Impact of UV-C light on storage quality of fresh-cut pineapple in two different packages

Impact of

UV-C light on storage quality of fresh-cut pineapple in two

different packages

Lara Manzocco*,Stella Plazzotta,Michela Maifreni,Sonia Calligaris,Monica Anese,

Maria Cristina Nicoli

Dipartimento di Scienze degli Alimenti,University of Udine,via Sondrio2/a,33100Udine,Italy

a r t i c l e i n f o

Article history:

Received21July2015

Received in revised form

28September2015

Accepted2October2015

Available online9October2015

Keywords:

Ultraviolet light

Quality

Fresh-cut

Packaging

Yeast

a b s t r a c t

The effectiveness of UV-C light treatments on microbial load and quality of fresh-cut pineapple sticks was

studied.At all tested?uencies(200e4800J/m2),UV-C light did not decrease the initial microbial load of

pineapple sticks.Nevertheless,pineapple sticks submitted to200J/m2UV-C light,packaged in con-

ventional PET/EVOH/PE trays and stored at6 C up to15days showed slower yeast and lactic acid

bacteria growth.In these samples,microbial counts were generally2log cycles lower that those observed

in the untreated sticks.UV-C light did not promote changes in colour and increased consumer prefer-

ence.Similar results were also obtained when UV-C light treatment was applied on pineapple sticks

previously packaged in highly UV-C light transparent PA/PE pouches to avoid post treatment

contamination.

?2015Elsevier Ltd.All rights reserved.

1.Introduction

Consumer demand for high quality and convenient fresh-cut

fruit is greatly increasing.These products are mainly represented

by single-serve units of fruit sticks,slices or cubes,usually packaged

in trays or pouches made of transparent plastic material(G?mez-

L?pez,Rajkovic,Ragaert,Smigic,&Devlieghere,2009).

Fresh-cut processing of fruit is well known to promote faster

deterioration in comparison with its intact counterpart(Rico,

Martín-Diana,Barat,&Barry-Ryan,2007).For this reason,the

shelf life of fresh-cut fruits tends to be very short.Since thermal

treatments would impair fruit fresh likelihood,non-thermal

physical treatments have been proposed to extend shelf life.

Among these,ultraviolet-C(UV e C)light has raised large interest in

the last decade(Soliva-Fortuny&Martín-Belloso,2003).

UV-C light treatment exploits the radiation from the electro-

magnetic spectrum from200to280nm.It is a powerful germicidal

method,being fast,economic and environmental friendly

(Barbosa-C a novas,Pothakamury,Palou,&Swanson,1998;Bintsis,

Litopoulou-Tzanetaki,&Robinson,2000).The technology is safe

to apply when some simple precautions are adopted to protect

workers from light exposure and generated ozone.Moreover,it has

not been reported to form known toxic or signi?cant non-toxic by-

products(Keyser,Müller,Cilliers,Nell&Gouws,2008).The anti-

microbial effect of UV-C light is due to its ability to damage mi-

crobial DNA,leading to cell death(Sastry,Datta,&Worobo,2000).

UV-C light treatments were also reported to modify fruit antioxi-

dant capacity and concentration of some bioactives(Freitas et al.,

2015).

The applications of UV-C light are mainly relevant to disinfec-

tion of:(i)air;(ii)liquids such as sewage ef?uents,drinking and

brewing water,cheese brines and fruit juices;(iii)packaging ma-

terials;(iv)food surfaces.To this regard,UV-C light has been pro-

posed to reduce the super?cial micro?ora of row meat,?sh,shell

eggs,bakery products and fresh-cut fruits(Bintsis et al.,2000;

Siddiqui,Chakraborty,Ayala-Zavalan&Dhua,2011).Food decon-

tamination by UV-C light is ef?cacious only if the accurate

enlightening of the surface is guaranteed(Gardner&Shama,1998).

The topography of the treated surface plays an important role,since

the germicidal effect of UV-C light is signi?cantly impaired in

shadowed zones(Gardner&Shama,2000).Similarly,products are

individually treated to prevent shadowing effects among different

food items and the treatment is generally applied on unpackaged

food to avoid the screening effect of packaging material and ensure

maximum decontamination effectiveness(Fonseca&Rushing,

2006).In any case,the eventual occurrence of a post-treatment *Corresponding author.

