PACKAGING TECHNOLOGY AND SCIENCEPackag. Technol. Sci. 2004; 17: 213–217DOI:10.1002/pts.657

Heat Penetration Characteristics and Shelf-lifeStudies of Mushrooms in Brine Processed inRetort Pouches

By V. Chandrasekar,1* T. K. Srinivasa Gopal2 and R. D. Rai11 National Research Centre for Mushrooms, Chambaghat, Solan 173213, HP, India2 Central Institute of Fisheries Technology, Matsyapuri Post, Cochin 682 029, India

White button mushrooms were washed, blanched and cut longitudinally into twohalves. 100g mushroom halves was placed into each retort pouch and 90ml hotbrine (2% salt, 0.1% citric acid) was added. Retort pouches (105mm thick) had anouter polyester layer (12.5mm), a middle aluminium layer (12.5mm) and an innercast polypropylene layer (80mm); pouch size was 20 ¥ 16cm, seal size 10mm and lipsize 4mm. Pouches were fixed with thermocouples for recording the coretemperature of the mushroom pieces, using a data recorder and a computer. Aftersealing and over-pressure retorting at F0 = 9.6, the pouches were stored at theambient conditions. The heat penetration parameters were calculated. The heatingcurve obtained was logarithmic in nature. Sensory evaluation of mushroom curryprepared from the stored mushrooms showed that the product had highacceptability (7.9 on a scale of 10) which reduced very slightly (to 7.5) duringstorage for 12 months. No deformity, leakage or spoilage was noticed and theproduct remained sterile and acceptable even after 12 months of storage at theambient conditions (20–30°C). Copyright © 2004 John Wiley & Sons, Ltd.Received 24 December 2003; Revised 1 April 2004; Accepted 16 April 2004

KEY WORDS: mushrooms in brine; retort pouch; packaging; storage; heat penetrationcharacteristics; post-harvest technology

* Correspondence to: V. Chandrasekar, Department of Agricultural Processing, Tamilnadu Agricultural University, Coimbatore641003, Tamilnadu, India.E-mail: vcsekar36@hotmail.com

Copyright © 2004 John Wiley & Sons, Ltd.

INTRODUCTION

Mushrooms have a very short shelf-life and can bestored only for a few days, even under the beststorage conditions. They are processed in variousforms for long-term storage. Drying is the widelyused and adopted preservation method for long-term storage of mushrooms. However, buttonmushrooms (Agaricus bisporus) are difficult to drydue to its shape and does not give an acceptableproduct after drying. Hence, they are canned intins with brine and traded across the world.1 Many

studies on the processing of mushrooms, e.g.drying, canning, pickling and steeping preserva-tion, have been reported.2

The flexible retort pouch is an ideal alternativeto metal containers for the packing and storage ofheat-processed foods. Flexible retort pouches,besides being cheaper, have many other advan-tages, such as easy bulk packing, less transporta-tion cost, rapid heat penetration and being easilydestroyed by incineration without causing envi-ronmental pollution.4 The retort pouch is slowlyreplacing cans in the food industry. At present, the

retort pouch has completely replaced the metal canfor the US military’s Meals-Ready-to-Eat (MRE)rations and is making slow and steady progress inthe commercial market. In Japan and Europe alsothe retort pouch has established itself in marketingfood products.5

Heat penetration and storage studies usingretort pouches have been done for fisheries prod-ucts6–9 and for storage of mushroom curry.10

In view of the lower heat processing needs andthe consequent less heat-induced damage to thefood in retort pouches, a study has been conductedon the storage of button mushrooms in brine inretort pouches and on the heat penetration char-acteristics of mushrooms in brine.

MATERIALS AND METHODS

Fresh white button mushrooms (Agaricus bisporus)supplied by the mushroom farm of M/s Hindus-tan Lever Ltd, Ooty, Nilgiris, were transported byrail overnight in air-conditioned wagons to Cochinand were stored at 0–4°C in a cooling chamber andprocessed within 24h of their harvest. The retortpouch used was 105mm thick, with a polypropy-lene inner layer (80mm), an aluminium middlelayer (12.5mm) and a polyester outer layer (12.5mm); enter dimension 20 ¥ 16cm.10 Empty weightwas 10g; the seal and lip size were 10mm and 4mm, respectively. The over-pressure autoclave of John Fraser and Son Ltd, UK, available at theCIFT, Cochin, was used for the study.

