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Arianto Passalli Sarjono, Suherman. (2022). Drying Onion Slices using

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Eduvest  Journal of Universal Studies

Volume 2 Number 7, July, 2022

p- ISSN 2775-3735- e-ISSN 2775-3727

DRYING ONION SLICES USING A FOOD DEHYDRATOR

Arianto Passalli Sarjono, Suherman

Universitas Diponegoro, Indonesia

Email: [email protected]

ABSTRACT

Shallots are one of the mainstay products of Demak Regency

which are continuously being developed. However, the Demak

Shallot Cluster faces a major obstacle, namely drying

technology, which is the main cause of the decline in

competitiveness, and farmers suffer huge losses. Therefore, in

this study, a study of the drying of sliced shallots using a food

dehydrator will be carried out. The research analysis includes

(1) Drying Characteristics, (2) Drying Rate Analysis, (3)

Application of Thin Layer Drying Model, (4) Rehydration Ratio

Analysis, (5) Color Analysis, (6) Flavonoid and Total Phenolic

Analysis, (7) Antioxidant Activity Analysis. The quality

parameters of shallot products in general will follow SNI 3159-

2013, this standard stipulates provisions regarding the quality,

size and hygiene of shallots (Allium cepa varascalonicum) of

the Alliaceae family for consumption, plus the strength of

onion bulbs, identification and quantification of flavonoid

compounds, and anthocyanin levels. The results showed that

the moisture ratio value in equilibrium was 9.34% with the

fastest drying occurring at a temperature of 60 oC , which was

0.938 g/minute. The three thin layer drying models were

analyzed to determine the appropriate thin layer drying model.

The Page model was chosen because it has an R value of 2 the

highest is 0.9353 and the lowest RMSE and x 2 values are

0.04354 and 0.0025 3. Changes in color and bioactive

compounds in the dried onion slices are caused by heat which

causes damage to bioactive compounds. Based on the

parameters that have been determined, a temperature of 50 o

C indicates the optimum temperature for drying shallot slices.

KEYWORDS

Shallots, Solar Dryer, Hybrid

Arianto Passalli Sarjono, Suherman

Drying Onion Slices using a Food Dehydrator 1.253

This work is licensed under a Creative Commons

Attribution-ShareAlike 4.0 International

INTRODUCTION

Shallots (Allium ascalonicum L.) is one of the horticultural crop commodities that

are widely consumed by the public as a mixture of cooking spices after chili(Suswadi &

Prasetyo, 2022). Apart from being a mixture of cooking spices, red onions are also sold in

processed forms such as onion extract, powder, essential oil, fried onions and even as a

medicinal ingredient to lower cholesterol levels, blood sugar, prevent blood clots, lower

blood pressure and improve blood flow. As a horticultural commodity that is widely

consumed by the public, the potential for the development of shallots is still wide open not

only for domestic needs but also for foreign countries (Sativa, Harianto, & Suryana, 2017).

Horticulture is a combination of Latin, hortus which means garden and culture

which means farming. Horticulture can be defined as a way of cultivating plants in gardens

and yards (Lang, 2014).

Shallots contain minerals such as calcium, phosphorus, iron, magnesium, potassium

and zinc and nitrogen, also contain vitamins such as vitamin A, vitamin C, thiamine,

riboflavin, niacin, pyridoxine, and folic acid (Stephen & Suresh, 2015). Vitamins catalyze

reactions in the body, are essential for many body functions, are effective in small but

necessary amounts.

Shallots are known for their potassium content. 100 g of shallots provide 180 mg of

potassium(Stephen & Suresh, 2015). Potassium helps maintain osmotic pressure in cells.

Catalysts carry out several energy reactions and help maintain blood pressure.

In the last decade, the need for shallots in Indonesia from year to year for both

domestic consumption and seeds has increased by 5%. This is in line with the increase in

the number of residents which also increases every year. The Central Statistics Agency

(BPS, 2016) stated that the production of shallots in Indonesia from 2011 to 2015 was

893,124 tons, 964,195 tons, 1,010,773 tons, 1,233,984 tons, 1,229,184 tons. In 2015 the

national shallot production decreased compared to 2014 which was 0.39%. According to

the Director General of Horticulture (2016), the area of shallot harvested in Indonesia in

2011-2015 was 93,667 Ha, 99,519 Ha, 98,937 Ha, 120,704 Ha, and 122.126 Ha. The

national harvested area of shallots in 2015 only grew by 1.18% compared to 2014. To meet

domestic needs, the government adopted a policy of importing shallots from abroad

although this would result in less desirable domestic production (Dewi, 2012). Thus, the

productivity and quality of shallots need to be increased to meet domestic demand.

In Indonesia, shallot is one of the horticultural crops that many people cultivate.

Shallots are called horticultural crops because they are a type of vegetable crop, namely the

area of plants that are harvested at once / exhausted / unloaded and the area of plants that

have been harvested many times (more than once) / has not been exhausted. Plants that are

harvested all at once/exploited/unloaded are plants that are immediately

dismantled/uprooted after harvesting, consisting of shallots, garlic, leeks, potatoes,

cabbage/cabbage, cauliflower, Chinese cabbage/mustard, carrots, radishes and red beans.

