Effect of different drying techniques on the nutrient and physiochemical properties of Musa paradisiaca (ripe Nendran banana) powder

Abstract

Musa paradisiaca (ripe Nendran) is the staple food of south India, especially Kerala. The present study analyzed the effect of different drying techniques, namely, freeze, spray and tray drying on the retention of nutrients especially micronutrients. Mineral content was determined by using Atomic absorption spectroscopy and Vitamin content was determined through High-performance liquid chromatography. This study aimed to analyze the availability of minerals and water-soluble vitamins in dried ripe banana powder. The micronutrient content of freeze-dried banana powder was observed to be with 486.92 ± 0.12 mg/100 g of potassium, 0.60 ± 0.005 mg/100 g of calcium, 3.10 ± 0.10 mg/100 g of sodium, 3.82 ± 0.02 mg/100 g of iron, 6.28 ± 0.04 mg/100 g of vitamin C and 0.606 ± 0.005 mg/100 g of vitamin B6. Along with micronutrient analysis, proximate, and various important physiochemical properties were also analyzed. The results showed that freeze-drying was the best technique to preserve nutrients present in ripe banana. Structure analysis of dried banana was done using scanning electron microscopy indicated that remarkable changes has occurred in both tray and spray dried banana when comparing to freeze dried banana. Data was analyzed by one-way ANOVA, found significantly differ at p < 0.05 with respect to drying methods.

Graphical abstract

Introduction

Fruits are essential constituents in the human diet since they are a good source of vitamins and minerals. The high content of fibers and vitamins makes banana fruit a functional food. It is one of the largest produced and most consumed fruit in India. India ranks first in the cultivation of banana (Santhosh and Appachanda, 2018). Among the many varieties of this fruit is Nendran which is considered a supreme variety for its carbohydrate and micronutrient content (Siji and Nandini, 2017).

Banana fruits are nutritious and easily digestible food. They are well known for their texture and aroma. The high mineral content allows it to serve as a mineral supplement in the diet. They have high potassium content, essential for the proper functioning of the heart and to maintain human blood pressure (Jyothirmayi and Rao, 2015). A study about the nutritional composition of ripe and unripe banana varieties in India, such as Robusta, Nendran, and Nyali poovan. They have proved that ripe Nendran variety has high nutrients and minerals content compared to other varieties. Nendran variety contains all the easily absorbable macro and micronutrients.

Minerals have a significant role in regulating functions and good health in the human body. Globally, banana is reported as the fourth most on-demand fruit after rice, wheat, and corn. The increasing demand for functional foods heralded an elevated interest in nutrients such as vitamins and minerals. Inadequate uptake of minerals causes several health problems. Thus minerals, as well as vitamins, must be preserved even after they are cooked. The preservation of essential micronutrients can only be done by using drying techniques (Mujumdar and Huang, 2007).

The quality and shelf life of ripe banana can be increased by drying. The dried banana powder can be used for the preparation of value-added products. A study conducted by Santhosh and Appachanda (2018) suggested that the formulation of value-added products will be a valuable tool to avoid the exploitation of banana. Snacks, instant mix, dietary food, etc., can be prepared from dried banana powder. New product development is considered to be an important area in the food industry. Consumer demands for new products are mainly based on two reasons: one should provide good nutrition, and the second feature should have additional health benefits. Therefore, bananas-based new product development could be considered to feed consumer demands Silva et al. (2015).

