Food microbiology.docx

**Food Microbiology** **Introduction to Food Microbiology** **A Brief History** - Early Food Preservation - 900 AD: Food poisoning recognized - 1795:Appert developed canning - 1854 -- 1864: Food Microbiology becomes a Science - Louis Pasteur **Ancient Practices** **Fermentatio...

**Food Microbiology** **Introduction to Food Microbiology** **A Brief History** - Early Food Preservation - 900 AD: Food poisoning recognized - 1795:Appert developed canning - 1854 -- 1864: Food Microbiology becomes a Science - Louis Pasteur **Ancient Practices** **Fermentation:** Used by ancient civilizations to create beer, wine, and leavened bread. These processes were empirical, without understanding the underlying microbial activity. **Preservation Methods:** Techniques like salting, drying, and smoking were developed to extend the shelf life of foods. **Key Figures** **Louis Pasteur (1822 -- 1895):** Demonstrated that microorganisms cause fermentation and spoilage. Developed pasteurization to prevent spoilage and kill harmful bacteria in beverages. **Robert Koch (1843 -- 1910):** Established Koch's postulates, which provided a systematic method to identify pathogens a systematic method to identify pathogens causing a specific disease, laying down the foundation for microbiology. **Timeline of Role of Microbes in Food** **Traditional Fermentation** - Used historically and currently in processes such as: - Alcohol production - Food Preservation - Taste and texture development - Active preservation of traditional techniques - Historical research into understanding early fermentation techniques in ancient cultures **Enhanced Fermentation** - Strain chosen, bred or engineered to improve taste, texture, & health - Using -omic tools to select and breed optimal strains for processes - Engineered strains producing additional vitamins, PUFAs, taste, odour in fermenting strains. **Animal Feed** - Biomass used in feed as: - Nutritional supplement - Primary food source - Nutraceutical and/or therapeutic platform - Strains chosen to match the needs of specific animals, methods, and aims. - Engineered into a therapeutic platform. - Biomass growth on waste substrate to optimize sustainability. **Ingredient Production** - Production and purification of native and recombinant food additives for - Nutrition - Taste/odour - Food processing - Engineered pathways to produce non-indigenous chemicals, proteins, or other biological substances. - Engineered living therapeutics, drugs delivered using probiotics. **Meat and Dairy alternatives** - Microbial meat analogues recreating nutrition, taste, and texture - Production of animal products components in cell factories - Engineered nutritional or texture elements allowing for closer meat resemblance. - Animal flavourings produced in cells **Single Cell protein** - Microbial food product including: - Primary protein source - Complete food source - Health supplement - Engineered to improve nutrition - Engineered into a therapeutic platform - Growth on waste substrates to optimize sustainability - Engineered taste compounds to improve organoleptic properties **Development of Food in Microbiology** **19^th^ Century** - **Pasteur's Contributions**: proved that microorganisms are responsible for spoilage and fermentation through his swan-neck flask experiments, leading to the development of sterilization and pasteurization techniques. - **Koch's Discoveries:** Introduced methods for isolating pure cultures and identifying pathogens, crucial for understanding foodborne illnesses. **20^th^ Century** - **Refrigeration:** Slowed microbial growth, significantly reducing food spoilage and extending shelf life. - **Antibiotics:** Introduced in food production to prevent and control bacterial contamination. **Advancements in Food Microbiology** **Microbial Genetics and Genomics** Understanding microbial DNA has allowed for genetic manipulation and the development of genetically modified organisms (GMOs) to enhance food safety and production. **HACCP (Hazard Analysis Critical Control Point)** A preventive approach to food safety that identifies critical control points in the production process to prevent hazards. **Probiotics and Functional Foods** Foods containing beneficial bacteria that promote health, such as yogurt with live culture **Detection of Organisms in Food** **Culture Dependent Techniques** Methods that rely in the