Cooking Treatment Effects on Sugar Profile and Sweetness of Eleven-Released Sweet Potato Varieties

Abstract

Cooking can significantly alter sugar content of sweet potato roots. Sweet potato roots were processed using three different cooking treatments, with the aim of investigating the effects of these methods on sugar profile and sweetness levels. Significant contribution of the cooking treatment and genotype, and their interaction on levels of the sugars were also determined. Moreover, sugar values were converted to relative sweetness per sucrose equivalent. The results revealed that cooking treatment produced the highest effect on sugar except fructose. Variability due to the interactions was significant and ranged from 2.60% to 11.74%. Whilst sucrose was the predominant in the raw form, maltose increased dramatically during cooking. Sweetness level increased substantially upon cooking and was highly dependent on initial sugar content, amylase activity and cooking treatment. Thus, evaluation of sweetness levels in sweet potato clones should not only be on the uncooked samples but should take into account the cooking methods employed.

Full text

Volume 7 • Issue 4 • 1000580
J Food Process Technol
ISSN: 2157-7110 JFPT, an open access journal
Open Access
Research Article
Journal of Food
Processing & Technology
ISSN: 2157-7110
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Owusu-Mensah et al., J Food Process Technol 2016, 7:4
http://dx.doi.org/10.4172/2157-7110.1000580
*Corresponding author: Owusu-Mensah E, Food Science and Technology
Department, College of Science, Kwame Nkrumah University of Science and
Technology, Kumasi, Ghana, Tel: +233-547335237; E-mail: e.owusu@cgiar.org
Received March 21, 2016; Accepted April 12, 2016; Published April 18, 2016
Citation: Owusu-Mensah E, Oduro I, Ellis WO, Carey EE (2016) Cooking
Treatment Effects on Sugar Prole and Sweetness of Eleven-Released Sweet
Potato Varieties. J Food Process Technol 7: 580. doi:10.4172/2157-7110.1000580
Copyright: © 2016 Owusu-Mensah E, et al. This is an open-access article
distributed under the terms of the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided
the original author and source are credited.
Abstract
Cooking can signicantly alter sugar content of sweet potato roots. Sweet potato roots were processed using three different
cooking treatments, with the aim of investigating the effects of these methods on sugar prole and sweetness levels. Signicant
contribution of the cooking treatment and genotype, and their interaction on levels of the sugars were also determined. Moreover,
sugar values were converted to relative sweetness per sucrose equivalent. The results revealed that cooking treatment produced
the highest effect on sugar except fructose. Variability due to the interactions was signicant and ranged from 2.60% to 11.74%.
Whilst sucrose was the predominant in the raw form, maltose increased dramatically during cooking. Sweetness level increased
substantially upon cooking and was highly dependent on initial sugar content, amylase activity and cooking treatment. Thus,
evaluation of sweetness levels in sweet potato clones should not only be on the uncooked samples but should take into account
the cooking methods employed.
Cooking Treatment Effects on Sugar Profile and Sweetness of Eleven-Released
Sweet Potato Varieties
Owusu-Mensah E
1,2
*, Oduro I
1
, Ellis WO
1
and Carey EE
2
1Food Science and Technology Department, College of Science, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana
2International Potato Centre (CIP), Kumasi, Ghana
Keywords: Cooking treatments; Sugar prole; Sweetness level;
Amylase activity; Maltose
Introduction
Sweetness, derived from sugars in the raw sweet potato root
and maltose formed during cooking, is the predominant attribute
controlling the taste of cooked sweet potato products [1,2]. e level
of sweetness in the root determines the type of product or formulation
that can be developed. A number of factors including maturity period,
storage, amylase potential, curing and baking treatment signicantly
inuence sweetness/sugar content of sweet potato roots [3-5]. Baking
treatment and the amylolytic potential nonetheless have the greatest
eect on sugar content of the nal product [6-8]. Baking generally
increases sugar content of sweet potato roots [9,10]. Increase in sugar
content during baking can be dramatic, leading to a very sweet product
[9]. ough eect of baking treatment on sugars of sweet potato roots
has been extensively investigated, limited data is available on other
cooking treatment such as steaming and microwaving. Nevertheless,
sweet potato roots are cooked by dierent treatments including
microwaving; baking, steaming and boiling prior to consumption with
the aim to increase the culinary properties and enhance digestibility
[11]. Temperature, time and mode of heat transfer dierentiate these
cooking methods. Conventional baking usually lasts for 60-90 min
at 180-220°C, depending on the genotype and tuber size [9]. Baking
temperature as reported by Simkovic [12] and Chan [6] can however
cause sucrose caramelisation, a phenomenon, which results in
conversion of sucrose to oligomers and polymers. Microwave cooking
employs a high temperature, short time heating mechanism to cook
food products [10]. Heat is transferred by convection and conduction
during baking whilst electromagnetic waves penetrate food materials
causing agitation and friction to produce heat for cooking during
microwaving [5]. e eect of steaming on quality characteristics of
sweet potato root has not been widely reported.
