Proximate and Amino acid Analyses of Full-fat Sunflower (Helianthus annuus L.) Seed Meal
Whole sunflower seeds (raw and roasted) were analyzed for proximate and amino acid composition. Proximate analysis of sunflower seeds were carried out according to standard procedures and the amino acid compositions of the samples were determined using the Technicon Sequential Multisample Amino acid Analyzer (TSM). The range of values obtained from the proximate composition of sunflower seeds were; for dry matter (96.64-98.43%), crude protein (18.70-20.07%), crude fat (23.98-24.86%), crude fibre (11.81-12.92%), ash (3.36-4.98%) and nitrogen free extract (36.71-37.68%). The crude fat content of sunflower was high as showed in the results. The results on amino acid profiles of raw and roasted sunflower seeds showed that the concentrations of most of the amino acids were actually increased with heat processing with the exception of proline, glycine, alanine, cystine, valine, methionine and isoleucine. Glutamic acid had the highest concentration of 13.98 g/16 gN in the raw seeds and 14.83 g/16 gN in the roasted seeds. The first limiting amino acid was found to be methionine with values of 1.22 g/16 gN and 0.79 g/16 gN in the raw and roasted seeds respectively. The second limiting amino acid was cystine (1.48 g/16 gN in the raw seed and 0.89 g/16 gN in the roasted seed). Arginine had the highest concentration among the indispensable amino acids with the value of 6.97 g/16 gN and 7.31 g/16 gN in the raw and roasted seeds, respectively. The concentrations of lysine in the sunflower seeds were also relatively high (4.91 g/16 gN for the raw seeds and 5.57 g/16 gN for the roasted seeds).
Received: June 23, 2010;
Accepted: October 09, 2010;
Published: February 26, 2011
Sunflower is an oilseed that is nutritious and unique in nature. A distinguishing
feature of the sunflower is that, its flowering head tracks the suns movement.
This occurrence is known as heliotropism. This property has been shown to increase
light interception and possibly photosynthesis (Putnam et
The domesticated sunflower has a single-stem and a large seed head. This is
in contrast to the wild variety that is highly branched with small heads and
seeds. The sunflower head is made up of 1,000 to 2,000 individual flowers that
are joined together to a base. The large petals that are found around the edge
of a sunflower are individual ray flowers, these do not develop into seeds.
Sunflower is not considered highly drought tolerant, but often produces satisfactory
results when other crops are damaged during drought (Putnam
et al., 1990).
Sunflower is one of the most important oil crops of major economic importance
and ranks second to soybean among all oil seeds globally as a source of vegetable
oil (Putt, 1978). Sunflower seed (full-fat) is grown
mainly for its oil and to a lesser extent for the confectionery market (Olomu,
1995). Most United States production is devoted to the oil-seed type of
sunflower, while a smaller percentage is grown for whole seed confectionery
uses such as candy, snack food and baked foods. Sunflower seeds are commonly
used as garnish or ingredients in many recipes, thickening soups, gravies and
sauces and as part of salads and cereals. Sunflower seeds are also used to produce
other things like medicine, paint, animal feed and bio-diesel (Putnam
et al., 1990). Sunflower oil is considered premium oil due to it
light colour, mild flavour, low level of saturated fats and ability to withstand
high cooking temperatures (Putnam et al., 1990).
Sunflower seed is rich in energy, since it has from 3,691 to 5,004 kcal of ME
kg-1 and from 19.9 to 43.4% of ether extract (Daghir
et al., 1980; Cheva-Isarakul and Tangtaweewipat,
1990; Tsuzuki et al., 2003). According to
Olomu (1995) full-fat sunflower seed has crude protein
of 17%, crude fat of 26.1%, crude fibre 29.1%, ash 3.1%, nitrogen free extract
18.8%, calcium 0.17% and total phophorus 0.53%. Tsuzuki
et al. (2003) in their study reported that sunflower seeds contained;
dry matter 93.10%, metabolizable energy 4,525 (kcal kg-1), crude
protein 21.75%, ether extract 39.89%, crude fibre 15.51%, calcium 0.33% and
total phosphorus 0.72%. Sunflower seeds are the best natural, whole food source
of vitamin E, almost all of which is alpha-tocopherol, the most biologically
active form (USDA Nutrient Database, 2002). Several authors
have reported the use of sunflowers seeds in livestock diets. Sunflower seed
meal has been incorporated in rations of poultry (Rose et
al., 1972; Uwayjan et al., 1983; Kashani
and Carlson, 1988; Karunajeewa et al., 1989;
Jiang et al., 1991; Olomu, 1995;
Villamide and Sanjuan, 1998; Tsuzuki
et al., 2003; Adeniji and Ogunmodede, 2006),
for rabbits (Akande et al., 2009) and swine (Olomu,
Nutritional data and information on sunflower seed are scanty and therefore this study was carried out to determine the proximate composition and amino acid profile of sunflower seeds as basis for evaluating its nutritional quality.
MATERIALS AND METHODS
The experiment was carried out in November, 2006 in Bauchi, Bauchi town is located at latitude 13° 30N and longitude 11° 50E. Bauchi State is located in the Northern Guinea and Sudan Savanna zones of Nigeria.
Processing of sunflower seeds: The seeds of sunflower were roasted in a wide aluminium frying pan to the temperature of about 80°C. The seeds were mixed together by constant stirring to prevent the burning of the seed coat and enhance even distribution of heat. The roasting of sunflower seeds took 1-2 min. The seeds were allowed to cool and then milled in hammer mill.
