Quality evaluation of oil by cold-pressed peanut from different growing regions in China.

In this study, twenty-six peanut varieties and their cold-pressed oils from eleven provinces in China were investigated for their oil content, acid value, peroxide value, fatty acid profiles, bioactive constituents, and induction period (IP) of lipid oxidation. Meanwhile, the effect of the geographical origin of peanut on the quality of cold-pressed peanut oils (CPOs) was studied. The average acid value of CPOs in southern China was higher than that in northern China (0.49 mg KOH/g versus 0.22 mg KOH/g, p > .05). In addition, the average of oleic acid content, ratio of oleic acid to linoleic acid (O/L), and IP were also higher in southern China than that in northern China (p < .05). However, the average content of campesterol, β-sitosterol, total phytosterol, linoleic acid, and ratio of unsaturated fatty acid to saturated fatty acid (UFA/SFA) exhibited reverse results (p < .05). At last, the comprehensive evaluation of CPOs based on principal component analysis (PCA) was performed. In all samples, Silihong from Liaoning province, northern China was No.1, and Zhonghua 21 from Xiaogan City, Hubei Province was No.4 which was the first one from southern China. Moreover, heat map clustering analysis further revealed the differences and similarities among different samples, and those results were in accordance with the comprehensive evaluation results.

INTRODUCTION

Peanut (Arachis hypogaea L.) is an economically important oil seed crop grown in tropical and subtropical agro‐climatic areas of Asia, Africa, and the Americas with the oil content in the range of 44%–56% (Verma et al., 2012). China, India, and the United States are the top three peanut producers in the world. By the end of 2020, the global peanut production reached 50.53 million metric tons, of which 36.02% was provided by China. Meanwhile, China is also a major consumer of peanut oil, consuming around 3.54 million metric tons in 2020–2021, accounting for 54.81% of the world's total domestic consumption (USDA, 2021).

Peanut oil is a rich source of dietary essential fatty acids including oleic acids (36% to 67%) and linoleic acids (15% to 46%), and O/L ratios are in the range of 1.19–4.46 (Akram et al., 2018). The previous studies have shown that O/L is associated with a lower risk of cardiovascular disease, and linoleic acid has a positive influence on coronary heart disease (Dun et al., 2019). Furthermore, it contains several biologically active ingredients for instance tocopherols and phytosterols. A‐tocopherol and γ‐tocopherol are the major form of vitamin E in peanut oil, which has good lipid antioxidant capacity (Carrín & Carelli, 2010). Phytosterols can retard the development of atherosclerosis, lower the risk of type 2 diabetes, and reduce the risk of colorectal cancer, which is conducive to human health benefits (Suchoszek‐Łukaniuk et al., 2011).

At present, studies tend to concentrate on the effect of different processing technologies on the chemical components and quality changes in peanut oil. However, different planting areas may lead to quality variation in peanut resources, which in turn leads to change in processed quality. Sanders et al. (1992) found that tocopherol content was obviously different in peanuts from various regions. The fatty acid composition and oil stability was variable depending on the growth location and cultivar (Campos‐Mondragón et al., 2009; Grosso & Guzman, 1995; Grosso et al., 1994). Although several researchers have confirmed the view that natural conditions played a significant role in oil stability and quality, differences in Chinese peanut varieties, especially from the north and south regions, have not been extensively studied. The south and the north have been the largest symbolic geographical division and two major peanut production areas since ancient times, which show a completely different ecological environment, reflected in climate, rainfall, soil, and sunlight.

The purpose of this research was to capture a more detailed understanding of the processing characteristics of peanut from different regions and varieties by evaluating the effect of different planting areas (north–south region) on the physicochemical and nutritional characteristics of cold‐pressed peanut oil, thereby providing scientific guidance for processing high‐quality peanut oil and breeding peanut varieties.

MATERIALS AND METHODS

Materials and chemicals

Twenty‐six peanut cultivars (Arachis hypogaea L.) planted from the Chinese main planting areas in September (October) 2019 were collected, cleaned, and dried at room temperature. With Qinling and Huaihe as dividing lines, fourteen kinds came from the southern region, including Sichuan (one cultivars), Guangxi (two cultivars), Guangdong (one cultivar), Jiangsu (one cultivar), Jiangxi (three cultivars), Hunan (two cultivars), and Hubei (four cultivars); twelve kinds came from the northern region, including Hebei (three cultivars), Henan (two cultivars), Shandong (four cultivars), Jiangsu (one cultivar) and Liaoning (two cultivars) regions. More details about peanut samples are listed in Table S1.

α‐, γ‐, and δ‐tocopherol (purity ≥98%), cholesterol (purity ≥99%), stigmasterol (purity ≥95%), β‐sitosterol (purity ≥95%) and campesterol (purity ≥98%), 5α‐cholestane (purity ≥97%), and N,O‐Bis (trimethylsilyl) trifluoroacetamide with trimethylchlorosilane (BSTFA+TMCS ≥ 98.5%, excluding trimethylchlorosilane) were purchased from Sigma‐Aldrich (Saint Louis, MS, USA). Chromatographic grade isopropanol and hexane were purchased from Merck (Darmstadt, Hesse, Germany). Other chemicals and reagents were of analytical grade and purchased from Chinese medicine group chemical reagent co., Ltd (Shanghai, China).

Cold‐pressed peanut oil extraction

All the above peanut seeds were pressed with a cold pressing machine (CA59G, German Monforts Group, Moenchen‐gladbach, North Rhine‐Westphalia, Germany) at a temperature below 60°C. Each oil obtained was centrifuged at 25,230 × g for 15 min (Avanti J‐26 XP, Beckman Coulter Inc., Brea, CA, USA) to remove residue and then kept cold (4 ± 2°C) for future experimental treatments.

Quality indices

The oil content in peanut seed was determined according to the GB 5009.6–2016 (CNIS, 2016), which involves the gravimetric analysis with analytical grade petroleum ether in a Soxhlet apparatus (B‐811; Buchi Labortechnik AG) for 8 hr. According to GB 5009.229–2016 and GB 5009.227–2016 (CNIS, 2016), the acid value and peroxide value are determined through titration method. The oil sample was fully dissolved in an organic solvent, and then titrated with KOH or sodium thiosulfate standard solution. Finally, the titration end point was defined by the color reaction of the indicator. The acid value was expressed as the milligrams of potassium hydroxide (KOH) required neutralizing 1 g of free fatty acid. The peroxide value was expressed as the millimoles of active oxygen in 1 kg of the sample.

Fatty acid profile

Preparation of fatty acid methyl ester (FAME) samples, reference to GB/T 5009.168–2016:60.0 mg (accurate to 0.1 mg) oil was taken into a 10‐mL centrifuge tube along with 4 ml isooctane and 200 μL of 2 mol/L methanol‐KOH solution. It was shaken for 30 s so that the sample mixed well, then set aside until clarified. Finally, 1 g of sodium bisulfate was fully used to neutralize potassium hydroxide. After the salt had precipitated, the upper phases were transferred to GC vials for testing.

