Influence of different drying techniques on quality parameters of mushroom and its utilization in development of ready to cook food formulation

Abstract

Three different drying methods: hot-air-drying (HAD), dehumidified drying (DD) and freeze drying (FD) were used to dry Indian white button mushrooms (Agaricus bisporus).  Dehumidified drying method has been proposed as an alternative technique  to improve the quality of dehydrated mushroom. Mushroom powder obtained by DD method had 33.29% protein, 17.21% uronic acid, and 10.93% ash content. It was  also a good source of ergosterol (422.18±5.80 mg/100 g dw), which is known as the precursor of Vitamin D₂. Ethanolic extract of mushroom powder showed good antioxidant activity  with lower DPPH IC₅₀ value (7.16±0.23 mg/mL) and also lower EC₅₀ value of ABTS (4.36±0.04 mg/mL). Mushroom powder is added to ready to cook green gram based chilla mix (vegetable omelette mix) at 10%, 20% and 30% levels. The effect of incorporation of mushroom powder on quality characteristics of the formulation was studied. The results showed that the ready to cook mix containing 20% of mushroom powder had protein: 23.33 g; total dietary fiber: 10.75 g; ergosterol: 79.08 mg and also important minerals like calcium: 99.57 mg; potassium: 1203.49 mg; magnesium: 137.80 mg and zinc: 2.23 mg in 100 g of formulation. The formulated products were shelf-stable at ambient temperature for three months.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05680-9.

Introduction

Mushrooms are known to contain various essential micro and macro nutrients as well as nutraceuticals with significant health benefits. Edible mushrooms are consumed for the high protein content, low fat and calorie value and they are also rich source of vitamins and minerals with a  distinguished umami flavor. India has gained global attention for the production of different exotic mushrooms. However, mushrooms are extremely perishable due to their high water content thus their shelf life is very short. Preservation of fresh mushrooms is one of the most efficacious ways to prolong the shelf life with intact nutritional composition for its use in off-season. Dehydration methods may alter the physicochemical or nutritional properties and microstructure of dried mushrooms. Currently a variety of drying techniques are applied in the processing of mushrooms. Controlled hot air drying (HAD) is a simple method for dehydration and is considered for cost effectiveness and speed. But this technique can impact adversely on the colour, taste and nutritional value of the dehydrated products (Argyropoulos et al. 2011). Freeze drying is also a well recognized method for dehydration with low degradation of nutrients and higher quality end products. Although, it is a costly technique. Other methods like microwave drying (MD), vacuum drying (VD) have also been successfully applied in preservation of mushroom (Tian et al. 2016). It is important to reduce the time of processing and also to optimize drying methods that can result in higher quality products cost effectively at low energy consumption. Dehydrated mushroom powders have great potential to be incorporated in food products to enhance their nutritional quality and also to increase the acceptability. Mushroom is the only vegetarian food source which is rich in the precursor of vitamin D having the potential to become the primary dietary source of Vitamin D₂ for a population avoiding animal and animal derived foods. Incorporation of mushroom powder into food products contributes to higher content of protein, minerals, dietary fiber and importantly pre-vitamin D₂. Agaricus bisporus popularly known as white button mushroom, contain various essential nutrients as well as bioactive components and are considered as one of the most widely produced and consumed edible mushrooms (Tian et al. 2012).The main objective of this work was to obtain mushroom powder (white button mushrooms) having higher nutrient retention by comparing the efficacy of different drying techniques which included hot air drying (HAD), dehumidified drying (DD) and freeze drying (FD). The mushroom powder obtained from optimized drying method, was incorporated into ready to cook chilla mix or popularly known as vegetable omelette which is a traditional popular Indian snack. Chilla or vegetable omelette is mainly prepared with unpolished green gram (Vigna radiate) or chickpea flour (Cicer arietinum) which can be spiced according to the choice. It has good acceptability and is very nutritious with respect to high protein content, minerals, dietary fiber and low-fat content. A ready to cook chilla mix was formulated with dehydrated mushroom powder at three different levels (10%, 20% and 30%). The effect of adding mushroom powder on the quality characteristics of ready to cook chilla was studied with respect to its nutrient composition and sensory quality. The chilla mix with 20% mushroom powder (optimal) and the control formulation (without mushroom powder) were further evaluated for storage stability during three months at accelerated (92% RH, 37 ± 2 °C) and ambient (65% RH, 27 ± 2 °C) conditions. The effect of storage conditions on the quality parameters of the formulated chilla mix was studied.

Materials and methods

Mushroom samples

White button mushrooms (Agaricus bisporus) purchased with healthy fruit bodies from a local market (Mysore, Karnataka) were washed and cut into slices (thickness 5 mm) and further processed on the same day.

Dehydration

Mushroom slices were dried by the following drying methods.

Hot-air-drying (HAD)

The sliced mushrooms were placed in a single layer on the trays and dried in a Cross-flow dryer (TECHNICO Laboratory Products Pvt. Ltd., India) at 55–58 °C for 6–7 h.

Dehumidified drying (DD)

Freshly sliced mushrooms were dried in Alpha inert gas drier connected with a dehumidifier (Model FFB170, Bry Air Pvt. Ltd., Asia). The average drying temperature was 52–55 °C, relative humidity was 22–25% and duration of drying was 6–7 h.

