多手段评测5种猕猴桃的挥发性风味成分

曾 硕1,郭新宇2,牛东升1,李 峰1*

1新疆农业大学食品科学与药学学院,乌鲁木齐 830052;2西北农林科技大学食品科学与工程学院,陕西杨凌 712100)

摘 要:【目的】筛选出合适的专用猕猴桃酿酒品种。【方法】利用SPME-GC-MS结合电子鼻及化学计量法对5种猕猴桃的挥发性成分进行测定。【结果】电子鼻测试中徐香猕猴桃对各传感器的响应强度最高。使用固相微萃取-气相色谱-质谱联用技术,共检测到94种挥发性成分。此外,75种的香气活力值(OAV)大于1,丁酸乙酯和辛酸乙酯在5种猕猴桃中均存在。主成分分析和正交偏最小二乘判别分析显示,5个猕猴桃品种在挥发性成分上存在显著差异。组合热图进一步表明,丁酸甲酯、丁酸乙酯、反式-2-己烯醛、己酸甲酯、正己醇和反-2-己烯醇在所有品种中含量较高。丁酸乙酯和正己醇分别在海沃德、徐香、红阳猕猴桃及华优、金艳猕猴桃中含量较高。【结论】丁酸乙酯和正己醇是猕猴桃风味的关键挥发性物质,能够增强猕猴桃的果香复杂性和整体风味。

关键词:猕猴桃;主成分分析;固相微萃取-气相色谱-质谱联用;风味组学;气味活度值

猕猴桃(Actinidia chinensis Planch.),又称奇异果,属于猕猴桃科(Actinidiaceae)猕猴桃属(Actinidia),是一种多年生落叶藤本植物[1]。猕猴桃富含糖类、酸类、多酚类化合物及抗氧化物质,特别是其丰富的维生素C含量,素有“维C之王”的美誉,广受消费者喜爱[2-3]。根据联合国粮食及农业组织(FAO)2022年的统计数据,全球猕猴桃产量已达到440万t,其中中国的猕猴桃挂果量及总产量稳居全球首位[4]。作为典型的呼吸跃变型果实,猕猴桃在完熟阶段采后贮藏稳定性差,促使产业界将其进行果酒深加工处理,通过特殊发酵工艺开发出含双重芳香特征(果香与酒香复合)并保留营养成分的特色果酒[5]。但受制于专用酿酒原料品种的缺失,当前猕猴桃果酒普遍存在香气平淡等问题,导致高端果酒市场拓展遭遇工艺瓶颈[6]

香气风味是水果品质的重要因素,主要来自醛类、酯类、醇类和萜类等化学成分[7]。猕猴桃的香气变化可分为3个阶段:猕猴桃自身挥发性物质、发酵过程中香气的生成以及陈酿阶段的香气演变[8]。猕猴桃品种的选择对酒体挥发性物质至关重要。近年来,关于不同猕猴桃品种对酒体挥发性物质的分析研究逐渐增多。Huang 等[9]采用HS-SPME-GC-MS法分析了不同澄清处理的5个猕猴桃品种与酿酒酵母结合发酵的猕猴桃酒,鉴定出34 种芳香化合物,包括15 种酯类、10 种醇类、4 种酸类和5 种醛类/萜类化合物。研究发现,澄清猕猴桃汁酿成的酒含有较高含量的酯类,而浑浊果汁(未澄清)酿造的酒和含果肉(未澄清)酿造的酒富含醇类,澄清果汁猕猴桃酒还展现出更多典型的奇异果香气。Zhang 等[10]通过核磁共振氢谱和多元分析,对绿色、黄色和红色猕猴桃的发酵风味和代谢特征进行综合评价,发现海沃德猕猴桃酒具有最突出的花香、果香和宜人香气,东红猕猴桃酒则表现出甘甜、饱满、平衡的口感。代谢组学分析表征了106 种化合物,主成分分析(PCA)和偏最小二乘判别分析(PLS-DA)有效地区分了3 种猕猴桃的香气和口感特征,表明不同品种对酒体风味有显著影响。Zhao 等[11]采用SPMEGC-MS 法分析了海沃德和Hort16A 猕猴桃发酵后的挥发物,发现67 种游离挥发物和79 种结合挥发物,其中乙醇是最丰富的游离挥发物,而萜类是最具代表性的结合挥发物。主成分分析表明,奇异果酒具有较大的香气潜力,聚类分析显示,两种猕猴桃的游离挥发物特征不同,但结合挥发物的组成相似。大量研究表明,挥发性有机化合物的特征受土壤气候条件、品种、成熟度以及生产技术等多方面因素的影响(包括收获及其后的处理、加工和贮存条件)[12-13]。目前,关于猕猴桃挥发物的研究主要集中在果实的生理发育和贮藏过程中挥发性有机化合物的含量变化方面,然而,关于猕猴桃不同品种挥发物组成的定性和半定量变化的研究则相对较少[14]

笔者选用徐香、海沃德、华优、金艳、红阳5种猕猴桃进行挥发性物质测定,采用固相微萃取-气相色谱-质谱联用(solid phase micro-extraction gas chromatography-mass spectrometry,SPME-GC-MS)分析技术结合电子鼻、化学计量学和感官评价对5 个不同猕猴桃品种的香气成分进行比较,以期为提高猕猴桃果酒香气物质含量提供理论基础。

1 材料和方法

1.1 材料与仪器

试材为徐香、海沃德、华优、金艳、红阳5 个品种,选择完整,无虫害、无破损的发育135 d的鲜果,采摘于陕西省眉县与周至县,于常温下后熟备用。2-辛醇为色谱级,购于中国索莱宝公司;氯化钠等分析纯购于中国索莱宝公司。

气相色谱质谱联用仪(GCMS-QP2010 Ultra,日本岛津公司);气相色谱柱(DB-1MS 毛细管柱,60 mm×0.25 mm×0.25 μm,美国安捷伦科技有限公司);PEN3 型便携式电子鼻(德国AIRSENSE 公司);50/30 μm DVB/CAR/PDMS 固相微萃取头(SAAB-57329U,美国Supelco公司)。

