 *Corresponding author.

Email: trozaina@umt.edu.my

eISSN: 2550-2166 / © 2020 The Authors. Published by Rynnye Lyan Resources

  Food Research 4 (4) : 1207 - 1216 (August 2020)
  Journal homepage: http://www.myfoodresearch.com

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Effect of cooking methods on nutritional composition and antioxidant

properties of lotus (Nelumbo nucifera) rhizome

1Chen, S.Y. and 1,2*Tengku Rozaina, T.M.

1Faculty of Fisheries and Food Science, Universiti Malaysia Terengganu, 21030 Kuala Nerus, Terengganu,

Malaysia
2Institute of Tropical Biodiversity and Sustainable Development, Universiti Malaysia Terengganu, 21030,

Kuala Nerus, Terengganu, Malaysia

Article history:

Received: 28 October 2019

Received in revised form: 18

February 2020

Accepted: 20 February 2020

Available Online: 11 April

2020

Keywords:

Lotus rhizome,

Proximate composition,

Minerals,

Vitamin C,

Antioxidant,

Cooking methods

DOI:
https://doi.org/10.26656/fr.2017.4(4).359

Abstract

Lotus (Nelumbo nucifera) rhizome possessed abundant nutrients such as vitamin C,

minerals and antioxidants. The consumption of lotus rhizome is limited in Malaysia due to

limited information on its nutritional values. Cooking or heat treatment may cause

nutritional changes in the food, however, there is a lack of study on the effect of cooking

methods on nutritional contents of lotus rhizome. In this study, the effects of cooking

methods (steaming, boiling and deep-frying) on nutritional composition (proximate,

vitamin C and minerals) and antioxidant properties (total phenolic content, total flavonoid

content, DPPH and ABTS scavenging activity) of lotus rhizome were investigated.

Results showed that boiling significantly increased moisture and crude fibre but decreased

ash, crude fat and crude protein contents of lotus rhizome. Meanwhile, deep frying

significantly reduced moisture and increased ash, crude fat, crude protein, crude fibre and

carbohydrate contents of lotus rhizome. Steaming induced no significant changes in

moisture, crude protein, crude fat, crude fibre, carbohydrate, vitamin C and mineral

(potassium, zinc and copper) contents when compared to the raw lotus rhizome. Boiling

significantly reduced the amount of vitamin C while deep frying caused a significant

reduction in total phenolic content, total flavonoid content and antioxidant activity for

both ABTS and DPPH assays of lotus rhizome. In conclusion, steaming would be the best

cooking methods for lotus rhizome while deep frying is not recommended to retain the

nutritional composition and antioxidant properties of lotus rhizome.

1. Introduction

Lotus (Nelumbo nucifera) in the Nelumbonaceae

family is an aquatic plant widely grown in Asian

countries such as China, Japan and India. It is cultivated

for food, ornamental and medicinal purpose (Zhao et al.,

2016). According to Wang (2014), lotus rhizome is rich

in starch, sugars, lipids, proteins, minerals, vitamins,

alkaloids, flavonoids and other biochemical substances.

It contains alkaloids that is used in treating arrhythmia,

sunstroke, fever, diarrhoea, dysentery, dizziness and

stomach problems (Shad et al., 2011). Furthermore, it

also has pharmacological activities such as anti-

diarrhoeal, anti-inflammatory, antioxidant, antipyretic,

diuretic, hypoglycaemic, immunomodulatory and

psychopharmacological activities (Bhardwaj and Modi,

2016; Yi et al., 2016). The extract of lotus rhizome

especially from its nodes contains a high amount of

antioxidant such as phenolic, tannin and flavonoid

(Moro, 2012).

Lotus rhizome has potential to be cultivated widely

as another important crop in Malaysia, just like sweet

potato or cocoyam, as it can be harvested year-round and

can be grown in an environment which is unfavourable

for other traditional agricultural crops. However, the

production of lotus in Malaysia is limited due to the low

market demand compared to other vegetables. The

consumption of lotus rhizome in Malaysia is limited to

Chinese and Indian population. The Malay population in

Malaysia rarely consumes the lotus rhizome since not

much information on the nutritional value of it is

available. The popularity of lotus rhizome is mainly due

to its attractiveness white colour and the crispness

texture (Li et al., 2017). The fresh lotus rhizome is

popular to be sliced and deep-fried as chips for snacks.

This is because deep-frying creates unique texture,

flavour and taste for the food (Oke et al., 2017).

https://orcid.org/0000-0002-0258-6557

https://orcid.org/0000-0002-2824-8118

 Chen and Tengku Rozaina / Food Research 4 (4) (2020) 1207 - 1216

eISSN: 2550-2166 © 2020 The Authors. Published by Rynnye Lyan Resources

According to Metha (2015), vegetables are cooked

before consumption to improve their palatability, aroma,

taste, appearance, and texture to achieve high acceptance

among consumers. Cooking or processing method

caused nutrients loss in food product and the amount of

loss was depended on the method used. The heat applied

during cooking caused the nutrients, which were

sensitive to heat, light, oxygen and pH, to be unstable

and lead to their thermal degradation (Omotosho et al.,

2016).

