Download Study on the Microscopic Identification of the Adulterated Plant

Discourse Journal of Agriculture and Food Sciences
www.resjournals.org/JAFS
ISSN: 2346-7002
Vol. 2(9): 264-269, September, 2014
Study on the Microscopic Identification of the
Adulterated Plant Origin Powdered Seasonings
Hongmei Zhu1 and Meng Zhao2*
1
College of Food Science and Technology, Shanxi Normal University, Linfen, 041004, China
2
College of life Science, Shanxi Normal University, Linfen, 041004, China
Abstract
The present study applied the microscopic powder identification technique to determining the
adulterated seasoning powders from several plant origins, such as chili, pepper, cumin and mustard.
The microscope observation results showed that the chili powder were adulterated with the fragments
of plant straws, foliage and other substances; the pepper powder were adulterated with starch, straws
and monosodium glutamate as well as some other substances; cumin and mustard powders were
adulterated with straws and starch, etc. The research results showed that the identification method
adopted in this study is suitable for determining the adulterated seasoning powders from different plant
origins, capable of distinguishing the pure product of the seasonings mentioned above from the
adulterated one and able to detect the micro-morphology of the adulterating substances directly.
Keywords: Plant origin, Seasoning, Adulteration, Microscopic identification
INTRODUCTION
Seasonings have the functions of enhancing the quality of dishes, stimulating people’s appetite and improving the
physique of human beings. At present, the seasonings adopted in the food industry of China can be divided into several
categories, including brewing, pickles, fresh vegetables, drysaltery and aquatic products, etc. Among these categories,
dried seasonings are mostly made through drying the root, stem, foliage, fruit and other parts of the plants, such as
pepper, chili, anise, fennel, mustard, cinnamon, ginger slice, ginger and tsaoko amomum fruit, which have a special
spicy or pungent taste. Most of the powdered seasonings from plant origins belong to this category, such as chili powder
and pepper powder. They are made through grinding the plant tissues and are widely applied in the food industry of
China, especially the traditional food. However, the adulteration of seasonings is a long-standing problem. As the current
detection methods used to identify the adulterated powdered seasonings are deficient, organoleptic inspection is the
most common method, or sometimes supplemented by physical and chemical inspection (Zhichun et al., (2011) and Ying
(2002)). The application of organoleptic inspection has some limitations, for it fails to identify the adulterating substances
precisely as the test object is single; physical and chemical inspection methods are more sensitive, but the tedious
procedures will cost a plenty of time and chemical reagent. By now, there is no generally applicable method which can
be used to identify the adulterated seasoning powders quickly and intuitively.
Powder identification technique has been widely used in the studies of the adulteration detection of Chinese herbal
medicines, which mainly use the characteristics of the plant tissues and cells to describe the medicinal properties of
herbs and determine if they are adulterated with other substances. This method has achieved favorable results in
detecting the microscopic characters and the adulteration of various Chinese herbal medicines, such as Herba
Dendrobii, Adenophora stricta, stem bark of Hippophae rhamnoides and sporopollen (Yujie et al., (1999), Shiming and
Yunyan (1989), Guojun and Lingwen (1956),Guojun et al., (1966)). In this study, the method of powder identification is
used in the adulteration detection of powdered seasonings from chili and cumin as well as other powdered seasonings,
providing a new identification method and a theoretical basis for the future studies on this field.
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MATERIALS AND METHODS
Materials
Chili powder, pepper powder, cumin powder and mustard powder were bought from the market and made in the
laboratory, respectively; those made by us in the laboratory were made from the raw materials which have been purified.
Methods
Take different kinds of the seasoning powders respectively, put them on the microscope slides and use glycerol
mounting medium for mounting; adopted Nikon Eclipse 50i biological microscope and Olympus SZX 7 stereo
microscope to observe and photograph the microscopic characters of the constituents of the seasoning powders and
identify the adulterating substances.
Results
The Microscopic Characteristics of Chili Powder and the Identification of Adulterating Substances
According to the microscope observation of the chili powder which made in our laboratory,it was mainlyconsisted of the
mixture of pericarp fragments and seed fragments; vascular fragments in internal chili pericarp can be observed also,
the pericarp fragments were in irregular shapes. For having been dehydrated and dried, they are in natural orange red to
bright red; the rectangular pericarp cells are mostly in uniform size with a diameter of about 50-70 μm; large intercellular
spaces (Figure 1a) are caused by cell dehydration and cell contraction in the drying process. Chili seed fragments are
shiny in white to light yellow, and most of them maintain the original circular edges (Figure 1b).