1.2 方法

1.2.1 试验处理 样品前处理:参考曾硕等[4]的方法将预处理的猕猴桃果实进行破碎打浆,同时添加50 mg·L-1 SO2进行护色,打浆机自动分离出猕猴桃汁与皮渣,将榨取后的猕猴桃浆用尼龙纱布多次过滤得到猕猴桃汁,待用。

1.2.2 挥发性成分的提取 吸取8 mL 猕猴桃原汁样装入20 mL 固相微萃取专用瓶中,依次加入1.5 g氯化钠和10.0 μL(终质量浓度为62.4 μg·L-1)内标2-辛醇,用PTFE-silicon 隔膜加盖密封。将新购买的萃取头进行老化处理,即将其插入250 ℃的GC进样口老化30 min。将待测样品放置在进样板上,萃取温度45 ℃,萃取60 min。吸附结束后,萃取头自动插入GC-MS 进样口,在230 ℃下解析2 min[15],进行GC-MS分析。

1.2.3 GC-MS条件 初始柱温为40 ℃,进样口温度为230 ℃。升温程序:起始温度为40 ℃,保持3 min,以3 ℃·min-1的速率升至110 ℃,再以4 ℃·min-1的速率升至120 ℃,然后以6 ℃·min-1 的速率升至210 ℃,保持9 min,最后以25 ℃·min-1的速率升至240 ℃,保持3 min。载气为He,流速为1.0 mL·min-1,不分流进样。质谱条件:电离方式为EI 源,电子能量70 eV;离子源温度是230 ℃;质量扫描范围为35~500 m/z[16]

1.2.4 电子鼻分析 该传感器阵列由10 种化学传感器组成:W1C(芳香成分苯类),W5S(氮氧化合物型),W3C(芳香型),W6S(氢化物型),W5C(芳香-烷基型),W1S(甲基类),W1W(硫-有机型),W2S(醇类、醛酮类),W2W(硫-无机型)和W3S(长链烷烃型)。参考Lan等[17]的方法稍作修改,所有样本均稀释至50倍,然后将每个处理的5 mL样本用移液管吸取并放入注射瓶中进行电子鼻分析。由注射器自动注入1 mL的气相样本,传感器响应在注入前的300 s冲洗时间后记录60 s。所有程序均在室温下进行。

1.2.5 香气活力值(OAV)的计算 香气活力值是评估香气成分对香气系统贡献的重要指标[18]。它通过将香气成分的浓度除以其感官阈值来计算。OAV值越大,表示该香气成分对整体香气的贡献越显著。OAV=Ci/OTi。

式中:Ci 为挥发性成分的质量浓度(μg·L-1);OTi为香气阈值(mg·m-3)。

1.2.6 定性方法 将未知化合物经计算机检索,同时与NIST library(107 k compounds)和Wileylibrary(320 k compounds,version 6.0)相匹配,进行定性分析并保留相似度高于85%的结果。

1.2.7 定量方法 参考Yang等[19]的方法,以2-辛醇为内标,用内标法对猕猴桃果酒中常见的代表性酸类、醇类、酯类、醛酮类等物质进行半定量计算,将各挥发性化合物和内标物的峰面积进行对比,得出挥发性物质的含量。各组分含量(ρ)(μg·L-1)=(各组分峰面积×内标物质量浓度)/内标物峰面积。

1.2.8 感官描述分析 根据国标GB/T 15038—2006《葡萄酒、果酒通用分析方法》[20]、国际CXS 349—2022《浆果标准》[21]及Liu等[22]制定感官评分标准。评价小组由10 名专业评鉴人员组成,试验在20 ℃恒温且通风的房间内进行,每位成员禁止交流,确保评价结果的独立性。风味评分采用0~20分制,每位评价员独立评分,最终得分取所有成员的平均分。感官描述词参照表1。

表1 感官描述词及其参比样品
Table 1 Sensory descriptors and the reference sample

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1.3 数据分析

采用Excel 2018、Mintab 18 对数据进行处理与分析,采用origin 2021 软件绘制堆积柱状图、聚类热图与雷达图,结果以平均值表示,每组试验3 次重复,差异显著性水平p<0.05。

2 结果与分析

2.1 不同猕猴桃原汁挥发性成分种类

根据图1 所示,徐香猕猴桃原汁中检测到的挥发性成分共有29 种,其中酯类物质占55%,醇类物质占28%。海沃德猕猴桃原汁中共有48 种挥发性成分,数量最多,其中酯类物质占60%,醇类物质占17%。华优猕猴桃原汁中检测到的挥发性化合物共有42种,酯类物质有16种,占总类的38%,而醇类物质占24%。金艳猕猴桃原汁中的挥发性成分共有42种,其中酯类物质18种,占总类的43%,醇类物质11种,占26%。红阳猕猴桃原汁中检测出28种挥发性化合物,其中酯类物质有19种,占总类的68%,醇类物质2种,占7%。

图1 猕猴桃原汁的挥发性成分种类
Fig.1 The types of volatile components in kiwifruit juice

2.2 挥发性风味成分分析

挥发性物质的不同组合赋予了猕猴桃原汁独特的风味特征[23],因此,不同品种的猕猴桃在香气、口感以及果汁的风味浓度上具有差异。如表2 所示,徐香猕猴桃原汁中,主要的挥发性成分包括反-2-己烯醇、丁酸乙酯、己酸甲酯、正己酸乙酯和反式-2-己烯醛。海沃德猕猴桃原汁中的主要挥发性成分为正己醇、丁酸乙酯、正己酸乙酯、苯甲酸甲酯和苯甲酸乙酯。华优和金艳猕猴桃原汁中,正己醇、异戊醇和丁酸乙酯是主要的挥发性成分。华优猕猴桃原汁中的主要挥发性成分为正己醇、异戊醇、丁酸乙酯。金艳猕猴桃原汁中的主要挥发性成分为正己醇、异戊醇、正己酸乙酯、2-甲基-1-丁醇。红阳猕猴桃原汁中的主要挥发性成分为反-2-己烯醇、桉叶油醇、丁酸乙酯、丁酸甲酯、正己酸乙酯和反式-2-己烯醛。在不同猕猴桃原汁中,正己醇、异戊醇和2-甲基-1-丁醇是海沃德、金艳和华优猕猴桃的主要醇类物质,它们分别具有草香与果香、麦芽与奶酪香以及香蕉香气特征。徐香和红阳猕猴桃原汁中,反-2-己烯醇和桉叶油醇含量较高,它们分别具有水果香和桉叶素的特征香气。

表2 5 种猕猴桃挥发性风味成分分析结果
Table 2 The analysis results of volatile flavor compounds in five types of kiwifruit

注:-表示未检出。下同。
Note:-indicates undetectable levels.The same below.

