发芽及挤压膨化对糙米挥发性风味物质的影响

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陈焱芳^,, 张名位, 张雁^,, 邓媛元, 魏振承, 唐小俊, 刘光, 李萍广东省农业科学院蚕业与农产品加工研究所/农业农村部功能食品重点实验室/广东省农产品加工重点实验室,广州 510610

Effects of Germination and Extrusion on Volatile Flavor Compounds in Brown Rice

CHEN YanFang^,, ZHANG MingWei, ZHANG Yan^,, DENG YuanYuan, WEI ZhenCheng, TANG XiaoJun, LIU Guang, LI PingSericultural & Agri-Food Research Institute, Guangdong Academy of Agricultural Sciences/Key Laboratory of Functional Foods, Ministry of Agriculture and Rural Affairs/Guangdong Key Laboratory of Agricultural Products Processing, Guangzhou 510610

通讯作者: 张雁,E-mail： zhang__yan_@126.com

责任编辑: 赵伶俐
收稿日期:2020-05-8接受日期:2020-08-31网络出版日期:2021-01-01

基金资助:

国家重点研发计划.2017YFD0400502
国家重点研发计划.2018YFD0401101-03
广州市科技计划.201807010061
广东省科技计划.2018A050506049
广东省重点领域研发计划.2020B020225004
广东省特支计划.2019BT02N112

Received:2020-05-8Accepted:2020-08-31Online:2021-01-01
作者简介 About authors
陈焱芳,E-mail： chen.y.f@foxmail.com。

摘要
【目的】通过分析糙米经发芽和挤压膨化前后挥发性风味化合物的变化,探讨发芽及挤压膨化处理对糙米挥发性风味化合物的影响效应,为评价和提升糙米挥发性风味提供参考。【方法】以糙米及其经发芽、挤压膨化和发芽-挤压膨化处理的样品为试材,采用顶空固相微萃取-气相色谱-质谱联用（HS-SPME-GC-MS）的分析方法,通过NIST14质谱数据库比对以及保留指数（RI）分析对挥发性风味化合物进行鉴定,以内标法测定其含量,通过气相色谱-嗅闻法（GC-O）明确糙米样品气味活性化合物构成谱,分析其整体风味轮廓,评价糙米样品的挥发性风味特征。【结果】共鉴定出挥发性风味化合物28种,主要为醛类、醇类、萜烯类、酯类、杂环及芳香烃化合物。糙米经挤压膨化,醛类、杂环及芳香烃等化合物含量显著增加,醇类和萜烯类含量显著减少,新检出酯类物质;糙米经发芽处理,醇类含量有所增加,醛类、萜烯类、杂环及芳香烃化合物含量减少,未检出酯类物质;发芽糙米经挤压膨化,醛类、萜烯类、杂环及芳香烃化合物含量增加,醇类化合物的含量减少,新检出酯类物质,且发芽糙米经挤压膨化后,醛类、萜烯类、酯类和杂环化合物含量显著高于糙米。主成分分析结果表明,庚醛、壬醛、苯甲醛、D-柠檬烯、甲苯和2-乙酰-1-吡咯啉等化合物含量增加与挤压膨化处理密切相关,2-乙基-1-己醇和3-甲基丁醇含量增加与发芽处理密切相关,乙酸乙酯、乙酸丁酯、二甲基硫醚和吡啶含量增加与发芽-挤压膨化处理密切相关。GC-O结果表明,共检出19种气味活性化合物,其中气味强度值（OIV）≥3的为己醛、庚醛、正己醇、1-辛烯-3-醇、2-乙酰-1-吡咯啉和对二甲苯。风味轮廓分析表明,糙米中蜡质气味强度最高,青草及坚果气味次之,花香及果香气味较弱。糙米经挤压膨化,坚果、青草和果香气味强度明显增加,蜡质气味强度明显减弱;糙米经发芽处理,蜡质、坚果、青草和花香气味强度均降低,果香气味强度不变;发芽糙米经挤压膨化,坚果、蜡质、青草和果香气味强度均显著增加。【结论】发芽处理对糙米中醇类的形成有一定促进作用,而其他挥发性化合物含量均有不同程度降低,导致整体风味强度下降;但糙米在发芽过程中通过生化作用可能产生了挥发性风味前体物质,从而促进发芽糙米经挤压膨化形成更多的挥发性风味化合物。挤压膨化处理对糙米及发芽糙米中醛类、萜烯类、酯类、杂环及芳香烃等挥发性化合物的形成有明显促进作用,且发芽糙米挤压膨化后挥发性风味化合物的含量增加显著高于糙米,整体风味强度均上升,其中坚果和果香气味强度显著增加。
关键词： 糙米;挥发性风味化合物;发芽;挤压膨化;气相色谱-质谱;气相色谱-嗅闻

Abstract

【Objective】The objective of this study was to investigate the effects of germination and extrusion process on volatile flavor compounds of brown rice by analyzing changes of the volatile flavor compounds of brown rice, so as to provide a reference for evaluating and improving the volatile flavor of brown rice. 【Method】The volatile flavor compounds of raw brown rice (RBR), extruded brown rice (EBR), germinated brown rice (GBR) and extruded germinated brown rice (EGBR) were analyzed by headspace solid phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS). The qualitative and relative quantitative analyses of the volatile flavor components were carried out by NIST14 database, retention index (RI), and internal standard. Gas chromatography olfactory (GC-O) was used to analyze the composition spectrums of the active odor compounds and their overall flavor profile as well as the volatile flavor characteristics of brown rice samples. 【Result】 A total of 28 volatile flavor compounds were identified, including aldehydes, alcohols, terpenes, esters, heterocycles and arenes. After extrusion, the contents of aldehydes, heterocycles and arenes in brown rice were increased significantly, while the contents of alcohols and terpenes decreased significantly; moreover, new esters were detected after extrusion. After germination treatment, the content of alcohols was increased, while the contents of aldehydes, terpenes, heterocycles and arenes decreased; however, esters were undetected after germination treatment. After extrusion, the content of aldehydes, terpenes, heterocycles and arenes in germinated brown rice were increased, furthermore, while the content of alcohols decreased; moreover, new esters were detected. What’s more, the contents of aldehydes, terpenes, esters and heterocyclic compounds in germinated brown rice were significantly higher than those in brown rice after extrusion. The principal component analysis showed that the increases of the contents of compounds, such as heptanal, nonanal, benzaldehyde, D-limonene, toluene and 2-AP, were highly correlated with extrusion, while the increases in contents of 2-ethyl-1-hexanol and 3-methylbutanol were highly correlated with germination, and the increases in contents of ethyl acetate, butyl acetate, dimethyl sulfide and pyridine were highly correlated with germination-extrusion treatment. GC-O results showed that 19 kinds of active odor compounds were detected, with the odor intensity value (OIV) of some compounds’ over ≥ 3, such as hexanal, heptanal, hexanol, 1-octene-3-ol, 2-acetyl-1-pyrroline and p-xylene. The flavor profile analysis showed that the odor intensity of wax was the highest in brown rice, followed by those of grass and nut, while those of floral and fruity odor were the lowest. After extrusion, the nutty, grassy and fruity odor intensities of brown rice were increased significantly, in contrast, the waxy odor intensity decreased significantly. After germination, the waxy, nutty, grassy and floral odor intensities of brown rice were decreased, however, the fruit odor intensity did not change. After extrusion, the nutty, waxy, grassy and fruity odor intensities of germinated brown rice were increased significantly. 【Conclusion】Germination could improve the production of alcohols in brown rice, while it could decrease the contents of other volatile compounds to some extent, resulting in the decline of overall flavor intensity. However, during the process of germination, brown rice could produce volatile flavor precursors through biochemical action, which could promote the formation of more volatile flavor compounds by extrusion in germinated brown rice. Extrusion could have a positive effect on the formation of aldehydes, terpenes, esters, heterocycles and arenes in brown rice as well as germinated brown rice. Moreover, the volatile flavor compounds content in extruded germinated brown rice were significantly higher than those in extruded brown rice. The overall flavor intensities of both raw brown rice and germinated brown rice were increased after extrusion, with the most significant increase in the nutty and fruity odor intensities.