E-mail address:lara.manzocco@uniud.it(L.Manzocco).

Contents lists available at ScienceDirect

LWT-Food Science and Technology

journal homepa ge:1cf566dd9a89680203d8ce2f0066f5335a8167f7/locate/lwt

1cf566dd9a89680203d8ce2f0066f5335a8167f7/10.1016/j.lwt.2015.10.007

0023-6438/?2015Elsevier Ltd.All rights reserved.

LWT-Food Science and Technology65(2016)1138e1143

微生物负荷？

剂量？

污染UV-C处理降低微生物生长速率，减缓色泽变化

托盘小袋子透明

恶化完整对应

热处理

损害可能性

开发

电磁光谱杀菌

预防

生成臭氧

消毒

污水厂排污饮用水

酿造水卤水

净化去污有效的

照耀

形貌

杀菌削弱

屏蔽效应？

屏蔽效应

净化

无论如何

PET：聚对本二甲酸乙二醇酯

EVOH：聚乙烯醇

PE：聚乙烯

PA：聚酰胺

contamination is expected to nullify the decontamination ef ?cacy of the UV-C light treatment.Based on these issues,ef ?cacious

implementation of UV-C light in the food sector depends on the possibility to ensure accurate treatment of 100%product surface and reduce the risk for post-treatment contamination.

The aim of the present paper was to evaluate the effectiveness of UV-C light in extending the shelf life of fresh-cut pineapple sticks

packaged in conventional plastic trays.The research was articulated in three parts.In

the ?rst one,the decontamination ef ?cacy of UV-C light on pineapple sticks was studied.In the second part the po-tential of UV-C light treatments in maintaining quality of pineapple sticks packaged in commonly used PET/EVOH/PE trays was evalu-ated.Finally,the ef ?cacy of UV-C light applied after fruit packaging in PA/PE pouches to avoid the risk for post-treatment contamina-tion was evaluated.The effect of the treatment was monitored by assessing the evolution of microbial counts,head space oxygen concentration,colour and consumer preference during storage of pineapple sticks at 6 C.2.Materials and methods 2.1.Sample preparation

2.1.1.Pineapple stick surface treatment

Pineapple (Ananas comosus,“Gold ”cultivar)fruits with similar size and soluble solid content (15±1 Brix)were purchased at the local market and stored at 6 C for 24h before treatment.Working area,boards,knives,containers and surfaces in contact with fruit

during processing were sanitized with ethanol.Crown leaves and fruit bottom were manually removed and the pineapples were

peeled,cored and wedged using a pull-down manual equipment (Multi 1000,Charlie's,CO,USA).Six sticks were obtained from each pineapple.Pineapple sticks were collected after 30min cutting operations and positioned between four UV-C lamps (15W/G15T8,

Philips,Oland)in a thermostated cell (8 C),in order to avoid temperature increase of the samples (Fig.1).

The irradiance on the pineapple stick surfaces was 40W/m 2.Samples were light treated for increasing time up to 2min,leading

to UV-C light ?uence on the pineapple stick surface ranging from 0to 4800J/m 2.

2.1.2.UV-C light treatment and packaging in PET/EVOH/PE trays

Samples were prepared by introducing two UV-C light treated (200J/m 2)pineapple sticks in PET/EVOH/PE (0.4mm)plastic trays

(190?137?38cm)and sealing the trays (Pro ?2,Orved,VE,Italy)with a PET/PE ?lm (0.064mm,26/70).Pineapple sticks not exposed to UV-C light and packaged in PET/EVOH/PE trays were also pre-pared as control samples.2.1.3.UV-C light treatment and packaging into PA/PE pouches

Samples were prepared by introducing one UV-C light treated (200J/m 2)pineapple stick into PA/PE pouches (30?15cm,0.090mm,20/70),which were then sealed (Easy Packer,AVC,Tor-ino,Italy).Pineapple sticks not exposed to UV-C light were also packaged into PA/PE pouches (control samples).

