Properties of some citrus seeds. Part 3.

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Properties of some citrus seeds. Part 3.

Evaluation as a new source of protein and oil

T. A. El-Adawy, E. H. Rahma, A. A. El-Bedawy and A. M. Gafar

1 Introduction

The shortage of oil and protein in several parts of the world are getting more acute with increasing population. Possible particle procedures to overcome this problem are the cultiva- tion of new crops and or the use of agricultural food processing by-products and wastes.

The focus of nutritionists interest and food chemists in the developing countries, especially Egypt, is to search for a cheap material with oil and protein of high industrial potential. In this respect, citrus seeds which remain in a big quantities, at a local factories, as waste products after the removal of the pulp and peel could be used.

The utilization of vegetable and fruit wastes was largely confined tomato and citrus waste [1]. At present citrus fruits are processed to produce juice and the wastes of this industry such as peels, seeds and pulps represent about 50% of the raw processed fruit [2]. Citrus by-products, which represent between 45 to 58% of the original material before juice extraction, can be classified into 3 main groups; (a) animal feed, (b) raw material suitable for production or recovery of valuable materials; and (c) food products [3].

Two of the most important by-products of citrus seeds are seed meal and seed oil. Citrus seeds contain about 36% oil and 14% protein [4]. The crude oil is used for detergent and soaps preparation, while the refined oil can be used for cooking pur- poses [5]. Habib et al. [6] recorded the following characteristic for the citrus seed oil; iodine value ranged from 91.4 to 99.3, acid value ranged from 0.21 to 1.2, saponification value ranged from 186.8 to 191.3, specific gravity ranged from 0.912 to 0.923 and refractive index ranged from 1.4681 to 1.4662 at 258C.

A high protein content meal is obtained by removal of ether soluble fat. Glasscock et al. [7] and Driggers et al. [8] studied the nutritive value of citrus seed meal. Citrus seed meals had higher glycine, cysteine, methionine and tryptophane and lower lysine than soybean meal [9]. Citrus seeds has an excel-

lent amino acids profile [10]. Therefore, the potential for utilizing such waste products for oil and protein production appears to be favourable.

The purpose of this report summarizes the chemical composition and minerals content of citrus seeds and their mixture.

The physico-chemical characteristics of oils of citrus seeds, the different classes of oils and the fatty acids composition of the oils as well as some nutritional quality of citrus seed flours.

2 Materials and methods

2.1 Materials

Citron Citrus aurantium, orange Citrus sinensis variety balady and mandarin Citrus mitis fruits were purchased from the local market of Shibin El-Kom city during the winter season of 1992.

2.2 Methods

2.2.1 Materials preparation

The fruits of each citrus variety were cut by sharp knife and the internal sound seeds were hand collected. The seeds were washed by tap water, then dried at 408C for 24 h in an electric air draught oven.

The citrus seed mixture sample was prepared by mixing an equal weights of each seeds variety (1 : 1 : 1, w : w : w). Dried seeds and their mixture were crushed using National type blender, sieved to remove most of the husk and fibers. The crude oils of citrus seed samples were extracted directly with n-hexane (BP, 678C) for 36 h using the cold extraction. Evaporation of hexane was performed on water bath and the produced oil samples were stored separately in a refrigerator inside a dark tight stopper glass for oil analysis. The defatted flours were air dried at room temperature (l258) and again ground to pass through a 60 mesh (British standard screen) sieve. The fine flour of each seeds sample was put in an air tight kilner jars and kept in a refrigerator until analysis.

2.2.2 Chemical composition

The contents of moisture, crude oil, crude protein (N66.25) and total ash of different citrus seed flours were determined as described in the AOAC [11]. Non-protein nitrogen was measured as nitrogen solu- The chemical composition and minerals content of citrus seeds and

its flours, the characteristics and structure of citrus seed oils as well as nutritional properties were studied. The citrus seeds and its flours were rich in oil and protein, respectively. Both citrus seeds and flours proved to be a good source for minerals K, Ca, P, Na, Fe and Mg. The flours of citrus seeds were rich in leucine, valine, total aromatic and total sulfur amino acids compared to FAO/WHO reference. Refractive index, specific gravity, melting point, colour and viscosity of citrus seeds oils differed slightly. Citrus seed oils had eight classes, according to the results of thin-layer chromatogram. Triglycerides were the

major oil class in all samples. The citrus seeds oil samples contained eight fatty acids while linoleic, oleic and palmitic acids were major acids. Some antinutritional compounds were detected in the flours.

