examples of the present invention described below are intended only to exemplify the present invention rather than to limit the technical scope thereof . the technical scope of the present invention is limited only by the description in claims . ros include reactive oxygen species in the narrow sense comprising superoxide anion , hydroxyl radical , hydroperoxide and singlet oxygen , and reactive oxygen species in the broad sense comprising an alkoxy radical , hydroperoxyl radical , a peroxyl radical , hydroperoxide , and a transition metal - oxygen complex and the like . among the ros , hydroxyl radical has the most potent oxidizing activity , but has very short lifetime . as such , it oxidizes non - selectively body components like nucleic acids , proteins , and lipids that are present in the vicinity of their generation site . however , peroxyl radical has a weak oxidizing activity but is relatively stable . as such , it can diffuse and cause a cell membrane damage via free radical chain reactions of polyunsaturated fatty acids . meanwhile , hydroxyl radical generates a peroxyl radical but no hydroxyl radical is generated from a peroxyl radical . since the working mechanism is different between a hydroxyl radical and a peroxyl radical , an effective antioxidant may be also different for each of them . for such reasons , in the present examples , an antioxidant effect was evaluated for both hydrogen peroxide and 2 , 2 ′- azobis ( 2 - amidinopropane ) dihydrochloride salt ( herein below , referred to as “ aaph ”), that are the representative examples of a compound which can generate hydroxyl radical and a peroxyl radical , respectively . as a positive control , carnosine having a known antioxidant activity was used . for the evaluation of an antioxidant effect on hydrogen peroxide , human neonatal skin fibroblast cells ( trade name : cryo nhdf - neo , manufactured by sankyo junyaku co ., ltd .) were inoculated to a 24 - well plate to have 1 × 10 5 cells per well . the cells were then cultured for four hours in a medium for cell culture ( trade name : d - mem ( 1 g / l glucose ), manufactured by wako pure chemical industries ) supplemented with 10 % bovine fetal serum ( herein below , referred to as a “ standard medium ”) in a 5 % co 2 and saturated water vapor atmosphere at 37 ° c . ( degrees celsius ). for the evaluation of an antioxidant effect on aaph , antibiotics ( penicillin , streptomycin , and fungizone ) were supplemented to the standard medium and the cells were cultured for one day . subsequently , the culture medium was switched to a medium for cell culture ( trade name : d - mem ( 1 g / l glucose ), manufactured by wako pure chemicals industries ) supplemented with 0 . 5 % bovine fetal serum ( herein below , referred to as “ low - serum medium ”) to which 0 . 01 % or 0 . 05 % carnosine , or 0 . 1 μm ( micro - molar ) or 10 μm ( micro - molar ) d - or l - aspartic acid had been added , and the cells were cultured for two days under atmosphere of 5 % co 2 and saturated moisture at 37 ° c . ( degrees celsius ). for the experiment for the evaluation of oxidative damages on aaph , the culture medium was switched to the medium for cell culture to which 5 ppm or 100 ppm carnosine , or 10 μm ( micro - molar ) d - or l - aspartic acid had been further added , and the cells were cultured for two days . the low - serum medium described above to which neither carnosine nor aspartic acid had been added was employed as a negative control . after culturing for two days , 1 mm or 4 mm hydrogen peroxide , or 50 mm or 100 mm aaph was added to the medium for evaluating an antioxidant effect , and the antioxidant effect was evaluated for carnosine or aspartic acid . the low - serum medium described above to which neither hydrogen peroxide nor aaph had been added was employed as a control for evaluation of toxicity of an antioxidant when no oxidant was added . two hours after the addition of hydrogen peroxide or aaph , alarmarblue ( trade name : biosource , manufactured by biosource international inc .) was added to have final concentration of 10 %. two to three hours later , according to the methods by ahmed s . a . et al . ( j . immunol . method ., 170 , 211 - 224 ( 1994 )) and the instructions provided by the manufacturer , the fluorescent intensity of the supernatant was measured with an excitation wavelength of 544 nm , and an emission wavelength of 590 nm . fig1 shows the results of the experiment obtained by examining the antioxidant effect of carnosine on hydrogen peroxide in cryo nhdf - neo cells . the error bars for each experimental condition indicate the standard deviations of the experimentally measured values obtained by repeating the experiment three times under the identical condition . the asterisk (*) indicates that t is less than 5 % by bonferroni / dunn test . the ratio of viable cells for the control group for evaluating toxicity of the antioxidant without addition of an oxidant was 102 % when carnosine had not been added . when the concentration of carnosine was 0 . 01 %, it was 100 %. when the concentration of carnosine was 0 . 