Food Microbiology, contamination & spoilage

1. Contamination of Cereals and Cereal Products

  • Cereal products include grains, meals, flours, pastes, and baked foods.

  • Harvested grains can contain a wide variety of microorganisms from soil, insects, etc.

    • Freshly harvested grains contain thousands to millions of bacteria and mold spores.

  • Major bacterial families on grains: Pseudomonadaceae, Micrococcaceae, Lactobacillaceae, Bacillaceae.

  • Milling Process:

    • Scouring and washing remove some microorganisms but most are removed during milling.

    • Further contamination can occur during blending and conditioning.

  • Bacterial content varies widely, with white wheat flour holding a few hundred to several thousand bacteria per gram.

2. Microflora in Wheat Flour

  • Common bacteria in wheat flour: Bacillus, coliforms, Micrococcus, etc.

  • Mold types: Aspergillus and Penicillium predominate, with some Alternaria spp.

  • Prepared flours show higher bacteria counts, particularly graham and whole-wheat flours.

3. Contamination During Baking

  • Freshly baked bread is generally free from microorganisms but becomes contaminated during cooling.

  • Contamination can occur from air, knives, or wrappers during slicing.

    • Ropiness in bread can be caused by surviving bacteria during baking.

4. Preservation of Cereal Products

  • Storage Conditions:

    • Cereal products can prevent microorganism growth as long as they remain dry.

    • Recommended storage temperature: around 4.4 to 7.2 °C.

  • Bakery products, having higher moisture, need special preservation techniques.

5. Asepsis in Food Preservation

  • Cleaning and sanitizing equipment is essential to prevent contamination from spoilage organisms.

  • Protect bread, cakes, and baked goods from mold and other microorganisms.

6. Use of Heat in Preservation

  • Baking usually destroys most microorganisms, though bacteria spores can remain.

  • Special breads have been successfully canned.

7. Use of Low Temperatures

  • Short-term storage of baked goods at room temp is common.

    • For longer storage, avoid warm conditions and refrigerate or freeze.

8. Chemical Preservatives

  • High moisture content in grains can lead to mold growth.

  • Effective agents: ammonia (2%) and propionic acid (1%) against mold in high-moisture corn.

  • Sodium, calcium propionate, and sorbates commonly used in bakery products.

9. Irradiation for Spoilage Control

  • Applications in bakeries include:

    • Ultraviolet rays for reducing mold spores in warm storage and bread packaging areas.

    • Ionizing radiation for preserving baked goods and destroying insects in stored grains.

10. Spoilage of Cereal Products

  • Microbial spoilage in grains can occur if moisture exceeds optimal levels (12-13%).

  • Factors for spoilage:

    • Microbial load, moisture, physical damage, and temperature conditions.

    • Common molds: Aspergillus, Penicillium, and Fusarium.

11. Key Points on Bread Spoilage

  • Molds are the most significant spoilage agents in bread, manifesting as:

    • Molding on exposed surfaces; most initiated during cooling or slicing.

  • Methods to prevent spoilage:

    • Clean air in production areas and prompt cooling and wrapping.

12. Common Spoilage Types

  • Ropiness caused by Bacillus subtillis or related species.

  • Red bread caused by pigmented bacteria like Serratia marcescens.

  • Chalky bread due to yeast and related fungi.

13. Pasta and Other Foods

  • Pasta and macaroni are generally shelf-stable but may suffer from gas production under certain conditions.

  • Spoilage of breakfast cereals and snacks is minimal due to low moisture hence microbial resistance.

Conclusion

  • Throughout grain handling and processing, sanitation, storage conditions, and careful monitoring of microbial content are crucial to prevent spoilage and enhance preservation.