The results revealed that, glucosides, stachyose, raffinose, trypsin inhibitor, phytic acid and tannins were present in all citrus seeds flours.

The data established that all flours were completely free from any agglutination activity. The biological values, true and apparent digestibility of mandarin seed protein were the lowest among all citrus seeds proteins by all measurements except the PER equations.

Menofiya University, Faculty of Agriculture, Food Science and Tech- nology Department, ET-32516 Shibin El-Kom, Egypt.

Correspondence to:

Dr. T. A. El-Adawy.

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386 Nahrung 43 (1999) Nr. 6, S. 385 – 391 ble in a 30% TCA according to Patel et al. [12]. Reducing sugars con-

tent was determined in the 70% ethanol extracts by phenol-sulphuric acid method according to Dubois et al. [13]. Sucrose and starch contents were determined as reducing sugars after complete acid hydrolysis. The factor of 0.95 and 0.90 were used to calculate the sucrose and starch, respectively. Crude fiber content was calculated by difference.

2.2.3 Physico-chemical characterization of oil

Specific gravity (258C), refractive index (258C), melting point, viscosity, colour, acid value, peroxide value, saponification value and iodine value of the oil samples were determined according to AOCS [14].

2.2.4 Fatty acid composition

The methyl esters of crude oil were prepared according to Chalvard- jian [15], using 1% of H2SO4in absolute methyl alcohol. A Perkin- Elmer gas chromatography (Model F22) with a flame ionization detec- tor was used in the presence of nitrogen as a carrier gas. A glass col- umn (2 m62.5 mm) packed with Chrom Q 80/100 mesh at a temperature of 2708C was used. Standard fatty acids methyl esters were used for identification. The area under each peak was measured and the percentage expressed in regard to the total area.

2.2.5 Neutral oil fractionation

This was carried out by thin layer chromatography using precoated plastic sheets (POLYGRAM SIL G, 0.25 mm silica gel, made in Ger- many) according to the method of Mangold and Malins [16]. The plate developing solvent system was petroleum ether (BP, 40 – 608C), diethyl ether and acetic acid (70 : 30 : 2, v : v : v). The fractionated oil classes were visualized by exposing to iodine vapour in closed vessel and identified by comparing its Rfvalues with those reported in literature. The quantitative content of each separated fraction type on the plate was measured using the densitometric method [17] and the area under each peak was measured by triangulation method.

2.2.6 Minerals content

The whole seeds and flour samples were digested by concentrated HNO3and HClO4(1 : 1, v/v) for 2 h (till the solution became colour- less). The total phosphorus was determined in the digested solution according to the method of Taussky and Shorr [18]. Na, Ca and K were estimated using emission flame photometer (Model Corning 410). The other minerals of Mg, Fe, Zn and Cu were determined using atomic absorption spectrophotometer (Perkin-Elmer Instrument Model 2380).

2.2.7 Amino acid profile

Amino acids were determined using a Mikrotechna AAA 881 auto- matic amino acid analyser according to the method described by Moore and Stein [19]. Hydrolysis of the samples was performed in the presence of 6 M HCl at 1108C for 24 h under nitrogen atmosphere sulfur-containing amino acids were determined after performic acid oxi- dation. Meanwhile, tryptophan content was chemically determined by the method of Miller [20] after alkaline hydrolysis.

2.2.8 Antinutritional factors

Total tannins were determined colorimetrically as described in AOAC [11]. Phytic acid was determined according to the method of Wheeler and Ferrel [21]. The glucosides were estimated according to the method of Stahl and Schild [22]. Trypsin inhibitor activity of citrus meals was determined according to the method of Kakade et al. [23].

The hemagglutinin activity was estimated according to the method of Liener and Hill [24]. Flatulence factors (stachyose and raffinose) were determined according to Tanaka et al. [25] using the TLC method.

2.2.9 In-vitro protein digestibility

This was measured by the method of Salgo´ et al. [26]. A two digestive enzymes (trypsin-pancreatin) system was used in pH-drop method.

