Effects of temperature and time on the physical characteristics of moist cakes baked in air fryer

Abstract

Baking temperature and time are among the conditions for producing good quality cakes. The aim of this study was to investigate the effects of baking temperature and time on the volume expansion, moisture content, and texture of moist cakes baked in either an air fryer or a convection oven. The cakes were baked under different conditions: (1) baking temperature of 150 °C, 160 °C, and 170 °C for both air fryer and convection oven and (2) baking time of 25, 30, 35 min for air fryer and 35, 40, 45 min for convection oven. Baking temperature and time were found to have a significant (p < 0.05) effect on the relative height, moisture content, firmness and color of the product but no significant effect on the springiness of the product. Based on the numerical optimization method, the optimum condition in an air fryer was 150 °C for 25 min. These optimized conditions resulted in higher relative height (37.19%), higher moisture content (28.80%), lower crumb firmness and chewiness (5.05 N and 1.42 N respectively) as well as higher overall acceptance score (5.70) as compared to optimum condition in convection oven (150 °C at 55 min). Moreover, baking in the presence of rapid air flow in an air fryer may be declared that it is possible to produce high-quality moist cake with minimum baking temperature and shorter baking time.

Introduction

Moist cake is one of most-favored shortcakes which appeals to all ages. Generally, it has a tender texture and is unable to last long (i.e. perishable). A cake of good quality has moist and fine grains, even crumbs, tender texture, optimum volume, delicate crust and is lightly browned (Conforti 2014). This product must meet the high-quality standards demanded by the consumers to maintain and expand the bakery products up to the international market.

The quality of a cake depends on several processing parameters, such as air flow, heat supply, humidity, oven load and baking time (Boulet et al. 2010). Different baking parameters give rise to distinct products. Based on previous studies on the effects of baking parameters, excessive baking temperature will result in high crust color, lack of volume, peaked tops, closely-packed or irregular crumbs and the downsides of under-baking. Otherwise, too low a baking temperature might result in pale crust color, large volume and poor crumb texture (Sani et al. 2014). Im et al. (2003) found that processing conditions, including baking temperature and duration, significantly influenced the physical qualities (e.g. specific volume, hardness, integrity and color) of the cake.

Apart from baking temperature and time, air flow also plays an important role in ensuring even temperature distribution, which has a significant effect on the quality of the finished product (Therdthai et al. 2004; Zareifard et al. 2009). Air flow enables convective heat transfer and reduces baking time, hence leading to enhanced oven performance (Khatir et al. 2012). In another study, various types of baking ovens—such as tunnel-type ovens, pilot plant ovens, microwave combination ovens and electric ovens—have different rates of air flow, which influence the distribution of temperature in the oven chamber (Khatir et al. 2012; Paton et al. 2013; Yolacaner et al. 2017; Zareifard et al. 2009).

Recently, a new rapid air flow technology was introduced. It can be used to cook various types of food, including bakery products such as cake. This technology works by circulating superheated air in the cooking chamber, hence potentially reducing the time and energy consumption during processing. The presence of air flow results in a more even distribution of temperature inside the oven chamber (Sani et al. 2014). Hence, the temperature setting can be manipulated to produce food of a similar quality (Wählby et al. 2000). However, to the best of authors’ knowledge, no report on cake-baking in air fryers has been found so far.

Response surface methodology (RSM) is a mathematical and statistical practice in which useful tools for development, improvement, and optimization of processes are employed. It is widely used to examine the interactions between factors and one or more response variables. Most researchers have used this method in optimize the formulations and effects of processing conditions on the quality of bakery products (Gan et al. 2007; Im et al. 2003; Omidiran et al. 2016; Peluola-Adeyemi et al. 2016; Shittu et al. 2007).

Numerous studies have focused on the effects of parameters such as baking temperature, time, and oven type on the qualities of breads instead of cakes (Flander et al. 2007; Purlis 2012; Shittu et al. 2007; Therdthai et al. 2002, 2004). Besides, many researchers have studied the effects of product formulations (e.g. types of flour, resistant starch, etc.) on the qualities of the final product (Gan et al. 2007; HadiNezhad and Butler 2010; Sanz et al. 2009). However, only a few studies have focused on the comparison of product qualities by varying the baking temperature and time in different air flow modes. These comparisons are important for the evaluation of the differences and similarities in the product qualities. Therefore, the aim of this study was to investigate the effects of air-frying temperature and time on the qualities of moist cakes (volume expansion, moisture content, texture and color of the cakes). This study was further extended to derive the optimum baking conditions based on the sensory evaluation air-fried moist cakes as compared to those baked in a convection oven.

