Studies On Thermal Processing Of Some Foods:

Magdy Fahmy Ahmed El-sheikh Omar

sujfMAR’Canning and thermal processing are the major section of thefood industries in Egypt. This study was carried out for:1- Studying changes that occur in chemical, microbial and sensoryattributes during blanching of green beans, peas and okra.Il- Isolation and identification of aerobes isolates (Bacillus spp.)i.e. B. subtilis, B. coagulans, B. stearothermophilus, B. cereusand B. Itcheniformis from green beans, peas and okra Decimalreduction time (D-values) and Z-values for these isolates weredetermined,Ill- Studying heat penetration of canned green beans, peas and okraeither in ’brine solution or in tomato sauce and find out thermalconstant parameter (fh, jh, jc).IV-Studying the optimum thermal process time.The results can be summarized as follows:1- Blanching of green beans, peas and okra in boiling water for 1,3 and 5 minutes decreased the chemical constituents.2- All major constituents of green beans, peas and okra i.e.protein, ash, fat and fiber were decreased after canningprocess. However, the higher a decremental reduction wasobserved when brine solution 1.5% was used compared withcanning in tomato sauce.3- Mineral contents including potassium, iron, phosphorus andcalcium were all decreased, whereas, sodium apparentlyincreased due to the addition of brine solution 1.5%.4- The initial microbial load of green beans, and okra (as a nooprotectedmaterial) was higher than green peas (as a protectedmaterial).5- Blanching reduced the total plate count of bacteria to over 90 _96%, according to different blanching times.6- Canned vegetables showed complete reduction of spore count,however, the total spores counts were lower than 30 spores per25 g.7- As for spore-forming bacteria count were recovered in higherquantities for samples thennal1y treated at 112.1°C (233.78°F)which represented 4, 2 and 5 spores/25 g, 2, 2 and 2spores/25g for mesophilic and thermophilic spores for samplesvegetables canned in brine solution, respectively. While, theywere 2, 1 and 2 spores/25g, 2, 1 and 2 spores/25g formesophilic and thermophilic spores for samples vegetablescanned in tomato sauce, respectively.8- The incidence of such species isolated and identified Bacillusfrom vegetables (green beans, peas and okra) out of 240colony either from raw or exhausted vegetables packed inbrine solution could be arranged in a descending order as 7, 7,6, 6, 6, 6, 5, 4 and 4 for B. subtilis, B. licheniformis, B.brevis, B. stearothermophilus, B. macerans, B. cereus, B.coagulans, B. polymexa and B. megatherium , for greenbeans. While, were 6, 6, 4, 4, 4, 4, 4 and 2 for B. cereus, B.megatherium, B. subtilis, B. licheniformis, B. brevis, B.stearothermophilus, and B. macerans, B. coagulans, for greenpeas. While, were 9, 9, 8, 8, 6,5, 4 and 3 for B. subtilis, B.brevis, B. polymexa, B. macerans, B. coagulans, B. cereus, B.stearothermophilus, and B. licheniformis for green okra,respectively. For the vegetables packed in tomato sauce couldbe arranged in a descending order as 7, 7, 7, 6, 6, 5, 5, 5 and 4for B. subtilis, B. ltcheniformts B. brevis, B.stearothermophilus, B. macerans, B. cereus, B. polymexa, B.coagulans, and B. megatherium ; for green beans. While,were 6, 6, 5, 5,4, 3, 3 and 2 for B. cereus, B. megatherium, B.licheniformis, B. subtilis, B. macerans, B. brevis, B.stearothermophilus, and B. coagulans, for green peas. While,were 10, 8, 8, 7, 6,5, 5, and 4 for B. subtilis, B. brevis, , B.macerans, B. polymexa, B. coagulans, B. cereus, B.stearothermophilus, and B. licheniformis for green okra,respectively.9- The results indicated that B. licheniformis and B. coagulanshad the least O-value at different heating temperature. While,B. stearothermophilus had the highest values at the sameheating temperature. While, the values of”O” for B. cereus,and B. subtilis appeared in between. It can be noticed thatD2120F in minutes for B. stearothermophilus , B. cereus, B.subtilis, B. coagulans, and B. licheniformis suspended inextract of vegetables and (brine-suace) were 230, 2.5, 2.5, 1.8and 1.6 minutes, respectively. While, the corresponding valueswere 28, 0.88, 0.95, 0.75, and 0.66 minutes at 230oP, 2.00,0.29, 0.29, 0.29 and 0.26 minutes at 250°F, respectively. Theresult indicate that the D-values for the same spores suspendedin phosphate buffer pH = 7 were 250, 3, 2.8, 2.1 and 2.00minutes at 212°P, 34, 1.05, 1.05, 0.85 and 0.85 minutes at230°F, 3.68, 0.37, 0.39, 0.33 and 0.32 minutes at 250oP,respectively.10- Z-values