|
|
Received: 26 April 2018 Revised: 20 June 2018 Accepted: 25 June 2018 DOI: 10.1002/fsn3.747
ORIGINAL RESEARCH
Determination of citric acid pretreatment effect on nutrient content, bioactive components, and total antioxidant capacity of dried sweet potato flour Chala G. Kuyu1
| Yetenayet B. Tola1
1
Department of Postharvest Management, Jimma University College of Agriculture and Veterinary Medicine, Jimma, Ethiopia
2
Food Science and Agricultural Chemistry, McGill University, Ste. Anne de Bellevue, QC, Canada Correspondence Yetenayet B. Tola, Department of Postharvest Management, Jimma University College of Agriculture and Veterinary Medicine, P.O. Box 307, Jimma, Ethiopia. Emails:
[email protected];
[email protected] Funding information Jimma University College of Agriculture and Veterinary Medicine
| Ali Mohammed1 | Hosahalli S. Ramaswamy2
Abstract Orange flashed sweet potatoes are rich and inexpensive source of diet and antioxidants. The purpose of this study was to evaluate the effects of CA pretreatments and convective hot air drying temperature on proximate composition, bioactive components, and total antioxidant capacity of flour of five orange flashed sweet potato varieties. Moisture, protein, ether extract, ash, carbohydrate, fiber, β-carotene, total phenolic compounds, and total antioxidant capacity in the dried flour samples were evaluated and reported in the range of 4.1–7.4%, 2.4–4.2%, 1.2–1.1.8%, 2.2–3.2%, 82.7–87.1%, 1.3–1.8%, 35.5–91.6 mg/100 g, 49.8–107.9 mg GAE/100 g, and 27.3– 85.4%, respectively. The interaction effects of varieties, drying temperature, and CA concentration were significant (p ˂ 0.05) except for fiber. Kulto and SPK006/6/6 performed better for most of the parameters studied followed by SPK00/06. For almost all varieties, samples dried at 55°C and after treated in 3% CA solution had the highest percentage in terms of proximate composition, bioactive components, and total antioxidant capacities. KEYWORDS
antioxidant, bioactive photochemical, drying, polyphenols, sweet potatoes
1 | I NTRO D U C TI O N
& Shao, 2006). Recent research indicates that bioactive compounds such as polyphenols have many physiological benefits such as an-
Sweet potato [Ipomoea batatas (L.) Lam.] is a highly nutritious modi-
tioxidant, antiinflammation, blood vessel relaxation, and capillary
fied root crop rich in carbohydrate, only next to rice, corn, and cas-
wall- stabilizing activities (Hassellund et al., 2013). They improve
sava (Zuraida, 2003). It is a starch root, which contains high amounts
blood lipid profiles by increasing plasma high-density lipoproteins
of β-carotene and amino acid (especially lysine) which is deficient
(HDL) and decreasing the low-density lipoproteins (LDL) (Qin et al.,
in other cereal products like rice (Hassellund et al., 2013). Besides
2009). Being rich in carotenoids, total polyphenol content, and
these, it also contains polyphones, which act as antioxidants to safe-
ascorbic acid, sweet potato is gaining importance as the least expen-
guard the human body from certain chronic diseases (Huang, Chang,
sive source of antioxidants (Alam, Rana, & Islam, 2016).
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. © 2018 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc. Food Sci Nutr. 2018;1–10.
www.foodscience-nutrition.com | 1
|
KUYU et al.
2
White fleshed sweet potato (WFSP) variety is the staple food for 13 million people in the Southern Regional State of Ethiopia
and two drying temperatures (55 and 65°C) in factorial arrangement, and replicated three times.
(Kurabachew, 2015). In contrast, the orange fleshed sweet potato (OFSP), known to be a good source of β-carotene and energy (293 to 460 kJ/100 g), is easy to cultivate and fairly drought-tolerant (Hagenimana et al., 2001). These characteristics make OFSP an excellent food and nutrition security crop to the region, but in terms
2.3 | Data collected 2.3.1 | Proximate composition analysis
of their nutrient content, bioactive components and antioxidant
For evaluating the effect of treatment on the nutritional quality
capacity are not characterized. Furthermore, despite its increasing
of the flour, all components of proximate composition were deter-
importance as a valuable crop for food security, so far value addition
mined using standard analytical methods of AOAC (2005) (methods
attempts have not been conducted in terms of production of de-
for moisture (925.09), dietary fiber (993.21), protein (960.52), fat
hydrated product and minimization of the associated after-harvest
(920.85), and ash (923.03)).