Materials and methods

Cake preparation

A modified chocolate moist cake recipe was used. The following ingredients were weighed using a digital balance (Excell, ALH3, Japan): cake flour (7.0%), cocoa powder (6.3%), castor sugar (12.5%), evaporated milk (20.3%), condensed milk (24.6%), baking powder (0.2%), soda bicarbonate (0.3%), vegetable oil (16.8%), eggs (11.3%) and vanilla essence (0.57%). All ingredients were purchased from Harmoni Ingredients Supply, Serdang, Malaysia. The batter was prepared according to a standard creaming method using a hand mixer (Panasonic, MK-GBI, Taiwan). A round stainless steel baking pan of 6-in. diameter was used.

Baking conditions

A commercial air fryer (Philips, HD9220, China) and an electric convection oven (CEO-TS42L, US) were used in this research. Three different baking temperatures were chosen (150 °C, 160 °C and 170 °C), while the baking times were 25, 30 and 35 min for the air fryer and 35, 40 and 45 min for the electric convection oven. The selected baking temperatures and times were chosen based on the results of preliminary experiments.

Experiment design and statistical analysis

In the determination of the optimum baking temperature and time, RSM was performed using the Design-Expert software version 10.0.3.1 (Stat-Ease Inc., Minneapolis, USA). A 2-variable, 3-coded level central composite design (CCD) was selected to accommodate the 13 experimental conditions (Gan et al. 2007). The independent variables were baking temperature (X₁; 150 °C, 160 °C, 170 °C) and time, X₂ (air fryer: 25, 30, 35 min; convection oven: 35, 40, 45 min). The experimental designs for the uncoded and coded values of the independent variables are shown in Table 1. The dependent values included the relative central height of the cake, moisture content, and texture characteristics. The regression coefficients of the individual linear, quadratic and interaction terms were determined using a second-order polynomial by the following equation:

$$Y=b_o+b_1{X}_1+b_2{X}_2+b_{12}{X}_1{X}_2+b_3{X}_1^2+b_4{X}_2^2$$ 1

The coefficients of the polynomial were represented by: Y, desired value of response (relative central height, crumb moisture content and firmness, chewiness and springiness); b_o, intercept; b₁, coefficient for baking temperature (first order); b₂, coefficient for baking time (first order); b²₁, coefficient for interaction between baking temperature and time; b²₃, coefficient for baking temperature (second order); b²₄, coefficient for baking time (second order); X₁, baking temperature (°C); X₂, baking time (min).

Table 1.

Experimental data on the responses of optimization baking parameters for moist chocolate cake baked using air fryer and convection oven

