Extrusion cooking, as a multi-step, multi-functional and thermal/mechanical process, has permitted a large number of food applications. Effects of extrusion cooking on nutritional quality are ambiguous. Beneficial effects include destruction of antinutritional factors, gelatinisation of starch, increased soluble dietary fibre and reduction of lipid oxidation. On the other hand, Maillard reactions between protein and sugars reduce the nutritional value of the protein, depending on the raw material types, their composition and process conditions. Heat-labile vitamins may be lost to varying extents. Changes in proteins and amino acid profile, carbohydrates, dietary fibre, vitamins, mineral content and some non-nutrient healthful components of food may be either beneficial or deleterious. The present paper reviews the mechanisms underlying these changes, as well as the influence of process variables and feed characteristics. Mild extrusion conditions (high moisture content, low residence time, low temperature) improve the nutritional quality, while high extrusion temperatures (P200°C), low moisture contents (<15%) and/or improper formulation (e.g. presence of high-reactive sugars) can impair nutritional quality adversely. To obtain a nutritionally balanced extruded product, careful control of process parameters is essential.

14 Foods containing elevated levels of health functional components such as resistant starch and 15 polyphenolic antioxidants may have beneficial effects on human health. Pasta incorporating 16 either red sorghum flour (RSF) or white sorghum flour (WSF) each at 20%, 30% and 40% 17 substitution of durum wheat semolina (DWS) was prepared and compared to pasta made from 18 100% DWS (control) for content of starch fractions, phenolic profile and antioxidant capacity, 19 before and after cooking. Total, digestible and resistant starch contents were determined by the 20 AOAC method; individual phenolic acids and anthocyanins by reverse phase-HPLC analysis;21 total phenolic content by the Folin-Ciocalteu method and antioxidant capacity by the ABTS 22assay. The addition of both RSF and WSF increased the resistant starch content, bound phenolic 23 acids, total phenolic content and antioxidant capacity at all incorporation levels compared to the 24 control pasta; while free phenolic acids and anthocyanins were higher in the RSF-containig pasta 25 only. Cooking did not change the resistant starch content of any of the pasta formulations. 26Cooking did however decrease the free phenolic acids, anthocyanins, total phenolic content and 27 antioxidant capacity and increased the bound phenolic acids of the sorghum-containing pastas. 28The study suggests that these sorghum flours may be very useful for the preparation of pasta with 29 increased levels of resistant starch and polyphenolic antioxidants. 30 31

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Fat provides important sensory properties to baked food products, such as colour, taste, texture and odour, all of which contribute to overall consumer acceptance. Baked food products, such as crackers, cakes and biscuits, typically contain high amounts of fat. However, there is increasing demand for healthy snack foods with reduced fat content. In order to maintain consumer acceptance whilst simultaneously reducing the total fat content, fat replacers have been employed. There are a number of fat replacers that have been investigated in baked food products, ranging from complex carbohydrates, gums and gels, whole food matrices, and combinations thereof. Fat replacers each have different properties that affect the quality of a food product. In this review, we summarise the literature on the effect of fat replacers on the quality of baked food products. The ideal fat replacers for different types of low-fat baked products were a combination of polydextrose and guar gum in biscuits at 70% fat replacement (FR), oleogels in cake at 100% FR, and inulin in crackers at 75% FR. The use of oatrim (100% FR), bean puree (75% FR) or green pea puree (75% FR) as fat replacers in biscuits were equally successful.

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