Understanding the microbiology of starter cultures is critical in the dairy industry. Several microorganisms including bacteria, yeast, moulds, and/or combinations thereof are necessary for milk fermentation during manufacturing of cheese and other fermented milk products.Understanding the #microbiology of #startercultures is key to understanding #fermentedfoods Click To Tweet
By far the most important group is the bacteria, mostly the lactic acid bacteria (LABs) e.g. Streptococcus, Leuconostoc and Lactobacillus. These three genera stand out as the most important in the dairy industry.
Why you should understand the microbiology of starter cultures:
- Streptococcus spp.are widely used in the cheese manufacturing industry, especially; Streptococcus lactis, Streptococcus lactis sub-specie diacetylactis, Streptococcus cremoris, and Streptococcus themophilus
- The entire group of starter culture bacteria are homofermentative, i.e. they produce only lactic acid from glucose.
- All starter culture bacteria are mesophilic exceptStreptococcus themophilus, which is thermoduric
- Of the genus Leucorostoc, only Leuconostoc cremorisand Leuconostoc dextranicum are used in dairy starter cultures. They are heterofermentative organisms, i.e. they produce lactic acid, carbon (IV) oxide (CO2), and aroma (volatile) compounds.
- The genus Lactobacillus has both homofermentative and heterofermentative species.
The most common starter culture bacteria spp. include:
- Lactobacillus bulgaricus
- Lactobacillus lactis
- Lactobacillus acidophilus
- Lactobacillus helveticus
- Lactobacillus casei
- Lactobacillus plantarum
The other not very common starter culture bacterial spp include:
- Streptococcus faecium: – mostly used in the manufacture of modified cheddar cheese in the USA
- Brevibacterium linens: – (related to Arthrobacter globiformis) used to impart a distinctive, reddish-orange colour to the rind of brick and limburger cheese.
- Propionibacterium freudenreichiishermanii: – manufacturers widely usethis in Swiss cheese varieties due to its ability to produce large gas holes (eyes) in cheese during the curing period.
- Bifidobacterium bifidium: – (previously known as Lactobacillus bifidus) reside in the gut of infants. It is used together with yoghurt or acidophilus milk starter culture to manufacture bioghurt, which is a therapeutic fermented milk.
It is important to note that the study of the microbiology of starter cultures also branches out to include even molds. Dairy manufacturers mainly use molds (moulds) to manufacture some semi-soft cheese varieties. They not only enhance the flavor and aroma but also modify (slightly) the body and texture of the curd.
Based on their color and growth characteristics, we can safely conclude that there are two types of molds, e.g.
- White molds include Penicillium camemberti, Penicillium caseicolum, and Penicillium candidum, which grow externally on the cheese e.g. Camembert and Brie.
- Blue molds such as Penicillium roqueforti, which grows internally in the cheese to produce blue cheeses such as Roquefort, Blue stallion, Danish blue, Gorgonzola, and Mycella
Other genera of molds with limited application include:
- Mucor rasmusen, used to manufacture ripened skim-milk cheese in Norway
- Aspergillus oryzae, used to make various varieties of Soya milk cheese in Japan.
The presence of yeasts in milk, besides the LAB cultures, results in a lactic acid/alcohol fermentation. This type of fermentation is limited to the manufacture of Kefir and Kumis in the dairy industry. Kefir starter culture contains Saccharomyces kefir and Torulopsis kefir.
Scientists have also isolated the following yeast spp. from Kefir:
- Mycotomla kefir
- Cryptococcus kefir
- Mycotomla lactosa
- Candida pseudotropicalislacosta