Interntionl Journl of Food Microbiology 0 (000) 1 www.elsevier.nl/ locte/ ijfoodmicro Microbil species ssocited with different sections of broccoli hrvested from three regions in Austrli b b, * Msdin Pdg, Gillin M. Herd, Jne E. Pton, Grhm H. Fleet CRC for Food Industry Innovtion, The University of New South Wles, Sydney, New South Wles 0, Austrli b Deprtment of Food Science nd Technology, The University of New South Wles, Sydney, New South Wles 0, Austrli Received October 1999; received in revised form 7 Mrch 000; ccepted April 000 Abstrct The microbil popultions ssocited with the different sections of broccoli hrvested from three loctions in Austrli were studied during storge t, 1 nd 08C. Bcteril nd yest popultions ssocited with the outer florets nd cut surfces of the stem were generlly 10-fold or more higher thn those ssocited with inner florets or non-cut stems, respectively. The predominting bcteril species vried with the origin of the broccoli. Pseudomons fluorescens, Ps. 7 corrugt nd Ps. viridiflv predominted t popultions of 10 10 cfu/ g on broccoli hrvested from Victori, Ps. fluorescens, Ps. mendocin nd Ps. frgii nd Arthrobcter spp. (10 10 cfu/ g) were prevlent on broccoli hrvested from Queenslnd. Broccoli hrvested from New South Wles exhibited predominnce of Ps. fluorescens, Arthrobcter spp. nd Enterobcter gglomerns (10 10 cfu/ g). Most species grew on broccoli during storge. Similr species were found t the different sections of broccoli, lthough, for some species there ws evidence of strin vrition t the different loctions nd for different temperture of storge. 000 Elsevier Science B.V. All rights reserved. Keywords: Broccoli; Microbil ecology; Qulity 1. Introduction 1990; Forney et l., 199). Although the onset of some of these disorders is nturl, physiologicl Broccoli (Brssic olerce L. Itlic group) is response of the plnt tissue, microorgnisms cn perishble vegetble. Posthrvest storge disorders mke significnt contribution to their development include yellowing nd opening of florets, loss of nd decrese in product shelf life (Lund, 1971, 199; stem firmness, development of undesirble odours Nguyen-the nd Crlin, 199; Brckett, 1997; Herd, nd soft rots (Lebermnn et l., 198,b; Lipton nd 1999). The most obvious nd frequently reported Hrris, 197; Shewfelt et l., 198; Berrng et l., consequence of microbil spoilge is soft rot of the broccoli florets (Ceponis et l., 1987; Lio nd *Corresponding uthor. Tel.: 1 1--8-; fx: 1 1-- Wells, 1987; Brckett, 1989). However, there could 8-91. be the other less obvious but, nevertheless, importnt E-mil ddress: g.fleet@unsw.edu.u (G.H. Fleet). influences of microorgnisms, since fresh, sound 018-10/ 00/ $ see front mtter 000 Elsevier Science B.V. All rights reserved. PII: S018-10(00)009-9
1 M. Pdg et l. / Interntionl Journl of Food Microbiology 0 (000) 1 broccoli my hrbour microbil popultions s high floret nd stem smples (Brckett, 1989). Moreover, s 10 cfu/ g t the time of hrvest (Brckett, 1989; these studies hve minly reported the occurrence of Mohd-Som et l., 199). Forney et l. (199) microbil groups such s the totl erobic flor, reported the presence of methnethiol off-odours in coliforms nd enterobctericee on the product, nd helthy looking pckged broccoli nd linked the provided little quntittive detil bout popultions occurrence of this voltile to the presence of of individul species present. However, it is known methnethiol producing bcteri. The yellowing of tht Pseudomons species my predominte on florets is the most evident sign of broccoli deterior- broccoli towrds the end of its shelf life nd cuse tion nd is plnt medited rection resulting from soft rot (Lio nd Wells, 1987; Brckett, 1989). the degrdtion of chlorophyll (Ceponis et l., 1987). We re interested in gining more precise in- The plnt hormone, ethylene, stimultes this rection formtion bout the species of microorgnisms tht (Arshd nd Frnkenberger, 199). However, mny colonise broccoli nd how they impct on broccoli bcteri re cpble of producing ethylene (Primrose, qulity. As the first stge of this objective, this pper 