Although eects of some cooking methods, especially baking, on
quality attributes of sweet potatoes have been evaluated comparative
studies with the view of understanding the eects of dierent cooking
treatments on sugar proles, sweetness and utilisation of sweet potatoes
are limited. Moreover the inuence of cooking treatments on sugars
of eleven ocially released sweet potato varieties in Ghana has not
been investigated. To better understand the contribution of dierent
cooking methods on sugar formation and sweetness of sweet potato
roots, individual sugar and sweetness levels of eleven released varieties
were determined following baking, microwaving and steaming.
Methodology
Experimental design
Triplicates of eleven sweet potato varieties released by Council for
Scientic and Industrial Research (CSIR) – Crops Research Institute
(CRI) were planted in a randomized complete block design on May
2014 at the CSIR-CRI experimental station, Fumesua, Ghana [13-15].
Harvesting was done four months aer planting (September, 2014)
and each plot was treated as a separate sample during laboratory
evaluations. Harvested roots were stored for a week at room condition
(25 to 30°C) prior to processing.
Sample preparation
Four medium-size intact roots of each variety were washed with
clean water, rinsed and air-dried. e clean roots were then quartered,
rinsed with de-ionised water and dried using paper towels. Each quarter
was sliced across its longitudinal axis to approximately 1.0 cm thickness
and composite samples from each plot, divided into four groups of 50
g. One group was designated as raw and the rest were subjected to three
dierent processing methods; baking, steaming and microwaving. For
baking, one group of the sliced samples was wrapped in aluminium foil
and placed in a forced air oven (Genlab MINI/50/DKG), which has
been preheated to 205°C, for 30 mins. For steaming, another group of

Citation: Owusu-Mensah E, Oduro I, Ellis WO, Carey EE (2016) Cooking Treatment Effects on Sugar Prole and Sweetness of Eleven-Released
Sweet Potato Varieties. J Food Process Technol 7: 580. doi:10.4172/2157-7110.1000580
Page 2 of 6
Volume 7 • Issue 4 • 1000580
J Food Process Technol
ISSN: 2157-7110 JFPT, an open access journal
root samples was placed in a Kitchen steamer with boiling water and
cooked for 10 min. e third group of the root samples was wrapped
in paper towel and moistened with about 5 mL of portable water and
microwaved (sharp microwave model R-228H) for 5 min inside a
plastic microwaveable food container. Cooked samples were allowed
to cool to room temperature for about 20 min, transferred to whirl-Pak
polyethylene bags and frozen at –20°C before drying using the freeze
dryer (True Ten, Ind, YK18-50, Taiwan). Dried samples were milled
and sieved as described in chapter four (under methodology) prior to
sugars determination.
Sugar determination
Freeze-dried and milled sweet potato samples were sent to the
Quality Plant Product Laboratory (Department of Crop Science,
University of Gottingen, Germany) for sugar analysis. Water extract of
the freeze-dried sweet potato samples (0.1 g in 100 mL) was used. e
samples were incubated in a water bath at 60°C for 1 h and treated with
0.2 mL Carrez I and Carrez II solution to remove proteins. Samples
were puried by centrifugation (Sorvall RC-5B Refrigated Superspeed,
GMI, Ramsay, USA) at 10,000 rpm for 10 min at 20°C. Sugars were
determined from the membrane-ltered supernatant (pores size 0.45
µm). Glucose, fructose, sucrose, and maltose were separated using a
LiChrospher 100 NH2 (5 µm) 4 x 4 mm pre-column in combination
with a LiChrospher 100 NH2 (5 µm) 4 x 250 mm separation column
(Merck KGaA, Darmstadt, Germany) and an acetonitrile: pure water
solution (80:20 v/v) as mobile phase at a ow rate of 1.0 mL min-1 at
20°C and an injection volume of 20 µL. Sugars were detected with a
Knauer dierential refractometer 198.00 (Knauer, Berlin, Germany).
