Izuzteno korisna prezentacija sa tipovima pitanja koja se mogu naći na testu-pitanja otvorenog i zatvorenog tipa, poveži, dopiši, razvrstaj, izračunaj, prepoznaj sliku itd.
Izuzteno korisna prezentacija sa tipovima pitanja koja se mogu naći na testu-pitanja otvorenog i zatvorenog tipa, poveži, dopiši, razvrstaj, izračunaj, prepoznaj sliku itd.
The document discusses pH and its impact on microorganisms. It defines pH as the negative logarithm of hydrogen ion concentration and describes the pH scale. It provides examples of the optimal and tolerated pH ranges for various bacteria, and discusses how pH affects the growth and development of different groups of microorganisms in foods. It also gives approximate pH values of various foods and explains how other environmental factors can interact with pH to impact microorganism growth.
15.uticaj procesnih parametara na rast i razmnožavanjeMaja Andjelkovic
Temperature is a key process factor that affects microbial growth and reproduction in foods. Microorganisms have three cardinal temperatures - minimum, optimum, and maximum temperatures - for growth. The optimum temperature for the growth of most pathogenic and spoilage microorganisms in foods is around 30°C.
The document discusses various extrinsic environmental factors that affect the growth of microorganisms, with a focus on temperature. It describes how microorganisms can be classified based on their optimal temperature ranges for growth, including psychrophiles, mesophiles, and thermophiles. The effects of temperature on microbial physiology and metabolism are explored, as well as its implications for food storage and safety.
Redox potential (Eh) is a physicochemical concept that reflects the ratio of oxidized and reduced forms of metabolites in a substrate. It acts selectively on the development of microorganisms in foods. Eh is expressed as a Eh-value, which is actually a measure of the oxidizing or reducing power of a chemical system. Reductions and oxidations are inseparable processes based on the transfer of electrons from one material to another. Materials that easily release electrons are good reducing agents, and those that easily accept electrons are good oxidizing agents. The redox potential of a substrate depends on pH, chemical composition, presence and mutual relationship of reductive (SH groups of proteins, hydrogen sulfide, ascorbic acid
The document discusses water activity (aw), which is an important factor that determines the development of microorganisms. aw represents the available water content in a substrate that microorganisms can use for their metabolic activity. It is defined as the ratio between the equilibrium vapor pressure of water in a food and the vapor pressure of saturated water vapor at the same temperature. aw values range from 0-1 and influence the growth and toxin production of various microorganisms. Foods are categorized based on their aw values as high, intermediate, or low moisture foods.
The document discusses pH and its impact on microorganisms. It defines pH as the negative logarithm of hydrogen ion concentration and describes the pH scale. It provides examples of the optimal and tolerated pH ranges for various bacteria, and discusses how pH affects the growth and development of different groups of microorganisms in foods. It also gives approximate pH values of various foods, meats, seafoods, and dairy products.
This document discusses nutrient utilization and microbial growth. It summarizes that microorganisms require nutrient-rich mediums containing amino acids and vitamins for growth. Milk contains low levels of free amino acids and peptides, so microbes have developed complex proteolytic systems to break down milk proteins into usable peptides and amino acids. These systems include extracellular proteinases and intracellular peptidases that hydrolyze proteins and peptides. The proteolytic system allows microbes to obtain essential amino acids needed for growth.
This document discusses the nutrients and conditions needed for the growth of microorganisms in foods. It notes that microbes break down proteins, fats, and carbohydrates in foods and can produce beneficial or harmful compounds. Under favorable conditions like sufficient nutrients and proper storage, microbe populations can increase exponentially to 107 cells/g within 8 hours. Controlling intrinsic factors such as pH, water activity, and antimicrobial components is important for microbiological control of foods.
This document discusses factors that influence the growth and development of microorganisms in food, including intrinsic, extrinsic, and implicit factors. Implicit factors relate to the microorganisms themselves, such as initial number, growth phases/reproduction rate, and interactions. A higher initial number of microorganisms and species adapted to the substrate and environment conditions allows for faster adaptation. Faster reproduction rates, represented by shorter generation times, also allow for more rapid growth under favorable conditions. Unfavorable substrate conditions prolong the generation time for all microorganisms.
1. Priprema namirnica za
mikrobiološko ispitivanje
Pravilniko metodama vršenja mikrobioloških analiza i
superanaliza životnih namirnica (Sl. List SFRJ, 25/80)
Sve vrste uzoraka namirnica za mikrobiološko ispitivanje
pripremaju se pod aseptičnim uslovima da bi se sprečila
kontaminacija uzorka mikroorganizmima iz okoline
-Meso i proizvodi od mesa
-Mleko i proizvodi od mleka
2. Meso i proizvodi od mesa
Meso trupova, polutki ili četvrtina, suvomesnati proizvodi:
površina mesa pripremljenog za ispitivanje opali se plamenom ili užarenom
metalnom špatulom. Sterilinim nožem ili makazama odstrani se sloj debljine
2-3 cm, a zatim se iz dubine izreže komad mesa 50-70g koji se potom usitni
i homogenizuje u tarioniku. Odmeri se 20 g uzorka i homogenizuje sa 180
ml fiziološkog rastvora (osnovno razređenje).
