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Essential oil extracted from peach (Prunus persica) kernel and its physicochemicaland antioxidant properties

Hao Wu

a,c

, John Shi

a,*

, Sophia Xue

a

, Yukio Kakuda

b

, Dongfeng Wang

a,c

, Yueming Jiang

d

, Xingqian Ye

e

,

aGuelph Food Research Center, Agriculture and Agri-Food Canada, Ontario N1G 5C9, Canada

bDepartment of Food Science, University of Guelph, Ontario N1G 2W0, Canada

cCollege of Food Science and Technology, Ocean University of China, Qingdao, Shandong 266003, China

dSouth China Botanical Garden, The Chinese Academy of Sciences, Guangzhou 510650, China

eDepartment of Food Science and Nutrition, School of Biosystems Engineering and Food Science, Zhejiang University, Hangzhou 310029, China

fHangzhou Wahaha Group Co., Hangzhou 310018, China

gDepartment of Plant Agriculture, University of Guelph, Vineland Station, Ontario L0R 2E0, Canada

a r t i c l e i n f o

Article history:

Received 9 December 2010Received in revised form19 May 2011

Accepted 19 May 2011Keywords:

AntioxidantFatty acidsFunctional foodPhenolic compounds

a b s t r a c t

Peach kernel oil was extracted using Soxhlet extraction with different solvents (petroleum ether, ethylether, chloroform and hexane). The physicochemical properties (acid value, iodine value, peroxide valueand saponiﬁcation value), the fatty acid composition, phenolic constituents and contents, and antioxi-dant activities of peach kernel oil were examined. As per our results, oil extracted with hexane has betteroverall quality. Its acid, peroxide, iodine and saponiﬁcation values were 0.895 mg KOH/g oil, 0.916 mg/goil, 36.328 mg/100 g oil and 101.836 mg KOH/g oil, respectively. Large proportions of unsaturated fattyacid (91.27%) and high content of phenolic compounds (4.1593 mg GAE/g), which contribute toconsiderably strong antioxidant activity, were found in oil. The main fatty acids found in the peach kerneloil were oleic acid (61.87 g/100 g oil) and linoleic acid (29.07 g/100 g oil). The HPLC analysis of phenoliccompounds showed that rutin, (-)-epicatechin gallate, hydrocinnamic acid, sinopinic acid, dithiothreitoland caffeic acid were major constituents. The results suggested that peach kernel oil is a good source ofthe unsaturated fatty acid, phenolic compounds with strong antioxidant activity, and has the potential tobe used as nutrient rich food oil. The results also veriﬁed that peach kernel meals contained higheramounts of total phenolic and stronger antioxidant activities than oils, enabling their application asingredients for functional or enriched foods.

1. Introduction

Peach is the third most important deciduous tree fruits wide, ranking after apples and pears. A signiﬁcant part of the har-vested peaches is processed resulting in a substantial amount ofwaste stones. Peach kernel contain almost 50 wt% of oils (Yolanda,Albertina, Juan & Pando, 2009). The peach kernel has slightly toxiceffects when used excessively due to its content of hydrogencyanide (prussic acid). Hydrogen cyanide is a chemical compoundwith extremely poisonous, because it binds irreversibly to the ironatom in hemoglobin, making it unavailable to transport the vital O2

world-to the body’s cells and tissues. The dose should not be excessive and

any excessive dose may cause headache, blurred vision, tions, or even death from respiratory failure. However, since theconcentration of hydrogen cyanide in peach kernel is small

products (Barceloux, 2008, chap. 5).

Peach kernel oil has been widely used in the cosmetics industryas an ingredient in soaps, shampoos, lotions, creams, and shampoosbecause it is a light, penetrating oil, and absorbs easily and does notleave a greasy feeling. Peach kernel oil is nutritionally attractive andhas an opportunity of producing high value products from the bio-waste in peach industry due to their unsaturated fatty acid andantioxidant constituents (Saadany, Kalaf, & Soliman, 2004). There-fore, peach kernel can be considered as an important source ofessential oil for the food and nutraceutical supplement industries.Fatty acids, especially, unsaturated fatty acids, are important asnutritional substances and metabolites in living organisms. Many

* Corresponding author. Tel.: ỵ1 519 780 8035; fax: ỵ1 519 829 2602.E-mail address:(J. Shi).