Air fryer								Convection oven
Parameters		Responses						Parameters		Responses
Xb1	X2	Yc1	Y2	Y3	Y4	Y5	Y6	X1	X2	Y6	Y7	Y8	Y9	Y10	Y11
160 (0)a	35 (1)	66.5	26.52	6.37	2.41	80.3	10.0	160 (0)	40 (0)	49.6	26.31	6.16	1.83	62.8	6.7
150 (− 1)	30 (0)	48.0	28.01	5.50	2.55	83.9	7.6	150 (− 1)	40 (0)	27.3	27.25	5.03	2.52	79.8	4.6
160 (0)	30 (0)	47.4	27.35	6.13	3.12	79.9	9.4	16 (0)	40 (0)	50.2	26.24	6.18	2.01	80.8	7.1
170 (1)	25 (− 1)	56.3	27.71	6.39	2.49	81.4	9.7	150 (− 1)	35 (− 1)	21.3	28.25	5.02	2.52	87.6	4.0
160 (0)	30 (0)	43.2	27.06	6.26	3.41	84.4	9.6	160 (0)	40 (0)	44.5	26.15	6.05	1.66	64.9	7.1
160 (0)	30 (0)	46.7	27.05	6.28	3.56	79.5	9.2	160 (0)	35 (− 1)	41.0	28.23	6.02	1.73	70.4	5.8
170 (1)	35 (0)	65.8	25.95	6.46	2.43	84.6	10.6	170 (1)	35 (− 1)	49.6	28.02	6.25	1.54	56.7	7.6
170 (1)	30 (0)	63.0	26.87	6.41	3.03	84.4	10.3	160 (0)	40 (0)	43.9	26.24	6.12	1.49	64.7	7.1
160 (0)	25 (− 1)	44.5	28.17	6.34	2.80	80.5	8.8	170 (1)	40 (0)	50.2	26.36	6.33	1.71	72.8	7.9
160 (0)	30 (0)	49.9	27.61	6.35	3.56	78.6	9.1	160 (0)	40 (0)	46.4	26.43	6.13	2.31	63.1	7.1
150 (− 1)	35 (1)	64.9	27.21	5.66	2.44	84.6	8.0	150 (− 1)	45 (1)	40.4	27.19	5.36	2.76	77.8	5.2
150 (− 1)	25 (− 1)	38.1	28.74	4.98	1.42	68.1	6.2	160 (0)	45 (1)	46.4	25.99	6.43	1.67	68.7	6.9
160 (0)	30 (1)	47.1	27.64	6.26	3.66	82.4	9.2	170 (1)	45 (1)	46.7	25.27	6.67	2.22	79.0	8.2

^aCoded value

^bX₁ = baking temperature (°C), X₂ = baking time (min)

^cY_1,6 = relative height (%), Y_2,7 = moisture content (%),Y_3,8 = firmness (N), Y_4,9 = chewiness (N), Y_5,10 = springiness (%),Y_6,11 = color change (ΔE)

The RSM also was used to perform the analysis of variance (ANOVA). The value of significance was set at 5%. The regression coefficient was used in the statistical calculation to generate a contour map based on the regression models.

Volume expansion measurement

The cake volume expansion was measured using the cross-sectional area-tracing method according to the AACC method (AACC 2000). The cake was assumed as a spherical cap and the height of the cake was measured using Vernier calipers. The schematic diagram of a half-cake sample is shown in Fig. 1a.

Fig. 1.

Schematic diagram for measurement of a volume expansion, b moisture content and texture

Moisture content measurement

2 g of crumb cake was weighed and placed in a dish. The initial and final moisture contents of the cake was analyzed using a moisture analyzer (Infrared moisture balance, MX-50, and Weighing, Adelaide) under standard drying and medium accuracy (0.05%/min) modes. The final moisture content of cake was analyzed by taking the sample cakes from texture analysis (Fig. 1b). The results obtained by this instrument were validated via the standard oven method for total solids and moisture in baked products, in overnight drying at 105 °C (AACC 2000).

Texture measurement

Firmness, springiness, and chewiness of the cakes were measured according to the AACC-approved Method (74-10A) using a TA-XT plus Texture Analyzer in the Texture Exponent software version 2.0.7.0 (Stable Microsystems, Godalming, UK) (AACC 2000). The crust surface was removed and three square blocks of crumb cake measuring 2.5 × 2.5 × 2.5 cm each were cut from the cake 1 h after baking (Fig. 1b). The test speed was 1 mm/s with 50% of the initial height of the sample achieved. A trigger force of 5 g was applied by a round plunger of diameter 36 mm (P/36). The samples were placed in an airtight plastic bag to avoid moisture loss and to be used for further analysis.

Color measurement

The top surface colour of the baked cake was measured with HunterLab Ultrascan PRO color spectrophotometer (Hunter Associates Laboratory, Inc., Reston, VA, USA) and expressed as the International Commission on Illumination (CIE) L*, a*, and b* color scale. The sample was sliced into cube of 3.0 cm and then hold on the device according to the point of the cake selected portion and the color was analyzed. The measurements of the surface of the cakes were made at positions similar sample measurement in texture analyzed. Total color change (ΔE) was calculated from Eq. 2;

$$\mathrm{\Delta }E=\sqrt{{\left(L^{\ast }-L_0\right)}^2+{\left(a^{\ast }-a_0\right)}^2+{\left(b^{\ast }-b_0\right)}^2}$$ 2

where L₀, a₀, and b₀ were selected as initial points and L*, a*, and b* of the baked cake crust surface.

