全州禾花鲤(Cyprinus carpio var. Quanzhounensis )俗名禾花鱼,原产于广西壮族自治区桂林市全州县,鱼种经过长期的稻田放养及驯化,因喜食水稻掉落的稻花而得名[1]。禾花鲤在分类学上隶属于鲤形目(Cypriniformes)、鲤科(Cyprinidae)、鲤属(Cyprinus),是历史悠久的稻田生态养殖品种之一[2]。与其他养殖鲤品种相比,全州禾花鲤体型更为粗短,全身深紫色呈半透明状,形成了有别于其他养殖鲤群体的独特表型[3],具有鳞细皮薄无细刺、肉嫩清香等特点,集美食与观赏性于一体[4]。禾花鲤是由中国稻鱼共生系统农作模式保存和维系而来的宝贵种质资源,因稳粮、增收、提质、促渔和可持续等优点而成为水产养殖的研究热点[5],是广西桂西北地区农民脱贫攻坚的主导养殖鱼类,也是广东粤北地区稻渔综合种养的主推种类之一[6]。
中国的“稻-鱼共生”养殖模式历史悠久[7],稻田的浅水环境可为鱼类提供优良的栖息环境和营养丰富的天然饵料,禾花鲤的天然饵料主要包括稻花、部分浮游植物、浮游动物以及底栖动物等[8];田中稻鱼可为稻田松土、除草除虫,其排泄物还可以提高土壤的肥力[9]。稻田养殖是中国大力支持发展和推广的一种水产养殖模式[10]。但随着人口的增加和居民经济水平的提高,稻田养鱼的产量已经满足不了人们对稻鱼等水产品的日常需求。同时在环境保护的高压下,“三网拆除”、大水面限养和池塘养殖等成为了水产品养殖的主体[11],其中池塘养殖是中国常见的最重要的一种人工养殖模式。养殖阶段是水产品土腥味形成的重要时期。一种水产品的土腥味会影响加工和销售等多个环节,土腥味太浓,将会提高后续食品加工和销售的难度,需要增加成本去除腥味。随着消费者对产品要求的提高,土腥味会降低产品的盈利能力,严重影响消费者对一种水产品的购买率和回购率[12]。
关于全州禾花鲤风味物质的研究,国内外较少见,仅有孙文波等[13]对稻田和池塘养殖两种模式下禾花鲤体内的氨基酸组成进行了分析。全州禾花鲤作为广西喜爱的稻田鲤鱼,其最流行的吃法是去胆后整体油炸或煎焖。因此,肌肉和肝胰腺中的腥味物质对全州禾花鲤食用价值有重大影响。本研究采用池塘和稻田两种养殖模式,对全州禾花鲤肌肉和肝胰腺中的腥味和鲜味物质进行比较分析,通过比较两种养殖模式下禾花鲤的腥味和鲜味物质的差异显著性,来判断两种养殖模式的优缺点,为推广禾花鲤的不同养殖模式提供理论依据。
1 材料与方法
1.1 试验材料
试验动物:(2.51±0.98)g全州禾花鲤苗,共900尾,采自海南省乐东县九所镇广西农业良种南繁基地。
仪器:TGL-16 高速冷冻离心机(湖南湘仪)、涡旋振荡仪(湖南湘仪)、移液枪(力辰科技)、液相色谱Waters Acquity UPLC、质谱AB SCIEX 5500 QQQ -MS 3.2。
标准试剂:甲醇、乙腈均购自美国Sigma公司,色谱级;甲酸铵、氨水购自上海阿拉丁生化科技股份有限公司;土臭素(GSM)、2-甲基异茨醇(2-MIB)、E-2-壬烯醛和次黄嘌呤核苷酸(IMP)标准品购自上海源叶生物科技有限公司。
1.2 试验方法
将900尾全州禾花鲤苗随机分为池塘和稻田2个试验组,每组设3个重复,投放密度为2 250尾/hm2。池塘组投喂配合饲料,每日早晚各投喂一次,总投喂量不超过全州禾花鲤体质量的3%;稻田组任其自然生长,不投喂任何人工饲料,养殖时长均为3个月。养殖结束后,从池塘组和稻田组中各随机捞出18尾全州禾花鲤,分别置于曝气自来水中暂养,禁食24 h。经间氨基苯甲酸乙酯甲磺酸盐(MS 222)麻醉处理后,用镊子去除背部鱼鳞和鱼皮以暴露肌肉组织,用剪刀剪取其背部两侧肌肉并剖取相应的肝胰腺,分别冻存于-80 ℃冰箱内待测。
