EFFECT OF MODIFIED ATMOSPHERE PACKAGING

EFFECT OF MODIFIED ATMOSPHERE PACKAGING ON CHEMICAL,TEXTURAL,MICROBIOLOGICAL AND SENSORY QUALITY OF SEER FISH(SCOMBEROMORUS COMMERSON) STEAKS PACKAGED IN THERMOFORMED TRAYS AT0–2C POULOSE YESUDHASON1,TERALANDUR KRISHNASWAMY SRINIV ASA GOPAL,CHANDRAGIRI NARAYANARAO RA VISHANKAR, KUTTANAPPILLY VELAYUDHAN LALITHA and

KESA V AN NAIR ASHOK KUMAR

Central Institute of Fisheries Technology

Matsyapuri po,Willingdon Island,Cochin-29,Kerala,India

Accepted for Publication July19,2008

ABSTRACT

The effect of modi?ed atmosphere on chemical,textural,microbiological and sensory quality of seer?sh(Scomberomorus commerson)steaks stored at0–2C for23days was studied.Of the chemical indicators of spoilage, signi?cant differences(P<0.05)in trimethylamine and thiobarbituric acid values were observed between air-and modi?ed atmosphere(MA)-packaged samples.Seer?sh under MA was acceptable on the basis of sensory and microbiological parameters even though the K value was more than95%, indicating that K value was not a suitable quality indicator.Based on the inosine to hypoxanthine observed in this trial,seer?sh was classi?ed as hypoxanthine producers.Bacterial counts of air-packaged seer?sh were always higher than MA-packaged samples.Based on sensory score and micro-biological data,the shelf life of?sh steaks packaged in MA21days whereas air-stored samples had a shelf life of12days only.

PRACTICAL APPLICATIONS

Modi?ed atmosphere packaging(MAP)techniques have recently become more common because of consumer demands for fresh foods with a prolonged shelf life.MAP is a promising technique for the preservation of seafood as it gives better shelf-life extension compared to icing.The present work deals about preservation of seer?sh steaks in ready-to-cook form under60% 1Corresponding author.TEL:+91-484-2666-880,FAX:+91-484-2668-212;EMAIL:yesucift@ https://www.wendangku.net/doc/024357945.html,

Journal of Food Processing and Preservation33(2009)777–797.

DOI:10.1111/j.1745-4549.2008.00311.x777?2009The Author(s)

Journal compilation?2009Wiley Periodicals,Inc.

778P.YESUDHASON ET AL.

CO2:40%N2at0–2C,and the effect of MAP for increasing shelf life.The study has clearly shown that preservation of seer?sh under MAP have more shelf life than in air.The extension of shelf life by using MAP of seer?sh could be commercially exploited.Moreover,as seer?sh has good demand from consumers,a proper preservation technique in the form of ready-to-cook?sh suggested in this paper is highly relevant.

INTRODUCTION

Fish is one of the most highly perishable food products,and the shelf life of such products is limited in the presence of normal air by the chemical effect of atmospheric oxygen and the growth of aerobic spoilage microorganisms. Modi?cation of the atmosphere within the package by decreasing the O2 concentration,while increasing the content of carbon dioxide and/or nitrogen, has shown to signi?cantly prolong the shelf life of perishable food products at chill temperature(Parry1993).Modi?ed atmosphere packaging(MAP),along with refrigeration,have become increasingly popular preservation techniques, which have brought major changes in storage,distribution and marketing of raw and processed products to meet consumer demands.The MAP system could provide further improvement in seafood shelf life,sensory quality and product range.Consumer demands for fresh and convenient foods free of chemical preservation has led to the use of MAP,and this technique may also reduce wastage and extend the shelf life of seafoods.The use of MAP to store food products can increase shelf life up to fourfold,which reduces economic loss,allows for longer distribution distances and supplies a better quality product(Farber et al.1990).MAP,utilizing combinations of CO2,N2and O2, has become common in many countries for both storage and retail display of meat.Studies have shown that MAP,in combination with icing,improves the shelf life considerably(Fey and Regenstein1982;Dalgaard et al.1993;Gopal et al.1996).The effect of MAP on the growth of microorganisms(Enfors and Molin1980;Hintlian and Hotchkiss1987;Pintado and Malcata2000),and MAP’s ability to lengthen the shelf life of several perishable products,such as meat,poultry,?sh and whey cheese have been studied(Wolfe1980;Daniels et al.1985;Hintlian and Hotchkiss1987;Pintado and Malcata2000).Most of the works have been reported by adopting MAP for temperate water?sh (Pastoriza et al.1998;Ozogul et al.2000;Arashisar et al.2004).However, collective works on various quality aspects of modi?ed atmosphere(MA)-packaged marine tropical?sh under refrigerated storage are found to be less.