growth of microorganisms on a specific media to identify and quantify them **Advantages** - Directly isolates and provides pure cultures of live organisms for analysis - Allows for enumeration and detailed study of microbial colonies. **Limitations** - Time consuming (several days to weeks) and labor-intensive - Not all microorganisms are culturable **Types of Culture Dependent Methods** **Plate Count Method** - Procedure: Serial dilution of food samples, nutrient agar plating, incubation, counting of colony forming units (CFU) - Applications: Commonly used for total viable counts in food samples. **Selective and Differential Media** - Selective Media: contain agents that inhibit the growth of unwanted microorganisms while promoting the growth of target ones. - Differential media: Distinguishes between species based on metabolic properties. **Enrichment Cultures** - Enhances the growth of specific microorganisms that may be present in low numbers - Procedure: Liquid media with specific nutrients and conditions that favor the growth of target microorganism before plating on solid media. **Non-Culture Dependent Techniques** Methods that detect microorganisms without the need for their growth in culture media **Advantages** - Faster results, often within hours to a few days - Higher sensitivity and specificity, capable of detecting viable but non-culturable (VBNC) microorganisms **Limitations** - May require sophisticated equipment and technical expertise - Typically more expensive in terms of initial setup costs. **Types of Non-culture Dependent Technique** **\-\-- Molecular Techniques \--** **PCR (Polymerase Chain Reaction):** Amplification of specific DNA sequences to detect the presence of pathogens. Identification of bacteria, viruses, and other pathogens in food samples. **qPCR (Quantitative PCR):** Provides quantitative data on the amount of microbial DNA present. Monitors microbial load and pathogen quantification. **Metagenomics:** Sequences all genetic material in a sample to profile entire microbial communities. Comprehensive analysis of microbial diversity and detection of unculturable organisms **\-\-- Immunological Techniques \-\--** **ELISA (Enzyme-Linked Immunosorbent Assay):** uses antibodies to detect specific antigens in food samples. Rapid detection of pathogens like *Salmonella, Listeria,* and *E. coli*. **Lateral Flow Assay:** uses antibody-antigen interactions in a simple, portable format. On-site, rapid screening for contaminants. **Biosensors:** Combine a biological component with a physicochemical detector to identify microorganisms. Uses Optical biosensors, electrochemical biosensors. Real-time, continuous monitoring of food for microbial contamination. **Case Study: Salmonella Detection** **Culture Dependent Methods** Enrichment: using selective broth like Rappaport-Vassiliadis to increase number of Salmonella cells. Selective media: Plating on XLD (Xylose Lysine Deoxycholate) agar to isolate and identify Salmonella colonies. Confirmation: Biochemical tests and serotyping for definitive identification **Non-Culture Dependent Methods** PCR: Targeting Salmonella-specific genes such as invA. ELISA: Detection of Salmonella antigens using specific antibodies. Biosensors: Rapid detection using devices tailored to Salmonella-specific markers **Why Study Food Microbiology** - Provide clean, safe, healthful food to consumer - Food permits growth - Control of microbial growth - Prevent food spoilage - Prevent food-borne illnesses - Food preservation and production **Food Borne Illnesses** - ERS Estimates: \$6.9 Billion/year cost of FBI - CDC estimates - 76 M cases of FBI/year - 325,000 hospitalization - 5000 deaths **What organism causes the most cases of food-borne illness annually?** *Campylobacter* **What organism causes the most deaths due to food-borne illness?