采用顶空固相微萃取法对GSM、2-MIB、E-2-壬烯醛进行检测并定量。利用Thermo Trace 1300气相色谱-ISQ7000质谱联用仪(GC-MS)、色谱柱DB-5ms(60 m×0.25 mm×0.25 μm)测定样品中的GSM、2-MIB、E-2-壬烯醛的含量。分别精密称取GSM、2-MIB和E-2-壬烯醛标准品适量,加入甲醇配制成含标准品最终浓度为5 000、2 000、1 000、500、200、100、50、20 ng/mL的系列溶液,移取100 μL系列溶液于20 mL顶空瓶中进样分析。根据不同浓度及相应浓度下标准品的峰面积绘制出标准曲线,用于样本中GSM、2-MIB、E-2-壬烯醛浓度的计算。
利用高效液相色谱串联质谱仪测定IMP含量。使用液相色谱Waters Acquity UPLC、质谱AB SCIEX 5500 QQQ-MS、色谱柱Acquity UPLC BEH Amide(1.7 μm×2.1 mm×100 mm)测定IMP含量。将精密标准品加入50%甲醇分别配制成不同浓度的系列溶液,根据不同浓度及相应浓度下标准品的峰面积绘制出标准曲线,用于样本中IMP浓度的计算。
1.3 数据处理
所有的测定数据均采用Excel 2019进行整理,采用SPSS 26.0进行单因素方差分析及检验方差齐性,根据方差齐性结果进行独立样本T检验,结果用均值±标准差(Means±SD)进行表示。
2 结果与分析
2.1 三种土腥味物质含量的比较分析
取样过程中,通过肉眼观察到暂养中的稻田组全州禾花鲤外观颜色更为艳丽,尾巴臀鳍边缘呈现亮橘色。去除鳞片和皮肤,暴露肌肉后,可观察到稻田组全州禾花鲤的肌肉亮度比池塘组的更亮,肌纤维面积大、密度低,而池塘组的肌纤维面积小、密度高。
两种养殖模式下禾花鲤肌肉中的三种土腥味物质含量结果如表1所示,池塘养殖和稻田养殖禾花鲤肌肉中的E-2-壬烯醛含量不存在显著差异(P>0.05);2-MIB和GSM含量存在极显著差异(P<0.01),稻田养殖模式全州禾花鲤肌肉中的2-MIB和GSM含量极显著高于池塘养殖模式(P<0.01)。
表1 两种养殖模式下全州禾花鲤肌肉中的三种土腥味物质含量
Tab.1
| 养殖模式 Aquaculture mode | E-2-壬烯醛/ng·g-1 E-2-nonenal | 2-甲基异茨醇/ng·g-1 2-MIB | 土臭素/ng·g-1 GSM |
|---|---|---|---|
| 池塘养殖Pond culture | 29.27±10.98 | 17.94±3.97 | 19.52±3.25 |
| 稻田养殖Rice field culture | 21.74±4.75 | 59.03±17.83** | 48.59±13.77** |
注:同列数据,*表示差异显著(P<0.05),**表示差异极显著(P<0.01)。下表同此。
Notes: Data in the same column,* indicated significant difference (P<0.05), ** indicated extremely significant difference (P<0.01). The same as below.
