RESEARCH QUALITY SWEET POTATOES ON SANDY SOIL

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Section economics &
tourism
RESEARCH QUALITY SWEET POTATOES ON SANDY SOIL
Dr. Reta Draghici1
Dr. Mihaela Croitoru1
Dr. Aurelia Diaconu1
Dr. Milica Dima1
Drd. Cotet Gheorghe1
1Research and Development Station for Plant Culture on Sands Dabuleni, Romania
ABSTRACT
In order to determine the content of different biochemical components in sweet
potato tubers under the conditions of sandy soils from Dăbuleni, the following varieties
were studied: Yulmi, Juhwangmi, Hayanmi, KSP 1, KSC 1, grown in transparent mulch
culture, in the first decade of May, in the climatic conditions of the period, 2015-2017.
All varieties studied showed a total dry matter content of over 30% and the highest
content was determined for KSC1 (38.87%). Also, the results obtained with respect to
the content of soluble carbohydrates, starch and C vitamin are similar to those in the
literature, the differences being due to the studied genotypes and the climatic conditions
in the culture area. The determinations made show that the highest total dry matter
content was recorded at 110 days after planting, 38.41% of the varieties average and,
depending on the variety, Yulmi showed the highest content (41.52% ). The maximum
starch content was determined at 100 days after planting, with an average varieties of
13.53%. The highest starch content was determined in the Juhwangmi (14.43%) and
KSP1 (14.22%) varieties. As for the content of C vitamin, it showed the highest values
in all varieties to 100 days after planting and then begins to diminish. Depending on the
years of study, the best results were determined in 2016. The very high temperatures in
the summer of 2017, with maximum over 40 °C in several days, along with the lack of
rainfall, had a negative impact on the accumulation of biochemical components studied
in tubers.
Keywords: sweet potato, quality, starch, C vitamin
INTRODUCTION
Christopher Columbus has discovered over 600 years ago the famous Land of
Spices, Peru in its current terms, and three plants that have revolutionized the food
industry over time: corn, white potatoes and sweet potatoes. Sweet potato is originally
from Central America or Northwestern South America and cultivates on large areas in
China, India, Japan, Africa, the US, the Mediterranean areas of Europe. But China is the
largest producer, covering about 80% of world production and offering over 100
varieties. Along with production, the nutritional quality of sweet potatoes highlights the
importance of this culture in human nutrition, still little known for consumers in
Romania. Different research has highlighted data on dry matter content, water, C

5th International Multidisciplinary Scientific Conferences on Social Sciences & Arts SGEM 2018
vitamin, carbohydrates, of sweet potatoes cultivated in different areas of the globe [1, 2,
4, 6, 7, 12, 13, 14].
Sweet potato plants grow best at an average temperature of 24 °C, with abundant sun
and warm nights. Annual precipitation of 750-1000 mm is considered the most suitable,
with a minimum of 500 mm, in the growing season. The crop is susceptible to drought
in the tuber initiation stage, 50-60 days after planting. Under the conditions of SCDCPN
Dăbuleni, the sweet potato developed during the vegetation period at an average air
temperature of 22.3 °C by the accumulation of biologically active 2266.3 °C [3].
MATERIAL AND METHOD
In the period 2015-2017, the following sweet potato varieties were studied at the
SCDCPN Dăbuleni (Romania): Yulmi, Juhwangmi, Hayanmi, KSP1, KSC1. The culture
was mulched with transparent white polyethylene film.
Determinations have been made regarding the biochemical composition of
sweet potato tubers in dynamics at 90 - 100 - 110 - 120 days after planting, in order to
determine the period when the accumulation of assimilates is maximal. The following
determinations were performed in the biochemistry laboratory:
• the water and the total dry matter (%) - gravimetric method;
• soluble dry matter (%) - refractometric method;
• soluble carbohydrates (%) - Soxhlet Fehling method;
• C vitamin (mg / 100g fresh substance) - iodometric method;
• starch (%) - colorimetric method;
RESULTS AND DISCUSSIONS
The results obtained concerning the biochemical composition of sweet potato
depending on the studied variety under the pedoclimatic conditions from Dăbuleni are
presented in Table 1. The total dry matterhas varied from 32.73% to the Iuhwangmi
variety and 38, 92% for the Hayanmi variety, with a varieties average of 36.28%. A
bigger quantity of total dry matter compared to the average of the varieties was
determined for the varieties: Yulmi (37.76%), KSC1 (38.48%) and Hayanmi (38.92%).