According to the 2015 Agricultural Data and Information System Center, in the

2010-2014 period (the last five years), the average growth of shallot harvested area in

Indonesia increased by 3.70% per year. Meanwhile, the average growth of shallot harvested

area in Java, in the period 1980-2014, was 4.29% per year.

The four shallot center provinces (Central Java, East Java, West Java, and West

Nusa Tenggara) contributed 86.24% to the average Indonesian shallot production. Central

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Java province gave the largest contribution, namely 42.70% with an average production of

439,851 tons.

Meanwhile, in 2016, Central Java was able to produce 5,466,846 quintal shallots

with a harvested area of 53,331 ha. Besides Brebes Regency, Demak, Pati and Kendal

Regencies are also the highest shallot-producing areas in Central Java.

In 2016, Demak Regency had a harvested area of 6,218 ha, a production of 599,053

quintals, and a productivity of 96.34 ku/ha. Mijen District is a sub-district that is included

in the Demak Regency area, and is the highest shallot-producing sub-district in the last 3

years. As for the shallot production data in Demak Regency, in the last three consecutive

years period 2014-2016, shallot production in Mijen District has increased in the 3 years

period. In 2014 shallot production was 160,926 (Ha/Kw), for 2015 shallot production

increased to 281,111 (Ha/Kw) and in 2016 shallot production increased even more with

total production of 317,755 (Ha/Kw). The data on the amount of production was obtained

from the Department of Agriculture of the Demak Regency in 2016.

One of the main obstacles faced by these farmers is the need for onion drying

technology. At the main harvest with abundant onion production, the selling price received

by farmers is very low, sometimes it is not even balanced with the production costs that

must be incurred, among others, for harvesters. Shallots are one of the perishable

agricultural commodities.

Decrease in the quality of onion after Harvesting that often occurs in shallots is the

growth of shoots, softening of tubers, growth of roots and rot and the emergence of a dark

mass due to high water content, activity of microorganisms, and molds. This damage results

in decreased shelf life and quality of shallots. The critical point of failure in post-harvest

handling of shallots, especially when harvesting occurs during the rainy season, is at the

stage of leaf drying or withering and tuber drying.

Failure of the leaf withering process can lead to bacterial infection of putrefactive

bacteria, while failure to dry the tubers can cause low shelf life, tubers rot quickly, sprout

and root out. Yield loss due to this damage can reach 20 – 40%. So far, the drying technique

used by farmers is drying in the sun which takes between 7-9 days. Drying with this

technique is of course very dependent on the weather conditions at the time of drying. When

the weather is sunny, drying can take place well, but on the other hand, when the weather

is cloudy or even rainy, drying cannot be done at all so that the onion bulbs rot quickly.

With closed sun drying technology, the limitations of open sun drying technology

can be eliminated. Therefore, in this research, the technology of drying shallots slices will

be applied using a forced convection drying method with a food dehydrator for drying

shallot slices. The function of the dryer is very useful in the process of drying shallot slices

and in maintaining the quality of the dried shallot slices.

Some of the advantages of using a food dehydrator as a drying device include the

temperature can be adjusted according to the desired conditions, having a ventilator and

cover so that it can avoid the entry of dust, dirt, insects and other contaminants that can

cause a decrease in the quality of the sliced shallots to be dried. Another advantage is that

the drying process of red onion slices does not take a long time, compared to drying directly

in the sun and also a food dehydrator can dry onion slices in greater numbers with a

multilevel rack system, in one rack it can be filled with 50-100 sliced shallots, with the

initial weight of the onion that has not been peeled and sliced, which is 100 gr.

Arianto Passalli Sarjono, Suherman

Drying Onion Slices using a Food Dehydrator 1.255

The specific objective of the study was to obtain technical data on the drying

process of shallot slices, including 1) Drying Characteristics, (2) Drying Rate Analysis, (3)

Application of the Thin Layer Drying Model, (4) Rehydration Ratio Analysis, (5) Color

Analysis, (6) Analysis of Flavonoid and Total Phenolic, (7) Analysis of Antioxidant

Activity. Through the forced convection drying method using a food dehydrator machine

or tool so as to speed up drying time, improve product quality, increase product yield,

reduce product damage, and perform scale-up.

RESEARCH METHOD

Determination of Research Variables

The variables in this study are using two variables, the first is a fixed variable

consisting of the weight of whole onions that have not been sliced weighing 100 grams and

sliced red onions that have been peeled and cleaned with a thickness of 2 mm.

