Effect of Hot Water Treatment on Postharvest Shelf Life and Quality of Broccoli

Agricultural Sciences in ChinaVol.2 No.4 469 - 472April 2003Effect of Hot Water Treatment on Postharvest Shelf Lifeand Quality of BroccoliWU Ping and LI Wu( Bejing Vegetable Research Center , Bejing 100089 ,P. R. China )Abstract : Broccoli was stored at0 , 10 ,or 20°C after immersion in hot water( 38 - 529C ) for 10 or 30min. Yellowing of broccoli was significantly slowed and shelf life significantly increased when broccoli wastreated with hot water at 42- 46C and then stored at 10 or 20C. Heat injury occurred when treatmentwas higher than 46C in some varieties. Broccoli lasted 2 - 3 days longer when stored at 10C and 1- 2 dayslonger when stored at 20C after hot water treatment at 469C. There was no significant effect of treatmenton shelf life after long time storage at 0C. Weight loss was reduced by hot water treatment and the respi-ration behavior of the broccoli was also changed.Key words : Broccoli , Hot water treatment , Storage , RespirationBroccoli ( Brassica oleracea L. var. italica ) is aiment. They are broccoli cv. Lilu ,cv. Luling and cv.highly perishable fresh vegetable. After harvesting , itB-53.turns to yellow and becomes unmarketable within 1 - 3The broccoli was immersed in the hot water at thedays at room temperature ”，Storage at low tempera-selected temperature ( between 38 and 52°C ) for 10 orture can reduce the rate of senescence. Storage in a30 min and then dried by shaking gently and leaving atcontrolled atmosphere ( CA ) or modified atmosphereroom temperature for 30 min. The treated broccoli were( MA ) can also extend the storage life of broccolif 2].then stored at the desired temperature(0 ,10 ,20 ).Zong et al.l31 reported that the shelf life of broccoli1.2 Packagingwas more than 4 weeks when held at 0C using MAThe broccoli for grading and color assay waspackaging.placed into a 0. 03 mm polyethylene bag with a foldedHeat treatments can also alter senescence of broc-opening. The broccoli that used for respiration meas-coli41. Forney'51 and Kazami et al. [6,7] reported thaturements was put into a container with a known volumedipping broccoli in hot water delayed yellowing of broc-when required.coli. Kazami et al.7 reported the effect of hot treat-1.3 Color assay and shelf life monitorments on loss of soluble protein , respiration and ethyl-The color was determined using a chromameterene production. In this experiment , the optimum hot( CR-200 ). Five broccoli heads from each treatmentwater treatment to maximize storage life of broccoli culti-were assayed. The protruding position of approximatelyvars that common to China was identified. The effects of3 cm from the flower centre was selected as the assa-treatments on weight loss and decay were also investiga-ying site. Three sites were assayed for each broccolited.head.General appearance( GA ) was determined using1 Materials and Methodsa scale where 5 was the best condition and 1 was the1.1 Hot water treatmentwors中国煤化工aterial reached aGA ofThree cultivars of broccoli were used in the exper-3 ,iMHCNMHGeendofitsshelflife.WU Ping( 1962- ) , Associate Professor , MSe , Tel :86-10-51503077 ;Correspondence Ll Wu , Professor , Tel 86-10-51503066 , Fax 86-10-88446286 ,E-mail : liwu@ public. bta. net. cn470WU Ping et al1.4 Respiration assay130The storage container was sealed before assay.125The CO2 concentration was determined by near infra120red( NIR ) analysis ( RLR -2000 ) after several hours.- + Control2 Results最115+42 C兰110士44C2.1 Quality changes and general appearance- --46C105* 48CThe most significant effect of hot water treatmenton the quality of broccoli was the retardation of yello-1000wing in the treatment range of 38- 50C. If treatedDays after harvest (d)with hot water higher than 48C , heat injury occurredFig. 1 Postharvest colour changes of broccoli at 10Cand off-odours were produced , so its edibility was lost.135 [It was found that broccoli cv. B-53 could be treated125 twith hot water at 48C and no obvious injury was前115+ Controlfound. For other two varieties , the best result was ob-一42'Ctained with 469C hot water treatment.