Physicochemical and phytochemical properties of foam mat dried passion fruit (Passiflora edulis Sims) powder and comparison with fruit pulp

Abstract

The aim of the present study was to develop purple passion fruit powder using the foam mat dried process. The possible effect of whipping time, methylcellulose concentration, and drying temperature on physicochemical and phytochemical properties of foam mat dried passion fruit was evaluated and compared with fruit pulp. The drying process was optimized using central composite design and optimum conditions were whipping time 2.78 min, methylcellulose 2.58%, temperature 44.05 °C. At the optimum condition vitamin C, total phenolic compound and hygroscopicity were 34.67 mg/100 g, 258.12 mg GAE/100 g, and 21.12%, respectively. The artificial neural network was applied to predict experimental outcomes. The phytochemical properties in terms of (±)-α tocopherol, D-α-tocotrienol, β-carotene, and phenolic acid were determined using RP-HPLC. The foam mate dried powder contained a higher amount of β-carotene (13.26 mg/100 g), total phenolic compound (258.12 mg/100 g) and phenolic acids than fruit pulp whereas fruit pulp was contented higher amount of (±)-α tocopherol (171.1 mg/100 g) and D-α-tocotrienol (27.19 mg/100 g). The study manifested foam mate drying as an effective way to develop passion fruit powder.

Electronic supplementary material

The online version of this article (10.1007/s13197-020-04596-y) contains supplementary material, which is available to authorized users.

Introduction

Passion fruit (Passiflora edulis) is an exotic tropical fruit belongs to the Passifloraceae family. Among the different species, two well-known edible passion fruit species are purple (Passiflora edulis Sims) and yellow (Passiflora edulis f. flavicarpa Deg.). The purple fruit is well recognized because of its nutritional benefits and medicinal properties (Patel 2009). The passion fruit is a promising source of various bioactive compounds such as vitamin C, vitamin E, phenolic compounds and carotenoids (Akter et al. 2011). Various types of polyphenol such as flavanols, flavonols, flavanones, anthocyanins, catechin, flavan-3ol, rutin are found in passion fruits (Rufino et al. 2010). Passion fruit also exhibits various antioxidant activity such as ferric reducing antioxidant, organic radical-scavenging capacity, 2, 2-Diphenyl-1-picrylhydrazil and ORAC-oxygen radical absorbance capacity (De Souza Schmidt Goncalves et al. 2010). It was also reported that passion fruit and its rind have the anti-hypertensive effect and vasodilatory effect on the human body (Devi Ramaiya et al. 2013). However, passion fruit is perishable and available for a short time. Thereby, it is need to protect by means of minimal processing.

To increase the shelf life and protect the phytochemical loss of passion fruit, it needs an effective way of drying. The application of foam mat drying techniques can be an effective way to increase shelf-life and decreases the phytochemical loss (Kadam and Balasubramanian 2011). In foam mat drying, for the porous structure of the foamed materials, mass transfer is faster, hence shorter the drying time apparently results in a higher quality of dried food product (Brygidyr et al. 1977). The foam mat dried powder from soy milk (Akintoye and Oguntunde 1991), star fruit (Karim and Wai 1999), cowpea (Falade et al. 2003), apple juice (Raharitsifa et al. 2006), mango (Rajkumar et al. 2007), banana (Thuwapanichayanan et al. 2008), mandarin (Kadam et al. 2011), tomato juice (Kadam and Balasubramanian 2011), sea buckthorn (Kaushal et al. 2013), and bael (Bag et al. 2011) were developed previously. However, there is scanty of research on foam mat drying of purple passion fruit. Moreover, there is no detail report on the phytochemical properties of foam mat dried passion fruit powder in terms of (±)-α tocopherol, D-α-tocotrienol, β-carotene, and phenolic acids.