Freeze drying (FD)

Freshly sliced button mushrooms were frozen in the freezer (RQVD-300 Plus, Remi, India) for 24 h. It was then dried in a freeze dryer (Model 2–16 LSC plus- Gamma, CHRIST, Germany) with a sublimator and vacuum station. The average operating pressure in the drying chamber reached 0.01–0.05 mbar. The temperature during the entire drying process did not exceed 25 °C.The average drying time was 26–27 h.

After dehydration process, the obtained dried mushrooms by different techniques were ground to fine powder using a grinder (Philips HL7756/00 750 W, Netherlands).

Physicochemical analysis of the mushroom powder obtained from different drying methods

Nutritional composition

The moisture (method 44–15), protein (method 46–10) and ash (method 08–01) content of the samples were estimated according to the standard methods of AACC (2012). Reducing sugar content was estimated using 3,5-dinitrosalicylic acid methods (Agbenorhevi and Kontogiorgos 2010). The uronic acid content was estimated using glucuronic acid as standard with a concentration ranged of 10–50 µg (Blumenkrantz and Asboe-Hansen 1973).

Bioactive compounds

Preparation of ethanolic extract of mushroom

The samples (typically 3 g) were extracted by stirring with 100 mL of 80% ethanol at 25 °C at 150 rpm for 24 h and filtered through Whatman No. 4 filter paper. The residue was then re extracted twice in the same way. The combined ethanolic extracts were evaporated at 40 °C to dryness and re-dissolved in ethanol at a concentration of 100 mg/mL, and stored at − 20 °C for further use. Bioactive compounds in the mushroom extracts were determined by colorimetric assays as well as with other combination of chromatographic and spectroscopic methods.

Total polyphenol contents

Total polyphenols in the mushroom extracts were determined by colorimetric assays as described by Barros et al. (2008a, b). Briefly, 1 mL of mushroom extracts was mixed with 1 mL of Folin and Ciocalteu’s phenol reagent. After 3 min, 1 mL of saturated sodium carbonate solution was added to the mixture and volume make up was done with distilled water to 10 mL. The reaction was kept in the dark for 90 min and subsequently absorbance was read at 725 nm. Total polyphenol content was expressed as mg of gallic acid equivalents (GAEs) per g of extract.

Antioxidant properties

The radical scavenging activity was assessed by DPPH and ABTS inhibition activity of ethanolic extract of mushroom following the method described by Barros et al. (2007) and Re et al. (1999). Radical scavenging activity (RSA %) was calculated by using the following formula: RSA % = [(A_control − A_test)/A_control] × 100, where A_control is the absorbance of the control reaction and A_test is the absorbance of the extract reaction. The extract concentration providing 50% radical scavenging activity (IC₅₀) was calculated using the formula: IC₅₀= [(ΣC/ΣI) × 50], where ΣC is the sum of concentrations of mushroom extract and ΣI is the sum of percentage of inhibition at different extract concentration.

Determination of ergosterol content

Dried mushroom powder (~ 2 g) was extracted with methanol/dichloromethane (75:25, v/v) at room temperature in a solid-to-liquid ratio of 1:25. The extracts were centrifuged at 10,000 rpm for 5 min. The extraction procedure was repeated three times. The total extracts were evaporated to dryness in a rotavapor at 40 °C. The resulting residue was dissolved in 1 mL of methanol and filtered through a 0.45 μm nylon syringe membrane and injected to HPLC (Barreira et al. 2014).

Chromatographic analysis

The analyses were performed by HPLC-UV (Model LC 10AS, Shimadzu). Chromatographic separation was achieved with a Supelco HPLC reversed-phase C-18 column (15 cm × 4.6 mm, 5 μm, Supelco) using a solvent system consisting of 70% acetonitrile and 30% methanol in an isocratic mode. The solvent flow rate was 1 mL/min and injection volume was 20 µL. Quantification was achieved by the absorbance recorded at 280 nm. Ergosterol was compared, quantified using obtained area of the ergosterol standard.

Color measurement

Color measuring system (Model CM3500D, Minolta spectrophotometer, Minolta Co., Ltd., Japan). The results were expressed in L*, a*, b* values. L* denotes the degree of lightness on 0–100 scale from black to white, a* is the degree of redness (+) to greenness (−), and b* is the degree of yellowness (+) to blueness (−). All analyses were performed in triplicate.

Microstructure analysis

A small section of dehydrated sample with dimensions of 5 × 1 × 1 mm was cut and gold plated. Scanning electron microscope (Model: S 3400 N, Hitachi Japan) was used to obtain the microstructure.

Rehydration ratio

The rehydration ratio (RR) of dried mushrooms was determined by the method as described by Wang et al. (2014). Rehydration ratio (RR) was calculated as:

$$\text{RR = Gf/Gg}\text{.}$$ 1

where Gf (g) and Gg (g) are the weight of the rehydrated and initial dried samples, respectively. The RR values were determined in triplicate.

Bulk and tapped density

The bulk density (ρ_bulk) and tapped density (ρ_tap) were measured and calculated by the method described by Jinapong et al. (2008).