Drying is the process of removal of moisture from the product to the predetermined level. It is the traditional method for extending the shelf life of the product. Drying can cause reduction of water activity, and thereby it reduces the contamination caused by microorganisms (Deepak et al. 2020). Tray drying is the most common drying technique used for food products (Misha et al. 2013); however, this method has many disadvantages, including poor quality with less efficiency and long drying time. The prolonged exposure to heat causes deterioration of quality attributes such as color, flavor, texture, and nutrient content. Spray drying is the most acceptable method for dehydrating fruits (Mariia and Ireneusz, 2020). It is extensively used in various food industries as it has less heat exposure and produces high-quality products at a lower cost. Freeze drying has been considered the most advanced method of drying. Heat-sensitive products can be dried using this method without changing their nutritional quality, taste, aroma, flavor, and color as recommended by Freeman and Whenham (2006). Banana consists of minerals like calcium, sodium, potassium, iron, and vitamins like B6 and vitamin C (Siji and Nandini, 2017). Hot air oven dried fresh ripe and unripe banana powder was studied for proximate composition and minerals to reveal biochemical changes during different post- harvest periods by Santhosh and Appachanda (2018). Studies suggest that micronutrient content varies according to different drying techniques. Increased temperature and duration of exposure result in the degradation of micronutrients. Spray and tray drying takes place in the presence of hot air, unlike freeze-drying. Hot air is highly efficient in removing moisture from the product however, it degrades the nutritional quality (Darmady and Barrington, 1954). Dried banana powder has many advantages when compared with raw bananas. The dried powder can be stored for a more extended period and can be used for instant cooking (Brouns et al. 2002).

The main objectives of this study were to (i) study the effect of different drying techniques on the retention of nutrients without affecting the sensory attributes and structure of the fruit. (ii) conduct physicochemical and morphological study of dried banana powder and (iii) evaluate Sensory characteristics study of banana powder using a five-point hedonic scale.

Materials and methods

Sample preparation

Completely ripe bananas of Nendran variety (22 brix and 56.6% of moisture content) were collected from the local market in Potheri, Chennai, Tamil Nadu, India. In spray and freeze-drying, same variety of banana were washed and steam-cooked in 20 ml of water for 10 min over a medium flame. The seeds were removed from banana by stainless-steel knife, otherwise it block the spray dryer nozzle and also prevent uniform particle size in paste before drying. Weight of the banana was 113 g which was reduced to 111 g when the seeds are removed. It was then ground as paste by food processor (750 Watts Preethi mixer, Chennai, Tamil Nadu, India) for 1 min at 10,000 rpm with 5 ml water/100 g fruit was added to obtain the paste consistency. The paste was spread onto steel plates at 3 mm thickness. In-tray drying, bananas (two) were washed, steam cooked, and sliced manually to 5–7 mm thickness with the help of a stainless-steel knife and transferred onto steel plates.

Drying methods

Drying banana paste was prepared based on the following procedure; for spray drying, the banana paste was mixed with 22.5% maltodextrin is recommended as one of the drying aid for high carbohydrate food matrix to obtain free flow spray dried powder (Mariia and Ireneusz, 2020).

Tray drying

Tray drying is the conventional method of drying. It consists of different trays stacked one over the other. Samples were prepared as per the procedure and kept in perforated trays in the tray drier. Drying was carried out at a temperature of 50–53 °C. Moisture is removed by forced conventional heating. The heat is transferred through the tray by hot air circulation by blower fans on the backside of the trays. Drying was done until it attained a constant weight. The observation of weight loss in the banana slice was recorded at an interval of 1 h till there is no changes in the weight. The dried banana slices after 14 h drying were powdered by using the same food processor by running for 2 min.

Freeze-drying

The samples were prepared as per the procedure. Freeze drying is the best drying technique in terms of nutrient retention (Ratti, 2001). The banana pastes from normal size banana of 180 ± 10 g weight was frozen in a layer of 3 mm thickness in a freezer at a temperature of − 45° ± 5 °C and was then dried under a vacuum (10 Pa absolute pressure) automatically in the freeze drier (Lyodel, 153-06-10, India). Frozen water was removed by sublimation. The water moves to the condenser located just below the freezing chamber and removed. The process continues until the puree is dried thoroughly. Dried flake was scraped from the plates and ground by mixers.