Therefore, in the present study foam mat drying of purple passion fruit has been carried out. The process was optimized using central composite design and predicted using the artificial neural network (ANN). Furthermore, the phytochemical content such as (±)-α tocopherol, D-α-tocotrienol, β-carotene and phenolic acids of passion fruit powder were investigated and compared with fruit pulp.

Materials and methods

Raw material

The fully ripe purple passion fruit (Passiflora edulis Sims) cultivar was purchased from the local market of West Kameng District, Arunachal Pradesh, in the month of August–September. To maintain the maturity and cultivar of passion fruits, sample from same firm was purchased repeatedly. Fruits were washed and graded manually. During grading only proper shape and size samples were separated for pulping. The pulp was separated and stored at − 20 °C for future analysis.

Chemicals

The HPLC grade standard for phenolic acids such as, ferulic acid, sinapic acid, syringic acid, hydroxybenzoic acid, coumaric acid, vanillic acid, caffeic acid, catechin acid, chlorogenic acid, (±)-α-tocopherol, D-α-tocotrienol, and β-carotene was purchased from Sigma-Aldrich Chemical Co. (St. Louis, Missouri, USA). Folin-Ciocalteu reagent, sodium carbonate, gallic acid, 2, 2′-diphenyl-1-picrylhydrazyl (DPPH), acetonitrile and methanol were purchased from Sisco Research Laboratories Pvt. Ltd. (Maharashtra, India) with analytical grade and used without further purification.

Foam preparation and drying process

Foam mat drying of passion fruit pulp was done in varying temperature (40–60 °C), methylcellulose concentration (1–3%) and whipping time (1–5 min). The methylcellulose was used as foaming agent and as well as foam stabilizer. The passion fruit pulp and methylcellulose mixture was whipped in a modified kitchen blender (Model # Rex 500; Make # Bajaj, Pune, India) with continuous incorporation of air in the mixture. The foamed mixture was spread on a tray with 3 mm of thickness and kept in the tray dryer (Model # IKON, Make # IKON instruments, Delhi, India) for drying at temperature 40–60 °C. Foamed samples were monitored every 30 min for its moisture loss by weighing the sample plates using an electric balance with an accuracy of ± 0.01 g. The drying was terminated when the final moisture content reached 6.5% (db) which corresponded to water activity of ~ 0.32 (Rajkumar et al. 2007). After drying, the sample was ground to powder and the powder was vacuum packed and kept for further studies.

Physical properties

Color of pulp was measured by using color measurement Hunter colorimeter (Model # Hunter ColorLab Ultrascan Vis, Make # HunterLab Reston, United States).

Physicochemical analysis

pH, °Brix and moisture content

The pH and °Brix of pulp were determined by using pH meter and refractometer. The moisture content of pulp was determined by AOAC 2000.

Vitamin C

The vitamin C of the sample was determined according to Abano et al. (2014). Sample (1 g) was weighed and taken for preparation of extract and ascorbic acid solution was used as standard.

$$\text{Ascorbic}\text{acid =}\frac{0.5}{V_1}\times \frac{V_2}{15}\times \frac{100}{s}\times 100$$ 1

where V₁ is the mL of solution taken for estimation, V₂ is the volume made up, S is the weight of sample.

Total phenolic content

The total phenolic content of passion fruit powder was determined using Folin–Ciocalteu assay (Sharma et al. 2016). For analysis, 20 μL of the sample was taken in a test tube and 1.58 mL of distilled water was added. Later, 100 μL of FC reagent was mixed and within 8 min 300 μL of sodium carbonate was added with the mixture. The samples were vortexed immediately and allowed to incubate in dark for 30 min at 40 °C. The absorbance was measured at 765 nm using spectrophotometer (Model: UV-2600, Thermo Fisher Scientific; Make: Waltham, Massachusetts USA). The phenolic content was expressed in µg Gallic acid equivalent/g.