1979; Fukud et l., 199; Nghm et l., 199) reports the predominnt microbil species ssocited including plnt ssocited species (Goto et l., 198; with different sections of broccoli hrvested from Weingrt nd Volksch, 1997), but their role in three loctions in Austrli, nd describes how these contributing to the yellowing of florets hs not been species chnge during storge of the broccoli t, 1 exmined. Off-flvour development due to ftty cid nd 08C. oxidtion is nother rection contributing to the loss of broccoli qulity (Zhung et l., 199) nd lipoxygense producing microorgnisms could possibly. Mterils nd methods contribute to this problem. New posthrvest processing technologies such s.1. Broccoli smples hot-wter dipping, cooling nd misting, nd controlled or modified tmosphere storge (Brth et l., Three independent experiments were conducted by 199; Zhung et l., 199; Forney, 199; Gillies nd selecting broccoli smples grown in three regions of Toivonen, 199) re designed to increse the shelf Austrli, nmely, the sttes of New South Wles, life of broccoli but could diversify the rnge of Queenslnd nd Victori. The broccoli were cominfluences tht microorgnisms hve on broccoli mercil smples obtined from the centrl Sydney qulity. mrkets nd hd been shipped to Sydney pcked in Broccoli hs heterogenous physicl structure tht boxes covered with crushed ice. Anlysis of the is likely to complicte n understnding of its broccoli commenced within 8 0 h fter hrvest. microbil ecology nd the contribution of this ecolo- Broccoli smples were stored in the lbortory gy to the loss of product qulity. The bulk of the under conditions simulting those tht occur during product is represented by the florets, of which there retiling in Austrli. Smples were plced in unre the outer more exposed surfces nd underlying covered pcking trys nd stored t, 1 or 08C less exposed regions. The florets re ttched to (18C), nd vrying reltive humidities of, 7 80, stem or stlk, the outer surfce of which is substn- 7 7 nd 7 7%, respectively. Ech try contilly different to tht of the florets. A prt of the tined 10 heds of broccoli of 00 00 g per hed. stem bers cut surfce where the portion of Two seprte btches of broccoli from ech region broccoli hs been detched from the rest of the plnt. were stored. Smples from ech btch were tken for This cut surfce exposes the inner tissues of the microbiologicl nlyses t three times during storplnt. Different microbil popultions my be ssoci- ge. These times were 0, nd 10 dys for storge t ted with these different prts of the broccoli. 8C; 0, nd 7 dys for storge t 18C nd 0, nd Previous studies on the microbil ecology of broccoli dys for storge t 08C. The lst (third) smpling hve not considered this possibility nd hve focus- time for ech btch ws selected when the broccoli sed mostly on the microbil popultions ssocited ws visibly spoiled nd considered uncceptble. At with whole sections of the florets (Berrng et l., this time, the florets were yellow nd the stlk hd 1990; Mohd-Som et l., 199, 199) or combined lost its firm texture. The second smpling repre-
M. Pdg et l. / Interntionl Journl of Food Microbiology 0 (000) 1 17 sented time tht ws hlfwy between the com- ccording to Bergey s Mnul of Determintive mencement of storge nd spoilge. At this stge, Bcteriology (Holt et l., 199) to confirm identificsmll proportion of the florets hd strted to become tions when the results given by the two utomted yellow nd the firmness of the stlk hd strted to methods were not in greement nd where doubtful decrese. A Chrom Meter CR-00 (Minolt, Jpn) profiles were obtined. Liquefction of pectte ws nd TA-XT texture nlyser (Arrow Scientific, used to differentite between Pseudomons fluores- Sydney) were used in these determintions. cens nd Pseudomons corrugt (Biolog identifiction) (Lopez et l., 199; Ctr et l., 1997). The.. Anlyses for bcteri nd yests isoltes of Arthrobcter were difficult to clssify nd some could not be relibly identified to species level. Duplicte smples from ech btch of broccoli Their genus identifiction ws confirmed by sewere septiclly seprted into four