Figure 1 The initial weight of the onion before being peeled and sliced with a weight of

100 gr

Furthermore, the second variable is the variable that changes, including the drying

temperature with variations in temperature of 40

C, 50

C, and 60

C, the method used

with a stacked rack system, and the drying of sliced shallots at each temperature (40

C, and 60

C) until it reaches a moisture content of ± 10% or the dry weight of sliced

shallots reaches a constant weight and for a drying time at a temperature of 40

C with a

drying time of 8 hours, a temperature of 50

C with a drying time of 5 hours 50 minutes,

and a temperature of 60

C with a drying time of 2 hours 30 minutes.

Figure 2 Sliced onion to be dried

Materials and Tools Used

The raw materials used in this study include shallots from Demak, for the materials

used in the sample testing (dried shallots with a thickness of 2 mm) carried out in the

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laboratory include standard phenolic determinations of gallic acid, Folin Cpa, Na2CO3 0.2

mM, Aquades, standard flavonoid determination material quercetin, 5% NaNO2, 10%

Al2Cl3, 1 M NaOH, filter paper, antioxidant determination material Methanol pa, DPPH

0.2 mM (Dissolve as much as 0.078 g in methanol pa to a volume of 1000 ml), the material

for determining the moisture content of silica gel, the material for determining the color of

the dried shallot slices with a thickness of 2 mm.

The drying equipment used is the Food Dehydrator ARD-PM88, weighing phenolic

determination tool, measuring pipette, suction cup, beaker, measuring flask, vortex,

centrifuge, vaccum filter, test tube, cuvette, uv vis spectrophotometer, weighing flavonoid

determination tool, pipette measuring tape, suction cup, measuring flask, centrifuge, glass

funnel, erlenmeyer separating funnel, test tube, cuvette, spectrophotometer. instrument for

determining antioxidant activity of scales, mortar hammer, measuring pipette, suction cup,

measuring flask, funnel glass, erlenmeyer, beaker, test tube, cuvette, spectrophotometer,

instrument for determining water content (oven method) weighing bottle, oven, desiccator,

analytical balance , the tool for determining the color of the color reader used is the Minolta

color reader.

Figure 3 Drying process with a food dehydrator

Trial Procedure

Material Preparation

For the preparation of the material to be dried, namely whole shallots weighing 100

grams, peeled, after that they were sliced with a thickness of 2 mm. With an initial moisture

content of 81.057% shallots were measured in an oven and calculated from the mass lost

at a temperature of 90-100

C until a constant weight was obtained.

Drying Stage

Prepare sliced shallots with a thickness of 2 mm and a weight of 100 g at each

operating temperature variable, namely 40

C, 50

C, 60

C. Pressing the Power button of

the dryer then placing the shallot slices by arranging them on the rack in the drying device.

solar food dehydrator, then records the change in the weight of the shallot slices every 10

minutes, each temperature of 40

C, 50

C, 60

C. After the drying stage of the shallot

slices is complete, the dried shallot slices will be tested in the lab for determine phenolic,

flavonoid, antioxidant, color, and % water content.

The steps in determining phenolics, flavonoids, antioxidants, color and moisture

content % namely Determination of Phenolics (Folin C Spectrophotometer Method) with

the procedure: 1. Preparation of standards used is gallic acid standard concentration made

(mg/l) is 0, 2, 5, 10, 25, 50 solutions can be used for further processes, 2 Sample

Arianto Passalli Sarjono, Suherman

Drying Onion Slices using a Food Dehydrator 1.257

preparation: for solid samples, the samples were crushed and then weighed as much as 0.5

- 2 g, then dissolved in methanol pa to 25 ml in a measuring flask, then homogenized and

allowed to stand for about 30 minutes, then filtered and if necessary centrifuged at 3000

rpm for 10 minutes and the supernatant was taken. The solution can be used for further

processing for liquid samples, take as much as 1 ml of the sample, add 5 ml of methanol

pa, place it in a test tube, homogenize using a vortex for 5 minutes. Filter the solution with

a vacuum filter, take the filtrate. The filtrate solution can be used for further processes, 3.

Determination of phenolics: 1 ml of sample or standard added 0.2 ml of folin c, 0.6 ml of

0.2 mM Na2CO3 homogenized by vortex for 5 minutes and allowed to stand for 120

minutes. Measure the absorbance at 765 nm.

Determination of flavonoids with the following procedures: 1. Preparation of

Standards: the standard used is quercetin, the concentration of the standard made (mg/L) is

0; 0.5; 1; 25; 50; 100, standard (100 mg/l) was prepared by dissolving 10 mg of quercetin

in distilled water to 100 ml. For other concentrations, it can be done by dilution from a

concentration of 100 mg/l, the solution can be used for the next process, 2. Sample and

Standard Preparation: a. For solid samples, the samples were mashed and then weighed as

much as 1 g, then dissolved in methanol pa to 10 ml in a measuring flask, then homogenized

and allowed to stand for about 30 minutes, then filtered with a vacuum filter and if

necessary centrifuged at 3000 rpm for 10 minutes and taken supernatant, b. For liquid

samples, take 1 ml of sample, add 5 ml of methanol pa, place in a test tube, homogenize

using a vortex for 5 minutes, filter the solution with a vacuum filter, take the filtrate. The

filtrate solution can be used for further processing. c. The solution can be used for the next

process, 3. Determination of flavonoids: take 0.1 ml of sample or standard solution, add

0.1 ml of 2% Al2Cl3, homogenize with a vortex, let stand for 60 minutes at room

temperature then add distilled water to 1 ml volume a red solution will be formed if there

are flavonoids, after that the absorbance is measured with a spectrophotometer at 420 nm.

