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Effect of Blanching and Frying Time on the Sensory Quality of Fried
Sweet Potato Chips
TEFERI DAMTO*, GEREMEW CHALA
Department of Post-Harvest Management
Jimma University
Jimma, Oromiya
ETHIOPIA
*teferidamto@gmail.com
Abstract: - Sweet potatoes are a significant crop and are popular among consumers, particularly as chips.
Frying of sweet potato slices is carried out to convert the roots to value added products. Frying method brings
out unique flavor and texture to the products that improve their overall acceptability. The aim of this work was
to determine the effect of blanching and frying time on sensory quality of fried sweet potato chips. Prior frying,
sweet potato slices were blanched in order to inactivate enzymes and impart flavor. The blanching treatments
were carried out at 65°C for 5 and 7 min and fried at 170°C for three different level of time (4, 5, and 6)
minute. The mean of color and oil taste of the blanched, treated chips were in the range of 3.53-2.9and 3.97-
2.9667, respectively. While, fried treated in the same parameters ranged between 3.8-.533, 92 and 3.5 and
3.667 respectively. The samples blanched at 5 minute and fried were gave darker chips compared to treated.
Fried sweet potato chips blanched at 7 minute had the best sensory scores for all sensory quality attributes. So
using this method is good for producing good quality chips. Therefore, treated with blanching and frying could
be used to make a higher quality product that is more attractive to product developers and consumers.
Key-words: sweet potato; frying; blanching; sensory quality; chips
1 Introduction
Sweet potato is native to tropical and subtropical
regions of the world and ranked the seventh most
important crop following rice, wheat, maize, potato,
cassava and barley (Woolfe, 1992). The sweet
potato is extremely important for worldwide food
security. Sweet potato is the second most important
root and tuber crop in the world after potato
(Horton, 1988). In Sub-Saharan Africa sweet potato
is the third most important tuber crop after cassava
(Manihotesculenta) and yam (Dioscorea spp.)
(Ewell & Mutuura, 2004).More than 140 million
tons of sweet potato is produced globally per year
(FAO, 2000). The world average storage root yield
of sweet potato has been estimated to be 14.8t ha-1.
China is the leading producer of sweet potatoes with
production reaching 75 million metric tons in 2011,
which accounts for approximately 73% of global
production (FAO, 2000).
In some of the world’s poorest nations, taro and
sweet potato are important part of food security
packages (Yared Dagne, 2014). Ethiopia ranks
fifteenth in the world in terms of sweet potato
production (Dan et al, 2013). In Ethiopia, sweet
potato is the second-most important root crop in the
country after enset. It provides a healthy diet for
millions of people across the country (Gurmu,
Hussein, & Laing, 2015). Moreover, it is commonly
cultivated as an integrated crop, along with
livestock, in the crop–livestock farming systems
(Belehu, 2003). Nationalities and Peoples’ Region
(SNNPRS) and Oromia are the main regions that
produce sweet potato in Ethiopia (Gurmu et al.,
2015). However, Ethiopia’s average sweet potato
storage yield is low with 8 t/ha, although the
potential yield is 30 - 73 t/ha, and the international
average is 14.8 t/ha (Belehu, 2003; Kivuva et al.,
2014).In Ethiopia sweet potato ranks the first in
total production (42.84%) and the second in area
coverage (25.43%) next to Irish potato from root
and tuber crops cultivated (CSA, 2014). Its root is
used as food and feed. As food the root is usually
consumed in boiled form. It is one of the cheapest
sources of vitamin A. It is tolerant to adverse
conditions like drought. It is an attractive food crop
among farmers because it requires less care and
input (CIP, 1995). It is a popular food in many parts
of Eastern Africa. It is drought resistant, hardy and
can grow in marginal areas, thus contributing to
improved food security. The young leaves and vines
can be consumed as vegetables or fed to livestock
(CTA, 2007). The average yield ha-1 of sweet
potato in Ethiopia is 33.74 ton ha-1 (CSA, 2014).
Teferi Damto, Geremew Chala
Food and Nutrition Science - An International Journal
http://iaras.org/iaras/journals/fnsij
ISSN: 2367-9018
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Volume 3, 2019
Sweet potato has numerous potential uses and
benefits. As food, Sweet potato storage roots are
boiled and eaten or chipped, dried and milled into
flour which is then used to prepare snacks and baby
weaning foods (Kidmose et al., 2007).Sweet
potatoes tubers have good nutritional value,
containing many vitamins, minerals, non-fibrous
complex carbohydrates and dietary fiber (Suda et
al., 2003). White and orange flesh sweet potato is
rich source of β-carotene (provitamin A), a very
good source of vitamin C and a good source of
copper, dietary fiber, vitamin B6, manganese,
potassium and iron, while purple-fleshed varieties
are rich source of anthocyanins (Baybutt et al.,
2000; Teow et al., 2007; Yang and Gadi, 2008).
Sweet potato serves as a stable food vegetable
(fleshy roots and tender leaves), snack food,
wearing food, animal feed, as well as a raw material
for industrial starch and alcohol. It is processed into
diverse products (Ukom et al., 2009).
Antioxidants such as vitamin C have been shown to
interact with and stabilize free radicals within the
body. This action decreases the risk eye problems,
like cataracts, many cancers and can help slow
down the aging process. Vitamin C is also necessary
for normal growth, absorption of iron, healing of
wounds, formation of important protein used to
make skin and stimulating the activity of the
immune system. It is also needed for the
maintenance of teeth and bones ( Babalola et al.,
2010).
One of the most important dietary compounds found
in sweet potatoes is β-carotene, an important
vitamin A source for human, which constitute 86 to
89% of orange and yellow fleshed sweet potatoes
(Woolfe, 1992). Also, Burri (2011) suggested that
orange-fleshed sweet potatoes are a nutritious and
sustainable source for preventing vitamin A
deficiency. Beta-carotene is most important as the
precursor of vitamin A in human diet which
maintains and protects eye tissues, but it has also
been linked to enhanced immune response and
suppressed cancer development. Carotenoids
generally cannot be manufactured by humans so it
must be added to their diet in appropriate amounts
(Kopsell, 2006).
1.1 Statement of Problem
Sweet potato (Ipomoea batatas L.) is one of the most
widely consumed tuber crops in the world .Sweet
potatoes tubers have good nutritional value,
containing many vitamins, minerals, non-fibrous
complex carbohydrates and dietary fiber; however
there is no sufficient technology that change this
product to more finished product.Therefore, the
application of new technologies to extend the post-
harvest life of this commodity is needed. Blanching
before frying also appears to be a good alternative.
1.2 Objective
The objective of this research is:
1.2.1 General Objective
To determine the effect of blanching and
frying time on the quality of fried sweet
potato chips
1.2.2 Specific Objectives
To evaluate the effect of different
blanching and frying time on sensory
quality of sweet potato chips
To determine the suitable treatment to
produce the acceptable organoleptic of
sweet potato chips
To examine the optimum blanching time ,
frying time and temperature of of sweet
potato chips
1.3 Significance of Study
The study is believed to be significant in that it will
be:
• Reduce postharvest loss of sweet potato in
Ethiopia
• Produce the best quality sweet potato chips
• Provide information on treatment the
parameters suitable for sweet potato chips.
• Reassure the consumer that a sweet potato
chip is safe for consumption and addresses
nutritional concerns.
1.4 Scope
The study generally covers:
The processing method for production of
sweet potato chips
Developments of quality attributes of chips
Sensory analysis majorly on Sensory
Evaluation
2 Literature Review
2.1 Nutritional Value
The nutritional composition of sweet potato which
are important in meeting human nutritional needs
including carbohydrates, fibres, carotenes, thiamine,
Teferi Damto, Geremew Chala
Food and Nutrition Science - An International Journal
http://iaras.org/iaras/journals/fnsij
ISSN: 2367-9018
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Volume 3, 2019
riboflavin, niacin, potassium, zinc, calcium, iron,
vitamins A and C and high quality protein (Tables 1
). Sweet potato particularly provides energy in the
human diet in the form of carbohydrates. According
to USDA (2009), besides carbohydrates, they are
also rich in dietary fiber and have high water
content and also provide 359 kJ energy with low
total lipid content, which is only about 0.05 g per
100 g. In addition, sweet potatoes also are high in
minerals such as potassium, calcium, magnesium,
sodium, phosphorus, and iron (USDA, 2009).
Because of the various roles that sweet potatoes play
around the world, the concept of nutritional quality
and its contribution must transform to meet specific
roles in human diet. For instance, staple type diets
could require high vitamin C, iron, potassium,
protein and as well as high fibre. Similarly,
supplemental types of sweet components. However,
as they will not be major food component, the level
of components may be more flexible and good.
The phytochemicals, such as carotenoids and
flavonoids, among the different varieties can differ
from each other. Teow and others (2007) assessed
the antioxidant activity, phenolic, and beta carotene
contents of sweet potatoes with different flesh
colors, which ranged from white, cream, yellow,
orange, and purple. White flesh sweet potatoes were
found to have the lowest antioxidant activity. The
orange flesh varieties had a medium range
antioxidant activity, and the darker orange flesh had
slightly higher antioxidant activity. The purple flesh
sweet potatoes had the highest antioxidant activity
values, which was similar to that of fruits and
vegetables, such as apples, avocado, cherries,
broccoli and eggplants. The purple flesh varieties
also had the highest phenolic content; contrastingly,
the white flesh sweet potatoes had the lowest
phenolic content. The anthocyanin content varied
among the sweet potato flesh colors, which the
purple and orange flesh varieties had anthocyanins
that were detectable. For beta carotene, the orange
flesh sweet potatoes had the highest amount versus
the other varieties (Teow et al 2007).