2.2.10 Biological value

Amino acid profile was used to determine the nutritive value of citrus seed flours and several mathematical formulas have been con- structed to describe these relationships. The indices were determined by mathematical formula according to Hidve´gi and Be´ke´s [27] to determine the chemical score (CS), Mitchell essential amino acid index (MEAAI), FAO/WHO index, Morup and Olesen’s index (MOI), Gauss-index (GI), transformed Gauss index (TGI), transformed Gauss-index corrected for digestibility (TGICD), and protein efficiency ratio (PER) values. The regression equations proposed by Als- meyer et al. [28] were followed:

PERA= 0.684 + 0.456 Leu – 0.047 Pro.

PERB= 0.468 + 0.454 Leu – 0.105 Tyr.

PERC= –1.816 + 0.435 Met + 0.78 Leu + 0.211 His – 0.944 Tyr.

3 Results and discussion

3.1 Proximate composition

The proximate composition of whole different citrus seeds, defatted flour and their mixture are given in Table 1. Citron seed and its flour were the lowest in moisture content than the other citrus products. Also, all citrus flours had a higher moisture content than its seeds. This could be due to oil extraction from the seeds and also moisture adsorption during preparation. The protein content was ranged from 15.9% to 19.9% for the seeds and 28.6% to 36.2% for its flours. This finding may focus the interest of utilizing citrus seed flours as a high protein source in some food formulations. As shown in Table 1 the non-protein nitrogen ranged between 1.5% to 2.0% and 2.1% to 2.8% for citrus seeds and its flours, respectively.

Regarding to the crude lipids content of citrus seeds and flours, it was noticed that citrus seeds are considered as a rich sources of lipids. The lipid content of citrus seed ranged from 38.9% to 42.6% which is much higher than some oil seeds i. e. cotton- seeds 18 – 22% [29] and soybean seeds 18 – 25% [30]. The lipids content of the different flours was in the range of 2.7%

to 3.2%, these differences in total lipids content of the studied flours is due to the preparing process. Citrus seed flours contained higher values of ash content (5.0% to 5.2%) than citrus seeds (3.1% to 3.4%). The crude fiber content of citrus seed products was ranged from 22.5% to 24.2% for the seeds and 31.7% to 32.1% for the flours. The main problem which pre- vent or reduce the utilization of citrus seed flours as a food ingredient is its high content of crude fibre, which decreases their protein in-vitro digestibility. Therefore, dehulling of these seeds is an important step to reduce or eliminate the effect of this determintal factor. Citrus seeds contained 12.2% – 18.1%

total carbohydrates. Meanwhile, total carbohydrates contents of the flours were 24.0%–31.9%. The observed increase of carbohydrates in all flours could be due to the removal of lipids during defatting process. Also, reducing sugars, sucrose and starch were determined, and the values were higher in citrus seed flours compared to the seeds. Total nitrogen, non-protein nitrogen, ash and total carbohydrates in mixed flour had a mean values between the three citrus varieties.

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3.2 Minerals profile

Mineral composition of citrus seeds and flours are shown in Table 2. The minerals K, Na and P were the major inorganic constituents of the ash, while Ca, Fe and Mg were also present in a considerable amounts. On the other hand, citrus seeds and flours are poor source for Zn and Mn. Meanwhile, potassium was the highest inorganic cation. This results agree well with those reported by Kamel et al. [31], who found that potassium content of citrus seed was 1 000 mg/100 g seed.

Defatting process of citrus seeds increased the level of all elements in citrus seed flours. The mixture of citrus seeds and its flour contained the highest value of phosphorus compared to mandarin and orange seed and their flours. This could be due to the mixing process. Our results confirm well with those reported by Moussa [32] for lemon seeds and flour.