According to the microscope observation, the inferior and adulterated chili powder sold in the market appeared in
various colors, such as red, grey and white. Those in grey or while are made through drying the seed coat of immature
chili; the cells of seed coat are in non-uniform sizes and the cell surfaces are wrinkled (Figure 1c). Besides the flesh and
seed fragments, the adulterated chili powder is also mixed with the powders of some other plants and substances,
including foliage, vessel, cilium, plant fiber. In the inferior chili powder, the adulterating plant foliage presents obvious
characteristics of foliage epidermis cells, including corrugated edges, closely arranged and no intercellular space; the
specific stomata on the epidermis of plant foliage can be observed also (Figure 1d). Adulterated chili powder was mixed
with plant cilium which is long and hollow with medulla (Figure 1e). In addition, large amount of scalariform vessels of
plant can be observed in the adulterated chili powder (Figure 1f), which should not be detected in chili fruits. The tissues
of plant cilium observed were in irregular fragments; the cells were elongated and fibrosis; they were deemed to belong
to the Graminaceous, such as the fragments of wheat straws, rice straws or corn husks (Figure 1g). Bits of cilium also
observed in the adulterated chili powder (Figure 1h), and pericarp fragments were observed with mould mycelia in the
sample of adulterated chili powder (Figure 1i).
The Microscopic Characteristics of Pepper Powder and the Identification of Adulterating Substances
Pepper fruit is spherical follicle which crazes along the ventral suturefrom the tip; as getting mature, it will develop into
two sections connected by a common base; the seeds are spherical and black. The epicarp of pepper is constituted by
1-layer epidermal cells; the cell walls are accreted from the textured cuticle and the lignified mesocarp. The endocarp is
thinly leathery and in light yellow which is schizogenous with the mesocarp. According to the microscope observation of
the pepper powder made in our laboratory, mainly has three different micro-structured fragments: the fragments of
pepper epicarp and mesocarp, the fragments of pepper endocarp and a little amount of the fragments of pepper seeds
(Figure 2a). Among them, the fragments of pepper epicarp and mesocarp are the characteristic constituents; the surface
of pericarp is brown or red brown with bulged texture; the endothecium of the connate mesocarp is also in brown or red
brown attached with white membranous constituents; the endocarp is yellow and will develop into loosened
membranous constituents after grinding; mashed pepper seeds are irregular particles, black and shiny (Figure 2a).
The adulterating substances of pepper powder are mainly composed of plant straws and starch. According to the
microscope observation, the straws are in non-uniform colors, including grey, yellow and light yellow and others; they
present the structure of lots of plant fibers which are distinguished from the membranous constituents of endocarp; the
adulterating starch is dyed in brown (Figure 2b). Some pepper powder is adulterated with monosodium glutamate
particles (Figure 2c).
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Figure 1: Micrograph of Chili Powder
Figure1a The microstructure of the fragments of chili flesh, showed the micro-morphology of
flesh cell, bar=80 μm. Figure 1b The microstructure of the fragments of chili seed, bar=0.5 mm.
Figure1c The microstructure of the flesh fragments of inferior chilli powder, showed the cell
walls of flesh were wrinkled, bar=125 μm. Figure 1d The microstructure of the adulterating
foliage of inferior chilli powder, and the arrow showed the unique stomata (ST) of foliage,
bar=200 μm. Figure 1e Themicrostructure of the adulterating cilium of inferior chilli powder,
bar=150 μm. Figure 1f Themicrostructure of the adulterating scalariform vessel of inferior chilli
powder, bar=100 μm. Figure 1g The microstructure of other adulterating plants of inferior chilli
powder, bar=0.5 mm. Figure 1-h The microstructure of the adulterating plant fiber of inferior
chilli powder, bar =125 μm. Figure 1i The microstructure of the fragments of inferior chilli
powder, the arrow showed the mould mycelia (MO), bar=1 mm.
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Figure 2: Micrograph of Pepper Powder,Cumin PowderandMustard Powder.
Figure 2a The microstructure of the of the fragments of pepper powder, the arrows showed the
mesocarp (ME) and endocarp (EN), respectively; some fragments of pepper seeds (SE) are
mixed together, bar=0.5 mm. Figure 2b The microstructure showed the pepper powder
adulterated with a great deal of starch, bar=0.5 mm. Figure 2c The microstructure showed the
pepper powder adulterated with monosodium glutamate (MG) particles that the arrow is pointing
at, bar =0.5 mm.