Table 1. The nutritional value of raw sweet potato
per 100g.
Nutrient
Units
Value per 100
grams
Water
G
77.28
Energy
kJ
359.00
Protein
g
1.57
Total lipid (fat)
g
0.05
Ash
g
0.99
Carbohydrate
g
20.12
Fiber, total dietary
g
3.00
Calcium, Ca
g
30.00
Iron, Fe
mg
0.61
Magnesium, Mg
mg
25.00
Phosphorus, P
mg
47.00
Potassium, K
mg
337.00
Sodium, Na
mg
55.00
Vitamin C
mg
2.40
Pantothenic acid
mg
0.80
Vitamin B-6
mg
0.21
Source: USDA (2009)
2.2 Types of Sweet Potato
There are hundreds of varieties of sweet potatoes
with colors ranging from white, orange, and purple.
Carotenoids and phenolic compounds give sweet
potatoes the distinct flesh color. White Delight is a
variety with white flesh, and NC414, NC415, Purple
04-069 and Okinawa are purple fleshed
(Leksrisompong et al 2012; North Carolina Sweet
Potato Commission 2015). The more consumer-
recognized orange flesh sweet potato varieties
include Beauregard, Hernandez,Jewel, Carolina
Ruby, Porto Rico, Cordner and Covington (North
Carolina Sweet Potato Commission 2015). Because
of the varying flesh colors, the nutritional content
can vary as well as the consumer acceptance.
2.3 Sensory Quality of Potato Chips
The sensory attributes of potato chips develop as a
result of structural changes, chemical reactions,
moisture loss and oil absorption in the raw potato
during chip processing. Therefore, the dry matter
constituents (e.g. starch, reducing sugars) of raw
potatoes are of the importance as the sensory quality
is largely dependent on the transformations of these
constituents during the frying process (Bennet,
2001).
Quality can be described as the requirements
necessary to satisfy the needs and expectations of
the consumer (Claudio, 2006). According to
Moreira et al (2006) states that the four principal
quality factors in foods are: (1) appearance,
Teferi Damto, Geremew Chala
Food and Nutrition Science - An International Journal
http://iaras.org/iaras/journals/fnsij
ISSN: 2367-9018
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Volume 3, 2019
including colour, shape, gloss; (2) flavour including
taste and odour; (3) texture; and (4) nutrition. Safety
is also an important factor. Sensory quality of a food
product relates directly to product quality as it is an
important aspect of the total product quality as
perceived by the human senses of sight, taste, smell,
hearing and touch. Appearance, flavour and texture
refer to sensory acceptability factors because they
are directly perceived by the senses (Moreira et al.,
2006). Bennett (2001) describes a quality chip as
one having as addle-shaped curl, light golden
colour, and having no blemishes. When placed in
the mouth, it is crisp, has a slight potato flavour, is
properly salted or seasoned and leaves a pleasant
aftertaste in the mouth .The sensory quality of
sweet potato potato chips is dependent on the
composition of the potatoes, the frying oil and the
processing parameters during chip manufacture
(Gillat, 2001)
Table 2. Below shows the nutritional value of sweet
potato chips per 100g. According to USDA (2010),
sweet potato crisps contain higher energy (2074.00
KJ) compared to raw sweet potato (359.00 KJ).
However, water content was reduced from 77.28 g
in raw sweet potato to 4.00 g in sweet potato crisps
due to evaporation during frying process. Besides
that, protein, carbohydrate, fat and dietary fiber
content in sweet potato crisps also higher than in
raw sweet potato.
Table 2. Nutritional value of sweet potato crisps per
100gram
Nutrient
Units
Value per
100 grams
Water g 4
Energy
kJ
2074
Protein
g
3.5
Total lipid (fat)
g
24.7
Ash
g
2.97
Carbohydrate
g
64.83
Fiber, total dietary
g
3.5
Sugars, total
g
7
Calcium, Ca
g
71
Iron, Fe
mg
2.55
Magnesium, Mg
mg
65
Phosphorus, P
mg
145
Potassium, K
mg
925
Sodium, Na
mg
35
Pantothenic acid
mg
1.55
Fatty acids
(Total sat.)
g
0.54
Fatty acids
(Total moonounsat.)
g
2.21
Source: USDA (2010)
2.3.1 Colour and Factors Affecting Colour of
Sweet Potato Chips
Colour is probably the most important visual
attribute in the perception of product quality among
the different classes of physical properties of foods.
Colour is an important visual appearance attribute
among the major factors influencing consumer
acceptability of fried products as it is the first
quality parameter evaluated by consumers. Colour
generally influences subjective sensory impression
as it is regarded as a predictor of other quality
characteristics such as flavour.For chips type
product, the lightness of crisps colour are most
desirable compared to golden and reddish brown
colour (Pokorny, 1999).
2.3.1.1 Reducing Sugar Content
During the frying process, the colour of sweet
potato slices changes due to the interaction of amine
group with a reducing sugar which lead to non-
oxidative browning known as Maillard reaction.
Asparagine is the common free amino acids present
in sweet potato. The higher level of reducing sugar
content (e.g. glucose and fructose) in the sweet
potato will contribute to darker colour of chips.
Therefore, pre-treatment applied to sweet potato
slices before the frying process to reduce reducing
sugar level in the sweet potato (Garayo& Moreira,
2002).
2.3.1.2 Frying Condition
Frying condition also is one of the important
variables that must be control to improve the colour
of sweet potato chips. It includes the frying
temperature, frying time and type of frying such as
deep fat frying or vacuum frying. If too high frying
temperature applied, the Millard browning reaction
would proceed to unacceptable level (Chen et al.,
2001). Regardless the frying type, conventional or
vacuum, frying at high temperature increase the
browning reaction as it is a temperature dependent
reaction. In terms of frying type, the colour of
vacuum fried sweet potato crisps is lighter than
those that fried under atmospheric condition. It is
because more Millard reaction occurred at the
atmospheric condition due to present of oxygen
(Garayo & Moreira, 2002).
2.3.2 Texture and Factors Affecting Texture of
Sweet Potato Chips
Texture is also a key parameter in the development
and acceptance of food products and an important
attribute in determining consumer acceptability of
fried foods (Krokida et al., 2005). Texture can be
defined as ‘all the rheological and structural
Teferi Damto, Geremew Chala
Food and Nutrition Science - An International Journal
http://iaras.org/iaras/journals/fnsij
ISSN: 2367-9018
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Volume 3, 2019
(geometric and surface) attributes of the product
perceptible by means of mechanical, tactile and
where appropriate, visual and auditory receptors
(Lawless & Heymann,1988). This attributes is
significant for the acceptability of chips product.
During frying, most of water evaporate and removed
from the sweet potato slices resulting in textural
changes. Texture attribute can be determined in
terms of crispiness and hardness of the chips
produced. Textural changes during frying are the
result of much physical, chemical and structural
change which produced during the frying (Troncoso
et al., 2009). A high quality of sweet potato chips
must have a very crispy texture as an indicator of
freshness of the chips (Troncoso & Pedreschi,
2007).Crispness is one of the textural characteristics
that are universally liked .One of the desirable
textural attributes of sweet potato chip is often
described as crispness(Kita et al., 2002). In foods
described to be crispy, crispness is the most
important quality attribute and its absence implies
poor quality and loss of consumer acceptance.
Crispness is associated with the textural experience
of eating a food item which fails in a brittle manner
(i.e. very suddenly and with relatively little
deformation) at a low load suggested that crisp
materials could generally be described as brittle,
stiff cellular materials derived either from expanded
starch or from starch-containing cellular materials
such as potatoes.
2.3.2.1 Frying Condition
As a source of carbohydrate, potato and sweet
potato mainly composed of starch component that
may changes upon heating When frying sweet
potato slices, starch granules are rapidly gelatinized
and cause strong structure of raw sweet potatoes
softening followed by formation of a firm and crispy
crust upon furtherheating(Pokorny,1999).According
Pokorny(1999),vacuum pressure was not
significantly affecting the texture of potato chips.
This indicate potato crisps fried under atmospheric
condition are very weak in structure and easily
collapsed during the rupture test (Garayo and
Moreira, 2002)
2.3.2.2 Thickness of Slices
Slice thickness affect the amount of curl, strength
and texture of crisps produced. Slices that are too
thin may give negative effect on the texture of chips
such as easily broken and oily of final products. On
the other hand, thick slices tend to have high
moisture content and less crisp (Bennett, 2001).
2.3.3 Flavour and Factors Contribute to Flavour
of Sweet Potato Chips
The flavour of sweet potato chips is more complex
than that of boiled, baked or mashed sweet potatoes,
since the cooking temperatures are higher, and the
absorbed oil contributes to the overall flavour
profile of the product (Scanlon, 2003). In fried
sweet potato products, flavour compounds are not
only inherent in the raw sweet potato but also from
the frying oil, Millard reaction products and from
the interaction of Millard reaction products with
lipid oxidation products. The complete composition
and understanding of fried sweet potato flavour has
not been fully established. Sensory differences in
the aroma and taste of sweet potato chips made from
different cultivars that varied in levels of dry matter,
sugars, amino acids and lipids.