Most consumers eat lotus rhizome because of its

mild sweet flavour or as a part of their traditional food

habit without knowing the nutritional value of lotus

rhizome. There is a lack of research done purposely to

investigate the effect of different cooking methods on the

nutritional composition and antioxidant properties of

lotus rhizome.  Li et al. (2017) focused on the effect of

steaming and boiling on the physicochemical properties

of lotus (Nelumbo nucifera) root, such as moisture

content, texture and volatile compounds

(methylcyclohexance and ethylcyclohexance). Another

study conducted by Zhao et al. (2016) investigated the

effect of heat blanching and calcium immersion on

physicochemical properties related to the texture of

rhizome. Meanwhile, Vora and Srinivasan (2015) studied

on the nutritional benefits of raw and fried lotus stems.

Frying caused the reduction of iron, calcium,

phosphorus, sodium and vitamin C content and increased

the amount of carbohydrate, protein and dietary fibre in

lotus stem (Vora and Srinivasan, 2015).

  The objectives of this study are to determine the

effect of cooking methods on the proximate composition,

vitamin C, minerals content, and antioxidant properties

of lotus (Nelumbo nucifera) rhizome. Information

obtained from this study would be beneficial to

consumers in choosing the good cooking method for

lotus rhizome and is expected to encourage its

consumption among various communities in Malaysia.

2. Materials and methods

2.1 Sample preparation and cooking treatments

Five (5) kg of lotus (Nelumbo nucifera) rhizomes

with an average length of 45.0-57.0 cm and width of 4.0-

5.0 cm were purchased from the farmer at Ipoh, Perak.

The samples were washed, peeled and sliced into 0.3 cm

of thickness. The lotus rhizome slices were divided into

four portions, where one portion was left as raw for

control while the other three portions were cooked by

steaming, boiling and deep-frying. The cooking

conditions were as follows:

Steaming: Lotus rhizome slices (0.9 kg) were

steamed for 30 mins in 3 L of 100oC boiling water in a

steamer until they were tender.

Boiling: Lotus rhizome slices (0.9 kg) were boiled

for 30 mins in 2 L of 100oC boiling water in a stock pot

until they were tender.

Deep frying: Lotus rhizome slices (0.9 kg) were deep

-fried for 1.5 mins in a saucepan with 350 mL palm oil

(Bagus, Sime Darby Plantation, Malaysia) at 170±2.0oC

until they were crispy.

All samples were cooked without adding any salt or

additional ingredients. The cooked samples were taken

for quick freezing in a blast freezer (Technomac,

Malaysia) at -20°C for two hrs and stored in a freezer

(Panasonic, Malaysia) at -20°C before further analysis.

2.2 Proximate analysis

Proximate analysis of lotus rhizome was carried out

according to AOAC (2005) methods. The samples were

dried in an oven (Chemopharm, Malaysia) at 105oC for

overnight for moisture determination. Analysis of ash

was carried out by heating the samples in a muffle

furnace (Carbolite, Malaysia) at 550oC for overnight.

Crude fat content was analysed using Labtec ST310

(Foss, Malaysia) with petroleum ether (EMSURE,

Germany) as extraction solvent. Crude protein content

was measured using a Kjeldahl method with Turbotherm

digestion unit (Gerhardt, Malaysia) and Vapodest 30S

distillation unit (Gerhardt, Malaysia). The conversion

factor for nitrogen-protein percentage used was 6.25.

The samples were boiled with 0.13 M H2SO4 (R&M

Chemical, Malaysia) and 0.31 M NaOH (R&M

Chemical, Malaysia) in Gerhardt Fibre Bag system for

determination of crude fibre content. The carbohydrate

content of the sample was calculated by subtracting

100% with the sum of percentage of moisture, ash, crude

fat, crude protein and crude fibre contents.

2.2.1 Oil uptake and moisture loss

The oil uptake and moisture loss of deep-fried lotus

rhizome were determined according to Kim et al. (2015)

method and calculated as follows:

Where WD = mass of cooked sample (g); Wd = mass of

raw sample (g); FD = fat amount of cooked sample (g/1g

wet basic); Fd = fat amount of raw sample (g/1g wet

basic); MD = moisture content of cooked sample (g/1g

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wet basic); and Md = moisture content of raw sample

(g/1g wet basic).

2.3 Vitamin C analysis

Lotus rhizome juice was prepared by grounding 10 g

of chopped lotus rhizome slices with 50 mL distilled

water (Hussain et al., 2016). The mixture was filtered

and added with 3% metaphosphoric acid (EMSURE,

Germany) until the volume became 100 mL.

Determination of vitamin C was carried out according to

Pegg et al. (2010) method. Lotus rhizome juice (10 mL)

was titrated with 2,6-Dichlorophenolindophenol

(DCPIP) dye solution until pink colour exists for 15 s.

The ascorbic acid content was calculated using the

formula below:

Where X = volume for test solution titration (mL) and B

= volume for test blank titration (mL).

2.4 Mineral analysis

Mineral extraction of lotus rhizome samples was

carried out according to AOAC (2005) method. Lotus

rhizome (1.5 g) was incinerated in a muffle furnace to

form ash to be evaporated to dryness on a hot plate

(Favorit, Malaysia) with 2 mL of concentrated HCl

(EMSURE, Malaysia). Subsequently, 10 mL of 20%

concentrated HNO3 (Merck, Germany) was added. After

incubation in water bath at 60°C for 1 hour, the mixture

was diluted into 100 mL with distilled water and filtered

using Whatman No.42 filter paper prior to analysis.