Keywords：brown rice;volatile flavor compounds;germination;extrusion;gas chromatography-mass spectrometry;gas chromatography-olfactory

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本文引用格式
陈焱芳, 张名位, 张雁, 邓媛元, 魏振承, 唐小俊, 刘光, 李萍. 发芽及挤压膨化对糙米挥发性风味物质的影响[J]. 中国农业科学, 2021, 54(1): 190-202 doi:10.3864/j.issn.0578-1752.2021.01.014
CHEN YanFang, ZHANG MingWei, ZHANG Yan, DENG YuanYuan, WEI ZhenCheng, TANG XiaoJun, LIU Guang, LI Ping. Effects of Germination and Extrusion on Volatile Flavor Compounds in Brown Rice[J]. Scientia Acricultura Sinica, 2021, 54(1): 190-202 doi:10.3864/j.issn.0578-1752.2021.01.014

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0 引言

【研究意义】糙米保留了米粒的米糠层、胚和胚乳,属于全谷物食品,不仅蛋白质、膳食纤维、维生素以及钙、铁、锌等重要矿物元素的含量显著高于精白米,还富含多酚、谷胱甘肽和γ-氨基丁酸等精白米中未检出或含量很低的活性成分,具有降血糖、降血脂、预防心脑血管疾病、改善新陈代谢及调节免疫等保健功效^[1,2,3,4,5]。随着我国生活质量的不断提高,营养均衡的饮食理念逐渐深入人心,作为世界上最大的稻米生产和消费国^[6],天然保健食品全谷物糙米的开发利用越来越受到重视^[7,8,9],改善糙米蒸煮性、消化性的加工技术也开始研发和推广^[2,10]。然而,影响糙米及其制品的关键挥发性风味成分长期以来未得到系统研究,有关全谷物糙米特征风味化合物的组成及其在加工过程中的变化少见报道。发芽及挤压膨化是目前糙米加工中应用较多的技术,有助于改善糙米的营养品质与消化特性,而有关发芽及挤压膨化对糙米挥发性风味物质影响的研究仍然比较欠缺。研究糙米经发芽及挤压膨化加工后,其挥发性风味化合物的变化规律,并分析糙米的整体风味轮廓,对改进糙米及其制品的挥发性风味感官品质具有参考意义。【前人研究进展】近年来,谷物发芽和挤压膨化技术得到了良好的推广应用。糙米发芽是提高其营养品质的天然过程,不仅可以将蛋白质、淀粉等大分子转化为更容易吸收的氨基酸、双糖、单糖等小分子营养物质,还能显著提高γ-氨基丁酸、烟酸及维生素B6等生理活性物质^[11,12]。关于发芽糙米挥发性风味的研究国内外有一些相关报道,WU等^[13]研究了不同发芽时间糙米蒸煮后挥发性化合物的含量变化,表明醛类和杂环化合物的含量先逐渐减少,发芽3 d后又逐渐增加。XIA等^[14]的研究表明,糙米发芽后总挥发性成分含量显著减少,而发芽糙米经高压处理后,其挥发性风味物质含量显著增加,特别是包括醛类、酮类和醇类在内的一些特征风味成分。糙米在挤压膨化过程中可发生分解、降解、变性和交联作用以及氧化、聚合、水解等各种化学反应^[15],其中,脂质和脂肪酸降解^[16]、糖类焦糖化^[17]、氨基酸Strecker降解^[18]以及还原糖和氨基酸的Maillard反应^[19]都可能形成挥发性风味化合物。HE等^[15]采用风味稀释法（AEDA）结合气相/嗅闻分析法（GC-O）分析了精白米和糙米在挤压膨化过程中挥发性风味化合物的变化,发现糙米中大部分挥发性风味化合物,尤其是2-乙酰-1-吡咯啉、1-辛烯-3-醇的风味稀释值（FD）显著高于精白米,挤压膨化显著提高了精白米和糙米挥发性风味化合物的FD值,对糙米中己醛、庚醛、辛醛、壬醛和癸醛等醛类挥发性风味化合物FD值的提升作用更为显著。方勇等^[20]探讨了金针菇-发芽糙米复配粉挤压膨化后挥发性物质的变化,结果表明发芽糙米经挤压膨化后挥发性化合物种类增加,有些醛类和醇类物质含量降低,吡嗪类含量增加,添加金针菇能够丰富和增强膨化产品的风味。张冬媛等^[21]在探讨速食糙米粉品质特性的过程中发现,发芽-挤压-淀粉酶协同处理可适当增加挥发性风味物质含量。【本研究切入点】目前,关于糙米挥发性风味的研究主要针对其蒸煮风味及糊粉类加工产品风味,糙米特征风味化合物的组成评价及其在加工过程中变化规律等方面的研究仍然比较欠缺,风味化学研究的不足阻碍了糙米及其制品感官品质的提升。【拟解决的关键问题】在前期优化建立的糙米挥发性风味化合物提取方法的基础上,系统分析发芽、挤压膨化、发芽-挤压膨化处理对糙米挥发性风味化合物含量、气味强度及其整体风味轮廓的影响。结合气相色谱-质谱（GC-MS）与气相色谱-嗅闻法（GC-O）分析糙米在发芽、挤压膨化及发芽-挤压膨化前后挥发性风味化合物的变化规律,通过主成分分析明确其气味活性化合物构成谱,采用风味轮廓分析评价其整体风味及特征,旨在为改善糙米及其制品的风味感官品质提供依据。

1 材料与方法

试验于2019年5月至2020年2月在广东省农业科学院蚕业与农产品加工研究所进行。

1.1 材料与试剂

糙米：购于黑龙江金都米业有限公司,品种为东农425,产自黑龙江方正县,于2018年10月收割,稻谷于当地当季常温贮藏。糙米样品均经过粉碎并过60目筛,分为4组：未经加工的全谷物生糙米（raw brown rice,RBR）、经挤压膨化处理的挤压膨化糙米（extruded brown rice,EBR）、经发芽处理的发芽糙米（germinated brown rice,GBR）、经发芽再挤压膨化处理的挤压膨化发芽糙米（extruded germinated brown rice,EGBR）;所有样品分析前均置于-18℃冷库冻藏。

