Effect of Slice to Solution Ratio on Mass Transfer and Sensory Quality

Abstract

Carrot is an important vegetable in human diet used for its delicious taste in salads as well as for the preparation of processed products. Osmotic dehydration is very useful technique used for the preparation of dried products. Hence the present experiment was carried out to optimize the slice to solution ratio for preparing osmo-dehydrated carrot slices. Slice to sugar solution ratio was varied from 1:2 to 1:6 and its effect on mass transfer kinetics and sensory parameters were assessed.

Carrot slices were dipped in 50o Brix sugar solution having 50 degree Celsius temperature for 4 hour.

It was observed that weight reduction, weight loss and solid gain percentage were increased with increase in slice to sugar solution ratio. While Moisture content of osmosed carrot slices was decreased with increase in slice to sugar solution ratio. However, sensory score was highest for 1:4 slice to solution ratio in respect of overall acceptability.

Introduction

Carrot is well known root crop for its nutritive value. Due to high moisture content, it’s shelf life is extended through different processing techniques.

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Drying and dehydration are very important methods for the preparation of low moisture processed products. In mechanical drying of fruits and vegetables, time required is quite more to achieve final required moisture content of dried product which adversely affects the final quality of processed product. Hence in recent years, some pre-treatments including osmotic dehydration, blanching, and microwave have been used for improving the quality of fruit products and reducing energy consumption (Levent and Ferit, 2011).

The pre-drying by osmosis, followed by a hot air drying has been widely used in producing dried and partially dried fruits (Netoetal.

, 2005). For osmotic dehydration, the influences of concentration and composition of osmotic solution, temperature, immersion time, pretreatments, agitation and solution to sample ratio on the process are important factors which affect the quality of final products (Singh and Gupta, 2007). Hence the present research investigation was carried out to assess the effect of slice to sugar solution ratio on mass transfer and sensory parameters of osmo-dehydrated carrot slices.

Materials and Methods

Preparation of sample:

Fresh, matured and uniform sized carrots were selected for experiment. The carrots were peeled and trimmed to remove undesirable portion. Blanched and pre-frozen carrot slices of

3 mm thickness were dipped in sugar solution of 50°Brix concentration having 50o C temperature for four hour duration of osmotic dehydration. Slice to solution ratio viz: 1:2, 1:3, 1:4, 1:5 and

1: 6 were used for the study. After four hours, the carrot slices were removed from sugar syrup as per different treatments and excess syrup was removed by using tissue paper. Osmotically dehydrated slices were then dried at 60 oC in tray dryer up to 6% moisture content.

Mass transfer of osmotically dehydrated carrot slices:

Osmotic dehydration kinetics for each sample were carried out. Water loss (WL), weight reduction (WR), and solid gain (SG) data were obtained according to the following expressions and presented in Figure 1. (Nazni and KarunaThara, 2011; Singh, etal., 2007).

WL (% ) = Water loss/100 g fresh fruit

= [(W0 –Wt) + (St –S0)] x 100 / W0

WR (%) = Weight Reduction / 100 g fresh fruit

= [Initial mass- Mass at time (T) ] / Initial mass

SG (%) = Solute gain/100 g fresh fruit

= (St –S0) x 100 / Wo

Where,

W0 -- Initial wt of fruit (g),

Wt -- Weight of fruit after osmotic dehydration for any time t (g),

S0 -- Initial weight of solids (dry matter) in the fruit (g), and

St -- Weight of solids (dry matter) of fruit after osmotic dehydration for time t (g).

Moisture content of osmosed carrot slices:

Moisture content of carrot slices after osmosis was determined by A.O.A.C. (1990).

Moisture content (%w.b) = (W1-W2) x 100 /W1

Where, W1= Weight of sample after osmosis (g),

W2= Weight of bone dried sample (g)

Evaluation of sensory quality:

Sensory quality of osmo- dehydrated carrot slices was carried out with the help of a 10-member semi-trained panel using a 9- point hedonic scale by standard method (ISI) (1971a-1971b). The various quality aspects considered were colour, appearance, texture, taste, favour, and overall acceptability. Overall acceptability was calculated by considering the average value of sensory score obtained for all other parameter. The average scores of all the 10 panellists were computed for assessment of different quality parameters and presented in Figure 2.

Results and Discussion

Mass transfer kinetics of carrot cubes during osmotic dehydration:

Data regarding weight reduction, water loss, solid gain and moisture content of carrot slices after osmosis of osmotically dehydrated carrot slices of 3.0 mm thickness differed significantly as influenced by slice to sugar solution ratio and are presented in Figure 1. The water loss, solid gain, weight reduction and moisture content of osmosed slices were influenced positively by slice to sugar solution ratio during osmotic dehydration. Maximum values for all this parameter were found for 1: 6 slice to solution ratio whereas minimum values were recorded for 1:2 ratio. In general, it was observed that weight reduction, sugar gain and water loss were increased with increase in slice to solution ratio. The increase of slice to solution ratio results in increasing the rate of osmosis up to a certain level. Thereafter, minimum difference was observed after increasing ratio from 1: 4 to 1: 6.

The Fruit to Syrup ratio above optimum (1:4) did not have much effect on mass transfer (Baratetal., 2001). Similar increasing effect in both the solid gain and water loss in osmotic dehydration was observed with increase in osmotic solution to sample mass ratio (Flink and Tortoe, 2010). This increasing trend may be substantiated by the fact that the higher SS ratio accelerated the driving force of the osmotic solution, enhanced the diffusion of solids from the osmotic solution to plant materials which improved the discharge of water from the plant materials to the surrounding medium (Tiroutchelvame D. etal., 2019). It is reported that the increase in fruit to sugar syrup ratio (from 1:1 to 1:4.5) resulted in increased weight loss during osmotic dehydration of banana (Bongirwar and Srinivasan, 1977).

Moisture content of osmosed carrot slices:

The initial moisture content of the carrot slices used for the study was 83% wet basis. Moisture content of carrot slices after osmosis differed significantly and presented in figure 1. It was observed from the data that the moisture content of the slices after osmosis decreased with increasing slice to solution ratio and ranged from 54.35 to 50.23 % (wet basis). However this decreasing rate was very less after increasing the slice to solution ratio from 1:4 to 1: 6. This reduction in moisture content may be due to increase of solution to sample ratio which results in increasing the rate of osmosis up to a certain level.( Milena Ruskova1, etal., 2015)

Sensory quality

Osmotically dehydrated carrot slices prepared by using different slice to solution ratio were assessed for different quality parameters viz; colour, appearance, flavour, texture, taste. Data pertaining to sensory parameters was found statistically significant and presented in Figure 2. From the scores, it is cleared that all sample were found acceptable in respect of sensory score obtained for individual characteristic. However, lowest score of overall acceptability was observed for the samples prepared by using 1:2 slice to solution ratio followed by 1:6 ratio. Sample prepared using 1:4 slice to solution ratio resulted into highest score for all the sensory attributes like colour and appearance, flavour, texture, taste and overall acceptability.

*- 1% level of significance

Conclusion

Weight reduction, water loss and solid gain increased with increases in carrot slice to sugar solution ratio. Moisture content of slices after osmosis decreased with increase in slice to solution ratio. However, 1:4 slice to solution ratio was found optimum in respect of mass transfer kinetics and overall organoleptic quality parameter for osmo-dehydrated carrot slice.