两种养殖模式下禾花鲤肝胰腺中的E-2-壬烯醛和GSM含量存在极显著差异(P<0.01),稻田养殖模式禾花鲤肝胰腺的E-2-壬烯醛和GSM含量极显著高于池塘养殖模式(P<0.01),2-MIB含量差异不显著(P>0.05)(表2)。
表2 两种养殖模式下全州禾花鲤肝胰腺中的三种土腥味物质含量
Tab.2
| 养殖模式 Aquaculture mode | E-2-壬烯醛/ng·g-1 E-2-nonenal | 2-甲基异茨醇/ng·g-1 2-MIB | 土臭素/ng·g-1 GSM |
|---|---|---|---|
| 池塘养殖Pond culture | 29.77±12.61 | 15.96±4.99 | 18.58±3.91 |
| 稻田养殖Rice field culture | 253.09±107.70** | 9.87±4.26 | 42.99±15.22** |
2.2 禾花鲤肌肉和肝胰腺中的IMP含量的比较分析
两种养殖模式下禾花鲤肌肉和肝胰腺中IMP的含量结果如图1所示,通过观察柱状图可以得出两种养殖模式的禾花鲤肌肉中IMP含量存在极显著差异(P<0.01),稻田养殖模式下禾花鲤肌肉的IMP含量[(2.30±0.39) ng·mg-1]极显著高于池塘养殖模式[(1.08±0.40) ng·mg-1]。两组禾花鲤肝胰腺的IMP含量差异不显著(P>0.05)。
图1
图1
两种养殖模式下禾花鲤肌肉和肝胰腺中的IMP 含量
注:柱子上,*表示两种养殖模式下肌肉之间或肝胰腺之间差异显著(P<0.05),**表示差异极显著(P<0.01)。
Fig.1
The content of a tasty substance in C. carpio var. Quanzhounensis under two aquaculture modes
Notes: Data in the same column,* indicated significant difference between muscles or between hepatopancreas under two aquaculture modes (P<0.05), ** indicated extremely significant difference (P<0.01).
3 讨论
3.1 禾花鲤体内的腥味物质分析
土腥味物质由多种不同的化学物质组成,种类繁多。淡水养殖鱼类的土腥味物质主要包括2-MIB、GSM、E-2-壬烯醛、3-庚酮和8-正十七烯等[14-15]。Howgate P等[16]和Khiari D等[17]等均证实造成淡水鱼类土腥味最关键的物质是GSM和2-MIB。王国超等[18]对罗非鱼的研究结果也证明,造成罗非鱼土腥味的主要因素是GSM和2-MIB。GSM和2-MIB是养殖水体中的常见物质且难以被排除,产自于水体中的放线菌和浮游藻类等,在养殖过程中通常被养殖鱼类吸收和富集,从而加重鱼体的土腥味[19]。程亚美等[20]对尼罗罗非鱼的研究结果也证实了这一点,与淡水养殖的罗非鱼相比,盐碱水体因能够抑制水体中浮游藻类的繁殖,从而显著减少罗非鱼的土腥味。
本研究结果中,稻田养殖模式下禾花鲤肌肉中的2-MIB和GSM含量极显著高于池塘养殖模式,肝胰腺中的E-2-壬烯醛和GSM含量极显著高于池塘养殖模式,表明稻田养殖模式下的禾花鲤肌肉的土腥味极显著浓于池塘养殖模式。E-2-壬烯醛是一种具有草腥味的腥味物质[21],因此稻田养殖禾花鲤肝胰腺中草腥味极显著浓于池塘养殖。推测是农作物施肥等原因,导致稻田养殖模式的水体中含有较高含量的营养物质和氮磷元素,更适宜各种浮游藻类大量繁殖,因此稻田养殖的水环境中土腥味物质含量高,再加之稻田中的禾花鲤会进食浮游藻类等,这为其肌肉和肝胰腺中土腥味物质的更多积累提供了方便。而池塘养殖模式的尾水处理系统可以及时排出因残饵粪便等而富营养化的水体,同时池塘中的水生植物可以很好地吸收氮磷,抑制蓝绿藻等藻类的生长繁殖,因此其水体中的腥味物质含量低于稻田养殖模式。
