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J. Agric. Food Chem. 2009, 57, 9524–9531 DOI:10.1021/jf902287e
Influence of γ-Radiation on the Nutritional and Functional Qualities of Lotus Seed Flour RAJEEV BHAT,*,† KANDIKERE RAMAIAH SRIDHAR,‡ ALIAS A. KARIM,† CHIU C. YOUNG,§ AND ANANTHAPADMANABHA B. ARUN§ †
Food Technology Division, School of Industrial Technology, Universiti Sains Malaysia, Penang 11800, Malaysia, ‡Microbiology and Biotechnology, Department of Biosciences, Mangalore University, Mangalagangotri, Mangalore 574 199, Karnataka, India, and § College of Agriculture and Natural Resources, Department of Soil Environmental Science, National Chung Hsing University, 250 Kuo-Khang Road, Taichung, Taiwan 40227
In the present study, we investigated the physicochemical and functional properties of lotus seed flour exposed to low and high doses of γ-radiation (0-30 kGy; the dose recommended for quarantine and hygienic purposes). The results indicated raw seed flour to be rich in nutrients with minimal quantities of antinutritional factors. Irradiation resulted in a dose-dependent increase in some of the proximal constituents. The raw and γ-irradiated seeds meet the Food and Agricultural Organization-World Health Organization recommended pattern of essential amino acids. Some of the antinutritional factors (phytic acid, total phenolics, and tannins) were lowered with γ-irradiation, while the seed flours were devoid of lectins, L-3,4-dihydroxyphenylalanine, and polonium-210. The functional properties of the seed flour were significantly improved with γ-radiation. γ-radiation selectively preserved or improved the desired nutritional and functional traits of lotus seeds, thus ensuring a safe production of appropriate nutraceutically valued products. KEYWORDS: γ-Irradiation; lotus seed flour; nutrients; antinutrients; protein digestibility; functional properties
INTRODUCTION
The paucity of protein-rich food and protein food supplements poses problems of malnutrition in children and lactating women in developing countries, and it has become a prime concern to food scientists, nutritionists, and local governments (1, 2). The scarcity of fertile land and an overdependence on cereal-based food products have also aggravated the protein deficiency problems in humans (3). To meet the ever-increasing protein demand, the exploitation of nonconventional seeds has become inevitable (4-7). Such explorations may assuage the problems of food security, agricultural development, self-dependence, and enhancement of the economy of developing countries. The little known lotus seed and its flour might significantly contribute to world food production due to its wide distribution and adaptability to adverse environmental conditions. Nutritionally, lotus seeds have been reported to be rich in proteins and consist of adequate amounts of essential minerals (8). Lotus seeds are in high demand in Indian Ayurvedic medicinal preparations and are also widely used in folk medicines to treat tissue inflammation and cancer, act as a diuretic (9), and treat skin diseases (leprosy), and they are used as an antidote against snake poison (10). The seeds also possess hepatoprotective, free radical scavenging (11), and antifertility (12) properties. *To whom correspondence should be addressed. Tel: þ604-653 5221. Fax: þ604-657 3678. E-mail:
[email protected] or
[email protected].
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Published on Web 09/24/2009
Radiation processing of plant produce has become an important physical preservation method to overcome the international quarantine barriers and to increase the safety and shelf life of the product, mainly by the elimination of spoilage microflora (13, 14). Irradiation, besides being successful in decontamination and disinfestation, is also known to improve the quality of fresh plant produce (e.g., legumes, seeds, and spices) requiring longterm preservation (15,16). Radiation processing is also efficient in decreasing or eliminating some of the antinutritional factors in seeds (17-19). Of late, with the increased database and scientific evidence, health conscious consumers are willing to use irradiated foods for safety concerns (20). To fill the existing gap in the knowledge on the effects of γ-rays (low and high dose) on the nutritional potential of lotus seeds, the current study was aimed to investigate in detail the nutritional and antinutritional compositions and the functional properties of raw and irradiated seeds. The results of this study will be useful to popularize lotus seed flour for the successful exploitation of its nutritional value in the production of safe and inexpensive food products. MATERIALS AND METHODS
Materials. Freshly harvested and dried lotus seeds (Nelumbo nucifera Gaertn.) from a single lot (25 kg) were procured from a local traditional supplier from North India. Seeds free from any apparent physical damage or insect infestation were chosen for the evaluation. The characteristic features (shape, color, length, width, and weight) of randomly selected seeds were also recorded.
