Effects Of Non-thermal Technologies On The Quality Of Grapefruit Juice

According to the health point of view, the production of citrus fruits such as grapefruit,oranges, tangerines, lemons and limes have been increasing day by day because people aremore concerned for their health. Citrus juice is very famous due to its delicious taste and ofplenty nutrients. The production and processing of grapefruit juice is ever increasing aroundthe globe. Its processing relies mainly on conventional methods such as pasteurization andsterilization which have been associated with high thermal inputs. Thermal processingmethods, especially sterilization and pasteurization have successfully been used to improvethe shelf life of food products by reducing enzyme activity and spoilage microorganism. Butthe high temperature during these processes causes adverse changes in the quality of the endproducts. It is recognized that the thermal treatment ensure the food safety and extend theshelf life of fruit based products but they also cause losses in nutritional and physicochemicalparameters. Thermal treatment particularly, causes numerous physical and chemical changesin the product that ultimately, impair sensory characteristics and may also reduce thebioavailability of some bioactive compounds.This is the driving force for the increased interest in alternative method of foodprocessing and preservation. In this regard, ultrasound and pulsed electric fields processingtechniques has been received much attraction and attention in food industry during recentyears for the production of fruit juices. Ultrasound is a kind of versatile and innovativetechnology due to its wide range of application. Effective mixing, enhancing mass transfer,reducing energy, low temperature treatment and increasing production rate are some of themerits of ultrasound processing. Also, pulsed electric fields (PEF) and high pressureprocessing (HPP) have received considerable attention in the food industry and theapplication of PEF and HPP has gained substantial consideration in the food industry becauseof its ability to substitute the thermal treatment in the last decade. These techniques arethought to be effective and promising non-thermal methods which may overcome theproblems associated with heat treatments such as physical and chemical changes, nutritionalloss and detrimental changes in sensory attributes. Its efficiency can be even further increasedby coupling with either heat or pressure, or both heat and pressure. The main purpose of thepresent study was to determine the potential of sonication, PEF and HPP technology forgrapefruit juice processing along with its effect on various physicochemical, bioactivecompounds, inactivation of microorganism and enzymatic activities of the finished products.Firstly, fresh grapefruit juice was treated with power ultrasound (for0,30,60and90 min,28kHz frequency at20°C) in a bath type sonicator which was initiated with theobjective of evaluating the effect of sonication treatments on some important qualityparameters of grapefruit juice such as physico-chemical (pH, acidity and oBrix), Hunter colorvalues (L*, a*and b*), cloud value, total antioxidant capacity, DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical scavenging activity, ascorbic acid, total phenolics, flavonoids andflavonols.. Results showed that there was significant improvement in the cloud value, totalantioxidant capacity, DPPH free radical scavenging activity, ascorbic acid, total phenolics,flavonoids and flavonols in all the juice samples sonicated for30,60and90min but nochanges occurred in the pH, acidity and oBrix value as compared to control. Some differencesin all color values were also observed, but the overall quality of grapefruit juice was improved,suggesting that the sonication technique may successfully be implemented for the processingof grapefruit juice.Secondly, sonication of grapefruit juice was processed in an ultrasonic bath at28kHzfrequency (amplitude70%), for0,30,60and90minutes at20°C. This research was focusedon the effects of ultrasound treatment on phenolics, minerals, viscosity, lycopene, totalanthocyanins, total carotenoids, microbial analysis and sugars. Results showed that significantincrease was observed in total carotenoids, lycopene, sugar contents (sucrose, glu cose andfructose) and phenolics whereas decrease in viscosity and microbes were obtained in all thegrapefruit juice samples sonicated for30,60and90min as compared to control. But themaximum improvement was observed in the sonication treatment for90minutes. The resultsof this study suggested that ultrasound treatment might improve the stability and quality ofgrapefruit juice and may represent a good alternative to conventional pasteurization for theprocessing of grapefruit juice.Fresh grapefruit juice samples were subjected to ultrasound treatment at varioustreatment times (30,60and90min) in a bath type sonicator at a frequency of28KHz,radiating70%power (420W) and20oC. Grapefruit juice samples were stored in sterilizedpolypropylene tubes at4±1oC for a period of28days. This study was initiated with theobjective of calculating the effect of ultrasound treatment and storage time on acidity, pH,oBrix, electrical conductivity (EC), hunter color values (L*, a*and b*), non-enzymaticbrowning (NEB), cloud value (CV) and bioactive compounds of grapefruit juice. Resultsshowed that there was no change in pH, oBrix and acidity, while a significant decrease in allthe color values (L*, a*and b*) and significant increase