序号Serial number CAS号CAS number名称Name保留时间Retention time/min分子式Molecular formula ρ/(μg·L-1)徐香Xuxiang海沃德Hayward华优Huayou金艳Jinyan红阳Hongyang 123456789 71-36-3 123-51-3 137-32-6 513-85-9 24347-58-8 7.613 9.825 9.951 11.913 11.457 C4H10O C5H12O C5H12O C4H10O2 C4H10O2 3.46-醇类Alcohols正丁醇1-Butanol异戊醇Isoamyl alcohol 2-甲基-1-丁醇2-Methyl-1-butanol 2,3-丁二醇2,3-Butanediol(2R,3R)-(-)-2,3-丁二醇(2R,3R)-(-)-2,3-Butanediol叶醇Leaf alcohol反-3-己烯醇(Z)-3-Hexenol反-2-己烯醇(Z)-2-Hexenol正己醇1-Hexanol庚醇Heptanol桉叶油醇Eucalyptol 1-辛醇1-Octanol苯乙醇Phenylethanol香茅醇Citronellol顺-4-庚烯-1-醇(Z)-4-Hepten-1-ol 1-戊醇1-Pentanol顺-4-庚烯-醇(Z)-4-Heptenol松油醇Pinolene alcohol醛类Aldehydes乙酸乙酯Ethyl acetate丙酸乙酯Ethyl propionate丁酸甲酯Methyl butyrate 2-丁烯酸甲酯Methyl 2-butenoate异丁酸乙酯Ethyl isobutyrate丁酸乙酯Ethyl butyrate乙酸丁酯Butyl acetate戊酸甲酯Methyl valerate异戊酸乙酯Ethyl isovalerate乙酸异戊酯Isoamyl acetate 2-甲基丁基乙酸酯2-Methylbutyl acetate丁酸丙酯Propyl butyrate戊酸乙酯Ethyl valerate己酸甲酯Methyl caproate 3-羟基丁酸乙酯3-Hydroxybutyl acetate丁酸异丁酯Isobutyl butyrate 2-己烯酸甲酯Methyl 2-hexenoate丁酸丁酯Butyl butyrate正己酸乙酯1-Hexyl acetate 3-甲硫基丙酸甲酯Methyl 3-methylthiopropionate乙酸己酯Hexyl acetate丁酸异戊酯Isopropyl butyrate-----2.03 17.48 4.39 0.37 0.19 16.76 4.36--25.76 9.99-0.36 928-96-1 928-96-1 928-95-0 111-27-3 111-70-6 470-82-6 111-87-5 60-12-8 106-22-9 6191-71-5 71-41-0 2398-93-2 10482-56-1 14.583 10.385 9.487 15.134 19.753 22.771 15.185 25.471 29.963 19.453 10.948 14.798 28.82 C6Hl2O C6H12O C6H12O C6H14O C7H16O C10H18O C8H18O C8H10O C10H20O C7H14O C5H12O C7H14O C10H18O 1.07 4.94 69.49 31.85 1.05 16.20 2.40----------62.86 23.43 10 11 12 13 14 15 16 17 18---0.29 1.02-41.55 0.59 2.70--13.40 0.65 2.31-88.80-1.44 0.31-0.22-0.78 0.37 4.52-0.460.32 0.45-0.21-------------19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 141-78-6 105-37-3 623-42-7 623-43-8 97-62-1 105-54-4 123-86-4 624-24-8 108-64-5 123-92-2 624-41-9 105-66-8 539-82-2 106-70-7 5405-41-4 539-90-2 2396-77-2 109-21-7 123-66-0 13532-18-8 6.529 8.971 9.379 10.548 10.647 12.259 12.804 13.131 14.554 15.521 15.644 16.391 16.491 17.573 17.766 19.041 19.213 20.783 20.93 21.494 C4H8O2 C3H5O2 C5H10O2 C5H8O2 C6H12O2 C6H12O2 C6H12O2 C6H12O2 C7H14O2 C7H14O2 C7H14O2 C7H14O2 C7H14O2 C7H14O2 C6H12O3 C8H16O2 C9H16O2 C8H16O2 C8H16O2 C5H10O2S--------17.34--1.53 1.59 0.81 621.80-5.06---0.11 1.13-0.18 8.41 0.09 1.39-0.81 1.04-288.10 1.57 203.80 0.66 0.25 0.75 0.76-0.80 0.98 1.44 0.93 2.20----6.72 0.06 438.80-1.88--------1.84 1.00 162.70-2.70 1.25 42.14 54.99 2.24--------3.04 0.57 22.00--1.99-0.52---31.15---0.24 0.06-0.19 0.11-0.16-1.60 5.36-14.40 59.08 39 40 142-92-7 106-27-4 21.622 23.55 C8H16O2 C9H18O2--2.09 9.06 1.04 0.10 2.99----

表2 (续) Table 2 (Continued)