losses (Tiruneh, 2017). The use of tuber crop in Ethiopia is limited, and it is consumed as an alternative carbohydrate source. This is generally performed with
2.3.2 | Total polyphenol content
fresh tuber as postharvest storage or processing technology is not
The total polyphenol contents were determined according to
yet well developed. Dehydration could be an inexpensive technol-
Blainski, Lopes, and De Mello (2013) which involved the reduction
ogy that can be easily adapted to reduce the losses and improve its
of Folin-Ciocalteu reagent by phenolic compounds. Absorbances of
utilization in food formulations. Proper drying of OFSP can result in a
prepared samples were measured at 765 nm using UV–Vis spectro-
stable product with better quality (Utomo, Man, Yaakob, Rahman, &
photometer (T80 Jiangsu, China). Gallic acid was used as the stand-
Saad, 2008) when assisted with predrying treatments. Singh, Raina,
ard, and the total phenolic contents were expressed as mg of gallic
Bawa, and Saxena (2003) used potassium metabisulfite and sodium
acid equivalent (GAE) per g of sample (mg GAE/g sample).
chloride to improve the quality of chips from sweet potato. Ahmed, Akter, and Eun (2010) also used sodium hydrogen sulfite to improve the flour quality of OFSP. It has been shown that losses of scaveng-
2.3.3 | β-Carotene determination
ing ability, total phenolic contents, and degree of oxidation increase
Extraction and determination of total β-carotene were based on
with increasing processing temperature and decrease when tuber is
the method described in Park (1987). After extraction, absorbance
soaked in citric acid solution (Shih, Kuo, & Chiang, 2009). On the con-
was read at 450 nm using UV–Vis spectrophotometer (T80 Jiangsu,
trary, short heating reduces the activity of endogenous polyphenol
China) and estimated against with concentration of β-carotene
oxidase which is responsible for oxidation of bioactive compounds
standard curve (Sigma-Aldrich).
(Ahmed et al., 2010). Therefore, this study aimed at to evaluate the effects of citric acid (CA) pretreatment and drying temperature on nutrient content, bioactive components, and antioxidant capacity of OFSP flours produced from different varieties.
2.3.4 | Determination of total antioxidant capacity and IC50 value Antioxidant capacity was determined according to the method of Lu
2 | M ATE R I A L S A N D M E TH O DS
and Foo (2000) which involved DPPH (2,2-diphenyl-1-picryl-hydraz yl) free radical scavenging assay. Briefly, 10 g of sweet potato flour was mixed with 100 ml methanol and the mixture was homogenized
2.1 | Sample collection and preparation
for 1 min in a homogenizer (POLYTRON® 2500E, Switzerland) and kept in a water bath at 20°C for 60 min. The samples were then
Five varieties (SPK00/06, SPK004/6/6, Guntute, Bucteca, and Kulto)
centrifuged at 748 g for 15 min, and the supernatant was taken for
of OFSP were collected from Jimma Agricultural Research Center.
analysis. The solvent extract of the sample was taken in 200, 400,
The roots were washed in tap water, and only those with uniform
600, 800, and 1,000 μl concentrations in a test tube, and the volume
overall appearance, size, and shape were selected for the study.
was made up to 1 ml with the solvent and 2 ml of 0.1 mM DPPH was
Tubers were then sliced into 1 mm size and dried for 8 hr (after pre-
added to each tube. The mixture was shaken well and incubated at
liminary work) after CA treatment (Ahmed, Akter, & Eun, 2011).