In India,research on MAP of freshwater as well as marine?sh were carried out(Gopal et al.1986,1990,1996;Lalitha et al.2005).However, limited information is available in the literature on the preservation of seer?sh,

despite the commercial importance of these marine ?sh species.Seer ?sh belongs to the family Scombridae and are one of the commercially important marine pelagic ?n?sh resources of India of high commercial value.Since seer ?sh grow to a large size and their meat quality is of high grade,they are in great demand all over the country.Shenoy and James (1976)studied the spoilage of spotted seer ?sh during ice storage and Rajesh et al.(2002)studied the storage characteristics of seer ?sh under vacuum packaging.However,more informa-tion on the use of MAP and its effect on chemical,textural,microbiological and sensory quality of seer ?sh is needed.The main objective of this study was to determine the effect of MAP using thermoformed trays on the shelf life of seer ?sh (Scomberomorus commerson )steaks by monitoring physical,chemi-cal,microbiological and sensory quality during storage at 0–2C.

MATERIALS AND METHODS

Fish Handling,Packaging and Storage Conditions

Fresh seer ?sh (https://www.wendangku.net/doc/024357945.html,merson )of average weight 2–2.5kg were obtained from the Fort Cochin landing center in Kerala,India.After washing with clean water,the ?sh were properly iced,with ?ake ice ratio of 1:3(w/w)in a rectangular,insulated polystyrene box and transported to the laboratory.Once at the laboratory,the ?sh were beheaded,gutted and washed with potable water and cut into steaks of thickness of 1.8–2cm and modi?ed atmosphere packaged by using a packaging machine (Dyno 500VG,Dynopack,Kristian-sand,Norway).Seer ?sh steaks weighing an average 100–110g were pack-aged with high-density polyethylene thermoformed trays that had a capacity of 260mL with dimensions of 540￥400￥430mm and thickness of 0.5mm.The tray had O 2permeability of 85cc/m 2/atmosphere/24h/room temperature (28–32C)and CO 2permeability of 255cc/m 2/atmosphere/24h/room tempera-ture.Trays were sealed with a ?exible packaging ?lm of 12-m m polyester laminated with 75-m m polyethylene and had an O 2permeability of 65cc/m 2/atmosphere/24h/room temperature and a CO 2permeability of 195cc/m 2/atmosphere/24h/room temperature (28–32C).High density polyethylene (HDPE)trays were sanitized by giving a dip treatment for 4–5min in 2ppm chilled chlorinated water.The ratio between the volume of the gas and weight of seer ?sh steaks (G/P ratio)was 2:1(v/w).Food grade CO 2and N 2gas mixture 60%CO 2:40%N 2was used to pack the product since a large number of studies have recommended the use of 60%CO 2:40%N 2for fatty ?sh.Gas composition was adjusted by using a gas mixer (MAP Gas Mix 9000-3/150v,PBI Dansensor,Ringsted,Denmark).The control (air-packaged)samples were packaged as well.All samples were stored in ice at 0–2C until the end of the

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780P.YESUDHASON ET AL.

storage(23rd day).Analysis was performed immediately after packaging and samples were removed periodically for physical,chemical,microbiological and sensory analysis.All measurements were performed in triplicate,unless otherwise stated.

Headspace Gas Analysis

Headspace gas was monitored at each sampling time in triplicate packs using a gas analyzer(Checkmate9900O2/CO2,DK-4100,PBI Dansensor). Three mL of gas was sampled from the package headspace with a needle and used for analysis.

Physical Analysis

Exudates loss was measured as the percentage loss of seer?sh steaks weight compared with the initial weight(Pastoriza et al.1996).

Texture pro?le analysis(TPA)was performed on seer?sh steaks of 20mm cubic using a food texture analyzer(Model LRX Plus,Lloyd Instru-ments Ltd,Lloyd Instruments,Hampshire,UK)by compressing them twice with5-point pin probe.Uniform samples were allowed for a compression of 40%with a trigger force of0.5kg at a speed of12mm/min using a50-N load cell.From the double compressions,parameters such as hardness I is the peak force during the?rst compression cycle(kgf);hardness II is the peak force during the second compression cycle(kgf);cohesiveness is the ratio of positive force area during the second compression to that during the?rst compression; springiness is the height recovered by the sample during the time elapsing between the end of the?rst compression cycle and the start of the second cycle (mm),chewiness is the product of gumminess￥springiness(kgf·mm)and gumminess is the product of hardness￥cohesiveness,were calculated as de?ned in the texture analyzer user manual.

