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\begin{document}

\title{Composition and Physicochemical Properties of Corn Wax}



\author[1]{Bao Kang}%
\author[1]{Yameng Liu}%
\author[1]{Ruinan Yang}%
\author[1]{Shaohua Liang}%
\affil[1]{Affiliation not available}%


\vspace{-1em}



  
  \date{May 08, 2024}


\begingroup
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\selectlanguage{english}
\begin{abstract}
Corn wax, as a kind of vegetable wax, is a by-product of the corn oil
industry. In this study, the corn wax was purified from the corn oil
refineries. The composition and physicochemical properties of corn wax
were studied to provide theoretical guidance for the production and
application of corn wax. The results showed that the purity of corn wax
was higher than 95\%, and the corn wax ester ranged from C42 to C58,
with C46, C44, and C48 being predominant. The fatty acid carbon atom of
corn wax was in the range of 16-30, with higher percentages of C20, C22,
and C24. The fatty alcohol of corn wax was in the range of C20-C32 and
dominated by C22, C24, C30, and C23. The physicochemical properties of
corn wax were also determined and compared with other vegetable and
animal waxes to get a more comprehensive understanding of corn wax. The
results showed that corn wax was a green and healthy natural resource
with great potential for application in food, health care, and medicine.%
\end{abstract}%



\sloppy


\textbf{*Composition and Physicochemical Properties of Corn Wax}

Bao Kang, Yameng Liu, Ruinan Yang and Shaohua Liang*

College of Food Science and Engineering, Henan University of Technology,
Lianhua Road 100, Zhengzhou 450001, Henan Province, P. R. CHINA

Correspondence to: Shaohua Liang, E-mail: lsh@haut.edu.cn.

\textbf{Abstract:} Corn wax, as a kind of vegetable wax, is a by-product
of the corn oil industry. In this study, the corn wax was purified from
the corn oil refineries. The composition and physicochemical properties
of corn wax were studied to provide theoretical guidance for the
production and application of corn wax. The results showed that the
purity of corn wax was higher than 95\%, and the corn wax ester ranged
from C42 to C58, with C46, C44, and C48 being predominant. The fatty
acid carbon atom of corn wax was in the range of 16-30, with higher
percentages of C20, C22, and C24. The fatty alcohol of corn wax was in
the range of C20-C32 and dominated by C22, C24, C30, and C23. The
physicochemical properties of corn wax were also determined and compared
with other vegetable and animal waxes to get a more comprehensive
understanding of corn wax. The results showed that corn wax was a green
and healthy natural resource with great potential for application in
food, health care, and medicine.

\textbf{Keywords:} Vegetable wax; Corn wax; Compositions;
Physicochemical properties

\textbf{Introduction}

Corn or maize (\emph{Zea mays L.} ) is an important cereal crop and is
widely grown worldwide (Wang \& Hu, 2021). China and United States are
the major producers and consumers. The global corn production and
consumption in 2020 were 1115 and 1140 million tons, respectively. While
the production and domestic consumption of China were 260 and 285
million tons, respectively. Due to the relatively large germ of corn,
corn contains higher oil content than other commercial cereals.
Therefore, corn might be used as a source of vegetable oil as well as a
staple food.

Corn oil contains high levels of unsaturated fatty acids (86\%), and the
percentage of linoleic acid is about 60\%. In addition, corn oil is
recognized as an ideal healthcare oil due to the highest level of
unsaponifiable matters (1.3\%-2.3\%) (Stamenkovi\selectlanguage{polish}ć \selectlanguage{english}et al., 2020). As the
principal unsaponifiable substances, tocopherol and phytosterols play a
significant role in regulating the level of cholesterol and preventing
cardiovascular diseases (Marinho et al., 2019). The nutritional benefits
force the popularity of corn oil, and the global corn oil market is
projected to reach 7.2 billion US dollars by the year 2022. Apart from
the desirable nutritional components, crude corn oil also contains some
undesirable ingredients such as waxes, pigments, and free fatty acids.
These components are needed to be removed by appropriate refining
processes. As an ester of a long-chain acid and long-chain alcohol, wax
could crystallize at low temperatures and cause turbidity in oils. Wax
content in corn oil is in the range of 150-500 mg/kg. To ensure the
physical stability of corn oils at low temperatures, a dewaxing or
winterization process is required to remove wax from corn oil.