Flowability and cohesiveness

Flowability and cohesiveness of the powder were evaluated in terms of Carr index (CI) (Carr 1965) and Hausner ratio (HR) (Hausner 1967) respectively. Both CI and HR were calculated from the bulk (ρ_bulk) and tapped (ρ_tap) densities of the powder as shown below:

$$\text{CI}=\frac{\mathrm{\rho }\text{tap}-\mathrm{\rho }\text{bulk}}{\mathrm{\rho }\text{tap}}\times 100$$ 2

$$\text{HR}=\frac{\mathrm{\rho }\text{tap}}{\mathrm{\rho }\text{bulk}}$$ 3

Water-holding and oil-holding capacities

Water-holding capacity (WHC) and oil-holding capacity (OHC) of mushroom powders were estimated following the methods described by Ahmedna et al. (1999).

Chilla mix formulation

Raw materials

Green gram flour (Vigna radiata), chickpea flour (Cicer arietinum), rice flour (Oryza sativa), turmeric powder (Curcuma longa) and red chilli powder (Capsicum annuum), roasted cumin seed (Cuminum cyminum), black pepper powder (Piper nigrum) and salt. Mushroom powder prepared by dehumidified drying method was used for the partial replacement of the green gram flour.

Process for the preparation of chilla mix

Control sample was prepared by mixing the ingredients in appropriate proportions with green gram flour (70%), chickpea flour (15%), rice flour (8%), turmeric powder (2%) and red chilli powder (1%), roasted cumin seed (1%), black pepper powder (1%) and salt (2%). All the ingredients were mixed in a Hobart mixer to form a homogenous blend. The chilla mix with mushroom powder was prepared by partially replacing the green gram flour and incorporating mushroom powder at 10%, 20% and 30% levels.

Proximate composition analysis of different blends of chilla mix

The moisture content (method 44–15), protein (method 46–10), fat (method 30–10) and ash (method 08–01) were estimated to the standard methods of AACC (2012) and dietary fiber (method 991.43) by AOAC (2016).

Sensory evaluation of cooked chilla

Chilla mix was weighed and water was added proportionately to make a fine batter. This was poured on to a hot pan and spread out into circular shape to obtain chilla. Sensory evaluation of freshly prepared chilla was carried out by trained sensory panelists. The prepared samples were coded with three digit random numbers and served to the panel members with a glass of warm water for intermittent cleansing of the palate between the samples. The employed method for conducting the sensory evaluation was quantitative descriptive analysis (QDA). Sensory traits (descriptors) were selected suitable for creating a scorecard for the analysis of the samples. The trained panelists (12) were requested to mark the distinguished intensity of each attribute presented in the scaled scorecard which ranged from 0 to 15 cm. In the scale of the score card 1.25 cm was affixed on both the ends which depicts the ‘Recognition Threshold’ and ‘Saturation Threshold’ respectively. The provided scores for all the sensory traits by the panel members were tabulated and calculated by the mean value for each attribute of a prepared sample. It indicated the judgment of the panel’s regarding the sensory quality of the product (Chetana et al. 2013).

Storage study

The storage stability of the formulated ready to cook chilla containing 20% mushroom powder and chilla without mushroom powder packed in metalized polyethylene pouches (MPE) were stored at accelerated (92% RH, 37 ± 2 °C), and ambient (65% RH, 27 ± 2 °C) storage conditions. The samples were withdrawn at intervals of 30 days and quality of the product was determined by evaluating moisture, water activity, color and also the ergosterol content.

Statistical analysis

All estimations were carried out in triplicates. The results are expressed as the mean values and standard deviation (SD). The results were analyzed by one-way analysis of variance (ANOVA) followed by Tukey’s HSD test with α = 0.05, using SPSS Version28 software.

Results and discussion

Effect of varying drying methods on the nutritional composition of dehydrated mushrooms

Nutritional composition of the white button mushroom powder dried by three different techniques was analyzed. The results are tabulated in Table 1. The moisture content of dehydrated mushroom powders dried by different techniques showed no significant difference. The protein content in FD samples (34.6%) was significantly higher (p < 0.05) than DD (33.29%) and HAD (32.83%) samples. Reducing sugar content was found to be significantly lower (p < 0.05) in the HAD samples compared to the other methods. This can be explained for the Maillard reaction that takes place in HAD condition which further leads to slight degradation of reducing sugars and protein contents (Pei et al. 2014). Uronic acid in HAD samples was significantly (p < 0.05) lower than DD and FD samples. Total sugars content in the samples showed in the order FD > DD > HAD but the difference is not significant.

Table 1.

