Semester of Graduation

Spring 2019

Degree

Master of Science (MS)

Department

Nutrition & Food Sciences

Document Type

Thesis

Abstract

Pecan nuts are a highly valued but underutilized crop. Pecan production generates nearly 150 million pounds of shell by-product annually in the United States, of which approximately 6 million pounds are attributed to Louisiana. Pecan shells are a rich source of various phenolic compounds with potential antioxidant properties. The main objective of this study was to determine the effect of pecan variety and method of extraction on the phenolic content and antioxidant activity of pecan shell extracts. A total of 20 different pecan cultivars from the same orchard, under similar growing conditions were processed to obtain defatted shell powder of about 50-100 µm size. The defatted shell powders (hexane 1:20 W/V) were then subjected to distilled water (at 98˚C for 30 min) and ethanol solid-liquid extraction (at 160 rpm for 1 h) processes, respectively. The resultant crude aqueous and ethanol extracts were lyophilized, and the obtained powdered extracts were analyzed for total phenolics and antioxidant activity by Folin-Ciocalteu, and DPPH. free radical assays, respectively. Crude and acid hydrolyzed (acidified methanol 1% HCl V/V, 2 h, 22oC) extracts from Nacono and Caddo cultivars were analyzed by reverse phase HPLC. Acidified methanol soluble components of Nacono ethanolic extracts where further characterized by flow injection electrospray ionization mass spectrometry (FIA-ESI-MS). Pecan cultivar significantly affected (PCaddo) to 153.54 (Cherokee) mg GAEg-1 dry extract with an average of 210.02±7.3 mg GAEg-1 and were significantly greater (P<0.05) than those obtained by aqueous extraction, which ranged from 253.75 (Curtis) to 114.63 (Jackson) with an average of 168.38±6.8 mg GAEg-1 of dry extract. Antioxidant activity of ethanolic extracts ranged from 840.6 (Maramec) to 526.74 (Caper Fear) and averaged 659.70±21 mg TEg-1, while aqueous extracts ranged from 934.9 (Curtis) to 468.3 (Elliot) with an average of 619.42±22 mg TEg-1. Acid hydrolysis removed interfering components from crude extracts and allowed for the elucidation of two peaks by RP-HPLC . The most abundant peak was attributed to gallic acid derivatives, and the other did not correspond to phenolic standards used for comparison. The major components identified by FIA-ESI-MS in acid hydrolyzed Nacono shell extracts were lignin degradation products lignols, dilignols, trilignols, and oligolignols. Monolignol fragments of G-unit isobaric dilignol were widespread. The findings of this study show promise to enhance Louisiana pecan revenue streams by utilizing pecan shells as an alternative natural source of antioxidants for use in various food applications.

Committee Chair

Adhikari, Achyut

Available for download on Sunday, May 31, 2020

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