Contents lists available atScienceDirect

LWT - Food Science and Technology

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / l w t

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kinds of fatty acids play an important role in the regulation ofa variety of physiological and biological functions (Zhao, Wang, You,& Suo, 2007). The main fatty acids found in peach kernel oil areabout 58% oleic acid and 32% linoleic acid (Kamel & Kakuda, 1992).Oleic acid is an 18-carbon monounsaturated fatty acid, essential inhuman nutrition and helps reducing triglycerides, LDL-cholesterol,total cholesterol and glycemic index (Eduardo, 2010). Also, theincrease in stability over oxidation of vegetable oil is attributed tooleic acid (Abdulkarim, Long, Lai, Muhammad, & Ghazali, 2007).The linoleic acid is an essential fatty acid from omega-6 group(18:2(n-6).) and very important for development and maintenanceof the nervous system and the physiological functions in humans,since it reduces total and LDL-cholesterol levels. Phenolic compo-

tannins have been the scope of many studies lately due to theirantioxidant effects.

Phenolic compounds make important contributions to thenutritional properties, sensory characteristics and the shelf life ofpeach kernel oil. However, the fate of individual phenoliccompounds in the course of peach kernel oil extraction as well astheir contribution to the overall antioxidant properties of oils hasnot yet been investigated.

The extraction technique used to obtain high aggregate valuecompounds from natural products is crucial for product quality.Soxhlet extraction is a standard technique and is the main referenceto which other extraction methods are compared. The advantage ofconventional Soxhlet is that the sample is repeatedly brought intocontact with the fresh portions of the solvent, thereby helping todisplace the transfer equilibrium. There is a wide variety of ofﬁcialmethods involving a sample preparation step based on Soxhletextraction (US EPA Method 3540, 1995; AOAC Method 963.15, 1990;British Standard, BS 4267, 1994, 8 p.). In short, Soxhlet extraction isa general, well-established technique which clearly surpasses inperformance other conventional extraction techniques.

However, there are only few studies on the extraction of peachkernel oil (Yolanda, Albertina, Juan & Pando, 2009), and the fattyacid proﬁle, polyphenolic compound, physicochemical propertiesand antioxidative properties of peach kernel oil were not wellestablished yet. Therefore, the objectives of this study were tocompare the efﬁciency of the extraction solvents; evaluate thequality of peach kernel oil through the physicochemical properties,fatty acid composition, proﬁle of phenolic compounds and anti-oxidant activity; and at last deﬁne the most effective solvent thatcan be used in the extraction of peach kernel oil with Soxhlet.2. Materials and methods

2.1. Materials

Peaches (Prunus persica) were harvested from orchard of land Research Centre (Ontario, Canada). Peach pits were collectedand cracked to obtain the kernel. The kernel were then ground ina food grinder (Waring commercial Co. Ltd., USA) to reduce the

a sieve (The W.S. Tyler Company of Canada Ltd., Canada), sealed ina plastic container and stored in a refrigerator until extraction. Thestorage conditions assured eliminating effects of oxygen andhumidity and to avoid oxidation of the dried peach pit powderduring storage time.

FolineCiocalteu reagent and 2, 20-Diphenyl-

b

-picrylhydrazyl(DPPH) were supplied by Sigma (St. Louis, MO, USA). Standards offatty acid methyl esters (FAME) (mixture 463) were obtained fromNu-Chek-Prep, Inc. (Elysian, MN, USA). Polyphenol standards forHPLC analysis were supplied as follows: keracyanin chloride,(ỵ)-catechin, (-)-epicatechin gallate, 3,4-dihydroxybenzoic acid,

rutin hydrate, procyanidin B2, ellagic acid, caffeic acid, dithiothreitol, protocatechinic acid, procatechol, gentisics acid,kuromanin chloride, vanillic acid, myricetin, hydrocinnamic acid,sinopinic acid, and obtained from Sigma (St. Louis, MO, USA). KI,Na2S2O3,KOH, phenolphthalein, HCl, starch indicator, I2, Br2werefrom Fisher Chemicals (Fair Lawn, NJ, U.S.A). The solvents employedfor extraction and HPLC performance were all obtained fromCaledon Laboratories LTD (Georgetown, ON, Canada).