Determination of mineral content of lotus rhizome was

carried out using Inductively Coupled Plasma-Optical

Emission Spectrometry (ICP–OES) (Optima 8300,

PerkinElmer, USA) according to Akpinar-Bayizit et al.

(2010) method.

2.5 Antioxidant analysis

2.5.1 Antioxidant extraction

Antioxidant extraction of lotus rhizome slices was

carried out according to Leong et al. (2012) method.

Chopped lotus rhizome samples were dried in an oven

(Southstar, Malaysia) at 50oC for 48 hrs until almost 5-

7% moisture content left. They were grounded to pass a

1 mm sieve. Lotus rhizome powder (5.0 g) was mixed

with 50 mL of methanol (EMSURE, Germany) for

overnight incubation in darkness at room temperature

(28°C). The mixture was centrifuged (Hettich

Zentrifugen, Malaysia) at 3000 r/min for 15 mins. The

supernatant was separated through filtration with

Whatman No.1 filter paper and was evaporated at 40oC

using a rotary evaporator (Buchi, Malaysia). The yield of

antioxidant extraction of lotus rhizome was calculated

using the following equation:

2.5.2 Total phenolic content (TPC)

Total phenolic content (TPC) in lotus rhizome was

determined using the Folin Ciocalteu method according

to Zhao et al. (2014). Lotus rhizome extract solution of

0.1 mL of 5 mg/mL was mixed with 2 mL distilled water

and 1 mL of Folin Ciocalteu phenol reagent (R&M

Chemical, Malaysia) for incubation in darkness at room

temperature (28°C) for 5 mins. A total of 5 mL of 20%

aqueous Na2CO3 solution (Bendosen, Malaysia) was

added followed by incubation for 60 mins. The

absorbance was measured at 735 nm using UV-Vis

spectrophotometer (Interscience, Malaysia) with distilled

water as blank. Gallic acid (R&M Chemical, Malaysia)

was used as standard. TPC (GAE/g DE) in lotus rhizome

was calculated through a linear regression equation

obtained from gallic acid standard graph.

2.5.3 Total flavonoid content (TFC)

Aluminium chloride coloration method was adopted

for the estimation of total flavonoid content (TFC) in

lotus rhizome according to Zhao et al. (2014). Lotus

rhizome extract solution of 0.6 mL of 10 mg/mL was

mixed with 3.75 mL distilled water and 0.225 mL of 5%

aqueous NaNO3 solution for incubation in darkness at

room temperature (28°C) for 6 mins. A total of 0.45 mL

10% AlCl3 solution (Sigma-Aldrich, USA), 1.5 mL of 1

mol/mL NaOH solution (R&M Chemical, Malaysia) and

0.975 mL of distilled water were added to the mixture

before incubation for 15 mins. The absorbance was

measured at 500 nm using UV-Vis spectrophotometer

(Interscience, Malaysia) with distilled water as blank and

catechin (TGI, Tokyo) as standard. TFC (CE/g DE) in

lotus rhizome was calculated through a linear regression

equation obtained from catechin standard graph.

2.5.4 DPPH radical scavenging activity

DPPH radical scavenging activity of lotus rhizome

extract was measured as in accordance to Zhao et al.

(2014) with slight modification. A series of lotus

rhizome extract solution (0.5 to 3.0 mg/mL) was mixed

with 5 mL of 0.1 µmol/L 2, 2-diphenyl-1-picrylhydrazyl

(DPPH; Sigma-Aldrich, Germany) solution in methanol

for incubation in darkness at room temperature for 30

mins. The absorbance was measured at 517 nm using UV

-Vis spectrophotometer (Interscience, Malaysia) with

methanol as blank. The following equation was used for

the calculation of DPPH free radical scavenging activity:

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Where Acontrol = absorbance of the control and Asample =

absorbance of the sample

A graph of scavenging ability against the

concentration of the sample extract was plotted to

determine the amount of lotus rhizome extract with 50%

scavenging activity (IC50) values.

2.5.5 ABTS radical scavenging activity

Analysis of 2,2'-azino-bis(3-ethylbenzothiazoline-6-

sulfonic acid) (ABTS) radical scavenging activity of

lotus rhizome extract was conducted using Wu et al.

(2011) method. ABTS+ radical solution was prepared by

incubating the mixture of 3 mL of 7 mM ABTS stock

solution (Sigma-Aldrich, USA) and 3 mL of 2.45 mM

potassium persulfate (EMSURE, Germany) at room

temperature for 16 hrs in darkness. The mixture was

diluted with 80% ethanol (HmbG Chemical, Malaysia) to

obtain absorbance of 0.70±0.005 at 734 nm using UV-

Vis spectrophotometer (Interscience, Malaysia). A total

of 0.3 mL of a series of lotus rhizome extract solution

(0.5 to 3.0 mg/mL) was mixed with 2.7 mL of ABTS+

radical solution and incubated for 30 mins. The

absorbance was measured at 734 nm using UV-Vis

spectrophotometer with methanol as blank. The

scavenging ability (%) and IC50 values were determined

as previously described for DPPH.

2.6 Statistical analysis

All analyses were carried out in the triplicate and

data was expressed in mean ± standard deviation form.