Determination of amylase activity
e 3,5-dinitrosalicyclic acid (DNSA) method for reducing sugars
was employed to determine the total amylase activity of the freeze-dry
sweet potato roots [16,17].
A unit (U) of amylase activity was dened as the amount of enzymes
required to release reducing sugars equivalent to one µmole of maltose/
min under the above stated conditions [16].
Calculation of sweetness level
In order to ascertain and compare sweetness levels among the
varieties, sweetness (sucrose equivalent) was calculated from the
equation: Sucrose Equivalent (SE) = 1.2 fructose + 1 sucrose + 0.64
glucose + 0.43 maltose [1,18]. Based on the SE values obtained, the
varieties were classied into four categories: non sweet (SE ≤ 12 g/100g
dry weight); low sweet (SE 13 – 20 g/100 g); moderate sweet (SE 21 – 28
g/100 g); and high sweet (SE29 – 37 g/100 g) [1].
Statistical analysis
Experimental means were calculated from triplicate values of
each variety per treatment. Data obtained were subjected to analysis
of variance using Statistical Analysis System (SAS) [19]. Signicant
dierences among means were assessed using Least Signicant
Dierence (LSD) at probability level of 5%.
Results and Discussion
Eect of cooking treatment, genotype and interaction on
sugars of cooked sweet potato roots
e eect of cooking, genotype and their interaction were
signicant on all sugars (maltose, sucrose, glucose and fructose),
though the percentage contributions varied considerably (Tables 1 and 2).
Cooking treatment showed the highest eect of the total variability on
the sugars except fructose. e eect was more profound on maltose
content with percentage variability of 90.12%. Nearly 80% and 53% of
the total variation in sucrose and glucose contents of the cooked roots
were due to the cooking treatment. Eect of genotype was highest on
fructose relative to the other sugars. While 45.68% of the variation in
fructose resulted from the genotypic composition of the roots, only
7.26% of the dierence in maltose content was due to genotypic eect.
Percentage variability resulting from genotypic eect on sucrose and
glucose was 16.93% and 38.82% respectively. Overall variation from
interactions between cooking treatment and genotype ranged from
2.60% to 11.47% of the entire dierences noticed. Although it was
signicant, it contributed the least of the total variation.
e results from the analysis of variation depict that changes in
sugar concentrations during cooking are signicantly dependent on
cooking treatment, genotype and interaction. Among these factors
cooking treatment exerted the highest eect. Its eect was more
profound on maltose content, which increased from 7.26% prior to
cooking to 90.12% aerward. Cooking increases temperature intensity
and penetration, and also facilitates breakdown of hydrolytic bonds
holding starch granules and other compounds. Such conditions
enhance the activity of native amylase resulting in starch degradation
and the production of sugars mainly maltose as observed in the
study [8,20]. Apart from fructose, changes in individual sugars were
remarkable. Response from fructose was higher for genotype eect
rather than cooking treatment.
Eect of cooking treatment on sugars of sweet potato roots
Table 3 shows the means and ranges in sugars as a result of the
dierent cooking treatments. Wide variation existed among the sugars
of the cooked sweet potato roots, with maltose and sucrose showing the
highest variability. Maltose was hardly present in the raw form whilst
sucrose (10.58%) predominated. is nding agrees with Morrison
[8] and Sun [10] who reported that sucrose is the major sugar in
raw forms and the most important sugar for predicting sweetness in
sweet potatoes [6]. Sucrose concentration, generally, increased slightly
Variety Skin Colour Skin Shape Flesh colour Yield (t/ha)
Apomuden Reddish brown Obovate Reddish orange 48.9
Bohye Purple Obovate Pale orange 16.8
Dadanyuie Dark purple Round elliptic White 10.5
Faara Deep purple Long elliptic Cream 16.9
Hi-Starch Creamy Elliptic Cream 14.7
Ligri Cream Round elliptic Pale yellow 16.3
Okumkom Cream Long elliptic Cream yellow 19.91
Ogyefo Purple Long elliptic White 25.9
Otoo Cream Long elliptic Light orange 30.7
Patron Dark yellow Long elliptic Dark yellow 15.9
Sauti Cream Long elliptic Yellow 15.4
Table 1: Phenotypic attributes and yield of the sweet potato varieties used for
assessment of changes in sugar content [3-5].
