Quality Evaluation of Walnuts from Different Regions in China

Abstract

This study analyzed and evaluated the basic crude fat contents, crude protein contents, phenolic compounds, lipid compositions (fatty acids, phytosterols, and tocopherols), and amino acid compositions of 26 walnut samples from 11 walnut-growing provinces in China. The results indicate that the oil contents of the samples varied from 60.08% to 71.06%, and their protein contents ranged from 7.26 g/100 g to 19.50 g/100 g. The composition of fatty acids corresponded to palmitic acid at 4.61–8.27%, stearic acid at 1.90–3.55%, oleic acid at 15.50–32.28%, linoleic acid at 53.44–67.64%, and α-linolenic acid at 2.45–12.77%. The samples provided micronutrients in widely varying amounts, including tocopherol, phytosterol, and total phenolic content, which were found in the walnut oil samples in amounts ranging from 356.49 to 930.43 mg/kg, from 1248.61 to 2155.24 mg/kg, and from 15.85 to 68.51 mg/kg, respectively. A comprehensive evaluation of walnut oil quality in the samples from the 11 provinces using a principal component analysis was conducted. The findings revealed that the samples from Henan, Gansu, and Zhejiang had the highest composite scores among all provinces. Overall, Yunnan-produced walnuts had high levels of crude fat, polyunsaturated fatty acids, and total tocopherols, making them more suitable for producing high-quality oil, whereas Henan-produced walnuts, although lower in crude fat, had a higher crude protein content and composite score, thus showing the best walnut characteristics.