Date of Graduation

8-2012

Document Type

Thesis

Degree Name

Master of Science in Food Science (MS)

Degree Level

Graduate

Department

Food Science

Advisor

Ruben O. Morawicki

Committee Member

Ya-Jane Wang

Second Committee Member

Danielle Julie Carrier

Keywords

Biological sciences, Fermentation, Lactic acid, Processing waste, Sweet potato

Abstract

Organic waste generated from industrial sweet potato canning is estimated to be 30% of incoming raw material. This waste contains carbohydrates (sugars and starch) that could be used as substrates for the production of useful compounds via fermentation (e.g. lactic acid), resulting in the production of value-added products. The goal of this research project is to produce a substrate from the sweet potato processing waste material that supports the growth of lactic acid bacteria, which results in the production of lactic acid. The sweet potato waste product was characterized, and found to contain 16.5% solids. The solids components were 18.5% ash, 4.4% protein, and the rest assumed to be carbohydrates. The carbohydrate component was found to contain 20.5% sugars, mostly in the form of sucrose, 19% soluble starch, and the rest assumed to be fiber. Conditions for enzymatic starch hydrolysis were explored, and using 80U glucoamylase/100 gram waste material for a 24 hour treatment at 35°C and pH 4 yielded a greater than 95% conversion efficiency to glucose while minimizing total enzyme required. Screening of 3 lactic acid bacteria strains in a control medium (YM Broth) yielded highest lactic acid production by Lactobacillus rhamnosus. Different dilutions of the hydrolyzed sweet potato waste, with and without pH control, were used as a fermentation substrate for L. rhamnosus, and lactic acid production was highest in the undiluted hydrolyzed waste at pH set point 5.0, yielding 10g/L in 72 hours. Lactic acid production from sweet potato waste will provide a valuable product from a waste stream for local processing facilities.

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