Chemical Analysis

Trimethylamine(TMA)was determined as trimethylamine nitrogen (TMA-N)by microdiffusion method(Conway1962).TMA-N was calculated and expressed in mg/100g of the sample.Thiobarbituric acid(TBA)value was determined according to the method of Tarladgis et al.(1960).TBA value was calculated and expressed in mg malondialdehyde/kg of?sh sample.All deter-minations were performed in triplicate.

The K value is de?ned as the ratio of sum of inosine(HxR)and hypox-anthine(Hx)to the sum of adenosine triphosphate(ATP)and related catabolites(adenosine diphosphate[ADP],adenosine monophosphate[AMP], inosine monophosphate[IMP],HxR and Hx)and expressed as a percentage.

K values were determined from the perchloric acid extract of ?sh meat by the method of Ryder (1985).Nucleotides,namely ATP,ADP,AMP,IMP,HxR and Hx,were analyzed using the high-performance liquid chromatographic method (Ryder 1985).Microbiological Analysis

Samples of seer ?sh steaks (25g)were aseptically removed from each package,and then diluted 10-fold in saline (0.85%NaCl)and homogenized for 60s in a stomacher (Lab Blender 400;Seward Medical,London,UK).The samples were serially diluted and plated onto appropriate media for enumera-tion of total aerobic bacteria and Enterobacteriaceae .Plate count agar (PCA 247940,BBL Difco)was for total aerobic counts by spread plating incubated at 37C for 48h.The violet red bile glucose agar (VRBGA,Oxoid code CM 485)for Enterobacteriaceae counts were incubated at 30C for 24h.The larger colonies with purple halos were counted.Microbiological counts were per-formed in triplicate and expressed as cfu/g.Sensory Evaluation

Sensory analysis was performed by a panel of seven untrained panelists.The panel assessed different attributes like appearance,odor,?avor and texture.Each sample was classi?ed using a 10-point hedonic scale,with 4being the acceptability limit.Special attention was given to the color and the presence of exudates in the pack prior to opening and the assessment of abnormal odors at the moment of opening the pack.Samples were cooked in 1.5%brine for 10min (Pastoriza et al.1998).Stick water was drained and allowed to cool to room temperature.Panelists were asked to score the odor,?avor and texture of ?sh,and then overall acceptance was determined.The score of seven assessors were averaged to give the panel mean score.Statistical Analysis

Results of chemical,microbiological and sensory analysis are reported as mean value ?standard deviation.Statistical analysis was done to ?nd the signi?cance difference by analysis of variance using SPSS 10.0(SPSS Inc.,Chicago,IL).

RESULTS AND DISCUSSION

Changes in Headspace Analysis

In air-packaged seer ?sh steaks at 0–2C,initial concentrations of CO 2

were 0.9%,but increased signi?cantly (P <0.05)to 11.9%at the 14th day.In

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EFFECT OF MODIFIED ATMOSPHERE PACKAGING ON SEER FISH STEAKS

782P.YESUDHASON ET AL.

samples packaged under60%CO2and40%N2,the level of CO2decreased signi?cantly(P<0.05)from an initial value of60%to22%at the14th day and to an almost constant21%at the end of the storage(23rd day).In the air-packaged sample,the increase in CO2concentration was noticed because of the increase in microbial growth,whereas in MAP initial decrease in60% CO2:40%N2packages was caused by gas being absorbed into the tissue. After that,microbial growth resulted in increased CO2concentration.These results con?rm a previous study by Dufresne et al.(2000).Stier et al.(1981) reported that in salmon?llets stored under60:25:15(CO2:O2:N2),CO2 concentrations declined from60%to20%.This supports our trial of MA with 60%CO2and40%N2,where the CO2concentration was21%at the?nal day of storage.In air-packaged seer?sh steaks at0–2C,the O2concentration was initially21.6%,but drastically reduced to0.080%by day12and remained at 0.076%until the14th day of storage(P<0.05).In seer?sh packaged under MA,the initial level of O2was<1%and changed to0.006%at the rejection day.Statistically signi?cant differences(P<0.05)in the O2concentration were found after the4th day and it was maintained until the end of the storage period.Decrease in O2concentration was reported by Reddy et al.(1996)for tilapia?llets,where the O2concentration dramatically decreased when the storage period increased.Changes in the composition of headspace gases were probably a direct result of postmortem metabolic and microbial processes. Changes in Physical and Chemical Indicators

