View of Rainbow trout (Salmo irideus) produced in Finland V. Heat penetration in canned trout products during processing

RAINBOW TROUT [SALMO IRIDEUS) _PRODUCED IN FINLAND

V. Heat penetration in cannedtrout products duringprocessing

Jorma J.

University

of

of

Received August 24, 1968 The keeping quality of canned foods is based upon sterilization inretorts at elevated temperatures and pressure. In commercial processing the heattreatment is kept as low as possible ^{to preserve} the nutritional value, ^texture, color, flavor and consistence of the packed foods as stable _as possible (Laine 1967). In commercial processing the bacterial endosporesarenotcompletely destroyed but_arebrought_todormancyso that theycannot causeany microbiological deterioration of the product (Stumbo 1965).

The proper sterilization for each product andcansize is determined by the heatpenetra- tion and theamountand thermal resistance of the spores in the product. When these facts areknown, the degree of adequate sterilizationcanbe theoretically calculated (Cheftel and Thomas 1963).

Since the death of bacteria is generally logarithmic in practice, itcanbe described mathe- matically in the same manner as a unimolecular_{or a} first-order bimolecular chemical reaction. Thermal destruction curves, often referred to as thermal death time curves, reflect the relative resistance of bacteria to different lethal temperatures. They can be conveniently constructed by plotting the logarithm of D or some multiple ofD, ^{which is} the decimeration time during which 90 per cent of the original amount of spores are destroyed in the direction of ordinates against exposure temperaturein the direction of abscissae (Stumbo 1965).

When this technique is usedtoestimate the initial number of spores and the number of those surviving the time t, D may be calculatedasfollows:

t

D ⁼

log^a logb where a ⁼ Initialpopulation

b ⁼Finalpopulation

D ⁼ Time required at any temperature to destroy90per cent of the spores orvegetative cells ofa given organism. Numerically, equaltothe number of minutes required for the survivor curveto traverse onelog cycle. Mathematically, equal to thereciprocal of theslopeof the survivorcurve.

t ⁼ The effective time ofheating inminutes at theparticulartemperature(Stumbo 1965).

Heat penetration is dependent upon the product, packaging material,filling and pro- cessing temperatures, pressure, cansize and filling degree. All these factors have ^apartial influence_on the total _orsterilization result (Ball and Olson 1957).

Measurements of the heat penetration should be done in the coldest _spot of the _can.

This varies accordingto the food material and _can size. Solid and semisolid products are heated mainly by conduction and the process is slow. In liquid ^andsemiliquid ^products convection helps ^{the heatmovement} and the process is fast (Stumbo 1965). In fishery products ^twophasesoccur, ^namelyaliquid brineor sauceand asolid fish phase. ^{In these} products conduction and convection^can be separated.

The mostcommon method of aiding the heat penetration is to rotate the cans during processing. Gisske (1961) has studied the processing ofmeatand sausage products under rotation. The optimal rotation speed for these products seemed ^to be 30—40 RPM, whereas60RPM had undesirable effects. Wirth (1967)concluded, that the optimal rotation speed for _meatproducts _was30 RPM. Glees (1963) indicated that rotation was the most important factor in reducing the processing times in big and high _cans. In these studies the heat penetration was calculated according to the time required to reach -)- 117°C.

In processing fishery products rotation also plays a role in improving the sterilization effect. Because of the finestructure offish,^{rotationcannotbeasfast}aswith the ^meatpro- ducts. A rotationof 10RPM is adequate in many instances inorder^tomake the sterilization moreeffective.

In the present study heat penetration is calculated for two fishery products prepared from rainbowtrout(Salmoirideus).

Material and methods

The ^test material consisted offresh, gutted and iced rainbow trout.Two different pro- ducts were made,^{namely trout in its own} juice and smokedtrout in vegetable oil. They werepacked incansofo 73 X 64 mm and073 X 103mm,respectively.

Trout in itsownjuicewaspreparedasfollows: The fishwerecutinto64 mm long pieces.

240 grams of fish were packed in to each _can and 2 per ^cent of salt and 0.2 per ^cent of spices were added. Smoked trout in vegetable oil was prepared as follows:

The troutwerebrined for ^two hours in a 15 per^cent salt solution. They^were then dried for 10 minutes at + 80°C. After drying they weresmoked at ⁺ 105°C for 50 minutes.

The smoked fish_werepacked ^{incans; the} proportionof fish and oil_was 60:40.

After sealing thecans wereprocessed in_aLabor-Rotomat autoclave _asfollows:

Upperdrum Lower drum Pressure

+ 130°C

+ 120°C 2 At

Movement 0and 10 RPM

Heat penetration measurements were done thermoelectrically using Ellab (Elektro- laboratoriet Ellab A/S, Copenhagen) thermocouples, model TCSC 19. The measuring point _was in all instances the geometrical centerof the_can. The results _wereregistered withacompensation multirecorder. The recorder registered thetemperatures in fourcans, the pressure in thedrum,and the rotation^atintervals of6 seconds.