Determination of antioxidants by the procedure: 1. Sample preparation: a. Solid

sample, mashed sample then weighed as much as 2.5 g, then dissolved in methanol pa to

25 ml in a measuring flask, so that a 10% sample solution was obtained, b. Homogenization

and allowed to stand for about 30 minutes, then filtered and if necessary centrifuged at

3000 rpm for 10 minutes and the supernatant was taken, c. For liquid samples, samples

were taken dissolved in methanol pa up to 25 ml in a measuring flask, until a 10% sample

solution was obtained, d. Homogenization and allowed to stand for about 30 minutes, then

filtered and if necessary centrifuged at 3000 rpm for 10 minutes and the supernatant was

taken. 2. Determination of Antioxidant Activity: a. A total of 1.5 ml of sample solution was

added with 3 ml of 0.2 mM DPPH solution, b. Homogenization and allowed to stand for

30 minutes, then the absorbance was measured at 516 nm, c. Perform the above procedure

on a blank that is 1.5 ml of methanol pa

Determination of Color (Minolta Color Reader Method) with the following

procedures: 1. The color reader tool used is the Minolta color reader, 2. Change the on-off

button to the on position to turn on the tool, 3. Adjust the position so that the sensor is in

contact with the sample to be tested. the color level is measured, 4. The sample must be

placed in a transparent container (glass or plastic), 5. Press the target button, which will be

followed by a beep sound, indicating the reading is complete, 6. Record the numbers L, a,

and b on the monitor screen of the instrument. color reader, 7. Press reset for the next

measurement, 8. Turn the on-off button to off to turn off the instrument, 9. Store the

instrument in a dry place away from sunlight.

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Figure 4 Color Reader Minolta CR-10

(Reference: Konica Minolta, 1996. Color Reader CR-10. Konica Minolta Inc.)

Determination of Moisture Content (oven method) with the following procedures: 1.

Wash the weighing bottle or beaker to be used as a sample holder, 2. Dry the weighing

bottle by heating it in the oven and then cooling it in a desiccator, 3. Weigh the weighing

bottle and record (a), don't forget to label, 4. Carefully weigh the sample as much as 1-2

grams (b) depending on the moisture content of the material and place it in a weighing

bottle, 5. Oven the sample along with the weighing bottle at a temperature of 100 ° C for 5

hours, then cool in desiccator, then oven again for 1 hour at the same temperature, cool in

a desiccator and then weigh, repeat the process until a constant weight is achieved (c). 6.

Heating can also be carried out for 24 hours at a temperature of 90 - 100 ° C, usually on

heating in this way a constant weight can be obtained.

Drying Data Analysis

Phenolic Analysis

The standard phenolic absorbance results that have been obtained are processed with

the help of a statistical program to determine a simple linear regression equation y = a +

b(x), where y = absorbance and x = phenolic concentration. The phenolic content was

determined with the help of the standard regression equation by taking into account the

weight of the sample used and the dilutions carried out. (Oluwaseun R. Alara, 2018.).

Flavonoid Analysis

The standard flavonoid absorbance results that have been obtained are processed

with the help of a statistical program to determine a simple linear regression equation y =

a + b(x), where y = absorbance and x = flavonoid concentration. The flavonoid content was

determined with the help of the standard regression equation by taking into account the

weight of the sample used and the dilutions carried out. (Oluwaseun R. Alara, 2018.).

Antioxidant Analysis

Antioxidant activity (%) =(1-s/b)×100%, where b is the absorbance of the blank and

s is the absorbance of the sample.

Moisture content calculation

To calculate the moisture content, dry and wet weight data is needed. (Nidhi, 2015):

Mc (wet basis) =

󰇛󰇜



100 (3.1)

Mc(dry basis) =

󰇛󰇜



100 (3.2)

















  (3.3)

Information :

Xn = Moisture Content

Wn = Initial Mass (grams)

Mbk = Dry Base Mass (grams)

Arianto Passalli Sarjono, Suherman

Drying Onion Slices using a Food Dehydrator 1.259

Drying rate calculation

To get the drying rate, data on sample weight reduction is needed for each (Nindhi,

2015) :

 





󰇛󰇜 



󰇛󰇜

 󰇛󰇜

( 3.4 )

Information:

DR = drying rate (g/s)

Mi = initial mass (g)

Md = final mass (g)

t = drying time ( minutes )

Product Quality Analysis

Chemical content

Fresh onions were measured soluble solids content (%), pH, and titrated acidity (g

citric acid / L) was measured. Ash content and moisture were also analyzed on fresh onions

and dried onions.

