Investigating The Potential Of Power Ultrasound In Pear Juice Processing

Pear(Pyrus bretschneideri R.)is the third most widely produced temperate fruit after grape and apple.China is the major shareholder contributing over 70%of the global pear production.Pear has a long history of over 2000 years as part of the traditional folk medicine for anti-inflammatory,anti-hyperglycemic and diuretic treatments in china.Less sodium,high potassium and low acidic in nature than apple makes pear a popular component in high acidic food products and baby food formulations.Thermal treatments are commonly applied for microbial and enzymatic control in food processing.However,these heat treatments also have damaging effects including nutrient losses,development of undesirable flavors and structural deteriorations in structural and functional properties.The need to preserve these bioactive compounds and meet the growing demands of consumer market with a safe and healthy food product has pushed the research community to develop processing techniques which can lessen heat losses.Ultrasound is one of those non thermal technologies gaining interest as an alternative to thermal processing.Ease of application,environment friendliness,low cost and efficiency are some of the main benefits.It has a wide range of applications in food industry especially liquid food systems including mixing,degassing,low temperature sterilization and homogenizations etc.Therefore the present study was designed to investigate the potential of ultrasound in pear juice processing.Quality parameters,bioactive compounds,enzymes,microbes,minerals,sugars and physicochemical properties were studied.The ultrasound processing conditions were also compared with conventional pasteurization effects and also against ultrasound pulse electric field combined treatments.Prolonged effects of treatments during shelf life were also studied.A preliminary study was carried out before every experiment to establish the processing limits for a stable product.At first,influence of sonication on physicochemical parameters(total soluble solids,pH.titratable acidity,cloud value),ascorbic acid,total phenols,flavonoids,antioxidant capacity,sugar contents(sucrose,glucose and fructose),minerals(Na,Fe,K,Mg,P,Ca,Mn,Zn and Cu).poly phenolic compounds(cholrogenic acid,caffeic acid,caechin,apicatechin and phlodridzin)and microorganisms(total plate count,yeasts and molds)of pear juice was studied.Ultrasound processing of fresh pear juice was carried out at amplitude of 70%(500 W)with a constant frequency of 25 kHz for 0,15,30,45 and 60 min at 25 ?.The results showed non-significant effect of ultrasound on total soluble solids,pH,and titratable acidity.Significant increase in cloud value,ascorbic acid,total phenols,total flavonoids,total antioxidant capacity,sugar contents,phenolic compounds and mineral elements(Na,K,Fe and Mg)whereas,decrease in microbial population and some mineral elements(P and Cu)were observed.Ca and Mn remained stable in all the ultrasonic treatments.Ultrasound processing for 60 min exhibited better results than rest of the treatments.It may be inferred that ultrasound processing may successfully be employed at industrial scale for producing safe and quality pear juice.Secondly microbial and enzymatic inactivation in fresh pear juice were studied under conventional and ultrasound pasteurizations.The ultrasound pasteurization conditions were 25,45 and 65? for 10 min using a 750 W probe sonicator(frequency 20 kHz and amplitude 70%)while conventional pasteurization conditions were 65 ? for 10 min and 95 ? for 2 min.Complete inactivation of enzymes(peroxidase,pectinmethylesterase and polyphenol oxidase)and microbes(total plate count,yeast and mould)were observed in conventional pasteurization at 95 ? but this treatment also showed highest losses in terms of ascorbic acid,total phenols,flavonoids and antioxidant capacity.Ultrasound pasteurization at 65 ? showed best results in terms of retention of ascorbic acid and other phenolic compounds with significant reduction in enzyme activities and complete inactivation of microbes.pH,acidity and soluble solids showed no significant change under conventional or ultrasound pasteurization treatments.Findings of the study indicate that pasteurization at low temperatures in combination with ultrasounds can successfully be employed for commercial processing of improved quality pear juice.Thermosonication has been found effective in low temperature food preservations,however its prolonged effects during shelf life of food systems is yet to be studied thoroughly.Microbial and nutritional aspects of pear juice subjected to conventional and ultrasound pasteurization and stored at 4 ? were studied.The conventional pasteurization was 95 ? for 5 min while US-pasteurizations(frequency 30 kHz,amplitude 70%)were 25.45 and 65 ? for 10 min,under a probe sonicator(750 W).US25 and US45 had shelf lives of 9,12 and 15 days,respectively.Ascorbic acid,total phenols,total antioxidant capacity and cloud value decreased in all treatments while pH,acidity and sugars remained stable.Both treatments(P95 and US65)remained viable after 21 days of storage however loss of bioactive compounds in P95 was significantly higher than US65 making US-pasteurization a promising pear juice processing technology at low temperature;retaining bioactive compounds,meeting safety standards and increasing shelf life.Combining non thermal technologies for preservation purposes is an emerging trend especially in liquid food processing.Fresh pear juice was evaluated for microbial and enzymatic inactivation under ultrasound(US)(750W,25kHz,70%,45?,10 min),pulse electric field(PEF)(30 kV/cm for 600 ?s at 80 mL/min flow rate)and in combination and compared with commercial pasteurization(P95)(95 ?,5 min).Enzymes(polyphenol oxidase,pectinmethyle esterase and peroxidase)and microbes(total plate counts,yeast and moulds)were found completely inactivated in P95 while it also exhibited highest losses intotal phenols,ascorbic acid and antioxidant capacity.US showed significantly better control over enzyme and microbes inactivation than PEF.The combined treatment.showed PPO,POD,PME and microbes 95.76%,93.37%,94.42%and completely inactivated comparing to control while retaining highest amount of ascorbic acid,total phenols and antioxidant capacity than rest of the treatments.pH,TSS,acidity remained significantly unchanged in all treatments.The results indicate a synergistic effect for achieving an improved quality pear juice.In general,findings of the present study indicate that ultrasound treatments could improve the quality of pear juice by improving its phyto-nutrients content.However combining ultrasound with mild heat treatment or PEF resulted in achieving the microbial and enzymatic control standards while avoiding heat losses which occur during conventional thermal processing.It proves to be a potential alternative for safe and nutritious pear juice processing at commercial level.