in EC, cloud value, total antioxidantcapacity (TAC), DPPH free radical scavenging activity, total phenolics (TP), total flavonoids(TF) and total flavonols was observed in all the juice samples sonicated for30,60and90min as compared to control. During the storage period, the NEB and hunter color values (L*, a*and b*) increased while CV, DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical scavengingactivity, TAC, TP, TF and total flavonols decreased significantly in all the ultrasoundtreatments but more stability in sonication treatment (US90min) as compared to controlduring storage period of28days. The findings of this study suggested that sonication (US90min) may successfully be employed for the processing of grapefruit juice at industrial scale.Grapefruit juice was investigated by using pulsed electric fields (PEF) with differentelectric field strengths (0,5,10,15,20and25kV/cm), with a flow rate of80mL/min, pulsefrequency of1kHz at40oC for600μs. Cloud value (CV), viscosity, non-enzymatic browning,total phenolics, DPPH free radical scavenging activity, total antioxidant capacity (TAC), totalanthocyanins, total carotenoids, oBrix, pH, electrical conductivity (EC), titratable acidity,sugars and hunter color values of the grapefruit juice were studied. In addition, the effect ofPEF treatment on microorganisms (total plate counts: TPC), yeasts and molds (Y&M) wasalso observed. Results indicated that no significant change was observed in pH, oBrix, EC,titratable acidity, sugars, total anthocyanins and color attributes with the increase of pulsedelectric strength as compared to control treatment. However, a significant decrease in non-enzymatic browning and viscosity while an increase in CV, DPPH free radical scavengingactivity, TAC, total phenolics and total carotenoids, with reduction of microorganisms (TPCand Y&M) was also observed with the increase of pulsed electric strength as compared tocontrol treatment. The present study suggested that the pulsed electric field at25kV/cm couldimprove the quality of grapefruit juice and may successfully be employed for the processingof grapefruit juice at industrial scale.The combined treatment of sonication and pulsed electric fields were used on thephysiochemical properties and bioactive compounds of grapefruit juice. The grapefruit juicewas treated by pulsed electric treatment at a flow rate of80ml/min with a pulse frequency of1kHz, electric field strength of20kV/cm and temperature at40oC for600μs, followed bysonication treatment in a bath type sonicator at a frequency of28kHz and a temperature of20oC. Results indicated that no significant change was observed in pH, acidity, oBrix andelectrical conductivity. However, a significant decrease in viscosity and increase in cloudvalue, antioxidant capacity, DPPH, phenolics, flavonoids and flavonols was observed after thecombined treatment.Thermosonication (TS) is an emerging non thermal processing technique for the liquidfood preservation and is employed to improve the quality and acceptability of grapefruit juice.In the present study, fresh grapefruit juice samples were subjected to TS in an ultrasonic cleaner with different processing variables, including temperature (20,30,40,50and60°C),frequency (28kHz), power (420W) and processing time (30and60min) for the inactivationof enzymes (pectinmethylesterase, peroxidase and polyphenolase) and microfora (total platecount, yeasts and molds). In addition, bioactive compounds infuenced by thermosonicationwere also investigated. The complete inactivation of microbes and the highest inactivation ofenzymes were studied at60oC for60min and also significant increase in total carotenoidsand cloud value was observed at60oC for60min. In this study, results indicate that theadvantages of thermosonication for grapefruit juice processing at low temperature couldenhance the inactivation of enzymes and microorganisms and it can be used as a potentialtechnique to obtain better results as compared to alone.The effects of HPP and low temperature pasteurization techniques on the quality ofgrapefruit juice were investigated based on pH, acidity, oBrix, viscosity, cloud value, huntercolor values, microorganisms, polyphenoloxidose (PPO), total carotenoids, total anthocyanins,total flavonoids and total flavonols. The grapefruit juice was treated with processing variablesof HPP treatment (0,150,200and250Mpa), temperature (30,40and50oC), for processingtime of3minutes and LTP treatment was done in the autoclave at70oC for90seconds. InHPP treatment (250MPa/60C/3min), a maximum reduction was observed inmicroorganisms and PPO whereas a maximum improvement was observed in cloud value,total carotenoids, total anthocyanins, total flavonoids and total flavonols as compared tocontrol and LTP. While oBrix, pH and acidity remains unchanged in all HPP treatments ascompared to control and LTP.Generally, the findings of the present study itemized that sonication, PEF and HPPtreatments could improve the quality of grapefruit juice by enhancing the nutritional valuewith special reference to increase bioactive compounds, phytonutrients and reduce themicroorganism and enzymatic activity. It may successfully be employed for commercialgrapefruit juice processing with improved quality and safety from the consumer’s health pointof view. Furthermore, the combination of sonication and PEF, and thermosonication can act asa probable hurdle to produce safe and good quality grapefruit juice without compromising itssensory, physical and chemical characteristics.