比较纳豆和熟大豆气味成分.pdf

Agric.Biol.Chem.,49(2),311~317,1985311Comparison of Compositions of Odor Components of Natto and CookedSoybeansEtsukoSugawara,Tetsuo Ito,*SatoshiOdagiri,* Kikue Kubota** and Akio Kobayashi**Iwate PrefecturalMorioka JuniorCollege, Sumiyoshi,Morioka 020,Japan *Department of AgriculturalChemistry,Iwate University, Veda, Morioka 020, Japan **Laboratoryoj Food Chemistry,Ochanomizu University, Bunkyo-ku,Tokyo112,JapanReceivedMay 1,1984Natto,atraditionalJapanesefoodproduct,waspreparedfromcookedsoybeansby fermentationand itsodor concentratewas obtainedwith a simultaneousdistillationand extraction system.Itwas compared to thoseobtainedfrom soybeanscooked for0~3, 3~5.5 and 5.5~8hr, respectively,bygaschromatographyandgaschromatography-massspectrometry.Inthe odorconcentratesof the cooked soybeans,hexanal,(£>2-hexenaland hexanolcontributingto the green and grassyodor of soybeansdisappearedor decreasedwhile the cooking was in progress.2- Pentylfuran and l-octen-3-olcontributingto the beany odor remained even if the soybeans were cooked for 8 hr and were fermented into Natto. In the odor concentrateof Natto, pyrazinesand sulfur containingcompoundswereimportant contributorsto the characteristicodor of Natto. As thebeanyodorwasnotdetectedforNatto,itwasconcludedthatthepyrazinesand sulfur containing compoundscause the characteristicodor of Natto and maskthe beany odor.Recently soybeans have been widely utilized as a food material.However, the green grassy and beany odor of soybeans limitthe develop- ment of new food items.A number of in- vestigatorshave reported on the volatileflavor compoundsidentifiedfrom soybeans, and keycompoundsofthecharacteristicsoybean fla- vor have been confirmed.1~6) But an effective procedure to eliminatethe objectionableflavor of soybeans has not been established. Inourcountry,thereare variouskindsof traditionalfoods made from whole soybeans and soybean protein,amongwhich Natto is one of the most interestingproducts because it is made from cooked whole soybeans,and it does not have the characteristicsoybeanodor. Itisexpectedthatinvestigationoftheodor components ofNatto willresultin not only the identificationofthecharacteristicodor com- pounds but also suggest someuseful method toeliminateormasktheunfavorableodorof soybeans. ToprepareNatto,soybeanswere soaked overnightand cooked for about 8 hr, and then fermented with Bacillus natto.Therefore we firstinvestigatedthe effectsof cooking time on the soybeanodor and then comparedthe odor of cooked soybeans to thatof Natto to clarify the effect of the fermentation on the odor. In spite of the fact that Natto retainsthe orig- inal bean shape, the odor is completely different from that of raw or cooked soybeans. Kosuge etal.7)reportedthattetramethylpyrazine wasacomponentoftheNattoflavor, but thecharacteristicflavorofNattohasnot been explainedin detail.8~10)In thisstudy,we triedto identifyas many Nattoodor com- pounds as possibleand determine the changes intheirconcentrationsduringthecooking and fermentation of soybeans. * Apart of this work was presentedat the Annual Meeting of the AgriculturalChemical Society of Japan,Sendai,March30,1983.312E. Sugawara et al.MATERIALSAND METHODSMaterials.Soybeans imported from China in 1980 were used.Nattowasprocessedaccordingtothetraditional method from the soybeans.Soybeans (300g) were soaked in 1.2 litersof water at room temperaturefor 15hr, and then cooked for 8 hr with a sufficientamount of water.The cooked soybeans were inoculatedwith B. natto(0.06g, NaruseFermentationChemicalLaboratory)and then incubatedat 37°C for 15hr.This Natto was designatedas the home-made one. Commercial Natto wasalso analyzed for comparison with the former.Preparationof odor concentratesof cooked soybeans. Soybeans (300 g) were soaked in 1.2 litersof water at room temperature for 15 hr. They were then subjectedto simul- taneousdistillationandextractioninamodified Nickerson and Likens'apparatus.n)Purifieddiethylether (50ml)wasusedasthe extractingsolventand steam distillation-extractionwas continued for 8 hr. The extract- ing solventwas replacedwithnew diethylether(50ml) after3and5.5hr,respectively,andthreeodorextracts(3hrcooked,5.5hrcookedand8hrcooked)were ob-tained.This procedurewas repeatedfor a total4.5 kg of thedriedsoybeans.Thecombinedetherextractsweredriedover anhydr.sodium sulfatefollowedby distillation of the ether under atmospheric conditions.Preparationof odor concentratesof Natto. Both home- made and commercialNatto (650 g) with 850 ml of water (pH 8.2) were subjectedto the same simultaneousdistil- lation and extractionfor 3 hr. This procedure was repeated for a total9.75kg of the samples and the odor con- centrates were prepared as above.GCand GC-MSanalysis.GCanalysiswas carriedout with a Shimadzu model GC-7Agas chromatographequip- ped with a FID and FPD. The column was a 0.25mmx 35 m PEG20MglassWCOT column. The oven temperature was programmedfrom 60 to 180°C at the rate of2°C/min. The temperature of the injectionport was maintain。