Spray drying

Sugar-rich products such as banana are characterized by stickiness. Thus, while spray drying; there may be chances for the sample to get stuck to the walls of the drying chamber. In order to prevent this, a drying aid was introduced by Chegini et al. (2008). In this experiment, maltodextrin was used as the drying aid as it forms an external layer over the droplets and prevents stickiness. The prepared banana paste from normal size banana of 180 ± 10 g weight was placed in a vessel where maltodextrin (22.5 g/100 g) and water (45.2 g/100 g) were added based on Urban et al. (2015). The samples were spray-dried at 130 °C with a feed flow rate of 0.75 L h⁻¹ with an outlet temperature of 90 °C. Spray drying was carried out in a batch process with a pressure nozzle atomizer. In the spray dryer, the liquid feed was converted to solid powder using atomization. Air was cleaned using a filter and introduced into the drying chamber through a nozzle. Dried powder (14.37 g) was collected in the outlet chamber.

Micronutrient analysis

Determination of minerals

Banana is rich in minerals like potassium, calcium, sodium, and iron. Mineral content was estimated by using Flame Emission Atomic Absorption Spectrophotometer (AAS) (Model no. Jencons, PEP7) at 598 nm of wavelength. First, 10 g of each dried sample was taken in a porcelain dish. It was then kept in a muffle furnace at 500 °C for 5 h. The samples were transferred into a 250 ml beaker with 50 ml of distilled water, and 15 ml of concentrated nitric acid. The beaker was then kept over the hot plate with continued heating. The samples were filtered and made up to 250 ml by adding distilled water. The standard stock solution of 100 ppm was prepared. Once the atomic absorption instrument was set up, and the samples, blanks, and standards were read at 589 nm in AAS. Then the mineral content was statistically analyzed by developing a calibration curve. The mineral content of raw banana (completely ripe) was also determined in a similar pattern as a control.

Determination of vitamins

Banana is rich in vitamin C and Vitamin B6. Vitamin content was analyzed through High-performance liquid chromatography (HPLC) (Shimtazu, Japan). The Standard of vitamin C was prepared accurately by weighing 10–20 g of vitamin powder in 1 ml of deionized water, and for Vitamin B6, the standard was prepared by adding 10–20 g of vitamin powder to 0.5 ml of Potassium hydrogen carbonate. Samples were prepared by accurately weighing 0.100 g of dried powder and adding 80 ml of water. It was then centrifuged at 4000 rpm for 25 min. The supernatant was taken for vitamin analysis along with the standard. The sample solution was filtered through a 0.25 µm filter. Columns of Acclaim PA, 3 µm, 3.0 × 150 mm with Column Temp: 25 °C. Mobile Phases were 25 mm phosphate buffer (pH 3.6), acetonitrile (7:3, v/v) with a flow rate of 0.5 mL/min. Vitamin content was quantified with the help of retention time and peak area. The vitamin content of raw banana was also determined in a similar pattern as a control.

Proximate analysis

Proximate analysis was carried out for the prepared sample and raw banana. Moisture content was measured by drying the samples at 104 °C in a hot air oven till the weight became constant (AOAC, 1995). Since the sample was already dried the time taken for the moisture content determination was less. The total carbohydrate content was analyzed by AOAC (1995) method using Anthrone reagent. The total carbohydrate content was estimated by hydrolyzing the polysaccharide into simple sugar through acid hydrolysis and the resultant monosaccharide determined by using a spectrophotometer at a wavelength of 670 nm. Protein content was estimated by the Kjeldahl method (AOAC, 2005). This method determines nitrogen content present in the sample, which is then converted as protein content by multiplying the nitrogen content with a conversion factor of 6.25. The fat content of the samples was estimated using the Soxhlet extraction method as AOAC (1995). 3 g of sample was packed in Whatman filter paper and kept inside the mantle for the extraction. Extraction was done for 6 h using hexane as the solvent. The crude fiber of the samples was estimated for 5 g of powder and 10 g of banana by acid–alkali hydrolysis method with reference to AOAC (1995). Ash content was determined using a muffle furnace at 500 °C for 3 h (AOAC, 2000). For ash content determination, 5 g of powder and banana samples were taken for analysis.