Specialty literature indicates a total dry substance content in sweet potato tubers ranging
from 19.69% to 46.12%, depending on variety, climate conditions and culture
technology [4, 7, 8, 13]. Under the conditions of the sandy soils of Dăbuleni, depending
on the studied variety and the climatic conditions, the total dry substance content can
reach up to 45%, so the results obtained are similar to those obtained in different areas
around the globe. The amount of water was on average 63.72% and falls within the
range shown in the literature. The soluble dry substance was between 9.36% for the
Iuhwangmi variety and 10.63% for the Hayanmi variety. Compared to the average of
the varieties (9.92%), higher values of the soluble dry matter were determined for the
varieties Yulmi (10.13%) and Hayanmi (10.63%). Varieties that showed a high content
of soluble dry matter also had a higher content of soluble carbohydrates. The
carbohydrate content ranged from 7.81% to the Iuhwangmi variety and 8.84% to the
Hayanmi variety, with an average of 8.26%. The accumulation of soluble carbohydrates
is influenced by variety, crop technology and climatic conditions. The soluble
carbohydrate content of sweet potato tubers is very variable ranging from 4.50% to
8.41% [5]. Tuber starch content ranged between 12.54% for the Hayanmi variety and

Section economics &
tourism
14.43% for the Iuhwangmi variety, with an average varieties of 13.40%. Research
carried out in different parts of the world showed a starch content of between 12.38%
and 17.76% [10, 11, 12].
Table 1. The biochemical composition of sweet potato depending of the variety
studied (2015-2017 average, at harvest - 120 days from planting)
Variety Total dry
matter (%)
Water
(%)
Soluble dry
matter (%)
Soluble
carbohydrates
(%)
Starch
(%)
C vitamin
(mg/100g
f.s*)
Yulmi 37.76 62.24 10.13 8.44 13.69 8.86
Iuhwangmi 32.73 67.27 9.36 7.81 14.43 9.97
Hayanmi 38.92 61.08 10.63 8.84 12.54 8.50
KSP 1 33.49 66.51 9.83 8.18 13,02 9.53
KSC 1 38.48 61.52 9.67 8.04 13.40 8.15
Average 36.28 63.72 9.92 8.26 13.40 9.00
Limits from
literature 18.50-46.12 53.88-81.50 8.50-11.20 4.5-8.41 12.38-
17.76 1.70-23.42
f.s*- fresh substance
In sweet potato tubers the C vitamin content ranged from 8.15 mg to the variety KSC1
and 9.97 mg to the variety Yuwangmi, with an average of 9 mg/100 g of fresh
substance. C vitamin is mainly altered by the genetic characteristics of varieties, and
differences in the chemical composition of tubers are conditioned by phenotypic
variability of tubers and variation in climatic conditions [13]. Values vitamin C content
of sweet potato tubers resulting from different studies ranged from 1.7mg to 24mg/100g
of fresh substance [1, 2, 6]. The accumulation of total dry matter in sweet potato tubers
is influenced by both the variety, the technological factors and the climatic conditions of
that period. The high temperature due to the atmospheric drought, characteristic in the
summer months for sandy soils, leads to an increase in total dry matter and a decrease in
the amount of water. The dynamics of total dry matter accumulation in tubers at 90
days, 100 days, 110 days and 120 days from planting in the five varieties is presented in
Table 2. The maximum accumulation of the total dry matter has been achieved at110
days after planting, with an average varieties of 38.41%. Depending on the variety, the
largest amount of total dry matter was determined in the Yulmi variety at 100 days after
harvesting (41.52%), it is also an early variety, and in the Hayanmi and KSP1 varieties
to 110 days after planting (40.73% and 40.72%).
