Article pubs.acs.org/JAFC
Characterization of the Key Aroma Compounds in Five Varieties of Mandarins by Gas Chromatography−Olfactometry, Odor Activity Values, Aroma Recombination, and Omission Analysis Zuobing Xiao,† Quyang Wu,† Yunwei Niu,*,† Minling Wu,† Jiancai Zhu,† Xuan Zhou,† Xiaomei Chen,† Hongling Wang,† Jing Li,† and Jiali Kong† †
School of Perfume and Aroma Technology, Shanghai Institute of Technology, Shanghai 201418, PR China ABSTRACT: In this study, volatile compounds of five varieties of mandarin juices [Tankan, Miyagawa, Mashui (MS), Skiranui, and Ponkan (PG)] were investigated by gas chromatography−olfactometry (GC−O) and gas chromatography−mass spectrometry (GC−MS). A total of 47 volatile compounds were identified by GC−MS. Partial least-squares regression was used to process the mean scores from sensory evaluation by panelists of volatile compounds and samples. The sample PG was associated with “fruity”, “floral”, and “sweet” notes, while MS was correlated with “green” and “peely” notes. In addition, 36 aroma-active compounds, including esters, alcohols, aldehydes, ketones, and monoterpenes, were detected by GC−O. According to the quantitative results, 29 aroma compounds were important, which indicated that their odor activity values (OAVs) were ≥1. On the basis of the GC−O results and OAVs of these volatile compounds, 22 odor-active compounds were mixed to simulate successfully the overall aroma of PG mandarin juice. Furthermore, omission experiments confirmed that nonanal, hexanal, linalool, and (R)-(+)-limonene were the key odorants for the overall aroma of PG juice sample and that β-ionone, decanal, γ-terpinene, and methyl butyrate were also important odor-active compounds. KEYWORDS: mandarin juice, aroma-active compounds, GC−MS, GC−O, OAV, aroma recombination, omission experiments, PLSR
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4 weeks of storage time while ‘W. Murcott’ was changed after it was stored for 7 weeks. There were no significant differences in volatile concentrations among the three temperatures (0, 4, and 8 °C), and they thought storage temperature did not effect on the flavor of ‘Owari’. However, Tietel9 found that changes of storage temperatures had no major effects on volatile contents in ‘Or’ mandarins, and 13 volatile compounds had accumulated after storage at 2 °C. Besides, Alonso10 discussed the effect of X-ray irradiation exposure on the volatiles of Spanish clementine mandarins. The statistical analysis indicated that the increases in acetaldehyde and ethanol after X-ray treatment did not reduce the consumer acceptance, so they thought X-ray irradiation is a harmless and highly effective quarantine technique for clementine mandarins. In addition, several studies have been concerned with the chemical composition of peel or leaf oils of mandarins.6,11−13 Gancel14 extracted and analyzed the volatile compounds of seven citrus hybrid leaves which share mandarins as their common parent and other citrus fruits (lemon, lime, grapefruit et al.) as the other parent. The results suggested that all of the hybrids were similar to their common mandarin parent in the composition of volatile compounds. Even if there were extensive studies about the volatile compounds of mandarins, there is still a lack of investigation of the flavor of Chinese mandarins, especially the mandarins that are grown in China. The aims of this study were (1) to
INTRODUCTION Citrus fruits are well-known and enjoyed worldwide because of their unique flavor and nutritional value. They are grown commercially in more than 135 countries in the world,1,2 and the production of citrus fruits in world was nearly 111.5 million tons in 2013.3 According to a previous report,4−6 citrus fruits, mainly including orange, lemon, mandarin, lime, and grapefruit, have a high commercial value due to great sales performance and are widely applied in food industry. Mandarin (Citrus reticulata Blanco) is a citrus fruit that has many diverse types, like satsumas, clementines, and tangerines. This kind of citrus fruit is thin-skinned, easy-peeling, and widely cultivated in the southern area of China. Mandarins are primarily used as fresh fruit and processed products, such as canned fruit, juice, and essential oil. The peel of this fruit could be used in herbal tea to aid against cough, and the essential oil is also widely used for flavor or fragrance.4 Flavor is one of the most important criteria to evaluate the quality of a fruit, together with its appearance, texture, and color, for purchase. Hence, it is necessary to investigate the aroma profiles in citrus fruit. Up to now, numerous investigations on the aroma of mandarin fruits have been carried out. Simón-Grao7 identified 38 volatile compounds, including terpenes, aldehydes, esters, and phenolic compounds, during the analysis of aroma compounds in 11 commercial mandarin cultivars which were grown in Spain. There is also a lot of research about the change of volatile compounds after different treatments. Obenland8 investigated the flavor qualities after different storage times and storage temperatures and then evaluated the sensory attributes of two mandarin varieties. They found that the ‘Owari’ mandarin’s flavor quality was reduced in © 2017 American Chemical Society
