Some food in this world are made using microorganism to produce a desire flavour, taste and texture of the food. For examples: yogurt, tapai, cheese, bread and others. Starter cultures is used in these food production. A starter culture is a microbiological culture which actually perform fermentation. These starters usually consist of a cultivation medium, such as grains, seeds, or nutrient liquids that have been well colonized by the microorganisms used for the fermentation.
These starters are formed using a specific cultivation medium and a specific mix of fungal and bacterial strains. microorganisms used in starters include various bacteria and fungi (yeasts and molds): Rhizopus, Aspergillus, Mucor, Amylomyces, Endomycopsis, Saccharomyces, Hansenula anomala, Lactobacillus, Acetobacter, etc. Tempe is a traditional food in Indonesia. It is made from soy beans which is fermented that resulting it to in a cake form, where soy beans are bounded together by thick mycelium of new growth of fungi.
Tapai is traditional fermented food found in East and South-east Asia. It is made from carbohydrate source like rice, glutinous rice and others. It fermented using mould or yeast. Another food, yogurt is the coagulated milk product that results from the fermentation of milk. Milk is fermented with the help of friendly bacteria that produce lactic acid, which curdles the milk and preserve it from spoilage. These microorganisms that are used to ferment the product can be stained with the gram staining.
Gram staining is the method of differentiating bacteria into 2 large groups of Gram-positive bacteria and Gram-negative bacteria based on their cell wall. Most of the bacteria or yeast in the starter cultures used are Gram-positive. Gram staining requires 4 types of solutions used in the procedure: crystal violet, mordant, alcohol and safranin. The Gram-positive microbes will have blue stain while Gram-negative stains pink after the procedure. Methylene blue solution is a basic dye which results a blue stain at the bacterial cell.
The microbe’s colony can be enumerated in order to get its population. The microbes need to go under serial dilution procedure to ease us to count their colony. Serial dilution method is the stepwise dilution of a substance in solution. Usually, ten-fold serial dilution is practiced in the microbiological procedure, where 1mL of extract is diluted in 9mL diluent or 10ml solution. The standard plate counting is the reliable method for enumerating the colony of bacteria or fungi.
So, a aliquot of each dilution need to be on the agar plate by using spread plate method. The type of agar plate can be used to enumerated these microbes are tomato juice agar and potato dextrose agar. Tomato juice agar (TJA) is used to lactic acid bacteria TJA is made up of 20gram tomato juice agar, 10gram digestive enzymes of casein, 10gram peptonized milk and 11gram agar. Potato Dextrose agar encourage the growth of fungi. This agar is made up of potato infusion, dextrose and agar.