Fatty Acid Stable Carbon Isotope Ratios Combined with Oxidation Kinetics for Characterization and Authentication of Walnut Oils

Abstract

Walnut oil is vulnerable to oxidation due to its high content of polyunsaturated fatty acids and adulteration due to its high price. This study investigated 12 typical walnut oils from six main walnut-producing areas in China, using differential scanning calorimetry (DSC), Rancimat test, gas chromatography (GC), elemental analyzer−isotope ratio mass spectrometry (EA−IRMS) and GC−IRMS combined with oxidation kinetic analysis, Pearson correlation analysis, and principal component analysis (PCA). The melting and crystallization profiles using DSC indicated that walnut oils with a relatively high crystal onset temperature tended to be more stable against oxidation. Oleic acid was found to be the most characteristic fatty acid in walnut oil, with a content ranging from 13.84 to 35.08%. Two walnut oils with the highest oleic acid contents of 35.08 and 32.78% had the highest activation energies in nonisothermal DSC. Their predicted shelf lives based on the Rancimat test were 3.5−4.0 times longer than that of the oil with the highest α-linolenic acid at 4 °C and 3.1−3.5 times longer at 25 °C. The δ 13 C values of walnut oils were determined by EA−IRMS, and the δ 13 C values of fatty acids were determined by GC−IRMS. Fatty acid stable carbon isotope ratios combined with PCA were successfully applied to intuitively discriminate different walnut oils. The results suggested that fatty acid δ 13 C values determined by IRMS combined with chemometrics and lipid compositions are promising as a powerful means of vegetable oil authentication and discrimination.

Stepwise Approach for Tracing the Geographical Origins of the Manila Clam Ruditapes philippinarum Using Dual-Element Isotopes and Carbon Isotopes of Fatty Acids

“…However, the classification rate of samples from Korea was correctly discriminated with respect to geographical origin. [66] and to the range of δ 13 C values of POM reported by Wu et al [67]. The δ 13 C values of the clam samples from DPR Korea were slightly lower than those of the samples from Korea.…”

“…The δ 13 C values of FAs can provide a highly precise description of food sources and establish the traceability of carbon flow as consumer FA δ 13 C values varying based on the primary producer [32]. In food authentication, although the use of this method to certify aquaculture products (e.g., seafood) has been rarely explored, its potential has been anticipated, and it has enabled food certification for walnut oil or organic milk [65,66].…”

Characterization of Predominant Aroma Components in Raw and Roasted Walnut (Juglans regia L.)

“…China is the largest walnut producing country in the world, contributing approximately 1,586,367 tons of walnut in 2018, followed by the USA and Iran. Mostly, about 70% commercial walnuts of the world were generated from these three countries (Amini and Ghoranneviss 2016;Zhang et al 2021). Walnut is a widely used ingredient in beverage and food of the high nutritional value, containing 14-18% protein and 70% fat (Martínez et al 2011).…”

Time-Series Lipidomics Insights into the Progressive Characteristics of Lipid Constituents of Fresh Walnut during Postharvest Storage

“…Walnut (Juglans regia L.) is the most widespread tree nut in many countries and offers enormous economic, ecological, and social potential . Because its kernel is rich in minerals, proteins, and lipids, walnut is included in the list of priority plants of Food and Agriculture Organization of the United Nations and is considered as a strategic nut crop for dietary diversity and human nutrition. , In recent years, the consumption of fresh walnut is increasing worldwide, as it has high nutritients and a unique and aromatic flavor, which is respected in some countries. Compared to dried walnuts, fresh walnuts exhibit superior antioxidant properties due to the abundance of antioxidant and phenolic compounds .…”

“…Compared to dried walnuts, fresh walnuts exhibit superior antioxidant properties due to the abundance of antioxidant and phenolic compounds . To date, chemical constituents, health benefits, and industrial uses of walnut and its byproducts have been investigated. However, to the best of our knowledge, the dynamic changes of lipid profile of fresh walnut during postharvest storage have not enough been evaluated …”