Vegetable wax is an essential industrial resource. It can regenerate and
can be used as a polishing agent, protective agent, and emulsifier for
manufacturing fiber. The processing and the application of vegetable wax
such as carnauba wax (CW), sunflower wax (SW), rice bran wax (RBW), flax
wax, and lacquer wax have gradually become research hotspots. Vali et
al. (2005) have studied the composition of purified RBW, and the results
showed that the physicochemical characteristics of the purified RBW were
comparable to CW, which made RBW could be used as a potential substitute
for CW. RBW could be used as a pastry release agent, chewing gum
plasticizer, or dibble coating to enhance the shelf-life of fruit
(Abhirami et al., 2020). Lozhechnikova et al. (2017) developed a simple
method to produce water-based wax dispersions using CW particles and
zinc oxide nanoparticles. Oregel-Zamudio et al. (2017) combined the
candelilla wax (CLW) edible film with \emph{Bacillus subtilis} for the
first time and found that it could effectively extend the shelf life of
strawberries. Patel et al. (2015) identified the critical gel
concentration of three vegetable waxes, and use a rheological
characterization to gain new insights into the gelation behavior of
natural waxes.

As a by-product of the corn oil refining industry, the production of
corn wax presents a gradual increasing trend. However, the properties of
corn wax were rarely studied. In industry, the utilization rate of crude
corn wax was shallow. Only a tiny part of the crude corn wax was
utilized after rough processing, and the rest was directly discarded,
resulting in a tremendous waste of resources. Therefore, it is necessary
to study the composition and physicochemical properties to understand
the actual value of corn wax to guide industry production. Crude corn
wax contains neutral fats, waxes, phospholipids, free fatty acids,
pigments, and proteins. In this study, corn wax was isolated and
purified from crude corn wax obtained from corn oil refineries. Then the
compositions of chain fatty esters, fatty acids, and fatty alcohols were
analyzed by the GC method. The physicochemical properties were also
characterized to provide data support for the comprehensive utilization
of corn wax.

\textbf{Materials and Methods}

\textbf{Materials and chemicals}

The crude corn wax samples (n=30) were supplied by Sanxing corn industry
technology Co., Ltd. (Shandong, China). Potassium hydroxide, sodium
hydroxide, potassium iodide, phenolphthalein, soluble starch, potassium
dichromate, cyclohexane, sodium thiosulfate, thiourea, ascorbic acid,
and n-hexane were purchased from Tianjin Kemiou Chemical Reagent Co.,
Ltd. (Tianjin, China). Chloroform, hydrochloric acid, nitric acid,
perchloric acid, sulfuric acid, and glacial acetic acid were purchased
from Luoyang Chemical Reagent Factory (Luoyang, China). Iodine
monochloride was purchased from Chron Chemical (Chengdu, China). Hexane
was of chromatographic purity, and the other reagents were of analytical
purity.

\textbf{Purification of corn wax from the crude corn wax}

Corn wax was purified by solvent defatting and bleaching, according to
the previous paper. Crude corn wax (180 g) was dissolved in acetone (900
mL), and the mixture was agitated and refluxed at 50\selectlanguage{ngerman}°C for 70 min in a
water bath. Then the mixture was cooled to room temperature, and the
insoluble wax was filtrated off by a water flow filter. The solvent of
defatted wax was removed by evaporation.

Bleaching must be carried out to remove the pigments and other
impurities in the defatted wax. The composite adsorbent made up of
active carbon and clay at a ratio of 4.5:1 (w/w) was used as the optimal
adsorbent. The defatted corn wax was put into a 100 mL three-port flask,
and the adsorbent was added to the flask at the dosage of 21\% (w/w).
The defatted wax was decolorized under vacuum at 89°C for 30 min. Then
the mixture was filtered immediately at 89°C for 120 min through a
Buchner funnel. The filtrate was poured into a mold and cooled to room
temperature. Finally, the refined corn wax product could be obtained.