2.1.4.Packaging into PA/PE pouches and UV-C light treatment

Samples were prepared by introducing one untreated pineapple stick into a PA/PE pouch.Pouches were then sealed and UV-C light treated (200J/m 2).The irradiance on the pineapple stick surface was 32W/m 2,due to the 20%screening effect of the plastic mate-rial.These samples were thus exposed to160J/m 2UV-C light ?uence.

All packaging materials were provided by Savonitti (Codroipo,Italy)and decontaminated before use by 10min UV-C light exposure.

2.1.5.Sample storage

Samples were stored for 15days in a thermostated cell at 6 C.At increasing times during storage,samples were removed from the thermostated cell and submitted to the analyses.2.2.Transmittance of plastic materials to UV-C light

Transmittance of plastic materials to UV-C light was determined

photometrically using a portable luminometer (HD-2102.2Delta Ohm,Padova,Italy)equipped with a UV-C (LP471UVC,Delta Ohm,

Padova,Italy)light probe.In particular,portions of PET/EVOH/PE trays,PET/PE ?lm and PA/PE pouches were placed on the lumin-ometer sensor and exposed to 40W/m 2irradiance of UV-C light.The irradiance of the light reaching the pineapple stick surface was measured as the ratio between the light irradiance inside the ma-terial (I)and the intensity of the incident light at its surface (I o ).

2.3.Soluble solid content determination

Pineapple soluble solid content was measured by a table refractometer (Unirefrax,Bertuzzi,Milan,Italy).Analysis was

(a)(b)(c)

Pineapple stick

5 cm

Fig.1.Schematic representation of:a)pineapple cutting (eee ),b)pineapple stick and c)position of pineapple stick during UV-C light treatment.

L.Manzocco et al./LWT -Food Science and Technology 65(2016)1138e 11431139

污染无效

实现部门

评估

清晰地

消毒

去皮去果芯楔入？

恒温器

辐照

量？

无UV-C 处理分别包装为CK

先辐照（两根紫外灯）后包装

先辐照（一根紫外灯）后包装

先包装后辐照

透明度/透射比

光度测量

光度计

探针

托盘薄膜保鲜袋

入射光

折射计

carried out on the solution obtained after homogenization(Polyton, Kinematica,Luzern,Switzerland)and?ltration of pineapple cubes through?lter paper(Whatman#1,Whatman International Ltd, Maidstone,UK).

2.4.Microbiological analyses

For microbiological analyses,25g of sample was diluted with 100mL Maximum Recovery Diluent(Oxoid,Basingstoke,UK)and homogenized for1min in a Stomacher(PBI International,Milan, Italy).Serial dilutions of each suspension were made in Maximum Recovery Diluent(Oxoid)and analysed for microbial counts. Appropriate aliquots(0.1or1mL)were spread on agar plates.Plate Count Agar(Oxoid)and Man Ragosa Sharpe(MRS)were used for enumeration of mesophilic and lactic acid bacteria respectively,and plates were incubated for48h at30 C.Oxytracycline-Glucose-Yeast Extract(OGY)agar(Oxoid),was used for enumeration of yeasts and moulds,and plates were incubated for72h at28 C. Violet Red Bile Glucose(VRBG)(Oxoid)was used for enumeration of Enterobacteriaceae,and plates incubated for24h at37 C.

2.5.Head space oxygen analysis

Analyses were carried out using a gas chromatograph equipped with a thermal conductivity detector(Fison8000,Fison In-struments,Milan,Italy)at180 C.A0.2mL aliquot of head space of the trays or pouches equilibrated at20 C for2h was withdrawn through an adhesive septum stuck to the cover?lm,using a manual sampling syringe(Dynatech,Batonrouge,LA,USA)and then injec-ted into the gas chromatograph.A Porapaqs80/100mesh column (2m?2mm)at70 C and200kPa was used.Nitrogen at27mL/ min was used as carrier gas.Peak area integration was performed using Chrom-Card(Chrom-Card Data System,v. 1.18,Thermo Scienti?c?).

