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Optimization of pumpkin seed cake and proso millet flour level in gluten free bread of enhanced nutritive value

Development of tailor-made gluten free products with an optimized chemical composition suited for those suffering from celiac disease and/or diabetes is needed. Celiac disease results in nutrient deficiency in about 30% of patients, and develops in about 10% of diabetes type 1 patients. Gluten free products are often a poor source of micronutrients and have a high glycemic index. The objective of this research was to optimize a gluten free bread recipe with whole grain rice and buckwheat flour as basis, by varying the amounts of pumpkin seed cake and proso millet flours. A by-product of the oil production industry, pumpkin seed cake, is a source of protein (51 g/100 g), fiber (17 g/100 g), and unsaturated fatty acids (18 g/100 g). An underutilized cereal, proso millet could be a useful raw material, since it is rich in folate, has a hypoglycemic effect and a high starch gelatinization temperature similar to that of rice starch which is mostly used in gluten free bakery products. Formulations (n=13) were prepared by varying the amount of pumpkin seed cake flour at 10, 20, and 30%, and the amount of millet flour at 10, 30, and 50%, following a central composite design, resulting in 9 recipes and 5 replications of the central point. The effect of pumpkin and millet flours was evaluated by measuring the content of bread protein, fat, ash share (AACC methods), determining the amount of dietary fiber (AOAC 991.43), carbohydrate amount, glycemic index (ISO 26642), as well as the color (CIELab system) and texture profile of the bread crumb (Texture analyzer). Specific aim was to improve the nutritive value (maximize share of protein, fiber and ash, while lowering the amount of carbohydrates, fat and simple sugars and the glycemic index), while maintaining the structure of the bread crumb intact (maximize the cohesiveness, resilience and springiness, while lowering hardness and chewiness). Addition of pumpkin seed cake lowered the amount of carbohydrates and raised fiber share, and was complemented by the addition of proso millet which raised minerals share, and reduced the amount of simple sugars and fat in the bread. When added in an amount higher than 13% pumpkin seed cake had a deteriorating effect on the bread crumb texture causing a rise of hardness and chewiness, while lowering its resilience and springiness. At 30% addition, proso millet flour neutralized the green color of the pumpkin seed cake, while at 50% it further improved lightness of the bread. The optimized recipe with 12.7% of pumpkin seed cake and 50% of proso millet flour, had a glycemic index 67 and contained 14.1 g/100 g protein, 31 g/100 g carbohydrates, 1.8 g/100 g fat, 2.5 g/100 g fiber, and could therefore be labelled as a “source of fiber” and “high in protein”. The proposed recipe could lead to an increase in the market supply of nutritive dense gluten free bread and potentially improvement of the nutritive status of celiac patients.

Gluten-free bread, Glycemic index, Optimization, Proso millet, Pumpkin seed cake

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