2.3.3.1 Lipid Oxidation
Lipid oxidation during frying is crucially important
as it will impart flavour to the fried products. When
oil is heated to elevated temperature, such as 180°C
in the presence of oxygen, they may undergo
oxidation and form hydroperoxides via free radical
pathway. These compound are unstable and will be
decomposed into secondary oxidation products
which mostly volatile.
2.3.3.2 Maillard Reaction
Other important reaction that contributes flavour to
the fried food is Maillard reaction. Even the
Maillard reactions are undesirable in production of
sweet potato chips; its roles has considered in terms
of development of flavour on the final products.
Maillard reaction occur when reducing sugars, lipid
oxidation products and amino acids reacts
heterocyclic compounds which give rise to food-
related flavours and odours. It also produces non-
enzymatic browning (Gillat, 2001).
2.3.3.3 Oil Uptake
Oil uptake during frying is also need to be
considered during frying because the fat content of a
product will also affect its flavour, odour and
general organoleptic properties. The frying oil not
only acts as heat transfer medium, because they are
heated to high temperatures approximately 170-
180°C, it will start to degrade through hydrolysis
and oxidation of fatty acids. The breakdown
products themselves give rise to flavour and can
further react with carbohydrates, proteins and their
decomposition products to produce taste
traditionally associated with fried food (Gillat,
2001)
Teferi Damto, Geremew Chala
Food and Nutrition Science - An International Journal
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ISSN: 2367-9018
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Volume 3, 2019
2.4 Effects of Pre-Treatment on Fried Chips
Pre treatments have a great effect particularly on the
sensory properties and oil contents of fried
products. The pre treatments are necessary before
processing in order to retain colour, inactivate
enzymes and/or enhance rate process. The ultimate
aim of pre treatment is to improve quality of final
product and reduce processing cost. Pre-treatment
are very important in order to control chemical,
physical and structural changes of raw material
during frying process which may contribute to
undesirable colour, texture and flavour of
chips.There are several types of pre-treatment that is
commonly use, such as blanching, drying, osmotic
dehydration and soaking in calcium carbonate
solution
2.4.1 Blanching
Blanching is a critical step in making sweet potato
french fries. Blanching alters textural properties and
imparts a soft or firm bite on sweet potato fries. The
combination of temperature and time in the
blanching process can create a creamy or firm
internal in the sweet potato fry through the level of
pectin and cell wall breakdown. Prior to drying,
most food products are usually subjected to some
form of pre-treatments, among which are hot water
blanching and sulphiting. Blanching helps to
inactivate enzymes that may lead to quality
degradation .Blanching inactivates enzymes,
improves the colour and texture of food products
and reduces deterioration such as development of
off flavor (Akpapunam et al., 20010). Osmo
dehydration reduce changes in the physical,
chemical properties and contributing to an
improvement in quality. Blanching of is principally
followed to inactivate the enzymes responsible for
enzymatic and oxidative browning. The common
methods of blanching include hot water, steam and
chemical blanching. The loss of nutrients takes
place during blanching which depends on
temperature and time of blanching (Bennet,
2001).When frying at high temperature blanched
material dries more rapidly than the unblanched one
(Moreira et al., 2008).
2.5 Product Quality Attribute
2.5.1 Oil Content
Oil content is one of the main quality parameters
and sweet potato chip industry. Some of the
parameters affecting the final oil content of fried
products are product shape, temperature and frying
time, moisture content, porosity, pore size
distribution, and pre and post treatments. Oil uptake
is essentially a surface-related phenomenon
resulting from the competition between drainage
and suction into the porous crust once the sweet
potato is removed from the frying oil and starts
cooling. During centrifugation, the centrifugal force
acts perpendicular to the surface of the chips and
separates the oil directly from the porous surface
(Kita et al., 2005).The total oil content of fried
products can be separated into two regions: the oil
on the core of the product (internal oil) that is
absorbed during frying, and the surface oil which is
absorbed during cooling. Less oil is absorbed during
the using different pre-treatment and de oiling steps
(Moreira et al., 2001)
2.5.2 True Density
True density is the weight of the material per unit of
true volume (kg/m3). True volume is the volume of
the material including liquids, where all the volume
of open and closed pores is excluded. A gas
pycnometer,an apparatus that uses gas displacement,
is generally employ to determine true density of
materials given that the gas used is capable of
penetrating all open pores up to the size of the gas
(usually helium) molecule (Kawas, 2000).
2.5.3 Bulk Density
Bulk density is the mass per unit bulk volume
(kg/m3), so it includes the air within the sample.
Bulk volume in food can be difficult to calculate by
its own geometrical characteristics since foods are
usually irregular in shape (Kawas, 2000).Bulk
volume of irregularly shaped materials can be
measured by volumetric displacement of glass beads
(Marousis et al., 1990), and by using liquid
displacement with toluene (Costa et al., 2001;
Lozano et al., 1983) or a water-ethanol mixture
(Moreira et al., 2008).
2.5.4 Porosity
Porosity is a global characteristic of pores,
which provides the volume fraction of total
pores compared with the total volume of sample
(Rahman, 1995). During frying liquid water
moves from inside of the chips to the
evaporation zone leaving the product through
the surface as vapor. Some of the vapor remains
trapped within the pores of the material due to
restrictive intercellular diffusion. The vapor in
this confined space will expand and become
super-heated, distorting the pore walls and
contributing for the chips porosity .The porosity
increase slightly with oil temperature, and that
Teferi Damto, Geremew Chala
Food and Nutrition Science - An International Journal
http://iaras.org/iaras/journals/fnsij
ISSN: 2367-9018
6
Volume 3, 2019
porosity rate has a similar behavior as the oil
content rate during frying (Moreira et al., 2008).
2.5.5 Microstructure
Starch granules are often considered as semi-
crystalline biopolymer entities where water
molecules form an integral component of the
crystalline domains. The ordered granule structure is
disrupt by heating with water; this is known as
gelatinization or melting (Parker and Ring, 2001).
Almost any application of starch involves
gelatinization the granule structure (Thiewes and
Steeneken, 1997).A characteristic of sweet potato
cells is the presence of a cell wall that limits the
expansion of the cytoplasm. The outer layer of the
cell wall is the middle lamella composes of pectic
material that cements cell together and is dissolved
during heating. Cells normally contain numerous
starch granules (Miranda and Aguilera,
2006).Extracellular starch occurs when the cells
rupture or disintegrate upon mechanical or thermal
stress during processing. The frying process
involves simultaneous heat and mass transfer that
causes significant microstructural changes to both
the surface and the body of the product. Gamble et
al (1987) examine the microstructure of sweet
potato chips using light microscopy. Also, integrity
of cell walls and the presence of a dense starchy
interior support the idea that oil cannot penetrate
into the cells during frying
2.6 Sweet Potato Chip Processing
In addition to the raw sweet potato characteristics,
the sweet potato chip processing steps are major
factors influencing the potato chip quality. From the
receipt of sweet potatoes at the processing plant and
subsequent processing steps, the chip manufacturer
ensures set specifications are maintained to yield
chips of uniform quality. Sweet potato chip
processing is a dynamic system of interdependent
steps linked together to convert a sweet potato into a
chip (Bennett, 2001).
Receiving washing peeling
trimming slicing Frying
Flavouring packaging
Fig.1 Schematic diagram of potato chip processing
2.6.1 Receiving
This is one of the critical steps as the decision to
accept or reject lot of sweet potatoes for processing
is made during this step. The suitability of sweet
potatoes for chip processing is established by
carrying out raw sweet potato quality assessments
on a representative sample of the lot immediately on
receipt of the potatoes at the processing plant. These
assessments include the determination of size and
shape, presence of defects (external and internal)
and specific gravity (solids content) (Bennett, 2001).
It was observed at the sweet potato chip
manufacturer that, a representative sample of the
potatoes was peeled, sliced and fried to visually
inspect the appearance of the chips against set
standards of colour and after-fry defects.
2.6.2 Cleaning, Peeling and Trimming
The peeling duration is dependent on the surface
characteristics of the sweet potatoes such as eye
depth, cortex thickness and surface injuries
(Lisiñska, 2004). The control of the peeling
operation is essential as insufficient peeling may
result in poor appearance of the chip (Bennett,
2001). Peeled sweet potatoes are passed on the
inspection belts where defects are trimmed off
(Bennett, 2001; Lisiñska, 2004). Presence of defects
such as bruises, green and dark spots, decayed
portions and eyes give a poor appearance to chips
(Lisiñska, 2004).
2.6.3 Slicing
The slicing operation is of fundamental importance
and among the most important steps to the
manufacture of high quality sweet potato chips
(Bennett 2001). The slicing step is known to impact
upon chip appearance, colour, texture, slice contour,
breakage, oil absorption, moisture content and
frying time (Miranda & Aguilera, 2006). According
to Bennett (2001) slices that are very thin have a
negative impact on colour and tend to be oil soaked
and easily broken, whereas, thick slices tend to have
a high final moisture content and are less crispy.
Uniformity between slices is extremely important as
it may create undesirable characteristics of both thin
and thick chips and affecting the sensory quality
(Bennett, 2001).
