Micro facts about food

Fermented foods are produced by

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