3.3 Amino acids profile

The results of the amino acids content of citrus seed flours are presented in Table 3. The results showed a slight differences in the amino acids profile between the studied citrus seeds flours. Arginine, glutamic acid and aspartic acid were the major amino acids in all flour samples. Their percentages were 14.1% – 16.3%, 17.1% – 19.3%, and 8.2% – 11.0% of the total amino acids, respectively. Compared to the FAO/WHO [33] reference pattern, citrus seed flours are rich in leucine except orange flour. The total aromatic amino acids of citrus seed flours had higher values (8.52, 7.61, 8.34, 8.19 and 6.0 g/

16 g N for citron, orange, mandarin and mixture seed flours and FAO/WHO, respectively). Threonine, sulfur amino acids, isoleucine, and lysine were slightly low in citrus seed proteins as compared to the reference pattern. Citrus seed flours are highly deficient in tryptophan than the reference pattern. (0.19, 0.27, 0.08, 0.18 and 1.00 g/16 g N for citron, orange, mandarin, mixed seed flours and FAO/WHO). The total concentration of essential amino acids in the FAO/WHO [33] reference was 36 g/16 g nitrogen, while it was 36.7, 35.1, 36.2 and 35.7 g/16 g of nitrogen for citron, orange, mandarin and their mixed flours, respectively. These results agree well with those reported of Moussa [32]. Generally, citrus seed flours have an excellent amino acids profile particularly sulfur containing amino acids and total essential amino acids. It is worthy to report that citrus seed flours have a potential use to improve the amino acids pattern of oil seeds, legumes, and wheat flour in food products. Also it is a good source for the most amino acids important and required in human and animals nutrition through blending with other vegetable materials.

3.4 Physico-chemical properties of citrus seed oils As shown in Table 4 refractive index, specific gravity, melting point, colour and viscosity for citrus seed oils were differed slightly. Generally, these results agree well with those reported by Abdo [34], Moharram [35], Moussa [32] and Youssef [36]

for specific gravity and refractive index, but sligthly lower than those reported by Kamel et al. [31] for melting point. The results of colour indicated that these seed oils could be used Table 1. Proximate chemical composition of whole citrus seeds, defatted flours and their mixture*.

Chemical constituents Citron seed Orange seed Mandarin seed Mixed seeds

Raw Flour Raw Flour Raw Flour Raw Flour

Total protein N66.25 [%] 19.93l0.41 36.20l0.92 17.01l0.61 33.14l0.83 15.87l0.60 28.56l0.94 17.32l0.67 31.38l0.82 Non-protein nitrogen [%] 1.70l0.14 2.12l0.17 2.01l0.11 2.84l0.16 1.54l0.10 2.63l0.14 1.74l0.13 2.73l0.13 Crude lipids [%] 40.38l2.71 2.93l0.31 42.59l2.43 3.29l0.43 38.86l1.95 2.67l0.22 40.63l2.02 3.04l0.51 Total ash [%] 3.39l0.17 5.07l0.26 3.17l0.23 5.02l0.32 3.14l0.19 5.22l0.34 3.21l0.18 5.12l0.27 Crude fibre (by difference) [%] 24.15l1.83 31.81l2.02 22.53l0.94 32.14l1.94 24.01l2.11 31.70l2.40 23.53l1.72 32.07l2.00 Total carbohydrates [%] 12.15l0.76 23.99l1.56 14.70l1.01 26.41l2.32 18.12l1.89 31.85l2.81 15.21l1.51 28.39l2.45 Reducing sugars [%] 3.24l0.12 6.92l0.46 3.86l0.21 8.16l0.62 6.63l0.59 11.75l1.03 5.62l0.74 10.17l0.89 Sucrose [%] 2.61l0.14 4.25l0.34 3.02l0.26 5.24l0.75 4.14l0.47 6.67l0.72 2.98l0.23 5.34l0.62 Starch [%] 6.30l0.50 12.82l0.76 6.82l0.54 13.01l0.97 7.35l0.83 13.43l1.06 6.71l0.54 12.88l0.94 Moisture [%] 6.37l0.17 10.30l0.20 8.70l0.15 12.41l0.24 8.61l0.19 12.51l0.29 7.29l0.18 12.03l0.24 Values on dry weight basis.

* Average of three determinationslstandard deviation.

Table 2. Mineral composition of whole citrus seeds, defatted flours and their mixture [mg/100 g dry sample)].

