Effect of pretreatment on oxalate content and physicochemical properties of taro starch tuber grown in North Sumatra, Indonesia

Abstract

Oxalate acid is one of the most common antinutrients found in many agricultural materials. Anti-nutritional factors are compounds capable of causing a reduction in the utilisation of nutrients when consumed as foods. Limitations in the use of food and feed occur due to the presence of these endogenous substances. This study investigates the effect of soaking in sodium chloride (NaCl) and boiling treatments on oxalate content in taro grown in North Sumatra. The results showed that all treatments had no significant effect on yield value. The soaking at 5% NaCl and boiling significantly reduced the oxalate acid content in direct relation to the longer soaking period and boiling time, respectively. The study found that boiling treatment for 5 min gave the best result in oxalate acid reduction, with 96.63% remaining at 42.42 mg/100 g compared to the fresh sample (1272.56 mg/100 g). Among all treated samples, only samples boiled for 5 min were considered safe to consume based on their toxicity level, which was below 50 mg/100 g but still not recommended since the value was above 25 mg/100 g. Further treatments need to be considered to lower the amount to below its safe level. All treatments showed no significant difference in colour property, which indicated that the treatments did not affect the sample characteristics, but the total starch content of the soaked sample was significantly reduced due to starch diffusion in water.

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Transactions on Science and Technology Vol. 11, No. 4-2, FSMP241, 2024
Mansoor et al., 2024. Transactions on Science and Technology. 11(4-2), FSMP241
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Effect of pretreatment on oxalate content and
physicochemical properties of taro starch tuber
grown in North Sumatra, Indonesia
Mansoor Abdul Hamid1,2#, Ivy Cyril2, Yeap Chi Hong2, Oslida Martony3,
M Yusuf Alfian Rendra Anggoro KR4, Titi Mutiara5
1 Food Security Research Laboratory, Faculty of Food Science and Nutrition, Universiti Malaysia Sabah, Jalan UMS, 88400 Kota Kinabalu, Sabah, MALAYSIA.
2 Faculty of Food Science and Nutrition, Universiti Malaysia Sabah, Jalan UMS, 88400 Kota Kinabalu, Sabah, MALAYSIA.
3 Jurusan Gizi dan Dietetika, Politeknik Kesehatan Kemenkes Medan, Jl. Jamin Ginting, Km 13.5, Kel. Lau Chi Medan, Tuntung 20136 Medan, Sumatera, INDONESIA.
4 Department Management, Faculty of Economics and Business, Universitas Muhammadiyah Makassar, Jalan Sultan Aluadin No.259, Gunung Sari District,
Rappocini District, Makasar City South Sulawesi, INDONESIA.
5 Department of Culinary and Fashion Education, Faculty of Engineering, Universitas Negeri Malang, Jalan Semarang 5, 65145 Malang, Jawa Timur, INDONESIA.
#Corresponding author: Email: chot@ums.edu.my; Tel: +6088-320000; Fax: +6088-320259.
ABSTRACT Oxalate acid is one of the most common antinutrients found in many agricultural materials. Anti-nutritional
factors are compounds capable of causing a reduction in the utilisation of nutrients when consumed as foods. Limitations in
the use of food and feed occur due to the presence of these endogenous substances. This study investigates the effect of
soaking in sodium chloride (NaCl) and boiling treatments on oxalate content in taro grown in North Sumatra. The results
showed that all treatments had no significant effect on yield value. The soaking at 5% NaCl and boiling significantly reduced
the oxalate acid content in direct relation to the longer soaking period and boiling time, respectively. The study found that
boiling treatment for 5 min gave the best result in oxalate acid reduction, with 96.63% remaining at 42.42 mg/100 g compared
to the fresh sample (1272.56 mg/100 g). Among all treated samples, only samples boiled for 5 min were considered safe to
consume based on their toxicity level, which was below 50 mg/100 g but still not recommended since the value was above
25 mg/100 g. Further treatments need to be considered to lower the amount to below its safe level. All treatments showed
no significant difference in colour property, which indicated that the treatments did not affect the sample characteristics, but
the total starch content of the soaked sample was significantly reduced due to starch diffusion in water.
KEYWORDS: Taro; Oxalate; Sodium chloride; Soaking; Boiling
Received 16 December 2024 Accepted 23 December 2024 Online 27 December 2024
© Transactions on Science and Technology
Original Article
INTRODUCTION
Anti-nutritional factors are compounds capable of causing a reduction in the utilisation of
nutrients when consumed as foods. Limitations in the use of food and feedstuff occur due to the
presence of these endogenous substances (Joshi et al., 2020). Their existence as a diverse range of
natural compounds is also said to be the dominant obstacle to the wider utilisation of many tropical
plants as they can reduce nutrient utilisation, in particular vitamins, proteins, and minerals, thereby
resulting in the prevention of optimal exploitation of the nutrients present in the foods and
subsequently causing a reduction in the nutritive value of the foods. If the nutritional value of food
ingredients is meant to be preserved, they must be reduced or eliminated. They are present in many
food substances in varying amounts, which are dependent on the chemicals employed in growing the
crops, the chemicals used during storage for the purpose of preserving the food substances, the type
of food, and the mode of propagation. However, large consumption of these antinutrients has been
proven to have deleterious effects on health, such as headaches, rashes, bloating, nausea, and
nutritional deficiencies. There are many types of antinutrients in plants, such as phytate, alkaloids,
cyanogenic glycosides, gossypol, and oxalates. In the case of oxalate, the consumption of excessive
amounts can induce hyperoxaluria, increase the risk of calcium oxalate stones, and even be fatal to
humans (Saiener et al., 2021). Humans should limit the intake of oxalate with a safety limit between
40 and 50 mg per day, especially patients with kidney stone problems, who are advised to limit their
total oxalate intake not to exceed 10 mg per day according to Brown et al. (2009). Therefore,

