Drying of Banana-Stepwise Effect in Drying Air Temperature on Drying Kinetics

1. INTRODUCTION

Agricultural products like vegetables and fruits play a vital role in nutrition supply and as human diet. Approximate loss of agricultural products in the developing country, like India after cultivation (Post- growing) is about 20-50%, which is actually the highest number counted as far as the economy is concerned. Banana is a highly popular fruit, which provides carbohydrates and other minerals in good quantity and is considered a prime fruit in India [1-3]. Due to limited shelf life of the banana, different methods of maintaining the quality like cooling methods [4-11] and freezing technology [12-19] were implemented. Being very sensitive to temperature, banana was exposed to drying processes to increase the life span [20-28]. Banana can also be dried by simply air drying and dehydration or freezing [29-31]. These methods of banana processing are found to have degrading effects like decolourization, unbalanced sugar content, texture difference, etc. Better quality banana products can only be produced with natural mild drying [32,33]. Drying mechanism was applied in different modes to achieve better and good quality of banana product. Drying mechanism is better applied with banana slices kept in the heat pump drying loop. Effect of temperature and thickness of banana slices are the predominant characteristics that play a role in the drying operation. Moisture diffusivity increases with a gradual increase in temperature, which is expected [33,34]. Energy and exergy analysis using first and second law of thermodynamics plays a vital role in determining the drying characteristic of banana under solar drying techniques [35]. Drying of banana not only includes the simple removal of moisture but also includes various other factors like shrinkage, texture, appearance and so on. Different parameters like pH, bulk density, yield, water holding capacity and oil holding capacity are specific in value to identify the optimum bananas crop. While observing the nutritional effect, it was found that moisture and other carbohydrates were reduced while drying and other ash moisture and protein-fats were increased. A significant effect in terms of reduction was also reported on specific anti-nutritional compositions, which is a breakthrough for the long usage of banana [36]. Application based study was also carried out on preparation of smoothies using dehydrated banana. Different compositions of dehydrated banana were taken into consideration for the preparation of smoothies focusing on parameters like color, texture, appearance, density, viscosity, flavor, sweetness determined experimentally or analytically [37]. A study on drying kinetics of two varieties of banana of Bangladesh was also compared at three different temperatures of 45 º C, 55 º C and 65 º C with different slices thickness. In the present work, experiment was done on three different varieties of banana (Dwarf Cavendish, Lacatan and Harichal) collected from three different locations of south Gujarat region namely Ankleshwar, Valia and Bahruch. Effect of drying phenomena on colour, appearance and texture was the motive of the work for the commercialization of banana chips with better quality. Better performance in terms of colour, shrinkage, texture, appearance was selected for the banana chips production commercially.

2. MATERIALS AND METHODS

Three different varieties of banana (Dwarf Cavendish, Lacatan and Harichal) were collected from different locations like Ankleshwar, Valia and Bharuch, Near South Gujarat region, India respectively. All these varieties were selected based on their source of growth. These three varieties had a moisture content of nearly 75-78% on wet basis. The initial moisture content was calculated by removing the moisture by drying in a heating oven for 24 hours at nearly 110 º C. To keep the result very accurate and precise, all the varieties of banana were taken from the same source and kept in the refrigerator under 5-7 º C till it is used. Diameter and Length measurements were performed using calipers and other measurement instruments considering 4-5% tolerance in each sample. With a margin of 22 ≤ D ≤ 26 mm and 130 ≤ L ≤ 150 mm, samples were given the shape of a cylinder. Some of the samples were soaked into the boiling water for 0.5-3 min to check the blanching effect. The soaked samples were also cleaned by an ashless paper to remove surface moisture. Continuous weight loss with respect to time and temperature and sample dimension change (Diameter, Length and Volume) were recorded simultaneously after each sample of banana with and without blanching operations, using natural draft tray dryer. The moisture loss was calculated on the weighting balance attached to the top of the dryer. The accuracy of the balance was kept ± 0.001 g. The experiments were performed at 60, 70 and 80 º C with time difference of 60, 120 and 180 min with and without blanching operations. Drying is conducted with moisture loss up to 15% (wet basis).

3. RESULT AND DISCUSSION

3.3. Shrinkage

While selecting the banana for the chips preparation in the market, shrinkage of banana is the key factor for consideration. In order to justify the shrinkage results physically, it is quite difficult to connect the relation of shrinkage. Experimentally, varieties of banana were observed after each run of drying and specifically, changes in volume, diameter and length were calculated on different basis. These dimensional parameters were related to moisture content of banana after the drying phenomenon. The proposed equations [37] were considered for further finding of every variety of samples of banana.

(1)

(2)

(3)

A, B, A′, B′ A", B" are the parameters calculated based on a slow and continuous regression method leading to R² values at different temperature, time and varieties as shown in Table 1. It was investigated through the data obtained by considering the calculation of all parameters and number of equations obtained, which then plotted leads to rigorous results. There is a slight difference in data observed for different temperature range for all three varieties of banana.

(V/Vo), (D/Do)² and (L/Lo) calculated values were obtained using a set of equations (1) to (3), while parameters were connected using a set of equation parameters (4) to (9) given below.

(4)

(5)

(6)

(7)

(8)

(9)

The average % AE for the (V/Vo), (D/Do)² and (L/Lo) for Dwarf Cavendish banana variety is 4.35, 4.78 and 1.65%, respectively, while maximum error observed is 8.40, 8.77 and 2.81%, respectively as shown in Table 2. There is not much difference in the % error of the variables calculated.

CONCLUSION

Dwarf Cavendish shows higher drying rate while comparing the rate of drying amongst all three varieties. Lacatan and Harichal were found to be less effective in drying mechanism. Appearance, colour and texture were improved for two varieties (Dwarf Cavendish and Harichal) at 70 º C and 80 º C of drying, while for Lacatan, not much changes were observed. This action could be due to the effect of drying time, different structure and initial moisture content. Initial moisture content in all the three banana varieties decreased to some specific time of blanching. Comparative study of experimental and calculated values of Volume, length and diameter (Table 2) reveals that as the temperature increases, initial moisture content decreases and shrinkage decreases consequently. Hence, drying time for the material can be automatically reduced. Looking to the characteristics of three different banana varieties, Dwarf Cavendish (from Ankleshwar region, South Gujarat, India) is highly recommended for the commercial production of banana chips as it has proved to be highly attractive in appearance, colour and texture even after long drying. Blanching also added acceptance features to this variety.

NOMENCLATURE

A, B, A′, B′ A", B" Constants in equation (1) – (3)

D & D_o Final and initial diameter of cylindrical banana sample, mm

L & L_o Final and initial length of cylindrical banana sample, mm

V & V_o Final and initial volume of cylindrical banana sample, mm³

T drying solid temperature, K

X moisture content of drying solid, kg moisture kg dry solid^-1

X_o initial moisture content of drying solid, kg kg^-1,dry basis

REFERENCES