sections; the quence nlysis of the 1s ribosoml DNA. (1s outer florets (top 1 mm); inner florets ( mm sequencing ws conducted by M. Moore, Deprtment below outer surfce); the stlk; nd cut stlk which of Biotechnology, UNSW). A totl of 1 isoltes of hd cm of exposed, cut surfce. Smples ( g) of bcteri were identified. The yests were not idenech section were mixed with ml of sterile 0.1% tified. bcteriologicl peptone wter (Oxoid, Melbourne, Austrli) nd homogenised in Stomcher (Col-.. Dt nlyses worth, Stomcher 00) for 1 min. The homogentes were diluted s required in 0.1% peptone wter, from Broccoli smples (btches) were obtined from which duplicte smples (0.1 ml) were spred onto ech loction on two seprte occsions. Duplicte pltes of Tryptone Soy Agr (TSA, Oxoid) sup- smples from ech btch were stored nd subject to plemented with 1% glucose. The pltes were incu- microbiologicl nlysis. Microbiologicl nlysis of bted t 08C for 8 h fter which the different ech smple ws done in duplicte. Men vlues morphologicl types of bcteril colonies were re- were clculted from these dt. A one-wy nlysis corded nd counted. In prllel with these nlyses, of vrince (ANOVA, Sttistic for WindowsE, smples (0.1 ml) were spred inoculted onto pltes SttSoft Inc., 199, OK) using Duncn s Multiple of Mlt Extrct Agr (MEA, Oxoid) supplemented Rnge test t P 0.0 ws performed on dt to with 100 ppm of oxytetrcycline (Sigm). These determine if there were significnt differences bepltes were incubted t 8C for 7 h to give counts tween counts on the different sections of broccoli for the yests. (Tbles 1 nd ). For ech btch of broccoli nd ech storge condition, four representtives of ech type of bcteril colony on the primry isoltion pltes were. Results purified by streking onto TSA 1 1% glucose. These bcteri were then identified to genus nd species..1. Microbil popultions on different prts of Conventionl morphologicl nd biochemicl criteri broccoli (Grm stin, cell shpe, motility, ctlse, oxidse, nd oxidtion/ fermenttion of glucose) were used to Tble 1 shows the bcteril popultions on differobtin genus identifiction (Brrow nd Felthm, ent prts of the broccoli obtined from three different 199). Species identifiction ws done using the regions. Popultions on the outer prts of the florets utomted BIOLOG Microsttion with Biolog GN were lwys higher thn those tken from the inner microtitre test pltes (Biolog Inc., Hywrd, CA, prts. This ws evident for unstored smples nd USA) (Biolog, 199) nd the utomted ATB identi- smples stored until spoilge t, 1 (dt not fiction system, using ID GN test strips shown) nd 08C. In severl cses, these differences (BioMerieux, Vitek-Austrli Pty Ltd). Becuse were greter thn 10-fold, nd were significnt t Biolog identifiction gve dt for 9 tests, we lso 9% confidence levels. The florets, especilly the used this system to differentite strins within the outer portions, exhibited higher popultions (10 sme species. Some conventionl tests were done0-fold) thn uncut stems. Cut surfces of the stem
18 M. Pdg et l. / Interntionl Journl of Food Microbiology 0 (000) 1 Tble 1 Popultions of bcteri on different prts of broccoli before nd fter storge t 8C (10 dys) nd 08C ( dys) Broccoli prts Bcteril counts (cfu/g) Victorin broccoli Queenslnd broccoli NSW broccoli Fresh 8C 08C Fresh 8C 08C Fresh 8C 08C Outer florets.0 10 7.8 10 7.8 10 9.1 10 1. 10. 10 1. 10.1 10. 10 Inner florets.7 10 b.1 10 b 7. 10 b. 10 1. 10 b. 10 b. 10 b. 10. 10 b Stem: cut surfces 1.7 10 c 9.7 10 7 1. 10 c. 10.8 10.1 10 c 1. 10. 10. 10 c Stem: uncut.7 10 d. 10 b. 10 d. 10 b 1. 10 b 1. 10 d.1 10 b 1.0 10 b 7.0 10 d Counts re the mens from the nlyses of duplicte smples tken from two different btches of broccoli. Mens in columns followed by the sme letters were not significntly different (P. 0.0). Tble Popultions of yests on different prts of broccoli before nd fter storge t 8C (10 dys) nd 08C ( dys) Broccoli prts Yest counts (cfu/g) Victorin broccoli Queenslnd broccoli NSW broccoli Fresh 8C 08C Fresh 8C 08C Fresh 8C 08C Outer florets.1 10 8. 10.7 10. 10. 10.0 10 1.9 10. 10 9.1 10 Inner florets.1 10 b.9 10 b 1.0 10 b.1 10.0 10 b 7.7 10 b 1. 