Composition of fatty acids (%) was detected by gas chromatography (7890A, Agilent, U.S.A), as described by the European standard EN14103 (2003). 1 μL FAME specimen with a split ratio of 80:1 was injected into the capillary column (HP‐INNOWAX, 30 m × 0.32 mm ×0.25 μm; Agilent, Santa Clara, CA, USA) at a flow rate of 1.5 ml/min with nitrogen as the carrier gas. Oven temperature of the instrument increased from 210°C (kept for 9 min) to 230°C at a rate of 20°C /min and held for 10 min. The temperatures of the injector and FID detector were set to 250°C and 300°C. Chemstation software was used to calculate peak areas and retention time of individual fatty acid, and the content was expressed as the mass fractions.

Determination of tocopherols by high‐pressure liquid chromatography (HPLC)

The indigenous tocopherol contents of the twenty‐six peanut oils were determined by using AOCS official method Ce 8–89 Tocopherols and Tocotrienols in Vegetable Oils and Fats by HPLC (AOCS, 2009). In brief, the samples were accurately weighed at 2.0 g and dissolved in n‐hexane with a 25‐mL brown volumetric flask and made up to volume. It was important that the test solutions are protected from light prior to analysis and analyzed on the day of preparation. 20 µl of the test solution was injected onto the analytical column packed with micro particulate silica having a mean particle size of about 5 µm (250 × 4.8 mm) and tocopherols were detected by the diode array detector (SPDM20A, Shimadzu, Tokyo, Japan) at specific wavelength. The isocratic mobile phase was a mixture of n‐hexane: isopropanol (0.5:99.5, v/v) at a flow rate of 1.0 ml/min. Standards of α‐, γ‐, and δ‐tocopherol were diluted with hexane and their concentration was determined by the absorbance maximums of the solutions using UV spectroscopy according to Beer's Law (λ = 292 nm, 298 nm and 298 nm). Calculations of the unknown were done by comparison of peak areas and the calculated concentrations of the standard solutions. Standard curves of each isomer covered five orders of magnitude and bracketed all sample concentrations. Identify the tocopherols present by reference to the chromatograms obtained from standards and record the areas of the tocopherol peaks. The results were achieved through the formula conversion and expressed in milligram per kilogram (mg/kg).

GC analysis of the phytosterols

Phytosterols were measured according to the method described by Azadmard‐Damirchi et al. (2010), after minor modification. The weighed oil sample (ca.20 mg) was added to 0.5 ml of 5α‐cholesterol solution (0.5 mg/ml), then mixed thoroughly with 10 ml of 2 M KOH in 95% ethanol in a ground‐glass tube, and shaken in a water bath at 60°C for 60 min. After cooling, 4 ml of water and 10 ml of hexane were added and mixed vigorously. Thereafter, the mixture was centrifuged at 4863 g for 5 min and the hexane layer containing unsaponifiables was separated. The above process was carried out for three times, and the collected extract redissolved into 1ml hexane solution after complete evaporation, bottled for further analysis. Gas chromatographic conditions included a DB‐5HT column (30 m × 0.22 mm ×0.1 μm; Agilent, Santa Clara, CA, USA) performed at a flow rate of 1.5 ml/min with helium as the carrier gas. The injection volume was 1 μL, flow rate was 2 ml/min, and the split ratio was 25:1. The program temperature was maintained at 60°C for 1 min. Then, the temperature was increased at a rate of 40°C/min to a final temperature of 310°C, and held for 10 min.

According to the retention times of reference samples of phytosterols in the chromatogram, each phytosterol in the analyzed oil samples was identified. Quantification was done relative to the 5α‐cholestane as an internal standard. The calculation method was as follows: where, X represents the content of a single sterol component, mg/kg; 0.25 represents the mass of 5α‐cholesterol, 0.5 mg / mL ×0.5 ml, mg; A represents a single sterol peak area; A represents 5α‐cholesterol peak area; M is the mass of the oil sample, g.

Oil stability

Oxidative stability was measured with the Rancimat 743 (Metrohm, Riverview, FL, USA), according to the method described by Yang et al. (2012). 3.0 g of oil samples were weighed into the reaction vessel in triplicate and heated to 110°C with an air flow of 20 L/h. Volatile products released during the oxidation process were collected in a flask containing distilled water. The oxidation process was recorded automatically by measuring the change in conductivity of the distilled water due to the formation of volatile compounds. The oxidative induction period (IP) was defined as the point of rapid change in the rate of oxidation, and the results were expressed in hours (h).

Statistical analysis and principal component analysis

The analysis was performed in triplicate. The obtained results were presented as the mean with standard deviation (SD). An independent sample t‐test (using SPSS 22 software; SPSS Inc., Chicago, IL, USA) was used to compare the mean value of two groups (CPOs in southern China versus. northern China). Mean differences were considered notably at the p <.05 level. The principal component analysis (PCA) and cluster analysis were performed for the nutritional comprehensive score of cold‐pressed peanut oils.

RESULTS AND DISCUSSION

Physicochemical characteristics

For such a large population like China, the development and utilization of edible oil is of vital importance. Peanuts can meet the oil intake needs of people and create a huge economic value. In addition, although peanuts are a high‐fat, energy‐dense food, clinical and epidemiological studies demonstrated that peanut consumption is not associated with weight gain (Mattes et al., 2008).

The oil content is an important feature of peanut seed evaluation, which may vary from 40% to 65% depending upon variety, season, and maturity. In this research, the influence of different provenances on the oil content of peanuts was emphasized, with the aim of providing reference for further selection of good seed materials with high oil content. On account of its guiding significance, the oil contents of twenty‐six peanut varieties ranged from 45.97% to 57.28% with statistical significance at the level of p <.05 (Table 1). The Luhua 9 (P10), coming from Xuzhou, Jiangsu, had the highest oil content (>57%). These values were in accordance with the report of Wang et al. (2012). In comparison to other typical oil crops, the peanut seeds contained a much higher proportion of oil than hemp seeds (26%–37%) and rapeseed (35%–39%) (Kriese et al., 2004; Yang et al., 2009).