Statistical analysis was carried out using one-way

ANOVA and Tukey’s-b using SPSS version 16 (SPSS

Inc., USA).

3. Results and discussion

3.1 Proximate composition

Table 1 shows the raw lotus rhizome contained

86.86% moisture, 1.05% ash, 0.14% crude fat, 2.34%

crude protein, 0.80% crude fibre and 8.81%

carbohydrate. This finding is in accordance with Wang

(2014) findings on lotus rhizome samples. Meanwhile,

Read (1982) reported that lotus rhizome contained 1.70%

protein, 0.10% fat, 9.7% carbohydrate and 1.10% ash.

The variation in the proximate composition of lotus

rhizomes in the present and previous studies may be due

to differences in the maturity level and planting location

of lotus rhizome samples. This finding is supported by

Agunbiade et al. (2017) and Chinomso et al. (2018) on

orange-fleshed sweet potato and on Moringa oleifera

leaves in their studies, respectively.

The moisture content of steamed (89.20%) and

boiled lotus rhizome (91.51%) was significantly different

with raw (86.86%) lotus rhizome (p < 0.05). A similar

result was reported by Bembem and Sadana (2013) and

Okibe et al. (2016) where the moisture content of their

potato and pumpkin leaves were higher after boiled,

respectively.   According to Lola (2009), fibre and other

chemical compounds presented in the vegetables

absorbed water during boiling.

In this study, the moisture content of the deep-fried

lotus rhizome was lowest (15.37%) compared to raw and

other cooked lotus rhizomes. This finding is in

agreement with Shunmugapriya and Kalaiselvan (2017)

who reported that fried garlic possessed the lowest

percentage of moisture content compared to steamed and

boiled samples. The high heat applied during deep-frying

caused the moisture escaped from food through

evaporation (Omotosho et al., 2016; Oke et al., 2017).

On the other hand, the ash content of deep-fried sample

was the highest (3.71%), followed by raw (1.05%),

steamed (0.69%) and boiled sample (0.17%). Boiling

might reduce more ash content than steaming due to the

leaching out of mineral into boiling water (Lola, 2009;

Wang et al., 2012). The ash increment occurred in deep-

fried samples was related to the moisture lost.

Dehydration concentrated the nutrient left in the sample

and thus increased the ash content in the fried product

(Yodkraisri and Bhat, 2012).

There was no significant difference (p > 0.05) found

between crude fat content of raw and steamed (0.11%)

samples and between crude fat content of raw and boiled

(0.06%) lotus rhizome (Table 1). A similar result was

reported by Hwang et al. (2012) on red pepper. A large

increase of crude fat content was found on the deep-fried

lotus rhizome in the present study and this is in

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Lotus rhizome
Proximate composition

Moisture (%) Ash (%) Crude fat (%) Crude protein (%) Crude fibre (%) Carbohydrate (%)

Raw 86.86±0.35c 1.05±0.05b 0.14±0.01b 2.34±0.17b 0.80±0.02c 8.81±0.51b

Steamed 89.20±0.25b 0.69±0.08c 0.11±0.01b 2.22±0.12b 1.01±0.06c 6.76±0.46b

Boiled 91.51±0.53a 0.17±0.01d 0.06±0.01b 0.77±0.05c 2.06±0.07b 5.43±0.46b

Deep fried 15.37±1.90d 3.71±0.25a 31.41±1.07a 8.33±0.38a 12.28±0.20a 28.91±2.67a

Table 1. Proximate composition on a wet weight basis for raw and cooked lotus rhizomes

Mean ± SD, n = 3. Values with different superscript letters in the same column are significantly different at p<0.05

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accordance with Omotosho et al. (2016) on unripe

plantain. Deep-fried food increased its fat content

through extra fat absorption from the frying oil and

decreased its moisture content through moisture escaping

from food due to high heat (Bordin et al., 2013).

The moisture loss and oil uptake of deep-fried lotus

rhizome were 73.88% and 31.27%, respectively. This

finding is in agreement with Manjunatha et al. (2012) on

Gethi (Dioscorea kammonensis kunths) strips. According

to Kita (2014), moisture loss would cause dehydration

which contributed to changes in cell structure and

formation of small channel matrix occupied subsequently

by the frying oil. Vigorous water escaped from vegetable

had limited the oil absorption during the frying process,

causing a higher rate of moisture loss than oil uptake

(Bouchon et al., 2003).

The highest crude protein content was found on deep

-fried (8.33%) lotus rhizome followed by raw (2.34%),

steamed (2.22%) and boiled (0.77%) lotus rhizome. The

large increment in crude protein content of deep-fried

food was contributed by the moisture loss which

concentrated the organic materials left (Vora and

Srinivasan, 2015) and by the hydrolysis of insoluble

protein compound which increased the protein

availability (Reid et al., 2016). Meanwhile, boiling

decreased crude protein content of lotus rhizome, which

is in accordance with the previous studies on potato

(Bembem and Sadana, 2013) and red pepper (Hwang et

al., 2012). Soluble nitrogenous substance leached out

into boiled water when cooked, causing more loss rather

than denaturation (Reid et al., 2016).