2.7 Potato Chip Frying
Frying is a dehydration process which involves heat
and mass transfer. In addition, different chemical
changes occur during frying such as protein
denaturation, starch gelatinization, surface
browning, rapid water evaporation and oil
absorption (Pinthus et al., 1995a).Oil absorption is
affected by various factors such as frying
temperature and time, food composition, porosity,
pre treatment and oil quality (Pinthus et al;1995b).
Food frying is a common process in the food
industry used to enhance the overall quality, texture
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and flavour of snack foods, dough nuts, chips,
french fries and poultry products (Chukwu, 2009).
Frying is a unit operation which involves the
immersion of food products in hot oil (175°C) until
the desired product attributes are obtained, from
creating the proper appearance to fully-cooked
product. During frying, heat and mass transfer takes
place simultaneously; heat is transferred from the oil
to the food, water is evaporated from the food
material and oil is absorbed (Krokida et al., 2001b).
At these high temperatures the food material
undergoes intense dehydration coupled with
structural changes (i.e. formation of pores and crust,
curling, expansion or shrinkage), physico- chemical
transformations (colour and flavour formation) and
microbiological inactivation (smith, 2005).The
desirable sensory properties of potato chips are
developed during frying and thus apart from the
quality of the raw sweet potatoes the conditions
during frying will affect the final product quality
(Hubbard & Farkas, 1999; Lolos, Oreopoulou &
Tzia, 1999).
2.7.1 Frying Temperature and Time
Frying time and temperature are processing
variables that the manufacturer manipulates in order
to produce optimum quality chips and depends on
the raw sweet potato composition and slice
thickness (Moreira et al., 1999; Gamble & Rice,
2003). These frying variables influence the texture
(Miranda et al., 2005), final oil content (Baumann &
Escher, 1995), colour and flavour (Pedreschi et al.,
2005). It is reported that higher temperatures yield
chips with less oil than lower temperatures since
hotter oil has a lower density and is not adsorbed as
easily whereas lower frying temperatures require
longer frying times, allowing the chip surface to
adsorb more oil (Saguy et al., 2001).
2.7.2 Frying Oil
The frying oil is the heat transfer medium and
contributes to the final characteristics of the fried
food (Stier, 2004; Vitrac et al., 2000). As the food
fries it absorbs part of the frying oil and thus it
contributes to the overall quality of the fried food
(Stier, 2004). Frying continuously at elevated
temperatures leads to oil breakdown
(Stier,2004).Basic deterioration reactions during
frying are hydrolysis caused by steam from the
food, oxidation caused by air (oxygen) and thermal
alterations caused by heat (Blumenthal, 2001).
3 Result and Discussions
3.1 Result (output of the experiment)
Table3. Main effect of blanching on sensory quality
of fried sweet potato chips
Factors Parameters
Blanching
time
Oil
taste
Colour Odour Texture flavour Overall
acceptability
0 2.9667B 2.9B 2.53B 2.9B 3.2B 2.9B
5
3.367
B
3.53
A
3.13
A
3.83
A
3.833
A
2.9
B
7 3.97A 3.3AB 3.3A 3.167B 2.9B 3.6A
*Means followed by the same letter within a column
are not significantly different p<0.05
3.2 Discussion
Sensory qualities are the main criterion that makes
the product to be liked or disliked. The average and
least means square of Sensory attributes scores of
liking chips from plum sweet potatoes blanched at
65°C at two blanched level with control at which
no blanched taken was presented in the above
tables.
3.2.1 Oil Taste
Oil taste is the parameters that give the product the
unique texture flavour combination that makes them
so desirable on the sense of smell. The sensory score
of oil taste for the three treatment chips samples had
ranged from 3.97 to 2.967. The highest score was
recorded when sweet potato was blanched at 7
minute. The least score was recorded with the
control treatment, which have no blanched taken
place. Blanching has a significance effect on control
and blanched at 5 as compared to 7. But blanching
has no significance effect between 0 and 5. Among
the treatment, treatment 7 has highly significance
over the other treatment. This shows that blanching
has significance effect on oil taste of the chips.
According to Kimberly Button (2015) pre
treatments, such as blanching and drying, can affect
oil uptake by the product and final product texture.
). In a study by Walter and others (2003), evaluated
the blanching of purple-fleshed sweet potato strips
with hot water blanching because hot water
blanching is the preferred method of French fry
manufacturers. The strips were blanched for 0, 5,
and 10 minutes in boiling water, which was about
98°C(208.4°F ).Oner and Wall used high
temperature blanching that readily decreased the
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force in which to penetrate the strips, and ultimately,
the softest texture was observed in the 10 minute
blanched strips. Although, the strips blanched for 10
minutes had more oil absorption after frying
because the surface cell integrity was damaged
allowing more water to release and oil to be
absorbed (Oner and Wall, 2012)
3.2.2 Colour
The sensory score of color for the three samples had
ranged from 3.53 to 2.9. Control is significant
difference as compared to the two treatments 7
minute and 5. But there is no significance difference
between treatment treated at 7 minutes and 5
minute. The highest score was recorded when sweet
potato is blanched at 5 minute. The least score was
recorded with the control treatment, which has no
blanched. This indicate that blanching has a
significance effect on colour. Blanching pre-
treatment is usually performed to prevent
development of off flavours and colour changes
resulting from enzymatic reactions; as well as to
decrease the initial microorganism load (Oluwole,
O.B et al., 2015). Blanching pre-treatment of potato
in hot water or chemical solutions before frying
have been reported to improve colour and texture
and could reduce oil uptake in some cases by
gelatinization of the surface starch (Bunger et al.,
2003; Rinac Brncic et al., 2004). Akpapunam and
Abiante (1991) showed that sweet potato slices
blanched in water and 1% sodium metabisulfite
solution, respectively, prior to the dehydration (at
70°C for 165 min) and frying (at 190°C for 2 min)
significantly improved the colour and general
acceptability of the chips compared to those
immersed in water, only. Colour of potato chips was
significantly influenced by blanching. Blanching
lead to lighter in colour potato chips than those of
the control after frying at 150°C (Pedreschi F.,et al
2005). Rodriguez et al (1999) found that reducing
sugars had the biggest influence on lightness,
producing the brighter colours when these sugars
were absent; however, reducing sugars did not
entirely predict colour quality when present at low
concentrations. Colour is one of the most important
quality factors that need to be considered during
frying. There is also similar observation found by
Olu Malomo et al (2013) blanching affect the
quality characteristics (colour) of sweet potato flour
produced compared to un blanched sweet potato
flour.
3.2.3 Flavour
Flavour is the sensation produced by a material
taken in the mouth, perceived principally by the
senses of taste and smell, and by the general pain,
tactile, and temperature receptors in the mouth. The
sensory score of flavour for the three treatment
chips samples had ranged from 3.833 to 2.9 the
highest score was recorded when the sample or
sweet potato blanched at 5 minute. The least score
was recorded with the samples blanched at7 minute
treatment. This show that 5(3.833) is highly
significance on the other two treatments (0 and 7).
But there is no significance effect between treatment
0 and 7. Luis (1997) established that flavour is one
of the important quality factors of potato chips and
is affected mainly by the type of oil used to fry
chips, flavour compounds inherent in the raw
potatoes, and added flavourings. According to
Dagne Tafa and Tigist Abebe (2018) blanching
improves the flavour of the chips.
3.2.4 Textures
Texture is also a key parameter in the development
and acceptance of food products and an important
attribute in determining consumer acceptability of
fried foods (Krokida, Oreopoulou, Maroulis &
Marinos-Kouris, 2001b; Miranda, Aguilera, &
Beriestain, 2005).The sensory score of texture for
the three treatments of chips samples had ranged
from 3.833 to 2.9. The highest score was recorded
when samples was blanched at 5 minute at constant
temperature and this indicate that treatment 5 has
highly significance difference on other two
treatment (0 and 7). The least score was recorded
with the control treatment, which has no blanched
even though there is no significance difference
between the two treatments (0 and 7). According to
Kita (2002), the crisp texture of potato crisps
depended on the content of starch in the tubers as
well as nitrogen substances and non-starch
polysaccharides. In a study by Walter and others
(2003), low temperature blanching (LTB) was used
to promote the firmness of sweet potato cylinder
strips.Agblor and Scanlon (2000) assessed that
texture and color of chips as affected by blanching,
drying, and frying. Leeratanarak et al (2006) found
that blanching reduced the hardness i.e. better
texture of the product, however, the use of different
blanching periods did not significantly affect the
product hardness. Blanching alters textural
properties and imparts a soft or firm bite on sweet
potato fries. The combination of temperature and
time in the blanching process can create a creamy or
firm internal in the sweet potato fry through the
level of pectin and cell wall breakdown (Kimberly
Button, 2015)
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3.2.5 Overall Acceptability
The overall acceptability refers to the
assumption taken from the aggregate effect of
the all consideration of the above quality
parameters. The sensory score of this overall
acceptability for the three treatments of chips
samples had ranged from 3.67 to 2.9. The
highest score was recorded when chips samples
was blanched at 5 minute. This indicates that
treatment 5 has no significance with treatment
7. The least score was recorded with the control
treatment, which has no blanched. This
indicates that blanching has significance effect
on control as compared to other two treatments
(5 and 7).