TABLE 1

Physiochemical of CPOs from twenty‐six peanut cultivars grown in China

Sample	Oil content (g/100g)	Acid value (mg KOH/g)	Peroxide value (mmol/kg)
P1	48.58 ± 0.48def	0.13 ± 0.00a	3.70 ± 0.15h
P2	47.03 ± 0.16b	0.24 ± 0.01efg	3.01 ± 0.02ef
P3	49.55 ± 0.03hij	0.32 ± 0.00k	3.57 ± 0.04h
P4	49.72 ± 0.03j	0.24 ± 0.00fgh	5.55 ± 0.20k
P5	49.11 ± 0.01fgh	0.11 ± 0.00a	3.06 ± 0.44ef
P6	49.05 ± 0.12fgh	0.27 ± 0.00j	3.40 ± 0.17h
P7	49.14 ± 0.43ghi	0.24 ± 0.01ghi	3.12 ± 0.11f
P8	48.44 ± 0.21de	0.19 ± 0.00c	1.94 ± 0.16a
P9	49.06 ± 0.33fgh	0.30 ± 0.01k	3.62 ± 0.02h
P10	57.28 ± 0.01o	0.23 ± 0.01fg	2.16 ± 0.18a
P11	52.76 ± 0.11m	0.20 ± 0.01 cd	2.05 ± 0.11a
P12	52.71 ± 0.02m	0.17 ± 0.01b	2.20 ± 0.04ab
P13	45.97 ± 0.25a	0.22 ± 0.01de	4.91 ± 0.01j
P14	51.61 ± 0.32l	0.48 ± 0.01o	4.10 ± 0.28i
P15	49.66 ± 0.08ij	0.45 ± 0.00n	2.82 ± 0.10cdef
P16	51.43 ± 0.30l	0.58 ± 0.00p	2.63 ± 0.16 cd
P17	48.08 ± 0.38 cd	0.43 ± 0.01m	2.57 ± 0.01c
P18	48.80 ± 0.28efg	0.22 ± 0.00f	2.13 ± 0.13a
P19	46.59 ± 0.43b	0.36 ± 0.01l	2.71 ± 0.02 cd
P20	53.92 ± 0.26n	0.13 ± 0.01a	3.75 ± 0.34h
P21	50.69 ± 0.04k	0.26 ± 0.01hij	2.97 ± 0.04cdef
P22	50.62 ± 0.11k	0.16 ± 0.01b	2.05 ± 0.11a
P23	51.71 ± 0.01l	2.74 ± 0.04q	3.58 ± 0.10h
P24	45.97 ± 0.09a	0.36 ± 0.01l	4.39 ± 0.16i
P25	47.08 ± 0.27b	0.27 ± 0.01ij	2.53 ± 0.12bc
P26	47.80 ± 0.17c	0.23 ± 0.01fg	2.53 ± 0.03bc

N means peanuts grown in the north; S means peanuts grown in the south; values in the columns with different letters (a‐q) are significantly different (p <.05).

Physicochemical analyses represent parameters related to the conservation and quality of the oil, and is receiving more and more attention from producers, researchers, and consumers. These indexes indicate the conservation state of the oil based on the impact of the major environmental oxidants, such as heat, light, and oxygen, elements that can accelerate the decomposition of glycerides, develop rancidity, and lead to the formation of free fatty acids in the matrices (dos Santos et al., 2019). The acidity value, ranging from 0.11 mg KOH/g to 2.74 mg KOH/g obtained from twenty‐six samples (p <.05), was within the permitted level provided in GB 2716–2018 (≤3 mg KOH/g). The peroxide value (PV), which indicates the concentration of peroxides and hydroperoxides formed in the initial stages of lipid oxidation, can reflect the extent to which an oil is oxidized (Ni et al., 2015). In general, oils with peroxide value higher than 4.5 mmol/kg cause undesirable health problems by increasing reactive oxygen species as well as secondary products of lipid peroxidation that stimulate cardiovascular and inflammatory diseases (Konuskan et al., 2019). Oils with peroxide levels higher than 5 mmol/kg are considered to be less stable, and they have a short shelf life. In the test samples, Yuhua10 (P4) and Local red peanut (P13), with an initial peroxide value up to 5.55 mmol/kg and 4.91 mmol/kg, respectively, performed relatively poorly, which would quickly become unsuitable for human diets.

Identification and quantification of fatty acids

Oil composition is critical to final product quality of peanut‐based products, including nutritional profile, physical properties, flavor, and shelf life (Braddock et al., 2010). As basic constituents of fats and oils, fatty acids in different varieties of peanut oils were evaluated and identified (Table 2). The major fatty acids present were palmitic acid (C16:0), oleic acid (C18:1), and linoleic acid (C18:2). Additionally, palmitoleic acid (C16:1), stearic acids (C18:0), and longer chain fatty acids, such as arachidic acid (C20:0), gadoleic acid (C20:1), behenic acid (C22:0), lignoceric acid (C24:0), occurred in minor quantities. Across overall samples, relative (%) concentration of oleic acid revealed the highest amounts varied between 36.10% and 47.66%, followed by linoleic acid and palmitic acid in smaller amounts of 30.53%‐40.86% and 10.17%‐12.61%. The sum of these three fatty acids accounted for 88.46%‐90.60% of total fatty acids, which was consistent with published data by Wang (2018). Statistical analyses showed there existed observable differences (p <.01) among the peanut cultivars tested. Akhtar et al. (2014) concluded the fatty acid composition of peanut oil was highly variable according to the environmental conditions, variety, and peanut maturity level.

TABLE 2

Fatty acid composition and average content (%) of CPOs from twenty‐six peanut cultivars grown in China