Exudates loss were found to be zero for air-packaged seer?sh steaks on the4th day,and increased signi?cantly(P<0.05)to0.322on the14th day when sensory rejection occurred(Table1).The MA-packaged samples had no exudates on the4th day and signi?cantly increased and reached the value of 1.92%on the?nal day of storage(P<0.05).Increase in exudates loss was found in all samples,but it was less pronounced in air–packed samples that showed signi?cant differences(P<0.05)compared with MA-packaged samples.It has been found by various authors that,the higher the levels of CO2,the higher the loss of exudation(Pastoriza et al.1996;Masniyom et al. 2002).This may be due to a greater loss of the water-holding capacity of muscle protein at lower pH values.Dalgaard et al.(1993)observed an increase in drip loss during MA storage of cod?llets.Pastoriza et al.(1998)observed increased exudation in MA-packaged?sh after7days of storage.Fey and Regenstein(1982)found increased drip losses for red hake,chinook salmon and to a lesser extent,sockeye salmon stored in60%CO2,21%O2and19%N2 compared to air-packaged products.

Initial hardness I value for seer?sh was2.62kgf and hardness of the two types of samples did not change much after an initial decrease at day4and

T A B L E 1.R E S U L T S O F H E A D S P A C E G A S A N A L Y S I S ,E X U D A T E S L O S S ,T B A A N D T M A O F S E E R F I S H S T E A K S D U R I N G S T O R A G E A T 0–2C F O R 23D A Y S

D a y s o f s t o r a g e a t 0–2C

A s s a y P a c k 04

8

12141821

23

C O 2

A i r 1.9?0.2c

2.1?0.2c

6.06?0.55b

11.4?0.9a

11.9?0.9a

–A

–A

–A

M A P 60.0?0.4a 26.5?3.3b

22.9?0.4c 23.7?1.9c 22.0?1.5c 22.2?1.4c

21.3?0.3c

21.0?0.4c

O 2

A i r 21.6?0.52a

19.3?1.90b

11.4?0.6c 0.08?0.03d 0.07?0.001d –A –A

A M A P 0.85?0.01a 0.85?0.02a 0.001?0.001b 0.001?0.001b 0.001?0.001b 0.003?0.003b 0.001?0.001b 0.006?0.005b

E x u d a t e L o s s A i r 0.0?0.00b 0.0?0.00b

0.0?0.00b

0.20?0.18a

0.32?0.05a

–A

–A

–A

M A P 0.0?0.00d 0.0?0.00d 0.50?0.15c

0.66?0.07b 0.69?0.10b

1.87?0.12a 1.87?0.05a

1.92?0.34a

T B A

A i r 0.08?0.001d 0.09?0.001d

1.03?0.010c

1.84?0.002b

2.94?0.041a –A

–A

–A

M A P 0.08?0.001d 0.09?0.001d 0.79?0.002c

0.98?0.000c

1.35?0.016b 1.85?0.43a

1.89?0.03a

2.07?0.02a

T M A

A i r 2.73?0.15e

5.46?0.23d

8.26?0.23c

11.8?0.20b

13.8?0.23a

–A

–A

–A

M A P 2.73?0.15e 2.73?0.11e

2.83?0.05e 2.83?0.05e 4.93?0.05d

5.60?0.15c 11.3?0.23b

11.7?0.05a

T h e d a t a a r e t h e a v e r a g e ?s t a n d a r d d e v i a t i o n v a l u e s .M e a n s i n t h e s a m e c o l u m n b e a r i n g d i f f e r e n t s u p e r s c r i p t s d i f f e r s i g n i ?c a n t l y .A :N o t e v a l u a t e d ,r e j e c t e d b a s e d o n s e n s o r y s c o r e .T B A ,t h i o b a r b i t u r i c a c i d ;T M A ,t r i m e t h y l a m i n e ;M A P ,m o d i ?e d a t m o s p h e r e p a c k a g i n g .

783

EFFECT OF MODIFIED ATMOSPHERE PACKAGING ON SEER FISH STEAKS

reached 1.82kgf on the 14th day for air-packaged samples (Fig.1a).In MA-packaged samples,after initial decrease,storage time did not effect over the storage period and when the ?sh was considered unacceptable on day 23,the hardness of ?sh was 2.08kgf.Samples stored in air packs were

very

00.511.522.533.50

2

4

6

8

1012141618202224

Storage days

H a r d n e s s I (K g f )

a

00.511.522.533.544.550

2

4

6

8

1012141618202224Storage days

H a r d n e s s I I ( K g f )

b

FIG.1.CHANGES IN HARDNESS I (a)&HARDNESS II (b)IN SEER FISH STEAKS STORED UNDER AIR AND MODIFIED ATMOSPHERES (60%CO 2:40%N 2)IN

THERMOFORMED TRAYS AT 0–2C FOR 23DAYS

Vertical bars represent standard deviation.Where bars are not visible,determinations

are within the size of symbols.