Andersson et al.,1996 reported that in the case
of potato processing, blanching is used to
inactivate peroxides, to improve the texture,
colour and, to some extent, the flavour of final
product. Potato blanching affects the enzyme
activity that leads to quality degradation (Tizita
Mamo, 2018). Potato product quality and
acceptability are related to colon and texture
(Pedreschi et al., 2005). Yost et al (2006)
showed that colour is the first attribute of a food
product that immediately convey a positive or a
negative connection of overall quality. Colour
also influences a consumer’s perception of
flavour, taste, and the intent to purchase a food
product according to Dagne Tafa and Tigist
Abebe (2018).Blanching pre-treatment of potato
in hot water or chemical solutions before frying
have been reported to improve colour and
texture and could reduce oil uptake in some
cases by gelatinization of the surface starch
(Bunger et al., 2003; Rinac– Brncic et al.,
2004).
3.3 Effect Frying Time on Sensory Quality of
Fried Sweet Potato Chips
Table 4.The main effect of frying time on sensory
quality of fried sweet potato chips
Factors Parameters
Frying Oil taste Colour Odour Texture Flavour Overall
acceptability
4
3.3667
A
3.8
AA
3.1667
AA
2.8
B
3.133
A
2.9
B
5
3.433
A
3.4
A
2.9667
AA
3.4
A
3.5667
AA
3.8
AA
6 3.5AA 2.533B 2.833A 3.7AA 3.233AA 3.4A
* Means followed by the same letter within a column
are not significantly different p<0.05
3.3.1 Oil Taste
Oil taste is the parameters that give the product the
unique texture flavor –combination that makes then
so desirable on the sense of smell. The sensory score
of oil taste for the three treatment chips samples had
ranged from 3.5 to 3.3667. The highest score was
recorded when sweet potato was fried at 6 minute.
The least score was recorded when chips sample
was fried at 4 minute. This result indicate that there
no significance among all treatments. The sweet
potato chips also had more oil uptake with the
longer frying time. The researchers indicated that
the oil uptake can be affected by cellular structures
in the different sweet potato varieties. Textural
properties were evaluated by a compression test.
The maximum force to compress decreased as
frying time increased. The force to compress did
increase slightly when the 4 to 5 minute frying time
was used, which may be attributed to the crust
development in the longer frying times. Crust
development and sealing of the surface of the sweet
potato fries can result in a low oil uptake. Other
factors that can affect texture of sweet potato french
fries are gelatinization of starch, sugar content, α-
amylase activity, breakdown of cell wall, and
protein denaturation while frying. All of the sweet
potato varieties browned more with increased frying
time due to the Maillard reaction that uses the
reducing sugars in the sweet potatoes. Overall,
Ginseng Red had the lowest oil content and the best
crispy texture (Odenigbo et al., 2012). Mellema
(2003) and Saguy & Dana (2003) observed that
consumers’ preference for low fat and fat-free
products were driving the food industry to lower oil
content in fried foods. Lisiñska (1989) reported that
potato chips high in oil content appear greasy/oily
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while those of very low oil content are of a hard
texture and lack flavour.
According to woolfe (1992) variation in oil taste
may be due to the different pre-frying treatments
used in the various studies. For instance, high initial
moisture content and blanching have been reported
to contribute to increased oil absorption in fried
sweet potato crisps (Woolfe, 1992). According to
deMan (1999), lower frying temperature and longer
frying time results in higher oil uptake. The author
however stated further that oil absorption depends
on conditions of frying and the nature and size of
the food. In the present study, at each frying
temperature, the fat content of the sweet potato
crisps reduced with increase in frying time. Frying
temperature and time, initial moisture content, pore
size distribution, porosity, the geometry of the
product, and pre and posttreatments are some
parameters which can affect the final oil content of
fried product (Saguy et. al., 1995; Moreira et. al.,
1997; Bouchon and Aguilera, 2001). Frying
temperature and time, initial moisture content, pore
size distribution, porosity, the geometry of the
product, and pre and posttreatments are some
parameters which can affect the final oil content of
fried product (Saguy et. al., 1995; Moreira et. al.,
1997; Bouchon and Aguilera, 2001). Potato strips
blanched at 97 °C for 2 min and subsequently fried
presented impaired color, loss of textural quality,
and increased oil absorption as compared to
unblanched ones (Alvarez et al.,2000).the frying
variables influence final oil content sweet potato
chips according to study (Baumann & Escher,
1995).
3.3.2 Colour
The sensory score of colour for the three samples
had ranged from 3.8 to 2.533. There is significant
difference between means at 5 minute and control,
even though there is no difference between
treatment treated at minutes and minute. The highest
score was recorded when sweet potato is fried at
4minute even though it has high mean there is no
significance difference with treatment 5 but, it has
high significance over the treatment 6. The least
score was recorded when chips sample was fried at
6 minute. This indicate that frying has significance
effect on treatment 6(colour). Sahin (2000) studied
the effects of frying time and temperature on the
colour kinetics of French-fried potatoes during
frying; the author developed a multiple regression
equation for total colour change as a function of
time and temperature. The equation showed that
increase in time and temperature increased total
colour change.
3.3.3 Flavour
Flavour is the sensation produced by a material
taken in the mouth, perceived principally by the
senses of taste and smell, and by the general pain,
tactile, and temperature receptors in the mouth. The
sensory score of flavour for the three treatment
chips samples had ranged from 3.566 to 3.133 The
highest score was recorded when the sample or
sweet potato fried at 5 minute and the least score
was recorded with the samples fried at 4 minute
treatment this indicate that there is no significance
difference between all treatment. In fried potato
products, flavour compounds are not only inherent
in the raw potato but also from the frying oil,
maillard reaction products and from the interaction
of maillard reaction products with lipid oxidation
products (Stier, 2000; Maga, 1994; Whitfield,
1992). Variations in flavour exist between varieties
although there is little published research (Dale &
Mackay, 1994). Ereifej, Shibli, Ajlouni & Hussein,
(1997) reported sensory differences in the aroma
and taste of potato chips made from different
cultivars that varied in levels of dry matter, sugars,
amino acids and lipids. The frying variables
influence the colour and flavour (Pedreschi et al.,
2005).
3.3.4 Textures
The sensory score of texture for the three treatments
of chips samples had ranged from 3.7 to 2.8. The
highest score was recorded when samples was fried
at 6 minute at constant temperature. Treatment 5and
6 have highly significance difference over the
treatment 4. But there is no significance difference
between 5 and 6. The least score was recorded
when the samples was fried at 4 minute. Frying has
significance effect on Treatment 4 as compared to
the two treatments (5 and 6). Crispness increased
with increase in frying time. This indicates that
frying temperature and time are important factors
affecting the sensory quality of sweet potato crisps.
(G. O. Fetuga et al., 2014). Verlinden et al(2000)
found that hot water blanching of potatoes at 55–75
°C affected their texture parameters, as per reducing
the maximum force and the rupture force of the
samples, and increasing the deformation at
maximum force and the rupture deformation. They
attributed this behavior the loss of turgor pressure in
the tissue during heating. Additionally, they found
that blanching/cooling before cooking had a
strengthening effect on potatoes, especially when
blanching treatments were longer. The frying
variables influence the texture (Miranda et al., 2005)
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3.3.5 Overall Acceptability
The overall acceptability refers to the assumption
taken from the aggregate effect of the all
consideration of the above quality parameters. The
sensory score of this overall acceptability for the
three treatments of chips samples had ranged from
3.8 to 2.9. The highest score was recorded when
chips samples was fried at 5 minute. Treatment 5
and 6 has high significance difference over
treatment 4 but, no significance between them. The
least score was recorded when samples was fried at
4minute.Frying has significance effect on Treatment
4 as compared to the two treatments (5 and 6). The
desirable sensory properties of potato chips are
developed during frying and thus apart from the
quality of the raw potatoes the conditions during
frying will affect the final product quality (Hubbard
& Farkas, 1999; Lolos, Oreopoulou & Tzia,
1999).According to study found G. O. Fetuga et al
(2014) taste, colour, flavour, crispness and overall
acceptability were significantly affected by the
individual and combined effects of frying
temperature and frying time. This indicates that
frying temperature and time are important factors
affecting the sensory quality of sweet potato crisps.
4. Conclusions
The effects of blanching and frying time on the
Sensory and nutritional characteristics of sweet
potato chips were investigated .These results
showed the blanching time treatment has effect on
the quality characteristics of sweet potato as
compared to unblanched samples. Blanching sweet
potato could be used to enhance the quality of food
products such as colour, flavour, texture, and overall
acceptability fried sweet potato treated with 5
minute was the best sample in all sensory
characteristics The sweet potato blanched at 7
minute was observed as a good quality than others
and in the case of time frying at 5 and 7 minute
resulted good overall acceptability So using these
method is good for producing good quality chips.
Generally, the pre-treatment improved the textural
properties of fried samples in terms of hardness,
springiness, chewiness, cohesiveness and,
adhesiveness. Therefore, treated with blanching and
frying could be used to make a higher quality
product that is more attractive to product developers
and consumers.
Acknowledgment:
Our first acknowledgement goes to the Almighty
God for His protection and grace throughout our
period of study. We would like to forward our
deepest gratitude to our advisor Ms. Addisalem
Hailu for her keen interest in our proposal work,
follow up of our progress, encouragement and
support. We are also grateful to the academic staff
of the Department of Post-Harvest Management for
imparting tremendous knowledge to us. We
appreciate Mr. Abebe Yimer for their constant
supervision and recommendation during our title
preparation and proposal work.