Sample	Palmitic acid	Palmitoleic acid	Stearic acid	Oleic acid	Linoleic acids	Arachidic acid	Gadoleic acid	Behenic acid	Lignoceric acid	∑UFA	∑SFA	UFA/SFA	O/L
P1	12.04 ± 0.13m	0.26 ± 0.01 cd	3.38 ± 0.03ef	38.67 ± 0.16d	39.72 ± 0.10p	1.41 ± 0.01ab	0.77 ± 0.01bcd	2.43 ± 0.02cde	1.34 ± 0.15c	79.41 ± 0.27jkl	20.59 ± 0.27def	3.86 ± 0.06ij	0.97 ± 0.00d
P2	10.47 ± 0.06b	0.22 ± 0.01bc	2.83 ± 0.03b	45.14 ± 0.12n	35.00 ± 0.08i	1.37 ± 0.04a	1.07 ± 0.02j	2.51 ± 0.04ef	1.41 ± 0.03efgh	81.42 ± 0.19no	18.59 ± 0.19ab	4.38 ± 0.06m	1.29 ± 0.00o
P3	10.74 ± 0.06de	0.32 ± 0.04ef	3.32 ± 0.02e	45.28 ± 0.12n	34.60 ± 0.11h	1.41 ± 0.07ab	0.87 ± 0.02fgh	2.32 ± 0.01bc	1.16 ± 0.01ab	81.07 ± 0.18n	18.94 ± 0.18b	4.29 ± 0.05l	1.31 ± 0.00p
P4	11.82 ± 0.04l	0.24 ± 0.02c	3.83 ± 0.03i	39.80 ± 0.11e	37.48 ± 0.09n	1.61 ± 0.04gh	0.95 ± 0.01i	2.72 ± 0.05gh	1.57 ± 0.02ij	78.46 ± 0.18cdef	21.55 ± 0.18jklm	3.64 ± 0.04bcde	1.06 ± 0.00f
P5	11.32 ± 0.04ij	0.74 ± 0.01k	3.84 ± 0.02i	40.38 ± 0.11f	36.97 ± 0.08m	1.60 ± 0.01fgh	0.87 ± 0.01gh	2.94 ± 0.05ij	1.36 ± 0.03defg	78.95 ± 0.16ghi	21.05 ± 0.16ghi	3.76 ± 0.04fgh	1.09 ± 0.00h
P6	10.15 ± 0.05a	0.47 ± 0.01h	3.03 ± 0.03c	44.19 ± 0.11l	36.07 ± 0.08k	1.38 ± 0.01ad	0.97 ± 0.01i	2.42 ± 0.04cde	1.34 ± 0.05cde	81.70 ± 0.18c	18.31 ± 0.18a	4.47 ± 0.05m	1.23 ± 0.01m
P7	12.28 ± 0.07o	0.30 ± 0.01de	3.42 ± 0.03fg	38.12 ± 0.10c	39.80 ± 0.12p	1.47 ± 0.01bc	0.84 ± 0.04efg	2.45 ± 0.03de	1.33 ± 0.03cde	79.05 ± 0.17hij	20.95 ± 0.17fgh	3.78 ± 0.04ghi	0.96 ± 0.00c
P8	10.17 ± 0.06a	0.76 ± 0.04k	3.43 ± 0.04fg	46.10 ± 0.13p	33.92 ± 0.11g	1.42 ± 0.03abc	0.86 ± 0.03fgh	2.17 ± 0.02a	1.20 ± 0.01ab	81.63 ± 0.16co	18.38 ± 0.16a	4.45 ± 0.05m	1.36 ± 0.00r
P9	11.30 ± 0.06hi	0.36 ± 0.01f	4.21 ± 0.06k	40.67 ± 0.10g	37.55 ± 0.11n	1.64 ± 0.02gh	0.74 ± 0.01abc	2.36 ± 0.03 cd	1.19 ± 0.02ab	79.31 ± 0.18ijko	20.69 ± 0.18efg	3.83 ± 0.04hi	1.08 ± 0.00g
P10	11.47 ± 0.11k	0.35 ± 0.00ef	2.55 ± 0.06a	39.70 ± 0.13e	38.70 ± 0.12o	1.35 ± 0.01a	1.13 ± 0.02k	3.15 ± 0.01kl	1.63 ± 0.02j	79.87 ± 0.24hm	20.13 ± 0.24c	3.97 ± 0.06k	1.03 ± 0.00e
P11	10.84 ± 0.06e	0.26 ± 0.02 cd	4.13 ± 0.04j	36.78 ± 0.11b	40.85 ± 0.14q	1.72 ± 0.03i	0.84 ± 0.02efg	3.14 ± 0.05k	1.47 ± 0.03hi	78.72 ± 0.21efg	21.29 ± 0.21hijk	3.70 ± 0.04defg	0.90 ± 0.00b
P12	10.61 ± 0.06c	0.18 ± 0.00ab	3.12 ± 0.04d	36.10 ± 0.13a	40.86 ± 0.11q	1.51 ± 0.04de	1.47 ± 0.02l	4.17 ± 0.04m	2.00 ± 0.03k	78.60 ± 0.22defg	21.41 ± 0.22ijkl	3.68 ± 0.05cdefg	0.88 ± 0.00a
P13	10.45 ± 0.04b	0.42 ± 0.01g	5.08 ± 0.02o	39.84 ± 0.12e	36.58 ± 0.10l	2.08 ± 0.03k	0.83 ± 0.01efg	3.26 ± 0.03l	1.48 ± 0.07hi	77.66 ± 0.20ab	22.34 ± 0.20no	3.48 ± 0.04a	1.09 ± 0.00h
P14	11.18 ± 0.04gh	0.37 ± 0.01f	3.38 ± 0.03ef	44.69 ± 0.11m	33.91 ± 0.09g	1.50 ± 0.04cde	0.90 ± 0.04h	2.65 ± 0.08g	1.45 ± 0.08fgh	79.86 ± 0.18m	20.15 ± 0.18c	3.96 ± 0.05k	1.32 ± 0.00q
P15	11.32 ± 0.04ij	0.34 ± 0.02ef	3.70 ± 0.03h	47.29 ± 0.13r	31.35 ± 0.11c	1.49 ± 0.01bcde	0.83 ± 0.01efg	2.37 ± 0.10 cd	1.34 ± 0.02c	79.80 ± 0.20lm	20.20 ± 0.20 cd	3.95 ± 0.05k	1.51 ± 0.00v
P16	12.61 ± 0.08p	0.17 ± 0.02a	4.10 ± 0.03j	42.38 ± 0.11i	35.05 ± 0.13i	1.53 ± 0.03pdef	0.73 ± 0.02ab	2.21 ± 0.03ab	1.25 ± 0.02bcde	78.31 ± 0.20de	21.69 ± 0.20klm	3.61 ± 0.04bcd	1.21 ± 0.00l
P17	12.17 ± 0.02no	0.64 ± 0.06j	4.07 ± 0.03j	45.62 ± 0.11o	31.70 ± 0.08d	1.60 ± 0.03fgh	0.72 ± 0.01ab	2.36 ± 0.01 cd	1.14 ± 0.02a	78.67 ± 0.11deh	21.33 ± 0.11hijk	3.69 ± 0.03cdefg	1.44 ± 0.00 t
P18	11.91 ± 0.02l	0.25 ± 0.01c	3.87 ± 0.01i	40.80 ± 0.13g	36.40 ± 0.11l	1.64 ± 0.01h	0.80 ± 0.01de	3.00 ± 0.15j	1.34 ± 0.02cde	78.25 ± 0.22d	21.76 ± 0.22lm	3.60 ± 0.05bc	1.12 ± 0.00i
P19	11.44 ± 0.02jk	0.35 ± 0.02ef	3.71 ± 0.03h	45.94 ± 0.10p	32.87 ± 0.13e	1.49 ± 0.04bcde	0.82 ± 0.04efg	2.16 ± 0.03a	1.24 ± 0.04bc	79.97 ± 0.16m	20.03 ± 0.16c	4.00 ± 0.04k	1.40 ± 0.00s
P20	11.52 ± 0.05k	0.73 ± 0.01k	4.07 ± 0.03j	42.76 ± 0.12j	33.68 ± 0.10f	1.73 ± 0.04i	0.87 ± 0.01gh	3.27 ± 0.04l	1.39 ± 0.04efgh	78.04 ± 0.20bc	21.96 ± 0.20mn	3.55 ± 0.04ab	1.27 ± 0.00n
P21	11.02 ± 0.01f	0.55 ± 0.02i	3.49 ± 0.02g	47.66 ± 0.13s	30.53 ± 0.11a	1.56 ± 0.03efg	0.98 ± 0.02i	2.77 ± 0.08h	1.46 ± 0.04gh	79.71 ± 0.19klm	20.30 ± 0.19cde	3.93 ± 0.05jk	1.56 ± 0.00w
P22	11.51 ± 0.05k	0.73 ± 0.04k	4.26 ± 0.03kl	45.98 ± 0.13p	30.86 ± 0.10b	1.74 ± 0.04i	0.78 ± 0.01cde	2.90 ± 0.03ij	1.26 ± 0.04bcd	78.35 ± 0.19cde	21.66 ± 0.19klm	3.62 ± 0.04bcd	1.49 ± 0.00 u
P23	11.16 ± 0.01g	0.45 ± 0.01gh	4.28 ± 0.01l	41.26 ± 0.07h	36.03 ± 0.11k	1.77 ± 0.08i	0.86 ± 0.04fgh	2.90 ± 0.03ij	1.31 ± 0.00cde	78.59 ± 0.14de	21.41 ± 0.14ijkl	3.67 ± 0.03cdef	1.15 ± 0.01k
P24	10.72 ± 0.02cde	0.37 ± 0.01f	5.16 ± 0.02p	43.35 ± 0.09k	34.10 ± 0.12g	1.88 ± 0.01j	0.71 ± 0.03a	2.47 ± 0.10de	1.26 ± 0.01bcd	78.52 ± 0.16defg	21.49 ± 0.16ijkl	3.66 ± 0.04cdef	1.27 ± 0.00n
P25	12.11 ± 0.02mn	0.36 ± 0.01f	4.62 ± 0.04n	40.67 ± 0.10g	35.81 ± 0.09j	1.73 ± 0.02i	0.77 ± 0.01bcd	2.61 ± 0.07fg	1.35 ± 0.02cdef	77.60 ± 0.17a	22.40 ± 0.17o	3.47 ± 0.04a	1.14 ± 0.00j
P26	10.62 ± 0.04 cd	0.18 ± 0.01ab	4.54 ± 0.01m	46.61 ± 0.06q	31.27 ± 0.10c	1.85 ± 0.02j	0.82 ± 0.02def	2.82 ± 0.04hi	1.31 ± 0.03cde	78.87 ± 0.14fgh	21.13 ± 0.14hij	3.73 ± 0.03efg	1.49 ± 0.00 u