C₅—C₂₅系列烷烃混标,上海安谱科学仪器有限公司;香芹酮标准品（色谱纯度>99%）,德国Dr.Ehrensorfer公司。

1.2 仪器与设备

固相微萃取手动进样手柄与50/30 μm DVB/CAR/ PDMS萃取头,美国Supelco公司;7890B/5977B MSD气相色谱-质谱联用仪,美国Agilent公司;嗅闻仪ODP3,德国Gerstel公司;20 mm钳口的100 mL透明顶空样品瓶,上海安谱科学仪器有限公司;HWCL-5集热式恒温磁力搅拌浴,郑州长城科工贸有限公司;LRHS-250-Ⅱ型恒温恒湿培养箱,上海跃进医疗器械有限公司;DS30-Ⅱ型双螺杆膨化机,山东赛信膨化机械有限公司。

1.3 试验方法

1.3.1 糙米发芽处理以生糙米为原料,参考文献方法^[10,22],略有修改。糙米经除杂清洗后用浓度为0.05%的次氯酸钠溶液浸泡30 min灭菌,再用蒸馏水漂洗数次后于28℃用0.05 mmol?L^-1 CaCl₂溶液浸泡24 h,糙米浸泡结束后用蒸馏水漂洗数次,转移糙米平铺于底部垫有双层纱布的浅槽容器中,糙米厚度约为5 mm,浅槽容器置于恒温恒湿培养箱避光催芽培养30 h（温度为29℃,相对湿度为95%）,期间不断喷洒蒸馏水保持糙米湿润。发芽结束后置于45℃热泵干燥箱干燥12 h。

1.3.2 糙米挤压膨化参考文献方法^[21],略有修改。调节物料水分含量约为14%,挤压机前端、中端和末端温度分别设置为60℃、98℃和134℃,螺杆转速29.6 Hz,挤出样品粉碎后过60目筛。

1.3.3 糙米挥发性风味化合物HS-SPME提取参考课题组前期研究,准确称取3.0000 g挤压膨化糙米粉,加入21 mL饱和NaCl溶液于体积为100 mL的顶空样品瓶中,放入转子后钳紧瓶盖。顶空瓶立即放入恒温磁力搅拌浴中,平衡和萃取温度均为51℃,平衡20 min,然后插入SPME纤维头,顶空萃取44 min。萃取完毕后,立即将SPME纤维头插入GC-MS进样口,于250℃解吸5 min。

1.3.4 GC-MS分析条件色谱条件：HP-5MS型（30 m×250 μm×0.25 μm）毛细管柱;载气为高纯氦气（99.999%）;恒流恒压模式,流量为1.7 mL?min^-1,压力为13.3 Psi,不分流模式;进样口温度250℃;升温程序：初始温度40℃,保持5 min,以3℃?min^-1升至85℃,保持5 min,以5℃?min^-1升至130℃,保持1 min,以15℃?min^-1升至230℃,保持3 min,总运行时间约为45 min。

质谱条件：电子轰击离子源（EI）,电子能量70 eV;传输线温度250℃,离子源温度230℃,四极杆温度150℃,接口温度280℃;扫描质量范围35—400 m/z。

1.3.5 定性与定量分析

1.3.5.1 定性分析利用GC-MS联用仪工作站的自动解卷积系统（AMDIS）与NIST14质谱库结合化合物保留指数值（retention index,RI）对挥发性成分进行鉴定。

RI的测定：对C₅—C₂₅正构系列烷烃混合标样进行GC-MS分析,记录保留时间,根据程序升温公式计算各化合物的保留指数^[23]。

$RI=100n+\frac{100({{t}_{x}}-{{t}_{n}})}{{{t}_{n+1}}-{{t}_{n}}}$

式中：t_n和t_n+1为碳原子数为n和n+1的正烷烃流出峰保留时间（min）;t_x为被分析组分流出峰的保留时间（min）,且t_n<t_x<t_n+1。

1.3.5.2 内标法定量分析通过色谱峰面积计算挥发性化合物的含量,根据前期预实验,每个样品中加入稀释后的香芹酮标准品4.785 μg,样品中挥发性化合物含量的计算公式如下：

挥发性风味化合物的含量（μg?100 g^-1）=$\frac{{{S}_{1}}}{{{S}_{2}}\times {{m}_{1}}}\times {{m}_{2}}\times 100$

式中,S₁为待测化合物的色谱峰面积,S₂为内标物的色谱峰面积,m₁为样品干基质量（g）,m₂为内标质量（μg）。

1.3.6 糙米挥发性风味化合物GC-O分析

1.3.6.1 GC-O分析条件 HS-SPME提取的挥发性风味化合物进GC分析,以分流比为3﹕1分别进入嗅闻仪和质谱检测器,其他色谱条件同1.3.4。嗅闻仪嗅闻口温度为150℃,加湿氮气通入流速为60 mL?min^-1。

1.3.6.2 GC-O气味强度分析选取4名（2女2男,年龄介于23—28岁）有相关感官评价经验的人员组成感官评价小组。嗅闻气味时使用ODP3配套设备即时记录挥发性风味化合物的出峰时间、气味描述和气味强度。参考文献方法^[24]将气味强度由弱到强分为四级,分别以1、2、3、4分的形式表示气味强度值（odor intensity value,OIV）。气味持续时间较短且能准确识别出气味的强度记为1分,能快速准确识别气味记为2分,能准确识别气味且持续时间较长的记为3分,能快速识别气味且持续时间长的记4分。每个样品由4名不同人员嗅闻,将记录得分求平均值后取整数作为该样品的OIV。

1.3.7 数据统计与分析

含量数据以均值±标准差（Means±SD）表示,采用SPSS 20对GC-MS数据进行显著性差异分析和主成分分析（PCA）,不同英文字母表示差异显著P<0.05;采用Excel 2019、OriginPro 9.0对数据进行统计分析及制图。

2 结果

2.1 不同糙米样品挥发性风味化合物分析

4种样品中共鉴定出挥发性风味化合物28种,主要为醛类、醇类、萜烯类、酯类、芳香烃及杂环化合物（表1）。由于鉴定出的烷烃类化合物不具备气味活性,因此未列出。.