Preference testing of the samples

Sensory evaluations of the baked moist chocolate cakes were conducted using 20 untrained panellists with random order numbers. The moistness, firmness, springiness, chocolate taste, aroma, and overall acceptance of the cakes were evaluated following baking under optimum conditions in an air fryer or convection oven. Each panellist was served with 2 samples (1 cake baked in an air fryer and convection oven respectively) in a random order. The samples were cut into 2.5 cm³ cubes and served in plastic containers with randomly-coded three digit numbers. The 7-point Hedonic Scale was used (7 = like very much, 4 = neither like nor dislike and 1 = dislike very much) (Omidiran et al. 2016). The mean scores for each characteristic was then analysed statistically.

Results and discussion

Model-fitting based on RSM

The independent and dependent variables were fitted into a second-order model equation (Eq. 1) and examined for the goodness of fit. Experimental data on the responds of optimization baking parameters using air fryer and convection oven was tabulated in Table 1. The model constants and coefficients of determination for each dependent variable are shown in Table 2. The estimated regression coefficient, R², should be at least 80% for good-fitting model (Gan et al. 2007). The results showed that the models for all the responding variables were highly compatible when their coefficients of determination were more than 80%, although this was not so for (1) chewiness following baking in a convection oven and (2) springiness after baking using both air fryer and convection oven. The closer the R² value to unity, the better the empirical model fits the actual data. Besides, the results showed an insignificant lack of fit for all the response variables. This indicates the failure of a model to represent data in the experimental domain at which points not included in the regression (Varnalis et al. 2004).

Table 2.

Regression equation calculated by RSM program for optimization of baking parameters for moist chocolate cake baked using air fryer and convection oven

Quality parameter	Equations	R 2	Significant	Lack of fit
Relative height (%)
Air fryer	Y1 = 47.94 + 5.68 * X1 + 9.72 * X2− 4.33 * X1X2 + 4.84 * X21 + 4.84 * X22	0.9284	0.0007	0.1377ns
Convection oven	Y6 = 46.37 + 9.58 * X1 + 3.60 * X2 − 5.50 * X1X2 − 6.25 * X21 − 1.30nsX22	0.9406	0.0004	0.4950ns
Moisture content (%)
Air fryer	Y2 = 27.36 − 0.57 * X1 − 0.94 * X2 − 0.13nsX1X2 − 0.29nsX21 + 0.17nsX22	0.9488	0.0002	0.9861ns
Convection oven	Y7 = 26.34 − 0.51 * X1 − 1.01 * X2 − 0.42 * X1X2 + 0.31 * X21 + 0.61 * X22	0.9776	0.0001	0.0586ns
Firmness (N)
Air fryer	Y3 = 6.28 + 0.52 * X1 + 0.13 * X2 − 0.15 * X1X2 − 0.39 * X21 + 0.01nsX22	0.9579	0.0001	0.1128ns
Convection oven	Y8 = 6.13 + 0.66 * X1 + 0.22 * X2 − 0.01nsX1X2 − 0.44 * X21 + 0.11 * X22	0.9962	0.0001	0.8279ns
Chewiness (N)
Air fryer	Y4 = 3.43 + 0.26 * X1 + 0.10nsX2 − 0.27nsX1X2 − 0.55 * X21 − 0.73 * X22	0.9021	0.0020	0.2248ns
Convection oven	Y9 = 1.82 − 0.39 * X1 + 0.14nsX2 + 0.11nsX1X2 + 0.40 * X21 − 0.01nsX22	0.7399	0.0497	0.6946ns
Springiness (%)
Air fryer	Y5 = 81.50 + 2.30nsX1 + 3.25nsX2  − 3.33nsX1X2 + 1.30nsX21 − 2.45nsX22	0.6627	0.1098	0.1375ns
Convection oven	Y10 = 67.72 − 6.12nsX1 + 1.80nsX2 + 8.03nsX1X2 + 7.44nsX21 + 0.69nsX22	0.7113	0.0686	0.8368ns
Color change (ΔE)
Air fryer	Y6 = 9.36 − 1.47 * X1 + 0.65 * X2 − 0.23nsX1X2 − 0.56 * X21 − 0.11nsX22	0.9806	0.0001	0.3558ns
Convection oven	Y11 = 6.93 + 1.65 * X1 + 0.48 * X2 − 0.15nsX1X2 − 0.45 * X21 − 0.35nsX22	0.9771	0.0001	0.1359ns