Table 2. Dynamics of accumulation of total dry matter in sweet potato
tubers depending on the variety (average 2015-2017)
Variety Total dray matter(%)
90 days 100 days 110 days 120 days
Yulmi 37.62 41.52 40.64 39.25
Juhwangmi 31.84 30.51 31.55 32.73
Hayanmi 36.93 40.14 40.73 38.92
KSP 1 38.28 39.00 40.72 33.49
KSC 1 38.64 38.26 38.40 38.48
Average varieties 36.66 37.89 38.41 36.57

5th International Multidisciplinary Scientific Conferences on Social Sciences & Arts SGEM 2018
Depending on the years of study, the best results were obtained in 2016 (Table 3). The
average amount of total dry matter in tubers was 41.33% and the varieties that have
accumulated for the highest amount were: Hayanmi (45.43%), KSP1 (44.90%) and
KSC1 (43.22%).
Table 3. Influence of study years to 110 days from planting
on total dry matter content
Variety Total dray matter (%)
2015 2016 2017 Average
Yulmi 43.38 39.47 40.08 40.64
Juhwangmi 33.05 33.62 27.99 31.55
Hayanmi 39.26 45.43 37.50 40.73
KSP 1 37.31 44.90 39.95 40.72
KSC 1 35.46 43.22 36.53 38.10
Average varieties 37.49 41.33 36.41 38.41
The sum of the degrees of
temperature (0C) 2679.7 2630.7 2727.4 2679.3
Rainfalls (mm) 231 122.6 206.6 187.7
Although the year 2016 was considered a dry year (especially in the summer
months), it was characterized by a lower number of degrees of temperature. The sum of
the degrees of temperature during the growing period was 2630.7 °C. Starch is the most
abundant reserve of carbohydrates in the plant and is found in leaves, flowers, fruits,
seeds, different types of stems and roots. Starch is used by plants as a source of carbon
and energy [9]. The biochemical chain responsible for starch synthesis involves glucose
molecules produced in plant cells by photosynthesis. Starch is formed in chloroplasts of
green leaves and amyloplasts, the organs responsible for the synthesis of starch reserves
from cereals and tubers [9]. Starch production in chloroplast is diurnal and is carried out
quickly by plants. On the contrary, amyloplastic starch reserves are stored in a few days
or even weeks. Starch is stored and cyclically mobilized during seed germination, fruit
maturation and tuber germination. The dynamics of starch accumulation in sweet potato
tubers at 90 days, 100 days, 110 days, and 120 days from planting in the five varieties is
shown in Table 4. The maximum starch accumulation was achieved at 100 days after
planting at varieties Hayanmi, KSP1 and KSC1, with a varieties average of 13.53%,
and for the Yulmi and Juhwangmi varieties, the maximum was achieved at 120 days
from planting (13.69% at Yulmi and 14.43% at Juhwangmi). Depending on the variety,
the largest amount of starch was determined in the Juhwangmi variety (14.43%) at 120
days after planting and in the KSP1 and KSC1 varieties at 100 days after planting.
Depending on the study years, the best results were obtained in 2016 (Table 5). The
average amount of starch determined in the tubers was 14,80% and the varieties that
have accumulated for the largest quantity were Juhwangmi (17,06%), Yulmi (15,14%)
and KSC1 (14,58%).

Section economics &
tourism
Table 4. Dynamic accumulation of starch in sweet potato tubers
depending on variety (2015-2017 average)
Variety Starch (%)
90 days 100 days 110 days 120 days
Yulmi 12.25 12.97 12.28 13.69
Juhwangmi 13.32 13.55 12.89 14.43
Hayanmi 12.41 12.98 12.34 12.54
KSP 1 12.50 14.22 13.24 13.35
KSC 1 11.95 13.90 12.60 13.02
Average varieties 12.48 13.53 12.67 13.40
Table 5. In$uence of the study years to 120 days after planting on the starch
content of sweet potato tubers
Variety Starch(%)
2015 2016 2017 Average
Yulmi 13.87 15.14 12.05 13.69
Juhwangmi 13.63 17.06 12.61 14.43
Hayanmi 12.80 13.53 11.29 12.54
KSP 1 13.90 13.69 12.46 13.35
KSC 1 13.15 14.58 11.33 13.02
Average varieties 13.47 14.80 11.93 13.40
The sum of the degrees of
temperature (0C) 2679.7 2630.7 2727.4 2679.3
Rainfalls (mm) 231 122.6 206.6 187.7
Subsequent research has shown that in sweet potatoes the sucrose and starch
content increases with the growing period from planting to harvesting, and glucose and
fructose decrease [15]. Based on these assertions, the data obtained from the sweet
potato varieties studied on the soluble carbohydrate and starch content correlates in that
the carbohydrate content decreases as the amount of starch in the tubers increases. The
established correlation is polynomial, with an insignificant correlation factor (r = 0.80)
(Figure 1). C vitamin is the main vitamin synthesized by plants, which participate in the
processes of formation of unsaturated fatty acids, the degradation of some amino acids
in the carbohydrate metabolism, iron metabolism, etc. C vitamin content of vegetables
and fruits varies within very wide limits, depending on species, variety, and agro-
climatic conditions. C vitamin content showed the highest values for all varieties 100
days after planting and began to diminish (10.39 mg of media varieties) (Table 6).