Physiochemical analysis

Physiochemical analysis was done for the dried porridge powders and raw powder. Water activity was measured using a water activity meter (Novasina -lab swift aw, India). One gram of sample was diluted with 5 ml of water and titrated against 0.1 normality sodium hydroxide with phenolphthalein indicator. The pH was estimated using a pH meter (Systronics Digital pH meter 335, India). Both pH and acidity were tested as per AOAC method (2000). Bulk density is expressed as the ratio of the mass of the sample to that of the volume occupied by the sample (Vanrnamkhasti et al. 2008). Each analysis was done in triplicate and values are expressed on a dry weight basis. Colour analysis was done using a hunter color lab XE color Quest. The color attributes were measures and expressed positive color values using L*, a* and b* as Lightness, Redness and Yellowness for the dried samples. Sensory analysis was done to find the consumer preference on dried banana powder, using a five-point hedonic scale. Samples were given to 5 trained panelists to assess the sensory attributes such as colour, taste, smell, texture, and appearance.

Hydration property

Water holding capacity was determined for 1 g of powder with 10 ml of distilled water. It was centrifuged at 5000 rpm for 25 min. The supernatant is discarded, and the residues were then weighed. The difference in weight of dried powder before and after centrifugation was measured as water holding capacity of dried banana powders with reference to Sawant et al. (2013).

Pasting property

The viscosity of slurry containing 3 g of dried powder with 2 ml of distilled water at 30 °C was determined using Brook’s field viscometer using spindle no: 18 rotating at 100 rpm and expressed in centipoise (cP) Khuthadzo et al. (2019).

Sensory analysis

Sensory analysis of the dried samples was done using a five-point hedonic scale. Samples were given to 5 trained panel members as per methodology (Ranganna, 1994). They provided the scores between 1 and 5. The selected sensory attributes such as colour, taste, smell, texture, and mouthfeel for the banana powers were studied.

Morphological study

Surface morphology analysis was conducted using FEI Quanta FEG 200- High-Resolution Emission Scanning Electron Microscope (FESEM) at a magnification of 5000 × and voltage of 10 kV. The samples were applied on an aluminum stub using double-sided tape. SEM analysis was used to evaluate the structure as well as the morphology of the samples. SEM analyses were considered to observe the sample’s interfacial properties, internal crack, and internal structure.

Statistical analysis

Data were analyzed statistically by one-way ANOVA using Minitab. All the analyses were done in triplicate, and data were as expressed as mean ± SD, and significance was accepted at p < 0.05 as per Duncan’s multiple tests.

Result and disscusion

Drying methods

The freeze-drying method produced the highest yield as 40.04% whereas the tray and spay dryer provided 31.31% and 13.54% yields on dry weight basis. The differences in the yield of the freeze-dried, tray dried and spray dried banana power observed. This is because of the temperature and duration of exposure to elevated temperature (Urban et al. 2015).

Micronutrient analysis

The micronutrient content of dried samples and the raw sample is given in Table 1. Ripe banana contains 546.48 ± 0.427 mg potassium/100 g. The results were close to the findings of (Jyothirmayi and Rao, 2015). The FDBP had a significantly higher level of potassium (486.92 ± 0.127) than the tray and SDBP. Banana dried under spray drying has least amount of potassium since spray drying was carried out at a high temperature, and the impact of high temperature reduced potassium content. However, freeze-drying time was more when compared to spray and tray-drying. Thus, the prolonged duration of exposure led to the loss of heat liable nutrients Randhir et al. (2008). The calcium content of banana powder did not differ, with respect to drying methods. Results showed significant changes in the sodium content of dried banana samples compared to raw banana. The losses were less pronounced in freeze dried sample. The low-temperature process of freeze-drying reduced the sodium content.

Table 1.