DL-2.2. Methods2.2.1. Oil extraction

Leimann, Pedrosa, and Ferreira (2008). The extractions were formed at least in duplicate, with different solvents: petroleumether, hexane, ethyl ether and chloroform, with polarities of 0.01,0.06, 2.9 and 4.4, respectively. The solvents chosen for presentstudy are normally used to extract oil from plant kernel. Thirtygrams of ground peach kernel was extracted in a soxhlet-extractor

temperature of 50C was chosen to avoid thermal degradation onbioactive compounds in the extracts. Also the temperate is in therange of boiling temperature of these solvent. The resultingextracts, obtained by the different methods were separated byevaporating the solvents used in a rotary evaporator under reducedpressure and at temperature of 50C. The obtaining the fractions

oil physicochemical properties were determined. The meals werealso collected after extracting oils, and weighted after evaporatingexcess solvent under nitrogen. The total yield of extracted oil foreach method was obtained by the mean value of extracted oil massdivided by mass of raw material used (30 g), on dry weightbase (d.b).

The Oils and their meals were evaluated to compare their totalphenolic content, phenolic proﬁles and antioxidant capacity.2.2.2. Physicochemical properties of peach kernel oils

Acid value, iodine value, peroxide value and saponiﬁcation value

(1990)methods. The hydrocyanic acid content of the extracted oilwas determined by the method ofBlinn and Boyd (1964).2.2.3. Fatty acid (FA) analyses

The fatty acid proﬁle was determined as fatty acid methyl esters(FAME) by gas chromatography. The methyl esters were preparedby following produces. Oils (50 mg) were dissolved in sodium dried

solution immediately becomes cloudy as sodium-glycerol tives were precipitated. After set for 5 min at room temperature,the reaction was stopped by adding a saturated solution of oxalicacid in diethyl ether (30

m

L) with brief agitation. The mixture wascentrifuged at about 1500 g for 4 min to precipitate sodium oxalate,and the solvent was removed in a gentle stream of nitrogen at roomtemperature. Fresh diethyl ether (1 mL) or hexane was added, andan aliquot of this was taken directly for GC analysis.

Palo Alto, CA, USA) equipped with aﬂame ionisation detector and

USA), a 100 m CP-Sil 88 fused capillary column (Varian Inc., sissauga, ON, Canada), and ChemStation software system (versionA.09, HewlettePackard, Palo Alto, CA, USA) were used for analysing

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4 min, increase by 13C/min to 175C, hold again at 175C for27 min, increase at 4C/min to 215C, and then hold at 125C for35 min. A FAME Standard (mixture 463) was used to identify theFAME and quantitative analysis. The FA amount was expressed aspercent of total FAs.

2.2.4. Determination of total phenolic content

Peach kernel oils (3 g) were extracted with 25 mL methanol,vortexed for 5 min, and then centrifuged at 4000 g for 10 min. Peachkernel meals (5 g) were extracted with 15 mL Meth/H2O (90:10, v/v)by continuous agitation for 30 min, and then centrifuged at 4000 gfor 10 min. The supernatant in each case was collected for phenoliccontent and antioxidant activity measurements.

Total phenolic content was determined by the FolineCiocalteumethod. A combination solution consisting of 0.2 mL sampleextract, 1.0 mL 0.25 N FolineCiocalteu reagent, 0.8 mL of Na2CO3

solution (7.5: 92.5, w/v,) and 2 mL distilled water were mixedwell in a 20 mL vial using a Vortex and incubated at room

determined at 765 nm against the blank (methanol replaced

content was expressed as gallic acid equivalent (GAE) in mg/gfresh weight (FW). Additional dilutions were made if the absor-bance value measured was beyond the linear range of the stan-dard curve.