呈105Generally , the ideal hot water treatment condition95 t- 48Cwas 469C for 10 min. After storage at 10 or 20C for3several days , the quality of the hot water dipped broc-coli did not change as much as those that were not trea-Fig.2 Postharvest colour changes of broccoli at 20Cted. No obvious heat injury on the surface of the broc-+ 42Ccoli head was found. .+44C40F士46C2.2 Postharvest color change35-量Control20-on broccoli is the retardation of yellowing , even inthose broccoli heads treated with higher temperaturewater and heat injury has occurred. In the range of 420172431855- 489C，the higher the hot water temperature , theFig. 3 Postharvest respiration rate of broccoli at 0°Chigher the hue angle of the broccoli after storage at 10or209C(Figs.1and2).2002.3 Respiration rates of postharvest broccoli160+量44'CThe respiration rate of postharvest broccoli was40120|determined for a combination of different hot water*-48Cg要100-treatments and storage temperatures( Figs.3 -5 ). The30-卡Controlrespiration rate of broccoli was significantly altered by50-the hot water treatments. At 10C , the broccoli treatedat 42 ,44 , and 469C all reached the highest respirationrate on the sixth day after harvest( Fig.4 ). However ,_461214the control reached its respiration peak on the fourth day中国煤化Iarvest(d)after harvest. However , changes to the respiration rateFig..MHCNMHGteofbroccoliat10Cof broccoli stored at 0 and 20C were difficult to deter-mine.Effect of Hot Water Treatment on Postharvest Shelf Life and Quality of Broccoli471500+-42C :8「400甘44C目42C■44C士46C■46C→+- 48"C■48CDControl200士Control1000205Days after harvest (d)Storage temperature (C)Fig. 5 Postharvest respiration rate of broccoli at 20CFig.6 Effect of hot water treatment on shelf life of broccoli( ev. B-53 )2.4 Weight loss of broccoli during storageThe weight loss of broccoli treated by 42 or 46C3 Discussionhot water decreased during storage( Table ). But theFrom the results of our three experiments , hot wa-weight loss of 489C treatment was much higher thanter treatment from 38 to 48C had the most obviousthat of the control.effect on slowing the rapid post-harvest yellowing ofbroccoli. Generally , the effect was the best when trea-Table The weight loss( % ) of broccoli after 14 days stor-ted at 46C for 10 min. Hot water treatment can alsoage at 10Cdelay the yellowing of broccoli if the temperature isTreatmentTreatment time( min )temperature( C )1030lower than 469C. Hot water treatment appeared to have385.36.1a larger effect when maintained for a longer time , that424.34.6was ,in general , the 30 min treatment was more effec-464.25010. 319. 8tive than the 10 min treatment. At higher temperature ,Control5.7heat injured was observed and was detrimental to broc-coli storage.2.5 The post-harvest shelf life of broccoliCultivar B-53 was able to endure the 48C treat-As the yellowing of broccoli was delayed by hot-ment for 10 min in our experiment. The treated brocco-water treatment , the shelf life of broccoli was therefore .li had no obvious heat injury or off-odours after storageextended( Fig. 6 ). After hot water treatment , the shelfand the yellowing was delayed significantly. The higherlife of broccoli was extended by 2 - 3 days when storedtolerant treatment temperature was different among vari-at 10C and 1 - 2 days when stored at 20°C. General-ous cultivars and the optimum temperature was also de-ly , after 489C hot water treatment , broccoli ( cv. Lilupendent upon the time of harvest. The ideal treatmentand Luling ) lost its commercial value and its shelf lifttherefore has to be determined for each season andwas noted as 0. However , broccoli ev. B-53 could beeach cultivar.treated with 48C hot water , and showed longer shelfThe growth conditions of broccoli can also influ-life( Fig. 6)ence the effect of postharvest heat treatment. In one ofThe visual quality , smell , and flavor of treatedour experiments , many fungi infected