Adv Cert_Nutrition - Tutorial (3 lectures)_updated 231125.pdf

Advanced Certificate in Nutrition Tutorial Dr. Rachel Ching [email protected] 1 Exam format – Module 3 (Food microbiology and Food safety) • Exam date: 15 Dec 2023 (Fri) • Exam duration: 1 hour • Exam format: • Section A (60%) – 30 Multiple-choice Questions • 4 options for each question • 1 m...

Advanced Certificate in Nutrition Tutorial Dr. Rachel Ching [email protected] 1 Exam format – Module 3 (Food microbiology and Food safety) • Exam date: 15 Dec 2023 (Fri) • Exam duration: 1 hour • Exam format: • Section A (60%) – 30 Multiple-choice Questions • 4 options for each question • 1 mark each • Section B (40%) – 2 Long Questions • Answer any 2 out of 3 questions • 10 marks each • Total marks: 50 marks 3 Topics 1. 2. 3. 4. 5. 6. 7. Foundation to food microbiology Microorganisms associated with food Useful microorganisms in food processing Food spoilage Factors influencing the growth of microorganisms Foodborne illness: bacteria Foodborne illness: virus, mold, and protozoa (& Food preservation) 4 Multiple Choice Question - Examples E.g.1. Which of the following statement about thermophiles is CORRECT? A. B. C. D. Salmonella spp. is a thermophile. The spore formed by thermophile is usually psychrophilic. Thermophiles can grow well at 600C. Thermophiles are sensitive to heat and killed at 1000C. (1 mark) 5 Multiple Choice Question - Examples E.g.2. Which of the following microorganism can form spore as a mean of reproduction? A. B. C. D. Staphylococcus aureus Vibrio cholerae Listeria monocytogenes Clostridium botulinum (1 mark) 6 Multiple Choice Question - Examples E.g.3. Which one of the following is LEAST likely to cause spoilage of food stored in refrigerator? A. Molds B. Thermophilic bacteria C. Yeasts D. Psychrophilic bacteria (1 mark) 7 Multiple Choice Question - Examples E.g.4. Which one of the following is an extrinsic factor for microbial growth? A. pH B. Water activity C. Salt content D. Gaseous concentration (1 mark) 8 Multiple Choice Question - Examples E.g.5. Which of the following is not a purpose of pasteurization? A. B. C. D. Kill all the spoilage microorganisms. Kill all the pathogenic microorganisms. Increase the shelf life of milk. Inactivate proteases in milk. (1 mark) 9 Multiple Choice Question - Examples E.g.6. What is bound water of food? A. B. C. D. Adding salt can increase the bound water content in food. The freezing point of bound water is 0˚C. Drying reduces the amount of bound water in food. Bound water supports the growth of molds. (1 mark) 10 Multiple Choice Question - Examples E.g.7. The food is called shelf stable if its water activity is less than ________. A. B. C. D. 0.9 0.8 0.6 0.5 (1 mark) 11 Multiple Choice Question - Examples E.g.8. Ergot poisoning is due to the consumption of food contaminated by ____________. A. B. C. D. Claviceps purpurea Aspergillus flavus Gambierdiscus toxicus Clostridium botulinum (1 mark) 12 Multiple Choice Question - Examples E.g.9. Which of the following statement about sterilization is CORRECT? A. Sterilization is a low temperature treatment to kill microorganisms. B. Sterilization is commonly used to treat heat sensitive food product. C. Sterilization can be used to produce canned food. D. Temperature used in sterilization is less than 100°C. (1 mark) 14 Multiple Choice Question - Examples E.g.10. Adding vinegar to preserve the food item like vegetable is called __________. A. B. C. D. Fermentation Pickling Curing Filtration (1 mark) 15 Long Question – Example 1 Refer to the following microbial growth rate curve: B C A Organisms can be classified based on the growth temperature a) State the term used to describe the organisms that can grow in the temperature range A, B, C (3 marks). b) Give an example of bacteria (name and state the food source) that can exist in range A, B, C (3 marks). c) Briefly describe TWO other factors that will affect the bacterial growth in 17 food (4 marks). Revision: L5. Factors Influencing the Growth of Microorganisms • Describe the key features of a microbial growth curve • Explain how different factors contribute to microbial growth • Differentiate between psychrophiles, mesophiles, and thermophiles based on the growing temperature • To recognize the various approaches employed to inhibit microbial growth in the food