Table 1
表1
表1不同糙米样品的挥发性风味化合物及其含量
Table 1Volatile flavor compounds and their contents in different brown rice samples

编号 Number	化合物 Compounds	保留指数 Retention index		含量 Content (μg/100 g DW)				鉴定依据 Identification
编号 Number	化合物 Compounds	Ref.	Cal.	糙米 Brown rice	挤压膨化糙米 Extruded brown rice	发芽糙米 Germinated brown rice	挤压膨化发芽糙米 Extruded germinated brown rice	鉴定依据 Identification
	醛类 Aldehydes			235.42	783.82	201.57	1407.58
A1	3-甲基丁醛 Butanal, 3-methyl-	658	653	—	12.84±0.15a	—	47.1±1.04b	MS, RI
A2	戊醛 Pentanal	697	705	—	—	—	13.61±2.49a	MS, RI
A3	己醛 Hexanal	803	803	183.10±8.51a	612.88±26.20b	171.31±11.86a	1191.02±61.49c	MS, RI
A4	庚醛 heptanal	903	906	10.81±0.27a	29.79±1.15c	7.39±0.78a	24.33±2.00b	MS, RI
A5	苯甲醛 Benzaldehyde	960	966	—	8.38±1.19a	—	11.15±1.21a	MS, RI
A6	壬醛 Nonanal	1106	1109	36.35±3.48b	119.93±6.24c	19.67±1.52a	114.43±1.18c	MS, RI
A7	癸醛 Decanal	1206	1210	5.16±1.06ab	—	3.20±0.36a	5.94±0.24b	MS, RI
	醇类 Alcohols			133.75	11.11	144.22	73.60
B1	正丁醇 1-Butanol	676	667	16.14±1.6a	—	16.53±5.65a	65.22±10.86b	MS, RI
B2	3-甲基丁醇 1-Butanol, 3-methyl-	736	737	—	—	2.11±0.29a	—	MS, RI
B3	正己醇 1-Hexanol	870	873	108.37±4.54a	—	119.72±1.48b	—	MS, RI
B4	1-辛烯-3-醇 1-Octen-3-ol	984	985	7.22±0.15a	11.11±0.87b	—	8.38±1.01a	MS, RI
B5	2-乙基-1-己醇 1-Hexanol, 2-ethyl-	1031	1032	2.02±0.22a	—	5.86±0.16b	—	MS, RI
	萜烯类 Terpenes			59.45	13.09	6.07	190.98
C1	α-蒎烯 alpha-Pinene	935	937	3.59±0.21b	—	1.08±0.12a	8.35±0.69c	MS, RI
C2	4-乙基己烯 1-Hexene, 4-ethyl-		947	—	3.22±0.44a	—	—	MS
C3	β-蒎烯 beta-Pinene	987	980	1.60±0.03a	—	—	—	MS, RI
C4	D-柠檬烯 D-Limonene	1029	1028	—	9.87±0.24b	5.00±1.43a	—	MS, RI
C5	对薄荷-1(7),3-二烯 β-Terpinene	1056	1030	54.26±7.88a	—	—	182.63±9.57b	MS
	酯类 Esters			0.00	250.24	0.00	555.04
D1	乙酸乙酯 Ethyl acetate	621	625	—	245.44±1.02a	—	547.10±17.58b	MS, RI
D2	乙酸丁酯 Acetic acid, butyl ester	815	820	—	4.80±0.78a	—	7.94±2.12a	MS, RI
	芳香烃Arenes			82.04	494.45	5.43	106.73
E1	甲苯 Toluene	760	765	33.50±5.17b	366.58±0.47c	3.99±1.08a	37.76±2.21b	MS, RI
E2	乙苯 Ethylbenzene	858	863	8.26±1.29a	17.53±0.64b	—	8.12±0.16a	MS, RI
E3	对二甲苯 p-Xylene	867	867	11.80±0.39ab	48.92±6.43c	1.44±0.61a	21.01±0.36b	MS, RI
E4	邻二甲苯 o-Xylene	888	891	28.48±1.44a	61.41±0.27c	—	39.84±0.13b	MS, RI
	杂环化合物 Heterocyclic compounds			2.03	91.83	5.63	177.50
F1	吡啶 Pyridine	741	748	—	—	—	74.22±14.72a	MS, RI
F2	2-乙酰-1-吡咯啉 2-Acetyl-1-pyrroline	918	921	2.03±0.4a	4.87±1.56b	—	0.59±0.2a	MS, RI
F3	2-戊基呋喃 Furan, 2-pentyl-	992	994	—	80.97±1.94b	5.63±0.86a	97.79±2.97c	MS, RI
	其他Others			0.00	0.00	0.00	4.90
G1	二甲基硫醚 Dimethyl sulfide	521	528	—	—	—	4.90±0.61a	MS, RI
G2	正丁醚 n-Butyl ether		987	—	5.99±0.11a	—	—	MS
	总计Total			512.70	1644.54	362.92	2511.43

DW：干基质量;“—”：未检测到：Ref.：参考NIST Chemistry Web Book中HP-5ms上的保留指数;Cal.：本试验条件下测定的保留指数
DW: Dry weight; “-”: Not detected; Ref.: The reference retention index shows in NIST Chemistry Web Book on HP-5ms column; Cal: The retention index calculated in this experiment

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生糙米（RBR）中鉴定出16种挥发性风味化合物总计512.70 μg/100 g,主要包括醛类4种共235.42 μg/100 g、醇类4种共133.75 μg/100 g、萜烯类3种共59.45 μg/100 g、芳香烃4种共82.04 μg/100 g;其主要挥发性风味化合物为己醛183.10 μg/100 g、壬醛36.35 μg/100 g、正己醇108.37 μg/100 g、对薄荷-1(7),3-二烯54.26 μg/100 g和甲苯33.50 μg/100 g等。挤压膨化糙米（EBR）中鉴定出17种挥发性风味化合物总计1 644.54 μg/100 g,主要包括醛类5种共783.82 μg/100 g、酯类2种共250.24 μg/100 g、芳香烃4种共494.45 μg/100 g、杂环化合物3种共91.83 μg/100 g;其主要挥发性风味化合物为己醛612.88 μg/100 g、壬醛119.93 μg/100 g、乙酸乙酯245.44 μg/100 g、甲苯366.58 μg/100 g和2-戊基呋喃80.97 μg/100 g等。发芽糙米（GBR）中鉴定出13种挥发性风味化合物总计362.92 μg/100 g,主要包括醛类4种共201.57 μg/100 g、醇类4种共144.22 μg/100 g、萜烯类2种共6.07 μg/100 g;其主要挥发性风味化合物为己醛171.31 μg/100 g、壬醛19.67 μg/100 g、正丁醇16.53 μg/100 g和正己醇119.72 μg/100 g等。挤压膨化发芽糙米（EGBR）中鉴定出21种挥发性风味化合物,总计2 511.43 μg/100 g,主要包括醛类7种共1 407.58 μg/100 g、萜烯类2种共190.98 μg/100 g、酯类2种共555.04 μg/100 g、芳香烃4种共106.73 μg/100 g、杂环化合物3种共172.60 μg/100 g;其主要挥发性风味化合物为己醛1 191.02 μg/100 g、壬醛114.43 μg/100 g、正丁醇65.22 μg/100 g、对薄荷-1(7),3-二烯182.63 μg/100 g、乙酸乙酯547.10 μg/100 g、吡啶74.22 μg/100 g和2-戊基呋喃97.79 μg/100 g等。RBR经挤压膨化,己醛、庚醛、壬醛、1-辛烯3-醇、甲苯和2-乙酰-1-吡咯啉（2-AP）等化合物含量均显著增加,EBR样品中新检出3-甲基丁醛、苯甲醛、4-乙基己烯、D-柠檬烯、乙酸乙酯和2-戊基呋喃等化合物,RBR样品中癸醛、正丁醇、2-乙基-1-己醇、α-蒎烯等化合物未在EBR样品中检出;RBR经发芽处理,壬醛、α-蒎烯、甲苯和对二甲苯的含量显著降低,正己醇和2-乙基-1-己醇的含量显著增加,己醛、庚醛、癸醛和正丁醇等化合物含量变化不显著,GBR中新检出3-甲基丁醇、D-柠檬烯和2-戊基呋喃,RBR中的1-辛烯-3-醇、β-蒎烯、对薄荷-1(7),3-二烯和乙苯等化合物未在GBR中检出;GBR经挤压膨化,己醛、庚醛、壬醛、癸醛、正丁醇、α-蒎烯和甲苯等化合物含量均显著增加,EGBR中新检出3-甲基丁醛、戊醛、苯甲醛、1-辛烯-3-醇、对薄荷-1(7),3-二烯、乙酸乙酯、乙酸丁酯、乙苯、二甲基硫醚、吡啶和2-AP等化合物,GBR中的3-甲基丁醇、正己醇和D-柠檬烯未在EGBR样品中检出。生糙米经发芽处理后,醇类和杂环化合物含量少量增加,其他各类化合物含量均减少,挥发性风味化合物含量降低了29.21%;生糙米和发芽糙米经挤压膨化后,挥发性风味化合物含量分别增加了2.21倍和5.92倍,且发芽糙米中醛类、萜烯类、酯类和杂环化合物的含量增加,显著高于生糙米;醇类化合物含量减少,显著低于生糙米。可见,挤压膨化对促进发芽糙米挥发性风味化合物产生的效果明显高于糙米。