2,2′-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity

The DPPH radical scavenging activity of the sample was measured according to the method described by Das et al. (2018). Briefly, 100 μL of extracts was added to 1.4 mL DPPH radical methanolic solution (10⁻⁴ M) and the absorbance was measured at 517 nm. For the analysis, Trolox was used as standard. The results were expressed by using the following equation:

$$\text{DPPH}\text{scavenging}\text{activity}\text{assay}=\frac{A_0-A_s}{A_0}\times 100$$ 2

where A₀ is the absorbance of blank and A_s is the absorbance of sample.

Hygroscopicity

The hygroscopicity of the sample was determined as described by Jaya and Das (2004). Briefly, 0.5 g sample was put in the pre-weighed petri dish and placed in a hermetically sealed glass desiccator, containing the salt solution of NaCl (75% RH) and stored at 20 °C. At a specific time interval, the weight gain of the sample was measured until the three consecutive observations became the same.

$$\text{Hygroscopicity}\left(\text{\%}\right)=\left(\frac{b+H}{a-H}\right)\times 100$$ 3

where H is the initial water content of the sample (0.5 g), b is the weight increase, and a is the initial sample weight.

FT-IR analysis

For the Fourier-transform infrared spectroscopy, the fruit pulp (0.1 mL) was placed on a multi-bounce ZnSe crystal of ATR-FTIR to identify the functional groups (Vardin et al. 2008). On the other hand, properly dried foam mat passion fruit powder (2 mg) and 50 mg desiccated KBr powders were thoroughly mixed in a mortar and pestle before pressing into a thin pellet. The IR-absorption spectra of the thin pellet were obtained using an FTIR spectrometer (Model # Nicolet Impact 410, Make # Thermo scientific, USA) equipped with KBr optics and a DTGS detector and the frequency range from 4000 to 400 cm⁻¹.

Phytochemical analysis

Phenolic acids

For phenolic acid analysis, 50 g of sample and 0.5 g ascorbic acid were mixed. In the mixture, 100 ml of 80% methanol was added and filtrated through Whatman No.2. The filtered was further washed with hexane to the other nonpolar compounds. Then the volume of the sample was made up to 50 mL with distilled water and pH was adjusted to 7.0 (Samyor et al. 2016). RP-HPLC system (Model # W2489, detector-2414, Make # waters corporation, USA) was used for the detection of phenolic acids and the UV detector was set at 280 and 360 nm. The column C18, 5.0 µm particle size (4.6 mm × 250 mm) was used for analysis. The 20 μL of the sample loop was used at 25 °C. The mobile phase was (eluent A) acidified water of pH 2.64 and acidified water: acetonitrile (20:80) (eluent B). The flow rate of the mobile phase was maintained at 0.8 mL/min with a gradient run. The phenolic acids were identified and quantified with respect to their standards calibration curves. The software empower 2 was used for analysing data.

(±)-α-tocopherol, D-α-tocotrienol and β-carotene

The (±)-α-tocopherol, D-α-tocotrienol and β- carotene were estimated by the method described by Aguilar-Garcia et al. (2007) with slight modification. Passion fruit pulp and powder (100 mg) were extracted twice with 6 mL of methanol. Then the extract was centrifuged for 10 min at 825g. The supernatant was collected and evaporated to 4 mL and volume made up to 5.0 mL with methanol in a volumetric flask. This solution was filtered with Whatman No. 1 filter paper and then, filtered through GD/X sterile 0.45 µm cellulose acetate filter media of 25 mm before being subjected to HPLC analysis.

For detection of (±)-α-tocopherol, D-α-tocotrienol and β- carotene, the same RP-HPLC (Model # W2489, detector-2414, Make # waters corporation, USA) as used for phenolic, was used with UV Detector at 292 and 325 nm. The C18, 5.0 µm (4.6 mm × 250 mm) column was used to separate the compounds. The mobile phase was a mixture of methanol and acetonitrile (20:80 v/v) at a flow rate of 0.8 mL/min with isocratic mode. The software empower 2 was used for analysing data.