The fresh mushrooms were washed in runningwater to remove dirt and compost residues. Theywere halved along the stem axis and blanched inbrine (2% salt, 0.1% citric acid; the latter is addedto prevent darkening of the mushrooms duringblanching) for 5min at about 90–94°C.11 The mush-rooms were immediately cooled in water. 100gmushrooms were filled manually in the retortpouch and 90ml hot brine (2% salt, 0.1% citric acid)was added, giving more than 50% of mushroomweight in each pouch.

After filling, the entrapped air was removed bya steam flushing method12 and sealed using animpulse heat-sealing machine.6 Some poucheswere fixed with glands and thermocouple tipsinserted into the mushroom pieces for recording

core temperatures.9 The pouches were arranged in perforated aluminium trays and loaded into an over-pressure autoclave. The thermocoupleoutputs were measured using an Ellab CTF 84 datarecorder and computer.

The retort temperature was maintained at 121°Cby passing steam and over-pressure was main-tained at 28psi throughout the heating and coolingperiods. The filled pouches were processed to a F0

(time in min at 121°C) value of 9.6. As soon as therequired F0 value was reached, the steam supplywas cut off and the pouches were cooled to 40°C(Tc) by circulating cooling water. After the process,the lag factor for heating (Jh), slope of the heatingcurve(fh), time (min) for sterilization at retort tem-perature (U) and lag factor for cooling (Jc) were cal-culated by plotting the temperature deficit (RT -Tc) against time on semi-log paper. The processtime (B) was calculated by a mathematicalmethod.13 Physical properties and the suitability ofthe pouches for food contact applications wasascertained by determining the overall migrationresidue,14 internal burst strength for seal integrity,15

heat-seal strength,16 tensile strength and elonga-tion at break.17

When the core temperature reached around40°C, the pouches were removed from the retortand wiped dry. The mushrooms were then storedat room temperature (20–30°C). The sterility of themushrooms in the pouches was determinedaccording to IS 216818 and the pH was determinedusing a digital pH meter. The post-packaging per-formance of mushrooms in retort pouches wasevaluated every 3 months during the storageperiod of 12 months. The first evaluation was doneafter allowing a stabilization period of 10 days. Theperformance of the pouch was evaluated fordefects such as pinholes, wrinkles/creases on theseal area, stain/rust spots, leakage of fluids,delamination, bulging due to gas formation, andshape and colour of the mushrooms.

A sensory evaluation of mushrooms stored inretort pouches was done after preparing a mush-room curry. The mushrooms were removed fromthe pouches, washed several times in water toremove the excess salt and the curry prepared byadding spices and salt, as followed for currypreparation using fresh mushrooms. The mush-room curry was evaluated on 10-point hedonicscale.9 Curry preparation and sensory evaluationwere done after every 3 months of storage.

V. CHANDRASEKAR ET AL.Packaging Technologyand Science

Copyright © 2004 John Wiley & Sons, Ltd. 214 Packag. Technol. Sci. 2004; 17, 213–217

RESULTS AND CONCLUSION

The F0 value recommended for processing ofmushrooms in brine is 8–1011,19 and for mushroomsin curry is 10–13.2.10 The processing was carriedout at retort temperature of 121°C until it attaineda F0 value of 9.6; at this value, the sterility testshowed that the samples were sterile with accept-able colour without breakage or softening of themushrooms. The mushrooms had a drainedweight of 98–99g against the 100g initial weight.Hence, the loss of solids in brine is 1–2%, even after12 months storage.

The time required for the retort to attain 121°C(“come-up time”) was 3min; this time should be asshort as possible.20 Actual process time was 17min,including 58% of come-up time, and gave a F0

value of 9.6; the lag factor for heating (Jh) and theslope of the heating curve (fh) were 0.46 and 20,respectively. The lag factor for cooling (Jc) was 1.3.The process time, calculated by the mathematicalmethod,13 was 15min and the fh: U ratio was 2.0.

Core temperature, retort temperature and F0 ofthe process are given in Figure 1. There was certain

decline in retort temperature as soon as the steamwas cut off and cold water circulated. This is essen-tial to cool the product quickly, avoiding over-cooking and preventing the growth of thermopiles.The heat penetration characteristics with referenceto cook value are given in Figure 2. The cook valuegives the optimal degree of tenderness in a fin-ished product. The mushroom had an acceptablecolour without softening with a cook value of 55min. The pH of the brine was 5.75 and thisremained unchanged during the 12 monthsstorage period.