\textbf{Gas chromatography of wax ester}

The purified corn wax (0.05 g) and n-hexane (6 mL) were placed in a 10
mL test and shaken until the wax was completely dissolved. Then mixture
sample (1 mL) was used to analyze the corn wax esters composition. The
corn wax esters composition was determined by gas chromatography (GC)
analysis using Agilent 7890A and a flame ionization detector (Agilent,
USA). The separation of wax esters was carried out on DB-1HT
dimethyl-polysiloxane non-polar column (28 m × 250 \selectlanguage{greek}µ\selectlanguage{english}m \selectlanguage{ngerman}× 0.1 \selectlanguage{greek}µ\selectlanguage{english}m). The
initial column temperature was 150\selectlanguage{ngerman}°C and held for 1 min, then increased
to 270\selectlanguage{english} at a rate of 25\selectlanguage{english}/min. Finally, the column temperature was
increased to 360\selectlanguage{english} at a rate of 5\selectlanguage{english}/min and maintained for 10 min. The
temperature of the injection and detector was 300\selectlanguage{english} and 350\selectlanguage{english},
respectively. The injection volume was 1 \selectlanguage{greek}µ\selectlanguage{english}L in spilt mode at a ratio of
20:1. Fatty acid esters were identified based on the retention time of
the standard and quantified by the peak area normalization method.

\textbf{Saponification of wax ester}

Saponification was carried out to release the fatty acid and fatty
alcohol of wax ester according to a previous study with a little
modification. Wax (1.0 g) and 30\% KOH in isopropanol (40 mL) were mixed
in a 100 mL flask. The mixture was refluxed at 100\selectlanguage{ngerman}°C for 6 h, and vacuum
evaporated to remove the solvent. Then 50 mL ethyl acetate was added and
mixed with the residue under stirring at 50\selectlanguage{english} for 2 h. The filtrate
(fatty alcohols) and filter cake (fatty acid salts) were obtained by
filtering. The filter cake was washed with ethyl acetate (3 x 20 mL),
and the filtrate was collected to analyze the composition of fatty
alcohols. The filter cake was acidified with 30 mL 30\% HCL at 50\selectlanguage{english} for 1
h. 20 mL distilled water was added to the acidified mixture, and the
fatty acids were extracted with ethyl acetate. The combined extract was
washed with water to neutral pH, and the ethyl acetate layer was dried
over anhydrous sodium sulfate. The ethyl acetate was removed by vacuum
evaporation, then the fatty acids were derivatized with boron
trifluoride for GC analysis. The filtrate was dried over anhydrous
sodium sulfate, and the composition of fatty alcohols was also analyzed
by GC.

\textbf{GC condition for fatty acids analysis}

The fatty acid composition was determined as methyl ester by GC analysis
using Agilent 7890A and a flame ionization detector (Agilent, USA). The
fatty acid methyl esters were separated on an HP-88 chromatographic
column (100 m x 250 \selectlanguage{greek}µ\selectlanguage{english}m \selectlanguage{ngerman}× 0.2 \selectlanguage{greek}µ\selectlanguage{english}m). The temperature was increased from
100 to 240\selectlanguage{ngerman}°C at a rate of 3\selectlanguage{english}/min and maintained for 40 min at 240degC.
The injection volume was 1 \selectlanguage{greek}µ\selectlanguage{english}L. The temperature of the injection and
detector was both 250. The nitrogen was used as the carrier gas, and
the split ratio was 10:1. The fatty acid methyl esters were identified
by the retention time and quantified by the peak area normalization
method.

\textbf{GC condition for fatty alcohols analysis}

Fatty alcohols analysis was carried out on Agilent 7890A equipped with a
flame ionization detector (Agilent, USA), and chromatographic column
DB-1HT (28 m \selectlanguage{ngerman}× 250 \selectlanguage{greek}µ\selectlanguage{english}m \selectlanguage{ngerman}× 0.1 \selectlanguage{greek}µ\selectlanguage{english}m) was used to separate fatty alcohols.
Analyses were performed under the following temperature program: the
initial temperature was 100  and held for 1 min; increased to 220 at a
rate of 50\selectlanguage{ngerman}°C/min; increased to 290°C at a rate of 15°C/min; increased to
320°C at a rate of 40°C/min and held for 6 min; increased to 360°C at a
rate of 8°C/min and held for 10 min. The injection volume was 1 \selectlanguage{greek}µ\selectlanguage{english}L. The
temperature of the injection and detector was 300\selectlanguage{ngerman}°C and 350°C,
respectively. The nitrogen was used as the carrier gas, and the split
ratio was 10:1. The fatty alcohols were identified by the retention time
and quantified by the peak area normalization method.

