Food Microbiology, contamination & spoilage

Contamination, Preservation, and Spoilage of Cereals and Cereal Products

Cereal Products Considered

  • Cereal products include grains, meals, flours, pastes, breads, cakes, and other baked goods.

Contamination of Grains

  • Microorganisms on Grains: Harvested grains carry microorganisms from the soil, insects, etc. Fresh grains can contain thousands to millions of bacteria per gram as well as mold spores.

  • Common Bacteria Families:

    • Pseudomonadaceae

    • Micrococcaceae

    • Lactobacillaceae

    • Bacillaceae

  • Milling Process: Cleaning and washing reduce some microorganisms, but milling (especially bleaching) leads to further reduction. Contamination can occur during blending and conditioning stages.

  • Flour Microflora:

    • Wheat flour may contain several bacteria types, including coliforms and Bacillus spores.

    • Mold spores mainly consist of Aspergillus and Penicillium, along with Alternaria, Cladosporium, etc.

Preservation Methods for Cereals

  • Storage Conditions: Keep cereals dry and at low temperatures (4.4 to 7.2 °C). Prevent moisture and pests.

  • Cleaning Equipment: Ensure proper sanitation to avoid contamination in baked goods.

  • Temperature Control: Should avoid rapid temperature changes to minimize moisture uptake.

Spoilage Mechanisms

  • Microbial Growth: Occurs when moisture content rises above 12-13%. Molds thrive with minimal moisture; yeasts and bacteria arise with higher moisture levels.

  • Common Spoilage Molds:

    • Aspergillus, Penicillium, and Fusarium are common mold genera involved in spoilage.

    • Growth requires favorable temperature and moisture.

Special Concerns in Bakery Products

  • Microbial Impact on Breads: Freshly baked bread, although initially free of viable microorganisms, is subject to contamination during cooling and slicing from knives and packaging.

  • Rope Spoilage: Caused by certain bacterial spores surviving baking and flourishing in humid environments post-baking.

Microbial Profile of Various Cereal Products

  • Table 11.1 lists microbiological profiles of cereal grains and products, indicating common bacterial and mold counts.

Aflatoxin Concerns

  • Mycotoxin Risk: Contamination with molds like Aspergillus flavus poses a risk of aflatoxin production, necessitating strict control measures to avoid mold growth.

Preservation Techniques for Bakeries

Use of Various Heat Treatments

  • Complete baking destroys most microorganisms but not all spores. Some molds might survive if conditions are right.

Effect of Freezing

  • Baked goods can be frozen successfully, preserving quality without significant microbial growth.

Chemical and Physical Methods

  • Chemical Treatments: Use of preservatives like sodium or calcium propionate is common in bakery products to prevent mold growth.

  • Irradiation: UV rays can reduce mold presence without significantly impacting bread quality.

Summary of Spoilage in Cereals and Bakery Products

Factors Leading to Spoilage

  • Moisture Levels: Key manager in microbial growth. Maintaining low moisture and proper storage conditions minimizes spoilage risks.

  • Microbial Load: Total microbial counts directly impact food safety and shelf life.