industry 21 Microbial growth curve 1. Lag phase (why?) • • Adapting to the growth conditions DNA and protein synthesis 2. Log phase (why?) • Favorable growth conditions • Support exponential growth 22 Microbial growth curve 3. Stationary phase (why?) • Reduced nutrients • Accumulating metabolic waste products 4. Death phase (why?) • Nutrients are depleted • Too much metabolic waste products 23 Factors influencing the growth of microorganisms Intrinsic factors: Extrinsic factors • • • • • • • Temperature • Atmosphere • Relative humidity Water activity pH Redox potential Nutrient content Biological structure Antimicrobial content 24 Intrinsic factors – Water activity • Water is required for microbial growth • aw of most fresh foods > 0.95 • aw of dehydrated foods < 0.60 • Minimal aw required for microbial growth: • Molds (0.8) < Yeasts (0.88) < Bacteria (0.9) • Food with aw < 0.6 = shelf stable 25 Intrinsic factors – Water activity • Water activity and control microbial growth • Decrease moisture content • Drying • Freeze drying • Increase the amount of bound water • Addition of solutes or ions • Freezing 26 Intrinsic factors – pH • pH ranges for microbial growth • Bacterial pathogens are usually unable to grow < pH 4.0 • Minimal pH required for microbial growth: Molds < Yeasts < Bacteria • Foods can be grouped as • High-acid food (pH < 4.6) e.g. fruits and fermented foods • Low-acid food (~ pH 4.6 – 7.0) e.g. some vegetables, meat and milk • pH 4.6 is the lower limit for the growth of spore forming Clostridium botulinum • pH and control microbial growth • Addition of weak acids (E.g. vinegar in pickling) • Fermentation 27 Intrinsic factors – Redox potential • Oxygen is a factor affecting the Eh of a food • Oxygen increases the Eh • Environment with a positive Eh à food favors oxidation • Called “Aerobic system” • Environment with a negative Eh à food favors reduction • Called “Anaerobic system” • Classification based on Eh range for growth Microorganisms Redoxpotential Aerobes Between +500 and +300mV Facultative anaerobes Between +300 and -100 mV Anaerobes Less than -100 mV 28 Intrinsic factors – Redox potential • Redox potential and control microbial growth • Prevent diffusion of oxygen • Prevent the increase of Eh • E.g. Special packaging to reduce O2 • Heating • Decrease Eh • Addition of reducing agents • Decrease Eh • E.g. ascorbic acid, sulfite, cysteine 29 Extrinsic factors – Temperature • Three groups of bacteria • Depending on the optimum growth temperature 31 Extrinsic factors – Temperature • Temperature danger zone: 5 - 60˚C • Do NOT keep the food in this zone for more than 2 hours • Temperature and control microbial growth • Refrigeration (2-8°C) • Freezing (-35-0°C) • Heat • Pasteurization • Sterilization 33 Extrinsic factors – 2. Atmosphere • Atmosphere • Presence and concentration of gases in the food environment • Microbes have different requirement • Aerobes; anaerobes; facultative anaerobes • Atmosphere and control microbial growth • Vacuum packaging • Modified atmosphere packaging (MAP) 34 Extrinsic factors – 3. Relative humidity • Amount of moisture in the air • Affect the water activity of food • Moisture gain or loss from the air • Relative humidity and control microbial growth • Proper packaging (E.g. water absorbent pad) • Controlled atmosphere storage (e.g. Low humidity atmosphere) 35 Revision: L6. Foodborne illness: Bacteria • Understand the difference between foodborne infection and intoxication • Explain the main causes of foodborne illness • Recognize the characteristics, reservoir, mode of transmission, associated illness of the microorganisms that commonly cause foodborne illness 36 Food spoilage: • Changes in food qualities (i.e. appearance, taste, smell, texture) which causes it to become undesirable or unacceptable for consumption. Food poisoning: • An illness caused by consumption of contaminated food/water leading to the appearance of clinical symptoms 37 Foodborne illness 1. Infectious agents (pathogens) • Bacteria • Molds • Viruses • Parasites (Protozoa) 2. A toxin or chemical 38 Types of foodborne illness • Foodborne infection • Caused by the consumption of food containing live pathogenic microorganisms which grow and establish themselves in the human intestinal tract • Foodborne intoxication • Caused by ingesting food containing toxins formed by microorganisms which resulted from the microbial growth in the foods • It occurs even in the absence of viable cells in consumed foods 39 Examples of pathogenic bacteria Foodborne Infection Bacteria Foodborne Intoxication • Vibrio parahaemolyticus • Staphylococcus aureus • Vibrio cholerae • Bacillus cereus • Salmonella • Clostridium botulinum • Escherichia coli Q1) Which one is psychrophilic? • Shigella Q2) Which bacteria can form spores? • Listeria monocytogenes Q3) Which bacterium is an aerobe? Q4) Which bacteria can produce neurotoxin? 