Element Citron seed Orange seed Mandarin seed Mixed seeds

Raw Flour Raw Flour Raw Flour Raw Flour

Macro elements

Potassium 762 1120 992 1 450 795 1 380 837 1 231

Sodium 168 272 225 371 213 357 207 331

Calcium 73.6 98.8 83.7 114.2 61.2 89.2 70.3 96.6

Phosphorus 105.7 300.0 49.2 78.3 39.7 59.0 103.5 240.7

Micro elements

Zinc 2.13 3.85 2.09 3.74 1.02 1.76 2.07 3.51

Iron 8.92 13.43 7.36 11.21 3.49 5.24 5.07 7.42

Copper 2.15 3.72 1.94 3.21 1.61 2.43 1.84 2.96

Magnesium 21.3 32.4 16.2 24.3 9.8 15.6 17.1 26.5

Manganese 1.47 2.52 1.05 1.93 0.74 1.58 1.37 2.25

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388 Nahrung 43 (1999) Nr. 6, S. 385 – 391

without further bleaching or decolorization process. This advantage has an economical value during oil processing.

The iodine values were 96, 103, 92 and 99 for citron, orange, mandarin and mixed seed oils, respectively; thus, citrus seed oils could be classified as a semi-drying oils. Man- darin seed oil had the highest acid value than other citrus seed oils (The acid values were 0.95, 0.67, 1.12 and 0.76 for citron, orange, mandarin and mixed seed oils, respectively). Generally these values are slightly higher than those reported by Abdo [34], and Moussa [32], but lower than those obtained by De Muigo et al. [37]. Saponification value ranged from 187.2 to190.2, ester number 186.8 to 189.5 and peroxide value 5.90 to 6.37, which are quite similar to those reported by Habib et al. [6] for Egyptian citrus seeds oils.

3.5 Citrus seed oil classes

The data of the individual oil classes of citrus seed oils are summarized in Table 5. Crude citrus seed oils contained eight

oil classes which appeared on the thin-layer chromatogram in the following sequence order from the front to the base line;

hydrocarbon, triglycerides, free fatty acids, sterols, diglycerides, monoglycerides, alcohol and phospholipids. Triglycerides were predominant oil class in all oils samples (Table 5) and accounted for 65.4 – 68.4%, followed by free fatty acids, then diglycerides. Citron seed oil proved to have the higher content of free fatty acids, but mandarin seed oil was the highest in triglycerides content. Orange seed oil contained an intermediate concentration for triglycerides and free fatty acids compared to the rest of the oil samples 65.4% and 13.4%, respectively (Table 5). The presence of monoglycerides and free fatty acids may be due to the partial enzymatic hydrolysis of reserve triglycerides in the citrus seeds during storage of the seeds. Gen- erally, these values agree well with those obtained by Mohar- ram [35] for orange seed oil and Tsuyuki et al. (38) for Japa- nese citrus seed oil. They reported that the citrus seed contained eight classes. Lemon seed oil showed seven oil groups [32].

Table 3. Amino acids composition of different citrus seeds flours [g/16 g N].

Amino acid Citron seed

flour

Orange seed flour

Mandarin seed flour

Mixed seed flours

FAO/WHO (1973)

Isoleucine 3.32 3.20 3.63 3.38 4.00

Leucine 8.13 6.81 7.60 7.41 7.50

Lysine 3.90 4.71 4.27 4.25 5.50

Cystine 1.89 1.44 1.66 1.69 –

Methionine 1.64 1.81 1.41 1.62 –

Total sulfur amino acids 3.53 3.25 3.07 3.31 3.50

Tyrosine 3.00 2.90 2.93 2.94 –

Phenylalanine 5.52 4.71 5.41 5.25 –

Total aromatic amino acids 8.52 7.61 8.34 8.19 6.00

Threonine 3.40 3.80 3.21 3.25 4.00

Tryptophan 0.19 0.27 0.08 0.18 1.00

Valine 5.67 5.51 5.99 5.71 5.00

Total essential amino acids 36.66 35.16 36.19 35.68 36.00

Histidine 2.45 2.75 2.48 2.54 –

Arginine 14.41 16.34 14.10 15.07 –

Aspartic acid 10.97 8.19 10.80 10.11 –

Glutamic acid 17.10 19.33 18.98 18.34 –

Serine 4.16 4.40 4.40 4.10 –

Proline 4.97 4.66 5.30 4.89 –

Glycine 4.49 5.21 4.61 4.74 –

Alanine 4.30 4.98 4.30 4.50 –

Total non-essential amino acids 63.34 64.84 63.81 64.32 –

Table 4. Physico-chemical characteristics of different citrus seed oils*.

