Studies On The Effect Of Adding Hydrogen Peroxide As A Milk Preservative:
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Gamal Fahmy El-nagar |
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Ph.D
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Benha University
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1993
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Milk.
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SUMMARY AND CONCLUSIONPrevention of raw milk spoilage during storage andtransportation can help to improve and enhance increased milkproduction and utilization. The use of hydrogen peroxide as amilk preservative was recommended by FAO in 1957. The use of H202must be with high concentrations to prolong the milk keepingquality which usually leads to deleterious effects in the liquidphase and the manufactured products. An alternative to preservea high milk quality is to activate the naturally occuringlactoperoxidase system (Lp-system). The IDF in 1988 reportedthat the Lp-system is an indigenous antibacterial system in milkand human saliva and its use in the presevation of raw milk havebeen recommended without any health hazards.Therefore, this investigation was planned to provide somedata on the effect of H202 per se and the Lp-system in thepreservation of raw cows’ and buffaloes’ milk under localconditions. It was worthwhile also, to evalute the feasibilityof using such milks in making low salt Domiati cheese andyoghurt.The investigation was carried out in three part.PartI: using hydrogen peroxide as a milk preservativeThe H202 concentration in milk of some collecting centersthat provide Misr & Food Company was determined. The H202concentration was followed up during the manufacture of milk.Also, some factors which affect the use of H202 in preservingmilk were studied. The results can be summarised as follows:I-The average concentration of H202 in milk of some collectingpoints ranged from 262.5 to 597.03 ppm.2-The average residual H202 in raw milk received by Misr Milk &Food Company ranged from 2.43 to 18.38 ppm for all collectingcenters of the surveyed gavernorates. The bulk milk from largefarms was free from H202•3-Milk samples containing 10 ppm H202 or lower producedpasteurized milk (90°C/15 sec.) free from residual H202• Thehigher content of H202 in raw milk produced more residual H202 inpasteurized milk. In Domiati cheese the residual H202 either incurd or whey was detected when the milk contains 25 ppm or more.The percentage of H202 decomposition decreased with increasingthe H202 concentration during heating of milk.4-The changes of pH were very limited in the low concentrations(200-350 ppm) when the milk stored at room temperature and thedecomposition of H202 was high. The pH of milk with high levelsof H202 (400-650 ppm) remained unchanged compared with thecontrol. The percent of recovery increased as the amount of addedH202 increased.Under cooling condition of milk storage the H202decomposition takes place in a low rate.S-Heating milk containing H202 showed that H202 is less stable athigher temperatures and the rate of decomposition is acceleratedat higher temperatures. Low levels of H202 added to milk are veryunstable and decompose rapidly.242 -6-Addition of H202 to raw milk increased the keeping quality ofmilk as evaluating by the bacterial count,titratable acidity andCOB test. The time of storage is dependant on the level of H20,added. The cows’ milk was found to be more stable than buffaloes’milk.7-There was a great reduction in H20, during milk separation, andthe rate of decomposition was affected by the H20, level in theseparated milk.Part II.Using lactoperoxidase system as a milk preservative.In this part some trials were carried out in order to attainthe maximum keeping quality of cows’ and buffaloes’ milks, whichwas evaluated by bacterial count, titratable acidity and COBtest.The results were as follws:I-The thiocyanate content in different kinds of milk variesgreatly. Sheep milk recorded the highest thiocyanate content asit reached up to 20.63 ppm. cows’, buffaloes’, goats’ milks andbulk raw mixed recorded 6.1,5.13,4.38 and 3.73 ppm respectively.2-Three combinations of SCN-:H,O, were used for application inpreservation of cows’ and buffaloes’ milk at ambient temp. Theseare 10:7.5,14:30 and 25:15 ppm of SCN-:H20,. The preservationeffect was more conspicuous by employing combination of 25:15followed by 14:30 and the lowest effect was 10:7.5 ppm of SCN-:H202 The keeping quality of cows’ milk was higher thanbuffaloes’ milk in all treatments.3-The effect of second dosing at 4 and 8 h interval showed thatthe selection of the 14:30 followed by adding 30 ppm H202 after4 h is more reseamable for application. The preservation of cows’and buffaloes’ milk was prolonged to 18 and 16 h successively.4-The electrophoretic patterns of