05 %, it was 97 %. the ratio of viable cells in the case of addition of 1 mm hydrogen peroxide was 45 % when carnosine had not been added . when the concentration of carnosine was 0 . 01 %, it was 51 %. when the concentration of carnosine was 0 . 05 %, it was 53 %. the ratio of viable cells in the case of 4 mm hydrogen peroxide was 14 % when carnosine had not been added . when the concentration of carnosine was 0 . 01 %, it was 21 %. when the concentration of carnosine was 0 . 05 %, it was 45 %. thus , when the concentration of hydrogen peroxide was 4 mm , a significant difference in the ratio of viable cells was observed for the case in which 0 . 05 % carnosine had been added compared to the ratio without addition of carnosine . based on the results above , the antioxidant effect of carnosine on hydrogen peroxide was confirmed in the experiment system of the present example . fig2 shows the results of the experiment obtained by examining the antioxidant effect of l - aspartic acid on hydrogen peroxide in cryo nhdf - neo cells . the error bars for each experimental condition indicate the standard deviations of experimentally measured values obtained by repeating the experiment three times under the identical condition . the ratio of viable cells for the control group for evaluating toxicity of an antioxidant without addition of an oxidant was 93 % when l - aspartic acid had not been added . when the concentration of l - aspartic acid was 0 . 1 μl ( micro - molar ), it was 88 %. when the concentration of l - aspartic acid was 10 μm ( micro - molar ), it was 97 %. the ratio of viable cells in the case of 1 mm hydrogen peroxide was 61 % when l - aspartic acid had not been added . when the concentration of l - aspartic acid was 0 . 1 μm ( micro - molar ), it was 62 %. when the concentration of l - aspartic acid was 10 μm ( micro - molar ), it was 62 %. the ratio of viable cells in the case of 4 mm hydrogen peroxide was 36 % when l - aspartic acid had not been added . when the concentration of l - aspartic acid was 0 . 1 μm ( micro - molar ), it was 33 %. when the concentration of l - aspartic acid was 10 μm ( micro - molar ), it was 32 %. based on the results above , a statistically significant antioxidant effect of l - aspartic acid on hydrogen peroxide was not observed . fig3 shows the results of the experiment obtained by examining the antioxidant effect of d - aspartic acid on oxidative damages induced by hydrogen peroxide in cryo nhdf - neo cells . the error bars for each experimental condition indicate the standard deviations of experimentally measured values obtained by repeating the experiment three times under the identical condition . the asterisk (*) indicates that p is less than 5 % by bonferroni / dunn test . the double asterisk (**) indicates that p is less than 1 % by bonferroni / dunn test . the ratio of viable cells for the control group for evaluating toxicity of an antioxidant without addition of an oxidant was 97 % when d - aspartic acid had not been added . when the concentration of d - aspartic acid was 0 . 1 μm ( micro - molar ), it was 86 %. when the concentration of d - aspartic acid was 10 μm ( micro - molar ), it was 97 %. in the case of 1 mm hydrogen peroxide , the ratio of viable cells was 55 % when d - aspartic acid had not been added . when the concentration of d - aspartic acid was 0 . 1 μm ( micro - molar ), it was 62 %. when the concentration of d - aspartic acid was 10 μm ( micro - molar ), it was 63 %. in the case of 4 mm hydrogen peroxide , the ratio of viable cells was 22 % when d - aspartic acid had not been added . when the concentration of d - aspartic acid was 0 . 1 μm ( micro - molar ), it was 29 %. when the concentration of d - aspartic acid was 10 μm ( micro - molar ), it was 34 %. thus , when the concentration of hydrogen peroxide was 4 mm , a significant difference in the ratio of viable cells was observed for the case in which 0 . 1 μm ( micro - molar ) or 10 μm ( micro - molar ) d - aspartic acid had been added compared to the ratio without addition of d - aspartic acid . based on the results above , the concentration - dependent antioxidant effect of d - aspartic acid on hydrogen peroxide was observed . 3 - 4 . antioxidant effect of carnosine in experiment for evaluating oxidative damages induced by aaph fig4 shows the experiment obtained by examining the antioxidant effect of carnosine in the experiment for evaluating oxidative damages induced by aaph in cryo nhdf - neo cells . the error bars for each experimental condition indicate the standard deviations of experimentally measured values obtained by repeating the experiment three times under the identical condition . the double asterisk (**) indicates that p is less than 1 % by bonferroni / dunn test . the ratio of viable cells for the control group for evaluating toxicity of an antioxidant without addition of an oxidant was 100 % when carnosine had not been added . when the concentration of carnosine was 5 ppm , it was 93 %. when the concentration of carnosine was 100 ppm , it was 103 %. the ratio of viable cells in the case of 100 mm aaph was 31 % when carnosine had not been added . when the concentration of carnosine was 5 ppm , it was 60 %. when the concentration of carnosine was 100 ppm , it was 85 %. when aaph had concentration of 100 mm , a significant difference was observed for the ratio of viable cells for the case in which carnosine had been added at the concentration of 100 ppm compared to the ratio without addition of carnosine . based on the results above , the antioxidant effect of carnosine on aaph was confirmed by the experiment system of the present example . 