Source of Variation *Variance (%)
Maltose Sucrose Glucose Fructose
Genotype (G) 7.26** 16.93** 38.82** 45.68**
Cooking treatment (CT) 90.12** 79.04** 52.60** 43.12**
GxCT 2.60** 4.03** 8.65** 11.47**
**Signicant at p < 0.05. *Calculated from sum of squares.
Table 2: Percentage variability of cooking treatment, genotype, and interactions on
sugars of cooked sweetpotato roots.

Citation: Owusu-Mensah E, Oduro I, Ellis WO, Carey EE (2016) Cooking Treatment Effects on Sugar Prole and Sweetness of Eleven-Released
Sweet Potato Varieties. J Food Process Technol 7: 580. doi:10.4172/2157-7110.1000580
Page 3 of 6
Volume 7 • Issue 4 • 1000580
J Food Process Technol
ISSN: 2157-7110 JFPT, an open access journal
when baked, though it was not signicant compared to the raw, but
remained constant at microwaving and decreased signicantly during
steaming. Glucose and fructose contents were not signicantly aected
by the dierent cooking treatments, although the levels were generally
lower compared to raw roots. Maltose content rose from 0.63% before
cooking to 20.13%, 14.35% and 5.07% aer baking, steaming and
microwaving respectively. It became the principal sugar following
baking and steaming. Increase in maltose content following cooking
has been observed in several sweet potato varieties [7,8,10]. Changes
in maltose and sucrose (the major sugars) concentrations per variety
during cooking were also assessed and results presented in Figures
1 and 2 respectively. Maltose, which was not detected in most of the
varieties prior to cooking increased dramatically aer baking and
steaming (Figure 1). Faara, Dadanyuie, Ligri Sauti and Apomuden
had the highest increase and Hi-Starch the lowest in maltose content
following baking and steaming. ough the eect of microwave
cooking was also positive and signicant on maltose content for all the
varieties, it was comparatively much lower to both baking and steaming.
In contrast, sucrose content decreased in some of the varieties while
increasing slightly or remaining the same in others during cooking
(Figure 2). Apomuden, Dadanyuie, and Hi-starch recorded a decrease
whilst Bohye, Faara, Otoo, Sauti and Ligri showed an increase aer
baking. Sucrose contents in Ogyefo, Okumkom and Patron were not
signicantly aected by baking treatment. Steaming reduced sucrose
content in all the varieties. e magnitude of reduction was extremely
high in Faara, which lost almost 96% of its sucrose content. Eect
of microwave treatment on sucrose was similar to that of baking.
While negatively aecting sucrose content in Apomuden, Bohye,
Hi-Starch, Ligri, Patron, and Sauti, microwaving enhanced sucrose
levels in Dadanyuie, Faara, and Otoo. Sucrose content in Ogyefo, and
Okumkom were not signicantly aected.
Concentration of sugars in sweet potato roots varies signicantly
during cooking, with the extent of variability being highly dependent
on; 1) initial sugar concentration, 2) amylase activity and 3) cooking
method employed. e impact of cooking treatment on sugar content
is related to temperature, time, and mode of heat transfer. Baking
treatment resulted in the highest sugar (maltose) formation mainly
due to the long cooking period (30 min) coupled with the high
temperature (205°C) employed. Moreover there was no direct contact
between the sample and the heating medium, a system that prevented
possible leaching of soluble sugars, during baking. Heat is transferred
from the periphery to the centre of the root by conduction in baking
as compared to microwaving for instance where electromagnetic
radiation penetrates the entire root causing agitation and friction to
produce heat for cooking instantaneously [5]. Hence baking utilises
more time, a system that allows adequate starch gelatinisation and
subsequent conversion to maltose by amylases [21,22]. It has been
demonstrated that increasing heating temperature over a time
frame increases starch degradation and maltose production [8,10].