Effect of different varying drying methods on chemical composition of button mushroom

Parameters	HAD*	DD	FD
Chemical composition
Moisture (%)	3.98 ± 0.34a	3.79 ± 0.68a	3.49 ± 0.38a
Protein (%)	32.83 ± 0.29b	33.29 ± 0.16b	34.6 ± 0.20a
Ash (%)	10.43 ± 0.11a	10.93 ± 0.48a	10.44 ± 0.10a
Uronic acid (% dw)	15.18 ± 1.27b	17.21 ± 0.77a	17.28 ± 0.44a
Total sugar (mg g− 1)	17.06 ± 1.06a	18.61 ± 2.75a	20.03 ± 4.32a
Reducing sugar (g g− 1)	2.81 ± 0.62c	3.67 ± 0.08b	4.03 ± 0.39a
Bioactive compounds and antioxidant properties
Total Polyphenols (mg/g dw)	1.94 ± 0.04c	3.69 ± 0.29b	4.52 ± 0.16a
Ergosterol (mg/100gm dw)	214.41 ± 3.2c	422.18 ± 5.8b	324.54 ± 17.9a
DPPH IC50 (mg/mL)	15.03 ± 0.56a	7.16 ± 0.23b	6.54 ± 0.03b
ABTS EC50 (mg/mL)	5.05 ± 0.02a	4.36 ± 0.04b	4.24 ± 0.01b
Color
ΔE	40.04 ± 0.3a	32.67 ± 0.7b	31.96 ± 0.5b
L*	60.00 ± 0.3a	67.88 ± 0.5b	70.32 ± 0.6c
a*	3.77 ± 0.05a	2.87 ± 0.1c	3.19 ± 0.1b
b*	13.86 ± 0.1a	13.71 ± 0.5a	16.65 ± 0.05b
Physicochemical parameters
Rehydration ratio (%)	3.18 ± 0.05c	4.26 ± 0.03b	4.84 ± 0.18a
Bulk density (g/cm3)	0.503 ± 0.002a	0.404 ± 0.003b	0.253 ± 0.001c
Tapped density (g/cm3)	0.631 ± 0.002a	0.506 ± 0.002b	0.318 ± 0.004c
CI (%)	20.34 ± 0.45a	20.22 ± 0.32a	20.54 ± 0.98a
HR	1.26 ± 0.007a	1.25 ± 0.005a	1.26 ± 0.015a
WHC (g/g)	2.25 ± 0.01c	2.99 ± 0.08b	4.82 ± 0.10a
OHC (g/g)	0.98 ± 0.06c	1.36 ± 0.12b	1.72 ± 0.06a

*HAD-hot air drying, DD-dehumidified drying, FD-freeze drying

Data are shown as mean ± SD (n = 3). Values within a row not sharing the same lowercase are significantly different as indicated by Tukey’s HSD test (p < 0.05)

Bioactive compounds and antioxidant properties

The changes in the bioactive components and antioxidant potential of the white button mushroom dried by different techniques were presented in Table 1. Previous studies have reported that the total polyphenol content in Agaricus bisporus ranged from 3.4 to 4.9 mg /g dw (Barros et al. 2008a, b). Similar range of polyphenol content has been observed in the current work. In the present study, it was noted that drying methods significantly (p < 0.05) affected total polyphenol content in the mushroom samples. FD samples showed highest retention of total polyphenols (4.52 mg GAE/g dw) followed by DD (3.69 mg GAE/g dw) and HAD samples (1.94 mg GAE/g dw). Similar trend in the retention of polyphenol content in freeze drying method than hot air-drying method also observed by Shams et al. 2022.The loss of polyphenols can be caused by both enzymatic and non-enzymatic reactions during the drying process.

Ethanolic extracts from mushrooms dried by different methods exhibited significant difference (p < 0.05) in antioxidant potential. Since the higher content of polyphenols correlated with the antioxidant potential, lowest DPPH IC₅₀ value resulted in the FD samples (6.54 ± 0.03 mg/mL) followed by DD (7.16 ± 0.23 mg/mL) and highest in HAD (15.03 ± 0.56 mg/mL) samples. But the difference was not significant between FD and DD method. Similar trend in ABTS IC₅₀ value was observed with the order: FD < DD < HAD. A lower IC₅₀ value indicates stronger radical scavenging potential. A study by Ji et al. (2012) similarly investigated the effects of drying methods (sun drying, hot-air drying, microwave-vacuum drying and freeze drying) on the antioxidant properties and phenolic contents in white button mushrooms fruiting bodies. They have also reported that drying techniques significantly affected the total polyphenol contents and antioxidant properties in button mushrooms similar with our study. Their study showed that hot air drying and sun drying significantly reduced the phenolic contents and antioxidant potential of the dehydrated mushrooms in comparison to freeze drying and microwave-vacuum drying methods.

Agaricus bisporus is reported to be the rich source of ergosterol in range 6.4–6.8 mg/g dw (Villares et al. 2014). Ergosterol in contact with air and heat is prone to oxidation. Drying methods influenced the ergosterol content of mushroom. DD samples (422.18 ± 5.8 mg/100 g dw) had significantly (p < 0.05) higher retention of ergosterol followed by FD (324.54 ± 17.9 mg/100 g dw) and HAD methods (214.41 ± 3.2 mg/100 g dw). The corresponding HPLC chromatograms of the mushroom samples dried by different techniques are presented in Supplementary Fig. 2.

