Chinese steamed bread (CSB) is a common staple food for Asians. CSBs are primarily fermentative products of water and wheat flour [1]. In recent decades, adding whole grains such as corn, highland barley, buckwheat, and oats to wheat flour, has become an important way to enhance the nutritional value of CSB, in line with societal changes in diet and health concepts [2, 3]. Consumption of whole grain-supplemented CSB reduces weight gain, improves blood sugar levels, reduces systemic inflammation, and down-regulates hepatic lipogenic gene expression [4]. Therefore, the addition of a variety of whole grains during the manufacture of CSBs is a technical approach to benefitting human health.
Corn is the most cultivated food crop globally and is a widely used agricultural product [5]. Corn is rich source of minerals, functional lipids, and carbohydrates. Rich dietary fiber can promote intestinal peristalsis and inhibit postprandial blood glucose elevation and fat absorption [6]. Replacement of an appropriate proportion of wheat flour with corn flour positively impacts the texture, functional evaluation, and sensory scores of the final products, including bread and cakes [7, 8]. The addition of corn flour is an intriguing option for the production of CSBs.
Presently, corn CSB is made using a commercial flour mix. However, there are three problems with commercial products. First, the amount of corn flour added is typically between 20% and 25%. Second, when multigrain flours such as corn flour are processed into CSB, the insoluble dietary fiber and ferulic acid in the bran cause the aggregation of gluten protein in the CSB, resulting in excessive hardness and reduced specific volume [9]. Finally, blending corn and wheat flours can result in lysine and tryptophan deficiencies in the final products. During corn flour production, the insoluble dietary fiber and ferulic acid are removed by hulling and degerming the corn kernels prior to pulverizing through 60-mesh to prevent texture deterioration in the processed products. However, the removal of dietary fiber results in the loss of corresponding functional properties of corn flour. If corn flour is pulverized into a superfine powder (100-mesh or above), insoluble dietary fiber may be retained with reduced gluten protein aggregation. Therefore, it is necessary to develop a novel commercial flour mix with higher corn flour content, good textural properties, and balanced amino acid content using 60-mesh unpeeled corn flour.
Oats are an important raw grain in the production of healthy foods. The addition of oats to steamed products confers an aromatic quality to the product and improves its sensory characteristics [10]. Phenolic acids and sterols in oats have antioxidant properties, and the protein, glucan, and lipid components in oats can lower blood cholesterol [11]. Oats have the highest lysine content among common grains. The addition of oat flour to a corn CSB can effectively supplement lysine, which is the most abundant amino acid in corn flour. Therefore, it is an effective way to improve the nutritional-limiting factors of the raw materials used in corn flour CSB.
The content of linear chain branches of internal starch modification varies among different grain varieties. The textural properties of the product will be affected differently by the addition of cereals with different levels of linear chain branches. In general, reducing amylose content reduces hardness and increases springiness of the products. In contrast, increasing amylopectin content increases hardness and decreases springiness [12, 13]. Few published reports have discussed the regulation of amylose and amylopectin to improve the quality of steamed bread products. It is thus of interest to develop new products using this approach.
In this study, processing characteristics were used to characterize three types of corn flour and their amylose content for CSB development. The textural characteristics (hardness, springiness, and chewiness) of CSB prepared with different amounts of Yunnan corn flour, Sichuan corn flour, and oat flour were considered to determine the best CSB formulation. The effects of different corn flour amylose contents on dough rheological behavior and microstructure were measured. CSB quality characteristics were analyzed using color metrics and sensory evaluation. The study findings should be useful for improving the utilization of maize resources in staple food products.