Effects of baking temperature and time on cake volume expansion

Cake volume expansion is important because it is used in the evaluation of cakes and their qualities (HadiNezhad and Butler 2010). A high-quality moist cake should have a consistent volume and uniform moisture, both of which are dependent on several factors, including the ingredients used in batter preparation and baking conditions such as baking temperature and time. The relative heights of the air fryer baked cakes and oven-baked cakes were used to evaluate the volume expansion (Table 1). The relative heights of the air fryer baked cakes and a convection oven air fryer baked cakes ranged from 38 to 66% and 21 to 50% respectively. The baking temperature in both air fryer baked cakes and convection oven-baked cakes showed a significant effect (p < 0.05) on the percentage of the relative heights of cakes (Table 2). A high baking temperature (170 °C) in an air fryer led to a greater increase in the relative heights of the cakes than those baked at 150 °C and 160 °C [Fig. 2A(a)]. In addition, air-frying gave rise to a slightly higher increment in the percentage of cake height than baking in a convection oven. This could be due to the enhanced air flow in the oven chamber and increased convective heat transfer, hence leading to greater volume expansion (Shahapuzi et al. 2012).

Fig. 2.

Response surface plot of the effect of baking temperature and time on A relative height, B moisture content, C firmness, D chewiness and E total color change of cakes using air fryer (a, c, e, g, i) and convection oven (b, d, f, h, j)

The present study found that air fryer baked cakes for 35 min at 150 °C produced 64.9% of the relative cake height, which was higher compared to those baked for 25 min [Table 1; Fig 2A(a)]. A longer heating time increases the evaporation of water during baking (Im et al. 2003), which causes the air bubbles in the cake to expand and form porous structures (Alifak and Sakıyan 2016), thus yielding a larger cake. Meanwhile, using convection oven for a longer time (45 min) at 150 °C showed a reduction in the relative heights of the cakes by 5.85% [Fig. 2A(b)]. This could have been due to the increased shrinkage at the end of the baking process (Sevimli et al. 2005). According to the multiple regression analysis, the interaction between baking temperature and time was acknowledged to have a significant effect (p < 0.05) on the relative heights of the air fryer baked cakes and oven-baked cakes (Table 2). Changes in the baking temperature and time produced different percentages of cake height increment at the end of the baking process. This can be concluding that the increments in the air-frying temperature and time will enhance the volume expansions of cake.

Effects of baking temperature and time on moisture content

Moisture content in a cake should be controlled in order to determine its quality and shelf-life. The optimal range of moisture content for a typical moist cake is between 25 and 30% (Cauvain and Young 2010). The final central moisture contents of the crumb cakes were between 25 and 28% on a wet basis (Table 1), in which the initial moisture content of the batter was 31.85% ± 0.18. Baking temperature had a significant effect (p < 0.05) on the moisture content of the crumb cakes (Table 2). This can be seen, whereby samples baked at 170 °C using the air fryer and convection oven resulted in lower moisture contents at 35 min and 45 min respectively (25.59% and 25.27% respectively) as compared to baking at a low temperature (150 °C) (Table 1). Increasing the baking temperature in the air fryer resulted in a linear reduction of the moisture content of the sample as illustrated in Fig. 2B(c). Increasing the baking temperature from 150 to 170 °C at 25 min in the air fryer gave rise to a 4.18% increment in moisture loss as compared to the samples baked in the convection oven at 35 min time baking. This was due to the increased air flow velocity as the top fan constantly distributed the heat in the air fryer, thus increasing heat penetration into the cakes (Shahapuzi et al. 2015).