Received: Revised: Accepted: Published: 8392
June 11, 2017 September 4, 2017 September 8, 2017 September 8, 2017 DOI: 10.1021/acs.jafc.7b02703 J. Agric. Food Chem. 2017, 65, 8392−8401
Article
Journal of Agricultural and Food Chemistry
The volatile compounds were determined by authentic standards, the retention index (RI), and comparison to the Mass Spectral Library (NIST08, Wiley7n. I). For calculation of RI a C7−C30 n-alkanes series (concentration of 1000 mg/L in n-hexane) from Sigma-Aldrich was used. To obtain a matrix that was similar to mandarin fruit juice, a model juice was prepared with some standard compounds in Milli-Q deionized water according to previous studies,15,16 the 100 g constitution of model juice (% w/w) contained the following compounds: sucrose, 5.0; fructose, 2.5; glucose, 2.5; citric acid, 1.0; tripotassium citrate, 0.5; ascorbic acid, 0.06; Milli-Q deionized water, 88.44. Quantification of volatile compounds was conducted by calibration curves that were obtained for each compound from eight different concentrations of model juice. The extraction of the standard volatiles for making the standard curve was the same as the sample extraction method. The calibration curves are shown in Table 1, where y represents the peak area ratio (peak area of volatile standard/peak area of internal standard) and x represents the concentration ratio (concentration of volatile standard/concentration of internal standard). The experiments were performed in triplicate. GC−Olfactometry Analysis. GC−olfactometry analysis was performed on an Agilent 7890A chromatograph coupled with a flame ionization detector (FID) and an ODP-2 olfactory detector port (Gerstel, Mühlheim an der Ruhr, Germany). The samples were analyzed on both an HP-INNOWax fused-silica capillary column (60 m× 0.25 mm × 0.25 μm, Agilent, Santa Clara, CA) and a DB-5 fused-silica capillary column (60 m × 0.25 mm × 0.25 μm, Agilent, Santa Clara, CA). The carrier gas was helium and the flow rate of carrier gas was 2 mL/min. The oven temperature was first increased from 40 °C (6 min), raised to 160 °C at the rate of 3 °C/min, and then raised to 230 °C (10 min) at the rate of 5 °C/min. The injector and FID detector temperatures were set at 250 and 280 °C. Meanwhile, the moist air was pumped into the sniffing port at 50 mL/min to quickly remove the odorant eluted from the sniffing port. Four well-trained panelists (two females and two males) were selected for GC−O investigation. The aroma intensities (AIs) were evaluated by use of a five-point intensity scale from “0” to “5”; “0” was none, “3” was moderate, and “5” was extreme. The experiments were carried out in triplicate for each sample by every panelist. Sensory Evaluation. Sensory evaluation was carried out in a sensory laboratory under guidelines and conditions according to the ISO 8589-2007. The aroma profiles of five citrus fruit juices were evaluated by 12 sensory panelists (5 males and 7 females). The sensory evaluation method was preformed according to the methods of previous studies17,18 with minor modifications. Five specific training sessions were carried out. In the first session, panelists generated descriptive terms for the citrus fruit juices; in the second and third, different aroma standards were presented and discussed by panelists. From these discussions, the six aroma terms (fruity, sweet, green, floral, peely, and woody) were selected for further descriptive analysis. The aroma descriptors were selected from previously studies17,19,20 and modified after discussion by panelists. In the fourth and fifth sessions, the mandarin juices were evaluated in two replications by using a 10-point intensity scale (0 = none, 1 = very low, 9 = very high) for each sensory descriptor. The reference materials of aroma were as follows: sweet (honey), fruity (crushed strawberries, raspberries, and blackberries), green (1 mg/L cis-3-hexenol in glycerol triacetate), floral (0.5 mg/L aqueous solution of 2-phenylethanol), peely (1 mg/L decanal in glycerol triacetate), and woody (5 g of oak wood chips in 100 mL of 10% ethanol−water solution). A content volume of 50 mL citrus fruit juice was placed in a 150 mL odorless plastic cup with a lid at room temperature in an individual booth and noted with a random number under clean air conditions. A gap of 20 s between each exposure was used to separate the individual odor assessments. The description of six descriptors and reference standards can be seen in Table 4. Odor Activity Values (OAV). The odor activity values of the volatile compounds were calculated by dividing the calculated concentrations with sensory thresholds, which were obtained from the literature.
identify the odor-active compounds in mandarin samples by gas chromatography−olfactometry (GC−O) and calculate the odor activity values (OAVs) of volatile compounds, (2) to establish the relationship between the sensory descriptor and volatile compounds of samples using partial least-squares regression (PLSR) analysis, and (3) to confirm the key odor-active compounds of mandarin juice according to the aroma recombination and omission experiments.