\textbf{Differential scanning calorimetry (DSC)}

Corn wax (10 mg) was placed in DSC, and the temperature was increased
from 30°C to 90°C at a rate of 30°C/min. The sample was cooled to 20°C
at a rate of 5°C/min and held for 20 minutes to allow complete
crystallization of the corn wax. Then the temperature was increased to
90°C at a rate of 5°C/min, and the nitrogen flow rate was 40 mL/min. The
temperature at the beginning of the first endothermic effect on the
melting curve and the shoulder temperature after the last endothermic
peak were used to characterize the melting range of the system.

\textbf{Physicochemical properties of corn wax}

The water and volatiles content (AOCS Ac 2-41), ash content (AOCS Ca
11-55), acid value (AOCS Cd 3a-63), peroxide value (AOCS Cd 8--53),
iodine number (AOCS Cd 1-25), saponification number (AOCS Cd 3b-76),
lead content (GB 5009.12-2010), arsenic content (GB 5009.11-2014) and
phosphorus content (AOCS Ca 12-55) of corn wax were determined according
to standard methods.

\textbf{Acetone insoluble in corn wax}

0.30 g corn wax (m\textsubscript{1}) was mixed with 10 mL acetone in a
15 mL test tube. The mixture was kept at 40°C for 1 h. Then the mixture
was centrifuged and the acetone layer was discarded. The mixture was
washed with acetone and centrifuged several times until the acetone
layer was colorless. The acetone was removed by vacuum evaporated, and
the residue was placed in an oven at 100°C to dry to a constant weight
(m\textsubscript{2}). The acetone-insoluble content (AI) and the purity
of the corn wax were calculated as follows.

\begin{equation}
\text{AI\ }(\%)=\frac{m_{2}}{m_{1}}\times 100\nonumber \\
 \end{equation}\begin{equation}
\text{Purity\ }\left(\%\right)=AI\ \left(\%\right)\ PC\ (\%)\nonumber \\
 \end{equation}

AI (\%): the acetone-insoluble content of corn wax. PC (\%): the
phospholipid content of corn wax.

\textbf{Statistics Analysis}

The data were expressed as mean values \selectlanguage{ngerman}± standard deviations of
triplicate experiments and analyzed by one-way analysis of variance
(ANOVA) using IBM SPASS Statistics 20. The significance of the
difference between samples was determined by Duncan's multiple range
test (\emph{p} \textless{}0.05).

\textbf{Results and Discussion}

\textbf{Composition of wax esters}

Corn wax was isolated and purified from crude corn wax obtained from
corn oil refineries. The purity of the corn wax was determined, and the
results were shown in Fig. S1. The purities of corn waxes produced from
different crude corn wax samples (n=30) under the same purification
process conditions were in the range of 95.29\% to 98.71\%.

The chromatogram of the corn wax ester was shown in Fig. S2A, and the
quantitative results were presented in Table 1. The wax esters of corn
wax ranged from C42 to C58. Most of the wax esters in corn wax were even
carbon chains, which were similar to the SW, and the wax recovered from
sunflower oil winterization waste (Chalapud et al., 2017; Redondas et
al., 2020). C44 (17.44\%-30.63\%) and C46 (24.99\%-30.12\%) were the
predominant wax esters of corn wax ester followed by C48
(12.22\%-18.06\%). The carbon numbers of the wax esters from refined
canola oils ranged from C36 to C56, with C36, C44, C46, and C48 being
the most common (Hu et al., 1993). However, C28 and C30 were the major
esters in sorghum wax (Harron et al., 2017; Hwang et al., 2002). Doan et
al. (2017) have researched the waxes ester distribution of some natural
waxes and found that the carbon chain lengths of SW, RBW, bees wax, CLW,
and berry wax were in the range of C44-C50, C44-C52, C40-C48, C34-C52,
and C34-C38, respectively. Compared with these waxes, the carbon chain
length of corn wax ester was longer and it might affect its
physicochemical properties, such as melting point. Wax esters have a
variety of important biological functions, such as protecting fruits
from desiccation, UV light, and pathogens (Kalscheuer et al., 2006). Wax
esters could also represent an excellent source for biodiesel
production, as wax esters have a higher energy density than the
triacylglycerol-type vegetable oils (Iven et al., 2016). They could be
used as an important economical oil in the medicine, cosmetics, and food
industries. At present, wax esters are mainly synthesized by expensive
chemical precursors or extracted from plant jojoba oil, which leads to
insufficient supply and high cost. As wax ester was the main component
of corn wax, corn wax has great potential for producing wax esters.