40 Revision: L7a. Foodborne illness: Virus, Mold, and Protozoa • Recognize the characteristics, reservoir, mode of transmission, associated illness of the microorganisms (virus, mold, and protozoa) that commonly cause foodborne illness 42 Virus and foodborne illness 1. Norovirus 2. Rotavirus 3. Hepatitis A virus 43 Mold toxins and foodborne illness • Mycotoxin related foodborne illness Molds 1. Ergot poisoning • Ergot (Claviceps purpurea): A group of molds produce toxins that affect neurons • Grows inside rye and sometimes wheat kernels 2. Aflatoxin poisoning • Aspergillus flavus and other Aspergillus species • Grow in grains and nuts to produce toxins • Aflatoxin: Carcinogenic 44 Protozoa and foodborne illness • Ciguatera food poisoning - A foodborne illness caused by eating reef fish (e.g. tiger grouper) contaminated with toxins called Ciguatoxins • Ciguatoxin • Heat-stable • Lipid-soluble neurological toxin • Accumulated in fish tissues • Toxin produced by microscopic dinoflagellate Gambierdiscus toxicus • Symptoms (onset time: 3-5hr) Parasites (Protozoa) • Gut illness: Vomiting, diarrhea, abdominal • Neurological numbness and tingling around lips, hands, feet 45 Revision: L7b. Food preservation • Recognize the objectives of food preservation • Understand the mechanism of different food preservation methods, and how each method manipulates the factors necessary for the growth of microorganisms • Recognize the differences between pasteurization and sterilization • Recognize the kinetics of thermal destruction of microorganisms 46 Food preservation • The process of treating and handling food to stop or slow down food spoilage, loss of quality, edibility, or nutritional value and thus allow for longer food storage • Objectives: • Prevent spoilage of food and food products and extend their shelf life • Ensure the safety of food products 47 Principles of food preservation • Elimination or inactivation of microorganisms • E.g. using heat to kill the microorganisms in food • Stopping the action of enzymes • To reduce the self-decomposition of food • Prevention of oxidation • To reduce the rate of lipid oxidation 48 Methods of food preservation A.Physical methods • Heating • Low temperature • Dehydration • Modified atmosphere packaging • Radiation • Filtration B. Chemical methods • Addition of acid • Addition of salt • Addition of sugar • Other food preservatives C. Biological methods • Fermentation 49 Heat treatment - 1. Pasteurization 72˚C HTST milk UHT milk 50 Heat treatment – 2. Sterilization • A process completely kills or removes all life forms, including bacteria and other organisms (E.g. endospores) in the material or an object • E.g. Wet heating at 121°C for 15-20 minutes • Sterilized food products are shelf stable for > 6 months • Canning • Commercial sterilization of low acid foods • Heating the product at 121°C for a duration • Sufficient to inactivate Clostridium botulinum spores by 12 log • Commercial sterilization of high acid foods • Heating the product at ~ 100°C • To destroy both vegetative cells and spores of spoilage microorganisms (particularly fungal spores) 52 Heat treatment – Thermal destruction kinetics Three important values used to measure the thermal-killing efficiency: D value, Z value, F value 53 Heat treatment – Thermal destruction kinetics Summary - D and Z values • D value and Z value relate the death of microorganism to time and temperature of heating, respectively • D value = Time required to destroy 90% of the microorganisms at a specific temperature • Factors affecting D value: Temperature and heat resistance of microorganisms • The unit of time and a temperature must be specified • E.g. D121 = 3.5 minutes • Z value = Temperature change required to achieve a 90% reduction in the D-value 54