Yeast is a type of fungi, a class of tiny organisms that includes mold and mildew. These one-celled organisms reproduce sexually and asexually by budding. Some types of yeast such as Candida albicans and Cryptococcus neoformans cause infections in humans. Candida albicans is best known for causing skin and vaginal infections, while Cryptococcus neoformans causes infection in people with impaired immune systems. Other yeast such as Saccharomyces cerevisiae are used to produce carbon dioxide and alcohol through the fermentation of carbohydrates. This is important for making alcoholic beverages. In baking, yeast is used as a leavening agent to help bread rise. It does this by fermenting carbohydrates in the dough to produce carbon dioxide. The carbon dioxide causes the dough to rise, while giving the bread a light, airy texture Deactivated yeast is also used as a nutritional supplement and as a vegan substitute for cheese because of its cheesy flavor.
Yeast extracts, hydrolyzed yeast and autolyzed yeast are used by the food industry as food additives. To make hydrolyzed yeast, enzymes are used to break yeast proteins down into smaller pieces. Autolyzed yeast are yeast allowed to die a natural death. Upon death, they release enzymes that break down their own proteins into a form that food manufacturers can use to add flavor to food products. Two common food products that contain autolyzed yeast extract are Marmite and Vegemite. Autolyzed yeast extract is used to add flavor to a variety of processed foods including soups and vegetarian meat substitutes. They enhance the taste of foods because of the free glutamic acid they contain. Glutamic acid stimulates the taste buds and gives foods a more powerful flavor. Yeast extract is also used in some products to replace the more controversial flavor enhancer, monosodium glutamate or MSG. There's some concern about using it as an MSG substitute since autolyzed yeast extracts can form MSG if they come into contact with salt in food. Yeast extracts are also referred to as hydrolyzed yeast protein.
Yeast extracts, or hydrolyzed yeast protein has applications that go beyond the flavoring of food. They're also important to the cosmetic and hair care industry. Hydrolyzed yeast protein is made by using acid to break down the peptide bonds that separate amino acids from one another. The product is then processed further to remove any non-protein impurities, resulting in a purified yeast protein product.
Yeast proteins are ingredients in some skin care products because of their skin conditioning and moisturizing properties. They also appear to enhance wound healing. A study published in the Journal of Burn Care and Research showed that a yeast extract applied topically accelerated wound healing in mice. In addition, yeast proteins are believed to increase the production of collagen by fibroblasts in the dermis of the skin. Collagen is the main structural protein in skin that gives it its support and youthful firmness. Collagen production slows down with age and the remaining collagen bundles and fibers become disorganized and damaged. Exposure to sunlight also accelerates the loss of collagen by activating enzymes that break it down. This is what causes skin to develop wrinkles and laxity that make it look less youthful. Therefore yeast extract and yeast proteins may help to fight skin laxity and keep wrinkles in check. Some skin care products that contain yeast protein include facial moisturizers, under-eye creams, body moisturizers and lip gloss.
Yeast proteins are also added to hair care products due to their hair conditioning properties. Yeast proteins coat the hair shaft and help to reduce static. This makes hair easier to style. Hair static can be a particularly frustrating problem in the winter when humidity levels are low, and hair care products that contain yeast proteins help with this problem. According to a study published in Cosmetics and Toiletries, yeast extracts increase the production of keratins that give hair its support, strength and resistance to breakage. That's why some manufacturers of hair care products add yeast extract and proteins to shampoos and conditioning products formulated for fine and damaged hair.