Micronutrient content of the ripened banana and dried banana powder

Micronutrients	Ripe banana (mg/100 g)	FDBP (mg/100 g)	TDBP (mg/100 g)	SDBP (mg/100 g)
Potassium	546.48 ± 0.42a	486.92 ± 0.12b	478.89 ± 1.01a	397.52 ± 2.16c
Calcium	0.613 ± 0.01a	0.60 ± 0.05b	0.59 ± 0.04c	0.54 ± 0.05a
Sodium	5.41 ± 0.01a	3.10 ± 0.10a	2.27 ± 0.05b	2.15 ± 0.13c
Iron	3.91 ± 0.03a	3.82 ± 0.02a	3.61 ± 0.01b	3.14 ± 0.18c
Vitamin C	9.08 ± 0.07a	6.28 ± 0.04a	2.18 ± 0.06b	1.66 ± 0.03c
Vitamin B6	0.65 ± 0.01a	0.606 ± 0.05a	0.57 ± 0.07b	0.52 ± 0.04c

Each data point represents the mean ± standard deviation of triplicate analysis. The multiple comparisons were determined by Duncan at p < 0.05 rows with the different letter are significantly different (p < 0.05)

A similar study conducted by Hu et al. (2006) discussed that freeze-drying and vacuum drying are the two best methods to retain the quality of food products. The FDBP has a higher iron level, almost close to the iron content of raw banana. Spray drying was the only drying technique that showed a significant difference (p < 0.05) in calcium content. When comparing to the ripe banana mineral content, freeze drying exhibited a statistically significant increase in sodium and iron content, while tray drying showed a statistically significant increase in potassium content.

Banana contains vitamins like vitamin B6, and vitamin C. Li et al. (2017) also reported that the loss of vitamin C, antioxidant content and changes in phenolic substances for selected subtropical fruit products at specific temperature and exposure to light and high temperature. Spray drying lead to loss of micronutrients due to exposure to high temperature. Retention of minerals and vitamins are the deciding factors for the quality of the dried product (Seongeung et al. 2018). High temperature and long exposure time affects the minerals and vitamins retentions. There is no such loss in the vitamin content of freeze-drying banana sample compared to spray-dried banana sample. Antioxidant vitamins such as vitamin A, C and E, and non-nutritional antioxidants polyphenols are present in carrot. It was reported that freeze dried carrot juice powder has more retention of antioxidants when compared to spray dried powder (Rishabh et al. 2021). The statistical analysis revealed that tray drying and spray drying have significant impact on micronutrients. Whereas, freeze drying does not have significant effect on micronutrients at p < 0.05 level.

Proximate analysis

Changes in the proximate components are given in Table 2. Carbohydrate content was high in the SDBP (62.23 ± 0.208) because of addition of maltodextrin. But drying techniques have no significant effect on protein content of banana powders. Similar results were also observed in a study conducted by Kaldy et al. (1979) in protein and amino acid content of legumes. The fat content of banana decreased by drying process. The low-fat content food are less prone to spoilage hence have longer shelf life (Santhosh and Appachanda, 2018). The results showed that spray dried banana powder have lowest fat content among three powders. Also, similar tends of results were stated by Urban et al. (2015) for selected dried fruits.

Table 2.

Proximate analysis of ripened banana and dried banana powder

Components	Ripened banana (g/100 g)	FDBP (g/100 g)	TDBP (g/100 g)	SDBP (g/100 g)
Carbohydrates	60.66 ± 1.15a	58.6 ± 0.57b	54.66 ± 0.57a	62.23 ± 0.20a
Protein	1.21 ± 0.01a	1.07 ± 0.05a	1.06 ± 0.57b	0.91 ± 0.04c
Fat	0.13 ± 0.02a	0.09 ± 0.05a	0.09 ± 0.01b	0.05 ± 0.01c
Fiber	4.60 ± 0.01a	1.80 ± 0.01a	1.60 ± 0.01b	1.49 ± 0.05c
Ash content	3.54 ± 0.05a	3.48 ± 0.02b	3.39 ± 0.02a	3.18 ± 0.06a
Moisture content	56.6 ± 0.57a	22.7 ± 0.62a	28.2 ± 0.46b	27.7 ± 0.46c

Each data point represents the mean ± standard deviation of triplicate analysis. The multiple comparisons were determined by Duncan at p < 0.05 rows with the different letter are significantly different (p < 0.05)