2.6.Colour

Pineapple stick colour was analysed using a tristimulus color-imeter(Chromameter-2Re?ectance,Minolta,Osaka,Japan) equipped with a CR-300measuring head.The instrument was standardised against a white tile before measurements.Colour was expressed in L*,a*and b*Hunter scale parameters(Chen,Zhu, Zhang,Niu,&Du,2010).For each sample,?ve measures were taken on each side of two different sticks(Fig.1).

2.7.Preference analysis and off-odour perception

A consumer survey was performed recruiting students and workers from the University of Udine,Italy.Seventy-?ve persons between the ages of18and55years,who consumed fruit at least once per day,approximately balanced between males and females, were used.The pair comparison method was used for detecting preference difference.Samples were indicated by a three-digit code and served the consumers paired with a just prepared pineapple stick,identi?ed as“reference”.Consumers were asked to identify the most preferred sample.Consumers were also asked to indicate the eventual perception of off-?avours.Off-?avour perception data were expressed as percentage of judges that identi?ed the defect as respect to the reference.

2.8.Statistical analysis

Analyses were carried out at least twice in two replicated ex-periments.Analyses of variance(ANOVA),with signi?cance level set to p<0.05,and linear regression analyses were performed using R(The R foundation for statistical computing,v. 3.1.1). Goodness-of-?t was evaluated by means of the determination co-ef?cients(R2)and the corresponding p-values.

3.Results and discussion

3.1.Decontamination of pineapple surface by UV-C light

Total viable count,yeasts,moulds,Enterobacteriaceae and lactic acid bacteria of control samples(Table1)were in the same magnitude range of fresh-cut pineapple reported in the literature (Montero-Calder?n,Rojas-Graü,&Martín-Belloso,2008).Micro-?ora of fresh-cut pineapple was mainly represented by yeasts, moulds and Enterobacteriaceae.These microorganisms have been previously reported as typical contaminants of most fruit de-rivatives(Raybaudi-Massilia,Mosqueda-Melgar,Soliva-Fortuny& Olga Martín-Belloso,2009).Lactic acid bacteria were also shown to be common contaminants of fresh-cut fruit(Gil&Allende,2012; Nguyen-The&Carlin,1994)but,in our experimental conditions, they resulted below the detection limit.Counts presented a high variability probably due to the non-homogenous contamination of the fruit tissue(Table1).Pineapple sticks,collected after30min cutting operations,were exposed to200J/m2UV-C light and sub-mitted to microbiological analyses(Table1).The treatment reduced Enterobacteriaceae below the detection limit(5CFU/g,0.7Log CFU/ g).On the contrary,UV-C light did not signi?cantly affect total viable bacteria,yeast and mould counts.This result con?rms the higher sensitivity of bacteria to UV-C light as compared to fungi (Koutchma,2009).An average value of1e2logarithmic reductions in microbial populations has been reported following UV-C light treatment(1200e4800J/m2)of fresh-cut fruits with a smooth surface such as apple and melon(Art e s-Hernandez,Robles,G?mez, Thomas-Callejas,&Art e s,2010;Fonseca&Rushing,2006;Man-zocco,Da Pieve,Bertolini,Bartolomeoli,Maifreni,Vianello&Nicoli, 2011;Manzocco,Da Pieve,&Maifreni,2011;Manzocco&Nicoli, 2015).Pineapple stick surface is actually characterised by a typical roughness due to the association of multiple fruitlets,which can internally trap microorganisms during fruit development (Rohrbach&Johnson,2003).Micro?ora can thus be shadowed in hidden nests that are not reached by UV-C light.This would explain the absence of a clear decontamination effect in UV-C light treated fresh-cut pineapple(Table1)as compared to other fresh-cut derivatives.

