1H NMR INVESTIGATION OF OIL OXIDATION IN MACADAMIA NUTS COATED WITH ZEIN-BASED FILMS

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TEL: 55-16-21072833; FAX: 55-16-221072902; EMAIL: odilio@cnpdia.embrapa.br

Abstract

ABSTRACT

The effectiveness of corn-zein edible coatings in blocking oil oxidation on macadamia nuts was studied by using high-resolution Hydrogen Nuclear Magnetic Resonance (1H NMR) spectroscopy. Formulations with a zein concentration of 4.0% by weight and oleic acid (OA) as a plasticizer in different proportions were evaluated. Accelerated oxidation was conducted by using an O2-reactor in a 60C water bath. The oil extracted from the nuts at the beginning of the study and after 10 and 30 days into the experiment were analyzed. Results from the 1H NMR analysis exhibited that the major products formed by lipid oxidation were conjugated dienes. The coatings were imperceptible to the naked eye, but textural changes were visible under scanning electron microscopy. The best coating formulation was a combination of zein with 0.25% OA, which completely inhibited oxidation. Plasticizer addition of 0.50 and 1.00% wt, however, had a negative effect on the coating's property as a barrier against oxygen, resulting in higher rates of oxidation than in the uncoated samples.

PRACTICAL APPLICATIONS

Hydrophobic zein-based edible coatings, as used in this study, are capable of acting as barriers against oxygen and water vapor by reducing, or even eliminating, undesirable oxidation in unshelled macadamia nuts during long-term storage. The results of our study have demonstrated the ease of forming stable coatings to reduce oxidative fatty rancidity. The films are invisible to the naked eye and do not produce visible changes in the texture and the color of the coated nuts. This study indicates that zein/oleic acid edible coatings are feasible to use for large-scale applications, providing an alternative way to improve the oxidative stability and eventually to lengthen the shelf life and quality of macadamia nuts.

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