10.7 10 8. 10 Stem: cut surfces 1.9 10 c 1.8 10 c 1. 10 b. 10 b.8 10 1. 10 b 1. 10 b. 10 b 1.1 10 b Stem: uncut 1.8 10 c. 10 b. 10 d.0 10 b.1 10 b. 10 b 1.0 10 b c c Counts re the mens from the nlyses of duplicte smples tken from two different btches of broccoli. Mens in columns followed by the sme letters were not significntly different (P. 0.0). section, either before or fter storge, gve higher.. Bcteril species ssocited with different popultions of bcteri thn uncut prts. In mny prts of broccoli cses, the differences were sttisticlly significnt nd, sometimes, greter thn 10-fold. The counts on Only Pseudomons species were isolted from ll prts of the broccoli incresed during storge t, broccoli obtined from Victori (Tble ). The sme 1 (dt not shown) or 08C. However, counts on species, Pseudomons viridiflv, Ps. corrugt nd broccoli obtined from Queenslnd nd New South Ps. fluorescens A were found on ll four prts of the Wles, were generlly less thn 10 cfu/ g, despite the broccoli. In greement with dt for totl bcteril product showing obvious signs of spoilge. Notbly, counts, higher popultions of the species were found broccoli obtined from the Victorin loction ex- on the outer prts of the florets nd on cut surfces of hibited the highest initil counts tht were bout the stem. Pseudomons viridiflv nd Ps. fluores- 100-fold greter thn those of Queenslnd nd New cens were predominnt species on the florets before South Wles smples. storge nd Ps. corrugt ws most prevlent on the Tble shows the popultions of yests found on cut surfce of the stem t this time. Popultions of ll different prts of the broccoli. Although the yest species incresed during storge of the broccoli t, counts were lower thn those of bcteri, the generl 1 (dt now shown) nd 08C, with the highest conclusions were similr. Higher popultions were popultions occurring on the outer prts of the present on the outer prts of the florets compred florets. Lowest popultions occurred on the uncut with inner florets, cut surfces of the stem exhibited section of the stem. The Biolog profiles differenhigher popultions thn the uncut sections nd, tited the isoltes of Ps. fluorescens into three overll, the highest popultions were found on the strins, A, B nd G bsed on results of tests such s outer florets. ssimiltion of donitol, m-inositol nd D-sorbitol.
M. Pdg et l. / Interntionl Journl of Food Microbiology 0 (000) 1 19 Tble Min species of bcteri isolted from Victorin broccoli before nd fter storge t 8C (10 dys) nd 08C ( dys) Broccoli prts Species Counts (cfu/ g) Initil 8C 08C Outer florets Pseudomons viridiflv. 10 1.9 10 1.1 10 Pseudomons corrugt. 10 7. 10 1.9 10 Pseudomons fluorescens A 7.0 10.8 10 1.1 10 Pseudomons fluorescens B 7.0 10 1. 10 1. 10 Pseudomons fluorescens G 9. 10.0 10.0 10 7 7 7 Inner florets Pseudomons viridiflv 9. 10 1. 10 9. 10 Pseudomons corrugt 7.0 10 1. 10.1 10 Pseudomons fluorescens A.0 10.7 10.0 10 Pseudomons fluorescens B. 10. 10. 10 Pseudomons fluorescens G 7. 10 1. 10 9.0 10 Stem: cut surfce Pseudomons viridiflv.9 10 1. 10 1.9 10 Pseudomons corrugt 1.0 10 1. 10. 10 Pseudomons fluorescens A. 10.7 10 1.0 10 Pseudomons fluorescens B. 10. 10. 10 Pseudomons fluorescens G.0 10 1. 10.0 10 Stem: uncut surfce Pseudomons viridiflv 1.0 10.0 10 7. 10 Pseudomons corrugt 1.1 10. 10. 10 Pseudomons fluorescens A 1.7 10.0 10 8.0 10 Pseudomons fluorescens B.0 10 1. 10. 10 Pseudomons fluorescens G. 10. 10. 10 Counts re the mens from nlyses of duplicte smples tken from two different btches of broccoli. Anlyses were done in duplicte. The inbility of Pseudomons fluorescens G to flor of Grm negtive nd Grm positive bcteril produce levn from sucrose, further differentited the species (Tble ). However, their popultions, both species (Holt et l., 199). Pseudomons fluorescens before nd fter storge were generlly 10 100-fold A demonstrted greter potentil for growth on the less thn those found on the btches of Victorin different broccoli prts. broccoli. Pseudomons fluorescens A predominted The temperture of storge hd selective effect in most cses, before