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determining the oxalate content of foods prior to their sale in marketplaces is crucial. According to
Abdel-Moemin (2014), foods are classified as having low oxalate content when less than 10 mg/100 g
and as having high oxalate content when more than 50 mg/100 g.
Oxalates are tasteless and odourless but we consume this compound every single day, and they
exist naturally in human bodies and in many fruits and vegetables, especially seeds and nuts. This
compound is widely distributed in plants in two forms, namely water-soluble and water-insoluble
forms, where the former contains sodium, potassium, and ammonium oxalate, while the latter
consists of calcium, magnesium, and iron oxalate (Joshi et al., 2020). The ability of oxalates to form
insoluble salts with divalent cations like magnesium or calcium is the dominant reason why large
dietary intake poses a considerable health concern to the public (Saiener et al., 2021). The most
dominant health effect of consuming large amounts of foods high in oxalates is the formation of
calcium oxalate (CaOx) kidney stones. Kidney stones are said to be one of the most painful and
common disorders of the urinary tract. This disorder starts with the stimulation of precursors to CaOx
kidney stones, which are urinary CaOx crystals, as a result of increased consumption of meals high
in oxalate content (Kumar et al., 2021). The most widely seen urinary stone is the calcium oxalate stone
(about 80%), with approximately 70% of stones containing calcium oxalate.
Due to its negative effect on human health, there is an intention to reduce its concentration to a
level that is safe to consume. One of the methods to inactivate or reduce oxalate in different foods is
through soaking. According to Saleh (2019), soaking the taro corm chips for 60 min using a salt
solution of calcium chloride of 5% was considered the optimal conditions to reduce their amount of
oxalate, whereby the content of oxalate in the taro corm chips showed a significant decrease from
294.3 mg/100 g to 35.1 mg /100 g. Furthermore, cooking by boiling is also used to inactivate or reduce
the oxalate content in different foods. According to the study carried out by Wanyo (2020), the total,
soluble, and insoluble oxalate contents of oxalate were generally reduced after the cooking by boiling
process. Moreover, the combination methods of soaking and boiling can be used to inactivate or
reduce the oxalate content in different foods as well. This can be seen from the study carried out by
Kumoro et al. (2014), in which soaking the taro corm chips in a 10% w/w baking soda solution for 2 h
prior to boiling them for 60 min at 90 °C could best reduce the content of calcium oxalate in the taro
corm chips. In this study, the effect of soaking with 5% NaCl and boiling treatment were investigated
based on the oxalate content and physicochemical properties of taro samples.
METHODOLOGY
Sample Collection and Preparation
The taro tubers planted for 24 months were harvested from a farm located at Tanjung Morawa,
North Sumatra, at a latitude of 3.5300°N and a longitude of 98.8078°E. The samples were then taken
to the Medan Healthy Polytechnic Laboratory for pretreatment before further analysis. The tuber
samples were peeled with a stainless-steel knife by removing the peel up to 1.0 ± 0.1 cm in thickness.
The peeled taro was washed properly with tap water and rinsed with distilled water before being
cut into small pieces (2 x 2 x 2 cm3). Pretreatment was done to the samples by soaking them in 5%
sodium chloride (NaCl) for 30 and 60 min, respectively, before rinsing with tap water. Another
pretreatment was boiling for 2 min and 5 min, respectively. All treated samples were then rinsed
and control sample with the same dimension (without treatment) were subjected to a drying process
in the cabinet dryer set at 60 °C for 16-18 h until the moisture content was consistent. The samples
were then ground and sieved into a powder with an 80 μm mesh. The weight of all samples was
measured to determine the yield recovery by using Equation 1.