\textbf{Composition of fatty acids of wax esters}

The composition of fatty acids released from wax ester was shown in Fig.
S2B and Table 2. The fatty acids carbon atom numbers of corn wax esters
were between 16 and 30, which was similar to RBW. The fatty acid carbon
numbers of RBW were between 16 and 32 (Dassanayake et al.,2009). The
fatty acids of corn wax esters were mainly saturated, with C20:0
(27.96\%-34.56\%), C22:0 (28.83\%-31.74\%), and C24:0 (14.22\%-17.61\%)
being predominate. Although these fatty acids also existed in common
peanut oil, rapeseed oil, etc., the content was much lower than corn
wax. The main unsaturated fatty acids were C18:1, C18:2, and C18:3, but
their percentages were very low. The content of saturated fatty acids of
corn wax ester was around 90\%. It was similar to the lacquer wax, in
which the total amount of saturated fatty acids was 83.62\% (Chen et
al., 2014). Because of the higher percentage of saturated fatty acids in
corn wax, corn wax has a strong antioxidant capacity.

The fatty acid carbon atoms of wax recovered from sunflower oil
winterization waste were in the range of 14-34, with the C16, C18, C30,
C32, and C34 fatty acids being the predominant (Chalapud et al., 2017).
Another result showed that the fatty acids of SW were in the range of
14-30 carbon atoms with higher percentages of C18:1, C20:0, and C16:0
(Carelli et al., 2012). It might be mainly due to the different
pretreatment and extraction process of the raw materials. Doan et al.
(2017) have found that the fatty acid portion of RBW, SW, bees wax, CLW,
carnauba Brazilian wax (CRBW), carnauba wild wax (CRWW) consisted mainly
of components with even alkyl chains between 16 and 24 carbon atoms. The
dominant fatty acid portion of bees wax were C16 and C18. Meanwhile,
CRBW and CRWW were rich in C24, C16, and C18. The montan wax esters
consisted of fatty acids with longer chains (C24:0-C32:0) (Tada et al.,
2014). It has been reported that bees wax and CW contained
straight-chain fatty acids of even carbon numbers exclusively (Asperger
et al.,1999). The composition of fatty acids varied in different raw
materials. Suitable materials could be selected according to the actual
needs.

\textbf{Composition of fatty alcohols of corn wax esters}

As presented in Fig. S2C and Table 3, the corn wax ester was composed of
fatty alcohols in the range of C20-C32 with higher percentages of
docosanol (C22), tetracosanol (C24), triacontanol (C30), and tricosanol
(C23). Their percentages were 10.81\%-24.28\%, 10.63\%-21.68\%,
6.35\%-14.74\%, and 3.69\%-14.71\%, respectively. The percentage of
octacosanol (C28) in corn wax ester was 4.4\%-10.98\%. Octacosanol, as a
promoter of calcitonin formation with extremely low side effects, is an
ideal natural food additive. Octacosanol is also a natural anti-fatigue
substance and could enhance endurance, regulate motor nerve function,
protect the liver, and reduce cholesterol and blood lipids contents
(Taylor et al., 2003). In addition, triacontanol (C30) is a plant growth
regulator. It could promote carbon and nitrogen metabolism and increase
the storage and accumulation of ATP to increase crop production.
Triacontanol also has inhibitory effects on various solid tumors, such
as liver cancer, bowel cancer, and lung cancer. At present, wheat germ
oil was used as the raw material to prepare octacosanol, while the bees
wax and RBW were used as the materials to prepare triacontanol. Corn wax
also contains a considerable amount of octacosanol (4.4\%-10.98\%) and
triacontanol (6.35\%-14.74\%) and could be used as one of the raw
materials for preparing these fatty alcohols. It is of great
significance to explore the high value-added substances of corn wax and
extend its potential application areas.