References:
[1] Abong GO, Ckoth MW, Imungi JK, Kabira JN,
Effect of Slice Thickness and Frying
Temperature on Color, Texture and Sensory
Properties of Crisps made from Four Kenyan
Potato Cultivars,American Journal Food
Technol 6, 2011: 753-762.
[2] Abong GO, Okoth MW, Karuri EG, Kabira JN,
Mathooko FM, Influence of potato cultivar and
stage of maturity on oil content of French fries
(chips) made from eight Kenyan potato
cultivars, African Journal of Food, Agriculture,
Nutrition and Development 2009.
[3] Agblor,A.,andM.G.Scanlon,Processing
conditions influencing the physical properties of
french fried potatoes, Potato Research
43,2000,163–178.
[4] Aguilera, J. M. & Gloria-Hernández, H, Oil
absorption during frying frozen parfried
potatoes,Journal of Food Science, 65, 2000,
476–479.
[5] Akpapunam, M.A. and D.A. Abiante, 1991.
Processing and quality evaluation of sweet
potato chips,Journal Plant Foods Human
Nutrition, 41,1991,291-297.
[6] Alvarez, C.A.; Aguerre, R.; Gomez, R.; Vidales,
S.; Alzamora S.M.; Gerschenson, L.N. Air
Dehydration of strawberries: Effects of
blanching and osmotic pretreatments on the
kinetics of moisture transport. Journal of Food
Engineering, 25, 1995, 167–179.
[7] Babalola, O.O, H.O. Adubiaro and O. Ikusika,
The effect of some processing methods on the
vitamin c content of sweet and irish
potato,Electron. Journal. Environmental
Agricultural Food Chemistry, 9, 2010, 679-681.
[8] Baik, O.D. and G. S. Mittal, Kinetics of tofu
color changes during deep-fat frying, Journal
Food Science Technology, 36, 2003, 43-48.
[9] Baumann, B. & Escher, E.,. Mass and heat
transfer during deep fat frying of potato slices I,
Rate of drying and oil uptake, Lebensmittel-
Teferi Damto, Geremew Chala
Food and Nutrition Science - An International Journal
http://iaras.org/iaras/journals/fnsij
ISSN: 2367-9018
12
Volume 3, 2019
Wissenschafft und Technologie, 28, 1995, 395–
403.
[10] Baybutt, R.C., L. Hu and A. Molteni,
Vitamin A deficiency injures lung and liver
parenchyma and impairs function of rat type II
pneumocytes,Journal of Nutrition, 130,
2000,1159-1165.
[11] Belehu, T, Agronomical and physiological
factors affecting growth, development and yield
of sweet potato in Ethiopia ,University of
Pretoria ,2003.
[12] Bennett, R. M., Managing potato crisp
processing. In: Rossell, J. B. (Ed.) Frying:
Improving Quality. CRC Press: Florida, 2010,
215-235.
[13] Blenkinsop, R. W., Copp, L. J., Yada, R.
Y,Changes in compositional parameters of
tubers of potato (Solanum tuberosum) during
low-temperature storage and their relationship
to chip processing quality,Journal of
Agriculture Food Chemistry, 50, 2002 ,4545-
4553.
[14] Blumenthal, M. M. & Stier, R.
F.,Optimization of deep-fat frying
operations,Trends in Food Science &
Technology, 2, 1991,144-148.
[15] Blumenthal, M. M., A new look at the
chemistry and physics of deep fat frying,Food
Technology, 45, (2),1991, 68–71, 94.
[16] Burri, B. J.,Evaluating sweet potato as an
intervention food to prevent vitamin A
deficiency,Compresive Review of Food
Science, 10,2011, 118-130.
[17] Bouchin P, Aguilera J, Pyle, Structure Oil-
Absorption Relationships During Deep-Fat
Frying,Journal of Food Science ,68,2003, 2711-
2716.
[18] Bouchon P., Hollins P., Pearson M, Pyle D.
L And Tobin M. J.,( 2001),Oil distribution in
fried potatoes monitored by infrared
microspectroscopy,Journal of Food Science, 66,
918–923.
[19] Bouchon, P. & Aguilera, J. M,
Microstructural analysis of frying of
potatoes,International Journal of Food Science
and Technology, 36,2001, 669-676.
[20] Bouwkamp, J. C,Sweet potato products: A
natural resource for the tropics,CRC Press,
1985.
[21] Brigatto Fontes L. C., Oliveria, F. G. and
CollaresQueiroz, F. P,Optimization of the deep-
fat frying process of sweet potato chips in palm
olein or stearin.,American Journal of Food
Technology 6(5), 2011,348-361
[22] Bunger, A.; Moyano P.; Rioseco, V,NaCl
soaking treatment for improving the quality of
french– fried potatoes,Food Research
International, 36,2003, 161–166.
[23] Caixeta, A. T., Moreira, R., & Castell-
Perez, M. E, Impingement drying of potato
chips,Journal of Food Process Engineering,
25(1),2002, 63-90.
[24] Chen, L.H. & Allison, M.(1982),Horizontal
transplanting increases sweet potato yield if
planted early, Research report 6 (20), Missouri
Agricultural & Forestry Experiment station,
Mississippi State University, Mississippi.
[25] Chi-Tang Ho & Shahidi F,Flavour
components of fats and oils,In: Shahidi, F. (Ed.)
Bailey’s Industrial Oil and Fat Products, Vol. 1,
6th ed. John Wiley & Sons, Inc: New York,
2005,387-411.
[26] Chukwu O, Nwadike N, Nwachukwu N,
Effects of cooking and frying on antioxidants
present in sweet potatoes (Ipomoea
batatas),Academic Research International
2(2),2012, 104-109.
[27] Claudio, P,The universe of food
quality,Food Quality and Preference, 17,2006,
3-8.
[28] Costa, R. M., Oliveira, F. A. R., &
Bouthcheva, G, Structural changes and
shrinkage of potato during frying,International
Journal of Food Science and Technology,
36,2001, 11-23.
[29] CSA (Central Statistical Agency) and
World Bank,Survey report. Ethiopia Rural
Socioeconomic Survey (ERSS), Addis Ababa,
Ethiopia. Retrieved 20 December 2016 from
http://siteresources.worldbank.org/INTLSMS/R
esources/3358986-1233781970982/5800988
1367841456879/9170025-1367841502220/
ERSS_Survey_Report.pdf, 2013.
[30] CSA (Central Statistical Agency). (2007).
[31] Farrell, M. J,The measurement of
productive efficiency,Journal of the Royal,1957
[32] CSA (Central Statistical Agency), Crop
Production Forecast Sample Survey, 2013/14.
Report on Area and Production for Major
Crops (for Private Peasant Holdings ‘Meher’
season). Addis Ababa, Ethiopia,2014
[33] CTA Practical Guide Series, No. 6, Making
sweet potato chips and flour.,www.cta.int,
Wageningen, The Netherlands,2007.
[34] Da Silva, P. F. & Moreira, R. G, Vacuum
frying of high-quality fruit and vegetable-based
snacks,LWT- Food Science and Technology, 41,
2008, 1758-1767.
Teferi Damto, Geremew Chala
Food and Nutrition Science - An International Journal
http://iaras.org/iaras/journals/fnsij
ISSN: 2367-9018
13
Volume 3, 2019
[35] Damodaran S, Parkin KL, Fennema
OR,Fennema‟s food chemistry,4th edition,Boca
Raton, FL: CRC/Taylor & Francis,2008.
[36] Dan. J., Mary. K. G., and Leigh A.,Sweet
Potato Value Chain: Ethiopia, EPAR (Evans
School Policy Analysis and Research) Brief No
219, Wevans School of Public Affairs,
University of Washigton,2013.
[37] Debnath S, Bhat KK, Rastogi NK , Effect of
pre-drying on kinetics of moisture loss and oil
uptake during deep fat frying of chickpea flour-
based snack food, LWT - Food Science and
Technology 36,2003, 91-98.
[38] DeMan, J. M, Principles of food chemistry.
Springer Science+Business Media, Inc. 519pp,
1999.
[39] Ereifej, K. I., Shibli, R. A., Ajlouni, M. M.
& Hussein, A, Chemical composition variations
of tissues and processing characteristics in ten
potato cultivars grown in Jordan,American
Journal of Potato Research, 74,1997, 23-30.
[40] Everette, J.D. and S. Islam,Effect of
extraction procedures, genotypes and screening
methods to measure the antioxidant potential
and phenolic content of orange-fleshed
sweetpotatoes (Ipomoea batatas L.)American
journal Food Technololgy,7,2012, 50-61.
[41] Fan, L., Zhang, M., & Mujumdar, A.
S,Effect of various pretreatments on the quality
of vacuum-fried carrot chips,Drying
Technology, 24, 2006,1481-1486.
[42] FAOSTAT, FAO
Statistics.http://faostat.fao.org/site/567/default.a
spx#ancor,2009.
[43] FAOSTAT, FAOSTAT Food and
Agriculture Organization of the United Nations,
Statistical Data base, Production 2009,
Accessed 5th January, 2012.
[44] FAO, Overview of Root and Tuber Crops-
Corporate Document Repository,Food and
Agriculture Organization of the United Nations.
New York, 2012.
[45] Farinu A, Baik OD, Heat transfer
coefficients during deep fat frying of sweet
potato: Effects of product size and oil
temperature, Food Research Institute 40, 2007,
989-994.