The drying method does not have impact on ash content of dried banana powder. The fiber content of the banana is very high (4.6 ± 0.01). There is no significant difference in the ash content of dried banana samples, as it is related to inorganic—minerals in the banana powers. However, a considerable quantity of changes in the fiber content of dried banana powders was observed. FDBP retained a higher amount of fiber (1.80 ± 0.01) due to low processing temperature. Minimum retention of dietary fiber was observed for spray drying. Moisture content is high for a FDBP and less for a SDBP. There is a reduction in the drying time and product quality of spray dried banana sample. Moisture content and water activity are the essential factors to estimate the shelf life of dried products. According to Ratti (2001), increase in the moisture content can lead to the microbial growth in the dried products, hence reduces the shelf life of the product. Abbasi and Azari (2009) stated that freeze drying is a simple, effective and innovative method to dry the fruits and vegetables with superior quality. Carbohydrate, protein, fat, ash, fiber and moisture content of dried banana powders were significant at p < 0.05 as per ANOVA. Freeze-drying exhibited the most significant increase when compared to other drying techniques. However, freeze-drying was not statistically significant for ash content and carbohydrate content.

Physiochemical analysis

The physicochemical analysis results are displayed in Table 3. The FDBP showed the highest bulk density. Higher the bulk density, the lower is the moisture content. Thus, high bulk density allows better storage life of the powder. The results agreed with previous findings of (Balasubramanian and Viswananthan, 2010) for low moisture products. They had shown that bulk density was high for the samples with low moisture content. Banana is acidic with a pH of 5.56 ± 0.05. The FDBP was highly acidic when compared to the tray dried and spray dried banana powder. Rapid drying causes the removal of water molecules by trapping acid molecules (Deepak et al. 2020), leads to loss of acids. The low moisture content of the FDBP had trapped more acid molecules thus, the pH value was also observed to be low for the freeze dried powder (4.52 ± 0.05).

Table 3.

Physiochemical analysis of ripened banana and dried banana powder

Components	Ripened banana	FDBP	TDBP	SDBP
Bulk density(g/cm3)	1.08 ± 0.01a	0.58 ± 0.06b	0.57 ± 0.06c	0.49 ± 0.01a
Acidity (%)	0.483 ± 0.01a	0.69 ± 0.01b	0.26 ± 0.05c	0.32 ± 0.01a
pH	5.56 ± 0.05a	4.52 ± 0.05a	4.92 ± 0.05a	4.91 ± 0.01a
Water activity	–	0.26 ± 0.02	0.38 ± 0.01	0.391 ± 0.05
Hydration property	–	–	1.876 ± 0.05	1.92 ± 0.05
Pasting property	2.214 ± 0.05a	146 ± 0.01a	1.45 ± 0.01b	1.41 ± 0.06c

Each data point represents the mean ± standard deviation of triplicate analysis. The multiple comparisons were determined by Duncan at p ≤ 0.05 rows with the different letter are significantly different (p ≤ 0.05)

Water activity was low for a FDBP and high for a SDBP. Water activity determines the amount of free moisture present in the product (Ratti, 2001). Hydration property (Water holding capacity) is the measure to determine the ability of the powder to absorb water and attain the desired consistency. There were no significant difference in the water holding capacity of dried banana powder with respect to drying method (Sawant et al. 2013). Higher the water holding capacity, more accessible is the powder’s capacity to swell and helps attain the desired consistency (Deepak et al. 2020). Adebowale et al. (2012) mentioned that higher water holding capacity results in a looser structure of starch polymers; the lower value of indicates the compactness of the starch structure. The pasting property (Viscosity) is high for a raw banana when compared to dried samples. The pasting properties of dried banana powders lesser than ripe banana, hence widely used in weaning food and similar product development (Usman et al. 2016). According to him the viscosity measures the resistance of flow and is an essential factor for process optimization and quality of the food. All the physiochemical analysis data were analyzed statistically using one-way ANOVA, was found to be significant at p < 0.05. The bulk density and acidity of spray dried banana powder and viscosity of freeze-dried powder was also differed significantly from ripe banana and other dried powders at p < 0.05 level.

