Agency Response Letter GRAS Notice No. GRN 000350

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CFSAN/Office of Food Additive Safety

February 4, 2011

John Husnik, Ph.D.
Phyterra Yeast Inc.
P.O. Box 21147
Charlottetown, PEI, C1A 9H6

Re: GRAS Notice No. GRN 000350

Dear Dr. Husnik:

The Food and Drug Administration (FDA) is responding to the notice, dated August 9, 2010, that Phyterra Yeast Inc. (Phyterra) submitted in accordance with the agency’s proposed regulation, proposed 21 CFR 170.36 (62 FR 18938; April 17, 1997; Substances Generally Recognized as Safe (GRAS); the GRAS proposal). FDA received the notice on August 11, 2010, filed it on August 19, 2010, and designated it as GRAS Notice No. GRN 000350.

The subject of the notice is Saccharomyces cerevisiae strain P1Y0, a variant of S. cerevisiae parent strain UCD2034, which is commonly used in the wine industry. The notice informs FDA of the view of Phyterra that S. cerevisiae strain P1Y0 is GRAS, through scientific procedures, for use as a yeast starter culture for alcoholic beverage fermentation such as grape must, brewing wort, and rice fermentations. The S. cerevisiae strain P1Y0 may be used in the reduction of hydrogen sulfide (H2S) concentration during the production of red and white wine, champagne, sherry, sake and other rice wines, and beer. Phyterra recommends using 0.2 grams of active dry yeast per liter of wine for grape must fermentation.

In an electronic mail to Phyterra dated February 2, 2011, FDA requested clarification regarding the applicability of Phyterra’s discussion of the wine-making process to alcoholic beverage fermentation in general. In an amendment dated February 3, 2011, Phyterra stated the following: “For each of the various products, bio-conversion of sugar to alcohol by yeast is the same. The raw substrate for providing the sugar may be different (grain, fruit or vegetable) and some of the processing steps to develop the individual characteristics of the products may also differ; however, our technology is applied to the yeast that is completing the bio-conversion of sugar to alcohol without hydrogen sulfide being produced - as described in the submission.”

Phyterra notes that the presence of H2S, a by-product of fermentation processes, is considered undesirable because of its odor. H2S forms other reactive compounds, such as mercaptans and thiols that further add to the undesirable odors and flavors of the product. The purpose of developing S. cerevisiae strain P1Y0 is to replace the MET10 allele of strain UCD2034 with a “low H2S” MET10 allele, to result in significant reduction in the production of H2S by the yeast.(1)

Phyterra describes published and unpublished information about the development of S. cerevisiae strain P1Y0 and the use of S. cerevisiae in general. Phyterra notes that S. cerevisiae is a human commensal organism, with an extensive history of safe use in the production of food and beverages, including alcoholic beverages. S. cerevisiae strain P1Y0 strain contains an allele of the MET10 gene from S. cerevisiae strain UCD932. The notifier refers to the MET10 allele from strain UCD932 as the “low H2S” MET10 allele. After replacement of the native MET 10 gene of strain UCD2034 with the “low H2S” MET10 allele, the modified strain was designated P1Y0. The “low H2S” MET10 allele differs from the native MET10 allele by only three nucleotides. This three-nucleotide difference results: (1) in two amino acid changes in the enzyme subunit it encodes and (2) in the enhancement of the sulfate assimilation pathway.

In the notice, Phyterra describes the process of introducing the “low H2S” MET10 allele into S. cerevisiae UCD2034 strain to create S. cerevisiae P1Y0 strain. Phyterra also describes the molecular characterization and stability assessment of the “low H2S” MET10 allele in S. cerevisiae strain P1Y0. Phyterra describes the construction of the recombinant yeast strain as “self-cloned,” i.e., the final strain designated P1Y0 contains genetic material exclusively from S. cerevisiae. Phyterra also states that the “low H2S” MET10 allele, which encodes the subunit alpha of assimilatory sulfite reductase in S. cerevisiae strain P1Y0, is not toxic or allergenic; and is not implicated in the formation of undesirable compounds.