nd fter storge. Its popultion on the species tht were predominnt t spoilge. At on different sections of the broccoli incresed during 08C, there ws predominnce of ll three species storge, especilly on the outer florets. Pseudomons on the most prts of the broccoli. However, t 8C frgii, which ws the lest prevlent of the isoltes t the contribution from Ps. corrugt ws notbly less. the initil stges (10 10 cfu/ g), exhibited strong Bsed on the Biolog identifiction profiles, there ws tendency for growth during storge, lthough its finl no difference between strins of Ps. corrugt popultions were often lower thn those of other isolted from the different prts of broccoli or species. Of the Grm positive isoltes, Arthrobcter broccoli stored t different tempertures. However, globiformis ws most significnt. Both species of some isoltes of Ps. viridiflv differed in their Arthrobcter were ble to grow during storge, bilities to utilize erythritol, succinic cid nd propi- especilly on the florets, where their popultions onic cids nd on this bsis, there were differences incresed by 10 100-fold. Stphylococcus between some strins isolted from the outer nd chromogenes ws lso isolted from this broccoli inner florets fter storge t 8C nd between some nd showed greter tendency for growth on the strins of the outer florets nd cut stem. inner florets nd cut surfce, lthough finl popul- The btches of Queenslnd broccoli gve mixed tions did not exceed 10 cfu/g. There were vri-
0 M. Pdg et l. / Interntionl Journl of Food Microbiology 0 (000) 1 Tble Min species of bcteri isolted from Queenslnd broccoli before nd fter storge t 8C (10 dys) nd 08C ( dys) Broccoli prts Species Counts (cfu/ g) Initil 8C 08C Outer florets Pseudomons fluorescens A. 10.0 10 1.1 10 Pseudomons mendocin. 10 1.1 10. 10 Pseudomons frgii 1. 10 1. 10 1.7 10 Arthrobcter globiformis 7. 10 1.9 10 8.0 10 Arthrobcter spp. 8.0 10 9.0 10 8.8 10 Stphylococcus chromogenes.0 10. 10. 10 Inner florets Pseudomons fluorescens A 1.9 10. 10 1. 10 Pseudomons mendocin.0 10.0 10 Pseudomons frgii. 10 7. 10. 10 Arthrobcter globiformis. 10.1 10 1. 10 Arthrobcter spp..0 10 1. 10.0 10 Stphylococcus chromogenes.0 10. 10. 10 Stem: cut surfce Pseudomons fluorescens A 1. 10.8 10 1.7 10 Pseudomons mendocin. 10. 10 7.0 10 Pseudomons frgii. 10 1.0 10 Arthrobcter globiformis 1.1 10 1. 10 9. 10 Arthrobcter spp..0 10 1.0 10.0 10 Stphylococcus chromogenes. 10 1. 10.0 10 Stem: uncut surfce Pseudomons fluorescens A. 10 1.1 10.7 10 Pseudomons mendocin.0 10 7. 10.8 10 Pseudomons frgii. 10. 10 Arthrobcter globiformis.0 10 1.7 10 1.9 10 Arthrobcter spp.. 10.0 10 1. 10 Stphylococcus chromogenes. 10. 10 1. 10 Counts re the mens from nlyses of duplicte smples tken from two different btches of broccoli. Anlyses were lso done in duplicte. tions in the strins of Ps. fluorescens A nd Ps.men- broccoli. It ws consistently isolted from the outer docin isolted from the different broccoli prts nd nd inner florets, nd cut stems fter storge, nd fter storge t different tempertures, but no con- ws the dominnt species on florets for broccoli sistent trends were observed. stored t 08C. Arthrobcter ilicus ws recovered The btches of broccoli from New South Wles from most smples of broccoli nd, in some cses gve the lowest popultions of microbil species (outer florets, cut surfces), it exhibited n bility to (Tble ). Pseudomons fluorescens A predominted grow during storge. Another Arthrobcter species on ll prts of the broccoli before storge nd, for ws recovered from the outer florets nd cut stem but some smples, fter storge. The Biolog profiles of it did not develop during storge. these isoltes showed some vrition in utilistion of methyl pyruvte nd erythritol but these vritions could not be relted to n influence of broccoli prt. Discussion or temperture of storge. Enterobcter gglomerns lso emerged s predominnt species in stored Our studies hve shown tht different prts of broccoli. Before storge, this species ws recovered broccoli hrbour different lods of microflor. The from outer florets t popultions of pproximtely outer sections of florets hve higher microbil popu- 10 cfu/g, but ws present below the detection limits ltions thn inner prts of the florets, nd sections of of our nlyses (100 cfu/ g) in other prts of the the stem with cut surfce exhibited higher popul-