Experimental design

The central composite design (CCD) followed by response surface methodology (RSM) was used to develop the relationship between the variables and optimise experimental conditions for foam mat drying. The independent variables were whipping time (1–5 min), methylcellulose concentration (1–3%) and drying temperature (40–60 °C). The ranges of experimental parameters were selected based on preliminary trials. Total twenty experiment were carried out (In supplementary Table S1). After data analysis, a second-order polynomial equation was developed as follows:

$$y={\beta }_0+\sum _{i=1}^n{\beta }_i{x}_i+\sum _{i=1}^n{\beta }_{\mathit{ii}}{x}_{\mathit{ii}}^2+\sum _{i=1}^n\sum _{j=i+1}^m{\beta }_{\mathit{ij}}{x}_i{x}_J+\psi$$ 4

The coefficient of the polynomial equation were ${\beta }_0$(constant),${\beta }_i$(linear effects), ${\beta }_{\mathit{ii}}$(quadratic effects) and ${\beta }_{\mathit{ij}}$(interaction effects). x_i and x_j are the coded independent variables.

Artificial neural networks

Artificial neural networks (ANNs) were used to predict the relationship between input and output parameters. Three independent variables, i.e., whipping time (min), methylcellulose concentration (%) and temperature (°C) were in the input layer and the output layer was vitamin C (mg/100 g), total phenolic content (mg GAE/g) and hygroscopicity (%). A neural network was trained using a single hidden layer with a 3-x-1 topology where x was the number of neurons in the hidden layer. To determine the optimum number of neurons in the hidden layer, x was varied from 1 to 20. The experimental data was used to train the neural network (In supplementary Table S1). A total of 20 data points were distributed into three sets: training (14 points), validation (3 points) and testing (3 points). The best training performance of the neural network was based on the minimization of root mean square error (RMSE) and the highest regression coefficient (R²).

Statistical analysis

The experimental design was done using Design expert 12.0 (Stat-Ease, Inc. Minneapolis, MN) software and data was analysis using Analysis of variance (ANOVA). Microsoft office excel 2007 was used for average, standard deviation calculation and t tests. The Origin 8.5 (Origin Lab Corporation, Northampton, USA) software was used for graphs. Further, mean data obtained in preliminary trial were statistically analyzed by employing Duncan’s Multiple Range Test (DMRT) to identify their significant difference at p = 0.05. All experiments were carried out in triplicates. Means and standard deviations of the data were calculated for each treatment.

Results and discussion

Preliminary trial

A preliminary trial was conducted to identify the effect of whipping time and methylcellulose concentration on foam density of passion fruit pulp. The density of foam was varied from 0.92 to 0.98 g/cm³. Figure 1a, b illustrated the effect of whipping time and methylcellulose concentration on foam density (FD). From Fig. 1a, it was observed that the FD of the mixture was constant up to 3 min of whipping and the highest FD was observed 4 min whipping. Raharitsifa et al. (2006) reported that foam density decrease with an increase in whipping time up to a certain point and thereafter FD increase may be due to excessive whipping (overbeating) and leads to a collapse of the foam. Falade et al. (2003) suggested that the amount of air incorporation during a whipping is inversely proportional to foam density. During foam mat drying of bael, Bag et al. (2011) reported that the foam density of stabilized foams was increased after 2 min of whipping. From Fig. 1b, it was observed that for the increase of methylcellulose concentration in fruit pulp, FD decreased up to 3% of methylcellulose. A similar type of result was also observed by Bag et al. (2011) during foam mat drying of bael fruit. Therefore, in further study, the whipping time varied from 1 to 5 min and methylcellulose 1–3%.

Fig. 1.