Phyterra describes the method of manufacture for S. cerevisiae strain P1Y0. S. cerevisiae strain P1Y0 is grown on cane sugar and molasses under highly aerobic conditions to assure good survival during fermentation. The strain is harvested via centrifugation, filtered, and the resultant mass is extruded and dried to obtain the final product. Phyterra notes that the method of manufacture is based on well-established procedures for the production of active dry yeast used in baking, brewing, or winemaking and is in accordance with good manufacturing practice.

Phyterra considers the potential dietary exposure to S. cerevisiae strain P1Y0 to be negligible because the processing procedures used in winemaking remove yeast cells, debris associated with autolysed yeast cells, and most protein released during autolysis of yeast cells.

Phyterra describes generally available information on winemaking procedures and states that use of S. cerevisiae strain P1Y0 does not lead to any changes in the procedures or in the composition of the wine with the exception of a lower H2S concentration. Phyterra states that the presence of the “low H2S” MET10 protein would occur only if the wine has been stored on lees after alcoholic fermentation. However, clarification processes, which are obligatory winemaking practices, will remove part of the MET10 protein, as well as larger polypeptide fragments of this protein. Hence, only the smaller polypeptides and amino acids of these proteins will remain in the wine. Phyterra further notes that the use of S. cerevisiae strain P1Y0, as compared to strain UCD2034, will not result in a significant difference in the overall amino acid profiles or peptide profiles in the final product.

Phyterra describes generally available information on the clarification of wine. During wine clarification, solid particles may be allowed to settle by gravity or centrifugation. Phyterra states that clarification removes most of the yeast cells. When the wine is kept on lees for ageing, the yeast cells undergo autolysis, releasing cellular materials that are degraded through the action of enzymes. Further, white wines can be treated with bentonite to remove all remaining protein. In red wines, tannins associate with proteins; this protein-tannin complex could be precipitated by adding gelatin or egg white albumin. Phyterra states that prior to bottling, most wines undergo filtration (e.g., with diatomaceous earth, cellulose filters, or membrane filters) that can also eliminate any remaining yeast cells. Phyterra concludes that use of S. cerevisiae strain P1Y0 in wine is generally recognized as safe and that such wines would be comparable to wines produced using other yeast strains.

Section 301(ll) of the Federal Food, Drug, and Cosmetic Act (FFDCA)

The Food and Drug Administration Amendments Act of 2007, which was signed into law on September 27, 2007, amends the FFDCA to, among other things, add section 301(ll). Section 301(ll) of the FFDCA prohibits the introduction or delivery for introduction into interstate commerce of any food that contains a drug approved under section 505 of the FFDCA, a biological product licensed under section 351 of the Public Health Service Act, or a drug or a biological product for which substantial clinical investigations have been instituted and their existence made public, unless one of the exemptions in section 301(ll)(1)-(4) applies. In its review of Phyterra’s notice that S. cerevisiae strain P1Y0 is GRAS for the intended uses, FDA did not consider whether section 301(ll) or any of its exemptions apply to foods containing S. cerevisiae strain P1Y0. Accordingly, this response should not be construed to be a statement that foods that contain S. cerevisiae strain P1Y0, if introduced or delivered for introduction into interstate commerce, would not violate section 301(ll).


Based on the information provided by Phyterra, as well as other information available to FDA, the agency has no questions at this time regarding Phyterra’s conclusion that S. cerevisiae strain P1Y0 is GRAS under the intended conditions of use. The agency has not, however, made its own determination regarding the GRAS status of the subject use of S. cerevisiae strain P1Y0. As always, it is the continuing responsibility of Phyterra to ensure that food ingredients that the firm markets are safe, and are otherwise in compliance with all applicable legal and regulatory requirements.

In accordance with proposed 21 CFR 170.36(f), a copy of the text of this letter responding to GRN 000350, as well as a copy of the information in this notice that conforms to the information in the GRAS exemption claim (proposed 21 CFR 170.36(c)(1)), is available for public review and copying at


Mitchell A. Cheeseman, Ph.D.
Acting Director
Office of Food Additive Safety
Center for Food Safety and Applied Nutrition

(1)Copper has traditionally been added to wine to remove sulfur compounds. Phyterra notes that adding S. cerevisiae strain P1Y0 to wine will achieve the same result.

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