** Salmonella **Spoilage Microorganisms** - Microorganisms that cause food to deteriorate and become unpalatable or unsafe. **Common Spoilage Microorganisms** **Bacteria:** Pseudomonas, Lactobacillus, Bacillus **Yeasts:** Saccharomyces, Candida **Molds:** Aspergillus, penicillium **Spoilage Mechanisms of Different Food Products** **Dairy Products** Mechanism: Lactic Acid bacteria produce lactic acid, leading to souring. Proteolytic bacteria break down proteins causing off-flavors. Common spoilage organisms: Lactobacillus and Pseudomonas **Meat and poultry** Mechanism: proteolytic bacteria break down proteins, causing foul odors and slime formation Common spoilage organisms: pseudomonas, clostridium, brochothrix **Fruits and Vegetables** Mechanism: yeast and molds metabolize sugars and organic acids, leading to fermentation and growth. Common spoilage organisms: Botrytis, Penicillium, Saccharomyces. **Canned Goods** Mechanism anaerobic: bacteria produce gas, causing swelling and spoilage Common spoilage organisms: clostridium, bacillus **Disease Causing Microorganisms (Pathogens)** Microorganisms that can cause foodborne illnesses when ingested **Common Pathogens** **Bacteria:** *Salmonella, E.coli, Listeria monocytogenes* **Viruses:** *Norovirus, Hepatitis A.* **Parasites:** *Toxoplasma gondii, Giardia lamblia* **Causative agents of Diseases and Associated Food Vectors** **Salmonella** - Disease: Salmonellosis - Symptoms: Diarrhea, fever, abdominal cramps - Common food vectors: raw or undercooked poultry, eggs, contaminated produce. **E. coli O157:H7** - Disease: Hemorrhagic colitis, hemolytic uremic syndrome (HUS) - Symptoms: sever stomach cramps, bloody diarrhea, vomiting. - Common food vectors: undercooked beef, contaminated raw vegetables, unpasteurized milk, **Listeria monocytogenes** - Disease: Listeriosis - Symptoms: fever, muscle aches, nausea, meningitis in severe cases - Common food vectors: ready to eat deli meats, unpasteurized dairy, smoked seafood **Spoilage Mechanisms in Dairy Products** **Milk** - Lactic acid bacteria ferment lactose into lactic acid, causing souring. Proteolytic bacteria break down casein proteins causing bitter flavors. - Common spoilage organisms: Lactobacillus and Pseudomonas **Cheese** - Mold growth on surface, yeast fermentation causing gas production and off-flavors - Spoilage microorganisms: penicillium, candida **Spoilage Mechanisms in Meat and Poultry** - Protein degradation: bacteria produce enzymes that break down proteins into amino acids and peptides, leading to foul odors. - Lipid oxidation: Microbial lipases degrade fats, causing rancidity. - Spoilage microorganisms; Pseudomonas, Clostridium, Brochothrix **Spoilage Mechanisms in Fruits and Vegetables** - Fermentation: yeast and molds metabolize sugars and organic acids, leading to fermentation and growth. - Mold growth: molds degrade cell walls, leading to soft rot and mycotoxin production. - Spoilage organisms: Botrytis, Penicillium, Saccharomyces. **Spoilage Mechanisms in Canned Goods** - Gas Production: Anaerobic bacteria produce hydrogen and CO2, causing cans to swell and sometimes burst. - Toxin production: some spoilage bacteria produce toxins that can cause food poisoning. - Spoilage organisms: clostridium, bacillus **The Microbiota of Food Products** **Exponential growth** - 20 minute generation time - Time 0: 1000/g - 30 min: 2000/g - 1 hour: 4000/g - 5 hours: 1,000,000/g **Microbial Growth Phases** A diagram of a line Description automatically generated **A --** Lag Phase **B --** Log/ Exponential phase **C --** Stationary Phase **D** -- Death phase **Intrinsic Factors** **pH** - Effects of pH - Enzymes - Nutrients - Other environmental factors - Temperature - Salt - Age - No known pathogen below pH 4.6 - *Clostridium botulinum* **Moisture** - Remove and/or bind moisture - Humectants - Dehydration - Water activity: Aw - Most fresh foods: Aw\>0.99  **Microbial Growth and Aw** - Halophilic: 0.75 - Xerophilic molds: 0.61 - Osmophilic yeasts: 0.61 - Lowest Aw for Pathogen Growth: 0.86 - *S. aureus* **Oxidation reduction Potential** - O/R Potential -- Eh - Ease with which substrate loses or gains electrons - Loss of electrons: oxidize - Gain of electrons: reduced - Aerobic - Anaerobic - Microaerobic - Facultative anaerobes **Others** - Nutrients - Fastidious vs. non-fastidious - Biological Structure - Antimicrobial factors - Naturally occurring factors **Extrinsic Factors** **Temperature** - Microorganisms grow over a wide range of temperatures - Psychotrophs - Mesophiles - Thermophiles - Psychroduric - Thermoduric **Other Factors** - Relative humidity of the environment - Can change the Aw - Environmental gasses - CO2, ozones **Presence of other microorganisms** - Competitive exclusion - General microbial antagonism - Lactic antagonism **Hurdle Concept** - Combine Intrinsic and Extrinsic Factors to Control Microbial Growth - Combination requires less severe treatments to foods to get desired inhibition