M. Pdg et l. / Interntionl Journl of Food Microbiology 0 (000) 1 1 Tble Min species of bcteri isolted from NSW broccoli before nd fter storge t 8C (10 dys) nd 08C ( dys) Broccoli prts Species Counts (cfu/ g) Initil 8C 08C Outer florets Pseudomons fluorescens A.7 10.0 10 1.1 10 Arthrobcter ilicus 1. 10.0 10.1 10 Arthrobcter spp. 9.0 10 Enterobcter gglomerns 1.1 10. 10. 10 Inner florets Pseudomons fluorescens A.0 10 1.7 10 1.1 10 Arthrobcter ilicus 1. 10 1. 10.0 10 Enterobcter gglomerns 1. 10 1.7 10 Stem: cut surfce Pseudomons fluorescens A. 10. 10. 10 Arthrobcter ilicus.0 10 1.1 10 Arthrobcter spp. 1.7 10 Enterobcter gglomerns 1.1 10.0 10 Stem: uncut surfce Pseudomons fluorescens A.0 10. 10 Arthrobcter ilicus 1.0 10 7.0 10 Counts re the mens from nlyses of duplicte smples tken from two different btches of broccoli. Anlyses were lso done in duplicte. tions thn uncut prts of the stem. In most cses, the used will hve significnt effect on initil microbil differences in counts were bout 10-fold nd signifi- popultions. The qulity of the ice used during cnt t the 9% confidence level. These differences shipment could be nother fctor. These vribles were mintined throughout storge of the broccoli require systemtic study since the initil contminnd were evident for both erobic plte counts nd tion lod of vegetble produce generlly hs n yest counts. Higher popultions on the outer florets importnt influence on subsequent qulity nd shelf would be consistent with the greter vilbility of life of the product (Lund, 199; Nguyen-the nd oxygen compred with inner prts of the florets, nd Crlin, 199; Ahveninen, 1997). the cut res of the stems would provide better As mentioned lredy, the microbil ecology of sources of nutrients for microbil growth. broccoli hs not been thoroughly described in previ- Initil microbil popultions vried for btches of ous studies. We hve determined the predominnt broccoli hrvested from different loctions. The bcteril species ssocited with broccoli hrvested broccoli obtined from Victori hd erobic plte from three different loctions, nd hve shown tht counts tht were bout 100-fold more thn broccoli different microflor occur on broccoli depending on obtined from New South Wles. These btches lso their origin. Pseudomons fluorescens ws the only showed 10-fold differences in their yest counts. It is species tht ws consistently isolted from ll btunlikely tht storge nd trnsport contributed to ches of broccoli. Moreover, it ws consistently found these differences since ll smples were similrly t ll sections of the broccoli. However, it ws not shipped under ice nd were exmined on the third necessrily the dominnt species ssocited with the dy fter hrvest. Literture vlues for the erobic broccoli smples. Only Pseudomons species were plte counts of fresh broccoli vry between 10 nd isolted from the btches of broccoli obtined from 10 cfu/ g nd between 10 nd 10 cfu/ g for Victori. In ddition to Ps. fluorescens, Ps. viryests (Berrng et l., 1990; Brckett, 1989; Mohd- idiflv nd Ps. corrugt were isolted from these Som et l., 199, 199). Our dt re consistent with btches of broccoli, sometimes t higher popultions these findings. It ppers tht the prehrvest environ- thn Ps. fluorescens. The initil popultions of these ment nd tretment of broccoli including qulity of species were quite high (pproximtely 10 cfu/ g) wter used for irrigtion nd types of grochemicls lthough the broccoli t this time ppered in