Figure 2d The microstructure of the cumin powder, the arrows showed the fragments of fruit
(FR) and ridge (SA), respectively, bar=0.5 mm. Figure 2e, The microstructure of the cumin
powder showed adulterated with plant fibers (FI), that the arrow is pointing at, bar=0.5 mm.
Figure 2f The microstructure showed the cumin powder adulterated with large amounts of
starch (STA), bar=0.5 mm. Figure 2g The microstructure of the mustard powder, shows the
fragments of mustard endosperm, bar=0.25 mm. Figure 2h The microstructure of the mustard
seed coat, bar=0.25 mm. Figure 2i The microstructure of the adulterated mustard powdermixed
with large amounts of starch, bar =0.25 mm .
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The Microscopic Characteristics of Cumin Powder and the Identification of Adulterating Substances
Cumin powder is made from the seeds of Cuminum cyminum which belongs to Umbelliferae. The seeds of Cuminum
cyminum are long and narrow shaped; the seed coat has grains and ridges. After grinding, the seeds appear in brown.
According to the microscope observation, three different fragments can be observed: the seed coat, ridge and
endosperm, respectively (Figure 2d). The fragments of the seeds of Cuminum cyminum arepresented in brown to dark
brown; the ridges are in cylindrical tubular structure. The endosperms of Cuminum cyminum are yellow stereoscopic
particles; the detached seed coat is yellow with cutin (Figure 2e).
Adulterated cumin powder is mainly mixed with plant straws and starch. Adulterating straws have the similar ridges
with the seed of Cuminum cyminum; they are also in cylindrical vascular structure but in longer size. Compared with
pure cumin powder, the straws have significantly more ridges (Figure 2e). The sample of cumin powder is also doped
with a great deal of starch (Figure 2f).
The Microscopic Characteristics of Cumin Powder and the Identification of Adulterating Substances
Mustard is a kind of powdered seasoning made through grinding mature mustard seeds. It belongs to Brassica of
Cruciferae. The structure of mustard mainly includes the seed coat and endosperm. It contains a lot of protein and fat
and basically without starch (Shuya et al, 2007). The pure mustard powder made in laboratory shows two different
structured fragments under the microscope, namely the fragments of mustard endosperm and seed coat. The fragments
of endosperm are uniform; mostly are yellow-green spherical or ellipsoidal particles (Figure 2g). According to the
microscope observation, the brown seed coat is in reticulated lamellar structure (Figure 2h). The adulterated mustard
powder has a lot of starch granules added (Figure 2i).
Discussions
Powder identification was first applied on the adulteration detection of the powder of Chinese herbal medicines. It has
achieved remarkable results in the identification of Herba Dendrobii, Adenophora stricta, stem bark of Hippophae
rhamnoides, and other Chinese herbal medicine (Yujie et al., (1999), Shiming and Yunyan (1989), Guojun and Lingwen
(1956),Guojun et al., (1966)). This kind of identification method is applied to not only the identification of the crude drug
of single Chinese medicinal herb, but also to that of pills and powders which are constituted by a variety of Chinese
herbal medicines (Guojun X and Lingwen (1956). In addition, powder identification is also used in the adulteration
detection of fodder (Xian et al., (2009) . The main principles of powder identification is to identify the character and purity
of the sample after being processed, especially being processed into powder, based on the attributes of the original
materials, such as its cell shape, crystal structure, form of tissue and histochemical reaction. In this way, the purity of the
identified materials and the microstructure of the adulterating substances can be observed fundamentally.
Food adulteration is mainly realized by means of blending, mixing, faking and whitewash. Blending is especially
adopted in the adulteration of liquid foods. The adulteration of seasonings is mostly done by mixing and faking, which
has been a long-standing problem. Now, on the research of adulterated seasonings, organoleptic inspection and ignition
test are the most common ways for adulteration detection. For example, pepper powder, mustard powder and ginger
powder mixed with bran, starchand other impurities can be detected based on the inherent flavors of the original
materials (Haisheng and Chunhua (1994) and Ruiliang and Hongning 1992)). In recent years, the methods of physical
and chemical analysis and molecular biology and other means have been introduced.For example, the method of gas
chromatography-mass spectrometry can be used to identify the animal and plant protein hydrolysate (Zhichun et al.,
(2011) and Shuya et al., (2007)). In present study, adulteration has been widely spread in the seasoning powders from a
variety of plant origins on the market. The method of microscopic identification can well distinguish the characteristic
constitutes and the adulterating substances, which is also much more intuitive, speedy, accurate and available than
organoleptic inspection and the physical and chemical identification.
ACKNOWLEDGEMENT
This study was supported by the National Natural Science Foundation of China (Grant No.31401435; No. 31300157).
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