Effect of a whipping time and b methyl cellulose on foam density of passion fruit pulp. Values with different superscripts are significantly different at p ≤ 0.05

Model fitting

All the experimental data were analysed using multiple regression analysis as shown in Table 1 and the correlation between the independent variables and dependent variables such as vitamin C, TPC, and hygroscopicity, were developed. After the analysis, a second-order polynomial relationship was developed between the variables. Significance test of the regression model, individual model coefficients and lack of fit were carried out as shown in Table 1. Results showed that the models developed for responses were highly significant (p < 0.05). In order to evaluate the model adequacy, correlation of determination (R²) of vitamin C (0.93), TPC (0.86) and hygroscopicity (0.86) were evaluated. Analysis of variance showed that R² of the models was higher than 85% and lack of fit was insignificant which showed interaction among the responses and predicted model was adequately accurate.

Table 1.

Analysis of variance for quadratic polynomial models

Source	Vitamin C		Total phenolic content		Hygroscopicity
	F-value	p value	F-value	p value	F-value	p value
Model	15.4300	< 0.0001	50.010	< 0.0001	6.9200	0.0028
X1	1.9700	0.0304	0.2300	0.0423	7.9700	0.0181
X2	1.5500	0.0419	2.1300	0.0448	12.70	0.0052
X3	108.24	< 0.0001	54.900	< 0.0001	4.18	0.0481
X1X2	0.0290	0.0010	1.1200	0.3158	0.034	0.0566
X1X3	0.0700	0.7968	6.102E−003	0.0393	5.32	0.0437
X2X3	2.70	0.1317	0.2400	0.6331	5.077E−003	0.9446
X21	7.45	0.0212	2.7300	0.0296	8.73	0.0144
X22	6.26	0.0313	1.3300	0.0083	9.00	0.0133
X23	8.63	0.0149	1.33	0.2764	3.55	0.0891
Lack-of-fit	4.26	0.0689	1.15	0.4404	0.73	0.625
R2	0.93		0.86		0.86

Response surface analysis of vitamin C

Equation 5 showed the relationship between vitamin C and independent variables. From Table 1 it was observed that the coefficient of determination (R²) was highly significant and lack of fit was insignificant which elucidated that model had efficacy to represent the relationship between vitamin C and methylcellulose concentration (%), whipping time (min) and temperature (°C).

$$\begin{array}{cc}\hfill \text{Vitamin}\text{C}=& 33.58-0.25x_1+0.22x_2-1.86x_3-0.061x_1{x}_2-0.062x_1{x}_3\hfill \\ \hfill & +0.38x_2{x}_{3}0.48x_1^2-0.44x_2^2+0.51x_3^2\hfill \\ \hfill \end{array}$$ 5

For the change of methylcellulose concentration, whipping time and temperature the vitamin C content was varied from 30.78 to 38.66 mg/100 g (Table S1). From Fig. 2a it was observed that up to 2% of methylcellulose concentration resulted in increases in the vitamin C (32.12 mg/100 g) in the powder and a further increase in concentration a decreasing pattern was observed in foam mat dried passion fruit powder. The increase in vitamin C content may be due to the hydrocolloidal activity of methylcellulose on vitamin C during drying. It was suggested that the functional groups of colloids might protect the vitamin C from water molecule and subsequent degradation. On the other hand, the increase in vitamin C may due to increase its bio-availability as results of cell wall rupture and the porous structure with an open solid matrix.

Fig. 2.

Effect of methyl cellulose whipping time and temperature (°C) on a, b vitamin C content, c, d total phenolic content, and on hygroscopicity of powder

It was also observed that for an increase of whipping time up to 3 min the vitamin C content of the powder increased and later a decreased pattern was observed (Fig. 2a). The increase in vitamin C content may be due to the release of vitamin C from the cell during mixing. However, a further increase in whipping time showed a decrease in vitamin C, which may be attributed to the structural breakdown and oxidative degradation. Temperature evinced a significant (p < 0.05) effect on the vitamin C content of the sample (Fig. 2b). As the temperature increased from 40 to 60 °C, the vitamin C content of foam mat dried powder decreased drastically and it can be ascribed to heat liability of vitamin C (Zhong et al. 2017).