In accordance with Glees (1963), ^heatpenetration^was measured with the aid of heat penetration- ^{or f}_h-parameters. Comparisons with nonrotating sterilization were made between the timesrequired ^{until -)- 117°Cwasreached.}

Thecooling^{curve was} constructed in thesame manner. Coolingwascomplete^{when the}

centerpoint^{of thecanreached}a temperatureof-f- ³⁰°C.

To obtain the heating ^curve, the differencebetween retort temperatureand food tem- perature wasplotted on the log scale against timeon the linear scale. This is conveniently accomplished byrotating the semilog paperthrough ^{180° and} labeling ^thetopline _{at one} degree below theretorttemperature,andthen^plottingthetemperatures directly.^{To obtain} thecooling curve, the difference between food temperatures wasplotted on the log scale against time_on the linear scale. In thiscasethesemilogpaperwasleft in its normalposition, the bottom line_was labeled_{at one}degree above the cooling_water temperature, and the temperatures were plotted directly (Stumbo 1965).

Results

The heatingcurves of thetwo troutproducts tested_are presented ^{in Fig.} 1. The results indicate that the heat penetration was more rapid in the smoked trout in vegetable ^oil (can size073 X 103mm) and that rotation aided the heatpenetration considerably. ^In his case the f_hll7 was reached in 32 minutes witharotation of10RPM and in 38 minutes without rotation. The trout in its _ownjuice (can^{size 073 X 64} mm) had^amuch ^slower heatingrateand f_hll7 was reached in 79 minutes with arotation of 10 RPM and 81.5 minutes without rotation. Due _to conduction therewas no great difference between the rotating and non-rotating sterilization.

When the coolingcurves wereplotted_on the log scale against timeonthe linear scale it wasfound thatthey^formedastraight line in all instances. Coolingwasconsidered complete when the temperaturereached ⁺ 30°C. With the smokedtrout in vegetable oil (can size

073 X 103 mm) the cooling timeswere 15.5 minutes for the rotating and 19 minutes for the non-rotating sterilization, and with the trout in its own juice 18.5 and 26 minutes, respectively.

Discussion

Heat penetration characteristics oftwo cannedtrout products were studied in aseries of experiments where theprocessingwas performed using both non-rotating androtating (10 RPM) sterilization techniques. The two trout products ^{tested were trout in its} own juice and smokedtrout in vegetable oil.The processing temperature (+ 120°C) and the pressure (2 At)werethesamein all the experiments.

The trout in its _ownjuice (can size 073 X 64mm) was asolid product where the heat penetration occurred by conduction. This _can be clearly seen from Fig. 1 where for the first 10—12 minutes of the operation the heatpenetration was notlogarithmic. ^{After this} the slope of thecurves both with the rotating and non-rotating processeswas gradual and fh117 was reached after 79 and 81.5 minutesrespectively. At the end of the processing, the differences in cooling timeswere greater, 18.5 minutes in the rotating and 26 minutes in the non-rotating sterilization. This_{seems to}be influenceb dy the forced convections of

the fish juice in the heated and rotated product. When the rotated and nonrotated pro- ducts, ^{which were sterilized to an F}O-value of7.5—8.5, ^were judged organolepticly, _no differences in appearance, structure, odororflavor wereobserved.

The smokedtroutin vegetable oil (can size073 X 103mm) ^{was a}product withasolid and aliquid phase. For this reason heatpenetration occurred both by convection and conduction. This_canbee_seen(Fig. 1)from the very short heating-up times and the steep heat penetration curves. Rotation aided the heat penetration considerably and was reached in the rotated products ^{in 32} minutes. The corresponding value for ^the non- rotated productswas 38 minutes. Thesame pattern wasobserved also in the coolingtimes, which_were 15.5 minutes for the rotated and 19 minutes for the non-rotated products.

When the rotated products,^which weresterilized toanF_c-value of7.5—8.5, ^werejudged organolepticly,_amarked difference in odor and flavorwasobserved in favour of the rotated products. Thestructurewas slightlybetter in the non-rotated products however.

On comparing ^{the two trout} products with each other, aclear difference in the heat penetrationwas observed(Fig. 1).In the smoked ^troutpacked ⁱⁿ oil,rotation had_afavor- able effect both_onthe heatpenetration and the quality of the product, whereas in thetrout in its _own juice, rotation had nopractical effect on the heat penetrationor the quality of theproduct. Rotation aided the cooling ofboth of thetroutproducts and the cooling time from+

117°C

30°G

These experiments indicated that thetechniques used in the sterilization of e.g. meat or vegetable products cannotbe directly applied tothe processing of fish products. Fish hasa finestructure, androtation speeds ^of20—40 RPM may cause defects in itsappearance.

