Effect Of Blueberry Juice And Sterilization Mechanism Exposed To High Hydrostatic Pressure (HHP)

Blueberry,the king of berries,possesses a variety of physiological health care function.In order to gain better commercial processing of blueberry juice,we used High Hydrostatic Pressure(HHP)to process fresh blueberry juice as a non-thermal processing technology in this paper.The impact on microbial,enzyme,quality and stability of anthocyanins of blueberry juice by HHP as well as the combinational effect of HHP,ultrasonic and mild temperature on E.coli O157:H7?PPO and anthocyanins were studied.The potential advantages of HHP in the processing of blueberry juice were explored.The sterilization mechanism of HHP was investigated based on cell membrane damage,sugar metabolism and gene transcriptional expression level of E.coli.The main findings were as follows.(1)The sterilization effect of HHP was better than that of heat treatment above450MPa.The activity of PPO and POD was completely passivated through heat treatment(80?,10 min).PPO was activated by low pressure(350MPa).When the pressure was less than350MPa or greater than 450MPa,the activity of PPO and POD declined slowly.At 550MPa,the activity of PPO and POD was passivated,but the effect was not significant with enzyme residues both above 80%.The resistance to heat and pressure of POD was stronger than that of PPO.(2)HHP could preserve the nutrients of blueberry juice efficiently.The integral colour of blueberry juice and its soluble solids content did not change significantly,the nutrients in blueberry juice were well retained which can be reflected by the less loss of total phenol and Vc,the protein content and pH value of juice decreased slightly.The total antioxidant content in the blueberry juice was well reserved under HHP.The antioxidant capacity decreased by2.7%at 350MPa,while the reduction of antioxidant capacity was14.41%after heat treatment.(3)Eighteen individual anthocyanins were identified in fresh blueberry juice.The reservation rate of anthocyanin in HHP treatment was analyzed,the degeneration kinetic models(the primary level)were generated.The reservationrate of anthocyanin did not change significantly until the pressure increased to 550MPa.The damage on anthocyanin by heat treatment(at 80?)was much more substantial than that by HHP.The results were very convincing that blueberry juice was rich in anthocyanin and the treatment of HHP just casted little effect on anthocyanin degradation.(4)Blueberry juice was treated by different means(HT,TS,MT,MS,MTS).E.coli O157:H7 was deactivated rapidly by MTS after 5min(5.85-log reduction),indicating that HHP significantly enhanced the inactivation of E.coli O157:H7.MTS retained higher levels of anthocyanin retention(97.49%)than heat treatment.Meanwhile,the residual activity of PPO decreased to 10.91%.The different treatments,such as SEM and TEM,could differentiate the destruction of E.coli cells.The combination of HHP,sonication,and mild heat guaranteed the safety of blueberry juice without compromising the retention of desirable antioxidant compounds.(5)The permeability of E.coli O157:H7 was heightened by HHP.The activities of the Na⁺/K⁺-ATP enzyme,Ca²⁺/Mg²⁺-ATP enzyme,H⁺-ATP(F)enzyme and H⁺-ATP(P)enzyme on the cell membrane were downregulated generally.The change of glycolytic related index had a certain correlation with the death of lethal E.coli O157:H7.The decrease of the dehydrogenase activity of E.coli O157:H7 tricarboxylic acid cycle was consistent with the death of E.coli O157:H7 basically.Enhanced membrane permeability of E.coli O157:H7 cells and impaired tricarboxylic acid cycle may be the main causes for the death of lethal E.coli O157:H7.(6)The whole genomic sequencing found that the genome of the sample contained4730 genes.Generally speaking,more differential genes were characterized by 50 MPa than that by 150 and 250 MPa.50MPa showed more up-regulated genes,while 150 and 250 MPa revealed more down-regulated genes.Different expressions of GO enrichment function were conveyed by different pressure.Most of the substance transport related genes were up-regulated,which most of the metabolism and plasma membrane associated genes weredown-regulated.KEGG enrichment analysis revealed that differentially expressed genes were enriched in 29,35 and 28 pathways after HHP treatment,respectively.The permease on ABC transporters pathway had a positive effect on the normal physiological activities of the cells;The quorum sensing genes of the cells in the Quorum sensing pathway were destroyed but not enhanced.The purine metabolism pathway influenced the heritage substance metabolism,energy metabolism and physiological environment of bacteria.The growth and reproduction of bacteria were effected in many aspects,which may bethe main reason for the sterilizationby HHP.