3 - 5 . antioxidant effect of l - and d - aspartic acids in experiment for evaluating oxidative damages induced by aaph fig5 shows the experiment obtained by examining the antioxidant effect of l - and d - aspartic acids in the experiment for evaluating oxidative damages induced by aaph in cryo nhdf - neo cells . the error bars for each experimental condition indicate the standard deviations of the experimentally measured values obtained by repeating the test three times under the identical condition . the asterisk (*) indicates that p is less than 5 % by bonferroni / dunn test . the triple asterisk (***) indicates that p is less than 0 . 1 % by bonferroni / dunn test . the ratio of viable cells for the control group for evaluating toxicity of an antioxidant without addition of the oxidant was 95 % when l - and d - aspartic acids had not been added . when the concentration of d - aspartic acid was 10 μm ( micro - molar ), it was 102 %. when the concentration of l - aspartic acid was 10 μm ( micro - molar ), it was 80 %. in the case of 100 mm aaph , the ratio of viable cells was 51 % when l - and d - aspartic acids had not been added . when the concentration of d - aspartic acid was 10 μm ( micro - molar ), it was 96 %. when the concentration of l - aspartic acid was 10 μm ( micro - molar ), it was 69 %. when aaph had concentration of 100 mm , a significant difference was observed for the ratio of viable cells for the case in which l - and d - aspartic acids had been added at concentration of 10 μm ( micro - molar ) compared to the ratio without addition of l - and d - aspartic acids . based on the results above , it was indicated that d - aspartic acid had more potent antioxidant effect on aaph compared to l - aspartic acid . based on the experimental results of the examples above , d - aspartic acid was found to have an antioxidant effect on both hydrogen peroxide and aaph . however , l - aspartic acid was found to have an antioxidant effect on aaph only . thus , it was indicated that d - aspartic acid is effective against both hydroxyl radical and a peroxyl radical , but l - aspartic acid is effective only against a peroxyl radical . formulation examples of a composition comprising aspartic acid according to the present invention , i . e ., an emulsion preparation , a patch , a tablet , a soft capsule , a granule , a beverage , a candy , a cookie , bean paste , a french dressing , a mayonnaise , a french bread , a soy sauce , yogurt , dried seasoning powder for rice , seasoning / sauce for natto , natto , unrefined black vinegar , cream , body cream , gel , a peel - off mask , a wet pack , an emulsion , a skin lotion , and an aerosol preparation , are given below . the aspartic acid in the formulation examples is either d - form and / or l - form . these formulation examples are all illustrative and not intended to limit the technical scope of the present invention . ( composition ) content (% by weight ) weak flour 45 . 0 butter 17 . 5 granulated sugar 20 . 0 aspartic acid 4 . 0 egg 12 . 5 flavoring agent 1 . 0 100 . 0 granulated sugar is added in portions to butter while stirring , to which an egg , aspartic acid and a flavoring agent are added and stirred . after mixing thoroughly , uniformly sieved weak flour is added and stirred at a low speed , and allowed to stand as a bulk in a refrigerator . thereafter , it is molded and baked for 15 minutes at 170 ° c . ( degrees celsius ) to obtain a cookie . ( composition ) content ( g ) soybean 1000 malted rice 1000 salt 420 aspartic acid 16 . 8 water remainder 4000 malted rice is mixed thoroughly with a salt . washed soybeans are soaked overnight in three times its volumes of water , which are then drained off , and new water is added while boiling , and poured into a colander to collect the broth ( tanemizu fluid ), to which aspartic acid is dissolved at 10 % w / v . the boiled beans are minced immediately , combined with malted rice mixed with salt , to which the tanemizu fluid containing aspartic acid dissolved therein is added and kneaded evenly to obtain a clay - like hardness . dumplings are made and stuffed in a container compactly without forming any voids , and the surface of the content is smoothened and sealed with a plastic film . after three months , the content is transferred to a new container and the surface is smoothened and sealed with a plastic film . instead of adding aspartic acid to the tanemizu fluid , a malted rice producing a large amount of aspartic acid may be employed . such malted rice can be selected by quantifying aspartic acid by the method described in japanese patent unexamined publication no . 