Bioactive compounds: total soluble phenolic content (TSP), flavonoids (F) and

antioxidant activity (AA).

Onion extract. Methanol extracts from fresh and dried shallot samples were prepared

according to the methodology described by Siddiq et al. Onions are ground in a coffee

grinder and mixed to obtain a homogeneous product. Samples were weighed (ca. 5.0 g fresh

or dry material), and extracted by sonication (40 kHz, 45 min, 25 C, ultrasound bath model

TB02TACA, TESTLAB SRL, Buenos Aires, Argentina) using 20 ml methanol:water

(80:20). , MeOH:H2O). The homogenate was then centrifuged at 10,000 g for 10 min using

the Biofuge 28RS Heraeus Sepatech Centrifuge (Heraeus Instruments, Hanau, Germany)

and filtered. Each homogenate was extracted twice and the combined fraction was diluted

to a final volume of 40 ml and used for further analysis.

Total soluble phenolic content (TSP) was determined by the FolinCiocalteu method,

using linear regression of calibration plots constructed using gallic acid. The results were

expressed as mg gallic acid equivalent (GAE) per 100 g shallots at fresh weight (fw) (mg

GAE/100 g fw) and at dry weight (dw) expressed (mg GAE/100 g dw). The flavonoid

content (F) was determined using the AlCl3 method according to the modified

methodology proposed by Ismail et al. The F content was calculated by linear regression

of the calibration curve construction using quercetin. The results are expressed as mg

quercetin equivalent (QE) per 100 g of onions on fresh weight (fw) (mg QE/100 g fw) and

on dry weight (dw) (mg QE/100 g dw). Antioxidant activity (AA) was determined using

the FRAP assay as described by Oyaizu. Trolox (0–50 M) was used as the standard

antioxidant and AA of the extract was expressed as microMolar equivalent of Trolox (µMol

TE) per g onion based on dry weight (dw) (µMol TE/g dw). The free radical scavenging

effect was assessed according to the procedure described by Brand-Williams et al. with

minor modifications to reduce testing time. Quercetin equivalent was used as the reference

compound. The concentration of the extract giving 50% radical scavenging activity (EC50)

was calculated. Absorbance measurements were carried out at 25°C, using a Multiscan FC

spectrometer (Thermo Fisher Scientific Corporation). All measurements were made in

triplicate.

Rehydration ratio

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After the drying process, the rehydration was evaluated to observe the possible

structural changes produced by the drying process. Rehydration was carried out at 25 ± 1

C. The dry sample (3 slices dried at each temperature) was put into 50 ml of distilled water

in a Petri dish for 3 hours (until the weight was constant). The sample is removed from the

water and then, its surface is covered with a piece of filter paper to soak up the excess

water. The rehydrated shallot slices were then weighed using an electronic scale (Taff-

Ware brand, type I – 2000, Max resolution 1000 g, d = 0.1 g). All experiments were carried

out 3 times and the average value of the rehydration ratio (RR) was taken. The rehydration

ratio can be calculated by the following formula:

RR =

󰇛󰇜

󰇛󰇜

Color Measurement

The color of the shallot slices was measured with a Minolta Chroma meter CR 400

color meter (Minolta Co., Osaka, Japan) before and after drying. The color meter is

calibrated against a standard calibration plate from a white surface and set to CIE Standard

Illuminant C. Values L*, a*, b* are the average of ten readings. The L* color brightness

coordinate measures the whiteness of a color and ranges from black at 0 to white at 100.

The a* chromaticity coordinates measure red when positive and green when negative, and

b* chromaticity coordinates measure yellow when positive and blue when negative

(Doymaz, 2003). Tugrul, & Pala, 2006).

RESULT AND DISCUSSION

Drying Characteristics

The process of drying thin layers of sliced onions using a food dehydrator at

temperatures of 40

C, 50

C, and 60

C starting at a moisture content of 85% was carried

out for 8 hours and stopped when the weight of the sliced shallots has reached a constant

or has reached equilibrium. . Connection drying time to moisture ratio on the drying of

sliced shallots is presented in Figure 4.1.

Figure 5 Relationship of drying time to moisture ratio

0.0

0.2

0.4

0.6

0.8

1.0

0 60 120 180 240 300 360 420 480

MR (

Moisture Ratio

)

Drying

Suhu 60˚C

Suhu 50˚C

Suhu 40˚C

Arianto Passalli Sarjono, Suherman

Drying Onion Slices using a Food Dehydrator 1.261

Figure 5 shows a decrease in the value of the moisture ratio with increasing drying

time. The time required for drying shallot slices using a temperature of 40

C to reach an

equilibrium weight of 9.34% is 7 hours. The drying time is slower than the drying of sliced

shallots using a temperature of 50

C and 60

C, namely for 3 hours and 5 hours.