© 2009 American Chemical Society
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J. Agric. Food Chem., Vol. 57, No. 20, 2009
Irradiation. The whole seeds (with the seed coat) (∼50 g) packed in polyethylene bags were exposed to various doses of γ-radiation (doses: 0, 2.5, 5.0, 7.5, 10, 15, and 30 kGy) at room temperature (25 ( 1 °C) from a 60Co (cobalt60) source (GC-5000, ISOMED, Bhabha Atomic Research Centre, Trombay, Mumbai, India). Fricke dosimetry was employed to measure the absorbed dose in the irradiated samples (21). All of the seed samples were stored in a deep freezer (-20 °C) until further analysis. Flour Preparation and Nutritional Analysis. The edible portions of the seeds (cotyledon) were separated physically with the help of a sharp stainless knife and were further ground into a fine powder ( 0.05). However, calcium, copper, zinc, and manganese did show some significant decrease (P < 0.05). Generally, minerals do not degrade on irradiation, but a change in their oxidation state might occur due to their varied extractability in a particular solvent. Apart from this, lotus seed being a biological sample, variations in mineral concentrations might naturally be present between each individual seed, which might give rise to varied results on irradiation. Another possible reason for the observed decrease in some of the minerals might be due to the presence of certain antinutrients at higher concentrations (like oligosaccharides, oxalates, protease inhibitors, saponins, and others) that could have increased on irradiation and possibly be capable of chelating the mineral cations, forming insoluble complexes leading to reduced bioavailability of trace minerals. However, the actual mechanism for decrease in some of the minerals is still obscure, which needs to be further investigated. However, this decrease in some of the minerals should not be an impediment for successful utilization of radiation technology, when considering the overall beneficial aspects related to safety. Amino Acids. The application of γ-radiation did not have much of a positive effect on the amino acids of the lotus seed flour and showed a significant reduction at all of the delivered doses (P < 0.05). In Table 3, the amino acid composition of the raw and γ-irradiated lotus seed flour has been compared with the FAO-WHO (31) reference patterns and soybeans (63). The acidic amino acids, glutamic acid and aspartic acid, were the major amino acids present in the seed flour. Except for valine, isoleucine, and histidine, other EAAs were not comparable with the FAO-WHO (31) reference pattern. The sulfuramino acids cysteine and methionine (1.9 vs 2.5%) and tyrosine and phenylalanine (5.84 vs 6.3%) in the raw seeds fulfilled
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J. Agric. Food Chem., Vol. 57, No. 20, 2009
Table 3. Amino Acid Composition of the Lotus Seed Flours Treated with γ-Radiation (mg/100 mg Crude Protein; n = 3)
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a
irradiation dose (kGy) amino acid
0
2.5
5
7.5
10
15
30
glutamic acid aspartic acid serine threonine proline alanine glycine valine cysteine methionine isoleucine leucine tyrosine phenylalanine tryptophan lysine histidine arginine
16.29 7.93 4.64 2.61 2.41 3.30 3.62 3.55 0.82 1.08 2.89 4.90 2.67 3.17 ND 4.24 1.93 6.97
12.97 6.29 3.85 2.10 1.98 2.75 2.91 2.90 0.77 0.76 2.36 3.98 2.19 2.57 ND 3.50 1.41 5.68
13.10 6.34 3.85 2.11 1.97 2.77 2.94 2.89 0.75 0.78 2.32 3.98 2.18 2.57 ND 3.50 1.38 5.71
13.10 6.34 3.85 2.12 1.95 2.78 2.94 2.89 0.74 0.79 2.31 3.98 2.18 2.56 ND 3.52 1.35 5.71
13.13 6.37 3.84 2.13 1.95 2.79 2.95 2.87 0.72 0.80 2.27 3.97 2.17 2.56 ND 3.51 1.34 5.72
13.10 6.32 3.90 2.13 2.02 2.76 2.94 2.94 0.74 0.82 2.36 4.01 2.17 2.61 ND 3.53 1.46 5.80
13.01 6.33 3.90 2.13 2.08 2.75 2.94 2.98 0.75 0.83 2.41 4.03 2.14 2.64 ND 3.54 1.57 5.92
FAO-WHO patternb
soybeansc 16.9d 11.3e 5.67 3.76 4.86 4.23 4.01 4.59 1.70 1.22 4.62 7.72 1.24 4.84 3.39 6.08 2.50 7.13
3.4
3.5 2.5f 2.8 6.6 6.3g 1.1 5.8 1.9
a ND, not detectable. b FAO-WHO pattern (31). c Bau et al. (63). d Glutamic acid þ glutamine. e Aspartic acid þ asparagine. f Methionine þ cysteine. g Tyrosine þ phenylalanine.