2.2 糙米挥发性风味化合物主成分分析

以糙米中挥发性风味化合物的含量为描述符,对糙米中醛类、醇类、萜烯类与酯类及其他化合物（含芳香烃及杂环化合物等）进行主成分分析,明确各类主要挥发性风味化合物含量变化与加工处理之间的关系。如表2所示,各类化合物主成分特征值均大于1,且累计方差贡献率均在90%以上,说明可以用前两个主成分来解释糙米样品中各类挥发性风味化合物的主要差异^[25]。

Table 2
表2
表2挥发性风味化合物主成分分析特征值及累计方差贡献率
Table 2Eigenvalues and cumulative contribution rate of volatile flavor compounds

化合物 Compounds	主成分 Principal component	特征值 Eigenvalues	贡献率 Contribution rate (%)	累积贡献率 Cumulative contribution rate (%)
醛类Aldehydes	1	5.083	72.620	72.620
醛类Aldehydes	2	1.821	26.013	98.632
醇类Alcohols	1	3.636	72.713	72.713
醇类Alcohols	2	1.013	20.263	92.976
萜烯类与酯类 Terpenes and Esters	1	3.817	54.529	54.528
萜烯类与酯类 Terpenes and Esters	2	2.629	37.563	92.092
其他Others	1	5.909	65.661	65.661
其他Others	2	2.823	31.367	97.028

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糙米样品挥发性风味化合物主成分载荷系数见表3;醛类、醇类、萜烯类与酯类、其他化合物在第一主成分（PC1）及第二主成分（PC2）上的负载量分布见图1,图中圆切线以外的化合物在PC1或PC2上的载荷系数绝对值大于0.9。

Table 3
表3
表3主成分载荷系数
Table 3Principal component load factor

编号 Number	化合物 Compounds	主成分1 Principal component 1	主成分2 Principal component 2
	醛类 Aldehydes
A1	3-甲基丁醛 Butanal, 3-methyl-	0.762	0.642
A2	戊醛 Pentanal	0.557	0.825
A3	己醛 Hexanal	0.859	0.509
A4	庚醛 Heptanal	0.976	-0.171
A5	苯甲醛 Benzaldehyde	0.975	0.218
A6	壬醛 Nonanal	0.993	-0.006
A7	癸醛 Decanal	-0.282	0.937
	醇类 Alcohols
B1	正丁醇 1-Butanol	-0.09	0.988
B2	3-甲基丁醇 1-Butanol, 3-methyl-	0.936	-0.06
B3	正己醇 1-Hexanol	0.827	-0.32
B4	1-辛烯-3-醇 1-Octen-3-ol	-0.997	-0.071
B5	2-乙基-1-己醇 1-Hexanol, 2-ethyl-	0.983	-0.182
	萜烯类与酯类Terpenes and Esters
C1	α-蒎烯 α-Pinene	0.636	0.772
C2	4-乙基己烯 1-Hexene, 4-ethyl-	0.148	-0.888
C3	β-蒎烯 β-Pinene	-0.597	0.557
C4	D-柠檬烯 D-Limonene	-0.072	-0.997
C5	对薄荷-1(7),3-二烯 β-Terpinene	0.742	0.668
D1	乙酸乙酯 Ethyl acetate	0.994	0.069
D2	乙酸丁酯 Acetic acid, butyl ester	0.986	-0.074
	其他Others
E1	甲苯 Toluene	0.973	-0.149
E2	乙苯 Ethylbenzene	0.968	0.093
E3	对二甲苯 p-Xylene	0.989	0.143
E4	邻二甲苯 o-Xylene	0.922	0.315
F1	吡啶Pyridine	0.951	-0.271
F2	2-乙酰-1-吡咯啉 2-Acetyl-1-pyrroline	0.949	-0.202
F3	2-戊基呋喃 Furan, 2-pentyl-	0.951	-0.271
G1	二甲基硫醚 Dimethyl sulfide	-0.135	0.991
G2	正丁醚 n-Butyl ether	0.596	0.775

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图1

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图1糙米样品挥发性风味化合物载荷图

A：醛类化合物在PC1及PC2上的负载量图;B：醇类化合物在PC1及PC2上的负载量图;C：萜烯类与酯类化合物在PC1及PC2上的负载量图;D：其他化合物在PC1及PC2上的负载量图。图中编号含义同表3（如“A1”代表“3-甲基丁醛”）
Fig. 1Loading plot of volatile flavor compounds PCA model from brown rice samples

A: Loading plot of PC1 vs. PC2 corresponding to aldehydes PCA model from brown rice samples; B: Loading plot of PC1 vs. PC2 corresponding to alcohols PCA model from brown rice samples; C: Loading plot of PC1 vs. PC2 corresponding to terpenes and esters PCA model from brown rice samples; D: Loading plot of PC1 vs. PC2 corresponding to other compounds PCA model from brown rice samples. The meaning of numbers in the figure is the same as table 1 (e.g. “A1” stands for “Butanal, 3-methyl-”)

如图1-A所示,醛类化合物主要分布在PC1正方向上,其含量增加主要与挤压膨化处理有关,如庚醛、苯甲醛和壬醛;部分醛类化合物分布在PC2正方向上,其含量降低主要与发芽处理有关,如癸醛。

由图1-B可知,醇类化合物主要分布在PC1方向上,PC1正方向上的化合物含量增加与发芽处理有关,如2-乙基-1-己醇和3-甲基丁醇,PC1负方向上的化合物含量降低与发芽处理有关,如1-辛烯-3-醇;而PC2正方向上的化合物,其含量增加主要与挤压膨化有关,如正丁醇。

如图1-C所示,酯类化合物分布在PC1正方向上,其含量增加主要与发芽-挤压膨化有关,如乙酸乙酯和乙酸丁酯;萜烯类化合物主要分布在PC2方向上,其含量变化主要与挤压膨化处理有关,PC2负方向表示含量增加,如D-柠檬烯。

