Fungal Culture Systems for Production of Antioxidant Phenolics Using Pecan Nut Shells as Sole Carbon Source

Medina Medina

doi:10.3844/ajabssp.2010.397.402

Abstract

Problem statement: Many agro-industrial wastes have little or none utilization, when these materials could be a very rich source of several value-added compounds, such as: the pecan nut shells, which contain Antioxidant Phenolic (AP) molecules like tannins. Approach: In this study, a bioprocess for the liberation of AP from Pecan Nut Shells (PNS) was described. A chemical characterization of raw material was evaluated to determine polyphenolic content of PNS, among other components. Several fungal culture systems were evaluated at 96 h fermentation processes and using PNS as sole carbon source. Solid (SSC) and Submerged (SmC) fermentations were carried out using three strains of Aspergillus niger. Culture medium was composed of a solid (10-50%) and a liquid (90- 50%) part in order to complete the 100% of the medium. Results: A high concentration (19%) of tannins was found in PNS on a dry basis, from which condensed tannins and their monomers were found as the main fraction (14%) of tannins of PNS, also on a dry basis. In the strain selection step, Aspergillus niger GH1 showed better growth on pecan nut shells compared to A. niger PSH strain, therefore, A. niger GH1 was used for later experiments. The highest concentration of AP was obtained with SSC inoculated with spores of A. niger GH1 on the 40% of solids system and in 20% solids system where, among the other systems both presented 114 mg TP g-1 of phenolics liberation at 24 h of fermentation. PNS is an important source of catechin, being this kind of compound which can be liberated in higher proportion compared to other phenolics compounds. Conclusion: This study demonstrated that fermenting PNS represent a good alternative to both use residues and obtaining AP.

Highlights

In North America, among the template weather zones of México and USA, the pecan nut tree grows producing nuts which have great demand in the food industry (Orzua et al, 2009)
It was observed that in both 20 and 40% of Pecan Nut Shells (PNS), the Having the sum of these compounds, in the Fig. 2 the TP pattern during the culture demonstrate that there is a phenolics liberation; consequence of the microbial hydrolysis of phenolics
Results of this study showed that PNS can be used for fungal culture processes by Aspergillus niger strains, due to the fact that condensed tannins is the mayor component of the shells and the possibility of our strains being capable of degrade hydrolysable and condensed tannins (Aguilar et al, 2004)

Summary

Introduction

In North America, among the template weather zones of México and USA, the pecan nut tree grows producing nuts which have great demand in the food industry (Orzua et al, 2009). There are four main groups of tannins, gallotannins, ellagitannins, condensed tannins and complex tannins (Khanbabaee and van Ree, 2001) According to other report, pecan nuts contain antioxidant phenolics and PNS contain higher amounts of these molecules, mostly condensed tannins (Villarreal-Lozoya et al, 2007). These compounds have many biological activities, such as antimicrobial, antimutagenic and antioxidant (AscacioValdes et al, 2010; Abdul Rahim et al, 2010). Filamentous fungi have been studied for biodegradation of tannins and liberation of phenolics (Aguilar et al, 2004; Mata-Gomez et al, 2009). Solid state cultures are systems which have received praise due to the higher yields of compounds of interest than submerged cultures and being a low cost

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