3.2 禾花鲤体内的鲜味物质分析
鲜味影响肉及其制品的品质与销量,而在与鲜味有关的化合物中,起关键作用的有氨基酸和核苷酸两类物质。氨基酸中,谷氨酸、天冬氨酸的鲜味最明显,是呈鲜味的特征氨基酸[22]。核苷酸有多种异构体,只有在5’碳原子上连接到糖和羧酸的才具有鲜味[23],如5’-肌苷酸、5’-鸟苷酸、5’-腺苷酸、5’-胞苷酸和5’-尿苷酸,其中鲜味最强的是5’-肌苷酸,即IMP[24]。IMP在动物活体内主要是通过从头合成途径和重新利用途径合成的,从头合成途径主要在胞液中进行,首先合成IMP,然后通过不同途径分别生成腺嘌呤核苷酸(AMP)和鸟嘌呤核苷酸(GMP),AMP再经腺苷酸脱氨酶脱氨生成IMP[25]。鱼肉的鲜味与IMP的含量息息相关,肌肉中较高的IMP含量可以使鱼肉鲜香可口,进而提高其经济价值[26]。在最具风味的野生鲤和淡水鱼的风味组成中,IMP含量占总核苷酸的60%,而三磷酸腺苷(ATP)、二磷酸腺苷(ADP)、肌苷、次黄嘌呤的含量很低,因此IMP被认为是相当重要的风味指标[25]。研究证实测定IMP的积累量还可以衡量海鲜的新鲜程度[27],这是因为IMP是动物死后在酶的作用下ATP的最终降解产物,而IMP的降解产物肌苷会产生苦味,影响肉的风味[28]。IMP更是一种强力助鲜剂,通过去除鲜味感觉部位的金属离子,使谷氨酸钠有效地作用于味觉神经上,从而增强鲜味。国内已有多位学者对鱼类肌肉的IMP含量开展研究,如叶春艳等[29]利用纸层析法研究了松花江鲤鱼肌肉IMP含量与鱼肉保鲜时间的关系;刘旭等[30]首次在国内测定比较了6种鱼类肌肉的IMP含量;李清等[31]测定分析并比较了3种不同水源池塘中鲤鱼、鲢鱼和草鱼3种鱼肉IMP的含量;杨娟宁等[32]测定比较了黄河鲤(Cyprinus carpio)、兰州鲇(Silurus lanzhouensis)和鲇(Silurus asotus)的肌肉IMP含量;赵叶等[33]研究表明饲料中添加谷氨酸可显著提高草鱼肌肉中IMP含量;Li K等[34]研究发现死亡后的鲫(Carassius auratus)在冰上贮存4 h后,其IMP含量达到最高值。
本研究结果显示,稻田养殖禾花鲤肌肉中的IMP含量极显著高于池塘养殖,表明稻田养殖模式下禾花鲤肌肉的鲜味程度更高,极显著高于池塘养殖模式。推测其原因是池塘养殖模式下禾花鲤的养殖密度高,水体中的溶解氧浓度下降,厌氧菌滋生,容易产生异味,导致禾花鲤肌肉的肌苷酸低,鲜味弱[31]。IMP的含量还与饲料组分有关,本试验中池塘养殖的禾花鲤进食人工饲料,而稻田养殖的禾花鲤以稻田中的天然饵料为食,这也是造成其肌肉IMP含量极显著性高于池塘养殖模式的原因。
4 结论
稻田养殖模式下禾花鲤肌肉中的2-MIB和GSM含量极显著高于池塘养殖模式,肝胰腺中的E-2-壬烯醛和GSM含量极显著高于池塘养殖模式;稻田养殖模式下禾花鲤肌肉中的IMP含量极显著高于池塘养殖模式。结果表明,相比于传统的稻田养殖,池塘养殖禾花鲤肌肉和肝胰腺中的土腥味没有增加,但鲜味减少。在池塘养殖中降低土腥味的同时保留鲜味是今后研究的方向。
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[J].
