| Plants in the genus of Allium(Liliaceae)are frequently important sources of perfumes,vegetables and medicines.At present,some manuscripts have been published that Allium tuberosum,Allium.fistulosum and Allium sativum possess antibacterial activity.Allium prattii is a characteristic medicinal and food homologous plant resource in Qinba Mountains Area.It can be used as medicine,wild vegetable or spice.However,there are no reports on chemical composition analysis,antibacterial activity and mechanism of Allium prattii.In view of this,this study analyzed and compared the chemical composition of water extract of Allium prattii(AP-A),water extract of Allium tuberosum(AT-A),ethanol extract of Allium prattii(AP-E)and ethanol extract of Allium tuberosum(AT-E),screened their antibacterial activity,discussed the antibacterial mechanism of the extract of Allium prattii against Staphylococcus aureus,and studied the effect of water extract of Allium prattii on crispy biscuits.The effects of AP-A on the flavor and shelf life of crispy biscuits were also studied.In order to provide a reference for the scientific development and comprehensive utilization of the resources of Allium prattii.The specific results are as follows:1.Chemical composition analysis.The contents of total flavonoids and total polyphenols in four extracts were determined.It was found that the contents of total flavonoids and total polyphenols in the ethanol extract of Allium prattii were the highest,reaching 88.16mg/g and 78.86mg/g,respectively.The ethanol extract of Allium tuberosum was the second,82.25mg/g and 73.28mg/g,respectively.The total flavonoids and total polyphenols in the water extract of Allium prattii were 73.48mg/g and 68.39mg/g,respectively;and the water extract of Allium tuberosum was the lowest,71.56mg/g and 67.99mg/g,respectively.Fourteen chemical constituents in four extracts were detected by high performance liquid chromatography(HPLC),including allicin and alliin,uracil,guanine,uridine,adenine,thymine,beta-thymidine,adenosine and 2'-deoxyadenosine,rutin,kaempferol,quercetin and isorhamnetin.Flavonoids were the highest in the four extracts,followed by sulfur compounds and nitrogen compounds.2.Screening of antibacterial activity.The antibacterial activities of four extracts against Escherichia coli,Staphylococcus aureus,Saccharomyces cerevisiae and Aspergillus niger were determined by double dilution method and Oxford cup method.The results showed that the minimum inhibitory concentration of AP-A,AT-A,AP-E and AT-E to Escherichia coli was 11,12,21 and 24mg/mL,the minimum inhibitory concentration to Staphylococcus aureus was 9,11,15 and 20 mg/mL,the minimum inhibitory concentration to Saccharomyces cerevisiae was 25,50,50 and 50mg/mL,and the minimum inhibitory concentration to Aspergillus niger was 50,50,100 and 150mg/mL,respectively.Inhibition zone experiment showed that the four extracts had certain inhibitory effects on Escherichia coli and Staphylococcus aureus,,and with the increase of extract concentration,the inhibition zone diameter also showed an increasing trend.The antibacterial effect of four extracts on Staphylococcus aureus was better than that of Escherichia coli.The antibacterial effect of water extract of Allium prattii on Staphylococcus aureus was better than that of water extract of Allium tuberosum;the antibacterial effect of alcohol extract of Allium prattii on Staphylococcus aureus was better than that of alcohol extract of Allium tuberosum.3.The exploration of antibacterial mechanism.By analyzing the effects of AP-A and AP-E on growth curve,extracellular metal ions,extracellular macromolecule content(protein,nucleic acid,polysaccharide),conductivity of culture medium,cell wall integrity,cell membrane permeability and ultrastructure of Staphylococcus aureus,the antibacterial mechanism was explored.The results showed that the extracellular K+,Ca2+,Na+,Mg2+ ions of Staphylococcus aureus were significantly increased,the contents of extracellular proteins,nucleic acids,polysaccharides and other macromolecules were significantly increased,and the conductivity of the culture medium was also significantly changed.Scanning electron microscopy showed that cell morphology changed,cell integrity was severely damaged,and bacteria adhered to each other and agglomerated.The results showed that the antibacterial mechanism of the extract of Allium prattii was mainly due to the destruction of the integrity of bacterial cell membrane and cell wall,resulting in changes in cell permeability,electrolyte dissolution,increased conductivity of bacterial fluid,overflow of macromolecule substances in cells,impairment of normal metabolism of cells,and ultimately leading to bacterial lysis and death.4.Development of crispy biscuits and determination of their shelf life.Taking sensory score as evaluation index,the formula of biscuit was optimized by single factor and orthogonal test.The optimum formula was 100g of low gluten wheat flour,55g of butter,30g of sugar,10g of water extract powder of Allium prattii,0.5g of salt,2g of baking powder and 35g of water.The quality of the biscuits was determined.The contents of moisture,fat,protein and ash were 2.80g/100g,14.36g/100g,8.12g/100g and 1.24g/100g,respectively.The bulk density was 0.5912g/cm3;the acid value was 0.75mg/g;the peroxide value was 0.017g/100g;the hardness was 11584.514g;the brittleness was 5435.055g;the cohesiveness was 0.044;the chewiness was 87.77;the elasticity was 0.177.The results show that the optimized biscuits are crisp in texture and good in taste.At the same time,the shelf life of biscuits was tested by ALST method.It was found that the addition of Allium prattii powder could prolong the shelf life of biscuits while giving the flavor of crisp biscuits. |
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