahim et al., 2015, Abugoch, 2009, Wang and Zhu, 2016).

Quinoa has been recognized as a complete food due to the well-balanced nutritional composition (Mota et al., 2015, Wang et al., 2015). Starch accounts for 48–69% of the dry matter in quinoa flour (Wang & Zhu, 2016). The protein content of quinoa has been reported in the range of 14–18%. (Abugoch, 2009, Wang and Zhu, 2016). The lipid content of quinoa has been estimated in the range of 4.4–8.8% which is above the average level of cereals (Wang & Zhu, 2016). Lipid in quinoa is made up of 55.6% of neutral lipids, 25.4% of polar lipids and 18.9% of total fatty acids (Przybylski, Chauhan, & Eskin, 1994). Quinoa can be a good source of dietary fibre (7–10%) (Abugoch, 2009). Quinoa is also rich in certain types of micronutrients such as minerals (e.g., potassium), vitamins (B6 and folate) as well as heath-beneficial bioactive compounds such as polyphenols (Abugoch, 2009, Tang et al., 2016). In particular, quinoa protein is well balanced in terms of amino acid composition and is gluten-free (Mota et al., 2015). It can be developed as gluten-free products to aid people with celiac disease. In light of the healthy nutritional components, quinoa has been processed into whole grain flour for the better retention of the minor nutrients. Various food products such as cakes, cookies and biscuits, noodles, steamed bread, and bread have been formulated from the quinoa flour (Nowak et al., 2016, Wang and Zhu, 2016). The quality of the quinoa-based products is much determined by the properties of the flour.

Since starch is the major component, it is expected that the properties of the flour, to a large extent, depend on the composition and properties of the starch (Wang & Zhu, 2016). Previous studies have well documented various aspects of quinoa starch. The starch is relatively low in amylose content (e.g., 11%), and has very small granules (∼1 to 3 μm) (Abugoch, 2009). The starch has unique properties such as low pasting temperature and high freeze-thaw stability (Abugoch, 2009). The properties of the whole grain quinoa flour are also likely affected by the presence of non-starch components such as proteins and lipids. This has been testified in other flour systems. For example, protein could affect the water-holding capacity, pasting properties and digestibility of cereal flour (Svihus, Uhlen, & Harstad, 2005). Polar lipids could form V-type inclusion complexes with amylose, which influences the starch properties such as gelatinization, retrogradation, and enzyme susceptibility (Singh et al., 2010, Svihus et al., 2005). Non-starch polysaccharides as dietary fibre could increase the viscosity of flour gel and form matrix with phenolics, which may retard the starch retrogradation and digestion (Svihus et al., 2005). Since the chemical composition of quinoa is rather different from that of common cereals, the roles of these non-starch components in flour properties remain to be extended to include whole grain quinoa systems.

The physicochemical properties of the starches isolated from these quinoa varieties have been characterized and presented in a recent publication (Li, Wang, & Zhu, 2016). In this study, the chemical composition and physicochemical properties of whole grain flour from 7 commercial quinoa varieties were analyzed. There are large variations in the composition and properties of the starches from these 7 quinoa samples selected for this study (Li et al., 2016). It may be expected that there would be a great variation in the flour properties as well. Therefore, the relationships of physicochemical properties between starch and flour are correlated by chemometrical analysis. The other components including protein, lipids, minerals, dietary fibre, and phenolics present in the whole grain quinoa flour are also taken into account for their effects on the flour properties.