Monitoring the oxidative stability and volatiles in blanched, roasted and fried almonds under normal and accelerated storage conditions by DSC, thermogravimetric analysis and ATR‐FTIR

Abstract

In this study, the effect of different cooking processes (blanching, roasting and frying) on the oxidative stability of almonds under normal storage and accelerated oxidation conditions were investigated. Fried almonds showed higher initial linoleic acid content due to oil frying medium migration to the samples. As oxidation time increased, a different trend in fatty acid composition was obtained depending on the oxidation conditions used. Samples processed at high temperatures presented an initial high PV, resulting in an advanced state of oxidation. A simultaneous formation of hydroperoxides and secondary oxidation compounds was observed in samples under normal storage, presenting raw samples of the lower PV and AV. Lower values of thermal parameters (DSC and TGA) were obtained with increasing oxidation time at 100°C. The most abundant volatile compounds (HS‐SPME‐GC‐MS) present in raw almonds were benzaldehyde, 1,3‐dimethyl‐benzene, 1,2‐dimethyl‐benzene, styrene, 3‐methyl‐1‐butanol, alpha‐pinene and limonene; whereas roasted almonds showed Maillard reaction volatiles such as pyrazines, pyrroles and furans; and fried almonds showed compounds derived from frying oil decomposition (trans,cis‐2,4‐decadienal and trans,trans‐2,4‐decadienal) and higher amounts of aldehydes (hexanal, octanal and nonanal). The generation of hydroperoxides, their degradation and the formation of secondary oxidation products were also investigated by FTIR analysis. Practical applications: Processing of almonds at high temperatures may result in quality deterioration, leading to oxidative rancidity. The studied techniques used in this paper can be useful for processors in order to monitor the oxidative degradation of nuts with storage time and to evaluate their acceptance on the market. In particular, the use of DSC, TGA and ATR‐FTIR could be suitable for studying the shelf life of processed almonds and saving time, which is very precious in quality control. The effect of different cooking processes (blanching, roasting and frying) on the oxidative stability of almonds under normal storage and accelerated oxidation conditions were investigated. Fatty acid composition, primary and secondary oxidation products, thermal parameters, volatiles and lipid degradation were assessed. Results indicate that processing and technological strategies should be used for almond production in order to obtain better oxidative stability and to assure preservation of their overall nutritional profile.