N means peanuts grown in the north; S means peanuts grown in the south; values in the columns with different letters (a‐w) are significantly different (p <.05).

Abbreviations: CPO, cold‐pressed peanut oil; SFAs, saturated fatty acids; UFA, unsaturated fatty acids; UFA/SFA, unsaturated to saturated fatty acids; O/L, oleic/linoleic ratio.

The appropriate proportion pattern of UFA/SFA has a positive role to guarantee the oxidation stability of vegetable oil and reduce the incidence of coronary heart disease (CHD). Either peanuts or processed peanuts have been confirmed to be beneficial for health mainly because of their desirable lipid profile, which is higher in unsaturated fatty acids than in saturated fatty acids (Akhtar et al., 2014). As described in Table 2, the percentage of unsaturated fatty acids (UFA), saturated fatty acids (SFA), and the ratio of UFA/SFA in examined samples were calculated. It was observed that CPOs possessed high levels of unsaturated fatty acids with the average value of 79.24% and less saturated fatty acids for 20.76%, which suggest that peanut oils could exert antioxidant properties, lower cholesterol, and even reduce the heart disease risk (Wang, 2018). The variation range of UFA/SFA value of peanut oils was 3.47–4.47, which was overlaid by equivalent data (2.05–4.62) collected from previous 45 samples analyzed by (Wang, 2018); the varieties with higher ratio were Shanhua9 (P6, 4.47), Luhua11(P8, 4.45), and Jihua4 (P2, 4.38).

As oleic and linoleic acid are so prevalent in peanut, the typical convention for reporting their concentrations is O/L ratio. High O/L characteristic could confer an evident health advantage to the consumer and has the potential to greatly enhance the marketability of peanuts. Cicero et al. (2008) has pointed there was an inverse relation between the O/L ratio of plasma LDL and biomarkers of oxidative stress according to a clinical trial. Moreover, O/L ratio is an important factor to estimate the stability of peanut oil and other derived products (Andersen & Gorbet, 2002; Young et al., 1974). A longer shelf life is relevant to higher ratio (Branch et al., 1990), which essentially attributed to that the linoleic acid with two double bonds is more susceptible to oxidative rancidity than oleic acid (one double bond)(Kratz et al., 2002). As observed in Table 2, remarkable differences were found within O/L ratios among varieties of peanut, and the range was 0.88–1.56, all lower than those (1.8–2.1) in literature (Mora‐Escobedo et al., 2014), which had a relationship with growth environment, cultivar, or processing methods (Grosso & Guzman, 1995). CPO from Tianfu18 (P21) grown in Sichuan contained higher oleic acid content and O/L ratio than the other varieties, suggesting its better oxidation resistance.

Bioactive components

Vegetable oil is one of the richest sources for vitamin E, which is as well as established to contribute to restrain oil deterioration. Accordingly, it is necessary to assess the oil tocopherol between different types. As shown in Table 3, CPOs had plentiful α‐, γ‐, and δ‐tocopherol, accounting for 61.98%, 36.03%, and 1.99% of the total and no tocotrienols could be detected. Among peanut accessions exanimated, the total tocopherol content showed significant difference (p <.01), which was in the range of 292–547 mg/kg and the mean was 390.65 mg/kg, accompanied with the highest amount for Silihong (P12) while Qinghua7 (P9) was at the lowest tocopherol level. Zhu et al. (2015) stated that the content of total tocopherols in commercially pressed crude peanut oil was 367 mg/kg, which was within the data range measured in the present work, but it would be reduced by 10.35% after chemical refining. Evidence (Kamal‐Eldin & Appelqvist, 1996) already proved the vitamin E distribution ratio in peanut oil was conducive to its function in the body, which was ascribed to the order of physiological activity of vitamin E isomers in the organism (δ‐tocopherol<γ‐tocopherol<α‐tocopherol). The α‐tocopherol, biologically and chemically the most active form of vitamin E, could act as the dominant lipid‐soluble antioxidant through breaking the lipid oxidation chain (Ekanayake‐Mudiyanselage et al., 2005). So Zhonghua21 (P25) from Hubei province with α‐tocopherol contents of 314.73 mg/kg could be inferred as the varieties with physiological activity and high antioxidant ability.