Colour

The highest possible L* value and the lowest ΔE value is considered as the bench mark in industry for the color quality of dried mushrooms and also consumer acceptance of the product in the market (Tian et al. 2016). Drying techniques significantly (p < 0.05) affected the L*, a*, and b* values of the samples showed in Table 1. This finding was consistent with the results reported by Wang et al. (2019), and Tian et al. (2016). Button mushrooms dried by FD method exhibited highest L* values and lowest ΔE values. Although ΔE values of FD samples did not significantly differ from DD method. The lowest L* values and highest ΔE values were obtained for the samples dried by HAD method. This indicates that during the HAD process non-enzymatic Maillard reaction occurred between proteins or amino acids and reducing sugars that might have caused the HAD samples to appear darker  (Isik and Izlin 2014). The images of the mushroom powders dried by different methods are shown in the Supplementary Fig. 1.

Effects of drying techniques on scanning Electron micrographs (SEM)

It can be observed (Fig. 1) that drying conditions affected the surface morphology of the dried material. The micrographs showed more severe surface shrinkage in HAD samples than DD and FD samples. The samples dried by dehumidified drying and freeze drying had smoother surface.

Fig. 1.

Scanning electron micrographs of white button mushroom dried by different methods. The magnification was set as ×100. (A) HAD (Hot air drying); (B) DD (Dehumidified drying) and (C) FD (Freeze drying) mushroom samples

A study by Argyropoulos et al. (2011) assessed the effect of three different drying techniques such as hot-air drying, hot air combined with microwave-vacuum drying and freeze-drying on the quality of dehydrated white button mushrooms (Agaricus bisporus). They have also reported that hot air dried samples had denser structure than the freeze dried samples similar with the present finding. The observed impact of drying on the surface morphology of mushrooms in the present work is also corroborated by the findings of Tian et al. (2016) and Pei et al. (2014).

Physicochemical properties

Rehydration ratio

Instant rehydration is one of the most important quality characteristics of dried products. The present study showed that the rehydration ratio (RR) of HAD, DD and FD samples were 3.18 ± 0.05, 4.26 ± 0.03, and 4.84 ± 0.19 respectively (Table 1). The RR of the sample dried by FD method is significantly (p < 0.05) higher than the samples dehydrated by HAD and DD method. As reported earlier, variations in the pore size of the product’s internal structure can influence on rehydration. Conventional hot air drying caused mushrooms to shrink significantly and form a dense structure leading to a lower ability to retain water during rehydration. This type of structure probably occurs due to collapse of capillaries (Wang et al. 2014).

Bulk and tapped density

The bulk properties (bulk and tapped density) of mushroom powders dried by different dehydration techniques were presented in Table 1. Both bulk and tapped densities are important features for classification of quality of the powders. In our study we found the bulk density (ρ_bulk) and tapped density (ρ_tap) varied significantly (p < 0.05) among the samples obtained from different drying methods. Bulk density and tapped density resulted in the order: HAD > DD > FD and the difference is significant. Different drying treatments and temperature might have affected the surface morphology which leads to the increase in the surface area of the products and thus resulted in different bulk and tapped densities of the powdered products (Magalhaes et al. 2017).

Carr index (CI) and Hausner ratio (HR)

The flowability and cohesiveness properties of the mushroom powders in terms of Carr Index and Hausner ratio were given in Table 1. From the table it can be seen that mushroom powder obtained from different methods did not significantly vary in terms of flowability and cohesiveness properties. The classification of powder flowability based on Carr index (CI) are very good (< 15), good (15–20), fair (20–35), bad (35–45), and very bad (> 45) (Carr, R 1965). The powder cohesiveness based on Hausner ratio (HR) is classified as low (< 1.2), intermediate (1.2–1.4), and high (> 1.4) (Hausner 1967). The Carr index (CI) resulted in the range from 20.34 to 20.54% and the HR showed in the range from 1.25 to 1.26 for all the mushroom powders. The results indicate good flowability and intermediate cohesiveness of the mushroom powders obtained by different drying methods.

Water-holding and oil-holding capacities

Water and oil holding capacities of the mushroom powders dried by three different methods were presented in Table 1. Both water and oil holding capacities exhibited significant (p < 0.05) difference among the samples obtained from different drying techniques. WHC resulted highest in FD samples (4.82 ± 0.10 g/g) followed by DD (2.99 ± 0.08 g/g) and HAD (2.25 ± 0.01 g/g) samples respectively. Similar trend has been observed in OHC of the mushroom powders obtained from different drying techniques in the order: FD > DD > HAD (1.72 ± 0.06, 1.36 ± 0.12 and 0.98 ± 0.06 g/g) and the difference is significant (p < 0.05). WHC and OHC mainly correlated to the chemical and physical structures of the dried powders and also on the particle size. A study by Yılmaz and Bastıoğlu (2020) also depicted that the drying condition (temperature, flow of air, time) might impact the WHC and OHC of the mushroom powder and their findings are having similar trend as the present work.

Nutritional composition of chilla mix containing mushroom powder

Even though freeze drying considered being one of the best methods for drying mushrooms, the present study has shown that dehumidified drying can be an alternative technique for dehydrating mushrooms at low energy consumption with improved quality of end product.