2.2.5. Proﬁle of phenolic compounds in peach kernel oil analysed byHPLC

method. An HP 1100 HPLC system equipped with an alphaBondC18 125A column (4.6 250 mm, particle size 5

m

m) and coupledwith Agilent 1100 series ChemStation software was used forquantifying the individual phenolic compounds. The mobile pha-ses consisted of 2.0% acetic acid in distilled water (A) and aceto-nitrile (B). The column was eluted at 1.0 mL/min under a lineargradient from 5% mobile phase B to 75% over 20 min, to 100% over5 min, isocratic for 5 min, to 25% over 5 min and to 5% over 5 min.

at 280 nm with an HP 1100 series ultraviolet (UV) Diode ArrayDetector. Standards were injected for identiﬁcation and quantita-tive analysis.

2.2.6. Radical-scavenging activity (DPPH)

The antioxidant activity was determined by DPPH methodwhich was based on the evaluation of the free-radical scavengingcapacity. In this method, the 2,2 diphenyl-1-picrylhydrazyl (DPPH)radical was used to measure the antioxidant activity. A 100

m

L ofsample diluted in the ratio of 1:100 with methanol:water (6:4) wasmixed with 2 mL of 0.1 mol/L DPPH in methanol. After incubating atroom temperature for 30 min in the dark, the absorbance of themixture was measured at 517 nm. Radical scavenging activity wasexpressed as the inhibition percentage.

2.2.7. Trolox equivalent antioxidant capacity (TEAC) assay

A distilled water solution of 5 mmol/L aqueous solution ABTS

ﬁltered through a 0.2

m

m Acrodisc PVDF syringeﬁlter to eliminatetraces of MnO2. This solution was then diluted in PBS (pH 7.40) to anabsorbance of 0.700 at 734 nm. Trolox standards were prepared

extract (0.2 mL) above and the Trolox standard were mixed witheach of 2 mL of the ABTS radical cation solution and then stirredvigorously. The absorbance was monitored at 734 nm over a 30 minperiod using a spectrophotometer. The activities of antioxidantswere estimated at least at three different concentrations within therange of the Trolox dose-absorbance response curve. Antioxidantactivity was expressed as

m

M Trolox Equivalent (TE)/100 g.2.3. Statistical analysis

The extractions and all analyses were carried out at least intriplicate and data were expressed as means standard deviation.A one-way analysis of variance (ANOVA) was performed to calcu-

difference) test. A probability value of p< 0.05 was consideredsigniﬁcant and only signiﬁcant differences were considered unlessstated otherwise.

3. Results and discussion

3.1. Physicochemical properties of oils

extraction, the solvent of ethyl ether provided signiﬁcantly highesttotal oil yield (0.38 0.07 g/g d.b), follow by chloroform extraction(0.35 0.06 g/g d.b). There no signiﬁcant difference was observedon the total oil yields that extracted by petroleamether(0.25 0.04 g/g d.b) and hexane (0.26 0.04 g/g d.b). The resultsindicated that peach oil has many intermediate to high polaritycompounds result in the obtained high oil yields. Moreover, theinteraction between solvent and solutes, both solvent polarity andtheir boiling temperature may contribute mean factors on the

kernel oil.

The acidity, iodine, peroxide and saponiﬁcation values are themajor characterization parameters for oil quality. The peach kerneloils were very light yellow in colour and had an acceptable odour.The hydrocyanic acid contents in all samples were not detected thatindicated the peach kernel oils were completely free from the toxichydrocyanic acid. The statistical analysis showed that different

properties and fatty acid proﬁle of the oils. The acid value wasa measure of total acidity of the lipid, involving contributions fromall the constituent fatty acids that make up the glyceride molecule(Ekpa & Ekpe, 1995). As shown in Table 1, the total acidity,

Table 1

Physicochemical property of peach kernel oils extracted with different solvents (means S.D.).

Saponiﬁcation value (mg KOH/g oil)165.701 3.872a156.599 4.205b154.275 2.876b101.836 0.702ca-bMeans within the same row not followed by the same letter differ signiﬁcantly (p < 0.05). Each experiment was performed in triplicates.