Proximate analysis: Proximate analyses of sunflower (both raw and processed
seeds) were carried out using the methods outlined by the Association of Official
Analytical Chemists (AOAC, 1990). The proximate compositions
of the sunflower seeds are presented in Table 1.
Amino acid analysis: The amino acid compositions of the samples were
determined using the method described by Speckman et al.
(1958). The samples were dried to constant weight and defatted. A known
weight of the defatted sample was hydrolysed under vacuum with 7 mL of 6 N HCl
in a sealed pyrex tube at 105°C for 22 h. Immediately after cooling, it
was filtered through non-absorbent cotton wool. The filtrate was dried at 40°C
using rotary evaporator.
The amino acids in the flask were diluted with 5 mL of acetate buffer (pH 2.0) and 5 to 10 μL was loaded into the cartridge of Technicon Sequential Multisample Amino acid Analyzer (TSM). The steam carrying the amino acid reagent mixture went through a heating bath where development of the coloured reaction product occurred. The absorbance was proportional to the concentration of each amino acid and was measured by colorimeter.
The proximate content of whole sunflower seed meal (both raw and roasted) is
shown in Table 1. The range of values obtained from the proximate
composition of sunflower seeds were; for dry matter (96.64-98.43%), crude protein
(18.70-20.07%), crude fat (23.98-24.86%), crude fibre (11.81-12.92%), ash (3.36-4.98%)
and nitrogen free extract (36.71-37.68%). The amino acid profiles of raw and
roasted sunflower seeds are presented in Table 2. The results
showed that the concentrations of most of the amino acids were actually increased
with heat processing, with the exception of proline, glycine, alanine, cystine,
valine, methionine and isoleucine. Glutamic acid had the highest concentration
of 13.98 g/6 gN in the raw seeds and 14.83 g/16 gN in the roasted seeds. The
most limiting amino acid was found to be methionine with values of 1.22 g/16
gN and 0.79 g/16 gN in the raw and roasted seeds, respectively. The second limiting
amino acid was cystine (1.48 g/16 gN in the raw seed and 0.89 g/16 gN in the
roasted seed). Arginine had the highest concentration among the indispensable
amino acids with the value of 6.97 g/16 gN and 7.31 g/16 gN in the raw and roasted
|| Proximate composition of raw and processed sunflower seeds
|| Amino acid profiles of raw and roasted sunflower seeds (g/16
|ND: Not Determined
The concentrations of lysine in the sunflower seeds were also relatively high
(4.91 g/16 gN for the raw seeds and 5.57 g/16 gN for the roasted seeds).
The chemical composition of sunflower seed depends on the weather, soil, variety
and method of cultivation of the crop (Karunajeewa et
al., 1989; Senkoylu and Dale, 1999). The range
of values obtained from the proximate composition of sunflower seeds were; for
dry matter (96.64-98.43%), crude protein (18.70-20.07%), crude fat (23.98-24.86%),
crude fibre (11.81-12.92%), ash (3.36-4.98%) and nitrogen free extract (36.71-37.68%).
The crude protein range of 18.70-20.07% obtained in this study is close to the
mean value of 21.75% reported by Tsuzuki et al. (2003).
The crude fat content of sunflower is high which indicates and confirms that
it is a good source of vegetable oil. Olomu (1995) reported
a crude fat of 26.1% for whole sunflower seeds which is slightly higher than
the range reported for sunflower in this study. The difference in values reported
for the crude fat may be due to type of processing method used before ether
The determination of amino acid composition is helpful in feed formulation,
it is also an important parameter in the evaluation of protein quality. Amino
acid compositions of sunflower seeds obtained in this study revealed that among
the essential amino acids, arginine had the highest concentration with the values
of 6.97 g/16 gN and 7.31 g/16 gN in the raw and roasted seeds, respectively.
These values were closely followed by leucine with the value of 6.70 g/16 gN
for the raw seeds and 7.09 g/16 gN for the roasted seeds. The concentrations
of the sulphur-containing amino acids (methionine and cystine) were drastically
decreased with heat processing. This is a reflection of the instability of these
amino acids when subjected to heat treatment. The values of methionine were
1.22 g/16 gN and 0.79 g/16 gN and those of cystine were 1.48 g/16 gN and 0.89
g/16 gN in the raw and roasted seeds, respectively. These sulphur-containing
amino acids were found to be the most limiting in sunflower seed. Similar reports
were made by Olomu (1995), but it however, contradicts
the findings of Vieira et al. (1992) who reported
that lysine was the first limiting amino acid in broiler sunflower meal-based
diets. According to Kashani and Carlson (1988) amino
acid composition of sunflower seed is variable, with levels of lysine and methionine
ranging from 0.56 to 0.66% and from 0.33 to 0.50%, respectively. The variation
in the chemical composition of sunflower meal that has been reported and may
be due to the method of processing and oil extraction (Karunajeewa
et al., 1989; Vieira et al., 1992).
Future use of sunflower seed meal in livestock feeds is a possibility if properly exploited. Heat treatment of sunflower seeds should be carried out with caution so as to prevent burning of the seed coat. It is necessary to supplement sunflower seed meal based diets with the sulphur-containing amino acids (methionine and cystine) in order prevent nutritional deficiencies of these essential amino acids.
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