Deep frying increased the crude fibre content of

lotus rhizome from 0.80% to 12.28%. Similar results

were observed on four varieties of potato (Murniece et

al., 2011), lotus stem (Vora and Srinivasan, 2015) and

purple flesh potatoes (Tian et al., 2016). This is probably

due to structural damage to the cells, which induced a

marked loss of other liposoluble compounds and

increased fibre content (Sun et al., 2014). Furthermore,

the increase in fibre content in cooked samples were due

to dehydration because of moisture loss (Vora and

Srinivasan, 2015). The highest carbohydrate content was

also found in the deep-fried lotus rhizome, followed by

steamed, raw and boiled lotus rhizome.

3.2 Vitamin C content

Table 2 shows the amount of vitamin C and minerals

in the raw and cooked lotus rhizomes in the present

study. The raw lotus rhizome contained 15.02 mg/100 g

vitamin C. This amount was higher than the vitamin C in

the lotus (Nelumbo nucifera) rhizomes reported by Shad

et al. (2011; 0.26-0.35 mg/g) but lower than USDA

(2016; 44 mg/100 g). The differences probably due to

cultural practice, maturity, preharvest climatic

conditions, harvesting method influenced the vitamin C

level in vegetables as stated by Lee and Kader (2000)

and Duya (2017).

Boiling and deep-frying significantly decreased the

vitamin C content in lotus rhizome. The amount of

vitamin C in the boiled and deep-fried lotus rhizomes in

the present study were 3.80 mg/100 g and 1.45 mg/100

g, respectively. This finding is in contrast with Ikanone

and Oyekan (2014) who reported that boiled Irish potato

and sweet potato lost more vitamin C than the fried

samples.  Meanwhile, previous studies showed that the

steaming cooking method retained more vitamin C in

potato tubers (Bembem and Sadana, 2013), and broccoli,

spinach and lettuce (Zeng, 2013) compared to the boiling

method. This probably due to vitamin C is a heat-

sensitive water-soluble nutrient as reported by

Igwemmar et al. (2013).

Apart from thermal degradation, vitamin C would be

lost through leaching out during boiling (Yuan et al.,

2009). Thus, boiling contributed to the highest reduction

of vitamin C content for lotus rhizome compared to deep

frying as it caused both thermal degradation and leaching

out of vitamin C. Moreover, oxidation of vitamin C

occurred easily in aqueous solution and could be

enhanced by higher temperature, physical damage and

relative humidity (Lee and Kader, 2000). In the deep-

fried sample, the loss of vitamin C was due to the higher

temperature (170oC) applied during frying. The rate of

vitamin C retention in cooked food was influenced by

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Lotus

rhizome

Vitamin C

(mg/100 g)

Amount of mineral (mg/100 g)
K Ca Mg Fe Zn Cu Mn Na P

Raw
15.02

±1.36a

2437.53

±37.95a

151.75

±1.76c

134.61

±1.34b

13.27

±0.32b

5.08

±0.07a

2.64

±0.05a

1.49

±0.02b

74.14

±0.89b

804.63

±5.63b

Steamed
13.40

±1.14a

2512.60

±37.06a

201.20

±1.67b

148.89

±1.31a

24.34

±1.37a

5.55

±0.45a

2.96

±0.45a

2.57

±0.03a

76.97

±1.27a

914.58

±3.29a

Boiled
1.45

±0.31b

617.30

±8.18c

263.27

±1.49a

113.95

±0.61c

12.02

±0.55b

3.52

±0.03b

1.61

±0.01b

2.61

±0.03a

43.70

±0.71d

376.50

±2.04d

Deep fried
3.80

±0.54b

1481.53

±29.92b

92.06

±1.92d

69.19

±1.07d

7.27

±0.73c

2.53

±0.27c

1.29

±0.01b

1.09

±0.01c

52.12

±0.57c

442.28

±4.52c

Table 2. Vitamin C and mineral composition of raw and cooked lotus (Nelumbo nucifera) rhizome.

Mean ± SD, n = 3. Values with different superscript letters in the same column are significantly different at p<0.05

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the size of cut, use of cooking media, time and

temperature of cooking (Severi et al., 1997).

3.3 Mineral composition

Raw lotus rhizome was composed of potassium

(2437.53 mg/100 g), calcium (151.75  mg/100 g), iron

(13.27 mg/100 g), zinc (5.08 mg/100 g), copper (2.64

mg/100 g), manganese (1.49 mg/100 g), sodium (74.14

mg/100 g), and phosphorus (804.63 mg/100 g) as shown

in Table 2. These findings were contradicted with USDA

(2016) which reported that there were about 556 mg

potassium (K), 45 mg calcium (Ca), 1.16 mg iron (Fe),

0.39 mg zinc (Zn), 0.26 mg copper (Cu), 0.26 mg

manganese (Mn), 40 mg sodium (Na) and 100 mg

phosphorus (P) presented in lotus rhizome.

Jongrungruangchok et al. (2010) stated that the minerals

of Moringa oleifera leaves obtained from different

regions in Thailand varied in mineral content because of

several reasons such as cultivated regions, growing

conditions, nature of soil, seasonal changes, genetically

different cultivars and storage conditions. Pongrac et al.

(2016) also found that the amounts of mineral

compounds for grains and sprouts were different from

each other when they were cultivated in tap water or

moderately mineral-rich water.

