Uticaj različitih temperatura sušenja sirnog zrna na sastav sirne grude dobijene od mleka u kome su obrazovani koagregati

The influence of different drying temperatures of curd particles in order to obtain curd particles with chemical composition characteristic for Dutch-type semi-hard cheeses was investigated. The experiments were performed with heat-treated milk at 87ºC for 10 minutes to induce chemical interaction between casein and serum proteins and to form the co-called co aggregates. The curd particles were dried at 42ºC and 45ºC for 60 minutes and two types of curd, named curd A and curd B were formed afterwards. The results of the experiments showed that the used temperatures had no significant influence on chemical composition of the curd. The average total solids of curd A was 49.09%, moisture in fat free basis (MFFB) 68.78% protein content 22.23%, lactose content 1.55%, ash 1.98%, titratable acidity 71.700T and pH 6.22. On the other side, the average values for curd B were 49.40%, 68.58%, 22.74%, 1.47%, 1.94%, 75.920T and 6.07, respectively. The use of different drying temperatures, as well as the other treatments (pressing, salting and ripening) provide conditions for semihard cheese producing, with the chemical composition similar to the Dutch-type semihard cheese prepared according to the traditional method.U radu je ispitivan uticaj različitih temperatura sušenja sirnog zrna sa ciljem dobijanja sirnog zrna koje je po sastavu karakteristično za polutvrde sireve holandskog tipa. U ogledima je korišćeno mleko kod kojeg je prethodnom termičkom obradom na 870C u toku 10 minuta, obrazovan hemijski kompleks između kazeina i serum proteina, poznatih u literaturi kao koagregati proteina mleka. Sušenje sirnog zrna izvršeno je na temperaturi od 420C, i nakon toga obrazovana sirna gruda A, i na temperaturi od 450C (sirna gruda B) u vremenu od 60 minuta. Rezultati istraživanja su pokazali da primenjene temperature sušenja nisu imale značajnijeg uticaja na hemijski sastav dobijene sirne grude. Prosečan sadržaj suve materije kod sirne grude A iznosio je 49.09%, sadržaj vode u bezmasnoj materiji sira (VBMS) 68.78% proteina 22.23%, laktoze 1.55%, pepela 1.98%, titraciona kiselost 71.700T i pH 6.22. Prosečan sadržaj suve materije kod sirne grude B iznosio je 49.40% vode u bezmasnoj materiji sira 68.58%, proteina 22.74%, laktoze 1.47% pepela 1.94%, titraciona kiselost 75.920T i pH 6.07. Primenom različitih temperatura sušenja sirnog zrna (42ºC i 45ºC), kao i daljim tehnološkim operacijama (presovanje, soljenje i zrenje) obezbeđeni su uslovi za dobijanje sira koji po hemijskom sastavu odgovara polutvrdim sirevima holandskog tipa, proizvedenim na tradicionalan način

Uticaj odabranih faktora koagulacije na hemijski sastav seruma dobijenog centrifugiranjem slatkog kazeinskog gela

Technological operations applied during curd processing influence syneresis and total solids content of cheese. Syneresis is not a simple physical process representing whey segregation due to curd contractions. Numerous factors can influence the process of syneresis. The aim of this work was to investigate the influence of various parameters (pH, quantity of CaCl2 added, temperature of coagulation and heat treatment) on induced syneresis. Reconstituted instant skim milk (control samples) and reconstituted instant skim milk heated at 87ºC for 10 min (experimental samples) were coagulated at 30ºC and 35ºC, and pH of 5.8 and 6.2 with 100, 200 and 400 mg/l of CaCl2 added. According to our results, these parameters had significant influence on nitrogen content of serum as well as on the distribution of nitrogen matter from gel into sera. Due to the formation of coaggregates the best rheological properties of gel were obtained for experimental samples coagulated with 400 mg/l of CaCl2 added at pH 5.8 and temperature of 35ºC.Tehnološke operacije koje se primenjuju za vreme obrade gruša, utiču na brzinu sinerezisa i na sadržaj suve materije sira. Sinerezis predstavlja izdvajanje surutke usled kontrakcija gruša i ne predstavlja jednostavan fizički proces. Na brzinu izdvajanja surutke odnosno sinerezis utiče veći broj faktora. U ovom radu je ispitivan uticaj različitih faktora primenjenog termičkog tretmana mleka, pH, količine dodatog CaCl2 i temperature koagulacije na količinu izdvojenog seruma odnosno sinerezis. Rekonstituisano obrano mleko (kontrolni uzorak) i rekonstituisano obrano mleko termički tretirano na 87ºC/10 minuta (ogledni uzorak) je koagulisalo pri različitim temperaturama 30ºC i 35ºC, pH vrednostima 5.8 i 6.2, kao i pri dodatku 100, 200 i 400 mg/l CaCl2. Na osnovu dobijenih rezultata može se zaključiti da ispitivani faktori koagulacije utiču na sadržaj azotnih materija u izdvojenom serumu. Kod oglednog uzorka u kojem je došlo do obrazovanja koagregata proteina mleka najbolje reološke osobine slatkog kazeinskog gela su dobijene pri sledećim uslovima koagulacije: 35ºC, pH 5.8 i dodatku 400 mg/l CaCl2