序号Serial number CAS号CAS number名称Name保留时间Retention time/min分子式Molecular formula ρ/(μg·L-1)徐香Xuxiang海沃德Hayward华优Huayou金艳Jinyan红阳Hongyang 41 42 43 44 45 46 47 48 49 50 51 52 53 93-58-3 111-11-5 105-79-3 93-89-0 106-32-1 2198-61-0 110-38-3 110-19-0 623-70-1 624-41-9 5837-78-5 2639-63-6 2315-68-6 24.783 26.2 27.358 27.848 28.846 30.693 34.895 11.2 13.887 8.658 18.234 28.76 31.179 C8H8O2 C9H18O2 C10H20O2 C9H10O2 C10H20O2 C11H22O2 C12H24O2 C6H12O2 C6H10O2 C6H12O2 C7H12O2 C10H20O2 C10H12O2 29.24 42.77--苯甲酸甲酯Methyl benzanoate辛酸甲酯Octyl acetate己酸异丁酯Isobutyl hexanoate苯甲酸乙酯Ethyl benzoate辛酸乙酯Ethyl octanoate己酸异戊酯Isopropyl hexanoate癸酸乙酯Decyl acetate乙酸异丁酯Isobutyl acetate巴豆酸乙酯Ethyl crotonate 2-甲基丁基乙酯2-Methylbutyl acetate惕各酸乙酯Tetradecanoic acid ethyl ester丁酸己酯Hexyl butyrate苯甲酸丙酯Methyl 3-methylthiophenylpropionate苯甲酸丁酯Butyl benzoate丁酸苯乙酯Phenyl ethyl butyrate丙酸甲酯Methyl propionate 2-甲基丁酸甲酯Methyl 2-methylbutyrate肉豆蔻酸异丙酯Isopropyl myristate 2-甲基丁酸乙酯Ethyl 2-methylbutyrate甲酸己酯Hexanoic acid formate 2-甲基丁酸丙酯Propyl 2-methylbutyrate 2-糠酸甲酯Methyl furan-2-carboxylate酸类Acids己酸Hexanoic acid异戊酸Isovaleric acid乙酸Acetic acid苯甲酸Benzoic acid醛酮类Aldehydes and ketones乙醛Acetaldehyde异丁醛Isobutyraldehyde 3-羟基-2-丁酮3-Hydroxy-2-butanone 2-己烯醛2-Hexenal反式-2-己烯醛(Z)-2-Hexenal 2-庚酮2-Heptanone苯甲醛Benzaldehyde 3-辛酮3-Octanone 2-辛酮2-Octanone癸醛Decanal大马士酮Damascenone 2-戊酮2-Pentanone己醛Hexanal异戊醛Isovaleraldehyde 2-甲基丁醛2-Methylbutanal苯乙醛Phenylacetaldehyde 2,3-丁二酮2,3-Butanedione 15.97-----11.86 58.50-0.93 31.36 3.89 0.92 0.53 0.42 2.83 1.90 0.48 4.56 0.63 1.30-1.00 0.16 0.74 0.54 0.21 0.70 0.29 1.86 0.70 0.20------------------------13.35-0.75--------0.480.19 54 55 56 57 58 59 60 61 62 136-60-7 103-52-6 554-12-1 868-57-5 110-27-0 7452-79-1 629-33-4 37064-20-3 611-13-2 34.217 35.923 6.818 11.335 44.404 14.381 15.125 18.68 19.283 C11H14O2 C12H16O2 C4H8O2 C6H12O2 C17H34O2 C7H14O2 C7H14O2 C8H16O2 C6H6O3 0.74 0.38---------------2.59 1.05 0.36 21.96 25.22 2.77 0.83 63 64 65 142-62-1 503-74-2 64-19-7 20.628 14.225 6.411 C6H12O2 C5H10O2 C2H4O2 7.95 0..48 1.28------------0.11---6665-85-027.305C7H6O2-2.75 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 75-07-0 78-78-4 513-86-0 505-57-7 6728-26-3 110-43-0 100-52-7 106-68-3 111-13-7 112-31-2 23726-93-4 107-87-9 66-25-1 590-86-3 96-17-3 122-78-1 431-03-8 4.555 6.844 8.539 13.671 13.971 15.918 18.707 20.318 12.481 29.076 34.686 8.102 11.951 7.285 7.538 22.297 6.207 C2H4O C4H8O C4H8O2 C6H10O C6H10O C7H14O C7H6O C8H16O C8H16O C10H20O C13H18O C5H10O C6H12O C5H10O C5H10O C8H8O C4H6O2--3.43 0.43 0.23 1.25----------------1.55---1.18 92.28----1.18 93.86--------0.32 1.80----------0.65 0.16-----0.23-0.33 0.56-0.19-1.23 0.30 0.17 0.43-0.41-0.25 0.52-0.20 0.36 0.11---0.15------------

表2 (续) Table 2 (Continued)

序号Serial number CAS号CAS number名称Name保留时间Retention time/min分子式Molecular formula ρ/(μg·L-1)徐香Xuxiang海沃德Hayward华优Huayou金艳Jinyan红阳Hongyang 841576-87-010.016C5H8O ----1.14 85 86 87 1111-78-0 100-42-5 1124-20-5 4.308 16.104 24.987 CH6N2O2 C8H8 C10H12 10.91 5.93 2.47--3.15 3.57 2.62 3.84----0.84 88 89 90 91 464-17-5 96-76-4 629-59-4 3033-23-6 30.32 37.759 32.673 25.973 C10H16 C14H22O C14H30 C10H18O 0.48 0.51-1.04-----0.09 0.17 0.05---0.73-92 93 94 109-66-0 527-84-4 99-87-6反式-2-戊烯醛(Z)-2-Pentenal其他Others氨基甲酸铵盐Ammonium carbamate苯乙烯Styrene 1-异丙烯基-3-甲基苯1-Isopropenyl-3-methylbenzene 2-莰烯2-Carene 2,4-二叔丁基苯酚2,4-Di-tert-butylphenol十四烷Tetradecane(2S-顺)-四氢化-4-甲基-2-(2-甲基-1-丙烯基)-2H-吡喃(2S-trans)-Tetrahydro-4-methyl-2-(2-methyl-1-propene)-2H-pyran正戊烷1-Pentane邻异丙基甲苯O-Isopropyl toluene 4-异丙基甲苯4-Isopropyl toluene 6.828 22.458 22.367 C5H12 C10H14 C10H14-----------2.88 0.58------4.07