Baking treatment at higher temperatures can however cause sucrose
caramelisation, a phenomenon, which results in conversion of sucrose
to oligomers and polymers as reported by Simkovic [12] and Chan
[6]. Hence the reduction in sucrose content of some of the varieties
(Figure 2) may be attributed to this eect. is nding corresponds
with Chan [6] and Morrison [8] who reported a decrease in sucrose
content of several sweet potato cultivars during baking. e rapid
heating mechanism of microwaving deactivated the native amylases
responsible for maltose formation, and consequently the reduction in
Figure 1: Changes in maltose content of sweetpotato roots as affected
by different cooking treatments; microwaving, steaming and baking.
LSD=0.30.
Individual Sugars
(% DM)
Cooking Treatment
Raw Baking Microwaving Steaming
Sucrose 10.58 (9-23)a11.01 (6-20)a10.72 (7-16)a 4.30 (0-8)b
Glucose 2.69 (1-4)a 1.10 (0-3)b 1.63 (0.4-5)b 1.55 (0-5)b
Fructose 1.58 (0-3)a 0.84 (0-2)a 0.92 (0-2)a 0.95 (0-4)a
Maltose 0.63 (0-1) a 20.13 (5-36)b 5.07 (2-15)c14.35 (2-27)d
Ranges of maeans are presented in brackets. a,b,c Figures in rows with the same
superscripts are not signicantly different (p < 0.05).
Table 3: Means and ranges of individual sugars in raw and cooked sweet potato
roots.
Figure 2: Changes in sucrose content of sweetpotato roots as inuenced
by three cooking treatments; microwaving, steaming and baking.
LSD=0.86.
Figure 3: Changes in sweetness levels of sweet potato roots after
baking. Standard error bars represent LSD at p<0.05.

Citation: Owusu-Mensah E, Oduro I, Ellis WO, Carey EE (2016) Cooking Treatment Effects on Sugar Prole and Sweetness of Eleven-Released
Sweet Potato Varieties. J Food Process Technol 7: 580. doi:10.4172/2157-7110.1000580
Page 4 of 6
Volume 7 • Issue 4 • 1000580
J Food Process Technol
ISSN: 2157-7110 JFPT, an open access journal
its levels [6,10]. Moreover, the short heating period of microwaving
does not enhance starch gelatinisation, a rate-determining step
in initial stages of hydrolysis [7,21]. Whereas baking resulted in a
dramatic increase in maltose content of Jewel, microwaving inhibited
its formation, reducing the total sugar content of the cooked product
[10]. Microwave cooking can therefore be an ideal method for food
preparations where high sugar content is not a desirable attribute. In
regions like Sub-Sahara Africa where less sweet potato varieties are
perceived to be the preferred choice Tumwegamire [23], microwave
cooking could be the recommended choice.
Steaming treatment resulted in an increase in maltose content
in all the varieties. On the contrary, it caused a reduction in sucrose
content in all the varieties compared to the raw roots. e heat transfer
mechanism of steaming treatment allowed direct contact between
the roots and the heat source. Such heat exchange technique allows
movement of soluble substances; where solutes move from high
concentration to low concentration. Sucrose, which was initially high
in the raw roots, may have consequently moved from the roots to the
steam. Hence the reduction in sucrose content observed in the roots
aer steaming.
Increase in sugars, particularly maltose, levels of sweet potato
root can also be attributed to the hydrolytic ability of native amylases
present in the uncooked roots. Sweet potato roots contain high
levels of amylases, mainly α- and β-amylase, which signicantly
inuence levels of sugar in processed sweet potatoes [24]. Amylases
hydrolyse gelatinised starch into maltose and short-chain branched
oligosaccharides (limit dextrins) during cooking resulting in a
sweet taste [8,22]. e amylase activity of the varieties was therefore
determined to ascertain the general hypothesis that amylases are also
responsible for the increase in sugar content.
Table 4 presents amylase activity of the sweet potato varieties
investigated. It ranged from 927.14 U/g in Ligri to 387.06 U/g in Hi-
starch. Based upon levels of activity found, Ligri, Dadanyuie, Sauti,
Ogyefo and Okumkom were grouped as very high amylase varieties.
