Properties of gluten-free pasta made from proso millet (Panicum miliaceum)

Proso millet is an excellent second crop in rotation with other cereals, with a short growing season and low water requirements. However, the market for millet-based foods is small, and hence most of the harvest is utilized as animal feed. As a gluten-free cereal of low glycemic index, millet has an attractive application potential that fits current food trends. This work was envisioned as promotion of proso millet across the value chain, by showing its suitability as an ingredient in gluten-free pasta. Six varieties were cultivated in two locations in the American Midwest. Samples were screened for compositional, functional and nutritional attributes. Based on the findings, four samples with different amylose contents and prolamin profiles were explored for pasta production. After recipe optimization, the pasta was analyzed for quality parameters (color, carotenoid content, optimum cooking time, cooking loss, firmness), nutritional properties (in vitro starch and protein digestibility), and sensory quality. All tests were also performed on two commercially available pasta types. The results allowed for a distinction between varieties better suited for pasta production and samples that displayed disadvantageous properties such as excessive bitterness and low firmness. Millet pasta was characterized as grainy and starch, but also as uniform. Moreover, the data demonstrated the positive impact of high amylose content and high-molecular weight prolamins on pasta quality, namely textural attributes. In particular, pasta with high-molecular weight prolamins was rated as firmer, more chewy and grainy. As knowledge about structural changes of millet proteins during processing is limited, protein characteristics (i.e., solubility, content of accessible thiols and protein secondary structures) were monitored across manufacturing stages (dough, raw pasta after sheeting, cooked pasta). Solubility of proso millet proteins was low and only marginally enhanced by agents that cleave hydrogen bonds, hydrophobic interactions or disulfide linkages. Moreover, the solubility significantly declined after cooking, and was overall more influenced by processing than by sample type. While this conveyed some benefits, in particular low cooking loss of millet pasta, it significantly correlated with low protein digestibility. By investigating protein secondary structure distribution, the observed properties could be related to a dominance of β-sheets in cooked millet pasta (93.9-99.9%), which negatively correlated with solubility, cooking loss and digestibility. In contrast, commercial wheat and gluten-free pasta retained some random and α-helical structures, which positively correlated with solubility, cooking loss and protein digestibility. Overall, proso millet can successfully be incorporated into gluten-free pasta, and several quality attributes are superior to commercial gluten-free pasta. However, recipe and processing optimization is needed to enhance digestibility and certain sensorial attributes.