2008 - 185558 . alternatively , a commercially available bean paste can be supplemented with aspartic acid or a salt thereof . ( composition ) content ( g ) salad oil 27 . 4 vinegar 30 . 4 sodium chloride 0 . 9 aspartic acid 0 . 30 pepper 1 . 0 60 . 0 vinegar is combined with sodium chloride and aspartic acid , and then stirred thoroughly to be dissolved . salad oil is added to the mixture and the mixture is stirred thoroughly and then pepper is added . ( composition ) content ( g ) salad oil 134 . 0 vinegar 5 . 5 sodium chloride 0 . 9 aspartic acid 0 . 5 egg yolk 18 sugar 0 . 2 pepper 0 . 9 160 . 0 an egg yolk ( room temperature ) is combined with vinegar , sodium chloride , aspartic acid and pepper , and stirred thoroughly using a whipping apparatus . stirring is continued while adding salad oil in portions to form an emulsion . finally , sugar is added and the mixture is stirred . ( composition ) content ( g ) hard flour 140 weak flour 60 sodium chloride 3 sugar 6 aspartic acid 2 dry yeast 4 lukewarm water 128 343 lukewarm water is combined with 1 g of sugar and dry yeast , which is then allowed to undergo a pre - fermentation . hard flour , weak flour , sodium chloride , 5 g of sugar and aspartic acid are placed in a bowl , into which the pre - fermented yeast is placed . after kneading thoroughly into a ball - like dough , a primary fermentation is conducted at 30 ° c . ( degrees celsius ). the dough is kneaded again and allowed to stand , and then shaped into suitable forms , which are subjected to a final fermentation using an electronic fermentation machine . after forming coupes , baking is conducted for 30 minutes in an oven at 220 ° c . ( degrees celsius ). ( composition ) content ( g ) commercially available soy 995 . 8 sauce aspartic acid 4 . 2 1000 commercially available soy sauce is supplemented with aspartic acid , and stirred thoroughly . instead of adding aspartic acid or a salt thereof , malted rice producing a large amount of aspartic acid may be employed for fermenting soy sauce . such malted rice can be selected by quantifying aspartic acid by the method described in japanese patent unexamined publication no . 2008 - 185558 . further , aspartic acid or a salt thereof may be added to commercially available soy sauce . ( composition ) content ( g ) milk 880 l . bulgaricus 50 s . thermophilus 50 aspartic acid 20 1000 fermentation is conducted at 40 to 45 ° c . ( degrees celsius ). other commercially available fermentation seed organisms may be employed and commercially available yogurt may be supplemented with aspartic acid . instead of adding aspartic acid or a salt thereof , a seed organism producing a large amount of aspartic acid may be employed . such an organism can be selected by quantifying aspartic acid by the method described in japanese patent unexamined publication no . 2008 - 185558 . further , aspartic acid or a salt thereof may be added to commercially available yogurt . ( composition ) content ( g ) commercially available natto 19 . 9 aspartic acid 0 . 1 20 instead of adding aspartic acid or a salt thereof , an organism producing a large amount of aspartic acid may be employed for producing natto . such an organism can be selected by quantifying aspartic acid by the method described in japanese patent unexamined publication no . 2008 - 185558 . further , aspartic acid or a salt thereof may be added to commercially available natto . ( composition ) content ( g ) commercially available 995 . 8 unrefined black vinegar aspartic acid 4 . 2 1000 instead of adding aspartic acid or a salt thereof , an organism producing a large amount of aspartic acid may be employed for producing vinegar , black vinegar or unrefined vinegar . such an organism can be selected by quantifying aspartic acid by the method described in japanese patent unexamined publication no . 2008 - 185558 . further , aspartic acid or a salt thereof may be added to commercially available unrefined black vinegar . ( composition ) content (% by weight ) stock solution of aerosol urea 65 . 0 preparation for external use dimethyl ether 35 . 0 100 . 00 stock solution of an aerosol urea external preparation and dimethyl ether are filled in a pressure resistant aerosol aluminum can of which internal surface is coated with teflon ( registered trade mark ) to prepare an aerosol preparation .
disclosed is a stable and safe antioxidant composition which can be used routinely . specifically disclosed is an antioxidant composition which contains one or more compounds selected from the group consisting of d - aspartic acid , derivatives and / or salts thereof . the composition may be used for the purpose of suppressing and / or improving skin conditions . the skin conditions may include , but is not limited to , fine wrinkles , a rough skin , a dry skin , a skin cancer , a skin allergy , an inflammation of the skin and a photosensitive dermatosis . the composition may be used for an external preparation for the skin , a food , and a pharmaceutical product for cataract .