Effects of modified atmosphere and vacuu

Short communicationEffects of modified atmosphere and vacuum packaging on microbiological and chemical properties of rainbow trout Oncorynchus mykiss fillets Xq kriye Arashisara, Olcay H

Short communication

Effects of modified atmosphere and vacuum packaging on microbiological and chemical properties of rainbow trout

(Oncorynchus mykiss) fillets

Xq kriye Arashisara, Olcay Hisara, Mqkerrem Kayab,*, Telat Yanika

a

Agricultural Faculty Fisheries Department, Atatu¨rk University, Erzurum 25240, Turkey

b

Agricultural Faculty Food Engineering Department, Atatu¨rk University, Erzurum 25240, Turkey Received 16 September 2003; received in revised form 7 May 2004; accepted 26 May 2004

Abstract

Microbial (psychrotrophic, mesophilic aerobic bacteria and Enterobacteriacae counts), and chemical analysis [pH, total volatile bases nitrogen (TVB-N), lipid oxidation (Thiobarbituric acid reactive substance, TBARS)] of rainbow trout (Oncorynchus mykiss) fillets in air (control), vacuum and modified atmosphere packaging (MAP) with various gas mixtures conditions at 4F1 8C were determined The gas mixtures evaluated were 100% CO2, 2.5% O2+7.5% N2+90% CO2and 30%

O2+30% N2+40% CO2 Psychrotrophic bacteria count was above 1107 cfu/g on the 12th day in 100% CO2 However; mesophilic bacteria count was below 1106 cfu/g at the end of the 14-day storage period Enterobacteriaceae count was significantly lower in samples packaged with MAP Lipid oxidation increased rapidly after 6 days of storage in the samples containing 30% O2 While minimum TBARS values were recorded in fillets containing 100% CO2and vacuumed fillets, the lowest TVB-N values were obtained in fillets with 100% CO2

D 2004 Published by Elsevier B.V

Keywords: Rainbow trout; Modified atmosphere packaging; Specified spoilage level; Psychrotrophic bacteria; TBARS

1 Introduction

Fresh fish are highly perishable products due to

their biological composition Spoilage of fish muscle

results from changes brought about by biological

reactions such as oxidation of lipids, reactions due to activities of the fish’s own enzymes, and the metabolic activities of microorganisms These activ-ities lead to a short shelf life in fish and other seafood

1996; Gram and Huss, 1996; Gobantes et al., 1998) MAP offers multiple advantages to the fish industry and the consumer Various atmospheres have been examined in fish packaging (Parkin et al., 1981; Barnett et al., 1987; Stammen et al., 1990; Farber,

0168-1605/$ - see front matter D 2004 Published by Elsevier B.V.

doi:10.1016/j.ijfoodmicro.2004.05.024

* Corresponding author Agricultural Faculty Food Engineering

Department, Atatqrk University, Erzurum 25240, Turkey Tel.: +90

442 231 22 04; fax: +90 442 236 09 58.

E-mail address: mkaya@atauni.edu.tr (M Kaya).

1991; Reddy et al., 1994; Randell et al., 1995; Randell

et al., 1997; Gimenez et al., 2002; Sivertsvik et al.,

2002)

Oxygen, nitrogen and carbon dioxide are the most

Gimenez et al., 2002) Oxygen causes oxidative

rancidity in fatty fish, stimulates growth of aerobic

bacteria and inhibits growth of strictly anaerobic

bacteria Nitrogen delays oxidative rancidity and

inhibits the growth of aerobic microorganisms by

displacing the oxygen in packs (Stammen et al., 1990;

Farber, 1991; Philips, 1996; Church, 1998) Since,

carbon dioxide acts as an antimicrobial agent (

Stam-men et al., 1990), it inhibits the growth of

micro-organisms during the logarithmic phase and extends

Church, 1994; Philips, 1996) Different concentration

of CO2has some effects on bacteria (Church, 1998)

Statham (1984)explains that bweak acids are known

to have antimicrobial activity in their undissociated

form; therefore carbonic acid is unique as a microbial

inhibitor since at pH values near neutrality at least one

half of the acid is in the undissociated form The pK

value for the first dissociation is 6.37 yielding

hydrogen and bicarbonate ionsQ

It was reported that high concentrations of CO2for

fish should be avoided since it dissolves into the fish

However, the use of a MAP with an enhanced carbon

dioxide level has been also shown to extend the shelf

life of fresh fishery products by retarding microbial

growth (Farber, 1991; Reddy et al., 1994; De La Hoz

et al., 2000; Emborg et al., 2002) Gas mixtures

containing CO2and O2have also extended the shelf

Debevere and Boskou, 1996; Pastoriza et al 1996)

significantly inhibited the microbial growth in cod

Stenstro¨m (1985), 35–100 CO2and O2or N2mixtures

in packed shrimp (Lannelongue et al., 1982) and 50–

100% CO2also greatly inhibited the microbial growth

and Matches 1984)