To evaluate if the decontamination effect of UV-C light can be improved by increasing the?uence of the radiation,samples were submitted to UV-C light up to4800J/m2and analysed for yeast and mould counts.The attention was focused on these microorganisms since their growth has been reported as the limiting factor for fresh-cut pineapple shelf life(Chonhenchob,Chantarasomboon,& Singh,2007;Raybaudi-Massilia,Mosqueda-Melgar,Soliva-Fortuny,&Martín-Belloso,2009).Collected data(Table2)showed large standard deviations in yeast counts that were reasonably the

Table1

Counts of total viable bacteria,yeasts,moulds,lactic acid bacteria and Enter-obacteriaceae(Log CFU/g±SD)of untreated pineapple sticks(Control)and pine-apple sticks exposed to200J/m2UV-C light.

Control UV-C light(200J/m2)

Total viable bacteria 2.7±2.4 2.9±2.0

Yeasts 3.9±3.1 3.7±3.2

Moulds 2.3±2.2 2.2±2.1

Lactic acid bacteria

Detection limit(D.L.):5CFU/g.

L.Manzocco et al./LWT-Food Science and Technology65(2016)1138e1143 1140

均质

过滤

滤纸

稀释

最大复壮稀释液

均质匀质器

连续稀释悬浮液

等分

平板计数琼脂乳酸杆菌培养基

计数嗜常温乳酸菌

土霉素葡萄糖酵母粉琼脂

结晶紫中性红胆盐葡萄糖琼脂

肠杆菌

气相色谱

TCD热导检测器

小份

平衡撤回

粘合剂隔板覆盖膜人工进样器

网柱

氮

三色色度计

偏好分析异味感知

招募

75个18-55

岁的每天吃

水果的人，

男女各半

鲜切菠萝作为参照

缺点

回归

拟合优度

决定系数

净化

总活菌数

量级

污染物

衍生物？

污染物

均匀

真菌

对数

果眼

其他同类鲜切产品

灭菌效果与UV-C

辐照剂量的关系酵母菌数标准差大

consequence of the high variability of the microbial load of the just cut pineapple sticks (Table 1).No yeast decontamination effect of pineapple sticks was observed even increasing the ?uence of the

UV-C light (Table 2).Analogous results were also detected for moulds (data not shown).Similar results were observed by Fonseca and Rushing (2006)who reported that treatments at increasing

UV-C light ?uence (i.e.from 1400J/m 2to 6900J/m 2)exerted the same effect on microbial population of watermelon cubes.This behaviour could be explained considering the super ?cial character

of UV-C light (Guerrero-Beltr a

n &Barbosa-Can ?;vas,2004):the application of UV-C light ?uence higher than that required to inactivate the super ?cial microbial population,physically exposed to the light,would not increase the decontamination ef ?ciency since light would be unable to affect microbial cells shadowed in

the inner parts of the fruit.By contrast,higher ?uence treatments have been associated to higher quality damage (Guevara,Tapia,&G o

mez-L o pez,2012;Nigro,Ippolito,&Lima,1998).Further exper-iments were thus performed by selecting the lowest level of UV-C light ?uence (200J/m 2)among those previously considered (Table 2).

Although UV-C light did not exert a signi ?cant decontamination effect just after the treatment (Tables 1and 2),it could affect mi-crobial growth during refrigerated storage of the product as well as promote changes in fruit metabolism,leading to changes in product quality (Lamikanra &Richard,2004;Mercier,Baka,Reddy,Corcuff,&Arul,2001).Additional trials were thus carried out to evaluate the effect of UV-C light treatment on microbial growth and quality of pineapple sticks on further storage at 6 C.

3.2.Effect of UV-C light treatment applied before packaging in PET/EVOH/PE trays

Fresh-cut fruit available on the market is commonly packaged in PET/EVOH/PE trays sealed with a PET/PE ?lm.The UV-C light

transmittance of these plastic materials resulted negligible.This means that,when the product is intended to be packaged in these plastic trays,UV-C light treatment should be necessarily applied before packaging.Pineapple sticks were submitted to 200J/m 2UV-C light ?uence,packaged in PET/EVOH/PE plastic trays,sealed with