在酯类物质方面,猕猴桃原汁中的主要酯类物质包括丁酸乙酯、丁酸甲酯、己酸甲酯、正己酸乙酯。其中,丁酸乙酯在徐香、海沃德、红阳猕猴桃原汁中含量较高,呈现清淡而舒爽的多种甜果香。丁酸甲酯、己酸甲酯、正己酸乙酯常伴随菠萝、香蕉、苹果、奶油香等气息,为猕猴桃的果香轮廓提供基础。酸类物质在猕猴桃原汁中的含量较低,但其对口感有一定的平衡作用。在海沃德和华优猕猴桃中检测到乙酸,乙酸适量贡献清香风味。此外,海沃德中还检测到己酸和异戊酸,红阳中检测到苯甲酸,华优中仅检测到微量乙酸。这些酸类物质虽含量不高,但与其他挥发性成分协同作用,共同构建了猕猴桃果实清新、酸爽、果香与甜香等多样化的香气层次,形成了复杂的风味复合体系。醛酮类物质在猕猴桃原汁中的含量较低,其中乙醛、己醛、苯甲醛和庚醛等物质可能对酒体的风味有一定影响。乙醛呈现青香和碰伤苹果香,己醛则有果香、青草香和叶香。部分猕猴桃原汁中还检测到了2-辛酮,具有水果香和花香。

2.3 OAV分析

基于SPME-GC-MS 分析的各成分含量,参考《化合物香味阈值汇编(第二版)》[24],并结合文献中的香气阈值[25-30],得到OAV 值大于1 的成分如表3所示。

表3 5 种猕猴桃挥发性成分香气描述及对应OAV
Table 3 Aroma descriptions and corresponding OAV(odor activity value)of volatile compounds in five kiwifruit varieties

序号Serial number名称Name阈值Threshold/(mg·m-³)香气活力值OAV徐香Xuxiang海沃德Hayward华优Huayou金艳Jinyan红阳Hongyang 123456789 44.4-正丁醇1-Butanol异戊醇Isoamyl alcohol 2-甲基-1-丁醇2-Methyl-1-butanol叶醇Leaf alcohol反-3-己烯醇(Z)-3-Hexenol反-2-己烯醇(Z)-2-Hexenol正己醇1-Hexanol庚醇Heptanol桉叶油醇Eucalyptol 1-辛醇1-Octanol苯乙醇Phenylethanol香茅醇Citronellol 1-戊醇1-Pentanol顺-4-庚烯-醇(Z)-4-Heptenol乙酸乙酯Ethyl acetate丁酸甲酯Methyl butyrate 2-丁烯酸甲酯Methyl 2-butenoate异丁酸乙酯Ethyl isobutyrate丁酸乙酯Ethyl butyrate乙酸丁酯Butyl acetate戊酸甲酯Methyl valerate异戊酸乙酯Ethyl isovalerate乙酸异戊酯Isoamyl acetate丁酸丙酯Propyl butyrate戊酸乙酯Ethyl valerate己酸甲酯Methyl caproate 3-羟基丁酸乙酯3-Hydroxybutyl acetate丁酸异丁酯Isobutyl butyrate 2-己烯酸甲酯Methyl 2-hexenoate丁酸丁酯Butyl butyrate正己酸乙酯1-Hexyl acetate 3-甲硫基丙酸甲酯Methyl 3-methylthiopropionate乙酸己酯Hexyl acetate丁酸异戊酯Isopropyl butyrate苯甲酸甲酯Methyl benzanoate辛酸甲酯Methyl octanoate苯甲酸乙酯Ethyl benzoate辛酸乙酯Ethyl octanoate己酸异戊酯Isopentyl hexanoate乙酸异丁酯Isobutyl acetate巴豆酸乙酯Crotonic acid ethyl ester 2-甲基丁基乙酯2-Methylbutyl acetate苯甲酸丙酯Propyl benzoate苯甲酸丁酯Butyl benzoate丁酸苯乙酯Phenylethyl butyrate丙酸甲酯Methyl propionate 0.078 0.006 0.14 0.013 0.004 0.04 0.034 0.023 0.003 1 0.022 0.012 0.1 0.153 0.000 5 0.88 0.03 0.1 0.000 11 0.000 053 0.01 0.011 0.000 069 0.018 0.058 0.000 58 0.13 0.5 0.009 4 0.05 0.028 0.003 0.05 0.017 0.07 0.001 5 0.5 0.05 0.04 0.2 0.028 0.05 0.05 0.001 5 0.001 5 0.001 5 0.35-1.0--26.0 2 913.0 31.4-------82.3 1 235.0 1 737.3 937.6 45.6 5 226.5 19.1 1 571.5 688.4 4 293.0 71.4 22.3 255.0-1 227.0 25.7 87.9--4 322.6 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46--------376.7--2 793.0 31.1 5.0 577.5-2 614.0-464.5 14.1-2.2 5.1---74.0 19.7-------51.0 15.9 7.4 11 705 660.0-460.5--37.7-1 636.0 158 113.0 9.0 2.9-1.58 27.0 1.18 9 603.3 142.7 3 842 264.0 66.0 22.7 10 869.0 42.2 13.8 1 690.6 11.1 1.9 233.0----126 230.0 6.0 8 272 075.0-170.0------31.7 1 724.1 1 257.7-286.2 25.0 1 505.0 18 330.0 44.8-------52.4 982.8 169.2--211.8-18.6---10 383.3-123.5 129.4 39 000.0-627.2 97.2 4.6 15.0 56.6 38.0 420.0 493.3 253.3---514.3 19 693.3--13.3-327.6 0.8-17.0-57.1 1 786.7-176.5---19 493.3 85.5-296.5-----------61.2 1.4 866.7-3.2 18.5 2.7 5.8 46.5 3.5--------------10 646.7 1.0-333.8-752.1-4.2 300.0 333.3 500.0 7.4

表3 (续) Table 3 (Continued)