It has been recommended that gas mixtures for the

(Cann et al., 1983; Cann et al., 1984, Church,

Stenstro¨m (1985) Considering this fact, the establish-ment of the gas mixtures related to the target product

is very important Thus, the present study was undertaken to determine the effects of vacuum and MAP atmospheres with various gas mixtures, 100%

CO2, 2.5% O2+7.5% N2+90% CO2and 30% O2+30%

mesophilic aerobic bacteria and Enterobacteriaceae counts), and chemical changes [pH, total volatile bases nitrogen (TVB-N), lipid oxidation (TBARS)] of rainbow trout (Oncorynchus mykiss) fillets during storage at 4F1 8C

2 Materials and methods 2.1 Preparation and storage of samples Fresh water rainbow trout with an average weight

of 200 g reared in a farm, located in Research and Extension Center of Fisheries Department in Agricul-tural Faculty at Atatqrk University in Erzurum, were transferred to the Meat Processing Laboratory in Food Science Department, and decapitated and filleted by hand Two fillets were obtained from each fish by removing the head and bone of fish The fillets were divided into five groups and packaged in five different atmospheres by using a Multivac packaging machine (Multivac A 300/16, Sepp Haggenmuller, D 87787 Wolfertschwenden, Germany) Packaging material was a film bag with 1525 cm OPA/EVOH/PE (Oriented Polyamid-EVOH-Polyetilen, UPM-Kym-mene Walki Films, Finland) and with low gas permeability (oxygen transmission rate of 5 cm3/m2/ days atm at 23 8C, nitrogen transmission rate of 1

water vapour transmission rate of 15 g/m2/days atm at

38 8C) The final gas/product ratio in all pouches was about 2:1 (v/w) for MAP conditions The composition

partner of PRAXAIR, Danbury) in the present study The fillets were inserted in film bags and sealed after removal of air in vacuum packaging The fillets were placed in film bags and sealed without removal

of air for the control group All of the fillets were

stored at 4F1 8C for 14 days The fillets in duplicate

were subjected to microbial, physical and chemical

analyzes on the 0, 2, 4, 6, 8, 10, 12 and 14thdays of

the storage period

2.2 Microbial analysis

Tissue samples were taken to determine total

aerobic bacteria and Enterobacteriaceae counts from

each of two different fish stored under five different

aseptically and homogenized for 1 min in a Stomacher

400 (Lab Stomacher Blander 400-BA7021,

Seward-medical) bag containing 0.85% NaCl solution Further

decimal dilutions were made and then 0.1 ml of each

dilution was pipetted onto the surface of plate count

agar (PCA, Merck) PCA plates were then incubated

for 7 days at 10 8C for psychrotorophic bacteria count

and for 2 days at 37 8C for mesophilic bacteria count

Enterobacteriaceae was determined in

Violet-Red-Bile-Glucose agar (VRBG-agar, Merck) plates

incu-bated anaerobically at 30 8C for 2 days All counts

were expressed as log10cfu/g.McMeekin et al (1993)

reported that usually a bspecified reactive levelQ should

be used to show unacceptable levels in food products,

therefore, a horizontal line was used in each figure to

show these spoilage levels in the present study

2.3 Lipid oxidation

Lipid oxidation, measured as Thiobarbituric acid

reactive substances (TBARS) values, was determined

2.4 Total volatile base nitrogen (TVB-N)

A vapour distillation method was used for total

Anony-mous, 1988) The results were expressed as mg

TVB-N/100g

2.5 pH value

The pH values were recorded by using a Schott

model pH meter (Schott, Lab Star pH) after

distilled water

2.6 Statistical analysis Psychrotrophic, mesophilic aerobic bacteria, Enter-obacteriacae counts, pH, total volatile bases nitrogen (TVB-N) and lipid oxidation (TBARS) of rainbow trout fillets in air (control), vacuum and modified atmosphere packaging (MAP) with various gas mixtures conditions at 4F1 8C were determined Data were checked for normal distributions with normality plots prior to one-way analysis of variance (ANOVA), and followed by Duncan’s multiple range test to determine significant differences among means at a=0.05 level (Duncan, 1971)

3 Results and discussion 3.1 Microbiological analysis The changes in mesophilic and psychrotrophic bacteria counts throughout the storage of refrigerated rainbow trout fillets packaged in air, vacuum, 100%