Property Citron seed oil Orange seed oil Mandarin seed oil Mixed seed oils

Refractive index (258C) 1.4681l0.001 1.4684l0.002 1.4672l0.001 1.4682l0.001

Density (258C) [g/cm³] 0.884l0.01 0.914l0.06 0.962l0.09 0.910l0.08

Melting point [8C] 7.00 7.00 7.00 7.00

Viscosity [10^–1PaNs] 0.05 0.07 0.08 0.07

Colour 2.6 R 3.1 R 7.4 R/0.2 B 4.0 R

Acid value [mg KOH/g oil] 0.953l0.08 0.673l0.09 1.120l0.09 0.762l0.06

Saponification value [mg KOH/g oil] 189.5l1.41 190.2l1.87 187.2l1.73 188.3l1.76

Ester value [mg KOH/g oil] 188.5l1.40 189.5l1.72 186.8l1.70 187.5l1.41

Peroxide value [meq O2/kg oil] 5.95l0.48 6.37l0.51 5.90l0.62 5.98l0.57

Iodine value (Hanus) [mg I/g oil] 96.23l1.34 102.57l1.57 91.54l1.09 99.25l1.07

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3.6 Fatty acids composition

Fatty acids composition of citrus seed oils are shown in Table 6. Citrus seed oils had high amounts of unsaturated fatty acids which consisted mainly of linoleic (33.2% – 38.4%) followed by oleic (22.3 – 26.0%) and at the last linolenic (2.6% – 9.6%) acids. Although, citron seed oil had the lowest content of oleic and linoleic acids compared to the other citrus seed oils; but it contained the highest amount of linolenic acid (9.6%). This increases its nutritional value as a source for this particular essential fatty acid. These results agree well with those reported by Hendrickson and Kesterson [39] for lemon seed oils, Witing et al. [40] for Arizona grapefruit seed oil and Abdo [34] for the Egyptian orange seed oil.

Palmitic and stearic acids were the major saturated fatty acids in all citrus seed oils and its percentage concentration was 24.7 – 29.5% and 4.3 – 5.3% of palmitic and stearic, respectively. The total saturated fatty acids content in the seed of citron, mandarin and mixture oils were almost the same (34%) and was higher than that in orange seed oil (31%).

These results are confirmed by the findings of French [41] for citrus seed oils, Filsoof and Mehran [42] for Iranian citrus seed oil and Abdo [34] for the Egyptian orange seed oil. Ara- chidic, lauric and myristic were traces in all oil samples compared to the other fatty acids. The same results were mentioned by Weerakoon [43], who found traces of lauric and arachidic in Ceylon sweet orange seeds.

The ratio between saturated and unsaturated fatty acids was 1 : 1.86; 1 :2.23; 1 : 1.92 and 1 : 1.93 in citron, orange, mandarin and mixture seed oils, respectively. These values are slightly lower than that reported by Moussa [32], who found that the ratio of lemon seed oil was 1 : 3.2. Citrus seed oils proved to be a good source for essential fatty acids, its content was more than 40% in all oil samples. Abdo [34] reported a value of 40.74% for essential fatty acids in Egyptian orange seed oil, which is very close to our finding. The total number of fatty acids was eight in citrus seed oils, while Habib et al. [6] found that the total number of fatty acids was 9, 17, 8 and 6 for orange, mandarin, lime and grapefruit seed oils, respectively.

These differences could be due to different varieties, cultivar, location, storage conditions and harvesting time [40].

Citrus seed oils are rich in both oleic and linoleic acids, such oils have a good semi-drying properties and could be used as an excellent edible cooking oil, salad oil or for marga- rine manufacture.

3.7 Antinutritional factors

Table 7 illustrates some antinutritional compounds found in the citrus seed flours. The results revealed that glucosides were detected and present in all citrus seed flours. Mandarin seeds flour contained the highest content of glucosides (0.94%) but citron seed flour was the lowest (0.70%). The flour produced from mixing these seeds together contained also an appreciable amounts of glucosides (0.81%). Ozaki et al. [44] found that the total glucosides in different citrus seeds were in the range of 0.31 – 0.87%. Our data in this regard are quite close to their value. Glucosides are the major problem in using citrus seeds as a protein source in food formulation since it has a very sharp bitter taste and this affects the taste of food products.

