Saccharification and co-fermentation of ammoniated corn stover hydrolysate by Phaffia rhodozyma for astaxanthin production

Authors: Stoklosa, Ryan; Garcia-Negron, Valerie; Johnston, David

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2026
Publication Date: 2/10/2026
Citation: Stoklosa, R.J., Garcia-Negron, V., Johnston, D. 2026. Saccharification and co-fermentation of ammoniated corn stover hydrolysate by Phaffia rhodozyma for astaxanthin production. Journal of the American Oil Chemists' Society. https://doi.org/10.1002/aocs.70051.
DOI: https://doi.org/10.1002/aocs.70051

Interpretive Summary: Corn stover is a waste byproduct consisting of stems and leaves left after corn harvest. To improve the value of this agricultural waste it can be directed towards processing to produce natural, bio-based chemicals using fermentation processing. One such chemical that can be generated using a yeast strain is astaxanthin, which is a natural red pigment. This chemical has high value as it can be utilized in various industries ranging from the food industry for use as a natural dye to pharmaceuticals. To produce the astaxanthin from the yeast this work first took corn stover and subjected it to chemical pretreatment using ammonia gas. This pretreatment changes the structure of the corn stover to make it amenable for proteins termed enzymes to break down the plant cell wall to sugars required for fermentation. A processing strategy termed simultaneous saccharification and fermentation (SSF) was employed whereby the release of sugars occurred at the same time as the fermentation to produce astaxanthin. Four different enzyme formulations were utilized to determine the best production of astaxanthin using the pretreated corn stover. Around 4 mg per L of astaxanthin could be generated from two separate enzyme formulations. Future work will look to improve the astaxanthin production from corn stover by considering other process variables that impact fermentation such as nutrient supplementation.

Technical Abstract: High value co-products generated from waste agricultural feedstocks are important components that can improve economic conditions for integrated biorefineries. Red pigmented carotenoids, such as astaxanthin, is one type of co-product that can add value to biorefineries based on its wide range of uses that include supplementing aquaculture feed, natural dyes for fabrics and food, and pharmaceuticals. In this work corn stover was ammoniated using the low moisture anhydrous ammonia (LMAA) process. The pretreated corn stover was then deconstructed and converted to astaxanthin using simultaneous saccharification and fermentation (SSF) with the yeast strain Phaffia rhodozyma. Four different commercially available cellulase enzyme formulations were used to release monomeric sugars during SSF. Two different enzyme formulations used for SSF processing allowed for 4 mg per L astaxanthin to be produced. One interesting finding obtained was that total sugar consumption did not necessarily correlate to higher astaxanthin titers. This result provides more evidence that astaxanthin generation from yeasts is tightly controlled based upon the availability of both carbon and nitrogen in the fermentation media.