Dried samples were subjected to sensory analysis. Figure 1 showed the average scores of sensory analyses as per five- point hedonic scale rating. The overall score for freeze, tray and spray dried sample was 5, 4, and 3 respectively. Freeze and tray dried samples have higher scores in color and taste compared to spray-dried banana samples. The reason was mainly due to the presence of maltodextrin. The most accepted color was for the FDBP. In appearance and smell, tray dried and spray dried sample has an unpleasant flavor and unaccepted appearance due to the high temperature. In the SDBP, the smell of maltodextrin was predominant (Deepak et al. 2020). The FDBP has retained the natural sweetness of banana than spray and tray dried samples. The FDBP has the softest texture. Although the SDBP had a fine texture, the other parameters were not suitable. However, the sensory attributes were higher in freeze dried banana (Deepak et al. 2020). Colour values of dried powder along with the raw powder are represented graphically in Fig. 2. There is no visible difference in the color value of dried samples. Freeze dried powder has a color value closer to that of raw banana powder. The drying methods have impact on the color values of dried banana powders, differed significantly at p < 0.05 level.

Fig. 1.

Sensory attributes of dried banana powder

Fig. 2.

Graphical representation of colour attributes of banana powders

Morphological study

The microstructure of ripe banana and dried banana were illustrated in Fig. 3. Raw banana has a spherical structure. For the FDBP, the size of the cavities increased, and the structure became rough and well organized. Since, freeze drying occurred due to the sublimation of frozen ice crystals formed in the ripe banana paste (Ratti, 2001). Tray dried banana powder (TDBP) showed significant changes in the structure. The volume of the cell was reduced, and the tissues became more collapsed. The SDBP showed a fragmented structure. High heat treatment converts the granular structure to amorphous mass. Hence, the structure became irregular, causing the breakage of cells. Moisture content was the only factor affecting the structure of the product (Lozano et al. 1983).

Fig. 3.

Scanning Electron Microscopy images for A Ripened banana, B FDBP, C TDBP, and D SDBP

Conclusion

This study was conducted to determine the best drying technique to retain nutrients in ripe (Nendran). From the report it was observed that drying methods have different effect on the chemical, physical and nutritional characteristics of the food material. Among three drying methods such as tray, spray and freeze- drying, the last one was best drying method for ripe banana. In case of spray and tray drying, the high temperature and prolonged duration of exposure reduced micronutrients and the proximate composition. The results described that sensory quality attributes of dried powder were better in FDBP than other methods. Correspondingly, highest retention of nutrient content was attained in freeze dried powder. Recently, freeze drying has become a well-recognized preservation techniques to heat sensitive—high nutrient products with minimal quality loss. Also physiological, physical, textual and sensorial changes were lesser than spray and tray drying powders. The statistical analysis indicated that freeze dried banana powder did not differed from ripe banana with respect to major proximate compositions, micronutrients and physiological compositions. Hence, freeze drying was recommended to be one of the suitable method for ripe banana powder from the work.

Abbreviations

AAS

Atomic absorption spectroscopy

ANOVA

Analysis of variance

FDBP

Freeze-dried banana powder

SDBP

Spray dried banana powder

SEM

Scanning electron microscope

TDBP

Tray dried banana powder

Author contributions

SK carried out the experiments, and wrote the manuscript, NG designed, executed and supervised the work, KA, RP, MME and MWQ edited the manuscript.

Funding

No external funding is applicable for the work. Only SRM Institute of Science and Technology Selective excellence funding was utilized for the project as mentioned in the acknowledgement.

Data availability

The research data are not shared.

Code availability

Not applicable.

Declarations

Conflicts of interest

The authors declare no conflict of interest.

Consent to participate

Not applicable.

Consent for publication

This is an original work being done and it is not being submitted to any other journals for publication. The data provided including figures and table can be used for publishing in JFST and they are not being provided to any other journals.

Ethical approval

Ethical approval is not required for this research.