Karakteristike zrenja sira tipa Kamambera proizvedenog od mleka kod koga je obrazovan kompleks između kazeina i serum proteina

The Camembert-type cheese was produced from milk in which complex between casein and whey protein is formed by heating at 87°C during 10 min. After cooling to 40°C, 0.35% yogurt culture, 400 mg/1 CaCl2, suspension of Penicillium candidum culture and rennet were added to milk. Cheese ripening occurred during 20 days in ripening room at 10°C and humidity of 90-95%. The yield of cheese increased because of great total nitrogen matter utilisation due to the formation of co-aggregates, namely nitrogen matter content of whey was 0.0651%, which is significantly less related to traditional manufacturing. The deepest changes during ripening were observed in milk proteins, as indicated by high value of ripening coefficient (maturity index). At the end of 20 days' ripening, the soluble nitrogen content was 83.97%, i.e. it was 8.76-fold greater than at the beginning of ripening. The pH of cheese showed permanent increase, it arose from 4.02 to 5.82 during investigated ripening period. Titratable acidity decreased during the first ripening stage (1-10 days), from 237.73T to 146.18°T, due to protein breakdown induced by proteolytic system of Penicillium Candidum and lactic acid neutralization. At the second stage of ripening, titratable acidy increased to 190.13°T at the end of ripening period. The sensory characteristics of cheese (aroma, flavour and texture) were characteristic of this cheese type.Sir tipa Kamamber proizveden je od mleka kod kojeg je zagrevanjem na temperaturi od 87°C u toku 10 minuta obrazovan kompleks između kazeina i serum proteina. Na temperaturi od 40°C dodato je 0.35% jogurtne kulture, 400 mg/1 CaCl2, suspenzija Penicilium candidum i sirilo. Zrenje sira je bilo na temperaturi od 10°C, pri relativnoj vlažnosti od 90-95%, u vremenu od 20 dana. Sadržaj azota u surutki iznosio je 0.0651% i bio je manji u odnosu na surutku koja se dobija pri tradicionalnoj proizvodnji sireva, što je imalo za posledicu i veći randman. Najdublje promene za vreme zrenja odvijale su se na proteinima. Nakon 20 dana zrenja sadržaj rastvorljivog azota u ukupnom azotu iznosio je 83.97% i bio 8.76 puta veći u odnosu na prvi dan zrenja. Kao rezultat izraženih proteolitičkih procesa i pH vrednost sira se permanentno povećavala. Na kraju ispitivanog perioda zrenja pH vrednost sira je iznosila 5.82. Senzorne karakteristike sira (ukus, miris, konzistencija) bile su karakteristične za ovu vrstu sira

Obrazovanje kompleksa između kazeina i serum proteina u termički tretiranom mleku