a PET/PE ?lm and stored at 6 C to simulate storage of fresh-cut fruit along the refrigerated chain.At increasing time during storage,samples were analysed for yeast and mould counts.Yeast counts of untreated pineapple sticks (Control)increased during storage approaching 5Log CFU/g after one week (Fig.2).On the contrary,yeast counts of samples submitted to UV-C light showed a slower increase during storage,remaining about 2Log units lower than that of the control during the second week of storage.Unlike yeasts,no signi ?cant changes were appreciable in mould counts in both untreated and UV-C light treated samples.Moulds remained almost constant (~2Log CFU/g)during the entire storage and not signi ?-cantly different from that of the just cut pineapple (Table 1).Mould growth was thus not an issue during product storage,possibly thanks to the formation of an anaerobic atmosphere due to the

intense pineapple tissue respiration within the sealed pack.To this regard,oxygen resulted completely consumed within 5days of storage,both in untreated and UV-C light treated pineapple sticks trays (Fig.3).This result suggests that a 200J/m 2UV-C light treatment did not modify the physiological respiration of the packaged fresh-cut fruit.Similar results were obtained by Chonhenchob et al.(2007),who observed a rapid consumption of head space oxygen of fresh-cut pineapple packaged in PET trays stored for 6days.

Complete depletion of oxygen within the sealed trays (Fig.3)

would favour lactic acid bacteria development during storage (Ahvenainen,1996).As expected,lactic acid bacteria count increased during storage and,after 15days,reached 4.3±0.2Log CFU/g in untreated pineapple sticks and 2.5±0.4Log CFU/g in UV-C light-treated ones.As previously observed for yeasts (Fig.2),also lactic acid bacteria counts of UV-C light treated samples resulted about 2Log lower than those of untreated ones.These data indicate a higher microbial stability of the UV-C light treated pineapple

sticks during storage.This result apparently contradicts data

showing no decontamination effect just after exposure of pineapple

sticks to UV-C light (Tables 1and 2).Due to the peculiar structure of

aggregate fruitlets in pineapple,microbial contamination is not limited to the stick surface.However,microbial analyses were performed on the entire fruit tissue and not only on a thin surface layer.It is thus reasonable that the eventual decontamination effect of UV-C light on pineapple surface was hidden by the overall mi-crobial count of the entire tissue (Tables 1and 2).When the product

Table 2

Log reductions in yeast count of pineapple sticks exposed to increasing ?uence of UV-C light.

Fluence (J/m 2)

Yeast log reductions ±SD

2000.63±0.25a 4000.86±0.85a 6000.66±0.27a 4800

0.70±

0.67a

a

Differences between means indicated by the same letter are not statistically different (*p <0.05).012345

60

5

10

15

Y e a s t s (L o g C F U /g )

Time (days)

Fig.2.Yeast counts during storage at 6 C of untreated (____)and 200J/m 2UV-C light treated (——)pineapple sticks packed in PET/EVOH/PE trays.

05101520

250

1

2

345

6

7

G a s c o n c e n t r a t i o n (%)Time (days)

Fig.3.Head space oxygen concentration during storage at 6 C of untreated (____)and 200J/m 2UV-C light treated (——)pineapple sticks packaged in PET/EVOH/PE trays.

L.Manzocco et al./LWT -Food Science and Technology 65(2016)1138e 1143

1141

刚切的菠萝菌落数变化大

UV-C 剂量增加对杀灭酵母菌霉菌

效果没有显著影响

类似的

发挥

抑制

UV-C 辐照剂量超过抑制表面菌落生长的所需剂量，过量UV-C 辐照对内部微生物细胞没有影响

高剂量影响品质

先辐照后包装

透射比

可忽略模拟

恒定不变的

消耗

有助于

矛盾

净化

特殊的

集合

果眼污染

was then stored,the effect of

inactivation of surface micro ?ora

became evident (Fig.2)allowing to clearly discriminate between UV-C light treated and untreated samples.UV-C light had no effect

on internalised micro ?ora but was probably able to inactivate

surface microorganisms responsible for the hygienic quality depletion during storage.

