Biological agents responible in Food Fermentations

1. Bacteria

a)Lactic acid bacteria

b)Types of commercial starter cultures

c)Conditions required for bacterial fermentations

d)Characteristics of important genera

2.Yeasts

3.Molds

Micro-organisms cause changes in the foods

– Help to preserve the food,

– Extend shelf-life considerably over that of the raw materials from which they are made,

– Improve aroma and flavour characteristics,

– Increase its vitamin content or its digestibility compared to the raw materials.

Biological agents responible in Food

Fermentations

Most fermentations require several species, acting simultaneously and/or sequentially to give product with desired properties ,including appearance, aroma, texture and taste.

Vinegar production is a joint effort between yeast and acetic acid forming bacteria. The yeast convert sugars to alcohol which is the substrate required by the Acetobacter to produce acetic acid through oxidation.

Role of fermenting microorganisms are;

Production of lactic acid, flavor, proteolytic activity, lipolytic activity, organic compounds, prevention of foodborne disease and spoilage, and change in texture of food. The most common groups of microorganisms involved in food fermentations are bacteria, yeasts and molds. Microbial enzymes also play important role in food fermentations.

In general, growth will be initiated by bacteria, fallowed by yeasts and then molds. The smaller microorganisms multiply and take up nutrients from the surrounding area most rapidly.

Bacteria are the smallest of microorganisms, fallowed by yeasts and molds. The smaller bacteria, such as Leuconostoc and Streptcoccus grow and ferment more rapidly than their close relatives.

Bacteria

a)Lactic acid Bacteria

i)Groups of LAB depending on glucose metabolism

ii)Groups of LAB depending on growth temperature

b)Types of commercial bacterial starter culture

c)Conditions required for bacterial fermentations

Lactic Acid Bacteria(LAB)

• İt is loosely defined as all members of fermenting bacteria producing lactic acid from hexoses and lack functional heme-linked electron transport system or cytochromes(no krebs cycle).

• Lactic acid bacteria compose a group of bacteria that degrade carbohydrate (e.g., fermentation ) with the production of lactic acid.

• The principle genera of LAB are

Lactobacillus,Lactococcus,Leuconostoc,Pediococc us, and Streptoccus(Table 2.2)

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