由图1-D可知,其他化合物（芳香烃及杂环化合物等）主要分布在PC1正方向上,其含量增加主要与挤压膨化有关,如甲苯、乙苯、对二甲苯、邻二甲苯、正丁醚、2-AP;而PC2正方向上的化合物,其含量增加主要与发芽-挤压膨化有关,如二甲基硫醚和吡啶。

2.3 糙米挥发性风味化合物GC-O分析

2.3.1 糙米样品挥发性风味化合物GC-O气味强度分析糙米样品中共分析出气味活性化合物（OIV≥1）19种,包括醛类6种、醇类4种、萜烯类2种、酯类1种、芳香烃4种、杂环化合物2种（表4）。

Table 4
表4
表4糙米样品挥发性风味化合物的气味属性及强度
Table 4Odor intensity and classification of volatile flavor compounds in brown rice samples

类别 Category	化合物 Compounds	气味 Odor	气味强度值 Odor intensity value
类别 Category	化合物 Compounds	气味 Odor	糙米 Brown rice	挤压膨化糙米 Extruded brown rice	发芽糙米 Germinated brown rice	挤压膨化发芽糙米 Extruded germinated brown rice
坚果 Nutty	戊醛 Pentanal	杏仁 Almond	0	0	0	1
	苯甲醛 Benzaldehyde	坚果 Nut	0	2	0	2
	α-蒎烯 α-Pinene	坚果 Nut	0	0	0	1
	2-乙酰-1-吡咯啉 2-Acetyl-1-pyrroline	爆米花 Popcorn	3	3	0	3
	2-戊基呋喃 Furan, 2-pentyl-	杏仁 Almond	0	1	0	2
果香 Fruity	壬醛 Nonanal	柑橘 Orange	1	2	1	2
	对薄荷-1(7),3-二烯 β-Terpinene	薄荷 Mint	0	0	0	1
	乙酸乙酯 Ethyl acetate	水果 Fruit	0	1	0	2
	对二甲苯 p-Xylene	甜香 Sweet	0	3	0	2
花香 Floral	甲苯 Toluene	花香 Flower	1	0	0	0
花香 Floral	乙苯 Ethylbenzene	芳香 Fragrance	0	1	0	0
青草 Grassy	己醛 Hexanal	青味 Green	1	3	0	3
	1-辛烯-3-醇 1-Octen-3-ol	蘑菇 Mushroom	3	3	0	2
	2-乙基-1-己醇 1-Hexanol, 2-ethyl-	青味 Green	2	0	2	0
	邻二甲苯 o-Xylene	青草 Grass	0	1	0	0
蜡质 Waxy	庚醛 Heptanal	脂肪 Lipid	2	3	0	3
	癸醛 Decanal	肥皂 Soap	2	0	0	2
	正丁醇 1-Butanol	西药 Medicine	2	0	1	1
	正己醇 1-Oexanol	树脂 Resin	3	0	1	0

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不同糙米样品中气味活性化合物的气味强度值差异明显。RBR中检出气味活性化合物10种,总OIV为20,其中强气味活性的化合物（OIV≥3）有3种,为正己醇、1-辛烯-3-醇和2-AP。RBR经挤压膨化,醛类、酯类和其他化合物气味强度增加,醇类化合物气味强度降低。EBR中检出气味活性化合物11种,总OIV为23,其中OIV≥3的5种,为己醛、庚醛、1-辛烯-3-醇、对二甲苯和2-AP。RBR经发芽处理,醛类、醇类和其他化合物气味强度降低。GBR中检出气味活性化合物4种,总OIV为5,OIV≥2的1种,为2-乙基-1-己醇。GBR经挤压膨化,醛类、萜烯类、酯类和其他化合物的气味强度均增加,醇类化合物气味强度降低。EGBR中检出气味活性化合物14种,总OIV为25,其中OIV≥3的3种,为己醛、庚醛和2-AP。

2.3.2 糙米样品挥发性风味轮廓分析根据气味属性将气味活性化合物分成坚果、花香、果香、青草和蜡质5类（表3）。计算归属于这5类气味的气味活性化合物的气味总强度,进行气味轮廓分析,得到糙米样品整体挥发性风味轮廓（图2）。

图2

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图2不同糙米样品的风味轮廓图

Fig. 2The flavor profile of different brown rice samples

RBR样品气味活性化合物中蜡质气味强度最高,青草和坚果气味强度次之,果香和花香气味较弱。RBR经挤压膨化,坚果、青草和果香气味强度明显增强,蜡质气味强度明显降低,花香气味强度不变;RBR经发芽处理,坚果、蜡质和青草气味强度均明显降低,花香气味强度有所降低,果香气味强度不变;GBR经挤压膨化,坚果、蜡质、青草和果香气味强度明显增强,花香气味强度有所增加。

RBR与GBR样品整体风味轮廓相似,GBR所含活性化合物的气味强度较低,RBR经发芽处理后风味强度整体降低,尤其是蜡质气味强度从最高降至最低;RBR和GBR经挤压膨化后气味强度均有明显提升,果香气味强度增幅相同,GBR样品中坚果、蜡质、青草和花香气味强度增加则高于RBR样品。EBR与EGBR整体风味轮廓较为相似,EGBR样品整体气味强度高于EBR样品。可见挤压膨化处理对GBR整体气味强度的提升更加明显,尤其是坚果气味强度,从GBR最低强度增加到了EGBR最高强度。

3 讨论

3.1 糙米挥发性风味化合物含量与其GC-O气味强度的相关性

糙米经挤压膨化或发芽处理,以及发芽糙米经挤压膨化处理前后,样品中大部分气味活性化合物气味强度的增强与减弱与其含量变化大致呈正相关,如糙米和发芽糙米经挤压膨化后,庚醛、己醛、壬醛、苯甲醛、乙酸丁酯、对二甲苯和2-戊基呋喃等化合物气味强度与含量均增加;糙米经发芽处理后,庚醛、己醛、壬醛、苯甲醛、1-辛烯-3-醇、甲苯和2-AP等化合物气味强度与含量均降低。也存在化合物气味强度与含量变化不一致的情况,如2-AP,糙米经挤压膨化后,其含量显著增加,而气味强度无差异。究其原因,2-AP在水中的气味阈值很低,为0.01 μg/100 g^[26],RBR样品中2-AP含量为2.03 μg/100 g,约为阈值水平的203倍,EBR中2-AP含量约为阈值水平的487倍,这些糙米样品中2-AP的含量远高于其阈值水平。据报道,运用GC-O气味强度评价挥发性风味化合物的气味活性时,由于受斯蒂文心理物理功效函数的影响,气味浓度在高于绝对阈值时存在一个差别阈值增加的过程,此时待测化合物浓度的变化并不能刺激感官强度的相等变化^[27],这可能解释了2-AP含量存在差异,但气味强度相当的原因。此外,GC-O嗅闻分析时,出峰时间相邻化合物的气味间存在加成和掩盖等相互作用,这对挥发性风味化合物的气味强度评价也会产生一定影响^[28]。

