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dc.contributor.authorMa, Yuanyuan
dc.description.abstractThe overall aims of this work were to ascertain the primary phenolic constituents in peanut skins (PS), and to determine if their antioxidant content and capacities are conserved through industrial dry-blanching and roasting processes. The first and second studies undertaken revealed that ground PS incorporation into peanut butters effectively enhances the total phenolics and fiber contents of the product, and offers product-line diversification while still retaining the product’s standard of identity. This research will aid the peanut industry via (1) by-product/waste stream utilization; and (2) diversification of product lines by creating a value-added peanut butter with potential health beneficial properties. Adding ground PS to peanut butter at 1.25, 2.5, 3.75 and 5.0% (w/w) resulted in a concentration-dependent change in the Commission Internationale de l’Éclairage L* C* h values. Peanut butters formulated with medium- and dark-roasted PS showed an increase in hardness, and were generally more adhesive than those without PS or with dry-blanched PS added. A marked change in spreadability was found with greater than 2.5% PS fortification. Incorporation of dry-blanched PS, especially at levels below 3.75%, showed the fewest differences in terms of physical properties of the peanut butters relative to the control. Importantly, a concentration-dependent increase in the total phenolics content (TPC) was evident with PS fortification. Dry-blanched PS possessed a TPC of ~166 mg (+)-catechin equivalents/g extract and yielded peanut butters with a 32, 33 and 38% higher TPC than that for light-, medium- and dark-roasted skin incorporation on a same mass basis, respectively. Correspondingly, dry-blanched PS addition at 1.25, 2.5, 3.75 and 5.0% (w/w) resulted in an increase in the TPC by 86, 357, 533 and 714%, respectively, compared with peanut butters devoid of PS fortification; the total proanthocyanidins content (TPACs) rose by 633%, 1,933%, 3,500%, and 5,033%, respectively. Normal-phase high-performance liquid chromatography (NP-HPLC) detection confirmed that the increase in the phenolics content was attributed to the endogenous PACs from the PS, which were characterized as dimers to nonamers by ionization mass spectrometry (NP-HPLC/ESI-MS). FRAP values increased correspondingly by 62, 387, 747, and 829%, while H-ORACFL values rose by 53, 247, 382, and 415%, respectively. The dietary fiber (DF) content of dry-blanched PS was 55%, with 89 to 93% being insoluble fiber. The third and fourth studies undertaken involved liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MSn) characterization of free, as well as soluble-ester and glycoside-bound phenolic compounds from dry-blanched PS. A large variety of phenolic compounds, including phenolic acids (hydroxybenzoic acids, hydroxycinnamic acids, and their esters), stilbenes (trans-resveratrol and trans-piceatannol), flavan-3-ols (e.g., (–)-epicatechin, (+)-catechin, and their polymers {the proanthocyanidins, PACs}), other flavonoids (e.g., isoflavones, flavanols, and flavones) and biflavonoids (e.g., morelloflavone), were identified in dry-blanched PS by this study. PS provide an abundant and inexpensive source of natural antioxidants, especially p-coumaroyl species and PACs. All of these studies indicated that processing is altering the content of the phenolics in PS, but their antioxidant efficacy is retained in the product.
dc.subjectPeanut Skins (PS), Peanut Industry, Dry-blanching, Roasting, Antioxidants, Phenolics, Proanthocyanidins (PACs), high-performance liquid chromatography (HPLC), electrospray ionization mass spectrometry (ESI-MSn).
dc.titleThe phenolics of peanut skins and their impact in peanut butter formulations
dc.description.departmentFood Science and Technology
dc.description.majorFood Science
dc.description.advisorRonald Pegg
dc.description.committeeRonald Pegg
dc.description.committeeRuthann B. Swanson
dc.description.committeeWilliam L. Kerr
dc.description.committeePhillip Greenspan

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