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MATERIALS AND METHODS
Materials and Chemicals. Standards of acetaldehyde, ethyl acetate, 1-penten-3-one, 1-penten-3-ol, ethyl propionate, methyl butyrate, 3-methyl-1-butanol, 2-methyl-1-butanol, (E)-2-pentenal, ethyl2-methylpropanoate, pentanol, 2-methylpropyl acetate, ethyl butyrate, hexanal, ethyl 2-methylbutyrate, ethyl isovalerate, ethyl valerate, (E)-2hexenal, (Z)-3-hexen-1-ol, hexanol, 3-methylbutyl acetate, styrene, heptanal, α-pinene, (E)-2-heptenal, heptanol, 1-octen-3-ol, methylheptenone, β-myrcene, ethyl hexanoate, α-phellandrene, p-cymol, (R)(+)-limonene, γ-terpinene, octanol, terpinolene, nonanal, linalool, 2-phenylethanol, citronellal, 1-terpinen-4-ol, decanal, α-terpineol, carvone, methyl eugenol, geranylacetone, β-ionone, and 2-octanol (internal standard) were purchased from Sigma-Aldrich Chemical Co. (St. Louis, MO). For determination of the retention index (RI), a mixture of hydrocarbons ranging from heptene (C7) to triacontane (C30) (SigmaAldrich Chemical Co, St. Louis, MO) was used and run at the experimental conditions described below. All of them were analytical reagents. Sucrose, fructose, glucose, citric acid, tripotassium citrate, and ascorbic acid were purchased from Sinopharm Chemical Reagent Co. Ltd. and they were ARG quality. Juice Preparation. In this study, a total of five mandarins (C. reticulata Blanco) were studied: Tankan (JG), Miyagawa-wase (YQ), Mashui (MS), Skiranui (CJ), and Ponkan (PG). They were purchased from local market in Shanghai. ‘Tankan’ were harvested from Guangdong province, ‘Miyagawa’ were harvested Zhejiang province, ‘Mashui’ were harvested from Guangxi province, ‘Skiranui’ and ‘Ponkan’ were harvested from Zhejiang province. All of them were harvested at maturity. Citrus fruits were washed with Milli-Q water, peeled, and squeezed into juice by a kitchen blender. Then the fruit juices were filtered through four layers of cheese cloth. The filtered juices were kept in a refrigerator (−10 °C) until analyzed. Extraction of Volatile Compounds of Mandarin Fruit Juices by HS-SPME. The extraction of volatile compounds was by HS-SPME and the extraction procedure was as follow: 8 g of fresh mandarin juice, 1.5 g of sodium chloride, and 10 μL of 2-octanol (200 mg/L, internal standard) were immediately transferred to a 15 mL headspace bottle (Reference 27385, Supelco, Bellefonte, PA) that had a PTFE− silicone septum. After that, we put the bottle into a thermostatic water bath. A 50/30 μm divinybenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fiber was exposed to the headspace of the sample (about 1 cm above the liquid surface) for 30 min at 45 °C without stirring and then desorbed into the injector port of a GC apparatus for 5 min. After each analysis, the fiber was inserted into a thermal heater for 15 min at 250 °C to make sure that no residue remained. Each mandarin juice sample underwent the same procedure that was described above. GC−MS Analysis. The volatile compounds were separated and identified on a 7890 gas chromatograph (GC) equipped with a 5973C mass selective detector (MS) (Agilent Technologies). Two dissimilar columns, an HP-INNOWax fused-silica capillary column (60 m× 0.25 mm × 0.25 μm, Agilent, Santa Clara, CA) and a DB-5 fused-silica capillary column (60 m × 0.25 mm × 0.25 μm, Agilent, Santa Clara, CA), were used to analyze the volatile compounds. The carrier gas helium was circulated at a rate of 1 mL/min in the constant flow mode and the injection port was set in a splitless mode for 3 min at 250 °C. The oven temperature was held at 40 °C for 6 min, raised to 160 °C at the rate of 3 °C/min, and raised to 230 °C for the last 10 min. For mass spectrometry analysis, electron impact mode (EI) at 70 eV was used and the MS scanning was from 30 to 400 amu. 8393
DOI: 10.1021/acs.jafc.7b02703 J. Agric. Food Chem. 2017, 65, 8392−8401
acetaldehyde ethyl acetate ethyl propionate ethyl 2-methylpropanoate methyl butyrate 2-methylpropyl acetate 1-penten-3-one ethyl butyrate ethyl 2-methylbutyrate α-pinene ethyl isovalerate hexanal 3-methylbutyl acetate ethyl valerate (E)-2-pentenal β-myrcene 1-penten-3-ol heptanal α-phellandrene (R)-(+)-limonene 2-methyl-1-butanol 3-methyl-1-butanol ethyl hexanoate (E)-2-hexenal pentanol γ-terpinene styrene p-cymol terpinolene (E)-2-heptenal methylheptenone hexanol nonanal (Z)-3-hexen-1-ol 1-octen-3-ol citronellal heptanol decanal
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1048 1060 1078 1114
1016 1029 1047
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