已有研究表明,单一化合物的GC-O评价结果不足以提供足够的样品感官信息^[29,30],本研究将GC-O气味强度法与风味轮廓分析结合使用,在分析具体挥发性风味化合物气味的同时,可从整体把握不同糙米样品的挥发性风味差异。在GC-O分析的基础上,本研究关于糙米样品挥发性化合物风味轮廓分析结果表明,各属性化合物气味总强度的变化与其含量的变化有正相关性,如糙米及发芽糙米挤压膨化后,坚果气味增强与苯甲醛和2-戊基呋喃等化合物的总含量增加有关,果香气味增强与壬醛、乙酸乙酯和对二甲苯等化合物总含量增加有关;这在一定程度上弥补了分析单一化合物时,气味强度与含量变化相关性较弱的不足。本研究采用风味轮廓分析辅助GC-O进行样品间气味强度的相对比较,也表明糙米样品的挥发性风味并不是气味活性化合物的简单加和,而是由这些化合物复杂的相互作用最终形成^[31]。

3.2 挤压膨化对糙米及发芽糙米挥发性风味化合物的影响

醛类化合物是挤压膨化后糙米样品中含量增加最多的挥发性风味化合物,糙米与发芽糙米经挤压膨化后醛类含量分别增加2.32倍和5.98倍,其中己醛、庚醛、壬醛和3-甲基丁醛等显著增加。究其原因,在挤压膨化的高温、高压和高剪切力作用下,脂肪酸可氧化分解或热降解产生醛类化合物^[32,33],如油酸氧化降解产生庚醛和壬醛^[19,34],亚油酸氧化降解产生己醛,亚麻酸可衍生形成苯甲醛^[19,35]。另外,亮氨酸经过Strecker降解还可产生3-甲基丁醛^[18,36]。尤其值得注意的是,糙米挤压膨化后,其醛类挥发性风味物质总量增加,而发芽糙米挤压膨化后,醛类增加,可见无论是醛类含量还是其增加幅度,挤压膨化发芽糙米均显著高于挤压膨化糙米,说明糙米在发芽过程中通过生化作用可能产生了更多的游离脂肪酸、游离氨基酸等小分子化合物^[37,38],并经挤压膨化后形成了醛类挥发性风味物质。

发芽糙米经挤压膨化后,萜烯类化合物含量增加,而糙米经挤压膨化后,萜烯类化合物含量降低,且挤压膨化发芽糙米中萜烯类物质含量显著高于挤压膨化糙米。萜烯类化合物合成前体主要为异戊烯焦磷酸（IPP）和二甲基丙烯焦磷酸（DMAPP）,且IPP和DMAPP主要通过甲羟戊酸（MVA）途径和2-甲基赤藓糖醇-4-磷酸（MEP）途径产生^[39,40]。一方面,糙米发芽过程中活跃的生化反应通过上述途径可能产生了更多的风味前体物质^[40],并在挤压膨化过程中形成了大量萜烯类化合物;另一方面,萜烯类化合物热稳定性较差^[41],高温高压的挤压膨化过程又会使萜烯类化合物含量降低,这可能是造成糙米与发芽糙米经挤压膨化后萜烯类化合物含量差异的主要原因。

此外,糙米和发芽糙米经挤压膨化后,乙酸乙酯、乙酸丁酯、甲苯、对二甲苯、2-戊基呋喃和2-AP等化合物含量均显著增加。其中,酯类化合物可由脂质和脂肪酸在挤压膨化过程中高温裂解和降解产生^[32,33,34],2-戊基呋喃可由油酸和亚油酸降解产生^[19,42],呋喃化合物也可由1,4-二脱氧酮糖与甘氨酸发生Maillard反应产生^[43],芳香烃化合物及2-AP可由挤压膨化过程中的Maillard反应和焦糖化反应产生^[18,44]。同样值得一提的是,上述这些挥发性风味物质无论含量还是增加幅度,挤压膨化发芽糙米均显著高于挤压膨化糙米,说明糙米在发芽过程中通过生化作用形成了相应的挥发性风味物质前体,经挤压膨化形成了更多的挥发性风味化合物。

综合以上分析可知,挤压膨化可通过美拉德反应^[45,46]、焦糖化反应^[44]、脂肪与脂肪酸的氧化和降解^[16,33,47]、氨基酸Strecker降解^[18,48]等途径促进糙米及发芽糙米中醛类、酯类、杂环及芳香烃等挥发性化合物的形成;而糙米经发芽处理,脂质、淀粉和蛋白质等大分子化合物可由生物酶降解产生脂肪酸、可溶性糖、氨基酸等可能形成挥发性风味化合物的前体物质^[49,50,51],进一步提高了挤压膨化后其中挥发性风味物质的含量。

4 结论

挤压膨化对糙米及发芽糙米中醛类、酯类、杂环及芳香烃等大部分挥发性化合物的形成有明显促进作用,尤其是发芽糙米挤压膨化后,其醛类、酯类、萜烯类和杂环化合物含量增加更为显著,其挥发性风味化合物的含量及增加幅度均显著高于糙米;糙米及发芽糙米挤压膨化后整体风味强度均上升,其中果香和坚果气味强度显著增加。

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中国农业科学, 2016,49(4):727-738.

DOI:10.3864/j.issn.0578-1752.2016.04.012 URL [本文引用: 1]

【Objective】In order to optimize the extrusion process conditions, the effects of extrusion operating parameters on nutritional quality, physicochemical properties and volatile aroma components in final products of germinated brown rice compounded of Flammulina velutipes were investigated. The study will provide theoretical basis for quality evaluation and development of functional snack foods. 【Method】 To analyze the effects of extrusion operating parameters on GABA content, soluble dietary fiber content, soluble protein content and radial expansion ratio, germinated brown rice compounded of Flammulina velutipes were extruded to obtain a composite type of puffed products with a twin-screw extruder at different moisture content, extrusion temperature and screw speed conditions. Changes of the amino acids content and physicochemical properties such as hardness, bulk density, water-absorption index, water-solubility index and color difference of germinated brown rice compounded of Flammulina velutipes extrudates were analyzed compared with non-supplemented germinated brown rice products. In addition, the volatile flavor compounds in the puffed products were also analyzed comparatively using electronic nose. 【Result】The quality properties of germinated brown rice compounded of Flammulina velutipes extrudateschanged with the extrusion operating parameters. The GABA content showed a trend from decline to rise as the moisture content kept increasing, dropped sharply as the extrusion temperature increased, and increased at first, but then decreased. With the moisture content, the extrusion temperature and the screw speed increasing, both the SDF content and the soluble protein content had a decline trend after an initial ascent. The radial expansion ratio decreased with the moisture content and the extrusion temperature increasing, while increased first but then decreased as the screw speed continued increasing. The optimal conditions of the extrusion were moisture content 17%, extrusion temperature 140℃ and screw speed 150 r/min from the single factor test. Under these conditions, the content of GABA, SDF and soluble protein were (210.44 ± 0.39) mg·kg^-1, (0.735 ± 0.028) g·100 g^-1 and (1.23 ± 0.01) mg·g^-1, respectively, and the radial expansion ratio of the extruded products was 2.67 ± 0.02. Compared with the un-extruded compounded powder and germinated brown rice extruded products, the total amount of amino acids of germinated brown rice compounded of Flammulina velutipes extrudatesincreased by 1.7% and 2.9%, respectively, and essential amino acid content increased by 2.8% compared with non-supplemented germinated brown rice extrudates, among which, the arginine and lysine content increased by 6.6% and 5.7% respectively, indicating that the addition of Flammulina velutipes powder could increase the amino acid content significantly. The extruded products from germinated brown rice compounded of Flammulina velutipes exhibited lower radial expansion ratio, lower degree of gelatinization, lower water-solubility index and lower L* value, but higher a*, b*and ΔE values than extruded products of non-supplemented germinated brown rice, which indicated that germinated brown rice compounded of Flammulina velutipes extrudates showed greater browning degree. The analytical results of electronic nose showed that the volatile flavor compounds were significantly different between the extruded products from germinated brown rice compounded of Flammulina velutipes and non-supplemented germinated brown rice, which reflected the overall flavor profile of different samples accurately and quickly. 【Conclusion】 The products of germinated brown rice compounded of Flammulina velutipes had comprehensive nutrition, good taste and unique flavor characteristics after the optimization of extrusion technology. Extrusion technology was an effective method to improve the nutritional quality and taste flavor of germinated brown rice.