The mushroom powder obtained from dehumidified drying method was incorporated into chilla mix at 10%, 20% and 30% levels and nutrition composition of the chilla mix formulations is given in Table 2. The moisture content in the control formulation (chilla without mushroom powder) significantly (p < 0.05) differ from the other blends of chilla with mushroom powders. Addition of mushroom powder significantly (p < 0.05) increased the protein content chilla mix in comparison to the control product. Chilla mix containing 30%mushroom powder showed highest protein content 24.17% and in control it was 21.71%. It was observed  that addition of mushroom powder did not significantly affect the fat content in the formulations. The total ash content was significantly (p < 0.05) lowest in the control chilla mix and increased proportionately with increasing percentage of mushroom powder addition. Supplementation with mushroom powder was found to increase the in total dietary fibre (TDF) content from 9.64% in control to 9.88% 10.75%, 11.65% respectively for 10%, 20% and 30 % addition of mushroom powder. The increase in TDF with mushroom powder addition was found be statistically significant at p < 0.05. Similarly, soluble dietary (SDF) and insoluble dietary fiber (IDF) also significantly increased in mushroom added chilla mix. Incorporation of the mushroom powder into chilla mix made it a good source of ergosterol, precursor of vitamin D₂. The chilla mix at 10%, 20% and 30% level of mushroom powder incorporation contained 41.10 ± 0.85, 79.08 ± 4.46 and 126.01 ± 2.89 mg of ergosterol per 100 g respectively (Supplementary data Fig. 2). The mushroom incorporated chilla mix can provide ergosterol to consumers who avoid animal foods.

Table 2.

Nutritional composition and physicochemical properties of chilla mix

Nutrients	Control*	10% MP	20%MP	30%MP
Moisture (%)	8.00 ± 0.13a	7.47 ± 0.16b	7.09 ± 0.19b	7.28 ± 0.24b
Protein (%)	21.71 ± 0.16d	22.83 ± 0.08c	23.33 ± 0.15b	24.17 ± 0.13a
Fat (%)	3.57 ± 0.08a	3.53 ± 0.04a	3.62 ± 0.06a	3.89 ± 0.07a
Carbohydrate (%)	61.27 ± 0.29a	59.52 ± 0.37b	58.70 ± 0.34c	57.12 ± 0.16d
Ash (%)	5.27 ± 0.01d	6.46 ± 0.07c	7.59 ± 0.07b	8.55 ± 0.13a
Total dietary fibre (%)	9.64 ± 0.11d	9.88 ± 0.06c	10.75 ± 0.07b	11.65 ± 0.08a
Soluble fibre (%)	1.72 ± 0.03d	1.93 ± 0.03c	2.15 ± 0.04b	2.35 ± 0.03a
Insoluble fibre (%)	7.31 ± 0.07d	7.94 ± 0.04c	8.64 ± 0.06b	9.17 ± 0.07a
Ergosterol (mg/100gm)	n.d**	41.10 ± 0.85c	79.08 ± 4.46b	126.01 ± 2.89a
Minerals composition (mg/100 g)
Calcium	70.59 ± 6.09d	80.55 ± 5.69c	99.57 ± 3.52b	106.34 ± 10.56a
Magnesium	111.17 ± 4.23c	135.21 ± 7.16b	137.80 ± 2.28b	153.38 ± 2.59a
Potassium	754.94 ± 9.91d	922.58 ± 11.47c	1203.49 ± 7.83b	1577.24 ± 48.26a
Sodium	318.01 ± 14.79c	392.95 ± 19.99b	490.83 ± 15.55a	533.48 ± 9.33a
Zinc	1.88 ± 0.02c	1.95 ± 0.04bc	2.23 ± 0.05b	2.79 ± 0.03a
Copper	0.70 ± 0.01b	0.85 ± 0.01b	1.06 ± 0.01b	2.00 ± 0.04a
Physicochemical properties
Bulk density (g/cm3)	0.347 ± 0.011c	0.502 ± 0.002b	0.509 ± 0.004b	0.539 ± 0.008a
Tapped density (g/cm3)	0.402 ± 0.001d	0.631 ± 0.005c	0.671 ± 0.001b	0.709 ± 0.021a
WHC (g/g)	1.42 ± 0.13c	2.11 ± 0.13b	2.44 ± 0.10ab	2.64 ± 0.09a
OHC (g/g)	0.72 ± 0.01d	0.77 ± 0.02c	0.84 ± 0.03b	0.89 ± 0.01a

*Control: Chilla mix without mushroom powder. 10% MP, 20% MP, 30% MP: 10%, 20% & 30% mushroom powder containing chilla mix

Data are shown as mean ± SD (n = 3). Values within a row not sharing the same lowercase are significantly different as indicated by Tukey’s HSD test (p < 0.05)