TABLE 3

Total tocopherols and total phytosterols, β‐sitosterol, stigmasterol, campesterol contents of CPOs from twenty‐six peanut cultivars grown in China (mg/kg)

Sample	β‐sitosterol	Stigmasterol	Campesterol	Total phytosterols	α‐ tocopherol	γ‐tocopherol	δ‐tocopherol	Total tocopherols
P1	843.43 ± 25.28l	197.59 ± 9.96abcde	136.44 ± 8.03efg	1177.46 ± 27.20k	282.46 ± 1.94m	104.45 ± 1.47c	9.91 ± 0.25i	396.82 ± 0.74hi
P2	1100.91 ± 50.27n	167.49 ± 6.98a	176.35 ± 8.19hi	1444.74 ± 65.44lm	247.71 ± 2.26i	136.59 ± 0.36g	7.59 ± 0.40g	391.88 ± 2.29g
P3	752.80 ± 16.36k	332.08 ± 14.88j	157.89 ± 10.83gh	1242.76 ± 42.07k	160.70 ± 0.11a	146.99 ± 1.20h	6.30 ± 0.32def	313.98 ± 0.77bc
P4	1054.54 ± 58.02n	277.72 ± 10.12hi	192.07 ± 9.22ij	1524.32 ± 38.68m	266.62 ± 1.61l	135.99 ± 0.76fg	14.17 ± 0.48k	416.76 ± 2.84j
P5	899.11 ± 33.63lm	302.65 ± 17.57ij	183.69 ± 10.08ij	1385.45 ± 61.28l	233.14 ± 0.69g	169.18 ± 3.22jk	4.41 ± 0.02a	406.72 ± 3.94j
P6	739.97 ± 21.79jk	253.84 ± 12.18gh	201.37 ± 14.97j	1195.18 ± 48.94k	266.68 ± 1.88l	133.96 ± 2.81fg	5.89 ± 0.20cde	406.51 ± 4.49i
P7	680.36 ± 28.15ij	171.82 ± 16.38ab	96.88 ± 10.35bcd	949.05 ± 54.89hij	269.15 ± 1.30l	159.11 ± 4.30i	9.73 ± 0.39i	437.99 ± 5.21l
P8	555.42 ± 27.90efg	193.82 ± 13.09abcd	96.02 ± 9.29bcd	845.25 ± 50.28efgh	242.88 ± 1.52h	138.12 ± 2.52g	8.16 ± 0.15gh	389.15 ± 0.85g
P9	404.66 ± 11.47bc	227.02 ± 16.91defg	94.31 ± 6.63bc	725.98 ± 35.00 cd	159.25 ± 6.63a	128.69 ± 1.99e	4.07 ± 0.21a	292.00 ± 8.83a
P10	910.58 ± 34.04m	303.19 ± 19.13ij	172.55 ± 11.31hi	1386.32 ± 3.60l	185.39 ± 0.18b	237.03 ± 4.51m	5.65 ± 0.07 cd	428.07 ± 4.26k
P11	662.51 ± 17.36hi	189.55 ± 5.65abc	131.97 ± 8.12ef	984.02 ± 31.13ij	256.77 ± 0.04kj	134.78 ± 1.47fg	4.40 ± 0.12a	395.94 ± 1.31gh
P12	1053.08 ± 50.97n	255.78 ± 9.26gh	313.54 ± 11.28k	1622.39 ± 30.43n	293.04 ± 0.67n	249.27 ± 2.53n	4.69 ± 0.54ab	547.00 ± 3.74n
P13	616.03 ± 20.46gh	185.57 ± 8.49abc	131.25 ± 9.13e	932.84 ± 38.08ghi	258.02 ± 2.96jk	145.05 ± 0.33h	13.00 ± 0.31m	416.07 ± 2.32j
P14	375.14 ± 28.79ab	312.61 ± 17.66j	65.24 ± 6.48a	752.98 ± 52.93cde	249.00 ± 0.64i	163.66 ± 3.22ijk	6.16 ± 0.49def	418.81 ± 2.10j
P15	367.00 ± 16.99ab	174.75 ± 12.67ab	77.73 ± 7.18ab	619.47 ± 36.84ab	226.74 ± 0.76ef	112.97 ± 4.84d	6.39 ± 0.41def	346.09 ± 3.67d
P16	400.70 ± 18.73b	224.81 ± 11.77defg	87.50 ± 3.54b	713.00 ± 34.04bc	254.97 ± 1.07j	108.05 ± 3.87 cd	6.79 ± 0.09f	369.80 ± 2.71f
P17	407.39 ± 15.80bc	178.83 ± 13.94ab	78.42 ± 4.19ab	664.63 ± 33.93abc	213.25 ± 0.57d	89.99 ± 2.47b	8.77 ± 0.61h	312.00 ± 2.42b
P18	567.22 ± 22.95fg	217.70 ± 9.96cdef	120.81 ± 7.29ef	905.72 ± 40.21fghi	260.07 ± 1.56k	88.98 ± 3.60b	6.78 ± 0.09f	355.82 ± 5.06e
P19	319.56 ± 14.16a	194.28 ± 12.32abcd	63.76 ± 5.49a	577.59 ± 31.98a	233.32 ± 1.89g	74.07 ± 0.25a	8.44 ± 0.18h	315.82 ± 1.81bc
P20	500.32 ± 20.73de	201.40 ± 15.49abcde	120.81 ± 8.83ef	822.52 ± 45.04def	226.20 ± 0.29ef	189.01 ± 1.82l	4.25 ± 0.07a	419.46 ± 2.03j
P21	694.23 ± 33.47ijk	228.70 ± 20.46efg	115.48 ± 14.31cde	1038.41 ± 68.25j	227.32 ± 3.26f	165.43 ± 6.09jk	9.99 ± 0.16i	402.73 ± 9.19hi
P22	467.51 ± 23.02 cd	245.36 ± 19.52fg	116.61 ± 8.55de	829.48 ± 51.09efg	299.99 ± 2.59o	148.14 ± 5.56hi	8.37 ± 0.30h	456.50 ± 7.86m
P23	652.96 ± 31.35hi	205.93 ± 21.73bcde	120.66 ± 14.43ef	979.54 ± 67.51ij	229.52 ± 2.88fg	158.02 ± 4.49i	5.17 ± 0.18bc	392.72 ± 1.79g
P24	519.29 ± 25.07def	223.60 ± 11.24dfg	138.40 ± 12.65efg	881.29 ± 48.97fghi	192.94 ± 1.27c	147.40 ± 1.63h	6.71 ± 0.53f	347.04 ± 0.17d
P25	561.14 ± 21.58efg	201.10 ± 15.52abcde	143.19 ± 10.94fg	905.42 ± 48.04fghi	314.73 ± 1.20p	124.39 ± 3.39e	19.07 ± 0.14l	458.19 ± 4.45m
P26	430.86 ± 19.64bc	377.23 ± 11.96k	87.54 ± 9.87b	895.63 ± 41.47fghi	222.33 ± 1.13e	93.84 ± 2.82b	6.57 ± 0.70ef	322.73 ± 2.39c

N means peanuts grown in the north; S means peanuts grown in the south; values in the columns with different letters (a‐p) are significantly different (p <.05).