FANG

, WANG H

, PEI

, MA

, TANG X

, YANG W

, HU Q

. Effect of extrusion on digestion properties and volatile compounds in germinated brown rice compound of flammulina velutipes flour
Scientia Agricultura Sinica, 2016,49(4):727-738. (in Chinese)

DOI:10.3864/j.issn.0578-1752.2016.04.012 URL [本文引用: 1]

张冬媛, 邓媛元, 张名位, 马永轩, 张雁, 魏振承, 张瑞芬, 刘磊, 唐小俊, 遆慧慧. 发芽-挤压-淀粉酶协同处理对速食糙米粉品质特性的影响
中国农业科学, 2015,48(4):759-768.

DOI:10.3864/j.issn.0578-1752.2015.04.13 URL [本文引用: 2]

【Objective】The objective of this experiment is to investigate the effect of germination–extrusion–thermostable α-amylase assisted processing on quality properties of instant brown rice powder, such as solubility, fluidity, chromaticity, flavor and starch digestion performance and so on, thus providing the reference for processing of instant brown rice powder with high quality. 【Method】Germinated brown rice was extruded with thermostable α-amylase (EGBRE). Meanwhile, three control treatments were prepared: germination-exrusion processing (EGBR), thermostable α-amylase-extrusion processing (EBRE) and only extrusion processing (EBR). Characteristics of the four kinds of instant brown rice powder were investigated, including water solubility index, water absorption index, agglomeration rate, dispersion time, viscosity, chromaticity, volatile substances, performance of starch digestion and overall sensory evaluation. 【Result】 Thermostable α-amylase significantly improved the solubility of the brown rice powder. Compared with EGBR, water solubility index of EGBRE increased by 2.11 times, and water solubility index of EBRE increased by 2.55 times compared with EBR. However, germination didn’t affect the solubility significantly. Thermostable α-amylase could reduce the viscosity observably. Compared with EGBR, the viscosity of EGBRE decreased by 60.0%. The viscosity of EBRE decreased by 31.3% compared with EBR. Germination had no significant effect on the viscosity of the paste. Thermostable α-amylase increased the total content of volatile substances, but the content of lipid oxidation products in germinated samples was lower. The germination-extrusion-thermostable α-amylase processing could significantly reduce the agglomeration rate and shorten the dispersion time. Compared with EGBR, EBRE and EBR, the agglomeration rate of EGBRE was reduced by 55.4%, 74.8% and 84.0% respectively, and the dispersion time was shortened by 27.2%, 17.3% and 52.5%. Meanwhile, the co-processing could significantly influence the angle of repose, so its fluidity was improved. However, the chroma of the powder increased appreciably. Besides, germination-extrusion-thermostable α amylase processing improved the digestibility of starch. Compared with EBR, the proportion of fast-digesting starch of the EGBRE increased, and the ratio of resistant starch decreased significantly.【Conclusion】EGBRE could significantly improve the quality characteristics of instant brown rice powder. This co-processing increased the digestibility of starch and the content of volatile flavor compounds, meanwhile, decreased the rate of agglomeration, dispersion time and viscosity.

ZHANG D

, DENG Y

, ZHANG

M W

, MA

Y X

, ZHANG

, WEI Z

, ZHANG R

, LIU

, TANG X

, TI H

. Effect of germination- extrusion-amylase assisted processing on quality properties of brown rice powder
Scientia Agricultura Sinica, 2015,48(4):759-768. (in Chinese)

DOI:10.3864/j.issn.0578-1752.2015.04.13 URL [本文引用: 2]

张名位, 陈恩成, 张雁, 张瑞芬, 池建伟, 魏振承, 唐小俊. 籼型黑米萌芽积累γ-氨基丁酸的工艺条件研究
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URL [本文引用: 1]

Germination treatment of brown rice can significantly increase the contents of nutrients and active substances such as γ-aminobutyric acid(GABA). To analyze the effect of germination conditions on the accumulation of GABA in indica black rice, the conditions such as immersion temperature, time, Ca²⁺ concentration in immersion solution, and germination temperature and time, etc. were optimized. Results show that the water regain and germination rate of indica black rice are affected by immersion temperature and time; the accumulation of GABA in the germination process is affected by Ca²⁺ concentration in immersion solution and germination temperature and time, etc.; the content of GABA under the conditions of immersion in 0.50 mmol/L CaCl₂ solution for 24 h at 28℃, and then germination for 30 h at 29℃ can reach 55.36 mg/(100 g), 3.9 times as that of before germination.

ZHANG M

, CHEN E

, ZHANG

, ZHANG R

, CHI J

, WEI Z

, TANG X

. Effect of technological conditions on γ-aminobutyric acid accumulation in germinated indica black rice
Transactions of the Chinese Society of Agricultural Engineering, 2007,23(3):213-218. (in Chinese)

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The mechanism for the contribution of subthreshold aroma constituents to the overall jasmine tea odor impression was studied on the basis of a sensory evaluation. Binary model aqueous solutions containing the authentic odorants of a jasmine tea infusion, (E)-2-hexenyl hexanoate (I), (Z)-3-hexenol (II), and indole (III), were each prepared in a concentration below the odor threshold. Each solution had no aroma, but when 4-hexanolide replaced only 5% of each odorant, the odor intensity of each model solution was significantly strengthened. An astringent note and heavy note were recognized for each solution as the commonly perceived characteristics from the sensory evaluation. The concentration of 4-hexanolide added was also at the subthreshold level. The results suggest mutual interaction between odorants I, II, or III and 4-hexanolide. The effect on the overall odor sensation of a jasmine tea infusion by adding 4-hexanolide at a concentration below its odor threshold was also studied. In this case, the intensity of both the sweet and astringent notes was significantly strengthened in comparison with the odor impression of the original jasmine tea infusion. This phenomenon is considered to have been a synergistic effect between subthreshold odor compounds in the jasmine tea infusion. The results of this study clarify for the first time that the subthreshold aroma constituents play an important role in the characteristic flavor of a jasmine tea infusion.

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