When milk is heated at temperatures higher then 80°C the complex of casein and whey proteins is formed, well known as milk protein coaggregates. The high temperatures markedly reduce casein sensitivity for rennet. Curd made from milk treated at the temperature higher than 80°C, was too soft, weak and had bad rheological and technological 'properties. By lower pH, higher concentration of Ca2+, proteins and temperature coagulation, rate of coagulation of milk was reduced and could give curd with good rheological properties, acceptable for cheese production. Our results show that whey, obtained from milk treated at different high temperatures, had less than 50% of nitrogen and by 60% less milk fat than whey obtained from the raw milk or milk pasteurized at lower temperature.Zagrevanjem mleka na temperaturama višim od 80°C obrazuje se hemijski kompleks između kazeina i proteina surutke (B)-laktoglobulina i a-laktalbumina), u literaturi poznati kao koagregati proteina mleka. Mleko u koine su obrazovani koagregati znatno sporije koaguliše pod dejstvom proteolitičkih enzima koji se koriste u sirarstvu, pri čemu se obrazuje gruš loših tehnoloških i reoloških osobina nepodesan za dalju obradu i preradu u sir. Kombinacijom faktora koagulacije (pH mleka, temperature koagulacije, koncentracije kazeina i koncentracije jona kalcijuma) mogu se u velikoj meri da poboljšaju tehnološke osobine ovakvog mleka i učine ga podesnim za preradu u sir. Obrazovanje koagregata predstavlja jedan od načina većeg iskorišćenja proteina mleka. Na ovaj način iz mleka u sir može da pređe preko 90% proteina, tako da surutka praktično sadrži neproteinski azot. Surutka koja se dobija prilikom izrade sireva na bazi koagregata proteina mleka sadrži manje od 50% azota i oko 60% manje mlečne masti u odnosu na surutku koja se dobija pri tradicionalnoj proizvodnji ovih sireva

Osobine koprecipitata dobijenih pomoću različitih kiselina i distribucija azotnih materija mleka

For the production of co-precipitates, skim milk (0.05 % milk fat) was used. The chemical complex between casein and whey protein was formed by heating of milk at 87°C during 10 min, and at 95°C during 20 min, respectively. The pasteurised milk (80-85°C during 20 sec) was used as a probe. Co-precipitates were obtained from heat-treated milk by coagulation with 2.8 M HC1, 1.4 M H2SO4, 2.8 M lactic and 2.8 M acetic acids, respectively. Co-precipitates obtained by acetic acid were rather dry, lax and white, while co-precipitates obtained by H2SO4 and HC1, respectively, were a little sticky, compact and had pronounced yellow undertone. Co-precipitates obtained by lactic acid were compact and softer, probably due to higher moisture content (67.32%). As a measure of recoveries of milk nitrogen matter into co-precipitates, sera nitrogen content was used. Milk sera obtained by separation of co-precipitates, had a little nitrogen matter content, regardless of the acid used (0.0440% for HC1; 0.0465% for H2SO4; 0.0500% for acetic acid and 0.0464% for lactic acid). Nitrogen matter that remained in sera represents non-protein nitrogen, which represents 4-6% of total nitrogen matter of milk. Utilisation of nitrogen matter was greater when milk was treated at 87°C during 10 min than by pasteurisation of milk. Co-precipitates obtained from heat treated milk (87°C; 10 min) by HC1 had 11.61%. Co-precipitates obtained from pasteurised milk had 11.38% nitrogen matter. Nitrogen matter utilisation was greater when lactic acid was used (11.62%). .Za dobijanje koprecipitata korišćeno je obrano mleko sa 0.05 % mlečne masti. Hemijski kompleks između kazeina i serum proteina obrazovan je zagrevanjem mleka na 87°C u toku 10 min, i na 95°C u toku 20 min. Kao referentni uzorak korišćeno je pasterizovano mleko (80-85°C, 20 sec). Koprecipitati su dobijeni koagulacijom tehnički tretiranog mleka pomoću 2.8 M HCl, 1.4 M H2SO4, 2.8 M mlečne i 2.8 M sirćetne kiseline. Koprecipitati dobijeni pomoću sirćetne kiseline bili su suvi i rastresiti, bele boje, dok su koprecipitati dobijeni pomoću HC1 i H2SO4 bili malo lepljivi, kompaktni, sa izraženom žućkastom nijansom. Koprecipitati dobijeni pomoću mlečne kiseline bili su kompaktni, mekši i imali su najveći sadržaj vode (67.32%). Kao merilo prelaska azotnih materija iz mleka u koprecipitate korišćen je sadržaj azota u mlečnom serumu. Mlečni serum posle izdvajanja koprecipitata imao je mali sadržaj azota, bez obzira na korišćenu kiselinu (0.0440% za HC1; 0.0465% za H2SO4; 0.0500% za sirćetnu i 0.0464% za mlečnu kiselinu). To znači da azotne materije koje su zaostale u serumu predstavljaju praktično neproteinski azot, koga prema literaturnim podacima ima 4-6% u odnosu na ukupne azotne materije mleka. Istraživanja su pokazala da se zagrevanjem mleka na 87°C u toku 10 min postiže znatno veće iskorišćenje azotnih materija mleka u obliku koprecipitata dobijenih pomoću HC1 (11.61%), nego kod pasterizovanog mleka (11.38%) i da je ono nešto veće kada se koprecipitati dobijaju koagulacijom pomoću mlečne kiseline (11.62%)

