Yeast Nutrients

Function

Fermentation is a biochemical process where the single-celled yeast (Saccharomyces cerevisiae) responsible for bread fermentation consumes nutrients to sustain itself and produce metabolites.  Sugar, primarily, provides the sustenance necessary for yeast to perform properly.

In baking, yeast is a major leavening agent. It produces carbon dioxide gas during fermentation, consequently creating the desired rise in dough and the formation of  a light, airy crumb grain rather than a dense crumb.

Types

Sugars: Wheat dough provides various sources of fermentable sugars whether those  occurring naturally in the flour (<0.5% glucose, fructose and maltose) or in the wheat bran (up to 3% sucrose). However, the most significant amounts of fermentable sugars in lean doughs are produced by amylase hydrolysis of damaged starch.

Monosaccharides such as glucose and fructose are the preferred sugar sources for S. cerevisiae. Disaccharides such as maltose and sucrose can also  serve as carbon source for the yeast. In sweet doughs, the sucrose content is rather high (30%) and can have a deleterious effect on the yeast due to extreme osmotic pressure exerted on the yeast cell walls.

Amino acids: Amino acids are rich sources of nitrogen essential for yeast cells’ growth. Dough mixing and subsequent baking release various amino acids such as arginine, lysine, ornithine, histidine, leucine and glutamates. These  amino acids can help maintain nitrogen supply for the yeast, provide precursors for flavor development and undergo Maillard reactions upon baking to produce baked products with unique color and flavor attributes.

Phosphorous: This nonmetal element is vital for yeast cells. If present in limited  amounts, fermentation may be incomplete.

Ammonium sulfate, ammonium chloride and diammonium phosphate (DAP): These inorganic compounds provide supplemental nitrogen and phosphorus to the yeast, in addition to their role  in crust firming, leavening, and pH control.

Vitamin B7 or Biotin: It Increases rate of yeast growth as well as its fermentation. A lack of biotin in yeast leads to undergrowth.  The most significant role of biotin, however, may be its involvement in the synthesis of adaptive enzymes necessary for sucrose fermentation.¹

Minerals: Metal elements such as potassium, calcium and magnesium act as key cofactors in enzymatic reactions and participate in the metabolism of yeast cells.²

Application

Bakers may opt to use yeast nutrients in no-time dough production runs where fermentation must take place at a high rate. Yeast nutrients are usually not needed for the production of artisan bakery products that involve long fermentation stages.³

Yeast nutrients are not strictly necessary in all bakery products. Ingredients such as wheat flour and milk solids, can provide sufficient amounts of nutrients for proper yeast function. under non-ideal conditions, yeast nutrients may be added  to enhance yeast activity.

In selecting yeast strains for bread dough, a distinction should be made between lean dough which contains low sugar concentrations and sweet dough (~30% sugars).  In lean dough, it is critical that the yeast can efficiently metabolize maltose while in sweet doughs or frozen dough, osmotolerance is an important consideration.

Mature wheat grains contain high levels of beta-amylases and low levels of the alpha-amylase; thus the need to supplement the flour with the alpha-amylase to increase the concentration of fermentative sugars.

FDA regulation

Yeast nutrients are considered food additives under 21 CFR 170. In accordance with this, yeast nutrients are allowed to come into contact with foodstuffs as they become a component of the food and affect the characteristics of the product and processing performance.⁴

According to 21 CFR 182 and §184.1, yeast foods are generally recognized as safe (GRAS) and can be used in food processing with no limitation other than current GMPs.⁵

References

1. De Rovira, D. “V” Dictionary of Flavors, 3rd edition, John Wiley & Sons Ltd, 2017, p. 314.
2. Bonjean, B., and Guillaume, L.-D. “Yeasts in Bread and Baking Products.” Yeasts in Food: Beneficial and Detrimental Aspects, Woodhead Publishing Ltd, and CRC Press LLC, 2003, pp. 289–303.
3. Suas, M. “Advanced Flour Technology and Dough Conditioners” Advanced Bread and Pastry: A Professional Approach, first printing, Delmar, Cengage Learning, 2009, p. 157.
4. U.S. Food and Drug Administration. “21 CFR 170 –Food Additives.” 1 Apr. 2017, https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?CFRPart=170. Accessed 30 July 2018.
5. U.S. Food and Drug Administration. “21 CFR 184 – Direct Food Substances Affirmed As Generally Recognized As Safe.” 1 Apr. 2017, https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?CFRPart=184. Accessed 30 July 2018.