序号Serial number名称Name阈值Threshold/(mg·m-³)香气活力值OAV徐香Xuxiang海沃德Hayward华优Huayou金艳Jinyan红阳Hongyang 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 11.7 0.5 0.45 0.2 0.004 8 0.001 8 0.000 15 0.62 0.002 7 0.001 0.1 0.79 0.085 0.001 3 0.23 0.002 6 0.000 125 0.35 0.23 0.000 35 0.1 0.000 72 0.000 18 0.3 0.1 0.17 0.004---------------2-甲基丁酸乙酯2-Methylbutyrate甲酸己酯Hexanoic acid formate 2-甲基丁酸丙酯2-Methylbutyl propionate 2-糠酸甲酯Methyl furan-2-carboxylate己酸Hexanoic acid异戊酸Isovaleric acid乙酸Acetic acid苯甲酸Benzoic acid乙醛Acetaldehyde异丁醛Isobutyraldehyde 3-羟基-2-丁酮3-Hydroxy-2-butanone反式-2-己烯醛(Z)-2-Hexenal苯甲醛Benzaldehyde 3-辛酮3-Octanone 2-辛酮2-Octanone癸醛Decanal大马士酮Damascenone 2-戊酮2-Pentanone己醛Hexanal异戊醛Isovaleraldehyde 2-甲基丁醛2-Methylbutanal苯乙醛Phenylacetaldehyde 2,3-丁二酮2,3-Butanedione氨基甲酸铵盐Ammonium carbamate 1-异丙烯基-3-甲基苯1-Isopropenyl-3-methylbenzene 2,4-二叔丁基苯酚2,4-Di-tert-butylphenol(2S-顺)-四氢化-4-甲基-2-(2-甲基-1-丙烯基)-2H-吡喃(2S-trans)-Tetrahydro-4-methyl-2-(2-methyl-1-propene)-2Hpyran正戊烷1-Pentane邻异丙基甲苯O-Isopropyl toluene 1.9 50.4 6.15 4.15 1 656.3 266.7 8 533.3----------1 000.0 4.4 3 430.0 733.3-159.3 230.0 12.5----------15.5---116.0--118.2---3.76----692.3----------5 200.0 1-----192.3 226.1-1 600.0 1.0 478.3---36.378.23-3.0 260.0 253.8 243.5-1 520.0-5 348.7 868.6 1.7 597.2-10.5 833.3 8.7------------8.4---73 74 75 0.5 0.005-------5.7 116.0-1-------

在猕猴桃原汁研究中,香气活力值(odor activity value,OAV)是评估挥发性化合物对香气贡献的重要指标。通常,OAV 值大于1 的化合物被认为是关键香气成分,对整体风味具有显著影响[31]。通过对OAV的计算,可以精准确定特定挥发性化合物的贡献,从而深入解析猕猴桃原汁的香气特征。这一指标在风味研究中发挥了不可或缺的作用,为香气特征分析提供了科学依据。

表3 数据显示,5 种猕猴桃原汁中共检测到75种OAV>1 的挥发性成分,其中徐香猕猴桃原汁含27 种,海沃德猕猴桃原汁含40 种,华优猕猴桃原汁含32 种,金艳猕猴桃原汁含31 种,红阳猕猴桃原汁含28 种。丁酸乙酯和辛酸乙酯为所有猕猴桃品种共有的关键挥发性成分,特别是丁酸乙酯,其OAV均大于100 000,具有浓郁的水果香气,是猕猴桃中的关键成分,这与赵玉等[32]对不同猕猴桃品种的关键香气成分的分析结果一致,丁酸乙酯在5 种猕猴桃中均被认为是主要的挥发性成分,并呈现出强烈的果香。

徐香猕猴桃原汁中OVA>5000 的挥发性成分包括桉叶油醇、丁酸乙酯、正己酸乙酯和苯甲酸甲酯;OVA>10的独有挥发性成分为2-丁烯酸甲酯、2-己烯酸甲酯、3-甲硫基丙酸甲酯和癸醛,其中癸醛OVA 值最高,具有独特的自然、清新香气。与徐香猕猴桃相比,海沃德猕猴桃中丁酸乙酯的OVA值约为前者的3 倍。海沃德猕猴桃原汁中OVA>5000的成分包括丁酸乙酯、异戊酸乙酯、正己酸乙酯、苯甲酸甲酯、乙酸和大马士酮;OVA>10 的独有成分为苯乙醇、顺-4-庚烯醇、异戊酸乙酯、巴豆酸乙酯、己酸、异戊酸和(2S-顺)-四氢化-4-甲基-2-(2-甲基-1-丙烯基)-2H-吡喃,其中异戊酸乙酯OVA 值明显高于其他独有成分,具有果香和花香特征。华优猕猴桃原汁中OVA>5000 的成分为丁酸乙酯和己醛,OVA>10 的独有挥发性成分包括异戊醛、苯乙醛、邻异丙基甲苯和乙醛,其中异戊醛OVA 值较大,具有香蕉和葡萄香气。金艳猕猴桃原汁中OVA>5000的成分为丁酸乙酯,OVA>10的独有挥发性成分仅有2,3-丁二酮,呈现黄油香和奶油香。红阳猕猴桃原汁中OVA>5000的成分包括丁酸乙酯、丁酸甲酯、正己酸乙酯和苯甲酸甲酯;OVA>1的独有成分为2-甲基丁酸乙酯、甲酸己酯、2-甲基丁酸丙酯、2-糠酸甲酯、苯甲酸和1-异丙烯基-3-甲基苯,其中甲酸己酯OVA值最高,散发浓郁的水果香味。

2.4 电子鼻分析结果

为验证不同猕猴桃品种的风味差异,使用电子鼻的传感器确定猕猴桃的风味成分分类。响应强度雷达图(图2)所示,海沃德、华优、金艳猕猴桃的传感器响应度较低,雷达线几乎重合。W5C(芳香-烷基型)、W3C(芳香型)、W2S(醇类、醛酮类)传感器响应强度对红阳和徐香猕猴桃响应度较高。W1W(硫-有机型)传感器对所有猕猴桃响应强度相对较低,这可能基于猕猴桃品种挥发性硫-有机型较少。徐香猕猴桃和红阳猕猴桃传感器响应度较高,但徐香猕猴桃在各传感器响应度都高于其他品种。以上结果说明电子鼻可以有效地区分不同猕猴桃间的气味物质差别。