Uticaj ispiranja sirnog zrna na sastav sirne grude dobijene od mleka u kome su obrazovani koagregati

The composition of curd A and curd B was investigated as influenced by the technological process known as curd washing after removing 1/3 or 1/2 of whey and replacing by the same volume of water at the drying temperatures of 42ºC and 45ºC, respectively. Milk used for experiments was heat-treated at 87ºC/10 min, during which the chemical complex between casein and whey proteins (milk protein co aggregates) was formed. It is shown that the applied drying temperatures of 42ºC (curd A) and 45ºC (curd B) do not have significant influence on the curd composition. The curd A and B gained without washing of the curd had 50.91% and 50.60% of moisture, respectively. If the curd washing process is applied after removing 1/3 of whey, the resulting curd has higher moisture content, 52.27% and 52.63%, respectively for the curd A and B. The highest moisture content in the curd is noted in the curd gained when 1/2 of whey is replaced by water during washing treatment. The same tendency is noted for the moisture in fat- free basis (MFFB), the parameter used for cheese classification. Also, it is observed that fat, protein and ash content are lower in the curd A and B when the curd washing process is applied than in the curd produced without the curd washing process. However, regardless of the increased moisture content of the curd gained by washing process, it is possible (even from heat-treated milk in which coaggreagates are formed) to achieve the average MFFB typical for semi-hard cheeses of Dutch type, by further technological processes such as molding, pressing, salting and ripening.U radu je ispitivan uticaj tehnološke operacije ispiranja sirnog zrna nakon odlivanja 1/3 i 1/2 surutke i dodatka iste količine vode pri temperaturama sušenja od 42ºC i 45ºC na sastav sirne grude (A i B). U ogledima je korišćeno mleko kod kojeg je prethodnim termičkim tretmanom na 87oC u toku 10 minuta, obrazovan hemijski kompleks između kazeina i serum proteina poznatih u literaturi kao koagregati proteina mleka. Rezultati istraživanja su pokazali da se hemijski sastav sirne grude bez primenjenog procesa ispiranja sirnog zrna pri različitim temperaturama sušenja 42ºC (sirna gruda A) i 45ºC (sirna gruda B) nije značajno razlikovao. Procesom ispiranja sirnog zrna izdvajanjem 1/3 surutke kod sirne grude A i B je uočeno povećanje sadržaja vode (52.27% i 52.63%), kao i ispiranjem pri izdvajanju 1/2 surutke (52.77% i 52.39%) u odnosu na sirnu grudu bez ispiranja sirnog zrna (50.91% i 50.60%). Isti trend je zabeležen i kod parametra voda u bezmasnoj materiji sira (VBMS), koji služi kao jedan od parametara za klasifikaciju sireva. Procesom ispiranja sirnog zrna (1/3 i 1/2) kod sirne grude A i B je uočeno blago sniženje sadržaja mlečne masti, proteina i pepela u odnosu na sirnu grudu kod koje nije primenjen proces ispiranja. Međutim, bez obzira na povećanje sadržaja vode u sirnoj grudi pri ispiranju sirnog zrna, tehnološkim operacijama kao što su kalupljenje, presovanje soljenje i zrenje moguće je postići prosečan sadržaj VBMS, koji je karakterističan za polutvrde sireve holandskog tipa, i od mleka u kome su obrazovani koagregati

Uticaj termičkog tretmana i dodate demineralizovane surutke u prahu na viskozitet čvrstog jogurta