M. Pdg et l. / Interntionl Journl of Food Microbiology 0 (000) 1 cceptble, unspoiled condition. Strins of Ps. For given species, the popultions vried with the fluorescens nd Ps. viridiflv hve been ssocited section of the broccoli, in ccordnce with the with the soft rot spoilge of broccoli florets (Hilde- conclusions lredy mentioned for totl erobic brnd, 1989; Wimljeew et l., 1987) nd similr counts. Outer florets hd higher popultions of soft rot spoilge of mrket broccoli (Lio nd Wells, individul species thn inner florets nd cut surfces 1987). Consequently, our finding of these species of the stem hd higher popultions thn uncut nd demonstrtion of their bility to grow on broc- surfces. Preliminry dt indicted strin vrition coli during storge re not unexpected. The temper- within some species nd tht loction on the broccoli ture of storge my determine which Pseudomons nd temperture of storge could select for the species eventully predominte nd this will depend development of prticulr strins. However, more on their reltive growth rtes t different temper- focussed study is needed of these concepts using tures. moleculr techniques to distinguish between strins. In ddition to Ps. fluorescens, the btches of We re not ble to implicte ny prticulr species Queenslnd broccoli hrboured Ps. mendocin nd in the spoilge of broccoli nd this will be the Ps. frgii. Pseudomons frgii is well-known subject of further study. Uncceptbility of the stored spoilge species in diry products where it forms broccoli ws primrily determined by yellowing of chrcteristic fruity-off flvors (Morgn, 197). Al- the florets, which is minly physiologicl response though it ws initilly present t low popultions of the plnt (Ceponis et l., 1987). Soft rot ws not (generlly less thn 10 cfu/ g), it showed good evident in our stored broccoli when the experiments bility to grow on the florets nd on the surfce of were terminted. Bcteril popultions (greter thn cut stems. 7 10 cfu/ g) sufficient to cuse n obvious spoilge The ssocition of Grm positive bcteri, espe- rection were found only on the btches of broccoli cilly coryneforms, with broccoli hs been reported from Victori. However, soft rot is only one mnibefore (Brckett, 1989; Mohd-Som et l., 199), festtion of the spoilge process. We re prticulrly lthough the significnce of this occurrence hs not interested in the contribution of the microbil flor to been described. Species of Arthrobcter were con- yellowing of the florets nd the development of off sistently isolted from ll sections of Queenslnd odours. Ethylene is importnt in stimulting the btches of broccoli nd, to lesser extent, from yellowing of florets (Wtd, 198; Arshd nd btches of New South Wles broccoli. However, Frnkenberger, 199). In future work, we will screen their initil popultions were lwys lower thn those our isoltes for the production of ethylene nd of Ps. fluorescens. Nevertheless, they were cpble methnethiol with the purpose of defining their of inititing growth during storge, especilly on the contribution to the yellowing nd off odour defects. Queenslnd broccoli. In ddition, they will be exmined for the production Members of the coliform nd Enterobctericee of pectinolytic enzymes nd biosurfctnts which re groups hve been reported s initil contminnts of two other importnt properties relted to coloniztion broccoli (Brckett, 1989; Mohd-Som et l., 199, nd spoilge of vegetbles (Lund, 199; Brckett, 199) lthough species identifictions hve not been 1997). given. Enterobcter gglomerns, in prticulr, is The conclusions of our study my be summrised often ssocited with fresh vegetbles (Nguyen-the s follows: nd Crlin, 199). Thus, its occurrence nd growth (i) The physicl structure of broccoli is heterogeon broccoli ws not unexpected. We found this neous which gives loclised vrition in the quntitspecies only on the btches of New South Wles tive popultions of ssocited microorgnisms. While broccoli where, fter storge, it ws more prevlent similr species were ssocited with the different on florets thn Ps. fluorescens. sections of broccoli, different strins could develop We found no evidence tht prticulr bcteril t different sections. species were ssocited with specific prts of the (ii) Broccoli hrvested from different geogrphicl broccoli. Similr species were isolted from the outer regions showed notble vritions in totl microbil nd inner florets, s were found on the stem sections. popultions nd ssocited species. These findings
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