Chemical Compositions of Walnut (Juglans regia L.) Oils from Different Cultivated Regions in China

Abstract

This study is a comprehensive report on the quality of Chinese walnut oil, which enriches the research of oil resources. A total of 16 walnut samples from China were selected, and walnut oils were obtained using the pressing process. The lipid compositions and micronutrient contents were analyzed. The fatty acids corresponded to palmitic acid (3.05–8.25%), oleic acid (12.56–26.03%), linoleic acid (51.21–68.97%), and linolenic acid (6.83–15.01%), and the main triacylglycerols were trilinolein (27.87–39.47%), followed by oleoyl‐linoleoyl‐linolenoyl‐glycerol (17.07–24.18%), dilinoleoyl‐oleoyl‐glycerol (9.65–15.46%), palmitoyl‐dilinoleoyl‐glycerol (5.96–14.98%), and dilinoleoyl‐linolenoyl‐glycerol (6.42–12.43%). In addition, high amounts of micronutrients, including phytosterol, squalene, tocopherol, and total phenolic content, were found in walnut oils ranging from 540 to 1594, 17 to 131, 345 to 1280, and 1.04 to 20.39 mg kg−1 among different samples, respectively. The differences in the geographical location and climate caused different regions of cultivation, which resulted in the differences in the chemical composition of walnut oil. Further multiple linear regression analyses between oxidative stability indices, fatty‐acid compositions, and micronutrients revealed that linoleic acid (R = −0.891; P < 0.05), α‐tocopherol (R = 0.713; P < 0.05), and total phenolic content (R = 0.369; P < 0.05) were the main factors that affect the oxidative stability of the walnut oil.

Phytochemical Content, Minor‐Constituent Compositions, and Antioxidant Capacity of Screw‐Pressed Walnut Oil Obtained from Roasted Kernels

“…About 0.2 mg of walnut oil was dissolved in 2.0 mL n‐hexane and added 0.5 mL 2 mol L −1 KOH–CH 3 OH to prepare fatty acid methyl esters as described in our earlier study . The fatty acid was analyzed using a 7820A gas chromatograph (GC) (Agilent, Palo Alto, CA, USA) and a Trace TR‐FAME capillary column (0.25 μm, 60 m × 0.25 mm, Thermo Fisher, Waltham, MA, USA).…”

“…Tocopherol was qualitatively and quantitatively identified using a high‐performance liquid chromatographic system (LC‐20AT, Shimadzu, Tokyo, Japan) consisting of an ultraviolet detector (SPD‐20A, Shimadzu) and a silica column (5 µm, 4.6 × 250 mm, Hanbon, Jiangsu, China); the method was described in our laboratory published paper . The mobile phase was a mixture of n‐hexane with isopropanol (98.5/1.5, v/v).…”

“…Gas chromatograph‐mass spectrum (GC‐MS) system (Thermo Fisher) was used to analyze phytosterol and squalene, which coupled to a FID (Thermo Fisher). And the determination was pretreatment as described in our earlier study . A DB‐5 capillary column (0.25 µm, 30 m × 0.25 mm, Agilent, USA) was equipped.…”

“…The polyphenols content was determined by spectrophotometer using Folin‐Ciocalteau's reagent according to the method described in our earlier study . In this procedure, a Sepax Generik Diol tube (Sepax Technologies, Inc., Newark, DE, USA) was activated by methanol and n‐hexane, 1.5 g walnut oil was dissolved in 6 mL n‐hexane and passed through the solid phase extraction column, oil was absorbed on solid phase extraction column.…”

Chemometrics‐based vibrational spectroscopy for Juglandis semen extracts investigation

“…Juglans regia L. has high calorie level, rich nutrient composition, antioxidant value, medicinal importance for human health due to their biochemical composition of polyunsaturated fatty acids (PUFAs), especially n‐3 and n‐6 PUFAs, 1,2 tocopherols, 3–6 protein and fibber, 7 melatonin, 8 folate, 5,6 tannins, 9 phytosterols, 10 and polyphenols 11,12 as well. The most abundant polyphenol in J. regia is the flavanone quercetin 13 .…”