Development and evaluation of wholegrain sorghum-based gluten-free pasta

Abstract

Pasta is a staple food that is popular all over the world, but it is a common component in the Western diet. It is traditionally made from durum wheat (Triticum turgidum subsp. durum) semolina, which is high in gluten content. Pasta is considered a healthier source of carbohydrates owing to its slow rate of starch digestion. Intake of slowly digestible starches is associated with lower postprandial glucose response, thus reducing the risk of metabolic diseases such as obesity, diabetes, and cardiovascular disease. Gluten-free (GF) versions of pasta and other staple foods have grown in popularity over the recent years due to the increase in diagnosis of gluten- or wheat-related health conditions such as coeliac disease, wheat allergy, and non-coeliac gluten sensitivity, and also due to individual choice. However, majority of commercially available GF pastas are made using rice or maize flour/starch, which are highly digestible.Sorghum (Sorghum bicolor L. Moench) is an important cereal crop worldwide but is not commonly considered a food source in the Western diet. It is a GF grain and has lower starch digestibility compared to most cereal grains. There has been increased interest in wholegrain sorghum as a food source as its low starch digestibility and high fibre and polyphenol contents are associated with reduced risk of diet-related chronic diseases. Therefore, wholegrain sorghum is a potential raw material for the development of GF pasta with added health benefits. Development of sorghum-based pastas has been attempted in previous studies, but still incorporated eggs and refined starches. In the current work, the aim was to develop a vegan GF pasta with low starch digestibility from a wholegrain sorghum-based composite flour, and to evaluate the pasta against a wholegrain durum wheat pasta in terms of cooking and texture qualities, starch digestibility, sensory perception and consumer acceptability.Six GF pastas were formulated from wholegrain red or white sorghum, brown rice, and chickpea flours obtained by hammer milling; further eight GF pastas were produced from flours obtained by pin milling. Hydrocolloids (guar gum and/or xanthan gum) were added to the formulations as gluten replacements. A control pasta was made from wholegrain durum wheat flour. In terms of cooking quality, the sorghum-based GF pastas showed excellent cooking losses (<6%). In addition, texture profile analysis revealed that higher proportion of sorghum flour resulted in pastas with higher hardness and adhesiveness, but lower cohesiveness. The addition of xanthan gum also resulted in similar effects. Adhesiveness and cohesiveness were significantly improved upon reduction of flour granularity as a result of pin milling, but are still not matching those of the durum wheat-based control pasta. Additionally, increasing hydrocolloid content from 2% to 3% did not result in significant improvements in texture.In vitro starch digestion was performed on five sorghum-based pastas (three white sorghum-based and two red sorghum-based) and the control pasta. During the intestinal phase of the in vitro digestion, it was observed that the sorghum-based pastas disintegrated more rapidly than the control pasta. This was attributed to the low cohesiveness of the sorghum-based pastas. The rate of disintegration was directly proportional to the rate of digestion, but the rates were not significantly different across all pastas. It was also found that the sorghum-based pastas, regardless of the rate of disintegration, had lower extent of digestibility than the control pasta.The sensory attributes and the acceptability of four white sorghum-based pastas were evaluated against the control by a panel of twenty volunteers. It was found that the graininess of the pasta, resulting from the coarse granularity of the raw materials, negatively influenced the sorghum-based pastas’ acceptability. Furthermore, the chickpea flavour present in the pasta was negatively perceived by volunteers of Caucasian background. The sorghum-based pasta formulation that was the most accepted was the pasta with 3% guar gum content.The results of the current work suggest that sorghum is a viable alternative to wheat for the production of pasta or noodles, to meet the increasing demand for GF products in industrialised countries where gluten/wheat-related health disorders are a growing concern, and to curb wheat import in developing countries where sorghum is readily available. Further modifications can be done to address the issues present in the current sorghum-based pasta formulations, such as reduction of flour granulation to improve cohesiveness, graininess, and structural integrity; and reformulation to obtain a flavour that would appeal to the Western palate.