Kobasice:
U sterilinom uslovima ukloniti omotač kobasice i uzeti 50-70 g uzorka. Posle
usitnjavanja odmeri se 20 g i homogenizuje sa 180 ml fiziološkog rastvora
(osnovno razređenje).
Konzerve od mesa
Površina ambalaže (lim, plastika, staklo i sl.) očisti se vatom natopljenom
alkoholom, a zatim opali plamenikom. Ambalaža se sterilno otvara i uzima
se 50-70 g uzorka. Posle usitnjavanja odmeri se 20 g i homogenizuje sa 180
ml fiziološkog rastvora (osnovno razređenje).
3. Meso i proizvodi od mesa
Riba, rakovi, školjkaši, ježevi, puževi, žabe:
- mase do 0,5 kg – ispiraju se pod mlazom sterilne vode, uklone se glave,
škrge, oklopi, ljuske, bodljike i peraja. Ostali delovi se u količini od najmanje
100 g usitne u tarioniku posle čega sa odmeri 20 g i homogenizuje sa 180
ml fiziološkog rastvora (osnovno razređenje).
- mase preko 0,5 kg – površina iznad dovoljno debelog dela muskulature
se sastruže ili se ukloni oklop, opali plamenom ili užarenom metalnom
špatulom. Sterilno se ukloni opaljeni sloj i iz dubine izreže 50-70 g. Posle
usitnjavanja odmeri se 20 g i homogenizuje sa 180 ml fiziološkog rastvora
(osnovno razređenje).
• Soljena riba:
Uzorak se dobro očisti od soli i dobro ispere sterilnom vodom. U tarioniku se
odmeri 50-70 g. Posle usitnjavanja odmeri se 20 g i homogenizuje sa 180
ml fiziološkog rastvora (osnovno razređenje).
4. Mleko i proizvodi od mleka
Mleko, pasterizovano mleko, kiselo mleko, jogurt, kefir:
Uzorak se dobro promeša, pipetom se prenese 20 ml u Erlenmajer i doda
se 180 ml fiziološkog rastvora (osnovno razređenje)
Zgusnuto mleko:
Površina ambalaže se obriše vatom natopljenom alkoholom i opali
plamenom. Sterilnim nožem se napravi otvor i pipetom prenese 20 ml u
Erlenmajer i doda se180 ml fiziološkog rastvora (osnovno razređenje)
Pavlaka:
Površina ambalaže se obriše vatom natopljenom alkoholom i opali
plamenom. Otvori se ambalaža i pipetom prenese 20 ml u Erlenmajer i
homogenizuje sa 180 ml 2% rastvora natrijum citrata (osnovno
razređenje)
5. Mleko i proizvodi od mleka
Maslac, margarin, majonez, salate sa majonezom, kremovi,
kolači sa kremom:
Aseptično se ukloni ambalaža. U erlenamjer se odmeri 20 g uzorka i
homogenizuje sa 180 ml 2% rastvora natrijum citrata koji je prethodno
zagrejan na 45oC.
Sirevi i kajmak:
Za tvrde sireve aseptično se ukloni površinski sloj 0,5-1 cm debljine i uzorak
uzima iz dubine. Za topljene sireve aseptično se ukloni ambalaža. Za meke
sireve (sveži, sitni sir) uzorak se dobro izmeša. Odmerava se 20 g uzorka i
homogenizuje sa 180 ml 2% rastvora natrijum citrata koji je prethodno
zagrejan na 45oC.
Mleko u prahu, sladoled, prašak za sladoled:
Odmeri se 20 g uzorka i homogenizuje sa 180 ml fiziološkog rastvora
zagrejanog na 45oC
6. Homogenizacija uzorka
- Tarionik i tučak:
uzorak se homogenizuje u tarioniku, a u
Erlenmajeru se priprema osnovno razređenje
mućkanjem ili vibriranjem u toku 15 minuta
Stomaher:
osnovno razređenje se priprema
homogenizovanjem uzorka u
sterilnoj “stomaher kesi” u
trajanju 1-2 min.
7. Priprema serije razređenja
9 ml FR, PPS, 2% Na-
citrat
10-2 10-3 10-4 10-5 10-6 10-7
10-1 9 ml FR / PPS / 2% Na-citrat
Osnovno razređenje FR – fiziološki rastvor
20 g uzorka + 180 ml PPS – pepton Physiological Salt Solution
FR / PPS / 2% Na-citrat (pepton 1g, NaCl 8,5 g, dest. voda 1000 ml)