Depending on the variety, the highest amount of C vitamin was determined in the
Juhwangmi (11.29mg) and KSC1 (10.70mg) varieties at 100 days after planting.

5th International Multidisciplinary Scientific Conferences on Social Sciences & Arts SGEM 2018
Figure 1 - Correlation between starch and soluble carbohydrate content of
sweet potato tubers
Table 6. Dynamics of C vitamin accumulation in sweet potato tubers depending on
the variety (average 2015-2017)
Variety C vitamin (mg/100g f.s*.)
90 days 100 days 110 days 120 days
Yulmi 7.63 9.68 10.55 8.86
Juhwangmi 7.77 11.29 9.97 9.97
Hayanmi 9.39 9.94 9.68 8.50
KSP 1 7.63 10.35 8.21 9.53
KSC 1 8.21 10.70 10.27 8.15
Average varieties 8.13 10.39 9.73 9.00
f.s*- fresh substance
Depending on the years of study, the best results were determined in 2016. The
very high temperatures in the summer of 2017, with maximum over 40 °C in several
days, along with the lack of rainfall, negatively influenced the accumulation of the
biochemical components studied in tubers (Table 7). The average amount of C vitamin
in the tubers was 13.55mg, and the varieties that accumulated the highest amount were:
KSC1 (14.78mg), KSP1 (13.90mg) and Juhwangmi (13.64mg).
Table 7. In$uence of study years to 100 days after planting on the C vitamin
content of sweet potato tubers
Variety / Year C vitamin (mg/100g f.s*.)
2015 2016 2017 Average
Yulmi 7.90 13.20 7.92 9.68
Juhwangmi 8.80 13.64 11.44 11.29
Hayanmi 7.92 12.22 9.68 9.94
KSP 1 8.36 13.90 8.80 10.35
KSC 1 8.53 14.78 8.80 10.70
Average varieties 8.30 13.55 9.33 10.39
The sum of the degrees of temperature (0C) 2679.7 2630.7 2727.4 2679.3
Rainfalls (mm) 231 122.6 206.6 560.2
f.s*- fresh substance

Section economics &
tourism
CONCLUSIONS
The sweet potato varieties studied during the period 2015-2017, in the conditions of the
sandy soils in southern Oltenia, behaved differently from the point of view of the
quality of tubers depending on the time of the variety and the climatic conditions.
The highest total dry matter content was determined at 110 days from planting, 38.41%
of the varieties average and, depending on the variety, Yulmi showed the highest content
(41.52%).
The maximum starch content was determined 100 days after planting, with an average
varieties of 13.53%. The highest starch content was determined in varieties, Juhwangmi
(14.43%) and KSP1 (14.22%). The data obtained are similar to those in the literature,
the differences being due to the studied genotypes and climatic conditions in the area of
culture.
As for the C vitamin content, it showed the highest values in all varieties at 100 days
after planting, after which it began to diminish.
Depending on the years of study, the best results were determined in 2016. The very
high temperatures in the summer of 2017, with a maximum of over 40 °C in several
days, along with the lack of rainfall, negatively influenced the accumulation of studied
biochemical components in tubers.
ACKNOWLEDGEMENTS
This research activity was carried out with the support of the Ministry of Agriculture
and Rural Development, Romania, through the ADER Sectorial Program 2015-2018
and was funded by the ADER Project 2.2.2./22.10.2015.
REFERENCES
[1] Aywa A. K., Nawiri M. P., Nyambaka H. N., Nutrient variation in colored varieties
of Ipomea batatas grown in Vihiga County, Western Kenya, International Food Research
Journal 20(2): Kenya, 2013, p.819-825.