Three types of trend were observed for the mineral

content in lotus rhizomes in the present study. The trends

were steamed > raw > deep-fried > boiled for K, Na and

P; steamed > raw > boiled > deep-fried for Mg, Fe, Zn

and Cu; and boiled > steamed > raw > deep-fried for Ca

and Mn. According to Ikanone and Oyekan (2014),

boiling caused a higher loss of Zn, Mg, Na and Ca and

lower loss of Cu and Fe for Irish and sweet potato

compared to frying. Contrastingly, boiling caused more

loss for Na and Ca but not for Zn and Mg compared to

frying in the lotus rhizome in the present study. Vora and

Srinivasan (2015) reported that frying reduced Na and Fe

in lotus stem whereas Okibe et al. (2016) reported that

steaming retained K, Na, Ca, Mg, Fe and P better than

boiling as minerals were soluble in water and could leach

out into boiling medium during cooking (Okibe et al.,

2016). The findings in Vora and Srinivasan (2015) and

Okibe et al. (2016) were in accordance with the present

study.

Generally, different type of mineral would undergo

different rate of losses even though they were treated

with the same cooking method. This condition was

contributed by different proportion of soluble salt, which

leach out easily to the water when heating, and insoluble

salt, which retained in the plant when heating (Faboya

and Aku, 1996). However, the increment of mineral

content might occur after the breaking down of plant

tissue which increased the mineral extractability. The

heat applied degraded the antinutrient hindered the

availability of minerals, causing minerals to be found in

the cooked medium (Oulai et al. 2013).

3.4 Antioxidant content

The highest antioxidant extraction yield was

obtained from raw lotus rhizome (4.03%), followed by

steamed (3.29%), boiled (2.23%) and deep-fried (1.19%)

lotus rhizome (Table 3). A similar trend was reported by

Sultana et al. (2008) on peas, carrot, spinach and white

turnip. The antioxidant extraction yield of raw lotus

rhizome was in agreement with Yang et al. (2007) who

reported that the extract yield was ranged from 4 to 5%

when using methanol as solvent. Contrastingly, the

antioxidant extraction yield of lotus rhizome in Wu et al.

(2011) and Zhao et al. (2014) studies were 10.70% and

5.30 to 6.84%, respectively. Soil nature and agro-

climatic condition caused different bioavailability of

extractable components in plant tissue and hence

contributed to the distinct values of extract yield of

antioxidant (Hsu et al., 2006).

Total phenolic content (TPC) of raw lotus rhizome

(50.66 mg GAE/g) was higher compared to the cooked

sample of lotus rhizomes (11.96 – 43.80 mg GAE/g).

This finding is in agreement with Zhao et al. (2014) who

found the TPC of lotus rhizome in their studies ranged

from 31.63 to 70.01 mg GAE/g. Contrastingly, Wu et al.

(2011) reported a lower result with 16.14 mg GAE/g of

TPC in the raw lotus rhizome. The variation in the TPC

was contributed by the distinct environmental and

geological conditions of planting region as reported by

Sultana et al. (2008). This is supported by Podsedek

(2005) who stated that the polyphenols content for

vegetable was varied due to factors such as varieties,

climatic conditions, cultural practices, maturity at harvest

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Lotus rhizome
Antioxidant

extraction yield (%)
Total phenolic content

(mg GAE/g DE)

Total flavonoid
content

(mg CE/g CE)

IC50 values of DPPH
radical scavenging

activity (µg)

IC50 values of ABTS
radical scavenging

activity (µg)

Raw 4.03±0.11a 50.66±4.49a 11.98±0.38a 1027 495

Steamed 3.29±0.13b 43.80±2.94a 10.65±0.65b 1186 569

Boiled 2.23±0.14a 20.78±1.70b 5.13±0.39c 1468 694

Deep fried 1.19±0.03a 11.96±0.85c 2.54±0.13d 1705 799

Table 3. Yield of antioxidant extraction, total phenolic content, total flavonoid content, IC50 values of DPPH and ABTS radical

scavenging activity for raw and cooked lotus (Nelumbo nucifera) rhizome.

Mean ± SD, n = 3. Values with different superscript letters in the same column are significantly different at p<0.05

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and storage conditions. Furthermore, boiling and deep-

frying decreased the amount of TPC of lotus rhizome

which was 20.78 mg GAE/g and 11.96 mg GAE/g,

respectively. Boiling contributed to the loss of

antioxidant content in vegetable due to leaching out of

phenolic compounds into boiling water (Sultana et al.,

2008; Hwang et al., 2012; Sengul et al., 2014).

Meanwhile, high heat applied during frying would lose

most phenolic content compared to other cooking

methods, i.e. which caused thermal decomposition of the

phenolic compound during frying (Turkmen et al., 2005;

Kalkan and Yucecan, 2013).

Total flavonoid content (TFC) of lotus rhizome

showed a similar trend with TPC, at which raw lotus

rhizome (11.98 mg CE/g DE) contained the highest

value of TFC, followed by steamed (10.65 mg/g DE),

boiled (5.13 mg CE/g DE) and deep-fried (2.54 mg CE/g

DE) lotus rhizome. Flavonoid compound which is

soluble in water could leach out during boiling (Bembem

and Sadana, 2012). Thus, boiled vegetable had a lower

TFC than steamed samples. The TFC of raw lotus

rhizome in the present study was in agreement with Zhao

et al. (2014) where the TFC in the lotus rhizome ranged

from 7.33 to 13.21 mg CE/g DE.

