Incorporation of mushroom powder into cereal food products

Abstract

Convenient cereal derived foods are becoming more popular in terms of consumer interest, however they can be considered as nutritionally imbalanced. For instance, cereal products which are mainly derived from refined flour, are often low in lysine, vitamins, minerals and fibre. In addition these products may be considered as energy dense and often exhibit a high glycaemic index. As consumers demand healthier food products, the cereal food industry has endeavoured to improve the nutritional content of products by increasing their composition of bioactive phytochemicals. On the other hand, mushrooms are the source of many nutrients, for example, the proportion of essential amino acids of most mushrooms is comparable to that of egg, especially lysine, which is an abundant essential amino acid in mushrooms, and is deficient in most cereals. Previous reports also have suggested that mushrooms are nutritionally incomplete due to the lack of essential sulphur amino acids, such as methionine and cysteine, these however are rich in cereals. Cereal products and mushrooms when consumed independently may not be able to support growth as effectively as animal foods, but the combination of cereal products and mushrooms makes it possible, to supply an adequate level of essential amino acids and provide a good balance of nutrients for human beings. In this study, four different kinds of mushroom powder (white button; shiitake; porcini and black ear mushroom) were incorporated into three different kinds of cereal product (fresh pasta; bread and hot extruded product), which utilised the cooking processes of cold extrusion, fermented cooking and hot extrusion respectively. The physical, chemical, textural, nutritional and microstructural properties of these products were determined. These products may introduce more edible mushroom species to western consumers’ diet using a relatively simple approach. A partial substitution of durum wheat semolina with different species of mushrooms was undertaken to increase the nutritional value of the pasta. The results showed that the addition of mushroom powder increased the cooking loss, as well as firmness of the pasta. Porcini and black ear mushroom incorporation significantly decreased the swelling index, water absorption index and moisture content values of the cooked pasta, while, for the white button and shiitake mushrooms, there was no noticeable effect on either index compared with the control sample. Furthermore, mushroom material enriched the protein (except black ear mushroom) and dietary fibre contents of the pasta samples compared with durum wheat only samples. Incorporation of mushroom powder significantly decreased the starch content, the extent of starch degradation and the area under the curve (AUC) of reducing sugars released during the digestion of pasta, while it also increased the total phenolic content and antioxidant capacities of samples. Powder from different mushrooms was used to replace high grade wheat flour at levels of 5 %, 10 % and 15 % to make novel breads. Bread physical and textural qualities, including height, specific volume, moisture content, hardness, springiness and gumminess were determined. The breads made with mushroom powder were smaller in specific loaf volume (except for the 5 % porcini mushroom) and exhibited reduced springiness and reduced height (except for the 5 % porcini mushroom) compared to the control samples. Additionally, starch characteristics (content, gelatinisation and digestibility), antioxidant capacities and microstructural properties (bread crust and crumb) of mushroom enriched bread samples were also investigated. The decrease of total starch content and increase of total phenolics of the breads were significant with increased mushroom powder content compared to the control. The reducing sugar released in an in vitro starch digestion of the control bread increased more rapidly than in the mushroom enriched breads. The area under the curve (AUC) values illustrated clearly that mushroom powder addition reduced the predicted glycaemic response of the bread. Mushroom powder incorporation also enhanced the antioxidant capacities compared to the control bread. Furthermore, mushroom powder altered the internal microstructure of the bread crust and crumb by affecting the interactions between starch and the other components of the bread. These results indicate that mushroom powder can be added to bread to deliver health benefits to consumers. Mushroom powders were also processed with semolina to produce hot extruded snacks. Similar to the other two products, a series of analyses were conducted in order to evaluate these functional hot extruded products comprehensively, including the nutritional profile, macrostructure, colour, textural properties, microstructure, starch characteristics (content, gelatinisation and digestibility) and antioxidant activities (total phenolic content, DPPH and ORAC). The results showed that different mushroom powders had different effects on the physical properties. Products with mushroom powder had a higher fibre content and decreased degree of starch gelatinisation, which might be responsible for the decreased glycaemic response. Additionally, incorporation of mushroom powder into hot extruded products resulted in delivering more phenolic compounds and antioxidant benefits to consumers.