[46] Gamble, M. H., Rice P. and Selman I.D,
Relationship between oil uptake and moisture
loss during frying of potato slices from C. V.
Record U. K. tubers. International Journal
Food Science Technolology. 22,1970,233-241.
[47] Garayo, J. & Moreira, R. G,Vacuum frying
of potato chips, Journal of Food Engineering,
55 (2), 2002, 181-191.
[48] Garayo, J, Production of low-fat potato
chips using vacuum frying. MS thesis, College
Station, Texas: Texas A&M University, 2001.
[49] Gertz, C., Klostermann, S., & Kochhar, S.
P,Testing and comparing oxidative stability of
vegetable oils and fats at frying temperature,
European Journal of Lipid Science and
Technology, 102, 2000, 543–551.
[50] Gillat, P, Flavour and aroma development
in frying and fried food. In: Rossell, J. B. (Ed.)
Frying: Improving Quality, CRC Press: Florida,
2001.
[51] Granda, C. & Moreira, R. G,Kinetics of
acrylamide formation during traditional and
vacuum frying of potato chips., Journal of Food
Process Engineering, 28, 2005, 478-493.
[52] Granda, C. & Moreira, R. G., and Tichy,
S.E,Reduction of acrylamide formation in
potato chips by low-temperature vacuum
frying,Journal of Food Science, 69(8), 2004,
405-411.
[53] G. O. Fetuga, T. E. Ajayi, and O. R. Karim,
Effect of frying temperature and time on
composition and sensory quality of sweet potato
crisps, Agriculture Research Article in AJRTC
11(1), 2014 ,17-25
[54] Guillaumin, R, Kinetics of fat penetration in
food. In: Frying of food: principles, changes,
new approaches. (Eds) G. Varela, A. E. Bende
& I. D. Morton. Ellis Horwood, Chichester,
England, 1988, pp. 82-90.
[55] Gupta, M. & Warner, K,Potato chip quality
and frying oil stability of high oleic acid
soybean oil, Journal of Food Science, 70, 2005,
395-400.
[56] Gurmu, F., Hussein, S., & Laing, M,
Diagnostic assessment of sweetpotato
production in Ethiopia: Constraints, post-harvest
handling and farmers’ preferences, Research on
Crops, 16(1), 2015, 104-115.
[57] Hubbard, L. J. & Farkas, B. E,A method for
determining the convective heat transfer
coefficient during immersion frying, Journal of
Food Process Engineering, 22(3), 1999, 457-
465.
[58] International Potato Center (CIP). (1995),
People centered research for sustainable
production. Circular, Vol (21:1), 1995
[59] Iyagmur Ravli, Improved vacuum frying
process for high quality sweet potato chips.
Submitted to the Office of Graduate Studies of
Texas A&M University in partial fulfillment of
the requirements for the degree of Master of
Science, 2012.
Teferi Damto, Geremew Chala
Food and Nutrition Science - An International Journal
http://iaras.org/iaras/journals/fnsij
ISSN: 2367-9018
14
Volume 3, 2019
[60] Kasahara, I., Osorio, F., Moyano, P.,
Pizarro, G., & Beltran, J, Study of texture and
glass transition of French fried potatoes
pretreated with soaking solutions,Journal of
Food Processing Preservation, 26,2002, 237-
257.
[61] Kawas, M. L, Characterization of product
quality attributes of tortilla chips during the
frying process. MS thesis. College Station,
Texas: Texas A& University, 2000.
[62] Kawas, M. L. & Moreira, R,
Characterization of product quality attributes of
tortilla chips during the frying process, Journal
of Food Process Engineering, 47(1), 2001, 97-
107.
[63] Kidmose, U., L.P. Christensen, S.M. Agili
and S.H. Thilsted, Effect of home preparation
practices on the content of provitamin A
carotenoids in coloured Sweet potato varieties
(Ipomoea batatas Lam.) from Kenya. Innovative
Food Science Emerg, 8, 2007, 399-406
[64] Kimberly Button, Processing Sweet
Potatoes into French Fries. B.S., University Of
Idaho, A Report Submitted In Partial
Fulfillment of the Requirements for the Degree,
2015
[65] Kita, A, The influence of potato chemical
composition on crisp texture, Food Chemistry,
76, 2002, 173-179.
[66] Kita, A & Lisiñska, G, The influence of oil
type and frying temperatures on the texture and
oil content of French fries, Journal of the
Science of Food and Agriculture, 85, 2005,
2600-2604
[67] Kivuva, B. M., Musembi, F. J., Githiri, S.
M., Yencho, C. G., & Sibiya, J. (2014),
Assessment of Production Constraints and
Farmers’ Preferences for Sweet potato
Genotypes. 2(1), 2014, 15-18
[68] Kochhar, S. P. & Gertz, C, New theoretical
and practical aspects of the frying process,
European Journal of Lipid Science and
Technology, 106, 2004, 722–727.
[69] Kopsell, D.A. and D.E. Kopsell,
Accumulation and bioavailability of dietary
carotenoids in vegetable crops, Trends Plant
Science, 11, 2006, 499-507.
[70] Krokida MK, Oreopoulou V, Maroulis ZB,
Marinos-Kouris D, Effect of pre-drying on
quality of french fries, Journal Food
Engenering 49, 2001, 347-354.
[71] Krokida, M. K., Oreopoulou, V., &
Maroulis, Z. B,Effect of frying conditions on
shrinkage and porosity of fried potatoes,
Journal of Food Engineering, 43, 2000, 147-
154.
[72] Krokida, M. K., Oreopoulou, V., Maroulis,
Z. B. and Kouris, D. M., Deep fat frying of
potato strips Quality issues. Drying
Technolology. 16, 2001:879-935.
[73] Krokida, M., Oreopoulou, V., Maroulis, Z.,
& Marinos-Kouris, D, Color changes during
deep fat frying, Journal of Food Engineering,
48, 2001, 219-225.
[74] Lawless, H. T. & Heymann, H, Texture
evaluation. In: Sensory evaluation of food.
Chapman & Hall: New York, 1998.
[75] Leszcyñski, W, Potato tubers as a raw
material for processing and nutrition. In:
Lisiñska, G. & Leszcyñski, W. (Eds.), Potato
Science and Technology ,Elsevier Science
Publisher: London, 1989,11- 108.
[76] Leeratanarak et al, Drying kinetics and
quality of potato chips undergoing different
drying techniques,2006
[77] Lisiñska, G., 1989. Manufacture of potato
chips and French fries. In: Lisiñska, G. &
Leszcyñski, W. (Eds.), Potato Science and
Technology. Elsevier Science Publisher:
London, 1989, 166- 233.
[78] Lisinska, G. & Leszczynski, W. (1989),
Potato science and technology, Elsevier,
Applied Science, London, 1989.
[79] Lolos, M., Oreopoulou, M. V. & Tzia,
Oxidative stability of potato chips: effect of
frying oil type, temperature and antioxidants,
Journal of the Science of Food and Agriculture,
79, 1999, 1524 – 1528
[80] Lourenco E, Neves V, Maraiza A,
Polyphenol oxidase form sweet potato:
Purification and properties, Journal Agriculture
Food Chemistry 40, 1992, 2369-2373
[81] Maga, J. A. (1994). Potato flavour, Food
Reviews International, 10, 1994, 1-48.
[82] Marousis, S. N. & Saravacos, G. D, Density
and porosity in drying starch materials., Journal
of Food Science, 55, 1990, 1367-1372
[83] Marquez G, & Anõn, M. C, Influence of
reducing sugars and amino acids in the colour
development of fried potatoes, Journal of Food
Science, 51, 1986, 157-160.
[84] Martin, F. L. & Ames, J. M, Comparison of
flavour compounds of potato chips fried in
palmolein and silicone fluid, Journal of the
American Oil Chemists Society, 78, 2001, 863-
866.
[85] Mela, D. J. & Christensen, C. M, Sensory
assessment of oiliness in a low moisture food,
Journal of Sensory Studies, 2, 1987, 273-281
Teferi Damto, Geremew Chala
Food and Nutrition Science - An International Journal
http://iaras.org/iaras/journals/fnsij
ISSN: 2367-9018
15
Volume 3, 2019
[86] Mellema, M, Mechanism and reduction of
fat uptake in deep-fat fried foods, Trends in
Food Science and Technology, 14(9), 2003,
364-373.
[87] Miranda, M. & Aguilera, J. M, Structure
and texture properties of fried potato products,
Food Reviews International, 22, 2006, 173-201.
[88] Moreira, R. G. & Barrufet, M. A, A new
approach to describe oil absorption in fried
foods: a simulation study, Journal of Food
Engineering, 31, 1998, 485-498.
[89] Moreira, R. G., Da Silva, P. F., & Gomes,
C, The effect of a de-oiling mechanism on the
production of high quality vacuum fried potato
chips, Journal of Food Engineering, 92, 2009,
297-304.
[90] Moreira, R. G., Sun, X., & Chen, Y, Factors
affecting oil uptake in tortilla chips in deep-fat
frying, Journal of Food Engineering, 31, 1997,
485-498.
[91] Moreira, R. G., Sun, X., & Chen, Y,Factors
affecting oil uptake in tortilla chips in deep-fat
frying, Journal of Food Engineering, 31, 1997,
485-498.