the treated broc-broccoli did not show the deterioration as hot injuredcoli中国煤化工ship between the extentbroccoli did after storage at 10 or 20C. There was no .of irMHCNMHGofthehotwatertreat-.obvious effect on the storage life by hot water treatmentment. However , the control was not infected greatly.when the broccoli was stored at 09C for 6 weeks.Hot water treatment in this circumstance was not bene-ficial.Three storage temperatures were selected in our472WU Ping et alexperiments( 0 , 10 , or 20C ). The results showedthe selling quality of broccoli can not be ensured. Duethat , hot water treatment could efficiently delay theto the limited mass production of broccoli by individualyellowing and elongate the shelf-life of broccoli whenfarmers , especially in spring , the farmers can not af-stored at 10 and 20C. When the broccoli was stored atford to purchase large amounts of pre-cooling0C , heat treatment had no obvious effect. After 6equipment and refrigerated transport. The problem ofweeks of storage , the untreated broccoli started tlower selling quality of broccoli will be solved to someyellow , lose moisture from the surface and show someextent if the shelf life is increased by 1 - 3 days by heatsigns of fungal infection. The treated broccoli also star-treatment.ted to lose moisture from the surface and become infec-ted by fungi. Thus , we conclude that heat treatmentAcknowledgmentsprior to storage at 0C will not be beneficial. BroccoliThis work was supported by ACIAR project 9416.can be stored well by packaging and other methods atWe are deeply grateful for this funding and we thank09C.Dr. Timothy J. O'Hare , Mr. Lung Wong and Mr.Heat treatment changed the respiration behavior ofZheng Shufang for their help and advice.postharvest broccoli so that the respiration peak of trea-ted broccoli was delayed. However , due to diffcultiesReferenceswith our method for measuring respiration rates , we can[ 1 ] WangC Y , Hruschka H W. Quality maintenance in polyethylene-packaged broccoli. Marketing Report of U. S. Agricultural Depart-not determine the exact respiration rate of the heat-trea-ment , 1977 :1085.ted broccoli. In the experiments ,3 - 4 broccoli heads[ 2 ] Barth M M ,Kerbel E L , Broussard s , Schmidt S J. Modified at-were placed in one container to assay. Difference be-mosphere packaging protects market quality in broccoli spears un-tween the individual broccoli heads in respiration andder ambient temperature storage. Journal of Food Science , 1993different fungal infections on each head will influence58(5 ):1 070-1 072.not only the exactness of the respiration rate but also[ 3 ] Zong R J ,Huang B Y ,Li W. Studies on storage technique ofbroccoli. Chinese Vegetables ,1985 ,( 1 ) ;48 -51.( in Chinese )the postharvest physiological state of other broccoli in[ 4 ] Paull R E. Postharvest heat treatments and fruit ripening. Post-same container. Hence , the experimental error will in-hanest Neus and Information , 1990 ,1(5 )355 - 363.crease , which should be corrected in further experi-[ 5 ] Forney C F. Hot-water dips extend the shelf life of fresh broccoli.ments.HortScience ,1995 ,30(5):1 054-1 057.Based on the theory and results of our experi-[ 6] Kazami D , Sato T ,Nakagawa H , Ogura N. Efect of pre-storagehot water dipping of broccoli heads on shelf life and quality duringments , this treatment has certain possibilities for appli-storage. Nippon Nogeikagaku Kaishi ,1991 ,65( 1 ):19 -26.( incation in China. In present , from harvesting to marketJapanese )of broccoli , there are at least 1- 2 days. In developed[ 7 ] Kazami D ,Salo T , Nakagawa H , Ogura N. Efct of pre-storagecountries there is a complete cold chain system to en-hot water dipping of broccoli heads on soluble protein , free aminosure the quality of postharvest broccoli. However ,acid contents and protease activities during storage. Nippon No-geikagaku Kaishi ,1991 ,65( 1 ):27 - 33.( in Japanese )methods widely used in deve-loped countries such aspre-cooling have not been applied broadly in China ,so中国煤化工MHCNMHG.