Tannins in citrus seed flours were very low (0.02 – 0.03%) compared to faba bean (1.68%), which has been reported by El-Adawy [45] or other legumes and oil seeds. Also, phytic acid content was low 0.17 – 0.26% as tannins. Khalil and El- Adawy [46] mentioned that white beans flour contains 1.31%

phytic acid. The low contents of phytic acid and tannins in these flours encourages its use in food preparation after a suc- cessful debittering process.

The content of flatulence-inducing factors (stachyose and raffinose) are present in all flours. Stachyose content was highest in mandarin seed flour (1%) followed by the mixed seed flours (0.9%). Mandarin and orange seed flours showed the lowest content of raffinose and stachyose, respectively. In the mixed seed flour the contents of stachyose and raffinose were 0.9% and 0.8%, respectively. To the best of our knowledge there are no data reported in the literature regarding the flatulence inducing factors in citrus seeds flours.

Also, the data proved the absence of haemagglutinin activity in all citrus seed flours. According to Rahma and Narasinga Rao [47] and El-Adawy and Khalil [48], the flours of lupin and roselle seed are also free from haemagglutinin activity.

Trypsin inhibitor activity was presented in all citrus seed flours, but at a very low activity compared to legumes or some oil seeds. The activity was between 5.1 and 10.9 TUI/mg protein in orange and mandarin seed flour, respectively. The values of trypsin for citrus seed flours were close to those reported by Mansour and El-Adawy [49] for fenugreek seeds, which had 6.02 TUI/mg sample. No literature data were found regarding the antinutritional factors in citrus seeds except glucosides.

Table 5. The percentage of oil classes of different citrus seed oils.

Oil class* Citron

seed oil

Orange seed oil

Mandarin seed oil

Mixed seed oils

Hydrocarbons Tr.** Tr. Tr. Tr.

Triglycerides 66.8 65.4 68.4 68.0

Free fatty acids 14.5 13.4 11.7 12.8

Sterols 2.18 3.52 3.27 3.14

Diglycerides 12.1 12.0 10.5 11.3

Monoglycerides 2.49 1.97 2.97 2.51

Alcohols Tr. Tr. Tr. Tr.

Phospholipids 1.96 3.66 2.64 2.23

* Average of three determinations.

** Tr. = Traces.

Table 6. Fatty acids composition of different citrus seed oils.

Fatty acid [%] Citron

seed oil

Orange seed oil

Mandarin seed oil

Mixed seed oils

Lauric C12 : 0 0.39 0.36 0.65 0.37

Myristic C14 : 0 0.43 0.44 0.61 0.46

Palmitic C16 : 0 29.52 24.73 28.12 28.54

Stearic C18 : 0 4.32 5.27 4.34 4.37

Oleic C18 : 1 22.25 26.00 24.89 24.53

Linoleic C18 : 2 33.21 38.44 38.26 38.25

Linolenic C18 : 3 9.56 4.58 2.58 3.11

Arachidic C20 : 0 0.32 0.18 0.55 0.37

Total Saturated fatty acids 34.98 30.98 34.27 34.11 Total-Unsaturated fatty

acids

65.02 69.02 65.73 65.89

Total essential fatty acids 42.77 43.02 40.84 41.36

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390 Nahrung 43 (1999) Nr. 6, S. 385 – 391

3.8 True and apparent digestibility of citrus seed flours

The true and apparent digestibility of citrus seed flours based on using trypsin-pancreatin are given in Table 8. The true digestibility values were 88.7, 93.3, 87.3 and 89.9% for citron, orange, mandarin and mixture seed flours, respectively.

However, apparent digestibility was in the same trend as true digestibility for the tested samples. The true and apparent digestibility were low in mandarin seed flour and high in orange seed flour. This could be attributed to the presence of trypsin inhibitor and tannins in mandarin flour (Table 7). Aw and Swanson [50] found that tannins adversely affect the nutritive value of black bean by decreasing the proteolytic enzymes digestibility. Generally, the value of true digestibility is slightly lower than those reported by Moussa [32] lemon seed flour, which found 98.2% for the true digestibility.