[92] Moreira, R.G., Castell-Perez, M.E. &
Barrufet, M. A, Deep-Fat Frying: Fundamentals
and Applications, Aspen Publishers:
Gaithersburg, 1999, 75-108.
[93] North Carolina Sweet Potato Commission,
Sweet potatoes101, Availablefrom:
http://www.ncsweetpotatoes.com/sweet-
potatoes-101/difference-between-yam-
andsweet-potato/. Accessed March 22, 2015.
[94] Odenigbo, A., Rahimi1, J., Ngadi1, M.,
Wees, D., Mustafa, A., and Philippe S, Quality
changes in different cultivars of sweet potato
during deep-fat frying, Journal of Food Process
Technology, 2012, 3:5.
[95] Olu Malomo, M. O. Jimoh, O. O.
Adekoyeni, O. E. Soyebi, E. A. Alamu, Effect
of blanching and unblanching on rheological
properties of sweet-potato bread, Journal
Academic Research International, ISSN-L:
2223-9553, ISSN: 2223-9944, 2013
[96] Oner M, Wall M, Processing conditions for
producing French fries from purple-fleshed
sweetpotatoes, American Society of Agricultural
and Biological Engineers 55 (6), 2012, 2285-
2291.
[97] Pedreschi, F. & Moyano, P, Effect of pre-
drying on texture and oil uptake of potato chips.
Lebensmittel-Wissenschafft und-Technologie,
38, 2005, 599-604.
[98] Pedreschi, F., Aguilera, J.M. & Pyle, L,
Textural characterization and kinetics of potato
strips during frying, Journal of Food Science.
66, 2001, 314–318.
[99] Pedreschi, F., Kaack, K., Granby, K.
Troncoso, E,Acrylamide reduction under
different pre-treatments in French fries, Journal
of Food Engineering, 79, 2007, 1287-1294
[100] Porkony, J,Flavor chemistry of deep fat
frying in oils. In Smouse, T. & Perkins, E. G.
(Ed.) Flavor Chemistry of Lipid
Foods,American Oil Chemists Society: Illinois.
potato chips. Plant Foods for Human Nutrition
41, 1988, 291-297.
[101] Rahman, S., Food properties handbook,
Boca Raton, Florida: CRC Press,1995.
[102] Rimac-Brnčić, S., Lelas, V., Rade, D. &
Šimundić, B, Decreasing of oil absorption in
potato strips during deep fat frying, Journal of
Food Engineering, 64, 2004, 237-241.
[103] Rodriguez-Saona L. E. & Wrolstad R E,
Influence of potato composition on chip color
quality, American Potato Journal, 74, 1997, 87-
106.
[104] Saguy, I. S. & Dana, D, Integrated approach
to deep fat frying: engineering, nutrition, health
and consumer aspects, Journal of Food
Engineering, 56, 2003, 143-152.
[105] Saguy, I. S. & Pinthus, I. J, Oil uptake
during deep fat frying: factors and mechanisms,
Food Technology, 49, 1995, 142-145.
[106] Saguy, I. S., Ufheil, G., & Livings, S, Oil
uptake in deep-fat frying: a review, Oléagineux
Corps gras Lipides, 5, 1998, 30–35.
[107] Sahin, S, Effects of frying parameters on the
colour development of fried potatoes, European,
Food Research and Technology, 211, 2000,
165-168.
[108] Scanlon, M. Commercial potato production:
Botany of the potato. Website:
http://www.gov.mb.ca/agriculture/crops/potatoe
s/bda04s02. Accessed 28 December 2006, 2003.
[109] Segnini, S., Dejmek, P. & Öste, R., A low
cost video technique for colour measurement of
potato chips. Lebensmittel-Wissenschafft und-
Technologie, 32, 1999, 216-222.
[110] Segnini, S., Pedreschi, F. & Dejmek, P,
Volume measurement method of potato
chips,International, Journal of Food Properties,
7, no. 1, 2004,37-44.
[111] Smith, O. Potato chips. In: Smith, O. &
Talburt, W. F. (Ed.) Potato Processing, 3rd ed.
The AVI Publishing Company,New York,1975,
305-321.
[112] Stier, R. F,Chemistry of frying and
optimization of deep-fat fried food flavour- An
Teferi Damto, Geremew Chala
Food and Nutrition Science - An International Journal
http://iaras.org/iaras/journals/fnsij
ISSN: 2367-9018
16
Volume 3, 2019
introductory review, European Journal of Lipid
Science and Technology, 102, 2000, 507-514.
[113] Stier, R. F, Frying as a science-An
introduction, European Journal of Lipid Science
and Technology, 106, 2004, 715-721.
[114] Suda, I., T. Oki, M. Masuda, M. Kobayashi,
Y. Nishiba and S. Furuta, Physiological
functionality of purple-fleshed sweet potatoes
containing anthocyanins and their utilization in
foods, Japan. Agriculture Reserch Q., 37, 2003,
167-173.
[115] Sylvia K and Walter W, Alkali-processed
sweetpotato french fries, Journal Food Quality
20, 1997, 1730-1735
[116] Szczesniak, A. S, Classification of textural
characteristics, Journal of Food Science, 28,
1963, 385-389.
[117] Szczesniak, A. S,Texture: Is it still an
overlooked food attribute? Food Technology,
44, no. 9, 86, 88, 90, 92, 95,1990
[118] Tafa D, Abebe T, Effect of bacterial wilt
disease, blanching and growing environment on
potato varieties (Solanum tuberosum L.) and
processing quality of potato chips, Acadamic.
Journal. Agriculture. Research. 6(2), 2018, 048-
056.
[119] Taiwo, K. A. & Baik, O. D, Effect of pre-
treatments on the shrinkage and texture
properties of fried sweet potatoes, LWT- Food
Science and Technology, 40(4), 2007, 661-668.
[120] Teow, C.C., V.D. Truong, R.F. McFeeters,
R.L. Thompson, K.V. Pecota and G.C.
Yencho,Antioxidant activities, phenolic and β-
carotene contents of sweet potato genotypes
with varying flesh colours. Food Chemistry.
103, 2007, 829-838.
[121] Troncoso E, Pedreschi F, Modeling water
loss and oil uptake during vacuum frying of pre-
treated potato slices, LWT-Food Science and
Technology 42, 2009, 1164-1173. Industry Hi-
Tech 22: 14-16. 5.
[122] Ufheil, G. & Escher, F, Dynamics of oil
uptake during deep-fat frying of potato slices.
Lebensmittel-Wissenschafft und-Technologie,
29, 1996, 640 –644.
[123] Ukom, A.N., P.C. Ojimelukwe and D.A.
Okpara, Nutrient composition of selected sweet
potato [Ipomea batatas (L) Lam] varieties as
influenced by different levels of nitrogen
fertilizer application. Pakistan Journal
Nutritional, 8, 2009, 1791-1795.
[124] USDA, National nutrient database for
standard reference release 27: Sweet potato,
raw, unprepared.
Availablefrom:http://ndb.nal.usda.gov/ndb/food
s/show/3242?fgcd=&manu=&lfacet=&format=
&count&max=35&offset=&sort=&qlookup=Sw
eet+potato%2C+raw%2C+unprepared,2009.
[125] Vitrac, O., Trystram, G. & Raoult-Wack, A,
Deep-fat frying of food: heat and mass transfer,
transformations and reactions inside the frying
material, European Journal of Lipid Science
and Technology, 102, 2000, 529-538.
[126] Walter W, Catignani G, Biological quality
and composition of sweet potato protein
fractions, Journal of Agricultural Food
Chemistry 29, 1981, 797-799.
[127] Walter W, Purcell A, Effect of substrate
levels and polyphenol oxidase activity on
darkening in sweet potato cultivars, Journal
Agricultura; Food Chemistry, 28, 1980, 941-
944.
[128] Walter W, Schadel W, Effect of lye peeling
conditions on sweet potato tissue, Journal Food
Science 47, 1982, 813-817.
[129] Walter W, Truong V. Simunovic N,
McFeeters R, Low-temperature blanching of
sweet potatoes to improve firmness retention:
Effect on compositional and textural properties,
Journal Food Science, 68 (4), 2003, 1244-1247.
[130] Whitfield, F. B, Volatiles from interactions
of Maillard reactions and lipids, Critical
Reviews in Food Science and Nutrition, 31,
1991, 1–5
[131] Woolfe, J.A, Sweet Potato: An Untapped
Food Resouce. Cambridge University Press,
Cambridge, UK, 1992m p.643.
[132] Yang, J. and R.L. Gadi, Effects of steaming
and dehydration on anthocyanins, antioxidant
activity, total phenols and color characteristics
of purple-fleshed sweet potatoes (Ipomoea
batatas), American Journal Food Technolology,
3, 2008, 224-234.
[133] Yared Dagne, Tewodros Mulualem, Asfaw
Kifle, Development of High Yielding Taro
(Colocacia esculenta L.) Variety for Mid
Altitude Growing Areas of Southern Ethiopia,
Journal of Plant Sciences. Vol. 2, No. 1, 2014,
pp. 50-54. doi: 10.11648/j.jps
[134] Yost et al (2006). Kinetics of potato color
and texture development during backing, frying,
and microwaving with the addition of liquid
smoke, 2010.
Teferi Damto, Geremew Chala
Food and Nutrition Science - An International Journal
http://iaras.org/iaras/journals/fnsij
ISSN: 2367-9018
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