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expressed as the acid value, was highest in ethyl ether extract(1.099 mg KOH/g oil), followed by hexane extract (0.895 mg KOH/goil) and the lowest value was found in the chloroform extract(0.608 mg KOH/g oil).

Peroxide value is one of the most widely used testings foroxidative rancidity in oils and fats. It is a measure of the concen-tration of peroxides and hydroperoxides formed in the initial stagesof lipid oxidation. Generally, the peroxide value should be less than10 mg/g oil in the fresh oils as any increase in this value (usually20 mg/g or above) results in rancidity of the oils (Pearson, 1976, pp.

widely in the extracts, ranging from 0.256 mg/g oil for the leum ether extract to 2.366 mg/g oil for the ethyl ether extract. Asigniﬁcant difference (p < 0.01) in the peroxide values wasobserved between the ethyl ether extract and others. The peroxide

chloroform extract (0.259 0.014 mg/g) were signiﬁcantly lowerthan all others.Ojeh (1981)reported that oils with high peroxidevalues are unstable and easily become rancid (having a disagree-able odour). The results suggested that the peach kernel oilsextracted with petroleum ether, chloroform and hexane could bestored with less deterioration than the oil extracted with ethylether. The acid and peroxide values were good indices for thestability of the oil. These two parameters of the peach kernel oil

Hosahalli, & Kyu, 2009).Farhoosh, Einafshar, and Sharayei (2009)

reported that the acid value of crude soybean oil and canola oilwere 1.89 mg KOH/g oil and 1.94 mg KOH/g oil, respectively. Theywere both higher than the acid value of peach kernel oils in thisstudy.Haﬁdi, Pilch and Ajanan (2005)showed the peroxide value of

peach kernel oils, as seen in our results. It clearly indicated that thepeach kernel oil may have low levels of oxidation.

The iodine value is used to determine the unsaturation of oilsand in assessing the stability of oil in industrial applications (Xu,Hanna, & Josiah, 2007). The range of iodine numbers were36.328e75.726 mg/100 g oil, thus, the peach kernel oil could beclassiﬁed as non-drying oil. The oil extracted with hexane had thelowest iodine value, which reﬂected its characteristics such ashigher resistance to oxidation, longer shelf life and higher quality.The differences in iodine values between oil samples maybe were

due to the different fatty acid compositions. The oil extracted withpetroleum ether has high monounsaturated fatty acids, whereasthe oil extracted with hexane contains more polyunsaturated fattyacids.

Saponiﬁcation index was highest in the petroleum ether extract(165.701 mg KOH/g oil), followed by the chloroform extract(156.599 mg KOH/g oil) while the lowest value was in hexaneextract (101.836 mg KOH/g oil). The saponiﬁcation index is a usefultool for the evaluation of the chain length (molecular weight) offatty acids occurring in the triacylglycerols in oil. The lowersaponiﬁcation value indicates a very high content of low molecularweight triacylglycerols. The results suggested that the oils extractedwith hexane had the higher fatty acid contents. It is important topoint out that, a strong correlation wasn’t observed between thephysicochemical properties and polarity of the solvents. Thesolvent polarity can be deﬁned as the molecule ability to participateon interaction with other similar polarity molecules. This lack ofany useful correlation suggests that apart from solvent polarity, oilsolubility in the solvents may play important roles.

3.2. Proﬁle of fatty acid (FA) composition in peach kernel oil extractThe total FA composition of the extracts obtained in this studywas determined by GC and was shown inTable 2. The FA proﬁle isa main determinant of the oil quality. The extracted oil containedmajor fatty acid compounds were oleic acid (61.87e65.74 g/100 goil), linoleic acid (25.89e29.07 g/100 g oil) and palmitic acid(5.632e6.355 g/100 g oil). These amounts of oleic acid were lowerthan those reported by Sánchez-Vicente, Albertina, Juan & Pando(2009). However, the amounts of linoleic acid and palmitic acidwere similar to the report of Sánchez-Vicente, Albertina, Juan &Pando (2009). The differences in genotypes, growing conditionsand perhaps the time of harvest and storage practices after col-

Renuncil, and Pando (2009). and those used in this study maycontribute to the observed differences.

