Uticaj odabranih faktora na tok kisele i sirišne koagulacije kozjeg mleka i kvalitet jogurta i sireva

Abstract

rasta. Njegov značaj sa socijalno-ekonomskog stanovišta posebno je veliki u pojedinim regionima, gde se znatna količina proizvedenog mleka koristi za konzumiranje ili prerađuje u veliki broj varijeteta sireva, koji često nose oznaku geografskog porekla, kao i jogurt. Cilj ove disertacije je bio da se detaljnije prouči efekat niza odabranih faktora na reološke parametre kisele i sirišne koagulacije kozjeg mleka, svojstva dobijenog gela kao i kvalitet proizvedenih jogurta i sireva. Za istraživanje je korišćeno mleko dve rase koza, Sanske i Alpske i obuhvaćena su sva tri laktaciona perioda (rani, srednji i kasni). Iako je fizičko-hemijski sastav kozjeg mleka veoma sličan kravljem, razlike na nivou strukture i svojstava pojedinih komponenata kozjeg mleka, pre svega proteina, predstavljaju uzrok njegovih drugačijih tehnoloških svojstava i značajan su faktor koji utiče na inferiorniju teksturu proizvedenog jogurta ili manji randman sira. Sa druge strane, pojedini procesni parametri u proizvodnji mlečnih proizvoda, poput termičke obrade mleka ili dodavanja kalcijum-hlorida, imaju dobro poznat efekat na kravlje mleko, ali njihov uticaj na kozje mleko je često drugačiji, zbog čega se postavlja pitanje njihove adekvatne primene. Ovo polje ispitivanja je još uvek otvoreno i potrebna su dodatna istraživanja u cilju optimizacije tehnoloških postupaka proizvodnje kozjih mlečnih proizvoda. Kako bi se istražio uticaj pojedinih faktora na svojstva kozjeg mleka tokom kisele i sirišne koagulacije kao i mogućnosti unapređenja kvaliteta jogurta i sireva, u okviru ove disertacije obavljen je niz ogleda. U prvom delu disertacije ispitan je uticaj dodatka izolata proteina mleka na reološka svojstva kisele koagulacije i kvalitet jogurta od kozjeg i kravljeg mleka, kako bi se utvrdile mogućnosti primene ovog dodatka za poboljšanje teksture kozjeg jogurta u poređenju sa jogurtom od kravljeg mleka. U drugom delu je istražen uticaj enzima transglutaminaze i dva termička tretmana mleka na tok kisele koagulacije kozjeg mleka i teksturu jogurta tokom perioda skladištenja. Efekti ovog enzima, termičkih tretmana i acidifikacije pod dejstvom starter kulture na proteine mleka i jogurta određeni su elektroforetski. Takođe, ispitan je i uticaj ovog enzima na preživljavanje starter kulture tokom skladištenja i obavljena je senzorna ocena ovih proizvoda. Efekti tri termička tretmana (72 °C/30 s, 85 °C/5 min i 95 °C/5 min) istraženi su u narednom delu ogleda u pogledu reoloških svojstava kiselog gela i teksture jogurta čvrstog tipa (eng. set style). Ovom prilikom je ispitan i uticaj koji ovi tretmani imaju na prosečnu veličinu kazeinskih micela metodom dinamičkog rasejanja svetlosti i proteinski profil tretiranih mleka. Sledeći segment disertacije obuhvatio je reološka ispitivanja uticaja niza faktora na tok sirišne koagulacije mleka i svojstva sirišnog gela. U okviru ovih ogleda ispitani su navedeni faktori: 1) koncentracija sirila (0,054 g/l, 0,020 g/l, 0,015 g/l i 0,010 g/l); 2) pH mleka (6,5, 6,3 i 6,1); 3) temperatura koagulacije (27, 31 i 35 °C); 4) period laktacije (rani, srednji i kasni) i 5) termički tretmani mleka i dodatak kalcijum-hlorida (65 °C/30 min, 80 °C/5 min i 90 °C/5 min, bez ili sa dodatkom 200 mg/l CaCl2)...

Goat's milk is a nutritionally high-value food whose production in the world has a growing trend. Its importance from the socio-economic point of view is especially great in some regions, where a significant amount of this milk is used for consumption or processed into a large number of varieties of cheeses, which often posess a geographical indication, and yogurt. The aim of this dissertation was to study in more detail the effect of a number of selected factors on the rheological properties of acid and rennet coagulation of goat's milk, the characteristics of the obtained gel as well as the quality of produced yoghurts and cheeses. Milk from two breeds of goats, Saanen and Alpine, was used for the research and all three lactation periods (early, middle and late) were included. Although the physicochemical composition of goat's milk is very similar to cow's milk, differences in the structure and properties of individual components of goat's milk, primarily proteins, are the cause of its different technological properties and are a significant factor affecting the inferior texture of yoghurt or lower yield of final cheese. On the other hand, certain process parameters in the production of dairy products, such as heat treatment of milk or addition of calcium chloride, have a well-known effect on cow's milk, but their impact on goat's milk is often different, which raises the question of their adequate application. This field of research is still open and further research is needed in order to optimize the technological procedures of goat dairy production. In order to investigate the influence of certain factors on the properties of goat's milk during acid and rennet coagulation, as well as the possibility of improving the quality of yogurt and cheese, a series of experiments was performed within this dissertation. In the first part of the dissertation, the influence of milk protein isolate on the rheological properties of acid coagulation and the quality of goat's and cow's milk yogurt was examined, in order to determine the possibilities of using this supplement to improve the texture of goat's yogurt compared to cow's milk yogurt. In the second part, the influence of the enzyme transglutaminase and two heat treatments of milk on the course of acid coagulation of goat milk and the texture of yogurt during the storage period was investigated. The effects of this enzyme, heat treatments and acidification under the action of starter culture on milk and yoghurt proteins were determined electrophoretically. Also, the influence of this enzyme on the survival of starter culture during storage was examined and a sensory evaluation of these products was conducted. The effects of three goat milk heat treatments (72 °C/30 s, 85 °C/5 min and 95 °C/5 min) were investigated in the next part of the experiment in terms of rheological properties of acid gel and texture of set type yogurt. On this occasion, the influence that these treatments have on the average size of casein micelles by the method of dynamic light scattering and the protein profile of treated milk was also examined. The next segment of the dissertation included rheological investigations of the influence of a number of factors on the course of rennet coagulation of milk and the properties of rennet gel. Within these experiments, the following factors were examined: 1) rennet concentration (0.054 g/l, 0.020 g/l, 0.015 g/l and 0.010 g/l); 2) milk pH (6.5, 6.3 and 6.1); 3) coagulation temperature (27, 31 and 35 °C); 4)lactation period (early, middle and late) and 5) heat treatments of milk and addition of calcium chloride (65 °C/30 min, 80 °C/5 min and 90 °C/5 min, without or with the addition of 200 mg/l CaCl2)...