784P.YESUDHASON ET AL.

similar to MA-packaged samples except at day 14.As in the case of hardness I,the value for hardness II decreased signi?cantly on day 4and reached 1.38kgf on the 14th day of storage for air-packaged ?sh (P <0.05).Samples packaged under MA showed signi?cant difference on the 4th day and the values remained unchanged signi?cantly throughout the storage period,which ended on the 23rd day with the value 1.63kgf (Fig.1b).In contrast,Morzel et al.(2000)observed that hardness (measured by TPA)decreased regularly during storage of both fermented and cured salmon.Initial cohesiveness was 0.19.For air-packaged samples,the value declined signi?cantly at day 4and decreased to 0.13kgf (P <0.05)on the 14th day.In MA-packaged samples,the values decreased with ?uctuation and reached the ?nal value of 0.15kgf.Generally,a slight decrease was noticed in all samples (Fig.2a),and the values

0.050.10.150.20.25

Storage days

C o h e s i v e n e s s

a

Storage days

S p r i n g i n e s s (m m )

b

Storage days

C h e w i n e s s ( k g .m m )

c FIG.2.CHANGES IN COHESIVENESS (a),SPRINGINESS (b)AND CHEWINESS (c)IN SEER FISH STEAKS STORED UNDER AIR AND MODIFIED ATMOSPHERES (60%CO 2:40%N 2)IN THERMOFORMED TRAYS AT 0–2C FOR 23DAYS.Vertical bars represent standar

d deviation.Wher

e bars are not visible,determinations are

within the size of symbols.

785

EFFECT OF MODIFIED ATMOSPHERE PACKAGING ON SEER FISH STEAKS

786P.YESUDHASON ET AL.

indicated that there was not much change in?sh muscle during storage.In general,a decreasing trend in the springiness value was observed in both air-and MA-packaged?sh during storage,and the springiness value of air-packed samples were similar to MA-packaged samples except at day14.

As in the springiness value,a decreasing trend in chewiness values was observed in both air-and MA-packaged?sh during storage.Statistically sig-ni?cant differences(P<0.05)were found over the storage period for air-and MA-packaged samples(Fig.2c).Decrease in chewiness values indicates that the?sh muscle becomes soft during storage.

The initial TBA value of air-packaged seer?sh was0.08mg malondialdehyde/kg of?sh and increased signi?cantly(P<0.05)to a value of 2.94mg malondialdehyde/kg of?sh after14days of storage,indicating that lipid oxidation occurred.In seer?sh stored under60%CO2:40%N2,TBA values increased to2.07mg malondialdehyde/kg at the23rd day of storage from its initial value.TBAvalues increased linearly(r2=0.99)in all the samples over the storage period(Table1).Signi?cant differences were found between air-and MA-packaged samples.The results indicated that seer?sh stored in MA were characterized by a rancid taste at the time of sensory rejection on the23rd day when the TBA value was above2.0.TBA values were in good agreement with the sensory scores and can be used as a chemical index in the case of seer ?sh stored under MA.TBA value in the range1–2mg malondialdehyde/kg of ?sh sample is usually taken as the limit of acceptability(Lakshmanan2000). Pastoriza et al.(1996)reported increased TBA values in salmon slices and hake slices stored under MA compared to samples stored under air.Similarly, Masniyom et al.(2002)found samples stored under80%and100%CO2 atmosphere had TBA values of less than4mg malondialdehyde/kg of?sh.

Linear increase(r2=0.99)in TMA content with increasing storage time was seen in both air and modi?ed atmosphere packaged samples and there was a signi?cant(P<0.05)difference between the air-and MA-packaged samples (Table1).Low levels of TMA in MA-packaged samples can be consequences of reduction in growth of aerobic,gram negative bacteria,including trimethy-lamine oxide(TMAO)-reducing bacteria Shewanella putrefaciens.TMA-N values of air-packaged samples were found to be higher(P<0.05)than those of MA-packaged samples.This was in agreement with Masniyom et al. (2002),who observed higher TMA values in sea bass slices stored in air compared with that stored under different MA conditions.Similarly,Pastoriza et al.(1996)reported that TMAO production was signi?cantly(P<0.05) reduced by storage under CO2(MAP).Ozogul et al.(2000)reported a value of 13.5mg%in herring kept in MAP(60%CO2:40%N2)for10days at2?2C. Similarly,in this trial,the TMA was found to be11.7mg%in the same atmosphere(60%CO2:40%N2)for seer?sh steaks at the end of the storage period.CO2signi?cantly(P<0.05)suppresses the formation of trimethy-

lamine for it to remain less than 10–15mg TMA-N/100g of ?sh –the upper limits of trimethylamine in refrigerated stored ?sh (Connel 1990).