Additional trials were performed to evaluate if UV-C light pro-moted a different evolution of the quality properties of fresh-cut pineapple during storage due to the different microbial growth (Fig.2)and the physiological response of fruit tissue to the radiation stress (Chonhenchob et al.,2007;Siddiqui,Chakrabotry,Ayala-Zavala &Dhua,2011).Evolution of colour,consumer preference

and presence of off-odours was assessed during refrigerated stor-age of untreated and UV-C light treated pineapple sticks.Results of colour analyses of pineapple sticks are shown in Table 3.It is well

known that UV-C light could induce undesired surface browning in

many fruits and vegetables (G o

mez,Alzamora,Castro,&Salvatori,2010).However,no signi ?cant trend in redness and yellowness of the pineapple sticks was observed during storage in all samples.Luminosity signi ?cantly decreased in untreated samples stored for more than 10days.A slight decrease of L*value was observed also

in UV-C light treated pineapple sticks.Other authors reported sig-ni ?cant changes in colour,associated with occurrence of trans-lucent areas,dry surface appearance or browning even in the absence of UV-C light treatments (Marrero &Kader,2006;Montero-Calder ?n,Rojas-Graü&Martín-Belloso,2008).This result suggests that changes in the appearance of fresh-cut pine-apple during storage would be attributable to the intrinsic vari-ability of the fruits,rather than to the application of UV-C light.

UV-C light treatment could promote changes in volatile composition of fresh-cut pineapple,altering the ?avour of the

product (Lamikanra &Richard,2004).To verify if UV-C light altered pineapple odour,sensory analysis involving consumers was per-formed.No signi ?cant perception of off-odours was detected dur-ing 15day storage in both untreated and UV-C light treated pineapple sticks (data not shown).This result suggests that UV-C

light did not induce a perceivable alteration in pineapple sticks odour.However,the high microbial load would be expected to promote off-odours development in untreated pineapple sticks.

The absence of ?avour changes could be explained considering that fruit ripening proceeded during storage,possibly masking the

eventual presence of off-odours.Difference in preference between untreated and light treated samples was also performed by a pair comparison preference test carried out on consumers.UV-C light treated samples were always preferred to the control ones and equally preferred to the just prepared pineapple sticks up to 6days (Fig.4).Although UV-C light did not affect colour and ?avour of

fresh-cut pineapple,the treatment allowed product quality reten-tion over a longer storage period,probably due to the lower mi-crobial growth of the product as compared to untreated samples.It could be hypothesized that UV-C light treatment leads to a signif-icant extension of shelf life of fresh-cut pineapple sticks well

beyond the 3e 5days nowadays indicated by the producers for this fresh-cut fruit category.

3.3.Effect of UV-C light treatment applied after packaging in PA/PE

pouches

The ef ?cacy of UV-C light treatment in extending the shelf life of

pineapple sticks could be impaired by the occurrence of post-treatment contamination before packaging.Packaging the pine-apple sticks in a highly UV-C light transparent material before UV-C light treatment could signi ?cantly reduce this risk.To verify this hypothesis,PA/PE ?lm was selected since it is characterised by an

80%UV-C light permeability and has been previously used to package different samples before UV-C light treatment (Manzocco,Panozzo,&Nicoli,2012).Pineapple sticks were thus individually

packaged into PA/PE pouches and exposed to 200J/m 2UV-C light.Additional samples were prepared by UV-C light treating pineapple sticks before packaging into PA/PE pouches.Differently from the trays,each pouch contained only one pineapple stick.Samples were then stored at 6 C up to 15days and analysed for total viable bacteria,yeast,mould and lactic acid bacteria counts.As shown in Fig.5,yeast counts of pineapple sticks submitted to UV-C light treatment before packaging into PA/PE pouches showed the same

behaviour already observed in the case of PET/EVOH/PE trays (Fig.2).Also mould and lactic acid bacteria counts showed the same behaviour observed in PET/EVOH/PE trays (data not shown).The similar performance of the plastic materials was also con ?rmed by head space analysis showing that oxygen in the pouches was

completely consumed within 5days,mimicking the trend observed for the PET/EVOH/PE trays (Fig.3).No signi ?cant differences were detected in yeast (Fig.5),mould and lactic acid bacteria counts of pineapple sticks exposed to UV-C light after packaging into PA/PE pouches as compared to samples packaged before UV-C light treatment.Although the lower radiation ?uence (80%)on the