Skim milk powder was reconstituted to obtain milk A (with 8.44% TS). Milk sample A was standardized with different amounts of demineralized whey powder (DWP) to obtain milk B (with 9.71% TS) and milk C (with 10.75% TS). Milk samples were heat treated at 85ºC/20 min and 90ºC/10 min, respectively. Untreated milk was used as control. Milk samples were inoculated with 2.5% of commercial yogurt culture (containing Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus in the ratio 1:1) at 43ºC. Samples were incubated until pH 4.6 was reached. Samples were immediately cooled to 4ºC and held at that temperature until analyses. Measurements of viscosity were done with Brookfield DV-E Viscometer. Spindle No 3 at 20 rpm was used for all samples. After 1 day of storage, set-style yogurt samples produced from untreated milk had the highest, while samples produced from milk heat treated at 90ºC/10 min the smallest initial viscosity, regadless of the dry matter content and composition. Average viscosity of set-style yogurts decreased with intensifying temperature of applied heat-treatment. During storage, set-style yogurt samples produced from milk heat treated at 90ºC/10 min had the least pronounced decrease of viscosity during shearing. After 14 days of storage, set-style yogurt samples produced from milk standardized with demineralized whey powder had higher viscosity than samples produced from basis milk.Obrano mleko u prahu je rekonstituisano i dobijeno je mleko A (sa 8.44% SM). Mleku A je dodavana demineralizovana surutka u prahu i dobijeni su uzorci mleka B (sa 9.71% SM) i mleka C (sa 10.75% SM). Svi uzorci su termički tretirani na 85ºC/20 min i 90ºC/10 min. Kao kontrolni uzorak korišteno je termički netretirano mleko. Svi uzorci su inokulisani na 43ºC sa 2.5% tečne jogurtne kulture (Lactobacillus delbrueckii subsp. bulgaricus i Streptococcus thermophilus u odnosu 1:1) i inkubirani do postizanja pH 4.6. Nakon fermentacije uzorci su ohladjeni na 4ºC i držani na toj temperaturi do analize. Viskozitet je određivan nakon 1., 7. i 14. dana skladištenja pomoću Brookfield-ovog viskozimetra DV-E pri brzini rotacije spindla od 20 o/min. Nakon 1. dana skladištenja, uzorci čvrstog jogurta proizvedeni od netretiranog mleka imali su najveće a uzorci proizvedeni od mleka termički tretiranog na 90ºC/10 min najmanje inicijalne vrednosti viskoziteta, bez obzira na sastav i sadržaj suve materije. Ujedno, srednja vrednost viskoziteta čvrstog jogurta se smanjuje sa povećanjem temperature primenjenog termičkog tretmana. Tokom skladištenja uzorci čvrstog jogurta proizvedeni od mleka termički tretiranog na 90ºC/10 min imaju najmanje izraženo smanjenje viskoziteta tokom vremena. Nakon 14 dana skladištenja uzorci jogurta proizvedeni od mleka standardizovanog DSUP imaju veće vrednosti viskoziteta od uzoraka proizvedenih od mleka A

Uticaj odabranih faktora na brzinu koagulacije mleka

The influence of pH (6.5 and 5.8), amount of added CaCl2 (0, 200 and 400 mg/l)), coagulation temperature (30ºC and 35ºC) and heat treatment of milk (65ºC/30 min and 87ºC/10 min) on the rate of rennet induced milk coagulation (s) were investigated. The time (s) from rennet addition to onset of gelation (as indicated by the first visible floccules) was measured. The milk samples heat-treated at 87ºC/10 min, with 400 mg/l added CaCl2, which were coagulated at 35ºC and pH 5.8, coagulated 23.28-fold faster than the same samples without added CaCl2, which were coagulated at 30ºC and pH 6.5. The results of investigations related to the influence of particular coagulation factors on the coagulation rate of heat-treated milk showed that at pH 6.5 the most pronounced influence was demonstrated by the amount of Ca2+ and temperature of coagulation. At pH 5.8, different amounts of Ca2 and used temperatures of coagulation did not influence coagulation rate regardless of the used heat treatment of milk. The influence of used heat treatment of milk was particularly pronounced during coagulation of samples without added CaCl2 that coagulated at 30ºC and pH 6.5. The used heat treatment of milk practically did not influence the milk coagulation rate at pH 5.8. The greatest influence on milk coagulation rate was showed by pH. This influence was the most marked in coagulation of samples in which the coaggregates were formed, regardless of the amount of added Ca2+ and used coagulation temperatures.U okviru ovih istraživanja ispitivana je brzina koagulacije mleka (s) u zavisnosti od pH mleka (6.5 i 5.8), količine dodatog CaCl2 (0, 200 mg/l i 400 mg/l), temperature koagulacije (30ºC i 35ºC) i režima termičke obrade mleka (65ºC/30 min i 87ºC/10 min). Kod svih ogleda odredjivano je vreme (s) od momenta dodavanja sirila do pojave prvih vidljivih pahuljica gruša. Uzorci mleka termički tretirani na 87ºC/10 min kojima je dodato 400 mg/l CaCl2, čija je temperatura koagulacije bila 35ºC, a pH 5.8 koagulisali su 23.28 puta brže u odnosu na iste uzorke kod kojih nije dodat CaCl2, čiji je pH bio 6.5, a temperatura koagulacije 30ºC. Rezultati istraživanja koji se odnose na uticaj pojedinačnih faktora koagulacije pokazala da je uticaj Ca2 s jedne strane i temperatura koagulacije s druge strane bio jače izražen kod mleka u kojem su obrazovani koagregati, pri čemu je ovaj uticaj bio naročito izražen pri pH 6.5. Pri pH 5.8 različite koncentracije Ca2+ i primenjene temperature koagulacije nisu imali veliki uticaj na brzinu koagulacije bez obzira na primenjeni režim termičke obrade. Uticaj termičkog tretmana naročito je bio izražen kod uzoraka bez dodatog CaCl2, čija je temperatura koagulacije bila 30ºC, a pH 6.5. Pri pH 5.8 brzina koagulacije praktično više nije zavisila od primenjenih režima termičke obrade mleka. pH mleka imao je najveći uticaj na brzinu koagulacije mleka. Uticaj pH najviše je bio izražen kod uzoraka u kojima su prethodno obrazovani koagregati pri svim koncentracijama Ca2+ i primenjenih temperatura koagulacije