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Yield recovery (%) = Weight of dried sample X 100 (1)
Weight of fresh sample
Oxalate Acid Determination
The taro samples were analysed for total, soluble, and insoluble oxalate in 0.50 ± 0.01 g of each
finely ground sample in duplicate using the method outlined by Savage et al. (2000). Insoluble oxalate
content (as calcium oxalate) was calculated by difference. Soluble oxalate was extracted with 40 mL
of nanopure water and incubated in a water bath at 80 °C for 15 min. Total oxalate was extracted
using 40 mL of 0.2 M HCl at 80 °C for 15 min. Extracted supernatants were filtered through a 0.45 mm
cellulose nitrate filter, followed by chromatographic separation and analysis using a Rezex ROA ion
exclusion organic acid column (Phenomenex).
Physicochemical Analysis
Physicochemical analysis of the taro samples included determination of moisture content, colour
and total starch. Moisture content was determined according to AOAC by the oven method (AOAC,
2000). The 2 g of sample was weighed into the crucible and weighed together with the crucible as B.
The crucible was put into an oven at 103°C overnight. Then, the crucible was cooled in a desiccator
and weighed again after dried. The difference in the weight of the sample before and after dried was
calculated as moisture content. Meanwhile, colour analysis was conducted according to the method
of Ng et al. (2018) with minor modifications using the colorimeter (HunterLab ColorFlex) with
CIELAB system. The total starch content analysis was done according to the method of Nilusha et al.
(2021) and the absorbance was measured by using the UV-Vis spectrophotometer at 490 nm at room
temperature.
Statistical analysis
Data analysis was performed using Statistical Package for Social Sciences (SPSS) version 28 with
significance levels set at p<0.05. Sensory evaluation test ranking data were analysed using Friedman’s
test, one-way ANOVA test and Tukey post hoc test.
RESULTS AND DISCUSSION
Yield Recovery
There was no significant difference (p>0.05) in the yield recovery of the treated samples in the
range of 15.21%–15.82%, indicating that the treatments did not influence the yield recovery. Based on
the yield obtained, the taro is considered good since most agricultural materials obtained a recovery
yield of 10–15% (Sadia et al., 2015). During drying treatment, free water in the sample will evaporate
after passing through the cell in capillary movement to the sample surface before hot air removes it
into the environment through the evaporation process (Jian & Jayas, 2021).
Oxalate Content
Table 1 indicates that the oxalate acid content in different treatments was significantly different
(p<0.05). Overall, the treated samples were significantly reduced in oxalate content as compared to
fresh samples. Fresh samples with the highest total oxalate acid (1272.56 mg/100 g) significantly
reduced (p<0.05) in oxalate content with the treatment given. The sample that was boiled for 5 min
significantly had (p<0.05) the lowest oxalate value (42.82 mg/100 g).