Table 3

L*,a*,b*Hunter scale parameter values of untreated (Control)and 200J/m 2UV-C light treated pineapple sticks packaged in PET/EVOH/PE trays during storage at 6 C.Sample

Colour parameter

Time (days)0

371015Control

L*73.9±2.1a 73.1±1.1ab 73.6±1.4ab 70.5±1.8c 70.5±1.7c a*à3.4±0.6a à4.4±0.4a 3.9±0.6a à4.3±0.5a à3.9±0.6a b*31.5±1.4b 29.1±1.6c 28.6±2.5c 26.9±1.3c 29.0±2.1c UV-C light (200J/m 2)

L*73.0±0.8ab 72.3±2.2ac 74.3±1.2a 71.4±1.5bc 71.4±1.9bc a*à4.1±0.5a à4.3±0.3a à2.7±1.9a à3.3±0.4a à3.5±0.2a b*

34.2

±1.4a

32.4

±1.6ab

22.8

±1.2d

28.2

±1.8c

28.5

±1.4c

a,b,c,d For each colour parameter,means indicated by the same letter are not signi ?cantly different (*p <0.05).

0204060801000

2

468

10

P r e f e r e n c e (%)

Time (days)

Fig.4.Preference (%)of untreated (____)and UV-C light treated (——)pineapple sticks stored at 6 C up to 10days.

L.Manzocco et al./LWT -Food Science and Technology 65(2016)1138e 1143

1142

失活

表面微生物菌群

明显的差别

内部

卫生

消耗

补充实验：UV-C 是否通

过影响微生物生长及果

实组织对辐照的生理反

应使鲜切菠萝贮藏期间品质性质产

生不同演变引起表面褐变

光度

UV-C 处理减缓L 下降

半透明

固有的

可归于鲜切菠萝外表变化归因于果实自身而非UV-C 处理

挥发性

查证

知觉 感觉

可感知的

香味减少是果实贮藏时成熟所导致

掩盖最终产生的异味

保留

先包装后辐照

功效

减弱

污染

渗透性以前

保鲜袋

托盘

包装前进行UV-C 辐照的菠萝条的酵母菌数霉菌数及乳酸菌数与图2趋势相同

模仿

包装前后辐照对酵母菌霉菌乳酸菌数量无显著差异

product surface due to the screening effect of the packaging ma-terial,pineapple sticks packaging before exposure to UV-C light did

not impair the

decontamination ef ?cacy of the treatment.Samples were submitted to analyses of colour,off-odours perception and consumer preference.No signi ?cant differences in the evolution of these properties were detected in the samples packaged in PA/PE pouches before UV-C light treatment as compared to those

observed in the samples exposed to UV-C light before packaging in both trays and in pouches.

4.Conclusions

UV-C light treatments were shown to exert a high potential for shelf life extension by decreasing microbial growth during storage.

The treatment resulted ef ?cacious even when the product was packaged before exposure to light,potentially allowing to prevent post-treatment contaminations during processing.However,it is evident that this goal requires packaging single fruit sticks to avoid shadowing effects among food items.In addition,it is necessary to

adopt unprinted packaging materials allowing transmittance of UV-C light and consider the application of a label or a secondary printable package to provide the consumer with the necessary information.Acknowledgement

This research was supported by Ministero dell ’Istruzione,dell ’Universit a e della Ricerca (Prot.957/ric 28/12/2012)“Long Life,High Sustainability ”.Project 2012ZN3KJL.References

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01234560

5

1015

Y e a s t s (L o g C F U /g )

Time (days)

Fig.5.Yeast counts during storage at 6 C of untreated (____)and 200J/m 2UV-C light treated (——)pineapple sticks individually packaged in PA/PE pouches before (closed symbols)or after (open symbols)UV-C light exposure.

L.Manzocco et al./LWT -Food Science and Technology 65(2016)1138e 11431143

包装材料的屏蔽效应使辐照剂量降至80%

包装后辐照的净化能力无差别

保鲜袋包装后辐照与辐照后托盘或保鲜袋包装在颜色、异味、消费偏好上无区别

发挥

有效的

透射

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