Yogurt Background Yogurt is a dairy product, which is made by blending fermented milk with various ingredients that provide flavor and color. Although accidentally invented thousands of years ago, yogurt has only recently gained popularity in the United States. It is believed that yogurt originated in Mesopotamia thousands of years ago. Evidence has shown that these people had domesticated goats and sheep around B.
Yogurt has been continually studied for its health benefits, particularly from the addition of probiotics. Current research has been investigating Yogurt fermentation to improve yogurt both in terms of its potential as a healthy food and as an appetizing product that appeals to the general population.
The Biochemistry Behind Yogurt Fig. Embden-Meyerhof-Parnas pathway proposed to be used by Streptococcus thermophilus with the homolactic fermentation of pyruvate into lactic acid.
This diagram also outlines the conversion of galactose into glucose to be used in the EMP pathway.
Courtesy of Zourari et al. Yogurt is a product of the acidic fermentation of milk. The lactose in the milk is converted to lactic acid, which lowers the pH.
When pH drops below pH 5, micelles of caseins, a hydrophobic protein, loses its tertiary structure due to the protonation of its amino acid residues. Yogurt production begins with the breakdown of lactose into glucose and galactose Fig.
The glucose produced from this catabolic step then enters glycolysis, producing pyruvate. It has been proposed that yogurt bacteria utilize the Embden-Meyerhof-Parnas pathway of glycolysis Fig.
Pyruvate then enters lactate fermentation, also known as homolactic fermentation, as it produces only lactic acid molecules. In other types of fermentation, such as ethanolic or heterolactic fermentation, the production of ethanol leads to other fermented foods and beverages such as sauerkraut, kimchi, and wine.
The production of lactic acid forms the basic structure and texture of yogurt. However, other molecules contribute to the taste of yogurt. These include acetaldehyde, an important flavor substance in yogurt, and tyrosine, a product of proteolytic activity, but can cause bitterness when the concentration is above 0.
Lactose catabolism into glucose and galactose. Courtesy of Thomas M. Terry at the University of Hamburg. A worker in a yogurt production facility. To see a video of how yogurt is made, click here. Yogurt production can occur both on a large scale as well as at home for individual consumption Fig.
This pasteurization step is important both for the consumer and the active cultures that will be added, since it eliminates potential competitors in the environment.Yogurt is pasteurized before the starter cultures are added to ensure that the cultures remain active in the yogurt after fermentation to act as probiotics; if the yogurt is pasteurized after fermentation the cultures will be inactivated.
Yogurt is a product of the acidic fermentation of milk. The lactose in the milk is converted to lactic acid, which lowers the pH. When pH drops below pH 5, micelles of caseins, a hydrophobic protein, loses its tertiary structure due to the protonation of its amino acid residues.
Yogurt Fermentation Lab Procedure There were 8 test tubes used, split into two groups of four. The first batch contained 5mL of whole milk and 5mL of Yoplait yogurt. In summary, commercial yogurt production is composed of the following steps: pretreatment of milk (standardization, fortification, lactose hydrolysis), homogenization, heat treatment, cooling to incubation temperature, inoculation with starter, fermentation, cooling, post-fermentation treatment (flavoring, fruit addition, pasteurization.
Yogurt is pasteurized before the starter cultures are added to ensure that the cultures remain active in the yogurt after fermentation to act as probiotics; if the yogurt is pasteurized after fermentation the cultures will be inactivated.
Yogurt, yoghurt, or yoghourt (/ ˈ j oʊ ɡ ər t / or / ˈ j ɒ ɡ ər t /; from Turkish: yoğurt; other spellings listed below) is a food produced by bacterial fermentation of milk. The bacteria used to make yogurt are known as "yogurt cultures".