Study On The Effect Of Sterilisation By Electrospray And Its Application In Honey Raspberry Wine

Sterilisation is one of the most important processes in the processing of liquid foods to ensure product quality and safety.Honey raspberry wine is a high-value low-alcohol drink that is compounded by honey and raspberry wine and is rich in active ingredients that are beneficial to human health.Due to the high sugar content of honey raspberry wine,long-term storage can lead to a proliferation of micro-organisms which can cause a deterioration in the quality of the product.Conventional heat treatment can result in the loss of active ingredients and special flavours in honey raspberry wine.It is therefore particularly important to choose a suitable non-thermal sterilisation technology.Electrospray refers to the use of pressure to inject a liquid into a metal needle with a high voltage power supply.When the electrostatic repulsion of the liquid droplets is greater than the surface tension,they break up into micron or even nano-sized electrically charged particles,thus forming a spray.As a new non-thermal processing technology,electrospray technology has good prospects for application in the field of enzyme inactivation and sterilisation of liquid foods.In this study,we investigated the effect and mechanism of electrospray sterilisation and its effect on the quality of honey raspberry wine using Saccharomyces cerevisiae,Escherichia coli and Staphylococcus aureus as research objects.Firstly,the effect of treatment parameters(voltage,flow rate and needle diameter)on the sterilisation of Saccharomyces cerevisiae,Escherichia coli and Staphylococcus aureus by electrospray was investigated.The results showed that voltage,flow rate and needle diameter significantly influenced the electrospray sterilisation effect.The effect of electrospray sterilisation is directly proportional to the voltage and inversely proportional to the flow rate and needle diameter.When the voltage exceeded 30 k V,the effect of electrospray was significantly increased.The effectiveness of electrospray sterilisation is related to the size of the microbial cells.The optimum parameters for electrospray sterilisation were obtained by response surface analysis using the total microbial lethality lg S in honey raspberry wine as the response value: voltage 50 k V,flow rate 0.15 m L/min and needle diameter 0.06 mm.The effect of different food components(glucose,starch,citric acid,sodium chloride and whey protein)on the sterilisation effect of electrospray was researched by analysing the main components in honey raspberry wine.The concentrations of starch and whey protein were negatively correlated with the lethality of three microorganisms,the concentrations of citric acid and sodium chloride were positively correlated with the lethality of three microorganisms,and the concentration of glucose had less effect on the effectiveness of electrospray sterilisation.Changes in the microbial mono-and mixed systems had little effect on electrospray sterilisation,while the environment in which the microorganisms were housed had a greater effect on the effect of electrospray sterilisation.Secondly,the effects of heat treatment(75°C,10 min)and electrospray at different voltages(10,30 and 50 k V)on the cell structure and function of the three microorganisms were researched.The results showed that there were significant differences in the rate of cell membrane breakage and mortality of the three microorganisms when the voltage was 10 k V or 30 k V,and the differences decreased when the voltage was increased to 50 k V.The absolute values of cell membrane potential,intracellular ATPase activity and the median particle size(D50)of the cell suspension decreased with increasing voltage of the electrospray.The absolute cell membrane potential and ATPase activity of the three microorganisms decreased after heat treatment,but the median particle size of the cell suspension increased.The electrospray and heat treatment resulted in an outflow of cell contents from the three microorganisms,causing an increase in the absorbance and conductivity of the extracellular solution.After electrospray(50 k V),the cells of Saccharomyces cerevisiae and Escherichia coli are severely damaged,with cell fracture or perforation,and the cells of Staphylococcus aureus show crumpling and perforation.Melting and aggregation of the three microbial cells occur after heat treatment.Finally,changes in the quality indicators of the honey raspberry wine during storage after the electrospray and heat treatments were researched.The results showed that the total number of colonies in the honey raspberry wine decreased from 4.50 log CFU/m L to 2.03 log CFU/m L and 1.94 log CFU/m L after electrospray and heat treatment respectively,with no significant increase during storage.There was a 22.3% decrease in anthocyanin content and a 37.2%increase in conductivity in honey raspberry wine after electrospray treatment,with no significant effects on physicochemical composition(p H,SS and TA),antioxidant composition(ellagic acid,ascorbic acid,SOD and total phenols),antioxidant capacity(DPPH and ABTS radical scavenging)and major flavour compounds(esters and ketones),which were stable during storage.All quality indicators in the honey raspberry wine decreased after heat treatment,with the ascorbic acid content gradually decreasing to non-detectable during storage,while the other indicators were relatively stable during storage.Compared to heat treatment,electrospray is more effective in sterilising honey raspberry wine while retaining its flavour,physicochemical composition and antioxidant activity.