**n.d. not detectable

Mineral composition

White button mushrooms (Agaricus bisporus) are rich source of potassium, magnesium, sodium, zinc, copper etc. (Rzymski et al. 2017). Incorporation of mushroom powder significantly (p < 0.05) increased its mineral content of chilla mix (Table 2). Calcium content increased by 50.64% in 30% mushroom powder supplemented product. Similarly, addition of 30% mushroom powder enhanced magnesium content of the chilla mix by 37.97%. Magnesium content in the mushroom powder containing chilla mix ranged from 135.21 ± 7.16 to 153.38 ± 2.59 mg/100 g  among the products,hence this formulation can be considered as a rich source of potassium and sodium. Potassium content was in the order: control < 10% MP < 20% MP < 30% MP, varying from 754.93 ± 9.91 to 1577.24 ± 48.26 mg/100 g of chilla mix. Sodium content was also found to increase significantly (p < 0.05) with mushroom powder addition, resulted highest content in 30% mushroom powder added chilla mix (533.48 mg/100 g). Zinc is a crucial micro nutrient for human nutrition. White button mushroom is fairly a good zinc source. Addition of mushroom powder increased the zinc content significantly (p < 0.05) up to 48.40% in the product. In the formulation of chilla without mushroom the zinc content was 1.88 ± 0.02 mg/100 g and with mushroom powder addition it was found to increase proportionately with an increase in addition  of mushroom powder. Copper content was also significantly (p < 0.05) enhanced with incorporation of mushroom powder which was found to be 0.70 mg/100 g in control and increased to 2.00 mg/100 g in 30%mushroom powder added formulation.

Physicochemical properties

Chilla mix with addition of mushroom flour showed higher bulk and tapped density when compared with the control (Table 2). Since the mushroom powder obtained from DD method showed good Water holding capacity (WHC) and oil holding capacity (OHC), thus incorporation of this powder into chilla mix increased the WHC and OHC of the formulated product than the control sample. These functional properties of flours plays important role in the preparation of food and also influences sensory attributes of the cooked food product.

Sensory evaluation of the cooked chilla

Sensory evaluation showed that the addition of mushroom powder significantly changed the colour of the products (Fig. 3). The colour of the prepared control chilla was lighter with a score of 2.83 but incorporation of mushroom powder at 10%, 20% and 30% levels made the products appear darker in colour. Addition of 30% mushroom powder being the darkest with a score of 12.83. Porosity of chilla also increased with the addition of mushroom powder. At 30% mushroom incorporation a slight disintegration of the product was observed, whereas the surface smoothness decreased with increase in mushroom powder addition. Control chilla had a pulsey aroma as it is mainly a green gram based product. Addition of mushroom powder to the formulation decreased the pulsey aroma and this was replaced by umami flavor making the chilla more aromatic and tasty. Mushrooms are known for its distinguished umami or meat like flavor which can enhance the aroma and acceptability of the food product (Poojary et al. 2017).Overall quality of the control chilla scored 9.2 while addition of mushroom powder up to 20% increased this score to 12.17, whereas addition of mushroom at 30% level decreased the score to 7.20.

Fig. 3.

(A) and (B) illustrates the changes in moisture and water activity at ambient and accelerated storage condition; (C) illustrates the changes in ergosterol content of 20% MP* (20% mushroom containing chilla) at both ambient and accelerated conditions during three months storage study. Note: Control: chilla mix without mushroom powder; 20% MP: 20% mushroom powder containing chilla mix. 

Quality characteristics of chilla mix in storage study

In the study it was observed that incorporation of mushroom powder at 20% level was optimal in terms of sensory attributes, colour and appearance. Hence, storage studies were carried out for chilla mix with 20% mushroom powder and the control (no mushroom powder added) and the results are shown in the Fig. 2. Moisture content of the control and 20% mushroom powder added chilla mix increased by 1.09 and 1.11 fold in ambient conditions, similarly it was 1.09 and 1.13 fold increase at accelerated conditions during the entire period of storage (Fig. 2).

Fig. 2.

 Images of cooked products. (A) Control; (B) Product with 10%; (C) 20% and (D) 30% mushroom powder; (E) Sensory evaluation scores of chilla mix with and without mushroom powders using 0–15 line. Note: Control: Chilla mix without mushroom powder. MP- Mushroom powder; 10%MP, 20% MP, 30%MP: 10%, 20% and 30% mushroom powder containing chilla mix

Water activity (a_w) refers to availability of free water in the samples that can facilitate the growth of bacteria, yeast and mold. It determines the shelf-life and stability of the product. The initial water activity of the control and 20% mushroom powder containing chilla mix were 0.439 and 0.363 which indicates good stability of the formulation (Jaworska et al. 2014). At ambient condition a_w of control formulation and 20% mushroom powder added chilla mix increased by 1.26 and 1.42 fold after three months of storage. In case of accelerated condition, a_w was found to be enhanced by 1.37 fold for the control and 1.55 fold for mushroom powder added chilla formulation (Fig. 2). Over the entire period of storage water activity of the samples did not exceed the critical level (> 0.700) which can enhance the growth of the micro organisms.

Ergosterol content decreased gradually in the first month of storage in mushroom powder containing chilla mix. After three months it was decreased by 29.39% at ambient condition and 37.51% at accelerated storage condition. Similar results have also been observed by Ekinci et al. (2014) in their study. They have also reported the degradation of ergosterol in tomato paste increased with increasing storage temperatures (28 and 37 °C) and time (0 to 10 months).