Faara, and Otoo are high-class varieties whilst Patron, Apomuden,
Bohye and Hi-Starch are considered moderate types. e level of
amylase activity correlated positively with the formation of maltose
aer cooking (Figure 1). Most of the high amylase varieties including
Dadanyuie, Ligri, and Faara of low initial total sugar content (Figure
1) showed very high increase in maltose content aer baking and
steaming. Similarly, Hi-starch with a lower amylase activity but
similar initial sugar content as that of Ligri for instance produced little
extra maltose, and was not signicantly dierent from the uncooked
roots. Apomuden with moderate amylase potential produced
moderate maltose content though it had the highest content prior to
cooking. is result supports previous ndings that maltose content
in cooked sweet potato is a function of amylase activity of the roots
[7,8]. However, it should be noted that dierent cooking treatments
produced signicantly dierent eects on sugar content of the cooked
roots (Figure 1). Baking treatment however results in the highest nal
sugar contents.
Baking treatment and sweetness of sweet potato roots
To study the eect of cooking treatment on sweetness levels of the
varieties, baking treatment, which resulted in the highest increase in
sugars, was selected. Individual sugars in raw and baked roots were
rst converted to sucrose equivalent (SE) based on sweetness factors
[25]. Such conversion allows easy comparison of sweetness among
sweet potato varieties. Kays [1] employed this method to evaluate the
sweetness levels of 272 baked sweet potato clones and categorised the
clones into ve main groupings based on SE: Very high ≥38; high 29-
37; moderate 21-28; low 13-20 and non-sweet ≤ 12 g per 100 g dry
mass.
Sweetness among the sweet potato varieties prior to and aer
baking is presented in Figure 3. e levels increased signicantly aer
baking in majority of the varieties, and the eect was more pronounced
in the high amylase types (Table 4); Faara, Ligri, Otoo and Sauti. e
increase also corresponded well with the maltose content aer baking
(Figure 1). Apomuden had the highest sweetness value of 29.79 SE, and
Hi-Starch the lowest of 10.79 SE prior to baking (Figure 3). e other
varieties had values in the range of 12 to 16 SE. Using the grouping by
Kays [1], the varieties fell under the following classes prior to baking:
Apomuden–High sweet; Bohye, Dadanyuie, Faara, Ligri, Okumkom,
Otoo, Patron and Sauti–Low sweet; and Hi-starch, Ogyefo and Sauti–
non sweet. However the levels of sweetness and subsequently the
sweetness categories of the varieties changed signicantly following
baking. Whereas Apomuden dropped slightly, but not signicant, from
high sweet category (29.79 SE) to moderate sweet (28 SE), majority
of the varieties including Dadanyuie, Faara, Ligri, Otoo and Patron
moved from low sweet to moderately sweet category. e increase
in SE of Bohye and Okumkom were not signicant enough to place
them in the moderate class. Whilst Ogyefo and Sauti increased in SE
values and were categorised as low and moderate sweet respectively,
Hi-starch, remained in the same non-sweet category following baking
[26,27].
Sweetness in sweet potatoes is a function of cultivar, amylase
activity, storage condition, and cooking treatment [1,5,6],. Nonetheless,
amylase activity, initial sugar concentration and maltose formed during
cooking are the most critical in determining the nal sweet sensation of
cooked root [1,8]. ese factors can completely change the sweetness
status of a variety as observed in Dadanyuie, Faara, Ligri, Sauti, Otoo,
Patron and Ogyefo (Figure 3) which were low or non-sweet prior to
cooking, but changed to moderate sweet when baked.
e sweet potato varieties in this study were also classied into
four general groups based on initial sucrose equivalent (SE) and
starch hydrolytic potential [8]. ese are low initial SE/low starch
hydrolysis; Low initial SE/high starch hydrolysis; High initial SE/low
starch hydrolysis and High initial SE/high starch hydrolysis. Figure 4
Figure 4: Classication of eleven sweetpotato varieties based on sucrose
equivalent (SE) derived from starch hydrolysis (using maltose as indicator)
during bakingand endogenous sugars (sucrose, glucose and fructose).
(-, -) – Low initial SE/low starch hydrolysis; (-, +) - Low initial SE/high starch
hydrolysis; (+, -) – High initial SE/low starch hydrolysis; (+, +) – High initial
sugar/High starch hydrolysis [11,14].