room temperature in the dark for 30 min. The decrease in absorbance of the resulting solution was then measured using UV–Vis spec-
2.2 | Experimental design and treatment combinations Experiments were carried out using a completely randomized design having five sweet potato varieties (SPK00/06, SPK004/6/6, Guntute, Bucteca, and Kulto), with two CA treatments (1 and 3%)
trophotometer (T80 Jiangsu, China) at 517 nm. Scavenging activity was calculated from absorbance values of samples and control sample using the following equation: ⎛ Ac − At As RSA (%) = ⎜ ⎜ Ac ⎝
⎞ ⎟ × 100 ⎟ ⎠
65°C
55°C
6.0 ± 0.3abcde
Guntute 6.7 ± 0.33ab
Kulto 4.6 ± 0.13ef
SPK004/6/6
2.4 ± 0.18 cd 3.0 ± 0.14abc
4.1 ± 0.17 4.1 ± 0.28f 4.2 ± 0.13f
Guntute Bucteca Kulto 2.217
abc
1.253
2.9 ± 0.17
2.4 ± 0.16 cd
f
SPK004/6/6
3.15 ± 0.14
4.2 ± 0.13f
4.2 ± 0.16
3.2 ± 0.12a
6.6 ± 0.35ab
Kulto SPK00/06
2.5 ± 0.16
6.7 ± 0.27
Bucteca a
cd
ab
f
2.9 ± 0.13abc
6.4 ± 0.14abc
Guntute
2.4 ± 0.34
6.1 ± 0.33
SPK004/6/6
cd
3.1 ± 0.32ab
abcde
3.1 ± 0.17
6.3 ± 0.13abcd
SPK00/06
5.0 ± 0.32
ab
cdef
Kulto
2.5 ± 0.16 cd
4.7 ± 0.24def
Bucteca
2.8 ± 0.14
5.4 ± 0.32
abcd
2.2 ± 0.32d
3.1 ± 0.12
ab
2.9 ± 0.33abc
2.55 ± 0.15
bcd
2.8 ± 0.15abcd
2.4 ± 0.14
Guntute
bcdef
4.9 ± 0.23
SPK00/06
cdef
7.4 ± 0.21
Bucteca
a
7.2 ± 0.22
cd
3.15 ± 0.25a
7.4 ± 0.13a a
Ash
MC
SPK004/6/6
SPK00/06
Varieties
1.645
3.7 ± 0.33bcd
3.2 ± 0.33cdef
3.6 ± 0.33
bcde
3.7 ± 0.33bcd
3.7 ± 0.33
bcde
4.2 ± 0.09a
3.8 ± 0.16
abcd
4.1 ± 0.33ab
3.9 ± 0.11
abc
4.0 ± 0.12ab
3.3 ± 0.19
cdef
2.6 ± 0.14fgh
2.5 ± 0.32
gh
3.0 ± 0.22efh
2.4 ± 0.21
h
3.7 ± 0.14bcd
3.3 ± 0.12
cdef
3.1 ± 0.18defh
3.2 ± 0.16
cdef
3.4 ± 0.32bcde
Protein
1.540
1.2 ± 0.07d
1.3 ± 0.12 cd
1.4 ± 0.11
cd
1.4 ± 0.11 cd
1.2 ± 0.13
d
1.8 ± 0.15a
1.8 ± 0.16
a
1.8 ± 0.15a
1.7 ± 0.14
ab
1.8 ± 0.11a
1.2 ± 0.08
d
1.3 ± 0.07 cd
1.4 ± 0.06
cd
1.5 ± 0.13bcd
1.2 ± 0.13
d
1.7 ± 0.15ab
1.6 ± 0.14
abc
1.7 ± 0.13ab
1.7 ± 0.14
ab
1.8 ± 0.12a
EE
1.860
86.0 ± 0.27ab
87.1 ± 0.28a
86.3 ± 0.30
a
86.5 ± 0.21a
86.2 ± 0.23
a
82.7 ± 0.24e
83.8 ± 0.29
de
83.4 ± 0.22de
84.5 ± 0.23
bcd
83.3 ± 0.23de
85.7 ± 0.22
abc
87.1 ± 0.27a
86.9 ± 0.24
a
86.6 ± 0.25a
86.6 ± 0.27
a
83.7 ± 0.25de
83.9 ± 0.26
de
84.2 ± 0.23cde
84.2 ± 0.23
cde
82.8 ± 0.24e
Total carbo.
1.020
370.4 ± 0.44abc
372.9 ± 0.40a
371.8 ± 0.37ab
373.6 ± 0.36a
370.8 ± 0.34abc
363.8 ± 0.33 fg
366.8 ± 0.41bcdef
366.4 ± 0.37cdef
368.9 ± 0.38abcde
365.4 ± 0.43defg
367.2 ± 0.33bcdef
370.6 ± 0.45abc
369.9 ± 0.37abcd
371.7 ± 0.33ab
367.2 ± 0.42bcdef
365.0 ± 0.33defg
363.3 ± 0.37 fg
364.5 ± 0.36efg
364.9 ± 0.43efg
360.9 ± 0.37 g
Energy (kcal/100 g)
Notes. CAC = CA concentration; EE = ether extract; Carbo = carbohydrate. Results are mean values of triplicate determination, and means with different letters across the column are significantly different (p