The heat-seal strength of the laminate was 60.75N/25mm width in the cross-direction and70.25N/25mm width in the machine direction.The bursting strength of the laminate is 21psi.Overall migration residue of the pouches used was 10mg/dm2, indicating its suitability for food con-tact applications. The tensile strength of the pouchwas 451kg/cm2 and 425kg/cm2 along the machinedirection and cross-direction, respectively. Theelongation at break was 20%. The bond strengthsof the inner polypropylene and outer polyesterlayers were 184g/10mm width and 110g/10mm

Copyright © 2004 John Wiley & Sons, Ltd. 215 Packag. Technol. Sci. 2004; 17, 213–217

HEAT PENETRATION AND SHELF-LIFE STUDIES Packaging Technologyand Science

140

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00.0 5.0 10.0 15.0 20.0 25.0

Time (min.)

Core Temperature

Retort Temperature

Fo

12

10

8

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2

0

Tem

pera

ture

F v

alue

(m

in.)

Figure 1. Heat penetration and F0 of cut mushrooms in brine in aretortable pouch.

width, respectively. The pouch withstood the pro-cessing temperature and pressure. No delamina-tion of the outer ply was noticed during heatprocessing. Defects affecting the pouch integrity,such as pinholes, wrinkles/creases on seal area,staining or rust spots, leakage of fluids or delami-nation of inner or outer laminates, were notdetected during the storage period. This shows thesuitability of the pouch for its use as a containerfor packing mushrooms in brine.

Sensory evaluation of mushroom curry pre-pared from the stored mushrooms was done every

3 months (Table 1) and showed that overall accept-ability was very good, with 7.9 initially and 7.5after 1 year of storage in ambient conditions.Among other characteristics, the colour had aminimum score of 7.0 initially and 6.6 after 12months of storage. No leakage, bad odour or anyother spoilage was noticed in the pouches duringa 1 year storage period.

REFERENCES

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2. Rai RD, Chandrasekar V, Arumuganathan T. Post-harvest technology of mushrooms. In Current Vistasin Mushroom Biology and Production. MushroomSociety of India: Solan, India, 2002; 225–236.

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6. Srinivasa Gopal TK, Vijayan PK, Balachandran KK,Madhawan P. In Advances and Priorities in FisheriesTechnology, Balachandran et al. (eds). Society of Fisheries Technologists (India): Cochin, 1998; 232–235.

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Copyright © 2004 John Wiley & Sons, Ltd. 216 Packag. Technol. Sci. 2004; 17, 213–217

140

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00.0 5.0 10.0 20.0 25.015.0

60

50

40

30

20

10

0

Core TemperatureRetort TemperatureCook value

Time (min)

Tem

pera

ture

Cg

valu

e (m

in.)

Figure 2. Heat penetration and cook value of cut mushroom in brine ina retortable pouch.

Table 1. Sensory evaluation of mushroomcurry prepared from mushrooms retort-

processed and stored in brine

Storage period (months)

Characteristics 0 3 6 9 12

Flavour 8.0 7.9 7.8 7.6 7.5Texture 8.6 8.5 8.4 8.3 8.2Taste 8.1 8.0 7.8 7.7 7.5Colour 7.0 6.8 6.7 6.6 6.6Overall acceptability 7.9 7.8 7.7 7.6 7.5

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8. Vijayan PK. Report on training programme onretortable pouch processing of fish and fish analysisat Tropical Development and Research Institute andMetal Box (R&D, UK) CIFT: Cochin, 1984.

9. Vijayan PK, Srinivasa Gopal TK, Balanchandran KK,Madhawan P. In Advances and Priorities in FisheriesTechnology, Balachandran et al. (eds). Society of Fisheries Technologists (India): Cochin, 1998.

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15. Duxbury DD, Sams PF, Howelwe WF, Gee JH, MillerWN. Feasibility Technical Report. US Army NatickDevelopment Center: Natick, MA, 1970; 72–77.

16. ASTM. Standard Methods of Tests for Seal Strength ofFlexible Barrier Materials. American Society forTesting and Materials: Philadelphia, PA, 1973; 68–88.

17. IS 2508. Specifications for Low-density Films, 2nd edn.Bureau of Indian Standards: New Delhi, 1984.

18. IS 2168. Specification for Pomfret Canned in Oil. Bureauof Indian Standards: New Delhi, 1971.

19. Brennan JG, Butters JR, Cowell ND, Lilley AEV. InFood Engineering Operations, 3rd edn. ElsevierApplied Science: London, 1990.

20. Anon. Laboratory Manual for Food Canners and Proces-sors, vol. 1. National Canners Association/AVI Publishing: Westport, 1968.

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HEAT PENETRATION AND SHELF-LIFE STUDIES Packaging Technologyand Science