Study and development of new functional foods containing cereals

The aim of this PhD thesis was the development of staple foods enriched with compounds, which have an important impact on the nutritional and physiological aspects. Selection of ingredients with high content of dietary fibre (inulin, β-glucans and resistant starch) has been performed to formulate functional foods. In particular, the effect of the ingredients on dough rheological properties, final products quality and on glycaemic response was evaluated in order to identify optimum formulation and manufacturing process conditions for high quality functional foods. In particular, the inclusion of inulin (short and long-chain: GR and HPX respectively) in extruded snack, at levels from 2% to 7%, lowered dough consistency due to a reduction in water absorption. Large differences in elastic properties of samples were observed between 25 and 95 °C due to incompatibility between inulin and starch and different kinetics of starch gelatinization; however, inulin GR had a greater effect than HPX. Short-chain inulin increased product expansion and hardness compared with the reference, while 7% of HPX decreased these parameters. Short-chain inulin lowered the extent of non-enzymatic browning. Snacks made with 5% inulin HPX can be used to enhance the fibre content without impacting negatively on product quality. A level of 8% of the two types of inulin and β-glucan (Barley Balance) were added to a gluten-starch model system, which represented semolina for pasta production. Dietary fibre ingredients were added individually and in combination. In general, when added individually, inulin lowered dough consistency, while β-glucan increased this parameter compared to control (without fibre). Moreover, the differences in elastic properties and kinetics of starch gelatinization suggested that short-chain inulin weakens dough structure, while Barley Balance increases elastic effective interactions. However, when dietary fibres were coupled, dough characteristics resulted similar to the gluten-starch model (control); the results suggested that a combination of inulin and Barley Balance allowed to obtain a dough suitable for functional pasta production. A method for predicting the glycaemic content of pasta was developed. With this purpose, a series of experiments were conducted to evaluate the effect of different sample preparation steps, prior to the in vitro starch digestion process, on the predictive in vitro glycaemic response of durum wheat pasta (control) and enriched with fibre (pea flour). The evaluation of the different methods of sample preparation illustrated that the maceration of pasta samples prior to starch digestion significantly increased the extent of starch degradation and hence the area under the curve (AUC) of reducing sugar released during the digestion process. Mastication of the samples prior to in vitro assessment increased the initial reducing sugar content of samples but yielded the lowest recorded AUC for all samples. The results indicate that the choice of the preparation step used prior to in vitro starch digestion procedures can significantly affect the predictive glycaemic response - AUC values of samples, and hence manipulate differences attributed to product composition or structure. This may have an impact in terms of choosing the most appropriate method of glycaemic analysis for the food industry. Based on the results obtained from the study of the gluten-starch model system and from the development of in vitro starch digestion analysis, pasta samples were made by replacing 15% of durum wheat semolina with inulin HPX, inulin GR, Glucagel, psyllium and oat material (added individually and in combinations). The cooking, textural, colour characteristics and predicted glycaemic response of the pastas were evaluated and compared to control sample containing exclusively durum wheat semolina. Generally, material addition to the durum wheat pasta increased the cooking losses, swelling index and water absorption, whilst reduced firmness and resistance to uniaxial extension of pastas. Raw spaghetti samples resulted significantly darker (L*) and more redness (a*) than raw control pasta. In the cooked pasta, all inulin enriched pasta samples were brighter than semolina pasta. Pasta containing 15% semolina of oat flour showed the best performance (except for the colour) compared to the other experimental pasta samples, but was significantly different to control durum wheat sample. Moreover, the inclusion of inulin GR had a less deteriorating effect when added in combination with oat flour. This illustrates that some fibre rich sources may act better in combinations than separately. In general, all enriched dietary fibre pasta sample showed a significant decrease in reducing sugars released and standardised AUC values compared to control pasta. However, this study showed that the combination of dietary fibres in pasta formulation led to an antagonistic effect on the predicted glycaemic response. The last product took in consideration in this research project was gluten free pasta, which was prepared substituting rice flour (reference) with 10, 15 and 20% of resistant starch type II (RS). Farinograph test registered no changes in water absorption at any level of substitution. The presence of fibre caused an increase in optimum cooking time and firmness parameters and a decrease in stickiness and cooking loss values; however, no significant differences among all levels of substitution (10-20%) could be appreciated. The loss of resistant starch content (31%) in raw gluten-free pasta suggested that processing conditions could be a critical point for resistant starch stability. Rhelogical on doughs obtained from all raw pastas showed different G' slopes for fibre-enriched samples compared with the reference, ascribable to some modifications in resistant starch granules during pasta cooking. This observation was confirmed by polarized light microscopy analysis performed on RS granules during heating process conditions. Based on these results, pasta samples made with 20% of RS can be considered as a food product source of dietary fibre.