Citation: Owusu-Mensah E, Oduro I, Ellis WO, Carey EE (2016) Cooking Treatment Effects on Sugar Prole and Sweetness of Eleven-Released
Sweet Potato Varieties. J Food Process Technol 7: 580. doi:10.4172/2157-7110.1000580
Page 5 of 6
Volume 7 • Issue 4 • 1000580
J Food Process Technol
ISSN: 2157-7110 JFPT, an open access journal
shows the classication of the sweet potato varieties assessed under this
grouping.
Hi-starch was the only variety belonging to the class of low initial
SE content coupled with low starch hydrolysis (-, -). It produced small
amount of maltose upon cooking (Figure 1) as a result of its low amylase
activity (Table 4). Natural inhibitors and starch-based structural
resistance to hydrolysis are also probably inhibitory mechanisms for
the low starch hydrolysis [8]. is lack of activity has been attributed to
a recessive allele called β-amy for which the variety Satsumahikari was
homozygous [8]. It is probable that Hi-Starch is the same variety since
it was introduced to Ghana from Japan. Amylase activity in this variety
was detected in vitro, but apparently was below the threshold required
for eective hydrolysis during baking. Dadanyuie, Ogyefo and Sauti
had low initial SE but produced signicant amounts of maltose when
baked (-, +) whilst Okumkom, Otoo, Patron and Bohye have moderate
to high initial sugar content and produced low levels of maltose upon
baking (+, -). e last group, Faara, Ligri and Apomuden, had relatively
high initial SE and moderate to high starch hydrolytic (+, +) potential
following baking. e outcome of this investigation establishes that
nal sweetness of cooked sweet potato roots is a function of initial
sugar content and amylase potential of the raw root. Hence it would
be unreliable to classify sweet potato clones in terms of sweetness prior
to cooking.
Conclusion and Recommendations
e ndings of this study indicate that cooking method, genotype
and their interactions signicantly inuences sugars and sweetness
of sweet potato root. Among these factors cooking treatment showed
the highest variability. Baking which lasted for longer time resulted
in the highest maltose formation. Maltose was barely absent in raw
roots but increased considerably aer cooking. e amount of maltose
synthesized was however dependent on the level of amylase present
in the raw root. Activity of amylases was facilitated by temperature,
time, and mode of heat penetration by the cooking method. Whilst
baking conditions enhances hydrolysis, electromagnetic radiation
generated by microwave cooking deactivates amylases, suppressing
maltose formation and rendering the product less sweet. Sweetness was
found to be dependent on initial sugar content, amylase activity and
cooking method. Cooking treatment should therefore be considered as
a key criterion when evaluating quality attributes of sweet potatoes for
appropriate utilization.
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Sweet potato varieties Total amylase activity Groupings
Ligri 927.14 (40.56) Very high
Dadanyuie 882.05 (26.82) “
Sauti 809.24 (30.45) “
Ogyefo 804.10 (30.67) “
Okumkom 779.25 (37.76) “
Faara 687.32 (50.34) High
Otoo 650.67 (20.45) “
Patron 489.81 (15.56) Moderate
Apomuden 454.10 (21.56) “
Bohye 414.26 (13.24) “
Hi-starch 387.06 (25.67) “
Grouping was based on ranges of amylase activity found: Very High (≥ 750), High
(749-550), moderate (549- 350), low (≤ 349). Standard deviations are presented
in brackets. LSD = 14.45
Table 4: Means and levels of amylases in sweet potato varieties.

Citation: Owusu-Mensah E, Oduro I, Ellis WO, Carey EE (2016) Cooking Treatment Effects on Sugar Prole and Sweetness of Eleven-Released
Sweet Potato Varieties. J Food Process Technol 7: 580. doi:10.4172/2157-7110.1000580
Page 6 of 6
Volume 7 • Issue 4 • 1000580
J Food Process Technol
ISSN: 2157-7110 JFPT, an open access journal
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Citation: Owusu-Mensah E, Oduro I, Ellis WO, Carey EE (2016) Cooking
Treatment Effects on Sugar Prole and Sweetness of Eleven-Released
Sweet Potato Varieties. J Food Process Technol 7: 580. doi:10.4172/2157-
7110.1000580
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