The fatty alcohols of corn wax were mainly saturated, and the
even-numbered carbon fatty alcohols had a higher percentage than
odd-numbered carbon fatty alcohols. The fatty alcohols composition of
RBW and wax obtained from refined canola oil were in the range of
C24-C38 and C16-C30, respectively (Dassanayake et al., 2009; Hu et al.,
1993). While the fatty alcohol composition of SW ranged from C18 to C34.
C24, C26, and C28 constituted majority parts (Carelli et al., 2012;
Chalapud et al., 2017). The composition of corn wax was summarized in
Table 4.

\textbf{The melting point of corn wax}

Corn wax was a mixture of wax esters formed by higher fatty acids and
higher monohydric alcohols. Its melting temperature could hardly be
expressed as an accurate temperature value but described as the melting
point range. As shown in Table 5, the melting point of corn wax was in
the range of 71°C-84°C. It was wider than the melting point of SW
(69.02°C-75.13°C) (Redondas et al., 2020). It has been reported that the
melting point of CW derived from different subspecies of carnauba tree
was 79.2°C-84.2°C, and the wax had eutectic behavior when exposed to
elevated temperatures (De Freitas et al., 2019). The melting point of
RBW was 77°C-79°C, while the melting points of different grades of CW
and sorghum wax were 78°C -86°C and 77°C -85°C, respectively. The
melting point of CLW was 69°C - 73°C (Navarro-Guajardo et al., 2017).

The main factors affecting melting temperature were the carbon chain
length, the unsaturation grade, and the placement of the ester bond of
the wax ester. It was known that the melting temperatures of wax ester
increased with the elongation of the carbon chain length. Unsaturated
fatty acids could melt at lower temperatures with less energy (Chalapud
et al., 2017). The melting point of CW was relatively higher than other
general vegetable waxes, so CW was often added to other waxes to
increase their melting points. Due to the broader range of corn wax
melting points, corn wax could also be a kind of additive to improve the
crystallization characteristics of other waxes.

\textbf{Chemical properties of corn wax}

For a more comprehensive understanding of corn wax, the basic chemical
properties of corn wax were determined, and the results were summarized
in Table 6.

The water content could directly affect the quality, storage, and
transportation stability of corn wax, as the water could react with the
residual neutral oil and accelerate the hydrolysis of the wax. Among the
30 samples, the water contents were all less than 0.05\%, and the lowest
was close to 0.01\% (Fig. 1A). The difference in water content between
the samples might be attributed to the difference in raw materials, the
preparation process, and the refining process.

The ash content reflects the content of inorganic substances in corn
wax. Vegetable waxes used for food were needed to meet the limitation
requirements of ash content to avoid inorganic contamination. For
example, the requirement of ash content for CW was less than 0.25\%
proposed by the Chinese national standard. As presented in Fig. 1B, the
ash content of corn wax was in the range of 0.001\%-0.009\%, and it was
much lower than the requirement for CW.

The acid value indicates the content of free fatty acids in wax. As
shown in Fig. 1C, the acid values of corn waxes were all less than 2
mg/g, and there were significant differences among different samples
(\emph{p} \textless{}0.05). The differences might be due to the varying
degree of deacidification of various raw materials, and the preparation
and refining processes of corn wax could also affect its acid value.
Doan et al. (2015) have studied the acid values of RBW, SW, bees wax,
CLW, CRBW, CRWW, and found that the acid values of these waxes were
13.25 mg/g, 5.00 mg/g, 19.10 mg/g, 12.62 mg/g, 5.88 mg/g, 6.34 mg/g,
respectively. The acid value of CW and sorghum wax were in the range of
2-10 mg/g and 10-16 mg/g, respectively (Hwang et al., 2002). Compared
with other kinds of waxes, the acid value of corn wax was lower, and it
indicated that the content of free fatty acids in corn wax was lower.

The peroxide value of corn wax ranged from 0.05 g/100 g to 0.22 g/100 g,
as shown in Fig. 1D. It was lower than the requirement of Chinese
national food safety standards for vegetable oil (0.25 g/100 g). The
lower peroxide value indicated that the degree of oxidation of corn wax
was low, and this might be due to the higher degree of saturation of
corn wax. The difference in peroxide value between samples might be
caused by the different raw materials and the degree of oxidation during
processing.