Response surface analysis of total phenolic content

The Eq. 6 shows the relationship between total phenolic content and independent parameters in passion fruit powder. The correlation coefficient (0.86) and lack of fit (0.440) of the developed model were elucidated that the developed model has efficacy to represent the relationship between parameters.

$$\begin{array}{cc}\hfill \text{Total}\text{phenolic}\text{content}=& 243.81+2.55x_1-7.78x_2-39.44x_3-7.34x_1{x}_2-0.54x_1{x}_3+3.42x_2{x}_3\hfill \\ \hfill & -8.56x_1^2-9.14x_2^2-5.97x_3^2\hfill \\ \hfill \end{array}$$ 6

The TPC content of the of foam mat dried passion fruit powder was varied from 182.5 to 319.62 mg/100 g. Figure 2c, revealed the steady increase in the total phenolic content up to 2% of methylcellulose and thereafter showed a decrease trend in the TPC in powder. The increase in TPC may be due to the stabilizing effect of methylcellulose, based on electrostatic interactions between the phenolic compounds and the dissociated carboxylic groups of the colloids (Hubbermann et al. 2006). Further increase in methylcellulose beyond 2%, there was a drastic decrease in TPC of passion fruit powder as shown in Fig. 2c. A higher methylcellulose contributed higher solid content, which might have a greater effect on the reactions between molecules of TPC lost during the drying process. The TPC of foam mat dried powder was increased with an increase in whipping time up to 3 min and thereafter the trend showed a decreasing pattern (Fig. 2c). The increase in TPC may be due to the release of TPC due to the cell lysis during whipping. However, a further increase in whipping time showed a decreased pattern of TPC, due to the structural breakdown and oxidative degradation of TPC. The foam mat drying temperature also affected the TPC in foam mat dried powder. The TPC of the foam mat dried powder decreased drastically with the increase of drying temperature from 40 to 60 °C (Fig. 2d). The decrease in TPC for an increase in temperature was obvious because of heat-sensitive and prone to oxidation which causes structural distraction thereby decrease the TPC in powder (Sharma et al. 2015).

Response surface analysis of hygroscopicity

The empirical relationship between whipping time, methylcellulose and temperature with hygroscopicity of foam mat dried powder were represented by Eq. 7. The correlation coefficient (R²) of the developed model was recorded as 0.86.

$$\begin{array}{cc}\hfill \text{Hygroscopicity}=& 23.86-1.95x_1+0.36x_2-3.78x_3+2.82x_1{x}_2-0.50x_1{x}_3-0.14x_2{x}_3\hfill \\ \hfill & +4.83x_1^2-2.43x_2^2-2.74x_3^2\hfill \\ \hfill \end{array}$$ 7

The hygroscopicity of the powder was varied from 9.57 to 41.51% (Table S1). The Fig. 2e, f showed the graphical relationship between processing parameters. From Fig. 2e, it was illustrated that with the increase of the concentration of methylcellulose up to a certain level (2%) there was a continuous increase in hygroscopicity (41.51%) and later decreased slightly. The increase in hygroscopicity of powder can be accredited to increase in available hydroxyl groups in the amorphous regions of the substrate as well as the surface crystalline regions and therefore, it can easily absorb the moisture from the atmosphere. Later the decrease in hygroscopicity may be due to the presence of an excessive amount of methylcellulose which slowly decreases the affinity to adsorb water. Moreover, methylcellulose is a material with low hygroscopicity, therefore higher amount of methylcellulose may decrease the hygroscopicity (Tonon et al. 2008). Figure 2e illustrated the effect of whipping time on the hygroscopicity of powder. With the increase of whipping time up to 3 min, the hygroscopicity (22.33%) decreased drastically and after that, a reverse trend was observed. Figure 2f illustrated that as the temperature increased (40–60 °C), hygroscopicity also increased. This is related to the water gradient between the product and the surrounding air and evinces moist powder.