[2] Collins W., Walter M., Potențial for Increasing Nutrițional value of sweet potatoes,
Proccedings of the first Internațional Simposium, Asian Vegetable Research and
Development Center Shanhua, Tainan, Taiwan, China, Publication Nr. 82-172, China,
1982, p. 355-363.
[3] Croitoru Mihaela, Diaconu Aurelia, Drăghici Reta, Dima Milica, The dynamics
accumulation of biochemical components in sweet potato tubers depending on the
variety in the conditions sandy soils of southern Oltenia, JOURNAL of Horticulture,
Forestry and Biotechnology, Volume 21(2), Romania, 2017, p. 103-112, Editura
Agroprint Timisoara.
[4] Hua Ji., Haixin Zhang, Hongtao Li., Yunchao Li., Analysis on the Nutrition
Composition and Antioxidant Activity of Different Types of Sweet Potato Cultivars,
Food and Nutrition Sciences, 6, China, 2015, p. 161-167.

5th International Multidisciplinary Scientific Conferences on Social Sciences & Arts SGEM 2018
[5] Lai Y. C., Huang C. L., Chan C. F., Lien C. Y., Liao W.C., Studies of sugar
composition and starch morphology of baked sweet potatoes (Ipomea Batatas(L.)Lam),
J Food Sci Technol., 2013, 50(6), Taiwan, 2011,p. 1193-1199.
[6] Otieno K., Makale J., Etemesi Z. W., The effect of partial substitution of proprietary
dairy meal supplement for lactating dairy cows with dehydrated milled sweet potato and
poultry litter on milk yield.In: Annual Report, KARI-Kakamega, Kenia, 2002, pp.93-98
[7] Rumbaoa R. G. O., Cornago D. F., Geronimo I. M., Phenolic content and antioxidant
capacity of Philippine sweet potato (Ipomoea batatas) varieties. Food Chem. 2009;113:
Philippine, 2009, p. 1133–1138.
[8] Sanoussi A. F., Dansi A., Ahissou H., Adebowale A., Sanni L. O., Orobiyi A., Dansi
M., Azokpota P., Sanni A., Possibilities of sweet potato [Ipomoea batatas (L.) Lam]
value chain upgrading as revealed by physico-chemical composition of ten elites
landraces of Benin, African Journal of Biotechnology, Vol. 15(13), Benin, 2016, pp.
481-489.
[9] Smith A., M., The Biosynthesis of Starch Granules, Biomacromolecules, 2 (2), UK,
2001, pp. 335–341.
[10] Suraji A., Senanayake K. K., Ranaweera D. S., Anil Gunaratne, Arthur
Bamunuarachchi, Comparative analysis of nutritional quality of five different cultivars
of sweet potatoes (Ipomea batatas(L) Lam) in Sri Lanka, Food Science and Nutrition,
Volume 1, Sri Lanka, 2013, p. 284–291.
[11] Thao H. M., Noomhorm A., Physiochemical properties of sweet potato and mung
bean starch and their blends for noodle production, Journal of Food Processing and
Technology, 2, Vietnam. 2011, p. 1-9.
[12] Tsakama M., Mwangwela A. M., Manani T. A., Mahungu N. M., 2010,
Physicochemical and pasting properties of starch extracted from eleven sweetpotato
varieties, African Journal Food Science Technology, 1, India, 2010, p. 90-98.
[13] Ukom A. N., Ojimelukwe P. C., Okpara D. A., Nutrient Composition of Selected
Sweet Potato [Ipomea batatas (L) Lam] Varieties as Influenced by Different Levels of
Nitrogen Fertilizer Application, Pakistan Journal of Nutrition 8 (11), Pakistan, 2009, p.
1791-1795.
[14] Wang S., Nie S., Zhu F., Chemical constituents and health effects of sweet potato.
Food Res Int. 2016 Nov; 89(Pt 1), China, 2016, p. 90-116.
[15] Wang S. J., Chen M. H., Yeh K. W., Tsai C. Y., Changes in carbohydrate content
and gene expression during tuberous root development of sweet potato. Journal of Plant
Biochemistry and Biotecnology, 15, Taiwan, 2006, p. 21-25.