Abstract
SUMMARYBecause of the higher content of unsaturated fatty acids (UNSFA) and phenolics, walnut kernels are vulnerable to oxidative rancidity and browning due to unfavorable postharvest handling procedures. This study investigates the impact of gum arabic coating enriched with γ-aminobutyric acid (GABA) on oxidative rancidity and browning of kernels during storage at 20 °C. The results showed that the walnut kernels coated with gum arabic (5%) enriched with GABA (0.1 mM) exhibited lower oxidative rancidity and browning, manifested by lower peroxide value and malondialdehyde accumulation along with higher whiteness index. Moreover, kernels had higher UNSFA/SFA ratio as a response to lower lipoxygenase activity and H2O2 accumulation. The reduced oxidative browning in coated kernels was accompanied with lower polyphenol oxidase and higher phenylalanine ammonia-lyase activity leading to higher accumulation of phenolics and increased DPPH• scavenging capacity. Based on our findings, gum arabic coating (5%) enriched with GABA (0.1 mM) may have a commercial potential for maintaining nutritional quality of walnut kernels.
Highlights
Owing to higher unsaturated fatty acid (UNSFA) content, walnut kernels are nutritionally important in human diet
Oxidative rancidity and browning During storage at 20 °C for 18 weeks, we recorded a significant increase in peroxide value (PV) and MDA accumulation and a decrease in whiteness index (WI) of kernels (Table 1), indicating oxidative rancidity and browning incidence manifested in kernels by irreversible UNSFA peroxidation via reactive oxygen species (ROS)/LOX and phenolic oxidation by polyphenol oxidase (PPO)
Oxidative rancidity of walnut kernels is a consequence of the peroxidation of UNSFA by ROS/LOX, and a decline in UNSFA/SFA ratio was concurrent with the higher PV and MDA accumulation, as oxidative rancidity markers
Summary
Owing to higher unsaturated fatty acid (UNSFA) content, walnut kernels are nutritionally important in human diet. It makes walnut kernels vulnerable to oxidative rancidity under unfavorable postharvest handling [1]. Oxidative rancidity is a result of UNSFA peroxidation by reactive oxygen species (ROS) accumulation or lipoxygenase (LOX) enzyme activity [2,3]. Oxidative rancidity is stimulated by a higher oxygenavailability, higher temperatures and by a long storage period. Peroxide and malondialdehyde (MDA) are the primary and secondary products of UNSFA peroxidation. The peroxide value (PV) and MDA accumulation are often used as oxidative rancidity markers [2,3]
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