The decrease in the value of the moisture ratio during the drying period is due to the

reduced moisture content of the material due to the mass transfer of water from the material

to the air (Sahoo et al., 2016). The difference in temperature used also affects the high

decrease in the value of the moisture ratio so that it affects the drying time used to achieve

the equilibrium weight of sliced shallots. This phenomenon can be caused by the use of

higher temperatures in the drying process which causes the heat transfer to be greater. As

a result, the process of transferring water mass from the material to the air is faster so that

the drying time used is also faster (Salamatullah, Uslu, Özcan, Alkaltham, & Hayat, 2021).

Research conducted by Hendrawan et al . (2018) on the drying of sliced shallots shows that

the value of the moisture ratio at equilibrium is 9.99%. The difference in the moisture ratio

value obtained can be caused by the initial moisture content of the material and the

thickness of the material used (Olubi, Oniya, & Owolabi, 2021).

Drying Rate Analysis

The drying rate data analysis showed that the drying of shallot slices occurred in the

falling rate period . Drying rate can be defined as the rate of evaporation of water from the

material into the air per unit time. The value of the drying rate of sliced shallots using a

food dehydrator at temperatures of 40

C, 50

C, and 60

C is presented in Figure 4.2.

Figure 6 Curve of drying rate

Figure 6 shows the drying rate at temperatures of 40

C, 50

C, and 60

decreased with increasing drying time due to a decrease in water content with increasing

time. The average drying rate of sliced shallots at each temperature of 40

C, 50

C, and

C were 0.865 g/minute, 0.904 g/minute, and 0.938 g/minute. Figure 4.2 also shows that

the higher the drying temperature used, the faster the drying rate that occurs.

The use of higher temperatures in the drying process can accelerate the drying rate

because the rate of evaporation of water from the material to the air also increases with

increasing temperature (Davodi-Boroujerd, Abasi, Arani, & Aslzaker, 2022). Then, the

drying rate decreases with increasing time. The drying rate that occurs at the beginning of

0 60 120 180 240 300 360 420 480

Drying rate

(g/min)

Drying

Suhu 60˚C

Suhu 50˚C

Suhu 40˚C

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drying is still relatively high because the free water content on the surface of the material

is still quite high. The free water content is easy to evaporate because it fills the cell cavities

and intercellular spaces (Kaveh, Abbaspour-Gilandeh, & Nowacka, 2021). Furthermore,

there is a decrease in the drying rate with increasing time because the remaining water

content in the material is water bound to the cells and tissues of the material making it

difficult to get out of the material. The bound water content is difficult to evaporate because

it is hygroscopically attached to the cell wall which in the end the drying rate of the shallot

slices becomes constant (Misha, Mat, Ruslan, Sopian, & Salleh, 2013).

Application of the Thin Layer Drying Model

The three thin layer drying models are used to predict the drying characteristics of

sliced shallots so that the drying process can be controlled according to the desired results.

Moisture Ratio (MR) data obtained from the experiment was plotted into three drying

models, namely Newton, Page, and Henderson & Pabis. The results of the constant values

for each tested model are presented in Table 1.

Table 1 Analysis results from thin layer drying model

Drying

Model

T (

RMSE

Newton

0.0064

0.9334

0.12280

0.01939

0.0067

0.9006

0.14177

0.03618

0.0068

0.8699

0.16687

0.08354

Page

0.0928

0.549

0.9353

0.04354

0.00253

0.1559

0.469

0.9032

0.05111

0.00522

0.3159

0.350

0.8859

0.04921

0.00969

Henderson

- Pabis

0.0039

0.538

0.8007

0.16415

0.03464

0.0043

0.446

0.6791

0.19536

0.06870

0.0046

0.370

0.5679

0.21825

0.14290

Table 1 shows the results of the constant value analysis of each model equation. The

drying model shows that Page's model has the highest R2 value between

0.8859

to 0.9353 and

the lowest RMSE and x2 values

between

0.04354 to 0.05111 and 0.00254 to 0.00969. This

indicates that Page's model is the most accurate model in describing the drying

characteristics of sliced shallots based on the resulting constant values.

The analysis of the R2 value

a test of a statistical model that describes how well

the variance of the model is with a series of observations. These measurements usually

summarize the difference between the observed value and the expected value in the model.

The closer the R2 value is to

, the more the model explains the observed variation, the

more perfect it is. Analysis of the value of x

is a statistical test used to determine whether

two variables have a significant difference between the observed and the expected. RMSE

value analysis is a measurement for the error rate based on the difference between the two

corresponding variables, the smaller the RMSE value, the more accurate a predictive model

is (Siami-Namini, Tavakoli, & Namin, 2018).

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Drying Onion Slices using a Food Dehydrator 1.263

Figure 7 The relationship between predicted MR and experimental MR in the Page .

model

Figure 7 shows the predicted MR and experimental MR at temperatures of 40

C, and 60

C using Page's model. The results of the relationship between prediction

MR and experimental MR show that the Page model is a drying model used to predict the

water content of sliced shallots at various temperatures so that the drying process can be

controlled according to the desired results (Santoso et al., 2018).