3.5 Antioxidant activity

Inhibitory concentration (IC50) values of DPPH

(1027 µg) and ABTS (495 µg) assay for raw lotus

rhizome were the lowest among all samples (Table 3).

The lowest IC50 value indicated the highest antiradical

activity (Leong et al., 2012). Thus, the raw lotus rhizome

contained the highest antioxidant activity compared to

the cooked samples. Meanwhile, Wu et al. (2011)

reported that the IC50 value of DPPH and ABTS assay

for the lotus rhizome extract in their studies were 458.58

µg and 4917.51 µg, respectively. Yang et al. (2007)

suggested that the extracting solvent used affected the

antioxidant activity of plant extract. The solvent

methanol used in the present study was found to have

higher antioxidant extraction yield and hence higher

antioxidant activity compared to the petroleum ether

used by Wu et al. (2011). In addition, the growing region

also influenced the antioxidant content and activity for

lotus rhizome extract (Zhao et al., 2014).

The IC50 value for ABTS assay of lotus rhizome in

the present study was lower than of DPPH due to the

different reaction of ABTS assay and DPPH assay. This

is in accordance with Al-Laith et al. (2015) findings on

three wild medical plants (Aizoon canariense,

Asphodelus tenuifolius and Emex spinosus). For

instances, ABTS cation radical could react with

hydrophilic and lipophilic antioxidant while DPPH

radical can only react with hydrophilic antioxidant

(Boligon et al., 2014).

Zhang and Hamauzu (2004) reported that cooking

reduced the antioxidant components and activity of

broccoli. In the present study, the IC50 value of DPPH

assay for steamed, boiled and deep-fried lotus rhizome

were 1186 µg, 1468 µg and 1705 µg, respectively; while

of ABTS assay were 569 µg, 694 µg and 799 µg,

respectively (Table 3). The steaming method caused the

least loss of antioxidant activity, followed by boiling in

both DPPH and ABTS assay. This is due to polyphenols

compound could dissolve in boiled water, thus boiling

caused a higher reduction in antioxidant activity in

vegetables compared to steaming (Hwang et al., 2012;

Sengul et al., 2014). Meanwhile, Kalkan and Yucecan

(2013) reported that frying caused the highest loss of

antioxidant activity in vegetables. Zhang et al. (2011)

suggested that long term exposure to the high

temperature degraded the antioxidant compound in

bamboo shoot.

4. Conclusion

Methods of cooking affect the nutritional

composition and antioxidant properties of lotus

(Nelumbo nucifera) rhizome. Boiling and deep-frying

brought prominent change on the moisture, ash, crude

fat, crude protein, crude fibre and carbohydrate content

of lotus rhizome whereas steaming brought only a small

change of proximate composition when compared to raw

lotus rhizome. In addition, steamed lotus rhizome caused

the lowest loss of vitamin C and minerals (K, Na, P, Mg,

Fe, Zn, Cu, Ca and Mn) while boiling gave the highest

loss of vitamin C and deep-frying gave the highest loss

of most of the minerals in the lotus rhizome. Deep frying

caused the significant degradation of antioxidant

properties, followed by boiling and steaming. Thus, deep

-frying is not recommended for healthy preparation as it

increased the fat content significantly in the final product

and contributed to a high loss of moisture, vitamin C,

minerals and antioxidant properties of lotus rhizome.

Overall, steaming is considered as the best cooking

methods for lotus rhizome as it retained proximate

composition, vitamin C, minerals, TPC, TFC, and

antioxidant activity better than boiling and deep-frying.

Conflict of Interest

The authors declare no conflict of interest.

Acknowledgments

Authors would like to thank the Faculty of Fisheries

and Food Science, Universiti Malaysia Terengganu for

the funding and the laboratory staff for their technical

assistance in this study.

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7 Kaedah (Adab-adab)
Salafus Soleh Dengan

Nas-Nas Mutashabihat

al-Imam Hujjat al-Islam al-Mujaddid

Abu Hamid Muhammad al-Ghazali

al-Shafi’e al-Ash’ari (505H)

Kitab: Iljam al-’Awam ‘an Ilm al-Kalam

www.penuntutilmu.com 1

Abdullaah Jalil
Universiti Sain Islam Malaysia (USIM)

Pendahuluan
• Imam al-Ghazali telah menggariskan panduan

yang sangat jelas dan mantap bagi orang awam
khasnya dalam beradab dengan nas-nas
mutashabihat agar tidak tergelincir dari hakikat
pegangan generasi Salafus Soleh di dalam
kitabnya “Iljam al-‘Awam ‘an ‘Ilm al-Kalam”.

• Kitab “Iljam al-Awam” adalah kitab terakhir  yang
ditulis oleh beliau di dalam bidang aqidah bagi
mempertahankan manhaj ASWJ Al-Ashairah di
dalam perkara ini.

• Kitab ini ditulis bagi menolak dakwaan golongan
Hashwiyyah (Mujassimah/Mushabbihah) yang
mengambil makna-makna zahir nas-nas
Mutashabihat sehingga mereka menyifatkan
Allah dengan sifat-sifat anggota dan jisim tetapi
menyangka bahawa mereka berpegang dengan
pegangan Salafus Soleh.