Table 4. EAA Score, IVPD (N = 5, Mean ( SD), and PDCAASa of the Flours of Lotus Seeds Treated with γ-Radiationb irradiation dose (kGy) 0
2.5
5
7.5
10
15
30
62.35 82.57 61.20 82.50 60.30 75.24 60.69 71.10 20.99 ( 1.92 b
62.65 82.00 60.80 81.07 60.15 75.80 60.52 70.53 20.23 ( 4.28 b
62.64 84.00 62.40 84.29 60.76 75.87 60.86 76.84 15.78 ( 0.24 a
62.65 85.14 63.20 86.07 61.07 76.51 61.03 82.63 15.41 ( 0.42 a
13.09 17.33 12.85 17.32 12.66 15.79 12.74 14. 91
13.30 17.41 12.91 17.21 12.77 15. 94 12. 85 14. 97
9.89 13.46 9.85 13. 30 9.59 11. 97 9.60 12.13
9.65 13.12 9.73 13.26 9.41 11.79 9.41 12.73
EAA score threonine valine cysteine þ methionine isoleucine leucine tyrosine þ phenylalanine lysine histidine IVPD (%)
76.76 101.43 76.00 103.21 74.24 92.70 73.10 101.58 37.90 ( 5.10 d
61.76 82.86 61.20 84.29 60.30 75.56 60.34 74.21 27.40 ( 1.3 c
62.06 82.57 61.2 82.86 60.30 75.40 60.34 72.63 20.17 ( 0.03 b PDCAAS (%)
threonine valine cysteine þ methionine isoleucine leucine tyrosine þ phenylalanine lysine histidine a
29. 09 38. 44 28. 80 39.12 28.13 35.13 27.71 38. 50
17. 20 23. 07 17.04 23.47 16.79 21. 03 16. 80 20. 66
12. 52 16. 65 12. 34 16.71 12.16 15. 21 12.17 14. 65
Calculated based on the FAO-WHO pattern (31). b Values across the row (for IVPD) with different letters are significantly different from each other (P < 0.05).
76 and 93% of the FAO-WHO (30) pattern, respectively. Except for tryptophan, the rest of the EAA in the raw and γ-irradiated seeds is on par with the Food and Agricultural Organization-World Health Organization-United Nations University (FAO-WHO-UNU) (64) pattern. The tyrosine in the raw as well as the irradiated seeds was higher than soybeans (2.14-2.67 vs 1.24%). The irradiation might have possibly changed the oxidative state, affecting the results of amino acids. According to Baudoin and Maquet (65), ecological conditions are known to markedly influence the total nitrogen of seeds, which in turn affect the relative proportions of the EAA (e.g., lysine, methionine, and cysteine). IVPD. In our study, the IVPD of the seed flour showed a significant, dose-dependent decrease (P < 0.05) (control, 37.90%, vs 30 kGy, 15.41%) (Table 4). Such a decrease in the protein
digestibility in the irradiated seed flour can be attributed to the increased high molecular weight polyphenolic compounds, which are capable of binding to the digestive enzymes and can act directly on the digestion of dietary proteins. Saunders et al. (66) have hypothesized that “IVPD” could be comparable to “in vivo protein digestibility” in rat models. However, the observed decrease in the IVPD should not be considered a hindrance when considering the overall beneficial aspects (for example, elevation of crude protein at certain doses, increase in linoleic acid concentration, water and oil absorption capacities, emulsion capacities, and decrease in some of the antinutrients) of radiation treatments of lotus seed flour. Further studies are warranted wherein studies can be pursued to evaluate the effects of radiation treatments on the in vivo protein digestibility to provide more clear information.
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Bhat et al.
Table 5. Fatty Acid Composition of the Lotus Seed Flours after γ-Radiation (mg/g Lipid) (n = 3, Mean)a irradiation dose (kGy) fatty acid
0
2.5
5
7.5
10
15
30
0.08 0.02 4.35 0.07 0.001
0.08 0.03 4.36 0.0003
0.10 0.03 4.37 0.0003
0.1 0.06 4.47 -
saturated fatty acids myristic acid (C 14:0) pentadecanoic acid (C15:0) palmitic acid (C16:0) heneicosanoic acid (C21:0) behenic acid (C22:0)
0.07 0.01 4.24 0.09 0.60
0.05 0.01 4.28 0.08 0.001
0.041 0.01 4.36 0.08 0.001
polyunsaturated fatty acids myristoleic acid (C14:1) elaidic acid (C18:1) oleic acid (C18:1) linoleic acid (C18:2) linolelaidic acid (C18:2) linolenic acid (C18:3) sum of saturated fatty acids sum of polyunsaturated fatty acids P/S ratio a
0.02 2.14 7.02 5.84 1.42 5.01 16.44
0.02 0.02 0.02 0.003 0.004 1.20 0.20 0.14 6. 40 6.00 1.20 2.97 6.12 6.88 7.63 5.80 5.77 4.00 2.21 1.82 1.40 1.37 1.22 4.42 4.49 4.52 4.47 4.50 14.82 16.33 12.7 9.09 9.45
3.28 3.35
3.63
2.81
2.03
2.10
0.01 14.53 1.44 4.63 15.98 3.45
-, not detectable; SDs for all of the values were