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Table 1. Reduction of oxalate content in taro by soaking and boiling treatments.
Taro sample
Total oxalate acid
(mg/100 g DM)
Soluble
(mg/100 g DM)
Insoluble
(mg/100 g DM)
Fresh
1272.56 ± 38.32a
133.44 ± 4.63a
1138.10 ± 40.24a
Soaking; - 30 min
377.87 ± 22.33b
76.41 ± 28.28b
301.07 ± 23.22b
- 60 min
149.10 ± 22.31c
40.67 ± 23.36c
108.43 ± 13.89c
Boiling; - 2 min
103.51 ± 19.92d
27.29 ± 5.71d
75.83 ± 16.31d
- 5 min
42.82 ± 7.10e
8.56 ± 1.90e
34.21 ± 2.62e
*Values are expressed as mean ± standard deviation; different letters indicate statistically significant
difference (p<0.05).
The longer soaking time of the taro corm chips in the added calcium salt solution is a favourable
condition for the leaching of the soluble oxalate (Saleh, 2019). The boiling treatment gave the best
effect in reducing oxalate acid content due to the fact that the high temperature of cooking by boiling
can result in the collapse of the calcium oxalate-containing cells and subsequently cause the oxalate
structure to break down. This is because high temperatures can result in better breakdown of the
spinach, and thus, the release of oxalic acid from the spinach is improved. Overall, from the treatment
given to the samples, only boiling for 5 min was considered to give less than 50 mg/100 g sample,
which is safe to consume based on toxicity level, but it is still not recommended since it is still higher
than 25 mg/100 g, which can cause kidney stones. So further treatments should be considered for this
taro sample to ensure it is safe for consumption.
Physicochemical Properties
Based on Table 2, it was indicated that all the control and treated taro samples had similar moisture
content (p>0.05) ranging from 9.27% to 9.49%, which has normal moisture content for flours with less
than 10% (Kumoro et al., 2014). The colour characters of all treated taro samples showed no significant
difference (p>0.05) based on L*, a*, and b* values.
Table 2. Moisture content, colour value and starch content of treated taro samples.
*Values are expressed as mean ± standard deviation; different letters indicate statistically significant
difference (p<0.05).
According to Jadhav & Nirval (2019), the colour of soy flour treated by soaking and boiling did
not have any significant effect on their moisture content and colour characteristics. The starch content
of all samples in the range of 69.13% to 77.91% showed that all samples had no significant difference
except for the sample treated by soaking with 5% NaCl for 60 min. Nagar et al. (2021) found that starch
content in the taro sample was in the range of 70–80%, but treatments of soaking and boiling showed
a decrease in their starch content, as observed by Soudy et al. (2010), who found that soluble
components in water such as protein and ash significantly decreased due to soaking treatment. It
Taro sample
Moisture
content (%)
Colour
L* a* b*
Starch
content (%)
Fresh
9.45 ± 0.08a
93.95 ± 0.08a
0.22 ± 0.05a
9.66 ± 0.60a
77.91 ± 2.15a
Soaking; - 30 min
9.27 ± 0.07a
91.99 ± 0.05a
0.25 ± 0.03a
9.60 ± 0.56a
73.89 ± 1.08ab
- 60 min
9.45 ± 0.05a
92.77 ± 0.06a
0.25 ± 0.05a
9.61 ± 0.63a
69.13 ± 3.01b
Boiling; - 2 min
9.34 ± 0.08a
92.94 ± 0.07a
0.22 ± 0.04a
8.86 ± 0.43a
76.21 ± 2.25a
- 5 min
9.49 ± 0.03a
93.53 ± 0.05a
0.23 ± 0.02a
9.12 ± 0.67a
76.33 ± 2.18a

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seems that this also occurred to the starch component in this study. Boiling time showed significant
reduction for soluble components that were boiled for up to 20 min (Amon et al., 2014), but in this
study, the boiling time for up to a maximum of 5 min did not show a significant effect in starch
reduction.
CONCLUSION
Based on the oxalate acid content in the treated sample, the sample treated by boiling for 5 min
was reduced to 3.37% which is considered safe to consume because the daily limit of oxalate is 40 to
50 mg. The normal level of urine oxalate excretion is less than 50 mg per day (mg/day). However,
the treatments should be given at a lower dose than 25 mg/100g DM since a higher level of urine
oxalate may increase the risk of developing kidney stones. The risk of stone formation seems to
increase even at levels above 25 mg/day, which is considered a normal level. Therefore, further
treatments and modifications must be made to the sample to lower the oxalate acid content to 10 mg
per 100 g of sample. The combination of soaking and boiling pretreatment should be considered in
future studies with a variety of parameters such as soaking time, boiling time, and NaCl
concentration. Another parameter to look into is the size dimension of the taro slice, it can be made
smaller to produce the most effective treatment effects. Additionally, baking is one of the methods
used to inactivate or reduce the oxalate content in food.
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