Effect Of Germination On Isoflavone,γ-aminobutyric Acid Contents Of Soybean Cultivars

Soybeans(Glycine max(L.) Merill) are one of the most important leguminous food crops in theworld, particularly in Asia.Soybeans are used in various food forms, including tofu, soybean sprouts,soymilk, soya paste and oil. Soy-based foods have increasingly gained more attention in recent yearsdue to the potential beneficial effects on human health. Soybean contains many nutrients that includedproteins, amino acids, unsaturated fatty acids, vitamins and minerals. In addition, it contains somefunctional active ingredients that can prevent osteoporosis and menopausal, improve skin elasticitycondition, lower cholesterol level, promote fat metabolism, antioxidant anti-cancer. Germination, as asafe and efficient food processing way, can adjust the composition and contents of nutrients in soybeans,but also can enriched lots of active substances that has multiple physiological and are benefit for humanbody, which included soybean isoflavones, γ- aminobutyric acid(GABA), et al.There are many researches about soybean germination, they indicated that soybean isoflavones is avaluable resources and how to take advantage of China’s soybean variety of resources is the challengewe face. Only by fully understanding the difference between different soybean varieties, we can makefull use of it and do it on the rational application. A very broad genetic diversity exists among soybeancultivars grown in China. Among them, three Zhonghuang series cultivars, ZH 13, ZH 30 and ZH 42,have been approved and recommended by the Chinese government authorities for their outstandingcharacteristics such as high yield, high protein content and wide environmental adaptability. Therefore,this study selected 3 soybeans included ZH 13, ZH 30 and ZH 42 as this experimental materials toresearch the influence of germination on polyphenols, isoflavones, GABA and antioxidant activity toexplore the correlation between high levels of enrichment and screening function of the activeingredient, finally to select the optimum soybean varieties with a high antioxidant activity. This study isorganized as follows:1. The results showed that the total isoflavone contents at peak level were 86.3, 81.0, and 42.3%higher than that of the un-germinated control for ZH 42, 13 and 30, respectively. GABA content of ZH13 in particular was a statistically significant 36.7-fold increase in day 5 germinated soybeans ascompared to un-germinated soybean. Such increases also led to significantly elevated antioxidantactivities. Moreover, germination can significantly suppress IL-8 expression in Caco-2 cells by ZH 13extract(P < 0.05) without cell apoptosis.2. The results showed that germination brought a remarkable increase in total phenolic content(TPC) values(P<0.05), Such increase in TPC values as a linear relationship to the gemination time,while regardless of the cultivar type. The maximum of TPC value was observed at the 7th day, and theZH 13 soybean demonstrated the highest TPC yield(0.47 GAE/ g d. m) among these TPC values.Comparing non-germinated soybean and after 7 days germinated for ZH 30, ZH 42, and ZH 13 soybean,the increase of 370%, 177.8%, and 485.7% in the TPC values were observed. The total isoflavonecontents in general increased to a significantly higher level and then decreased during germination in allthree cultivars. While the highest total isoflavone content in the ZH 13 seeds(3 796g/g d. m.) wasobservedonday3,thatinzh30peakedatday2(1823g/gd.m.).zh42soybeanwasthefastestinreachingthepeaktotalconcentrationat2832g/gd.m.onday7.thetotalisoflavonesdecreasedgraduallyafterpeakingandreachedthelowestlevelat3262(day7),1348(day5),2060(day5)g/gd.m.forzh13,30,and42,respectively.amongthedifferentisoflavoneforms,malonylglucosideswerethemostpredominantgrouprepresenting53.4%ofthetotalisoflavoneonaverage.boththetotalmalonylglucosidesandthetotalβ-glucosides(sumofdaidzin,glycitinandgenistin)reachedthepeaklevelonday3,2and1forzh13,30and42,respectively,anddecreasedtowardstheendoftheexperiment.inaddition,similartotheisoflavonecontents,gabacontentalsoincreasedsharplyini-tially,andstartedtodecreaseafteritreachedthemaximumvalueondifferentdaysdependingonthecultivar.themaximumgabacontentingerminatedzh13seedswas3.28mg/gd.m.onday5;however,thatforzh30was1.53mg/gd.m.onday6andzh42(1.02mg/gd.m.)onday4.remarkably,thepeakgabacontentofzh13wasa36.7-foldincreasewhencomparedtothatoftheun-germinatedsoybean(day0).amongthethreetestedcultivars,germinatedzh13seedsproduced2-3timeshighergabathantheothertwocultivars,suggestingthiscultivarcanbeagoodcandidateforsupplementinggaba,anon-proteinogenicaminoacidwithmanyhealthbenefits.3.thisstudyshowedthatgerminationcanincreasetheantioxidantactivityofzhsoybean,althoughthefrapvaluesdidnotincreaselinearlyingerminationperiods.theantioxidantactivityvaluesinnon-germinatedsoybeanwere7.36,8.19,2.83μmolfe2+/gd.m.,respectively.withtheextensionofgerminationtime,totalantioxidantactivityofzhincreasedprominently(p<0.01).theantioxidantactivityincreasedrapidlyatthe6 th,7thdayofgerminationandthefrapvaluesreachedtothemaximum(19.71,17.52,13.89μmolfe2+/gd.m.)in7-day-germinatedsoybean.althoughtheincreasingspeedofantioxidantactivityinzh42soybeanwashigherthanthatinzh13 soybean,thevaluewaslowerinzh42soybean.attemptswereconductedtocorrelatethetpcandtheantioxidantactivitiesusingthepearson’scorrelationcoefficients(r).ingeneral,soybeanseedswithhighertpcalsohadhigherantioxidantactivity.forexample,tpcofzh13correlatedwellwiththefrapanddpphassay(r=0.9598and0.9086,respectively),suggestingthetpcmayhavecontributedtotheantioxidantactivities.thetotalantioxidantactivitiesdidnotcorrelatewellwiththetotalorindividualisoflavonesduringgermination(r=0.1209–0.6812).itshowedthatgerminationsignificantlyincreasedil-8inhibitionbyzh13extract(p<0.05)inaconcentration-dependentmanner..therewasnosignificantdifferenceincellviabilitybetweenposandzh13 extractiontreatedgroups,whichmeansthegerminatedzh13extracthadnodetectablecytotoxicity.thissuggeststhatotherphenoliccompoundswithstrongerantioxidantactivitymayhavebeenproducedduringgermination.4.thisstudyindicatedthatgerminationcanincreasethevaluesoffunctionallyactiveingredientandimprovetheantioxidantactivity.mostimportantly,thezh13 soybeanhasagreatpotentialtobedevelopedintonutritionalandfunctionalfoodswithhighcontentsofisoflavones,gabaandantioxidantactivity.thisstudyalsodisseminatesanimportantinformationforfurtherstudiesontheutilizationofgerminatedsoybeanasafunctionalfoodsource.