All oil samples had high amounts of the unsaturated fatty acid(UFA) that primarily were oleic and linoleic acids. In the peach oilsextracted with various solvents in this study the UFA content waswell over 90% and was not signiﬁcantly different from each other.The total polyunsaturated fatty acids (PUFA) content (29.11 g/100 g

Table 2

Fatty acid composition (%w/w) of oils extracted with different solvents (means S.D.).

a-bMeans within the same row not followed by the same letter differ signiﬁcantly (p < 0.05). Each experiment was performed in triplicates.

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oil) of the peach kernel oil extracted with hexane was signiﬁcantlyhigher than others (25.92e26.06 g/100 g oil), but the total mono-unsaturated fatty acid (MUFA) contents in the hexane extracted oil

differences on PUFA and MUFA contents in the extracted oil by theother three solvents.Natália, Bruna, Maria, Julian and Sandra (2010)

reported the use of solvents presenting polarity indexes (PI) lowerthan 4.4 enhanced the extraction of oleic acid and linoleic acidamong the UFA. But in present study, no relation was founded

research, peach/almond samples were submitted to Soxhlet for 6 hat the solvent boiling point temperature, while our results arebased on peach kernel oil, extracted in Soxhlet for 24 h at 50C. Thedifference may be attributed to the different extract temperatureand time.

Amounts of fatty acids in the peach kernel oils were in the orderof MUFA> PUFA > SFA (total saturated fatty acids) irrespective ofthe solvent used. Peach kernel oil presented relatively low contentsof saturated fatty acid, high contents of unsaturated fatty acidscompared with other common vegetable/fruit seed oils, such ascanola, corn, grape seed, olive, peanut, sesame, soybean and walnut(Fasina, Craig-Schmidt, Colley, & Hallman, 2008; USDA, 2006).Based on the contents of SFA, USFA, MUFA and PUFA the fatty acidcomposition of peach kernel oil is similar to almond oil (SFA 8.84 g/100 g, USFA 91.16 g/100 g, MUFA 65.64 g/100 g and PUFA 25.52 g/100 g, respectively) (Fasina et al., 2008).

The unsaturated fatty acids are very important for the stabilityof oils because of the chemical reactions occurring at the doublebonds. The rates of those oxidation reactions depend on thenumber of double bonds in the carbon chain. Therefore oils witha high proportion of oleic acid are more stable than others. Oleicacid is less susceptible to the oxidation than polyunsaturated fattyacid from the n-6 series (linoleic acid).

The linoleic acid as an essential fatty acid contributes healthbeneﬁts for human body and it is preferred by industries when oilhydrogenation is required (Kamel, Karim, Mouna, Mohamed, &Brahim, 2009). Based on the results of physicochemical propertiesand fatty acid proﬁle of the peach kernel oil, it can be concludedthat the peach kernels can become valuable resource to producehigh value essential oil products. The high quality and nutritionalvalue of peach kernel oil has potential application in human foods.3.3. Total phenolic content

The phenolic compounds are the main component responsiblefor antioxidant activity, is mainly due to their redox properties,which can play an important role in absorbing and neutralising freeradicals, quenching singlet and triplet oxygen, or decomposing

content through the method of Folin-Ciocalteau represents a goodestimative of antioxidant potential of food samples.

The total phenolic contents of kernel meal and oil by different

signiﬁcantly higher amount of total phenolic contents compared tothe oils (6.992e7.951 mg GAE/g). The oils extracted with solventsresulted in low phenolic contents (3.829e4.1593 mg GAE/g), indi-cating that only parts of the phenolic content were transferred tooils. The loss of phenolic compounds in extracted oils is likely dueto the thermal impact and its insolubility in oil. The results sug-gested that after oil extraction, the meals still can be used forantioxidant extraction or functional ingredients. Although thepolarities of chloroform and ethyl ether were stronger, hexane

Moreover, the values of the total phenolic contents were notsigniﬁcantly different. This indicates that not only the solvent

characteristics such as polarity affected the total phenolic content,but also the solubility of phenolic compounds, the localization ofthese compounds in the tissue matrix, and characteristics of matrixmust also be involved. The results suggested that the best methodto produce high extraction yield and total phenolic content forpeach kernel oil is Soxhlet extraction with hexane as solvent.3.4. Phenolic proﬁles

In the oils and meals, a total of 15 phenolic compounds was

spectra with standards, and are shown inTable 3. There are yetsome other unidentiﬁed compounds due to the lack of standards.The meals extracted with petroleum ether and ethyl ether showedthe most complex phenolic proﬁle with eight phenolic acids and sixﬂavonoids.