The K value of fresh seer ?sh steaks was 12.6.The K value for seer ?sh steaks packaged in either 100%air or MA increased to greater than 95%with length of the storage.The K value showed a linear increase with the storage time for air-packaged samples and reached 95.3%at the time of sensory rejection on the 14th day.There were no signi?cant (P >0.05)difference for air-packed and MA-stored samples during storage except on day 14,but the values signi?cantly increased throughout the storage period and reached 96.6on the 23rd day of storage.The initial value obtained in this study was in agreement with Reddy et al.(1994)and Ozogul et al.(2000),who reported 12–13%for freshly caught tilapia and herring.The present study indicated that the presence of CO 2did not alter the rate of degradation of nucleotides.In this trial,we found that MA-packaged seer ?sh steaks were still acceptable on the basis of sensory score and total bacterial count even though the values were greater than 95%,which indicated that K value was not a suitable freshness indicator for MA-packaged seer ?sh steaks stored at 0–2C.Similar results were reported by Reddy et al.(1994),who found that the K value for tilapia ?llets packaged in air and MA increased with the length of storage and reached 95.39%in MA-packaged ?llets stored at 4C for 30days,which were still acceptable based on sensory odor.

ATP has previously been used as biochemical indicators of rigor state in fresh ?sh.After the ?sh have been caught,the levels of ATP decreased and degraded by endogenous enzymes in ?sh during the early stages of the storage period.In seer ?sh steaks stored under air,the amounts of nucleotides such as ATP,ADP and AMP remained almost constant during storage,and very low concentrations of all these nucleotides were observed.IMP was the most prominent nucleotide in the early period of iced storage followed by AMP.Initial AMP concentration was 4.5m mol/g,and it was signi?cantly reduced to 0.03m mol/g on the 14th day for air–packaged samples,and it was almost zero for MA–packaged samples at the time of sensory rejection (P <0.05)(Fig.3a,b).Initial IMP concentration was 5.06m mol/g,and it was signi?cantly decreased to 0.29m mol/g for air–packaged samples on the 14th day and 0.12m mol/g for samples kept under 60%CO 2:40%N 2at the time of sensory rejection (Fig.3a,b).Signi?cant differences in IMP reduction were found between air and MA packages,and the reduction was slow in MA packages.IMP concentration reduced rapidly,resulting in an increase in K value with increasing storage time.The loss of IMP through degradation to HxR and Hx would cause a loss of fresh desirable compounds,and the K value increased and reached over 95%from an initial value of 12.6%.A similar observation was found by Ozogul et al.(2000),reporting that IMP decrease was rapid in air-packaged samples compared with MA-packaged samples.Inosine

787

EFFECT OF MODIFIED ATMOSPHERE PACKAGING ON SEER FISH STEAKS

012345670

2

4

681012

14

16

Storage days

n u c l e o t i d e c o n c e n t r a t i o n ( m i c r o m o l e /g )

IMP Hx

a

1234567

Storage days

n u c l e o t i d e c o n c e n t r a t i o n (m i c r o m o l e /g )

IMP Hx b

FIG.3.CHANGES IN INDIVIDUAL NUCLEOTIDES (ATP,ADP,AMP,IMP,Hx,HxR)IN SEER FISH STEAKS STORED UNDER AIR (a)AND MODIFIED ATMOSPHERES

(60%CO 2:40%N 2)(b)IN THERMOFORMED TRAYS AT 0–2C FOR 14AND

23DAYS RESPECTIVELY

Vertical bars represent standard deviation.Where bars are not visible,determinations are within the size of symbols.ATP,adenosine triphosphate;ADP,adenosine diphosphate;AMP,adenosine

monophosphate;IMP,inosine monophosphate;Hx,hypoxanthine;HxR,inosine.

788P.YESUDHASON ET AL.

concentration increased from an initial level of 0.78to 1.1m mol/g,on the 14th and 23rd day of storage for air-and MA-packaged samples with 60%CO 2,but the increase was not regular.Initial hypoxanthine level was 0.66m mol/g and increased gradually to 6.36m mol/g during storage (P <0.05)for air-packed samples.Samples kept under 60%CO 2and 40%N 2showed signi?cantly (P <0.05)higher value 6.0m mol/g on the 18th day,then the value decreased to 5.0m mol/g on the 23rd day (Fig.3b).Hx was found to be the major metabolite at the end of the storage in air-and MA-packaged seer ?sh.Parkin et al.(1981)reported that air-packaged rock?sh and salmon in exhibited increased Hx level over time,while in MAP,the values were erratic and concluded that Hx values are invalid for ?sh in MAP.In this trial,we found that it agreed well with sensory,biochemical and microbiological parameters than other individual nucleotides and it can be an indicator of freshness for seer ?sh stored at 0–2C.Similarly,various authors recognized that Hx content in ?sh can be an accurate indicator of ?sh freshness in many ?sh species (Burns et al.1985;Zhang and Lee 1997).The concentration of Hx has been proposed as an index of freshness of ?sh but it does not always correlate with sensory quality (Jones et al.1964).Ehira and Uchiyama (1987)de?ned ?sh where the ratio of HxR to Hx is 5:1as HxR producers,and where the ratio is 1:5as Hx producers.Based on the HxR to Hx ratio observed in this trial,seer ?sh were classi?ed as hypoxanthine producers.Microbiological Analysis