3.9 Biological values computation of the citrus seed flours

The nutritional quality of a protein is principally governed by its amino acids composition. Amino acids contents shown in Table 3 were further used to conclude certain nutritional parameters (Table 9). On the basis of chemical score, the first limiting amino acid was tryptophan (chemical score ranged from 5 to 18%) for all citrus seed proteins, while the second limiting amino acid was isoleucine for orange seed protein and methionine for the other citrus seed proteins. Generally, the values of chemical score were lower than those reported by Ory et al. [10] for citrus seed proteins. The FAO/WHO index was almost same for citron, orange and mixture seed proteins and higher than that of mandarin seed protein. However, the biological values of mandarin seed proteins were lower than those of other citrus seed proteins for all measurements except Table 7. Antinutritional factors content of different citrus seed flours*.

Antinutritional component Citron seed flour Orange seed flour Mandarin seed flour Mixed seed flours

Glucosides [%] 0.70l0.03 0.76l0.01 0.94l0.03 0.81l0.02

Tannins [%] 0.03l0.002 0.02l0.003 0.03l0.004 0.03l0.004

Phytic acid [%] 0.17l0.03 0.26l0.06 0.23l0.04 0.20l0.03

Stachyose [%] 0.80l0.10 0.65l0.14 1.00l0.15 0.90l0.10

Raffinose [%] 1.00l0.13 0.85l0.09 0.80l0.14 0.80l0.13

Haemagglutinin activity [HU/g flour] 0.00 0.00 0.00 0.00

Trypsin inhibitor [TIU/mg protein] 5.19 5.10 10.86 6.89

Table 8. True and apparent digestibility of different citrus seed flours*.

Property Citron seed flour Orange seed flour Mandarin seed flour Mixed seed flours

True digestibility (TD) [%] 88.73l1.05 93.26l1.32 87.30l0.99 89.92l1.16

Apparent digestibility (AD) [%] 75.27l0.97 79.53l1.10 76.93l0.94 76.39l0.92

* Average of three determinationslstandard deviations.

Table 9. Biological values computation by different methods for citrus seed flour.

Methods of evaluation Citron seed flour Orange seed flour Mandarin seed flour Mixed seed flours

Chemical score (CS) [%] 13 18 5 12

First limiting amino acid Tryptophan Tryptophan Tryptophan Tryptophan

Second limiting amino acid Methionine Isoleucin Methionine Methionine

FAO/WHO index [%] 25 25 5 25

Mitchel essential amino acids index (MEAAI) [%] 54.3 56.3 50.1 55.3

Morup and Olesen’s index (MOI) 71.2 70.1 48.2 68.3

Gauss index (GI) 72.0 49.7 5.4 57.6

Transformed Gauss index (TGI) 87.0 80.8 51.8 83.2

Transformed Gauss index corrected to digestibility (TGICD) [%]

77.2 75.3 45.2 74.8

Protein efficiency ratio (PER)* A 2.97 2.20 2.30 2.47

B 2.91 2.32 2.43 2.59

C 2.92 2.13 2.06 2.43

* Where:

PERA= 0.684 + 0.456 Leu – 0.047 Pro.

PERB= 0.468 + 0.454 Leu – 0.105 Tyr.

PERC= –1.816 + 0.435 Met + 0.78 Leu + 0.211 His – 0.944 Tyr.

(8)

Nahrung 43 (1999) Nr. 6, S. 385 – 391 391

the protein efficiency ratio (PER) calculated by equations A and B were higher than orange seed protein. Generally, the observed biological values for citrus seed protein were higher than those of other citrus seed proteins, which is mainly due to the higher content of essential amino acids in citrus seed protein than that in others (Table 3). The values of FAO/WHO, transformed Gauss index and transformed Gauss index corrected for digestibility are almost in agreement with those reported by Moussa [32] for lemon seed protein, which found its values were 32.6, 88.6 and 94.0, respectively. Finally, the mixing process for different seeds could increase the biological values than mandarin seed protein. Therefore, it is interesting to utilize mixed citrus seed flours through blending with legumes and oil seed proteins to improve and increase its biological values.

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Received: 26 October 1998.

Accepted: 19 Januar 1999.