图2 5 种猕猴桃的电子鼻分析结果Fig.2 Electronic nose analysis results of five kiwifruit varieties

2.5 挥发性成分含量PCA、PLS-DA和组合热图分析

PCA主成分结果如图3-a所示,PC1和PC2的方差贡献率分别为82%和16%,累计贡献率超过90%,最初的两个主成分能够有效地捕捉样品中的大部分信息,具有较高的参考价值[33]。结合PLSDA 图(图3-b),足以反映不同猕猴桃中挥发性化合物的显著差异。由热力组合图(图3-c)可知,丁酸甲酯、丁酸乙酯、反式-2-己烯醛、己酸甲酯、正己醇、反-2-己烯醇是5种猕猴桃所有挥发性物质平均含量较大的一组。不同猕猴桃品种聚集成不同区间,表明各品种之间的挥发性成分存在显著差异。华优和海沃德猕猴桃在图中组间距离近说明挥发性物质上差异较小,丁酸乙酯是海沃德、徐香、红阳猕猴桃共同且组内含量最多的挥发性物质。

图3 5 种猕猴桃挥发性风味成分PCA(a)、PLS-DA 图(b)及组合热图(c)
Fig.3 PCA(a),OPLS-DA plots(b),and heatmap(c)of volatile flavor components in five kiwifruit varieties

图3 (续) Fig.3 (Continued)

2.6 感官评价

采用感官评价分析了猕猴桃的香气特征和感官特征的差异,采用花香、草本气息、香甜感、苹果香、杏香、浆果香、清新感、橙香等11个描述词对样品的香气特征进行分析,结果如图4 所示,5 种猕猴桃的花香、浆果香、橙香较为明显,徐香猕猴桃虽然挥发性成分浓度较高,但可能基于醇类、醛类不平衡造成香气错位。海沃德猕猴桃的清新感、草本气息突出,综合来看香气丰富且平衡。海沃德猕猴桃成熟晚,同时是所有猕猴桃中最耐贮存的,脆绿色的果肉吃起来味道清甜,挥发性物质含量也是本试验检测最高的,适合成为猕猴桃果酒专用原料。

图4 5 种猕猴桃的描述性感官评价
Fig.4 Descriptive sensory evaluation of five kiwifruit varieties

3 讨 论

猕猴桃起源于中国,历史悠久。因其果实富含维生素C、矿物质和纤维素等营养成分,被誉为“水果之王”,具有极高的经济价值[2]。目前,关于猕猴桃果酒提升香气的研究大多集中在不同酵母发酵后释放的风味物质,认为酵母菌种的差异会使同一品种水果发酵的果酒具有不同的香味品质,近年来也有通过其他处理来研究猕猴桃品种酒香气风味[9,34],而忽视了原料猕猴桃品种香气风味的研究。尽管目前有不同品种猕猴桃香气成分的研究,但由于研究对象数量少、研究深度不够等问题,不足以支撑专用酿酒原料的选择。

SPME-GC-MS 法凭借无需溶剂、简便操作、高效提取和高选择性等特点,广泛应用于挥发性成分的测定[9]。笔者在本研究中鉴定了94种挥发性化合物,其中包括18 种醇类、44 种醛类、4 种酸类、18 种醛酮类和其他10 种成分。醇类和醛类化合物在猕猴桃香气成分中占比较大,与Lan 等[17]的研究结果一致。海沃德猕猴桃原汁含有48种挥发性化合物,居所有品种之最,而徐香猕猴桃则具有最高的挥发性化合物总含量。

从含量上看,丁酸乙酯含量在海沃德、徐香和红阳猕猴桃中最高,而正己醇则在华优和金艳猕猴桃中含量较高。根据OAV>1 的分析,丁酸乙酯和辛酸乙酯被确定为5 种猕猴桃品种的共性标志性成分,赋予猕猴桃以果香和类似白兰地的气味。Vítová等[35]研究表明,OAV值大于1的成分中,丁酸乙酯、辛酸乙酯、乙酸甲酯、乙酸乙酯、乙醇和乙醛是猕猴桃香气的重要来源。这表明丁酸乙酯和辛酸乙酯可能是猕猴桃香气特征的关键成分,并且它们可能共同作用,增强猕猴桃的水果香气。

电子鼻是一种快速的气体检测技术,虽然目前关于电子鼻在猕猴桃香气分析中的应用研究较少,但它已被用于不同品种猕猴桃间挥发性物质的差异分析。电子鼻传感器对W5C(芳香-烷基型)、W3C(芳香型)、W2S(醇类、醛酮类)等传感器的响应值主要反映了猕猴桃的挥发性物质差异,主要呈味物质包括醇类、酯类、醛酮类和芳香族化合物。这与Zhang 等[10]对3 种猕猴桃及其果酒香气的电子鼻检测结果相似。根据SPME-GC-MS的结果显示,醛类和酯类化合物是所有猕猴桃品种中含量最高的挥发性成分,这与电子鼻检测中W5C(芳香-烷基型)、W3C(芳香型)以及W2S(醇类、醛酮类)传感器在各猕猴桃品种中表现出的较高响应强度相一致。同时,W1W(硫-有机型)传感器的响应强度相对较低,这表明硫-有机型化合物在猕猴桃香气成分中含量较少,这一结论也得到了SPME-GC-MS测定数据的支持,即硫-有机型化合物种类很少且浓度较低。电子鼻传感器中响应度最高的是徐香猕猴桃,这意味着该品种含有最高浓度的挥发性成分。这一结论得到了SPME-GC-MS测定的佐证,分析显示徐香猕猴桃的挥发性成分质量浓度达到1 226.083 μg·L-1,明显高于其他品种。然而,在感官分析中,海沃德猕猴桃的醇类和酯类平衡性更为突出,而徐香猕猴桃可能因某些成分浓度过高,导致香气错位,总体来说带给人的香气不如海沃德。不同猕猴桃品种在挥发性物质含量上的差异,主要由遗传背景、果实成熟过程、代谢途径、环境因素和果实结构等因素共同作用,导致了各品种香气和风味的多样性[36-37]