for different species of Bacillus were computed fromthe thermal death time curves. The Z-values irr’F for sporesof B. coagulans, B. cereus, B. subtilis, and B.stearothermophilus suspended in extract of vegetables with(brine-sauce) were 46.44, 43.92, 43.56 and 18.6°P,respectively.11- Least significant difference (L.S.D.) was calculated tocompare between Fh at different retort temperature whichindicated that increasing retort temperature (Tr) from 112.1 °Cto 116.0°C to 120.2°C was accompanied by significantdecreasing in Fs-value from 5.97 to 5.05 to 5.20 which are theaverage from the three vegetables canned in brine solutionwhile were from 25.9 to 24.4 to 22.1 for canned in tomatosauces (P< 0.05). Heating and cooling curves parameter werecombined with heat resistant parameters of isolated sporeformerto evaluate the carried out thermal process.12- Thermal process-time of 35, 25 and 15 min. at 112.10C,116.0°C and 120.2°C after come up times of3.5, 4.5 and 5.5min., for canned green beans in brine, 1.5, 1.8, 2.0 min. forcanned green peas m brine, while were 1.3, 1.5, 2.0 min. forcanned green okra In brine, respectively, was resulted in Fvaluesof 4.91 - 15.54, 7.02 - 16.03, and 9.23 - 12.58,4.6-18.16,0.66 - 12.39, and 9.22 - 13.31, 4.22 - 14.00,6.77-14.96, and 7.94 - 12.38 for canned green beans, peas and okrain brine solution, respectively. These calculation were basedon previously determined ”2” values of24.2, 25.8, 10.34 and24.4°C for B. subtilis, B. coagulans, B. stearothermophilus,and B. cereus respectively. On the other hand, thermal processtime of (60 - 65), (45 - 50) and (30 - 35) min. at 112.10C,116.0°C and 120.2°C after come up times of3.2, 3.5 and 4.5,3.0, 3.5 and 4.5, 3.0, 3.8 and 4.25 min. for canned greenbeans, peas and okra in tomato sauce, respectively, wasresulted in F-values of 4.08 - 16.02,4.18 -14.25, and 5.16-12.95, 4.35 - 17.60, 6.19 - 16.69, and 4.92 - 11.66, 4.34 _17.29, 5.78 - 16.33 and 4.83 - 11.14 for canned green beans,peas and okra in tomato sauce, respectively. These F-vaIuescalculated at the previously Z-vaIues.Calculated F-values to cover 12 D concept is 2.52 min.while calculated F-values to cover the commercial concept is10.68, 10.10 and 10.64 ( based on Dr = 2.0 for B.stearothermophilus ) this indicate that holding time atdifferent retort temperature for all vegetables underinvestigation is not enough to cover the commercial conceptfor B. stearothermophilus and covered other Bacillus. So, theoptimum thermal process time to cover the required F-valueswas evaluated. The evaluated optimum thermal process timeswere found to be 33.88 - 89.33, 27.38 - 80.06 and 33.16 -87.65 at 112.1°C, 23.16 - 38.50, 20.80 - 35.35 and 23.25 -38.60 min. at 116°C, 19.84 - 20.90,15.90 - 17.13 and 19.56-20.80 min. at 120.2°C for canned green beans, peas and okrain brine, respectively. On the other hand, the evaluatedoptimum thermal process times were found to be 65.61 -121.31, 44.27 - 96.95 and 58.27 - 113.76 min. at 112.1°C,57.07 - 70.70, 42.74 - 56.03 and 49.91 - 63.66 min. at 116°C,45.29 - 46.09,28.62 - 30.03 and 42.86 - 43.97 at 120.2°C forcanned green beans, peas and okra in tomato sauce,respectively.So, it IS recommended to avoid usmg of retorttemperature of 112.1°C (233.78°P) which required longholding time (reach from 89.33min. for canned vegetables inbrine solution and 121.31 min. for canned vegetables intomato sauce) In turn, may affect on the nutritional, physicalproperties of the product and degredation of quality and costenergy and labor (soft product) also, to avoid using retorttemperature 120.2°C (248.36°F) which required short holdingtime (reach from 20.9 min.in canned vegetables in brinesolution and 46.78 min. for canned vegetables in tomatosauce), in tum, may affect on the quality and physicalproperties of the product (hard product) it recommended theuse of retort temperature II6.0°C (240.80°F), for 38.50,35.35 and 38.6 min. for canned (green beans, peas and okra)vegetables in brine solution ,72.70, 56.03 and 63.66 min. forcanned vegetables (green beans, peas and okra) in tomatosauce to give a good organoleptically.I3.0rganoleptic evaluation showed that there were significantdifference between different blanching time. Also, betweendifferent thermal process (temp. - time) either for cannedvegetables in brine solution or tomato sauce for all vegetablesunder investigation. It is clear that blanching time for 3 min. at95°C was the best blanching time also, retort temp. 116.0°C wasthe best temperature to give a good organoleptic quality.