Effect of pumpkin and spinach powder on physicochemical and sensory properties of fortified sponge cake

Fruit fibre have better quality due to higher total and soluble fibre content, water and oil holding capacity and colonic fermentability, as well as lower phytic acid content and caloric value (Sharoba et al., 2013). In the fresh mass of the pumpkin (Cucurbita moschata), total carotenoid content, a major contributory factor in the high nutritional value of pumpkins, ranges from 2 to 10 mg/100 g, the content of vitamins C and E accounting for 9–10 mg/100 g and 1.03–1.06 mg/100 g, respectively (Hosseini Ghaboos et al., 2016; Nawirska et al., 2009). Pumpkin fruit is also a valuable source of other vitamins, e.g., vitamin A, B6, K, thiamine, and riboflavin, as well as minerals, e.g., potassium, phosphorus, magnesium, iron and selenium (Mirhosseini et al., 2015; Obradović et al., 2015). Since pumpkin is a valuable micronutrients source, dried pumpkin could be processed into powder for foods to increase fibers, vitamin A and mineral contents. In addition, pumpkin powder can be used in bakery products because of its highly-desirable flavour, sweetness and deep yellow-orange colour (Salehi, 2020). The influence of replacement of wheat flour with pumpkin powder (at five levels of 0, 2.5, 5.0 7.5 and 10 %) on textural properties and sensory qualities of biscuit was studied by Kulkarni and Joshi (2013). As the replacement level of wheat flour with pumpkin powder increased, the firmness and fracturability values were increased. Biscuits with more pumpkin powder had a more yellow colour than those with less pumpkin powder. According to the sensory evaluation results, biscuits containing 2.5 % dried pumpkin powder had the highest total acceptance score. The iron and β-carotene content of biscuits increased with increasing pumpkin powder levels. Spinach is a good source of minerals (Fe, Mn, Zn and Mg), vitamins (E, A, C, K, B1, B6 and B2), protein, fibers and antioxidants, making it a suitable ingredient to be used in the formulation of food products with high nutritional and biological values (Slavin and Lloyd, 2012). El-Sayed (2020) studied the effect of spinach nano-powder (0.5-2%) addition on the quality of ultra-filtered soft cheeses. The author demonstrated that by increasing of spinach powder concentration with retentate, the content of fibers, minerals, total phenolic content, and antioxidant activity of samples was enhanced. In this study, pumpkin and spinach powders were used to improve and enhance the quality of sponge cake due to their high nutritional value, fiber, β-carotene and minerals (calcium and iron).

At first, the pumpkin and spinach were dried and powdered in controlled conditions. Fresh pumpkins (Cucurbita moschata) were purchased from local market. The pumpkin slices with 5 mm thickness were dried in an oven (65°C). The dried pumpkins were milled, powdered and passed thru a 125 mesh screen (Hosseini Ghaboos et al., 2016). The ingredients used in the formula of sponge cakes were cake flour (100 g), sucrose (70 g), sunflower oil (60 g), fresh eggs (70 g), whey (4 g), baking powder (1.5 g), vanilla (0.5 g), water (40 g) and nonfat dry milk (20 g) powder. Sucrose and sunflower oil were poured into a bowl, and mixed for 10 min. Whole egg was added to the bowl, and then mixed for 4 min. The sifted cake flour, whey, baking powder, vanilla, water and nonfat dry milk powder was gradually poured into a bowl, and mixed for 3 min. Water was added to the bowl, and then mixed for 1 min. For each cake, 45 g of cake batter was poured into a cake pan and baked at 195°C for 25 min in a oven toaster. The cakes were allowed to cool for 20 min, and then were removed from the pans. The cooled cakes were packed in polypropylene bags at room temperature before physico-chemical and sensory evaluation analyses. The test sponge cake samples prepared with 0% (control), 5%, 10%, 20 and 30% replacement of cake flour with blend of pumpkin and spinach powder. The blend of pumpkin and spinach at concentrations of 0, 10, 20 and 30% were used in sponge cake formulation and the dough viscosity and physicochemical, color, texture and sensory properties of the product were studied. The texture profile analysis of sponge cake samples from the midsection of the cakes were performed using a texture analyzer (TA-XT Plus, Stable Micro Systems Ltd., Surrey, UK) with a 36 mm diameter cylindrical probe, 50% compressing and a test speed of 1.0 mm s−1 . The crust of cake samples was removed in cake texture determination. A double cycle was programmed and the texture profile was determined using Texture Expert 1.05 software (Stable Microsystems). Other parameters were defined as: pre-test speed 2.0 mm s−1, post-test speed 2.0 mm s−1 and trigger force 5 g. The texture parameters recorded were firmness, cohesiveness, springiness and resilience, and the texture parameter of cake was averaged from 3 replications. Statistical analysis was performed in factorial arrangement based on completely randomized design and comparing was performed at the average at 5% level using Duncan's multiple range test.

With increasing percentage of pumpkin and spinach powder in sponge cake formulation showed that fiber, iron and calcium percentages of samples were increased from 1.60 to 10.04%, 9.78 to 50.93 ppm and 0.19 to 0.42, respectively and there was a significant difference between treatments (p < 0.05). Also, β-carotene, protein, moisture and density of cakes increased significantly with increasing percentage of powder replacement (p < 0.05). By increasing the percentage of substitution of powders in sponge cake formulation from 0 to 30%, the viscosity of cake batters at shear rate of 90 s-1 was significantly increased from 16.72 to 30.82 Pa.s (p < 0.05). According to the results of image processing, as the percentage of pumpkin and spinach powder increased in the formulation, the a* index decreased and became negative indicating that the samples became greener with increasing replacement percentage.

The firmness of cakes enriched with pumpkin and spinach powder was obtained in the first day and on the 14th day in the range of 2.071-5.427 N and 3.354-6.207 N, respectively. Based on the sensory evaluation results, the sample containing 20% pumpkin and spinach powder had the highest overall acceptance score.