Processing Techniques for the Improvement of Peanut Meal

Abstract

Peanut meal is characterized as the non-food grade material that remains after the extraction of oil from peanuts (Arachis hypogaea L.). Oil is extracted from peanuts that are considered not suitable for human consumption due to discolored, broken, or aflatoxin contaminated seed. Peanut meal is a rich source of protein (45-60%) and can be used in food products if the aflatoxin, an unavoidable contaminant in peanut crop, was eliminated. Recent trends have shown that plant proteins are increasingly being used as a less expensive alternative to animal proteins for fulfilling basic nutritional needs. Technologies are needed to expand the applications for this commercially available material, which is currently sold at a low economic value as either animal feed or fertilizer, dependent upon its aflatoxin concentration. The objectives of this research were to improve the value of peanut meal: 1) through enzymatic hydrolysis to enhance protein functional and nutritional properties, and 2) by sequestering the aflatoxin from contaminated meal using a non-nutritive adsorbent.

Defatted peanut meal dispersions (10% w/w) were hydrolyzed with commercial proteases (Alcalase, pepsin and Flavourzyme) and soluble fractions (hydrolysates) were collected for subsequent testing. Degree of hydrolysis ranged from approximately 20-60% for Alcalase, 10-20% for pepsin and 10-70% for Flavourzyme from 3-240 min. Low molecular weight peptides (<14 kDa) were observed in all hydrolysates as determined by SDS-PAGE. Results indicated that total soluble material increased a minimum of 30% regardless of protease at 240 min and antioxidant capacity of all hydrolysates was greater than unhydrolyzed controls. Specifically, Alcalase hydrolysates had the greatest antioxidant capacity and total soluble material. These results suggest that peanut meal could be made more valuable via enzymatic hydrolysis to create small peptides with improved functional and nutritional properties.

A method of reducing aflatoxin within peanut meal was also investigated, as it is imperative to have <20 ppb for peanut products intended for human applications. The in vitro efficacy of sodium bentonite clay, Astra-Ben 20â„¢ (AB20), to sequester aflatoxin from contaminated meal was studied. Aqueous peanut meal dispersions (10% w/w) were adjusted to pH 2 and 8 and randomly assigned to one of three treatments: control (no clay), 0.2% AB20 (w/w), or 2% AB20 (w/w). Results revealed that the addition of clay significantly lowered the aflatoxin concentration in the soluble and insoluble fractions to a level that would be permissible by the FDA for use in food products. The pH of the soluble samples did not significantly affect the ability of clay to bind aflatoxin. Soluble fractions subjected to 2% AB20 treatment had significantly lower protein solubility and total soluble material than their respective pH 2 and 8 controls. This novel research not only provides an avenue for high protein peanut meal soluble fractions to be used safely in human food applications, but also for the insoluble fractions to be sold as animal feed at a higher price due to the decreased level of detectable aflatoxin.