Considerable variability in phytosterols was detected among the peanut oils selected across the country (p <.01), the content varied between 577.59 mg/kg and 1622.39 mg/kg. The top three sterol‐containing CPOs were Silihong (P12, 1622.39 mg/kg), Yuhua10 (P4, 1524.32 mg/kg), and Jihua4 (P2, 1444.74 mg/kg). Phytosterols are not only known as an important antioxidant that protects the oil against autoxidation (Khallouki et al., 2003), but also have physiological properties such as anticancer (Awad et al., 2000), anti‐inflammatory, and antitumor (Mariod et al., 2011), with an ability to even lower plasma cholesterol and LDL cholesterol (Oliveira Godoy Ilha et al., 2020). Most plant species, such as peanuts, comprise dominant β‐sitosterol, which is one of the most representative phytosterol along with stigmasterol and campesterol present in concentrations of 319.56–1100.91 mg/kg, 167.49–377.23 mg/kg, and 63.76–313.54 mg/kg. In the present work, the β‐sitosterol content corresponds with the results obtained by Zhang et al. (2012) (388–1157 mg/kg), with an increase in the stigmasterol content than that reported in the same work (3.1–226 mg/kg); the latter may be influenced by genotype and growing environment.

Stability of peanut oil

The Rancimat method can automatically detect the change in the conductivity of water caused by the volatile substances, which is produced by oil oxidation such as carboxylic acids and draws a curve of the change in conductivity over time to obtain IP value under conditions of forced oxidation. As presented in Table 4, the antioxidant times of peanut oils could last for 6.98–10.61 hr. Antioxidant capacity may be associated with the oleic/linoleic ratio, sterols, and tocopherols. The correlation analysis revealed there was a positive correlation between the IP and oleic/linoleic ratio (r = 0.654, p <.01). Meanwhile, the IP showed no correlation with tocopherol and phytosterol.

TABLE 4

IP value (h) of CPOs from twenty‐six peanut cultivars grown in China

Sample	IP	Sample	IP	Sample	IP	Sample	IP
P1	7.29 ± 0.20abc	P8	9.16 ± 0.21k	P15	8.69 ± 0.10hij	P22	10.61 ± 0.25l
P2	8.61 ± 0.23hi	P9	7.17 ± 0.11ab	P16	8.15 ± 0.13efg	P23	8.25 ± 0.11fgh
P3	8.06 ± 0.20ef	P10	8.08 ± 0.11ef	P17	8.57 ± 0.11hi	P24	8.37 ± 0.14fghi
P4	7.32 ± 0.14abc	P11	6.98 ± 0.14a	P18	7.84 ± 0.10de	P25	9.00 ± 0.11jk
P5	7.35 ± 0.20bc	P12	7.33 ± 0.17abc	P19	8.47 ± 0.13ghi	P26	9.15 ± 0.08k
P6	8.45 ± 0.17ghi	P13	7.65 ± 0.11 cd	P20	7.42 ± 0.23bc
P7	8.29 ± 0.14fgh	P14	8.28 ± 0.13fgh	P21	7.87 ± 0.08de

N means peanuts grown in the north; S means peanuts grown in the south; values in the columns with different letters (a‐l) are significantly different (p <.05).

Abbreviations: CPO, cold‐pressed peanut oil; IP, oxidation induction period.

This situation was most likely to related to the high level of unsaturated fatty acids in peanut oil (>70%), while the low contents of endogenous vitamin E, phytosterols, and other antioxidant substances were not effective enough in preventing the oxidation of peanut oil. Therefore, it was reasonable to consider that peanut oil was easily oxidized in the storage and edible procedure, and the generated peroxide was quickly decomposed into aldehydes and ketones, which caused the rancidity of peanut oil (Balasubramaniam et al., 2019) and reduced the quality of peanut oil.

Effect of the growing regional on peanut oil

The north and south regions, as China's most important geographical division, may affect peanut varieties and their oil products’ quality. Considering the practical production demand, it is critical to master the qualification difference of CPOs in different planting sites of China. In this study, main quality indexes of peanut oils from two major growing areas were analyzed as follows. Taking oil content into consideration first, the mean value of the northern samples was 50.20%, while the slightly lower value of 49.28% appeared in the south, and significant differences were not found (p >.05). This finding coincided with the conclusion drawn by Zhang et al. (2006) that the oil content of rapeseed increases with the elevation of latitude in the planting area. The physicochemical properties of CPO illustrated acid values of northern samples varied from 0.11 mg KOH/g to 0.32 mg KOH/g, which were far lower than the values for southern oils (0.13–2.74 mg KOH/g); moreover, PVs of oils were 1.94–5.55 mmol/kg with a mean of 3.11 mmol/kg for northern peanuts and 2.04–4.91 mmol/kg with a mean of 3.12 mmol/kg for southern peanuts, respectively. It could be seen from the analysis that the above two indicators did not show a significant difference in value (p >.05). As far as fatty acids, no significant difference appeared in palmitic acid (C16:0) between CPOs from two regions (p >.05) with the average percentage of 11.10% and 11.41%. As a monounsaturated omega‐9 group fatty acid, oleic acid (C18:1) provides hypolipidemic effects and can prevent cardiovascular diseases (Jones et al., 2014). Here, the oleic acid of northern CPOs was measured to be 40.91%, was significantly lower than that of southern varieties (43.92%), which suggested that peanuts in southern China were more beneficial for human nutrition than northern samples as a whole owing to its higher content of oleic acid (Matthaus & Musazcan Ozcan, 2015). In addition, linoleic acid is omega‐6 group fatty acids, which in the north with the average content of 37.62% were found to be conspicuously higher than that (33.58%) of the other region. The increase in linoleic acid accompanying a decrease in oleic acid appears to be more marked in the south varieties and the largest change in composition appears to be in the Tianfu18 variety. Regarding the UFA/SFA ratio, higher value was obtained from north in both regions. This trend was similar to the conclusion published by Caporaso (2016), who suggested the ratio of unsaturated fatty acids (UFA) to saturated fatty acids (SFA) increased with the increase of latitude. However, the southern samples exhibited greater O/L ratio (1.32) in comparison to northern samples (1.10) with a significant difference (p <.01). Of the twenty‐six varieties examined, Chinese peanuts showed significant differences in phytosterols relative to planting sites, where northern content ranged from 725.98 mg/kg to 1622.39 mg/kg with an average of 1206.91 mg/kg, and southern content ranged from 577.59 mg/kg to 1038.41 mg/kg with an average of 822.75 mg/kg; γ‐tocopherol and total tocopherol at a higher amount with 156.18 mg/kg and 401.90 mg/kg in the CPOs originated from the north when compared to southern samples. It could be seen from the induction time analysis that southern samples had a mean IP of 8.45 hr, 7.78% higher than that of northern samples with significant differences (p <.05), which indicated that peanut oil obtained from southern China might be relatively more stable as a whole.