Changes in total aerobic mesophilic count are presented in Fig.4.Total aerobic mesophilic bacterial count on seer ?sh muscle was 4.31log 10cfu/g,and over the next 8days of storage,counts were 1–2log cycles higher than the initial count (P <0.05).At the time of sensory rejection on the 14th day,the count reached >7log 10cfu/g for air-packaged seer ?sh.In ?sh samples stored under MA,wide ?uctuations were noticed up to 14days.The count gradually increased thereafter and reached 7.0log 10cfu/g on the 23rd day of storage at 0–2C when the samples were rejected based on sensory parameters.The initial aerobic mesophilic count of 4.31log 10cfu/g for fresh seer ?sh was below the proposed lower limit of 5￥105cfu/g for fresh ?sh (ICMSF 1986)indicating good quality ?sh.The initial mesophilic counts were within the range (103–105)established earlier for fresh tropical ?sh (Dalgaard et al.1993).The total aerobic mesophilic counts at 37C was signi?cantly higher from day 4to the entire storage period (P <0.05)in seer ?sh stored under air than that stored under MA at 0–2C.The lower count in MA was due to the inhibitory effect of CO 2on the growth of mesophilic bacteria.Similar observations were reported earlier for Catla catla and seabream samples packaged under air and MA (Gopal et al.1990,1996),for salmon (Salmo salar )(Pastoriza et al.1996),

789

EFFECT OF MODIFIED ATMOSPHERE PACKAGING ON SEER FISH STEAKS

Atlantic herring (Clupea harengus )(Ozogul et al.2000),sea bass (Masniyom et al.2002)and pearl spot samples (Lalitha et al.2005).Gopal et al.(1990)reported that a mixture of 80%CO 2and 20%O 2was more bene?cial in extending the shelf life of Catla catla ,and total viable counts were signi?-cantly higher in ?sh stored under air than that stored under https://www.wendangku.net/doc/024357945.html,litha et al.(2005)reported a delay in the growth of aerobic bacteria in pearl spot pack-aged under gas mixtures 60%CO 2:40%O 2and 70%CO 2:30%O2.It was noticed that the shelf life of seer ?sh based on the total aerobic mesophilic bacterial counts was in good agreement with sensory evaluation.In air-packaged seer ?sh,the shelf life was 12days and the shelf life was extended nine more days when ?sh were stored under 60%CO 2:40%N 2compared to air-packed samples.Our results indicated that storage under MA was effective in inhibiting the total aerobic mesophilic count and achieving an extension of shelf life of fresh seer ?sh.

The counts of Enterobacteriaceae in fresh seer ?sh were 2.2log cfu/g (Fig.5).The counts increased greater than 1log at the time of rejection (14th day)in seer ?sh steaks stored under air at 0–2C.In MA packages,signi?cant inhibition (P <0.05)was observed during the initial stage,then <1log increase was noticed at the time of rejection (23rd day).The limit of Entero-bacteriaceae count in fresh ?sh is 103cfu/g and it was observed that

their

33.544.555.566.577.50

2

4

6

8

1012141618202224Storage days

l o g c f u /g

FIG.4.CHANGES IN TOTAL AEROBIC MESOPHILIC COUNT AT 37C IN SEER FISH STEAKS STORED UNDER AIR AND MODIFIED ATMOSPHERES (60%CO 2:40%N 2)IN THERMOFORMED TRAYS AT 0–2C FOR 23DAYS.VERTICAL BARS REPRESENT STANDARD DEVIATION.WHERE BARS ARE NOT VISIBLE,DETERMINATIONS ARE

WITHIN THE SIZE OF THE SYMBOLS

790P.YESUDHASON ET AL.

