Bacteriological Analysis of Milk PDF
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Uploaded by EnviousZeugma
Ain Shams University
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Summary
This document provides a detailed account of various bacteriological techniques applied for the analysis of milk samples. It covers topics like pasteurization, sterilization, direct microscope methods, and specific tests like methylene blue and litmus milk reactions. The explanations are accompanied by images and diagrams to visualize the processes and results.
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# Section 9 - Bacteriological Analysis of Milk - Milk is a nutrient medium for pathogenic and non-pathogenic bacteria ## Bacteriological Standards for Milk: - **Pasteurization:** Heating (62°C for 30 minutes) - **Sterilization:** Arnold Heating (71.6°C for 15 seconds) - **By Pourplate:** *...
# Section 9 - Bacteriological Analysis of Milk - Milk is a nutrient medium for pathogenic and non-pathogenic bacteria ## Bacteriological Standards for Milk: - **Pasteurization:** Heating (62°C for 30 minutes) - **Sterilization:** Arnold Heating (71.6°C for 15 seconds) - **By Pourplate:** * Total Colony Counts * Coliform tests * Culture of pathogens * Testing for the heat-sensitive enzyme phosphatase - **Or direct microscope** ## Direct microscope: - **1: Loop from any dairy product** - **2: Airdry** - **3: Wash + Xylene 3 minutes + Alcohol** - **4: Fixation** - **5: Stain w/ "methylene blue"** - **6: Wash** - **7: Dry of heat** - **8: Examination** ### Results: * **Streptococcus:** <br> * **2 minutes** * **Bacillus** * **Lactobacillus (Short rod)** * **Cocci** ## Methylene blue: - **1 mL of raw milk + 1 mL of methylene blue + 5 drops of oil (to prevent oxygen reduction)** - **The color of methylene blue changes from blue to white** - **Methylene blue is used to differentiate between pathogenic and non-pathogenic bacteria** ### Results * **White:** abnormal milk * **Blue:** normal milk * **No bacteria** ### Microorganisms Concentrations: * **Short time reduction:** high concentration * **Long time reduction:** low concentration ## Quality: * **2h:** poor * **2-6h:** fair * **6-8h:** good * **above 8h:** excellent # Litmus Milk Reaction: - **Used to differentiate between microorganisms** - **Lactose fermentation:** enzyme beta-galactosidase * **Lactose --> glucose + galactose --> pyruvic acid** * **Litmus milk pH 7 (neutral) --> purple** * **Litmus milk pH 4 (acidic medium) --> pink** - **Gas production:** microorganisms hydrolyze protein, producing gas - **Litmus reduction:** purple --> white * **Reduction by microorganisms** - **Curd formation:** microorganisms produce acid and form curd (hard acid curd). The curd is formed by coagulating milk protein # Alkaline Reaction: - **Casein --> amino acids --> blue** - **Proteolysis (peptonization)** - **Hydrolyze the milk proteins (primarily casein) into their basic building blocks** - **Large quantities of ammonia** - **This results in an alkaline pH in the medium** - **Deep purple in the upper portion of the tube** - **The medium begins to lose a body and becomes translucent and brown** - **Whey - the protein is hydrolyzed to amino acids** # Reactions of Litmus Milk: * **Acid pH:** pink or red color * **Alkaline pH:** purple- blue color * **Reduction:** white * **Acid curd:** hard curd with clear supernatant * **Digestion:** dissolution of the clot with clear-gray color * **Rennet curd:** soft curd followed by peptonization * **Gas production:** bubbles in coagulated milk * **Negative test:** color and consistency remain the same