The iodine number is a measurement of the degree of unsaturation. The
result showed that the iodine number of corn wax was 5.17 g/100 g-8.86
g/100 g (Fig. 1E). It has been reported that the iodine number of RBW
was in the range of 8-15 g/100 g (Dassanayake et al., 2009). The
limitation of iodine number for lacquer wax was less than 25 g/100 g put
forward by the Chinese national standard, and the iodine number of corn
wax was far below it. This could be attributed to the lower content of
unsaturated fatty acids in corn wax.

The saponification number is related to the content of unsaponifiable
matters, free fatty acids, monoglycerides, and diglycerides of wax. It
can reflect the purity of wax. The lowest saponification number of corn
wax was 69.16 mg/g, and the highest was 81.66 mg/g (Fig. 1F). The
saponification numbers of RBW, SW, bees wax, CLW, CRBW, CRWW were 78.17
mg/g, 64.58 mg/g, 36.88 mg/g, 7.14 mg/g, 72.64 mg/g, 74.81 mg/g,
respectively (Doan et al., 2015). The saponification numbers of CW and
sorghum wax were 77-95 mg/g and 16-49 mg/g, respectively (Hwang et al.,
2002). The limit value of saponification number for RBW was 70-95 mg/g
proposed by the Chinese enterprise standard, and it was similar to corn
wax.

As heavy metals, lead and arsenic pose a threat to human health and
especially show a high risk to the nervous system. The lead and arsenic
in vegetable waxes are generally from the additives used in the oil
refining processes. The lead and arsenic contents of corn wax were found
to be in the range of 0.04-0.10 ppm and 0.01-0.06 ppm, respectively
(Fig. 2A, Fig. 2B). The lead and arsenic contents of corn wax were far
below the China permissible limits for RBW and met the food safety
requirements, providing security for the application of corn wax.

\textbf{CONCLUSIONS}

Corn wax was purified from the crude corn wax, and the compositions of
corn wax esters, fatty acids, and alcohols were analyzed. Corn wax
esters were between 42 and 58 carbon atoms, with C44 and C46 being
predominant. C20:0, C22:0, and C26:0 were the primary fatty acids and
C22, C24, C30, and C23 were the primary fatty alcohols. The
physicochemical characteristics of the corn wax were studied, and it was
found that the melting point of corn wax was in the range of 71°C-84°C.
The lower contents of water, ash, and heavy metals represented that corn
wax was of high quality and safety. By comprehensively studying the
composition and physicochemical properties of corn wax, it was found
that corn wax could be applied to food, health care, daily chemicals,
and medicine as other vegetable waxes. This study could contribute to a
comprehensive understanding of the properties of corn wax and provide
guidance for the future development and utilization of corn wax.

\textbf{ACKNOWLEDGMENTS}

This study was supported by the National Key Research and Development
Program (2018YFD0401100) from the Ministry of Science and Technology of
the People's Republic of China.

\textbf{AUTHOR CONTRIBUTIONS}

All authors contributed to the study conception and design. All authors
read and approved the final manuscript.

\textbf{DECLARATIONS}

\textbf{Conflict of interest}

The authors declare that the research was conducted in the absence of
any commercial or financial relationships that could be construed as a
potential conflict of interest.

\textbf{Compliance with ethics requirements}

This article does not contain any studies with human or animal subjects.

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\textbf{Fig. 1} The physicochemical properties of corn wax.
\textbf{A}The water content of corn wax. \textbf{B} The ash content of
corn wax.\textbf{C} The acid value of corn wax. \textbf{D} The peroxide
value of corn wax. \textbf{E} The iodine value of corn wax. \textbf{F}
The saponification value of corn wax

\textbf{Fig. 2} The heavy metals content of corn wax. \textbf{A} The
lead content of corn wax. \textbf{B} The arsenic content of corn wax

\textbf{Fig. S1} The purity of corn wax

\textbf{Fig. S2} The composition of corn wax. \textbf{A} The gas
chromatogram of corn wax esters. \textbf{B} The gas chromatogram of corn
wax fatty acids. \textbf{C} The gas chromatogram of corn wax fatty
alcohols

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