CO2, 2.5% O2+7.5% N2+90% CO2and 30% O2+30%

mesophilic and psychrotrophic bacteria count in fillets under different atmosphere conditions increased with length of storage at 4 8C After 6 days in air, packaging psychrotrophic and mesophilic bacteria

respectively However, growth of aerobic bacteria in

during storage, psychrotrophic bacteria count reached

count reached 105cfu/g at 14th day of storage Effects

lower than that of the 100% CO2(Fig 1a and b) An explanation for this situation could be the high

fungustatic properties It is known that antimicrobial effect of CO2 increases depending on the solubility which is increased by the low water temperature (Stammen et al., 1990; Ashie et al., 1996) and CO2

prolongs lag phase of bacterial growth and increases generation time (Philips, 1996) Delaying of bacterial growth in fish fillets packaged in MAP including

various CO2contents was also previously reported in

some studies i.e in cod (Cann et al., 1983), in rainbow

Gimenez et al., 2002), in sole (Lopez-Galvez et al.,

1998) and in herring fillets (Randell et al., 1997)

The effect of storage time x atmosphere interaction

on Enterobacteriaceae count was important

( pb0.05) Enterobacteriaceae count was below

and 90% CO2on day 8 It reached to 105–106cfu/g in

control and vacuum packaged samples in day 6 of

storage time MAP caused a significant decrease in

Enterobacteriaceae count in fillets and the lowest

average was obtained in fillets packaged under 100%

CO2 Enterobacteriaceae counts in fillets packaged

40% CO2, respectively (Fig 1c) Similarly,Stenstro¨m

(1985)found that CO2 concentration was an

impor-tant factor in cod fillets stored at 2 8C in MAP and

effec-tively Some other studies have also shown that

Enterobacteriaceae family species in Sole fillets (Lopez-Galvez et al., 1998), in hake steaks (Ordonez

et al., 2000) and in salmon steaks (De La Hoz et al.,

delayed spoilage of fresh seafood by inhibiting psychrotrophic, aerobic and Gram-negative bacteria (Finne, 1982)

3.2 TVB-Nitrogen Storage timeatmosphere interaction had

values were above 20 mg/100 g in all groups except in

reached above 25 mg/100 g in all groups except the

Finally, they reached above 35 mg/100 g in all samples at day 14 The findings of the present study suggested that 25 mg/100 g TVB-N level in tissue can

Fig 1 Changes in psychrotrophic (a), mesophilic (b), Enterobacteriaceae (c) counts, TVB-N levels (d), TBARS levels (e) and pH values (f) on rainbow trout fillets storaged in different atmospheres at 4 8C Upper areas of horizontal lines are unacceptable in each figure.

be considered as the highest acceptable level for

rainbow trout similarly toGimenez et al (2002)

3.3 Lipid oxidation

Oxidative rancidity may become a problem if

higher than normal levels of oxygen are used (Finne,

1982).Stammen et al (1990) reported that rancidity

due to oxidation of polyunsaturated fatty acids

(PUFA) in some fish may be a problem in modified

atmosphere with O2 No significant differences were

group with respect to TBARS value The highest

average TBARS value was obtained from fillets

packaged with 30% O2(Fig 1e) Similar results were

packaged in MAP.Gimenez et al (2002)reported that

lipid oxidation was significantly higher in gas

pack-ages with 20% and 30% O2than in those with 10% O2

in rainbow trout fillets There were fluctuations in

TBARS values, the possible reason for that may be

that the different modified atmospheres could produce

different oxidation products (Raharjo et al., 1993; Doe

et al., 1998)

Storage timeatmosphere interaction had

TBARS values increased rapidly after day 6 in gas

higher TBA values were determined from 40%

40% CO2+60% N2) in swordfish steaks packed under

different gas atmospheres

3.4 pH

Statham (1984) reported that pH values were

slightly reduced in fish flesh with the dissociation of

carbonic acid in general Storage timeatmosphere

interaction did not affect significantly pH values (Fig

1f) No significant differences were observed among

pH values determined from different atmosphere

conditions SimilarlySilva and White (1994)did not

find significant differences between packing

Barnett et al (1982) reported also no significant

changes in pH values of salmon flesh reared in sea

storage time on pH was significant ( pb0.05) The highest average pH (6.47) was obtained on day 12 (Fig 1f) All of the pH values except control group were in accordance with the findings ofGimenez et al (2002)

3.5 Conclusions

Fig 1a–c shows clearly that bacterial growth is increasingly depressed by higher concentrations of

CO2 Fig 1e shows that oxidation products are depressed by lower concentrations of oxygen

recom-mended for lean fish, it has been found to be the worst choice for fresh water rainbow trout stored at 4 8C This is because of the increased oxygen It is not surprising that it is worse than air which has 20% oxygen If much of the CO2becomes dissolved in the flesh the atmosphere surrounding the pack will have

an even higher concentration of O2and N2 than the original mixture

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