Chemistry and Biochemistry

Larry Kirk



Comparison of nutrients in organically grown versus conventionally grown oranges

This is a collaborative research project which involves Dr. Kathryn Silliman and students from both the Dept. of Chemistry and Biochemistry and the Dept. of Nutrition Food Science. Our research centers on the comparison of agricultural growing practices (certified organic vs conventional) with respect to their effects on the nutrient levels of locally grown naval oranges (Orland, CA). In the 2006 growing season we sampled oranges at three different times during the growing season and measured levels of ascorbic acid (Vitamin C) and simple carbohydrates. The results showed that the organically grown oranges were higher in both ascorbic acid and simple carbohydrates. This work was done by Bethany Schaarschmidt who received a masters degree in Nutrition.

We have been currently developing methods to measure other nutrients besides ascorbic acid and simple carbohydrates. We have worked out methods to measure: (1) total phenolics (Folin assay) ; (2) total antioxidants (FRAP assay) ; (3) organic acids (HPLC assay). We would also like to measure carotenoid levels as well. These methods were developed by Stephanie Mendes who is currently a biochemistry major.

During the naval orange growing season in spring 2008, we are planning a study to measure the levels of all of these nutrients. We also plan to do a taste comparison study along with the biochemical assays. Heather Pate along with other students will work on this project.

Beer waste used as a nutrient to grow lactic acid producing bacteria.

This work is a collaboration with Dr. Larry Hanne (Dept. of Biological Sciences) and Dr. Joe Greene (Dept. of  Mechanical Engineering). The research is also supported by Sierra Nevada Brewing Company, Inc. as well as an ARI grant. The purpose of this research is to use beer waste, specifically the spent yeast remaining after the beer is bottled (called beer bottoms), as a growth nutrient for a lactic acid producing bacteria. If successful, the lactic acid would be isolated and used to prepare a biodegradable polylactate polymer.

This is the early stages of this project and the goals have been: (1) to test various bacteria and strains of bacteria to find the highest lactic acid producer : (2) develop methods to remove the antibacterial compounds in the beer waste (bittering compounds) ; (3) develop methods to pretreat the beer yeast waste so it will effectively substitute for nitrogen and carbohydrates in the growth media ; (4) optimize the lactic acid production using a batch procedure and (5) develop methods to isolate lactic acid from the bacteria.

Portrait of Larry Kirk