Most of the drying of agricultural products occurs in the falling rate period and the

movement of water during this period is controlled by internal diffusion. Analysis in this

period was carried out to understand the drying kinetics by determining the effective

diffusivity ( Deff ) (

Afifah

et al., 2017). The results of the calculation of the D

eff value

for all

treatments are presented in table 8.

Table 2 Effective diffusivity (Deff) value of

drying

shallot slices at various temperatures

Drying Temperature (

Effective Diffusivity (m

/s)

1.58 x 10

-9

1,744 x 10

-9

1.866 x 10

-9

Based on Table 2, the value of the effective diffusivity ( Deff ) for

drying

sliced shallots

at temperatures of 40

C, 50

C, and 60

C is 1.58 x 10

-9

/s, 1.74 x 10

-9

/s, and 1.86

-9

/s. This value is considered acceptable for most agricultural products. The higher

the drying temperature, the higher the product temperature, which encourages the

movement of water in the product through diffusion and then evaporates into the air

(Herlina & Suherman, 2020). Several other studies have shown that the Deff value in sliced

garlic on drying using an oven dryer at a temperature of 60

C and 70

C is 8.11 x 10

-11

/s and 1.22 x 10

-10

/s (Roman et al. , 2019). The difference in effective diffusivity

values between agricultural commodities is possible due to differences in the structure of

the dried material including differences in material thickness (Widowati et al., 2017).

Rehydration Ratio Analysis

The rehydration ratio is one of the important parameters of the quality of a drying

product. Rehydration properties are the ability of drying products to absorb water so that

they are close to their fresh condition. The results of the study for the effect of drying

0.00

0.10

0.20

0.30

0.40

0.50

0.00 0.10 0.20 0.30 0.40 0.50

MR Prediction

MR Experiment

Suhu 60˚C

Suhu 50˚C

Suhu 40˚C

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temperature on the rehydration ratio of sliced shallots are presented in Table 3.

Table 3 Value of rehydration ratio of drying products at various temperatures

Drying Temperature (

Rehydration Ratio

5.28

4.92

4.64

Figure 8 Effect of drying temperature on product rehydration ratio

Figure 8 shows the value of the rehydration ratio obtained from the comparison of

the mass of sliced shallots after being rehydrated to the mass of dried shallots slices. The

results showed that the rehydration ratio of sliced shallots for temperatures of 40

C, 50

C, and 60

C was 5.28; 4.92; 4.64. The higher the drying temperature used, the lower the

value of the rehydration ratio. This can be due to the red onion slices which are very

sensitive to temperature so that the tissue is easily damaged if dried at too high a

temperature (Ali Asgar, 2013).

Widyasanti et al. (2018) stated that the higher the rehydration ratio value, the higher

the ability of drying products to absorb water, and the better the elasticity of the cell walls

and vice versa. A high value of the rehydration ratio is needed in drying products because

it shows that the product is close to its original shape which means it has good physical

quality.

Color Analysis

The appearance of a product, especially its color, is very important in influencing

the preferences and decisions of a buyer. Therefore, the color of the dried shallot slices is

an important parameter to measure. The results of the analysis of the effect of drying

temperature on the values of L, a, and b shallot slices are presented in Figure 9

40˚C 50˚C 60˚C

Rehydration

Drying Temperature (

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Drying Onion Slices using a Food Dehydrator 1.265

Figure 9 Effect of drying temperature on the values of L, a, and b shallot slices

The results showed that the drying temperature had a very large effect on the color

of sliced shallots. Both the values of L (brightness level), a (red intensity), and b (yellow

color intensity) decreased with increasing drying temperature used. Sliced shallots in fresh

condition had the highest L, a, and b values of 61, 19, and 19. Meanwhile, sliced shallots

dried at 60

had the lowest L, a, and b values of 25, 4, 1.

The lower L value in the dried product indicates the darker the color of the product.

The decrease in the brightness of the shallot slices at higher drying temperatures can be

caused by the high protein content in the shallot slices. In addition, the decrease in the

brightness of the shallot slices can be caused by the Maillard reaction during the drying

process. The Maillard reaction is a reaction between reducing glucose and primary amino

acid groups which can produce brown or melodic nitrogen polymers . The decrease in the

value of L was also followed by a decrease in the values of a and b which could be due to

the intensity of the red and yellow colors being very sensitive to heat. This is also supported

by the research of Wijaya and Wahyono (2018) which states that the presence of drying

temperature and blanching time gives a decrease in the values of a and b .

Analysis of Flavonoids and Total Phenolic

According to Tiho et al . (2017), polyphenols are a large group of phytochemical

compounds in onions. Polyphenols also have aromatic ring components, which include

flavonoids and phenols. The results of the study for the effect of drying temperature using

a food dehydrator on flavonoids and total phenolics in sliced shallots are presented in

Figure 10.