Optimisation and validation of foam mat drying parameter

In the optimization step, after response surface analysis the foam mat drying process was optimized on the basis of highest desirability. The optimum condition was selected on the basis of the highest TPC, vitamin C, and lowest hygroscopicity. The optimum foam mat drying conditions were, whipping time 2.78 min, methylcellulose concentration 2.58%, and drying temperature 44.05 °C. At the optimum condition, the predicted value of response was vitamin C 34.67 mg/100 g, TPC 258.12 mg/100 g, and hygroscopicity 21.12%. After optimization, the process parameters were validated. During validation, the experiment was conducted at the optimized condition and observed that the experimental value of total phenolic content (255.87 mg GAE/100 g), vitamin C (33.28 mg/100 g) and hygroscopicity (21.98%) have not differed significantly with the predicted data. The result has the evidence to support that the developed model can efficiently optimize the process.

Artificial neural network modeling

Artificial neural networks are basically computational models based on biological neural processes that predict models. ANN is a non-linear mathematical tool comprises of interconnected adaptive processing elements ‘‘neurons” that are actually grouped in input, hidden and output layers, which eventually send messages to others (Basheer and Hajmeer 2000). The experimental data were used to develop the ANN model.

ANN model was developed using a multi-layer perceptron with logistic sigmoidal function. The CCD data were categories as training (14), testing (3) and validation (3), to measure the performance of the developed ANN. The coefficient of determination (R²) was used to determine the efficacy of the developed ANN model. For TPC, the best ANN model was obtained with one hidden layer and ten hidden neurons with a coefficient of determination of 0.94. Similarly, for vitamin C (R² = 0.96) and hygroscopicity (R² = 0.89), the best ANN models were obtained with one hidden layer with ten hidden neurons. A comparison between RSM and ANN model (In supplementary Fig. S1). The coefficient of determination (R²) of ANN model for vitamin C, total phenolic content and hygroscopicity values were higher than RSM which inferred that ANN has a higher ability to predict the experimental outcome than the RSM models.

Physicochemical comparison of fruit pulp and powder

FT-IR analysis

FT-IR analysis of pulp and foam mat dried passion fruit powder are depicted in Fig. 3. Pulp showed the spectral stretching ranging from 964.78 to 3995.34 cm⁻¹, whereas foam mat dried pulp ranged from 857.81 to 3012.33 cm⁻¹. Band of C=O stretching was mainly due to the presence of a carboxyl (–C=O) group of phenolic compounds. A stretching characteristic peak at approximately 3420 cm⁻¹ and 2937 cm⁻¹ was due to the O–H stretching band. The C=O carbonyl group characteristic peak was observed at 1650 cm⁻¹ vibration (Santhiya et al. 2002). Peaks were seen more prominently in the passion fruit powder than pulp.

Fig. 3.

FT-IR spectra of passion fruit a pulp and b powder

Physicochemical properties

The physicochemical properties of pulp and optimized foam mat dried powder are shown in Table 2. The L, a, and b values of the foam mat dried powder differed significantly concerning to fruit pulp. The powder showed more brightness and redness than fruit pulp. The DPPH scavenging activity and vitamin C content was less in optimized powder (60.53 ± 0.21% and 35.19 ± 0.20 mg/100 g) than the raw fruit pulp (90.53 ± 0.10% and 65.19 ± 0.51 mg/100 g), whereas the TPC content of passion fruit powder (210.11 ± 0.23 mgGAE/100 g) were slightly higher than raw fruit pulp (206.29 ± 0.10 mgGAE/100 g). However, previous researchers were reported quite low amount of TPC in passion fruit juice and varied from 103 to 150 mg GAE/100 g (de Oliveira et al. 2009; Martínez et al. 2012). It might be due the difference in cultivar of passion fruit.

Table 2.