4 结 论

笔者采用SPME-GC-MS 法联合电子鼻全面分析了5种猕猴桃香气成分,结果表明,猕猴桃香气来源丰富,不同品种猕猴桃挥发性成分差异较大,丁酸乙酯是5 种猕猴桃共有的贡献度最大的挥发性成分,通过PCA、PLS-DA、组合热图及OVA分析,丁酸乙酯和正己醇被确定为猕猴桃的关键挥发性物质。

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Multi-method evaluation of volatile flavor compounds in five kiwifruit varieties

ZENG Shuo1,GUO Xinyu2,NIU Dongsheng1,LI Feng1*
(1College of Food Science and Pharmacy, Xinjiang Agricultural University, Urumqi 830052, Xinjiang, China;2College of Food Science and Engineering,Northwest A&F University,Yangling 712100,Shaanxi,China)

Abstract:【Objective】Fruit wine, as a food of fruit processing, not only enhances the flavor diversity of kiwifruit but also increases its biological activity, leading to the production of kiwifruit wine with a unique flavor,combined fruit with wine aromas,and rich nutrition.The aroma of fruit is a key factor affecting the quality of fruit wine,as it directly impacts the wine's aroma and overall quality.The primary aroma of fruit wine is determined by the fruit variety and origin.However,due to the lack of specialized kiwifruit varieties,the current kiwifruit wines often exhibit such shortcomings as a sour taste,flat aroma,and unbalanced flavor, which restrict the high-quality development of the kiwifruit wine industry. The purpose of this study is to provide a valuable theoretical foundation for the fermentation process of kiwifruit wine and the selection of specialized brewing materials.【Methods】In this study,five kiwifruit varieties (Xuxiang, Hayward, Huayou, Jinyan, and Hongyang) were selected as raw materials.The volatile components of these five kiwifruit varieties were determined using the solid-phase microextraction(SPME) combined with the gas chromatography-mass spectrometry (GC-MS) and chemometrics. The volatile components were compared, and an electronic nose was employed to distinguish the odor substances among the different kiwifruits.The aroma activity value(OAV)was used to assess the contribution of volatile components to the overall aroma,and sensory analysis was performed to describe the olfactory sensations induced by the different kiwifruit aromas.The volatile components of these five kiwifruits were analyzed using SPME-GC-MS,electronic nose technology,and chemometric methods.【Results】In the electronic nose test,the sensor responses of Hayward,Huayou,and Jinyan kiwifruits were weak,with their radar plots nearly overlapping.In contrast,the W5C,W3C,and W2S sensors of Hongyang and Xuxiang kiwifruits showed strong responses, while the W1W sensor had relatively low response intensity across all varieties.Among the five varieties,Xuxiang kiwifruit exhibited the strongest responses to all sensors,which corresponded to the highest concentration of volatile substances,particularly alcohols and esters.The electronic nose proved to be very effective in distinguishing the odor substances of different kiwifruit varieties.Through SPME-GC-MS analysis,94 volatile compounds were detected,including 18 alcohols,44 aldehydes,4 acids,18 aldehydes and ketones,and 10 other compounds.The Xuxiang kiwifruit juice contained 29 volatile compounds,Hayward 48 compounds,Huayou 42 compounds,Jinyan 42 compounds,and Hongyang 28 compounds.Among these,alcohols such as 2-methyl-1-butanol,isoamyl alcohol,phenylethanol,hexanol,and eucalyptus oil were the most abundant.Esters included methyl benzoate, ethyl octanoate, ethyl hexanoate, and ethyl isovalerate, while acids such as 2-methylbutyric acid,octanoic acid,and benzoic acid were present in relatively high concentrations.Aldehydes and ketones such as acetaldehyde, benzaldehyde, hexanal, and trans-2-hexenal were also abundant. These compounds are considered key contributors to the characteristic aroma of kiwifruit. Moreover,75 compounds had an odor activity value(OAV)greater than 1,with Xuxiang kiwifruit juice containing 27 such compounds,Hayward 40,Huayou 32,Jinyan 31,and Hongyang 28.Among the volatile substances with an OAV greater than 1, butyl acetate and ethyl octanoate were present in all five kiwifruit varieties,playing significant roles in enhancing the fresh,fruity,and tropical aromas.Principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) revealed significant differences in the volatile components across the five kiwifruit varieties.The heatmap further indicated that ethyl butyrate,butyl acetate,trans-2-hexenal,methyl caproate,n-hexanol,and trans-2-hexenol were present in high concentrations across all varieties.Ethyl butyrate was the most abundant volatile compound in Hayward,Xuxiang,and Hongyang kiwifruits,while butyl acetate and n-hexanol were most abundant in Hayward, Xuxiang, and Hongyang kiwifruits. Huayou and Jinyan kiwifruits showed higher concentrations of n-hexanol.Sensory evaluation and electronic nose data suggested that Hayward kiwifruit,which contained the most volatile components,performed best in descriptive terms,being rich in alcohols and esters,with a balanced presence of acids and aldehydes and ketones,resulting in a pleasant aroma.【Conclusion】Butyl acetate and n-hexanol are the key volatile compounds that enhance the complexity and overall flavor characteristics of kiwifruit.Hayward kiwifruit is recommended as the optimal raw material to enrich the aroma profile in kiwifruit wine production.

Key words:Kiwifruit;Principal component analysis;Solid-phase microextraction-gas chromatographymass spectrometry;Flavoromics;Aroma vigor value

中图分类号:S663.4

文献标志码:A

文章编号:1009-9980(2025)07-1518-14

DOI:10.13925/j.cnki.gsxb.20250100

收稿日期:2025-03-03

接受日期:2025-03-20

基金项目:23年天池英才引进计划-青年博士(2223RSTTCYC)

作者简介:曾硕,男,在读本科生,研究方向为食品质量与安全。E-mail:2273039035@qq.com

*通信作者Author for correspondence. E-mail:18089209017@163.com