Screening Of The Lactic Acid Bacteria Against Alternaria And Its Effects On Quality And Physiology Of Korla Fragrant Pear

Korla fragrant pear is one of the most famous characteristic fruit and plays an important role in Xinjiang.However,a variety of diseases occur during storage and transportation.The black spot disease caused by Alternaria is one of the main diseases.Lactic acid bacteria(LAB)are recognized as safe probiotics all over the world.There are broad development prospects to apply LAB in fragrant pear for biological control of black spot disease caused by Alternaria.The anti-Alternaria LAB were from dairy products and applied for the storage of fragrant pear.The effects of anti-Alternaria LAB fermentation broth on the storage quality and physiology changes of the fragrant pear were explored.It was of great significance for the application of LAB to control the black spot disease of fragrant pear.The main contents are as follows:(1)The anti-Alternaria LAB were screened from 110 LAB strains isolated from Xinjiang dairy products using the dural culture method and the activity of anti-Alternaria were analyzed by three fermentation patterns: solid state fermentation,static fermentation and shaking fermentation.The results showed that four strains of LAB with inhibitory activity on Alternaria were screened out and three of them were Lactobacillus pentosus,the other one named Lactobacillus paracasei.At the same time,the highest inhibitory activity on Alternaria was from shaker fermentation broth.The maximum inhibition zone diameter is 21.17 mm and it had a bright prospect of application to control black spot disease caused by Alternaria.(2)LAB 86(L.pentosus ZWQ86)was used as the object and it had significant inhibition on the A.gaisen which isolated from the local fragrant pear infected by black spot disease.The biological characteristics of active substances in the fermentation broth of LAB 86 were preliminarily explored.The results showed that after heated for 10 min at 100?,there was no significant difference between the treatment and the control group(P>0.05),which indicated a good heat tolerance.The anti-Alternaria activity of the fermentation broth can be well maintained when the p H was below 4.0.However,the anti-Alternaria activity was significantly decreased when p H was above 5.0 and the broth was treated with pepsin and trypsin(P<0.05).These demonstrated the active substance in the L.pentosus ZWQ86 fermentation broth may be an alkaline-sensitive compound containing certain amino acid residues.(3)Taking Korla fragrant pear as the object,the effects on the storage quality of fragrant pear treated with L.pentosus ZWQ86 fermentation broth.The results showed that contrasted with the control group,the weight loss rate of the treatment group was significantly reduced(P<0.05)and the decrease of fruit firmness and vitamin C was effectively delayed.Meanwhile,the accumulation of malondialdehyde in the fruit was decreased to a certain extent.The treatment with L.pentosus ZWQ86 fermentation broth had the function of maintaining the quality of fragrant pear.(4)The combination of injury inoculation and fermentation broth treatment was used to detect the changes of defense enzyme activity in the process of storage of fragrant pear.The results showed that the treatment of fermentation broth can effectively inhibit the growth of Alternaria on the surface of pear and reduce the decay rate of pear fruit.However,there was no significant enhancement on the activity of POD,PPO,PAL and the content of total phenol and flavonoid in the treatment groups.The active substance in the fermentation broth cannot play the role of plant inducer.(5)The combination of injury inoculation and fermentation broth treatment was used to detect the changes of reactive oxygen metabolism in the process of storage of fragrant pear.The results showed that the fermentation broth of L.pentosus ZWQ86 did not show a significant increase in CAT activity while the CA can significantly reduce the superoxide anion production rate and hydrogen peroxide content and play a role in prolonging the storage time of fragrant pears.