Physicochemical compositions of pulp and powder

Parameters	Passion fruit pulp	Foam mat dried powder
Moisture content (%)	82.25 ± 0.01*	6.52 ± 0.02
L	36.68 ± 2.02*	53.13 ± 1.17
a	3.793 ± 0.61*	12.97 ± 0.39
b	19.82 ± 1.44	22.65 ± 0.39
DPPH scavenging activity (%)	90.53 ± 0.10*	60.53 ± 0.21
Total phenolic content (mg GAE/100 g)	206.29 ± 0.10	210.11 ± 0.23
Vitamin C (mg/100 g)	65.19 ± 0.51*	35.19 ± 0.20

Values expressed as mean ± SD (n = 3). Values with superscripts in the row indicate that there is significant difference between samples (p ≤ 0.05) from t tests

Where, L value (0–50) indicates darkness and a high number (51–100) indicates lightness, a-value indicates redness to greenness and b-value indicates yellowness to blueness

Phytochemical analysis

The vitamins and phenolic acids in pulp and powder were identified and quantified by RP-HPLC (Table 3). The β-carotene, (±)-α-tocopherol and D-α-tocotrienol were detected at the retention times of 3, 3.5 and 3.8 min, respectively. The β-carotene content in the foam mat dried powder (13.26 mg/100 g) was higher than the pulp (11.79 mg/100 g). Cavalcante et al. (2011) stated that compounds like carotene and vitamin accumulation in passion fruit are contributed by various internal as well as external factors viz., maturity stage, cultivation system, etc. The amount of (±)-α-tocopherol (171.1 mg/100 g) and D-α-tocotrienol (27.19 mg/100 g) was found higher in pulp than powder (Table 3). Six phenolic acids were prominently observed in the raw pulp as well as foam mat dried powder. The pulp sample was predominately contented coumaric acid (268.75 mg/100 g), syringic acid (643.46 mg/100 g) and sinapic acid (1630 mg/100 g), whereas the foam mat dried powder was predominant with chlorogenic (790.33 mg/100 g), trans-ferulic acid (3402 mg/100 g) and vanillic acid (893.87 mg/100 g).

Table 3.

Quantification of vitamins and phenolic acids of passion fruit pulp and foam mat powder

Phytochemicals	Retention time (min)	Passion fruit pulp (mg/100 g)	Foam mat dried passion fruit (mg/100 g)
1. Beta carotene	3	11.79*	13.26
2. (±)-α-tocopherol	3.5	171.1*	15.2
3. D-α-tocotrienol	3.8	27.194*	11.98
Phenolic acid
1. Caffeic acid	14.66	NA	NA
2. (±) Catechin hydrate	13	NA	NA
3. Chlorogenic acid	13.8	789.00	790.33
4. Þ- Coumeric acid	17.25	268.75	266.25
5. Transferulic acid	14.36	766.26*	342
6. 4-Hydroxybenzoic acid	18.03	NA	NA
7. Syringic acid	15.06	643.46	639.6
8. Sinapic acid	17.8	630*	523.33
9. Vanillic acid	14.96	873.75*	893.87
Total phenolic acid		4971.22	6515.38

Values with superscripts in the row indicate that there is significant difference between samples (p ≤ 0.05) from t tests

Conclusion

The foam mat dried passion fruit powder was develop and the process was optimized using CCD. The optimum process conditions of foam mat drying were whipping time 2.58 min, methylcellulose concentration 2.58%, and drying temperature 44.05 °C. The experimental outcomes were predicted using ANN and showed higher efficiency than the polynomial model. Quantitative comparison of pulp and powder revealed that (±)-α-tocopherol and D-α-tocotrienol were higher in pulp whereas β-carotene was higher in powder. In passion fruit pulp, coumaric acid, syringic acid, and sinapic acid were predominant whereas, in foam mat powder chromogenic acid, trans-ferulic acid, and vanillic acid were higher. The study manifested that foam mat drying is an efficient way to develop passion fruit powder and can be used in many food products as a substitute for artificial additives.

Electronic supplementary material

Below is the link to the electronic supplementary material.