Micro L10 PART1 Food Microbiology Methods

Food Microbiology

• Food microbiology examines food for safety standards, including internal company standards.
• It checks food materials for adherence to standards.
• It identifies specific microorganisms or groups to ensure quality.
• Quality control is a key objective.

Methods for Food Microbiological Examination

• Culture-Based Methods: These are classical methods to isolate, enumerate, and identify microorganisms.

  • Plate Count Methods (SPC): Measures viable microorganisms in a sample using spread and pour plate techniques.
  • Selective and Differential Media: Used to isolate specific types of microorganisms (e.g., MacConkey agar for coliforms).
  • Enrichment Culture Techniques: Enhances the growth of specific microorganisms in low concentrations.
  • Most Probable Number (MPN) Method: Statistically estimates microbial populations in a sample.

• Microscopic Methods:

  • Direct Microscopic Count (DMC): Directly observes bacteria under a microscope (e.g., Petroff-Hausser counting chamber).
  • Fluorescence Microscopy: Uses fluorescent dyes to identify live/dead cells (e.g., acridine orange or DAPI stains).

• Biochemical Methods:

  • Catalase and Oxidase Tests: Identify specific metabolic properties of microbes.
  • Fermentation Tests: Identify specific metabolic properties of microbes.
  • API (Analytical Profile Index) Systems: Identify specific metabolic properties of microbes.

• Rapid Detection and Enumeration Techniques:

  • Immunological Methods:
    • Enzyme-Linked Immunosorbent Assay (ELISA)
    • Latex Agglutination Tests
  • Molecular Methods:
    • Polymerase Chain Reaction (PCR): Detects specific DNA/RNA of microorganisms.
    • Quantitative PCR (qPCR): Quantifies microbial DNA.
    • Loop-Mediated Isothermal Amplification (LAMP)
  • Biosensors: Detects microbial metabolites or microbial activity in food samples.

• Advanced and Emerging Technologies:

  • Next-Generation Sequencing (NGS): Provides a detailed microbial profile of food samples.
  • Microarrays: Detect multiple genes simultaneously.
  • Whole Genome Sequencing (WGS): Detailed microbial profile.

• Physicochemical Methods:

  • ATP Bioluminescence Assay: Measures ATP to estimate microbial contamination.
  • Mass Spectrometry (e.g., MALDI-TOF): Measures ATP to estimate microbial contamination.

• Rapid Automation-Based Systems:

  • Automated colony counters (e.g., Petrifilm)
  • Real-time PCR-based systems.

Sampling

• Sampling Plan: Identifies problems related to food microbial examination.
• Number of Samples: 5-10 samples per batch or square root of the number of packs/patch.
• Samples must be representative.

Sampling Plans Design

• One-Class Sampling Plan: Two-Class sampling plans, consist of specifications (n, c, m).

  • n: Number of sample units from a lot for examination
  • c: Maximum acceptable number of sample units that may exceed m.
  • m: Maximum number of relevant bacteria per gram (value greater than m is marginally acceptable or unacceptable).

• Example: In examining 10 samples for a pathogen (Salmonella), if detected, the whole batch is unacceptable. A quality value (M) separates marginally acceptable from unacceptable batches.

Choosing a Sampling Plan

• Choosing the correct plan depends on health hazard degree and usage conditions.
• International Commission on Microbiological Standards for Foods (ICMSF) suggests specific sampling plans for various food types (raw meat, processed meat, poultry, sea foods, vegetables, fruit, cereal, infant foods, dietetic foods, bottled water).

Microbiological Criteria for Ice Cream

• Specific Microorganisms and criteria of absence or presence in specific quantities are given.
  • Listeria monocytogenes: Absent in 1g, sampling size n = 5, acceptance criteria c= 0.
  • Salmonella: Absent in 25g, sampling size n = 5, acceptance criteria c= 0.
  • Clostridium: m =10, M =10², n = 5, c = 2.
  • Staphylococcus aureus : m = 10, M=10², n =5, c= 2.
  • Aerobic colony count (30°C): m = 10², M = 5x10⁵, n = 5, c = 2.

This quiz focuses on the various methods used in food microbiology to ensure food safety and quality. It covers both culture-based and microscopic techniques for examining microorganisms. Test your knowledge on vital methods such as plate count, selective media, and enrichment culture.