Fresh

40˚C 50˚C 60˚C

Color

L, a, b

Drying Temperature (

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Figure 10 Effect of drying temperature on flavonoids and total phenolic

The results showed that the drying temperature had a big effect on the flavonoid

content and total phenolic in the sliced shallots. The content of flavonoids and total

phenolic increased from fresh sliced shallots to dried shallot slices. The highest value of

flavonoid content and total phenolic content of sliced shallots was obtained at a temperature

of 40ºC, namely 226 mg QE/100 g and 730 mg GAE/100 g, while the lowest flavonoid and

total phenolic content of sliced shallots was obtained at a drying temperature of 60ºC,

namely 141 mg QE. /100 mg and 486 mg GAE/100 g.

The increase in the flavonoid content and total phenolic content of fresh shallot

slices against dried shallot slices could be due to the inactivation of the polyphenol oxidase

enzyme (Khatulistiwa et al., 2020). In addition, the increase in the flavonoid content and

total phenolic content of shallot slices due to drying can also be caused by the release of

polyphenolic compounds during the drying process (Roman et al ., 2020). According to

Lisanti et al . (2015), drying accelerates the release of bound polyphenolic compounds

during the breakdown of cellular constituents. Meanwhile, in the drying of sliced shallots

after a temperature of 40

C the content of phenolic compounds decreased which could be

caused by damage to bioactive components such as polyphenol compounds due to

excessive heat (Oniya et al., 2021).

Antioxidant Activity Analysis

Antioxidants are compounds that are able to inhibit or prevent cell damage due to

oxidation by free radicals (Artanti and Lisnasari , 2018). The results of the study for the

effect of drying temperature using a food dehydrator on the antioxidant activity of sliced

shallots are presented in Figure 11.

100

200

300

400

500

600

700

800

Fresh

40˚C 50˚C 60˚C

Drying

Total Fenolik (mg GAE/100 g dw) Flavonoid (mg QE/100 g dw)

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Drying Onion Slices using a Food Dehydrator 1.267

Figure 11 Effect of drying temperature on antioxidant activity

The results showed that the drying temperature had a very large effect on the activity

of sliced shallots. The antioxidant activity increased from fresh sliced shallots to dried

shallot slices. The highest antioxidant activity of sliced shallots was obtained at a drying

temperature of 40ºC, which was 73%, while the lowest antioxidant activity of sliced

shallots was obtained at a drying temperature of 60ºC, which was 45%.

Flavonoids and total phenolic compounds are compounds that have the ability as

antioxidants. According to Molaveisi et al . (2018), flavonoids and total phenolics can act

as antioxidants because of their ability to donate hydrogen atoms to free radicals, and as

metal binders. The increase in antioxidant activity of fresh shallot slices against dried

shallot slices could be caused by the release of polyphenolic compounds (flavonoids and

total phenolic) during the drying process (Roman et al ., 2020). According to Lisanti et al

. (2015), drying accelerates the release of bound polyphenolic compounds during the

breakdown of cellular constituents. Meanwhile, in the drying of sliced shallots after a

temperature of 40

C, the antioxidant activity decreased which could be caused by the

higher heating temperature resulting in secondary metabolite compounds that act as

antioxidants (polyphenol compounds) being damaged (Molaveisi et al ., 2018).

CONCLUSION

The decrease in moisture ratio is influenced by an increase in temperature, due to

a decrease in air humidity so that heat and mass transfer also increase, and the moisture

content of the material will decrease more quickly. Meanwhile, the drying rate on a food

dehydrator with variable temperatures of 40

, 50

, and 60 o as well as traditional drying

were 0.865 g/minute, 0.904 g/minute, and 0.938 g/minute, respectively . The fastest drying

rate occurs in the drying process at a variable temperature of 60

C. Then the drying rate

will decrease with increasing drying time, because the moisture content of the material also

decreases.

The mathematical model of thin layer drying that is suitable for drying shallot

slices using a food dehydrator is the Page model because it has the highest R2 value of

0.9353 and the lowest RMSE and x2 values

are 0.04354

and 0.00253. The content of total

phenolic, flavonoid, and antioxidant activity found in sliced shallots before drying was 730

mg GAE/100 g, 210 mg QE/100 g, and 71%, respectively. Meanwhile, the total phenolic,

flavonoid, and aa content found in sliced shallots dried at 60

were 486 mg GAE/100 g,

Fresh

40˚C 50˚C 60˚C

Antioxidant

Drying

Aktivitas Antioksidan (%)

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Volume 2 Number 7, July 2022 
 
 
1.268    http://eduvest.greenvest.co.id 
141  mg  QE/100  mg,  and  45%, respectively.  The  decrease  in  bioactive  compounds  on 
drying at higher temperatures was caused by the destruction of bioactive components such 
as  polyphenol  compounds  due  to  too  high  heat.  The  use  of  a  higher  temperature also 
reduces the color degrees of L, a, and b so that the color of the dried red onion slices 
becomes darker. The rehydration ratio was determined to determine the parameters of good 
physical quality of the drying product. The highest rehydration ratio value was obtained at 
a drying temperature of 40 
o 
C. 
 
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