Comprehensive score and cluster analysis

Principal component analysis (PCA) was performed to reveal the relationships among twenty‐six CPOs from eleven provinces in China based on the nutrition component (phytosterol composition, tocopherol composition, oleic acid, linoleic acid, and IP) under consideration. In order to avoid the impact of the dimension and order of magnitude of each indicator on the evaluation result of peanut oil, the original data were standardized. The result showed that the cumulative variance contribution rate for the first three principal components was 77.01% (PC1=41.63%, PC2=20.64%, and PC3=14.74%, respectively, Table 5). PC1 mainly included the campesterol, β‐sitosterol, γ‐tocopherol, and linoleic acid content (principal component loading was 0.43, 0.42, 0.34, and 0.46, respectively), PC2 mainly included the δ‐tocopherol and α‐tocopherol content (principal component loading was 0.57 and 0.59, respectively), whereas PC3 was contributed by the stigmasterol content (0.41) and IP value (0.49). Consequently, the three principal components instead of the original 9 indicators could evaluate the CPOs’ nutritional quality.

TABLE 5

Variance contribution ratios of principal components of the quality characteristics of CPOs from twenty‐six peanut cultivars grown in China

Component	Initial eigenvalue			Extraction Sums of Squared Loadings
	Total	% of Variance	Cumulative %	Total	% of Variance	Cumulative %
1	3.75	41.63	41.63	3.75	41.63	41.63
2	1.86	20.64	62.27	1.86	20.64	62.27
3	1.33	14.74	77.01	1.33	14.74	77.01
4	0.67	7.48	84.49
5	0.56	6.22	90.70
6	0.42	4.63	95.33
7	0.25	2.78	98.10
8	0.14	1.54	99.64
9	0.03	0.37	100.00

According to the eigenvalue in Table 5 and principal component loading, the function expressions of the three principal components were obtained:

X1‐campesterol, X2‐stigmasterol, X3‐β‐sitosterol, X4‐δ‐tocopherol, X5‐γ‐tocopherol, X6‐α‐tocopherol, X7‐oleic acid, X8‐linoleic acid, X9‐IP.

Then, the proportion of eigenvalue corresponding to each principal component to the sum of the total eigenvalue of the extracted principal component was used as the weight to calculate the comprehensive model of the principal component:

Finally, according to the comprehensive evaluation function, the comprehensive scores of twenty‐six CPOs were calculated. The higher the comprehensive score, the better the nutritional quality of the peanut oil. As it can be seen from Table 6, among the top 10 samples, there were seven peanut varieties from northern China, and Silihong (P12), Yuhua 10 (P4), and Huayu 18 (P1) were the top three regions. The highest comprehensive score of peanut variety from southern China was Zhonghua 21 (P25) which was 1.08.

TABLE 6

Comprehensive evaluation of CPOs from twenty‐six peanut cultivars grown in China

Ranking	Code	Growing location	Score
NO.1	P12	Liaoning Province	3.05
NO.2	P4	Kaifeng City, Henan Province	1.65
NO.3	P1	Hengshui City, Hebei Province	1.17
NO.4	P25	Xiaogan City, Hubei Province	1.08
NO.5	P10	Xuzhou City, Jiangsu Province	0.88
NO.6	P7	Rushan City, Shandong Province	0.87
NO.7	P11	Jingzhou City, Liaoning Province	0.84
NO.8	P5	Puyang City, Henan Province	0.83
NO.9	P13	Huaian City, Jiangsu Province	0.68
NO.10	P2	Baoding City, Hebei Province	0.63
NO.11	P6	Linyi City, Shandong Province	0.47
NO.12	P23	Gucheng City, Hubei Province	−0.05
NO.13	P18	Guangxi Province	−0.07
NO.14	P20	Jiangxi Province	−0.40
NO.15	P22	Yongzhou City, Hunan Province	−0.55
NO.16	P21	Nanchong City, Sichuan Province	−0.59
NO.17	P3	Shijiazhuang City, Hebei Province	−0.60
NO.18	P16	Nanchang City, Jiangxi Province	−0.64
NO.19	P24	Xiangyang City, Hubei Province	−0.64
NO.20	P8	Jiaozhou City, Shandong Province	−0.68
NO.21	P14	Jiangxi Province	−0.92
NO.22	P9	Yantai City, Shandong Province	−0.96
NO.23	P17	Zhanjiang City, Guangdong Province	−1.43
NO.24	P19	Guangxi Province	−1.50
NO.25	P15	Ganzhou City, Jiangxi Province	−1.55
NO.26	P26	Huanggang City, Hubei Province	−1.58

NO.1‐NO.26 represents the peanut oil ranking from high to low comprehensive score.

To further analyze the nutrition component of cold‐pressed peanut oil from different varieties, the results were presented as a heat map added to the dendrogram (Figure 1). As seen from the picture, twenty‐six samples were divided into two categories. P12, P4, P1, P25, P10, P7, P11, P5, P13, P2, P6 (No.1–11) were clustered together to form the first group, and their score was above 0. The heat map showed that the content of campesterol, β‐sitosterol, α‐tocopherol, and linoleic in the first group was higher than that of other group which is consistent with the result of comprehensive evaluation based on PCA. On the whole, it could be concluded that the top ranking of peanut oil quality is mostly in the north.

FIGURE 1

Heat map of all peanut seed oils using composition data for sterols, tocopherols, oleic acid, linoleic acid, and IP. The way cluster analysis indicates the closeness of the peanut species (horizontal) to each other. 1–26 represents peanut oils named P1–P26 in the paper

CONCLUSIONS

For the current study, peanut varieties in China contained relatively high levels of oil varied from 45.97% to 57.28% and rich in oleic (36.10%‐47.66%) and linoleic acid (30.53%‐40.86%). Meanwhile, CPOs could be considered a good nutrition source, which consist of copious α‐,γ‐, and δ‐tocopherol and β‐sitosterol, stigmasterol, campesterol. The physicochemical characteristics under evaluation were as follows: the acid value (0.11–2.74 mg KOH/g) and peroxide value (1.94–5.55 mmol/kg). Besides, CPOs had strong oxidation stability with an induction period of more than 7 hr. Among all tested varieties, Silihong could be characterized for exhibiting higher nutritional level with the comprehensive scores of 3.05, followed by Yuhua10 (1.65) and Huayu18 (1.17). The cluster analysis results indicated that most of the peanut samples with scores above 0 were from northern China. Conclusively, it was preliminarily believed that high‐quality cold‐pressed oil might be easy to form in peanut varieties from northern China, but further research is necessary.

CONFLICT OF INTEREST

The authors declare that they have no conflict of interest.

AUTHOR CONTRIBUTION

Huang Ying: Conceptualization (lead); Investigation (equal); Methodology (lead); Writing – original draft (lead). Liu Changsheng: Data curation (equal); Supervision (equal). Huang Fenghong: Funding acquisition (equal); Project administration (equal); Resources (equal); Writing – review & editing (equal). Zhou Qi: Formal analysis (supporting); Funding acquisition (supporting); Software (supporting). chang zheng: Data curation (equal); Formal analysis (lead); Software (equal); Writing – review & editing (lead). Liu Rui: Funding acquisition (supporting); Resources (supporting). Huang Jiazhang: Project administration (supporting); Supervision (supporting).

Supplementary Material

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