HPLC analysis revealed the presence of dithiothreitol, rutin andcaffeic acid as the major phenolic compounds in the oils extractedwith petroleum ether, chloroform and ethyl ether. Rutin isconsidered to be one of the most important phenolics compoundsthat effectively boosts vitamin C’s efﬁcacy, improve eye health,strengthen fragile capillaries, reduce cholesterol, improve bloodcirculation, and act as antioxidants. Dithiothreitol and caffeic acidcan repress the activation of pro-carcinogens and can activateenzymatic systems (Phase II) as well as prevent oxidative damageto the DNA which has been shown to be important in the in the age-related development of some cancers (Vattem, Ghaedian, & Shetty,2005).

Rutin was the predominant phenolic compound in the oilextracted with hexane accounting for 76.65 g/100 g of the totalamount. In contrast, the major phenolics compounds in the mealswere different compared to their corresponding oil extracts. Theprocyanidin B2 and the hydrocinnamic acid were the predominantphenolic compounds in the meals extracted with petroleum etherand ethyl ether, and the hydrocinnamic acid, the rutin were thepredominant phenolic compounds in the meals extracted withchloroform and hexane.

Because of the different number and arrangement of thehydroxyl groups as well as the presence of electron-donatingsubstituents in the ring structure of phenolic compounds, thepolarity of phenolic compounds were different. So, the oils andmeals extracted with solvents with different polarities mightcontain different types of phenolic compounds. Our studies on theoils and the meals showed differences on the phenolic composi-tions and contents compared with peach puree and concentrate

Fig. 1. Total phenolics content of peach kernel oils and meals extracted with differentsolvents. The mean value obtained from three replications (oils,meals).

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(Bengoechea, Sancho, & Bartolome, 1997), which pointed out thatchlorogenic acid, was the main phenolic compound in both peachpuree and concentrate. This indicates that the phenolic compoundsare different in the peach kernel oil and meal.

antioxi-dant activities compared to the phenolic acid fraction (Thorsten,Andreas, Dietmar, & Reinhold, 2009). Rutin is one of the mostimportantﬂavonoids. Oil extracted with hexane was characterisedby high rutin content, which may account for the high totalphenolic content. However, we could not determine whichphenolic compounds actually contributed to the total antioxidantactivity of oils and meals. The phenolic acids andﬂavonoid poly-phenolics present in extracts may contribute individually orsynergistically to the antioxidant activities.

Interestingly, the phenolic contents determined by theFolineCiocalteu method exceeded the total amount of individualphenolics as quantiﬁed by HPLC. This is probably due to the factthat all monomeric, oligomeric and polymeric polyphenols were

molecular compounds were covered by HPLC. A similar enon has been described for the determination of the total phenoliccontent of residues of grape seed oil (Thorsten et al., 2009).

phenom-3.5. Antioxidant activities of meals and oils

The DPPH radical scavenging is a common method to evaluatethe ability of antioxidant components to scavenge free radicalsgenerated. Only the oil extracted with hexane exhibited strongerDPPH radical-scavenging activity, compared with the meals (Fig. 2).In addition, the oil extracted with hexane is more active, comparedto the meal. It has been reported that free radical-scavengingactivity is greatly inﬂuenced by the phenolic composition of thesample (Cheung, Cheung, & Ooi, 2003). Thus, the antioxidantactivity of the oils and meals extracted from peach kernels may beattributed to their phenolic contents in the samples. Although theoil extracted with hexane contained lower amount of totalphenolics than that of meal, it showed a higher DPPH radical-scavenging efﬁciency than their meal, which could be attributedto their high rutin content.