preserved milk proteins in bothcows’ and buffaloes’ were discussed,Part III. Utilization of preserved milk in the manufacture ofsome dairy products.This part was undertaken to use cows’ and buffaloes’ milktreated with H202 (at levels of 200 and 250 ppm respectively) ortreated with Lp-system (14:30 ppm SCN-:H202 ) followed after 4 hby a second dose of 30 ppm H202 in the manufacture of Domiaticheese-like and yoghurt,The results can be summarized as follows:Section A: Domiati cheeseSeven treatments were done: cheese with 10% salt,5% salt,Lp-system + 5% salt,H202 + 5% salt, unsalted, Lp-system(unsalted) and H202 (unsalted).I-The treatment of milk cheese with the preservatives increasedthe coagulation time and yield while it slightly decreased thecurd tension the effect was more pronounced in the treatment withH202 than Lp-system. Also the effect of salt was discussed.2-The unsalted cheese was spoiled after the manufacture eithertreated or untreated.3-Treatment of cheese milk with preservatives e.g. Lp-system/H202or salt increased the moisture content and decreased the acidityin the resultant cheese.4-Using Lp-system and H202 treatments have no effect on saltcontent of the cheese. This is abvious in salt/water ratio.Storage of cheese decreased the salt content. Also, thetreatments have no effect on fat content.S-Treatment of cheese milk with preservatives have no effect onT.N. content of the resultant cheese but the differences are dueto variations in the moisture and salt contents. The T.N.decreased gradually during storage.6-The soluble nitrogen increased gradually during ripening. Itwas decreased as the salt content increased. However, decreasingthe salt (5% salt) raised the acidity and inhibit the proteolysisof protein and lowered S.N. content. Activation of Lp-system orH202-treatment reduced the S.N. content especially in the latter.The same trends was observed with tyrosine and tryptophancontent, shilovitch No. and TVFA content.7-There was no apparent differences in the electrophoreticpatterns of cheese protein due to the Lp-system or H202-reatments.a-The microbiological analysis of the cheese (T.C, coliforms,lipolytic and proteolytic bacterial count) showed that Lp-systemand H202-treatments have an inhibitory effect on all the floraexisted, and that H202-treatment has a stronger antimicrobialeffect than Lp-system.9-Using Lp-system treatment produce cheese with satisfactoryquality and ranked high scores within the visinity of that madeby the traditional method (10% salt). H202-treatment aquiredlower scores.Section B: Yoghurt1-Lp-system and H202-treatments delayed the sitting time in cows’and buffaloes’ milk.2-The curd tension and curd synersis from Lp-system treatment wasalmost the same as control in both cows’ and buffaloes’ while theH202-treatment caused a softening in the curd with high amount ofwhey exuded.3-There was a slight decrease in the pH and increase in theacidity of the yoghurt made from preserved milk than the controlin both cows’ and buffaloes’.4-No probable differences could be seen in T.S.,Fat and T.N. ofyoghurt due to preservatives. But, they were higher in buffaloes’yoghurt than that of cows’.5-A slight variations were observed in N.P.N. ,T.V.F.A. andacetaldehyde contents due to Lp-system and H202-treatment ofyoghurt milk and also due to kind of milk.6-The electrophoretic patterns of yoghurt protein made fromuntreated,Lp-system and H,02-treated milk were almost similar inboth cows’ and buffaloes’.7-The lactic acid bacteria, coliform and yeast & moulds countswere the highest in untreated yoghurt and they decreased in Lpsystemand H,O,-treated yoghurt and the reduction was moredrastic in the latter.B-The Lp-system treatment has no effect on the quality of yoghurtas the sensory scores were almost the same as control. While theHzOz-treatment affected the quality of yoghurt and it ranked thelowest score points. Yoghurt prepared from buffaloes’ milk ofdifferent treatments scored higher points than that from cows’milk. Storage improved the quality of yoghurt till 5 days afterwhich the quality decreased.9-The effect of storage for 5 and 10 days was discussed forall parameters.Conclusion-The keeping quality of raw milk can be prolonged to 10 h byactivation the lactoperoxidase system using 14:30 ppm of SeN:HzOz. While the storage period can be prolonged to over 16 h byadding second dose of 30 ppm HzOz after 4 h from the first dose.-The previous preserved milk (16 h) by Lp-system treated milk canbe manufactured to low salt Domiati cheese (5% salt) with a goodquality.-The Hzoz-treated milk with a concentration of 200 and 250 ppm(for cows and buffaloes) can be manufactured after preservation(16 h) to yoghurt and the treated milk can be manufactured to lowsalt Domiati cheese (5% salt) with an acceptable quality. |
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