In solidproducts rotation hadnopractical effecton the heating time.However, when the fishwas packed ⁱⁿoil, rotationaided the heatpenetration ^and improved ^the qualityof the product.

Summary

In thepresent study^theheat penetration ^{oftwocannedtrout}productswasinvestigated.

Heatpenetration ^was measured and f_hll7 parameter were calculated. Inthe processing, acomparison with^anon-rotating (10 RPM) sterilizationwas made.

The results indicated that smoked trout in vegetable oil (can ^{size 073} X 103 mm) reached f_hll7 in 32 minutes with_arotation of10RPM and in 38 minutes without rotation.

The corresponding values for ^troutin its^ownjuice^(cansize073 X 64^mm)were 79and

Fig. 1. Heating curves obtained in the sterili- zation of troutinits own juice (can size 73_X 64mm) and smoked troutinvegetable oil can size 072_X103 mm) with _arotation of0 and 10 RPM.

x x troutinitsownjuice,0 RPM A Atroutinits_ownjuice, 10 RPM

smoked troutinvegetable oil, 0 RPM A —Asmoked troutinvegetableoil, 10 RPM

81.5 minutes. At the end of the processing the cooling time from ⁺ 117°C^to -f- ^30°Cwas 15.5 minutes for the smoked trout in vegetable oil witha rotation of 10 RPM and 19 minutes in the non-rotating sterilization. The corresponding values for the troutin its own juicewere 18.5 and 26 minutes.

REFERENCES

Ball,C. O. and Olson, C. F. W. 1957.Sterilization infood technology. McGraw-Hill^BookCo., Inc., 654p. NewYork, Toronto,London.

Cheftel, H.and Thomas, ^G. 1963. Principles and methods of establishing thermalprocessesfor canned foods. Translated from French. Bull. 14, 78p.Paris.

Gisske, W. 1961. Neue Erkenntnisse über die Methodik des Erhitzens von Fleisch und Fleischwaren.

Die Fleischwirtsch. 13: 550.

Glees,A. 1963.Der Einfluss vonÜberdruckund Wasserumwälzung während der Standsterilisation und der Einfluss der Kopfraumgrösse und des Dosenformates während der Rotationssterilisation auf der Wärmegang vonFleischkonserven. Ibid. 15: 279.

Laine,J. J. ^1967.Sterilointimenetelmien vaikutus säilykkeidenlaatuun. Lihapäivät 1967.Helsingin Yli- opiston Lihateknologian laitos, 47.

Stumbo, C.R. 1965.Thermobacteriology infoodprocessing. Academic Press, 236p.New York,London.

Wirth,F. 1967. Einflüsse auf die Hitzedurchdringungvon Fleisch- und Fleischwaren-konserven bei der Rotationssterilisation. Die Fleischwirtsch. 47: 471.

SELOSTUS

TUTKIMUKSIA SUOMESSA KASVATETUSTA KIRJOLOHESTA (SALMO IRIDEUS) V. Lämmön siirtymisestä tölkitetyissä kirjolohituotteissa sterilointikäsittelyn^aikana

Jorma J.Laine

Helsingin Yliopisto, Lihateknologianlaitos

Suoritetussatutkimuksessa seurattiin lämmön siirtymistä kahdessa kirjolohisäilykkeessä sterilointikäsit- telyn aikana. Lämmön siirtyminen mitattiin lämmönnousu- eli avulla. Lämmönnousu laskettiin prosessin alusta siihen hetkeen, jolloin lämpötila tölkin geometrisessä keskipisteessä saavutti

+ 117°C.Kokeet suoritettiinkäyttäen liikkuvaa (10 kierrosta minuutissa) ja seisovaa sterilointitekniikkaa.

Tulokset osoittivat, ettäsäilykkeissä, joissa savustettukirjolohi olipakattu öljyyn (rasiakoko 0 73 x 103 mm)fhll7°C saavutettiin 32minuutissa liikkuvassaja 38 minuutissa seisovassa steriloinnissa. Vastaa- vat arvotsäilykkeissä,joissakirjolohi oli pakattu omaanliemeensä(rasiakoko ⁰73 X64 mm) olivat 79 ja 81.5 minuuttia.Jäähdytysajat ^{+ 30°C:een}eri tuotteilla olivat seuraavat: savustettukirjolohi öljyssä 15.5 minuuttia liikkuvassa ja 19 minuuttia ^seisovassa steriloinnissa, sekä kirjolohi omassa liemessään 18.5 minuuttia liiikkuvassa ja 26 minuuttia seisovassa steriloinnissa.