Colour of the ready to cook formulation is one of the important quality parameters that affect the appearance of the food product. Initial colour values of the chilla formulations showed that control formulation is slightly lighter and yellowish than the mushroom added chilla mix (Table 3). This is because of the yellow colour of the green gram flour in control; addition of mushroom flour decreased the yellowness and lightness of the formulation. Both the storage temperature and duration significantly (p < 0.05) affected the colour values (Lightness; L*, redness; a*, yellowness; b*) of the chilla formulation with or without mushroom powder. During the storage condition both the products became darker (Lower L* values) and somewhat more yellowish (higher b* values) irrespective of storage conditions. The storage temperature significantly (p < 0.05) lowered the L* value of the products and was lowest in accelerated condition for both chilla formulations. Similarly, yellowness of products (higher b* values) was higher under accelerated storage condition than that of the ambient condition. Reduction in L* value is mainly caused by Maillard reaction that might take place in higher water activity levels. Similar effects have also been observed in previous studies (Rao et al. 2013).

Table 3.

Effect of storage on the colour of the control and 20% mushroom powder containing chilla mix

Samples	Storage temperature (°C )	Parameter	Storage durations (months)
			0	1	2	3
Control*	27 °C	L*	84.80 ± 0.01a	83.96 ± 0.30b	83.32 ± 0.47b	83.02 ± 0.23b
		b*	24.76 ± 0.01d	35.54 ± 0.34c	37.64 ± 0.41b	38.34 ± 0.07a
		ΔE	28.02 ± 0.01d	38.08 ± 0.42c	40.28 ± 0.54b	41.03 ± 0.12a
	37 °C	L*	84.80 ± 0.01a	82.34 ± 1.71b	82.25 ± 0.80b	82.23 ± 0.39b
		b*	24.76 ± 0.01d	36.99 ± 0.42c	39.71 ± 0.61b	40.15 ± 0.40a
		ΔE	28.02 ± 0.01d	40.03 ± 1.00c	42.61 ± 0.87b	43.01 ± 0.50a
20% MP	27 °C	L*	75.15 ± 0.01a	74.06 ± 0.43b	73.23 ± 0.53c	73.48 ± 0.69c
		b*	21.32 ± 0.01b	26.57 ± 0.29a	26.51 ± 0.05a	26.88 ± 0.35a
		ΔE	31.04 ± 0.01c	35.57 ± 0.29b	36.12 ± 0.37a	36.16 ± 0.15a
	37 °C	L*	75.15 ± 0.01a	74.17 ± 0.72b	73.07 ± 0.22c	69.66 ± 1.65d
		b*	21.32 ± 0.01b	26.56 ± 0.62b	26.33 ± 1.09b	27.01 ± 0.25a
		ΔE	31.04 ± 0.01d	35.51 ± 0.36c	36.61 ± 0.30b	38.55 ± 0.48a

*Control: chilla mix without mushroom powder; 20% MP: 20% mushroom powder containing chilla mix

Data are shown as mean ± SD (n = 3). Values within a row not sharing the same lowercase are significantly different as indicated by Tukey’s HSD test (p < 0.05)

The products stored at ambient and accelerated conditions during the 3 months of storage study remained microbiologically safe and coli-aerogenes bacteria, yeast and mold count, were not detectable throughout the period. However, no preservative was used during the storage study and products were shelf-stable for 3 months without significant changes in the sensory evaluation.

Conclusion

Dehumidified drying (DD) technique was found to be an efficient method for dehydrating mushrooms. The dried mushroom powder obtained from DD method showed conservation of nutrients, color and also satisfactory physicochemical characteristics which makes it suitable for incorporation into food product formulation. Addition of this mushroom powder at 20% level into ready to cook chilla mix boosted its nutritional quality. The formulation can be considered as a rich source of protein, total dietary fiber, soluble and insoluble fiber and also high in minerals like magnesium, sodium, potassium and copper. This food formulation was found to be  a fair source of ergosterol which is precursor of Vitamin D₂. Chilla mix with 20% mushroom powder scored highest in  sensory evaluation in terms of colour, umami flavour and taste. The formulatedproduct can be stored at ambient temperature up to three months without significant degradation of its quality.

Supplementary Information

Below is the link to the electronic supplementary material.

Abbreviations

HAD

Hot air drying

DD

Dehumidified drying

FD

Freeze drying

RH

Relative humidity

ABTS

2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonate)

DPPH

2,2-Diphenyl-1-picrylhydrazyl

ERG

Ergosterol

HPLC

High performance liquid chromatography

RR

Rehydration ratio

ρ_bulk

Bulk density

ρ_tap

Tapped density

CI

Carr index

HR

Hausner ratio

WHC

Water-holding capacity

OHC

Oil-holding capacity

SEM

Scanning electron microscopy

MP

Mushroom powder

a_w

Water activity

Authors’ contributions

MD: Conceptualization, Data curation, Formal analysis, Methodology, Funding acquisition,Writing of original draft; Writing—review & editing. VPM: Data curation, Formal analysis, Methodology. VG: Data curation, Formal analysis, Methodology. RC: Conceptualization, Data curation, Formal analysis, Methodology. GSK: Conceptualization, Data curation, Formal analysis, Methodology, Funding acquisition, Investigation, Supervision, Validation, Project administration, Resources, Writing—review & editing.

Funding

Moumita Das acknowledges the University Grant Commission (UGC), Government of India, for financial assistance (UGC-Ref. No.-1651/ (NET-JAN 2017).

Data availability

Not applicable.

Code availability

Not applicable.

Declarations

Conflict of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper..

Ethics approval

Not applicable.

Consent to participate

Not applicable.

Consent for publication

Not applicable.