Apart from baking temperature, baking time also had a significant effect (p < 0.05) on the moisture contents of the crumb cakes (Table 2). A longer baking time led to reductions in the central moisture contents of the crumb cakes. As per Fig. 2B(c), when the baking temperature was constant (170 °C), an increase in the baking time from 25 to 35 min in air fryer caused the moisture content of crumb cake decreased from 27.75 to 25.95%. Meanwhile, an increase in the baking time from 35 to 45 min in the convection oven also resulted in a decrease in the moisture content of cake (28.19–25.32%) [Fig. 2B(d)]. This corresponded to the results of a previous study (Şakıyan 2014), whereby a longer baking time in an oven caused a reduction in the moisture content. This could be related to longer contact times of the cakes to heat, leading to increased evaporation of water vapour (Alifak and Sakıyan 2016). ANOVA results showed that the interaction between baking temperature and time significantly affected the moisture contents of the crumb cakes (p < 0.05). The moisture contents of all the cakes baked at different temperatures and times were within the acceptable range for typical moist cakes.

Effects of baking temperature and time on texture

The textures of the cakes in this study were described in terms of firmness, chewiness, and springiness. Analysis of variance indicated that baking temperature in an air fryer and a convection oven had the most significant effect on the firmness of the moist cakes (Table 2). The effects of baking temperature and time on the firmness of air fryer baked cakes and convection-oven baked cakes are shown in Fig. 2C(e), (f) respectively. The hardness significantly decreased with the decrease in baking temperature for all baking times for both air fryer and convection oven (p < 0.05). When the baking temperature in the air fryer was reduced from 170 to 150 °C (with a baking time of 25 min), the firmness of cake decreased from 6.39 to 4.98 N (Table 1). The firmness of the air fryer baked cake at 150 °C for 25 min decreased by 28.31%, while that for the convection oven-baked cake at 150 °C for 35 min decreased by 24.50%.

Only baking temperature was found to significantly affect the chewiness of the air fryer baked cakes and convection oven-baked cakes (p < 0.05) (Table 2). As can be seen in Fig. 2D(g), when the baking temperature decreased, the chewiness of the air fryer baked cakes also decreased. For the air fryer baked cakes for 25 min, a decrease in the baking temperature from 170 to 150 °C led to a decrease in the chewiness from 2.49 to 1.42 N. By decreasing the baking temperature, the chewiness of the convection oven-baked cakes increased [Fig. 2D(h)] due to the presence of a small volume of air cells inside the cake which gave a higher mechanical strength. Baking time did not have a significant effect on the chewiness of the air fryer baked cakes and convection oven-baked cakes.

Analysis of variance showed that the R² values for the springiness of the samples baked in an air fryer and a convection oven were insignificant for secondary regression equations (Table 2). Both baking temperature and time did not affect the springiness (Table 2).

Effects of baking temperature and time on color

The evolution of color is an important appearance quality of cake product and important physical property to represent the influence of different baking modes on the baking cake. According to the experimental conditions, the total color change (ΔE) values of cake using air fryer and convection oven were ranged from 6.2 to 10.6 and 4.0 to 8.2, respectively (Table 1). The higher total color change values were obtained due to the higher baking temperature especially air fryer baked cakes. Baking temperature was found to has a significant effect than baking time on the total color change in both air fryer baked cakes and convection oven-baked cakes (p < 0.05) (Table 2).

It can be seen that increase in baking temperature and time for both baking modes increased the total color change of cakes [Fig. 2E(i), (j)]. This will enhance the Maillard reaction occurred more rapidly (Mohamad et al. 2015). As the temperature and time increases, the low moisture content of cake produced and enhances the high color changing, thus resulted in an increase in the hardness of cake. The water activity was also decreased at the product surface when the temperature and baking time increases, thus enhanced the formation of color compound (Purlis 2010). Therefore, reducing in baking temperature and time will reduce the total color change of cakes.