count was ?103cfu/g throughout the storage.The initial level of Enterobac-teriaceae noticed in seer ?sh was in general agreement with the observations made earlier in marine ?sh from temperate (Koutsoumanis and Nychas 1999)and tropical waters (Manju 2005).The Enterobacteriaceae counts in ?sh are related to the hygienic status of ?sh,and their presence can be related to contamination of fecal origin.The growth of Enterobacteriaceae population in seer ?sh stored under air at 0–2C has been observed during this trial and similar observations were made earlier (Arashisar et al.2004).The contribu-tion of Enterobacteriaceae in the ?nal ?ora was very low or nil,and therefore,this ?ora was not likely to be responsible for spoilage of seer ?sh stored under air or MAP at 0–2C.Signi?cantly (P <0.05)lower counts in seer ?sh steaks stored under MA compared with air pack samples may be attributed to the inhibitory action of CO 2.Sensory Analysis

Detailed patterns of changes in sensory parameters for seer ?sh steaks packaged in air and modi?ed atmosphere stored at 0–2C are shown in the Fig.6a,b.Fresh seer ?sh steaks were generally considered to have very

high

0.511.522.53

3.54Air pack MAP

l o g c f u /g

FIG.5.CHANGES IN ENTEROBACTERIACEAE COUNT IN SEER FISH STEAKS STORED UNDER AIR AND MODIFIED ATMOSPHERES (60%CO 2:40%N 2)IN THERMOFORMED TRAYS AT 0–2C FOR 14AND 23DAYS,RESPECTIVELY .VERTICAL BARS REPRESENT STANDARD DEVIATION.WHERE BARS ARE NOT VISIBLE,DETERMINATIONS ARE

WITHIN THE SIZE OF THE SYMBOLS

791

EFFECT OF MODIFIED ATMOSPHERE PACKAGING ON SEER FISH STEAKS

overall acceptance.There was a signi?cant reduction (P <0.05)in sensory parameters of all samples with the storage period increased.As the days of storage in ice progressed,the sweet taste of the muscle was lost and the texture became soft (Fig.6a).All samples developed a ?shy odor as the storage time

0123456789

100

2

4

6

8

1012141618202224Storage days

S e n s o r y s c o r e (F l a v o r & T e x t u r e )

a

246810

2

4

6

8

10

12

14

16

18

20

22

24

Storage days

S e n s o r y s c o r e (O d o r & O v e r a l l a c c e p t a n c e )

b

FIG.6.SENSORY CHANGES FOR FLA VOR AND TEXTURE (6a)&ODOR AND OVERALL

ACCEPTANCE (6b)IN SEER FISH STEAKS STORED UNDER AIR

AND MODIFIED ATMOSPHERES (60%CO 2:40%N 2)IN THERMOFORMED TRAYS

AT 0–2C FOR 23DAYS

Vertical bars represent standard deviation.Where bars are not visible,determinations

are within the size of symbols.

792P.YESUDHASON ET AL.

increased (Fig.6b).For the air-packaged samples,the deterioration occurred after 12days of storage as evidenced by strong ?shy and putrid odor.The observation was in agreement with a previous report by Shenoy and James (1976),who reported that the ice-stored spotted seer ?sh were acceptable for 13days based on sensory evaluations.The samples kept under MA exhibited high scores for ?avor,texture,odor and overall acceptance compared with air-packaged seer ?sh https://www.wendangku.net/doc/024357945.html,ing a sensory score of 4as the acceptance limit,it was found that samples kept under modi?ed atmosphere were accept-able up to 21days of storage by maintaining their sensory characteristics.Results were in good agreement with Masniyom et al.(2002),who reported that odor,?avor and overall acceptability of CO 2-enriched samples were acceptable throughout storage for 21days.Our observation was also in agree-ment with Gopal et al.(1996),who reported that sensory characteristics of sea bream ?llets were better in MA-packaged samples compared with air-packaged samples in ice.Reddy et al.(1995)reported that at 4C storage,MA-packaged tilapia ?llets maintained their sensory acceptability for up to 25days on the basis of odor characteristics.

CONCLUSIONS

Seer ?sh steaks packaged under MA showed signi?cant delay in chemi-cal,microbiological and sensory deterioration.MAP-stored samples signi?-cantly reduced the TMA-N level and TBA values compared with air-packaged samples.The K value was not a suitable quality indicator of spoilage and seer ?sh was classi?ed as hypoxanthine producers.Mesophilic bacterial counts were signi?cantly low for MAP samples compared with air-packaged seer ?sh samples,which was due to the inhibitory effect of CO 2.Seer ?sh steaks packaged in air and MA were acceptable,by sensory and microbiological data,at the 12th and 21st day of storage,respectively,and the extension of shelf life using suggested gas composition could be commercially exploited.

ACKNOWLEDGMENT

The authors would like to thank Dr.K.Devadasan,Director,CIFT,Cochin,India,for providing the facilities to do this work.

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2017山香教育理论基础整理笔记(教育学、心理学、教育心理学)

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