Micro facts about food

Fermented foods are produced by

Controlled activity of bacteria, yeasts, and molds

What is fermentation?

Strictly means that an organic compound serves as electron acceptor

• Food scientists use fermentation generally to include any desirable change in food by microbes

Intrinsic factors

Inherent conditions of food

• affect which microbes predominate

Water availability - moisture

• Water activity (aw) used to indicate amount of water available

  • Water has an aw of 1.0

  • Fresh foods typically have an aw above 0.98

  • Jam: aw of 0.85

  • Some cakes: aw of 0.70

  • Bacteria require an aw above 0.9 for growth

  • Fungi can grow at an aw as low as 0.8

How does pH influence microbial growth?

Many bacterial species, most pathogens cannot grow below pH 4.5

• Lactic acid bacteria are an exception, can grow at pH 3.5

  • Produce lactic acid

  • Used to make foods from meat, dairy, vegetables

  • fungi can grow at lower pH than most spoilage bacteria

• PH can determine whether toxins can be produced

  • <pH 4.5 Clostridium botulinum does not grow or produce toxin

The lactic acid bacteria

• Obligfate fermenters, produce lactic acid as end product

• Tart taste of

  • Dairy - yogurt, sharp cheeses

  • Vegetable - pickles, soy sauce, sauerkraut, kimchi

  • Meat - some sausages e.g. pepperoni

• Group includes species of:

  • Lactobaccilus

  • Lactococcus

  • Streptococcus

  • Leuconostoc

  • Pediococcus

  • Some produce other flavorful and aromatic compounds

The yeast Saccharomyces cerevisiae converts sugars into…

• Ethanol … alcohol

• CO2…carbonation

Sugar sources

• Bread… wheat sugars

• Beer… malted barely

• Wine… fruit, mostly grapes

• Spirits … distilled variety of alcoholic fermentations

Strains of brewer’s yeast used

• Lager yeast:

  • Saccharomyces pastorianus (a hybrid of S. Cerevisiae) ferments at 8-14 degrees C and take 10-21 days

  • Ale yeast: Saccharomyces cerevisiae ferments at 14-23C and takes 5-7 days,

  • Excess yeast is removed

  • Beer is aged

• Beer is filtered then kegged, bottled, or canned

Cocoa

• Spontaneous fermentation for about 6 dats

• Pink beans turn organ brown and flavor improves

• Microbes

  • Yeast

  • Lactic acid bacteria

  • Acetic acid bacteria

  • Bacillus species

• Afterwards they are sun or artificially sun dried