Uticaj odabranih faktora koagulacije na indukovani sinerezis

Syneresis is the process of whey separation induced by gel contraction resulting in rearranging or restructuring of casein matrix formed during enzymatic coagulation. Numerous factors can influence the process of syneresis. The influences of pH, calcium concentration, temperature of coagulation of milk and applied heat treatment on the syneresis induced by different intensity of centrifugal force have been investigated. Coagulated samples were centrifuged at 1000, 2000 and 3000 rpm for 5 min, respectively. Reconstituted skim milk powder (control sample) and reconstituted non-fat milk heat treated at 87ºC/10 min (experimental sample) are coagulated at temperatures of 30ºC and 35ºC, at pH value of 5.8 and 6.2, and with the addition of 100, 200 and 400 mg/l of CaCl2, respectively. Centrifugation at 1000 rpm of both control and experimental samples didn’t recover any sera, regardless of the applied coagulation conditions. This indicates that the intensity of centrifugal force wasn’t strong enough to disrupt gel structure and cause syneresis. When the intensity of centrifugal force was increased up to 2000 rpm, the syneresis was induced, but the degree of syneresis depended on the applied factors of coagulation, primary on the applied heat treatments and temperature of coagulation. The amount of added CaCl2 didn’t have a significant influence on the induced syneresis at 2000 rpm. The induced syneresis was very significant for both control and experimental samples when the intensity of centrifugal force of 3000 rpm was applied. It was also noted that curd produced from heat treated milk in which milk protein coaggregates were formed, released less sera regardless of the applied coagulation factors.Sinerezis je proces izdvajanje surutke usled kontrakcije gruša, pri čemu dolazi do rearanžiranja, ili prestruktuiranja kazeinske mreže, koja je nastala tokom enzimske koagulacije, na koji utiče veliki broj faktora. U ovom radu je ispitivan uticaj pH, koncentracije Ca2+, temperature koagulacije mleka i uticaj termičkog tretmana na indukovani sinerezis pod uticajem različitog intenziteta centrifugalne sile. Koagulisani uzorci mleka centrifugirani su pri 1000, 2000 i 3000 o/min u vremenu od 5 minuta. Rekonstituisano obrano mleko u prahu (kontrolni uzorak) i rekonstituisano obrano mleko termički tretirano na temperaturi 870C/10 minuta (ogledni uzorak) je koagulisalo pri različitim temperaturama 30ºC i 35ºC, pH vrednostima 5.8 i 6.2, kao i pri dodatku 100, 200 i 400 mg/l CaCl2. Centrifugiranjem kontrolnih i oglednih uzoraka pri 1000 o/min, bez obzira na uslove koagulacije nije dovelo do izdvajanja seruma iz gela, pa se može zaključiti da intenzitet primenjene centrifugalne sile nije bio dovoljno veliki da naruši strukturu gela i izazove sinerezis. Sa povećanjem intenziteta centrifugalne sile (2000 o/min), dolazi do većeg, ili manjeg stepena pojave indukovanog sinerezisa, a uočava se uticaj ispitivanih faktora koagulacije, pre svega primenjenih termičkih tretmana, pH vrednosti temperature koagulacije, a u manjoj meri i količine dodatog CaCl2 na količinu izdvojenog seruma. Pri delovanju centrifugalne sile većeg intenziteta (3000 o/min), kod kontrolnih i kod oglednih uzoraka u znatno većoj meri je uticalo na količinu izdvojenog seruma. Takodje je uočeno da gel dobijen od mleka u kojem su obrazovani koagregati, pri svim ispitivanim faktorima koagulacije, izdvaja manju količinu seruma u odnosu na kontrolne uzorke