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Imam al-Ghazali berkata di awal kitab ini:

“ Amma ba'd (Adapun selepas tu):

sesungguhnya engkau telah bertanya kepadaku -
semoga Allah memberi petunjuk kepadamu -
tentang khabar-khabar (al-Quran dan al-Sunnah)
yang boleh membawa kepada sangkaan Tashbih
kepada orang-orang yang lemah dan jahil dari
kalangan al-Hashwiyyah yang sesat apabila mereka
mengiktiqadkan pada Allah dan sifat-sifatNya
dengan sesuatu yang Maha Tinggi lagi Maha Qudus
(Suci) Dia daripadanya seperti rupa, tangan, kaki,
turun, berpindah, duduk di atas Arash dan tetap di
atasnya dan apa yang seumpamanya lantaran
mereka mengambil makna-makna zahir khabar-
khabar (al-Quran dan al-Sunnah), dan (dalam masa
yang sama) mereka menyangka bahawa apa yang
mereka i'tiqadkan adalah mereka i'tiqad para
Salaf......”

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Berikut adalah tujuh (7)
prinsip yang telah

ditakhrijkan oleh beliau
berdasarkan al-Quran dan al-

Sunnah serta amalan dan
perkataan para Salafus Soleh

berkenaan hal ini.

www.penuntutilmu.com 4

Imam al-Ghazali:
7 Kaedah (Adab-adab)
Salafus Soleh Dengan

Nas-Nas Mutashabihat

1 al-Taqdis

(Mentaqdiskan)

 التقديس

Mensucikan Allah daripada

jismiyyah (sifat-sifat jisim) dan

perkara-perkara yang berkaitan

dengannya.

2 al-Tasdiq

(Membenarkan)

 التصديق

Beriman dengan sabdaan Nabi 

dan apa yang Baginda sabdakan

adalah haq; dan Baginda dalam

sabdaan Baginda adalah benar; dan

apa yang Baginda katakan adalah

benar dalam bentuk yang Baginda

katakan dan maksudkan.

3 al-I’tiraf bi al-‘Ajz

(Mengiktiraf

kelemahan)

بالعجز االعتراف

Hendaklah seseorang itu mengakui

dan mengiktiraf bahawa

pengetahuan maksud hakikat

sebenar adalah di luar

kemampuannya; dan pengetahuan

maksud hakikat sebenar itu

bukanlah tanggungjawab dan

pekerjaannya (tidak diperintah oleh

Shara’ untuk mengetahuinya).
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4 al-Sukut

(Berdiam diri)

 السكوت

Tidak bertanyakan makna sebenarnya

dan tidak mendalami maknanya; dan

hendaklah dia tahu bahawa

pertanyaannya mengenai maknanya

adalah bid’ah; dan pendalaman

maknanya boleh membahayakan

agamanya; dan dia boleh terjebak

dalam kekufuran oleh sebab itu.

5 al-Imsak

(Menahan)

 اإلمساك

Tidak menukar bentuk nas-nas

mutashabihat tersebut dengan

ditambah  dan dikurangkan

sebahagiannya; atau dikumpulkan

atau diasingkan; dan tidak

menukarkannya

(menterjemahkannya) ke bahasa yang

lain ; bahkan nas-nas (al-Quran dan

hadis) tersebut tidak dibaca melainkan

dengan bentuk, lafaz dan ibarat

(susunan) yang asal.

Imam al-Ghazali:
7 Kaedah (Adab-adab)
Salafus Soleh Dengan

Nas-Nas Mutashabihat

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6 al-Kaff

(Menegah)

 الكف

Menegahkan dirinya daripada

menyelidik dan memikir

tentangnya.

7 al-Taslim li ahlih

(Menyerahkan

kepada yang

ahli)

 التسليم ألهله

Kalaulah seseorang itu tidak mampu

memahami nas-nas tersebut kerana

kelemahan dirinya, hendaklah dia

tidak mengi’tiqad yang demikian

(kelemahan) kepada Rasulullah ,

para anbiya’, siddiqin dan awliya’.

Imam al-Ghazali:
7 Kaedah (Adab-adab)
Salafus Soleh Dengan

Nas-Nas Mutashabihat

www.penuntutilmu.com 7

Nas Arab

www.penuntutilmu.com 8

Sedikit Ulasan
• Pada pandangan penulis, huraian al-Imam al-

Ghazali adalah huraian yang terbaik dalam
menggambarkan kaedah dan adab-adab para
Salafus Soleh apabila mereka berdepan dengan
nas-nas Mutashabihat. Ia adalah karamah
ma’nawiyyah yang dikurniakan Allah kepada beliau.

• 7 kaedah ini adalah merupakan hakikat pegangan
para Salafus Soleh yang perlu dipegang dengan
kukuh oleh masyarakat awam agar mereka tidak
tergelincir ke dalam fitnah-fitnah ahli-ahli bid’ah al-
Hashwiyyah yang masih wujud sehingga hari ini.

• Akhir kata, marilah kita sama-sama membaca al-
Fatihah dengan niat sebagai hadiah kepada imam
kesayangan kita – al-Imam al-Ghazali - dan semoga
Allah  mengurniakan kita limpahan kurniaan yang
telah Dia kurniakan kepada al-Imam al-Ghazali agar
kita terus berada di atas jalan Ahli Sunnah dan
Jamaah (al-Ashairah dan al-Maturidiyyah) sehingga
bertemu-Nya. Amin.

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