Optimization and verification of model

The optimum baking conditions for moist cakes in an air fryer and a convection oven were determined by numerical optimization of the baking temperature and time. With definite goals for each criterion, the ranges were selected accordingly with some alterations. The predicted values for each of the responding variables are shown in Table 3. Based on the ranges selected, it is suggested that the optimum conditions for the baking of moist cakes is 150 °C, for 25 min in an air fryer, and 150 °C and 35 min in a convection oven. The experimental values of all the responses were compared with those predicted by the equations of the model (Table 3). The cakes baked at a minimum baking temperature and time in the air fryer had a higher moisture content (28.80% ± 0.18) and relative height (37.19 ± 1.35), apart from lower firmness (5.05 N ± 0.05) and chewiness (1.42 N ± 0.03) as compared to those baked in the convection oven under similar conditions. The results showed that the experimental and predicted values were within the range, and the percentages of error between the experimental and predicted values were less than 10%. Therefore, the model can be used to optimize the baking conditions for moist cakes.

Table 3.

Predicted (Pred.) and experimental (Exp.) values of the response variables at optimum condition

Response variables	Air fryer (5.11 m/s)			Convection oven (0.08 m/s)
	Optimum values		Error (%)	Optimum values		Error (%)
	Exp.a	Pred.		Exp.	Pred.
Relative height (%)	37.19 ± 1.35	35.00	6.26	32.55 ± 1.54	35.00	7.00
Moisture content (%)	28.80 ± 0.18	28.77	0.10	27.64 ± 0.36	28.35	2.50
Firmness (N)	5.05 ± 0.05	5.14	1.75	5.09 ± 0.06	5.00	1.80
Chewiness (N)	1.42 ± 0.03	1.53	7.19	2.25 ± 0.07	2.19	2.74
Total color change (ΔE)	6.00 ± 0.14	6.40	0.07	4.55 ± 0.07	5.3	0.16

^aMean ± standard deviation

Sensory attributes of moist chocolate cakes

Figure 3 presents the mean scores for moisture, firmness, springiness, chewiness, aroma, sweetness and overall acceptance of air fryer baked cake and oven-baked cake. The results showed that there was no significant differences between air fryer baked cake and oven-baked cake on overall acceptability score (just varied from 5.35 to 5.70). In comparison, air fryer baked cakes was higher with scores 6.55 ± 0.69 in terms of moisture as compared to oven-baked cake which obtained 5.15 ± 0.81. This is in agreement with the experimental data results that show air fryer baked cakes has 28.8% of moisture content and oven-baked cake has 27.64%. According to Cauvain and Young (2010) the acceptable moisture content of moist cake has moisture content in range of 25–30%. There was no significant difference between air fryer baked cake and oven-baked cake on the aroma and sweetness scores with scores 6.10–6.35 and 5.90–6.25 respectively but still acceptable by panelist.

Fig. 3.

Radar chart on the sensory attributes on the optimized moist chocolate cake using air fryer and convection oven

In terms of firmness and chewiness, air fryer baked cakes scores (5.40 ± 0.50 and 5.05 ± 0.76 respectively) and oven-baked cakes scores (5.05 ± 0.83 and 5.25 ± 0.55 respectively) shows no significant differences between each other. This is an agreement with experimental data results that show no significant difference in firmness values of air fryer baked cake and oven-baked cake which are 5.05–5.09 N, 1.42 N–2.25 N respectively (Table 1). Therefore, the mean score indicates that the air fryer baked cake and oven-baked cake contributed adequately to these textures of cake which the panelists appreciated more. With regards to both sensory and instrumental texture properties, the texture attributes were closely associated with the sensory characteristics of the cakes.

Conclusion

Baking with the used of rapid air technology highly influences the baking conditions as the rapid hot air forced a pass over the product and heater surface by every circulation cycle. Baking conditions such as baking temperature and time have a significant effect on the quality of the cake (relative height, moisture content, firmness, chewiness and color) except springiness. As compared to baking in a convection oven, an increase in the air-frying temperature and time had the most significant effect (p < 0.05) towards the qualities of moist cakes in terms of cake volume expansion, moisture content, firmness and total color change. Statistical analysis of the data revealed no significant differences (p > 0.05) in the springiness at different baking temperatures and times for both baking modes. Optimum air fryer conditions resulted in moist cake samples with a relative height of 37.19% ± 1.35, moisture content of 28.88% ± 0.18, firmness of 5.05 N ± 0.05, chewiness of 1.42 N ± 0.03 and high overall acceptability (5.70 ± 0.66).