Uticaj sadržaja suve materije, primenjenih termičkih tretmana i perioda skladištenja na viskozitet tečnog jogurta

Skim milk powder reconstituted to 8.44% TS, 9.65% TS and 10.84% TS respectively was used for investigation. Untreated milk and milk heat treated at 85ºC/20 min and 90ºC/10 min, respectively, were used for the investigation. Milk was inoculated with 2.5% of yogurt culture (containing Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus in the ratio 1:1) at 43ºC. Samples were incubated until pH 4.6 was reached. Samples were immediately cooled to 4ºC and held at that temperature during 14 days. Acid casein gel was stirred after 1, 7 and 14 days of storage. Measurements were done at 30 rpm during 2 min, at 20ºC. According to the investigation, it could be concluded that both applied heat treatment and dry matter content influence viscosity of stirred yogurt. Viscosity increases when dry matter content increases. The smallest viscosity had yogurt produced from untreated milk with 8.44% TS, while samples produced from milk with 10.84% TS had the highest viscosity. Applied heat treatments had significant influence on viscosity of yogurt gained by stirring of acid casein gels after 7 and 14 days of storage. Stirred yogurt produced from milk heat treated at 90ºC/10 min had a higher viscosity than samples produced from milk heat treated at 85ºC/20 min. Storage period influenced average viscosity of stirred yogurt. Samples of stirred yogurt produced from milk with 8.44% TS showed a decrease of average viscosity during storage regardless of the applied heat treatment of milk. The highest average viscosity had samples produced from milk with 10.84% TS.U okviru ovih istraživanja korišćeno je rekonstituisano obrano mleko u prahu sa 8.44% SM, mleko sa 9.65% SM i 10.84% SM. Za fermentaciju je korišćeno termički netretirano mleko i mleko termički tretirano na 85ºC/20 min i 90ºC/10min. Fermentacija je izvršena na temperaturi od 43ºC, sa dodatkom 2.5% tehničke jogurtne kulture (Lb. delbrueckii subsp. bulgaricus i Str. thermophilus u odnosu 1:1). Fermentacija je prekinuta pri pH 4.6. Uzorci su zatim brzo ohlađeni na 4ºC i skladišteni na toj temperaturi u toku 14 dana. Kiseli kazeinski gel je pre merenja viskoziteta razbijan nakon 1, 7 i 14 dana skladištenja na 4ºC. Sva merenja su vršena pri brzini rotacije spindla od 30 obrt/min tokom 2 min, na temperaturi od 20ºC. Na osnovu istraživanja može se zaključiti da na vrednost viskoziteta tečnog jogurta dobijenog nakon razbijanja kiselog kazeinskog gela utiču primenjeni termički tretman i sadržaj suve materije. Sa povećanjem suve materije povećava se i viskozitet tečnog jogurta. Najmanji viskozitet je imao jogurt proizveden od termički netretiranog mleka sa 8,44% SM, a najveći jogurt proizveden od mleka sa 10,84% SM. Primenjeni termički tretmani mleka imali su značajan uticaj na viskozitet tečnog jogurta dobijenog razbijanjem kiselog kazeinskog gela nakon 7 i 14 dana skladištenja. Tečni jogurt dobijen od mleka termički tretiranog na 90ºC/10 min imao je veći viskozitet od uzoraka proizvedenih od mleka termički tretiranog na 85ºC/20 min. Period skladištenja je uticao i na srednju vrednost viskoziteta tečnog jogurta. Kod tečnog jogurta sa 8,44% SM srednja vrednost viskoziteta se smanjuje tokom perioda skladištenja bez obzira na primenjeni termički tretman mleka. Najveće srednje vrednosti viskoziteta imali su uzorci proizvedeni od mleka sa 10,84% SM