1h NMR Investigation of Oil Oxidation in Macadamia Nuts Coated With Zein-Based Films

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.

Revisão: coberturas comestíveis protetoras em frutas: fundamentos e aplicações

“…Essas alterações estruturais reduzem as propriedades de barreira e a aderência (ASSIS e SILVA, 2003), e facilitam a proliferação de fungos. Assim, elevadas adições de plastifi cantes devem ser evitadas, as quais, muitas vezes, inviabilizam o uso da formulação como formadora de cobertura protetora (COLZATO et al, 2011).…”

“…Embora o uso de pincel (HARALAMPU, 1990;CHLEBOWSKA-SMIGIEL et al, 2007) e o spray também tenham sido utilizados para alguns casos (ANDRADE et al, 2012), a imersão é o procedimento que garante que toda a superfície entre em contato com a solução fi lmogênica e uma leve agitação permite o desprendimento de bolhas, possibilitando uma deposição mais homogênea. Uma sequência lógica de formação de cobertura pode então ser resumida segundo o esquema ilustrativo da Figura 3.…”

A review of analytical methods measuring lipid oxidation status in foods: a challenging task

“…However, that is a very expensive methodology and requires special skills to interpret the spectra. The use of 1 H and 13 C NMR spectroscopy in food, applied by different research groups [138][139][140][141][142][143][144][145][146], has proved to be very useful in evaluating the oxidative status of the lipid fraction, as well as in providing information on the nature (main functional groups) and concentration of the compounds found (i.e. hydroperoxides, carbonyl compounds and dienes).…”

Effect of zein coating enriched by addition of functional constituents on the lipid oxidation of roasted hazelnuts

“…At the end of storage period, decreases of 18%, 30%, and 38% were noted in K 232 values of HCZE, HCZ, and HCZT samples, respectively, compared to control. In their study, Colzato et al () showed that conjugated dienes were the major products in macadamia nuts underwent accelerated oxidation assay. At the end of storage period, K 270 value of uncoated hazelnut samples increased gradually up to 0.61 while that of coated samples was around 0.2–0.3.…”