The TEAC assay is widely applied to assess the total amount ofradicals that can be scavenged by an antioxidant, i.e. the antioxi-dant capacity. The results of the TEAC analysis for peach kernel oilsand meals are shown inFig. 3. All the oils and meals inhibited theoxidation of ABTS-ỵradical to varying degrees. In the present study,

the oil with the highest antioxidant activity was extracted with

chloroform and ethyl ether, which had TEAC values of 65.22 and63.95

m

m TAE/100 g, respectively. Highest antioxidant capacity inthe meals was found in the extracts with petroleum ether

(Fig. 3) and this trend was similar to the changes in total phenoliccontent.

Polyphenols have been reported to be responsible for the oxidant activities of botanical extracts. The DPPH assay and TEACassay have been used to measure antioxidant activity and theresults generally correlate with total phenolic content. A directcorrelation between radical-scavenging activity and phenoliccontent of the oils and the meals was observed. The TEAC and DPPHantioxidant activity values were increased with increasing phenoliccontent of the oils and the meals analysed, in agreement withprevious works in different foodstuffs (Ismail, Chan, Mariod, &Ismail, 2010).

anti-Regression equation was used to determine the correlationcoefﬁcient (R2) on the plot of total phenolic content against TEAC orDPPH. The correlations between the total phenolic content and theantioxidant activity based on TEAC was high (R2¼ 0.9566), whilethe correlation between total phenolic content and DPPH was low(R2 ¼ 0.5913). It is due to a different mechanism and reaction

Fig. 2. Antioxidant activity of peach kernel oils and meals extracted with differentsolvents on DPPH reduction. The mean value obtained from four replications (oils,Table 3

Phenolic compounds (mg/g) of peach kernel oils and meals extracted with different solvents (means S.D.).Phenolic compounds

(mg/g)

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between individual polyphenol compounds with DPPH or TEAC.DPPH is measure as free radical scavenging activity based on thereduction of 1,1-diphenyl-2-picrylhydrazyl. TEAC is a measurementof antioxidant strength based on Trolox Equivalency. Most phenoliccompounds have deoxidization properties (TEAC), but not allpolyphenols compounds can react with free radical (DPPH), so thecorrelation between total phenols and TEAC is positively higherthan DPPH. Several studies had reported a good correlationbetween the phenol content of plant extracts and antioxidantactivity (Bahorun, Luximon-Ramma, Crozier, & Aruoma, 2004;Djeridane et al., 2006), but other studies report a poor correlation(Sellappan & Akoh, 2002). As indicated above, not only phenolic

non-phenolic, such as fatty acid proﬁle, could contribute to the overallantioxidant potential.

4. Conclusions

Peach kernel oils were extracted by organic solvents leum ether, ethyl ether, chloroform and hexane) and evaluated fortheir characterization and quality analysis. According to the anal-ysis of physicochemical properties, fatty acid proﬁle, total phenolsand antioxidant capacity based on DPPH radical-scavenging andTEAC, the results showed that these oils are rich in oleic acid andlinoleic acid, indicating that they are stable and tolerant torancidity. The effects of different extraction solvents signiﬁcantlyinﬂuenced the physicochemical properties of oil, and the phenoliccomposition and antioxidant properties of the meals and extractedoils. The results suggested that the oil extracted with hexane hasbetter quality. Hexane has been widely used for extraction in foodindustry due to it is easily be evaporated from extracts. This oilmay be considered as an important source of unsaturated fattyacid and has the potential to be used as nutrient rich food oil.

contained higher amounts of total phenolic and stronger dant activities than oils, enabling their application as ingredientsof functional or enriched foods. The results of present studyprovide useful information for essential oil and food industry. Asa bio-waste in peach processing industry, the peach kernel haspotential applications in the food industry. Due to its specialcomposition, rich in polyunsaturated fatty acids, including linoleicand oleic acids, and in antioxidant compounds. In food applica-tions, it can be substituted for olive oil and grape seed oil in saladproducts such as salad oil, salad dressing, dips, and sauces, and itcan also be used as cooking oil.

Authors gratefully acknowledge the contribution of the MOE/AAFC Program and Guelph Food Research Center, Agriculture andAgri-Food Canada.

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