| Onions belong to the genus Allium,which contain large numbers of bioactive substances.The thiol compounds in the onions have antibacterial and antibacterial effects.The study of thiol compounds is also a hot topic in current research.In this study,onion peels of the red and white onions were used as raw materials,and the best process method for the natural fermentation of onion peels to produce thiol compounds was investigated by orthogonal test.The bacteriostatic active substances in the onions were extracted by this process method,and antibacterial test of fungi(Fusarium sulphureum and Alternaria alternate)and bacteria(Alternaria alternate)were conducted by the extracts.The potential antibacterial properties of the extracts against phytopathogenic bacteria in plants and pathogenic bacteria in food were studied.Through plant infestation tests,the changes of some stress-resistant substances(enzymes)in plants were studied when potato tubes and apple tissues were infected by Fusarium sulphureum and Alternaria alternately.The results showed that:1.The effects of material liquid ratio,salt-material ratio,fermentation time and fermentation temperature on the extraction of thiol compounds from onions were studied.The best process parameters of thiol compounds in the extract of fermented red onion peels were1:30(g : m L)of material liquid ratio,1:15 of salt-material ratio,fermentation time for 7 d,fermentation temperature at 40 ?.Under this condition,the extraction rate of the red onion peels thiol compound was 0.45%.The best process parameters of thiol compounds in the extract of fermented white onions were 1:40(g : m L)of material liquid ratio,1:15 of salt-material ratio,fermentation time for 9 d,fermentation temperature at 40 ?.Under this condition,the extraction rate of the red onion peels thiol compound was 0.46%.2.The antibacterial activities of the extracts extracted by naturally fermented onion peels with thiol-containing compound for red onions at 0,0.18,0.36,0.54,0.72,1.08,1.44,1.80g/L,and for white onions at 0,0.18,0.36,0.54,0.72,1.08,1.44,1.80 g/L were investigated,respectively.Within the experimental range,RECCs and WECCs could effectively inhibit the growth of F.sulphureum,A.alternata and S.aureus.The results showed that the antibacterial effect of RECCs on F.sulphureum was stronger than that of WECCs,while the antibacterial effects of WECCs on A.alternate and S.aureus were stronger than that of RECCs.When the concentration of RECCs were 2.70,5.52 g/L,the germination of spores of F.sulphureum and A.alternate could be completely inhibited.When the concentration of WECCs were 2.76,3.70 g/L,the germination of spores of F.sulphureum and A.alternatecould be completely inhibited.However,the inhibitory effect on bacteria was relatively weaker.When the concentration of RECCs reached up to 9.00 g/L and the concentration of WECCs reached up to 4.60 g/L,the growth of S.aureus could be completely inhibited.3.In the tuber infection test of potato:(1)RECCs and WECCs could prevent the accumulation of malondialdehyde content.When the treatment time was 4 d,the content of MDA was the most affected.At this time,the MDA activities of potato tubers treated by RECCs and WECCs were 24.77% and 25.45%,lower than those of the control group,respectively.(2)The activity of GEL and ?-GLU were decreased.When the treatment time was 6 d,the GEL and ?-GLU activities had reached up to the maximum value within the entire treatment range.At this time,the activity of GEL in potato tuber of blank control group was 5.70 ± 0.10 mg/h.g;the GEL activities of potato tuber treated with RECCs and WECCs were 4.31 ± 0.10 mg/h.g and 3.15 ± 0.14 mg/h.g,respectively,which were 44.74% and24.39% lower than those of blank control group.(3)The biological activities of PAL and POD enzymes in potato plants could be significantly increased after treatment with RECCs and WECCs.When the treatment time was 2 d,the PAL activity of potato tuber treated with blank control group,WECCs and RECCs were 80.33 ± 5.51,91.67 ± 1.53 and 120.00 ± 5.00(0.01?OD290/h.g.m),respectively.At this moment,the activity of PAL of potato tuber was reached the highest.When the treatment time was 6 d,the activity of POD had reached up to the maximum value.The POD activities of potato tuber treated with blank control group,WECCs and RECCs were 117.67 ± 10.41,194.33 ± 7.37,289.33 ± 11.02(?OD470/min.g),respectively.The results indicated that RECCs and WECCs increased the disease resistance ability of potatoes and the effects on the ability of potato disease resistance were RECCs >WECCs.4.In the tissue infection test of apple,when the treatment time was 6 d,the PPO was the maximum value;the contents of PPO in the tissues of apples treated by WECCs and RECCs were 57.96 ± 2.24 and 46.28±0.90(?OD420/min.g),respectively.When the treatment time was 4 d,the POD reached the maximum value,and the contents of POD in the tissues of apples treated by WECCs and RECCs were 12.42 ± 0.56 and 8.61 ± 0.71(?OD470/min.g),respectively.When the treatment time was 4 d,the PAL was the maximum value of the whole treatment time.The contents of PAL treated by WECCs and RECCs were 54.92% and 23.00%higher than the blank control group,respectively.In the infection tissues of apples treated by RECCs and WECCs,the activities of intracellular defense enzymes such as PPO,POD and PAL would be increased,otherwise,the activity of MDA enzyme and the accumulation of its content would be decreased.infection by pathogens,the effects on disease resistance of apple tissues: WECCs > RECCs.In summary,by optimizing the fermentation process of the thiol compound in the onion peels,the extract of onion peels has a good antibacterial effect in the bacteriostatic test,which could increase the content of MDA in the plant and the activity of defense enzyme,decrease the activities of cellulase and glucosidase.RECCs and WECCs could be used as inhibitors of plant diseases to reduce plant diseases.However,it should be further studied before it become a new type of biological pesticide. |
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