罗非鱼肉中土臭素和2-甲基异莰醇的测定
[J].通过微波蒸馏-固相微萃取-气相色谱-质谱方法测定罗非鱼肉中土腥味物质--土臭素和2-甲基异莰醇的含量。对微波蒸馏功率、微波蒸馏时间、载气气流等实验参数进行优化。结果表明：确立的最佳条件为微波功率360W(仪器额定功率的40%)、微波时间6min、载气流速60mL/min；在优化条件下，罗非鱼肉中的土腥味物质能最大限度地被检测出来，土臭素和2-甲基异莰醇的检测限分别达到了0.044μg/kg和0.095μg/kg，且它们在0.5～20μg/kg范围内呈较好的线性关系，r2分别达到了0.998和0.991，实验中土臭素和2-甲基异莰醇的回收率分别为42.7%、61.9%；最终利用该方法测得所购罗非鱼肉中土臭素和2-甲基异莰醇的含量分别为4.97、1.21μg/kg。
盐碱水和淡水养殖模式下尼罗罗非鱼肌肉品质比较
[J].为了解盐碱水和淡水养殖的尼罗罗非鱼（Oreochromis niloticus）肌肉品质的差异，对不同养殖模式（淡水养殖和盐碱水养殖）下的尼罗罗非鱼肌肉的营养成分以及感官特征进行分析和比较。结果表明，盐碱水养殖尼罗罗非鱼肌肉总体感官评分高于淡水养殖。盐碱水养殖的尼罗罗非鱼肌肉粗蛋白含量为19.74%，显著高于淡水养殖，水分含量为74.83%，显著低于淡水养殖，其他基础营养成分差异不显著。盐碱水养殖和淡水养殖的尼罗罗非鱼的必需氨基酸与氨基酸总量比值分别为41.76%和41.52%，必需氨基酸与非必需氨基酸比值分别为71.69%和70.99%，2种养殖模式下养殖的尼罗罗非鱼肌肉的氨基酸组成均符合联合国粮农组织（FAO）和世界卫生组织（WHO）的理想模式，属于优质蛋白质源。盐碱水养殖的尼罗罗非鱼肌肉的不饱和脂肪酸含量为61.66%，二十碳五烯酸和二十二碳六烯酸（EPA+DHA）的含量为5.77%，n-3/n-6的值为0.57，均显著高于淡水养殖。盐碱水养殖的尼罗罗非鱼肌肉的鲜味氨基酸总量为194.43 mg/kg，甜味氨基酸总量为1 214.90 mg/kg，总游离氨基酸量为1 752.40 mg/kg，均显著高于淡水养殖。盐碱水养殖的尼罗罗非鱼肌肉和盐碱水养殖水样中异味物质（土臭素和二-甲基异茨醇）含量均显著低于淡水养殖组。综上，盐碱水养殖的尼罗罗非鱼肌肉的营养价值和感官特征明显优于淡水养殖。
Identification of compounds characterizing the aroma of fresh whitefish (Coregonus clupeaformis)
[J].
Hypoxanthine enhances the cured meat taste: hypoxanthine-induced cured meat taste
[J].We evaluated the enhancement of cured meat taste during maturation by sensory analysis. We focused on the heat-stable sarcoplasmic fraction (HSSF) to identify the factors related to cured meat taste. Because the dry matter of HSSF contained more than 30% nitrogen, nitrogen compounds such as free amino acids, small peptides and adenosine triphosphate-related compounds seemed to be the important components of HSSF. The samples cured with HSSF for 2 h exhibited the same taste profile as ones cured without HSSF for 168 h. Therefore, the changes in the amount and fractions of nitrogen compounds were examined in HSSF during incubation from 0 to 168 h. The concentration of hypoxanthine (Hx) gradually increased, while inosine-5'-monophosphate decreased during the incubation. The samples cured with pickles containing various concentrations of Hx were subjected to sensory analysis. The addition of Hx, in a dose-dependent fashion, enhanced cured meat taste by maturation for 2 h. It was concluded that Hx is essential for the enhancement of cured meat taste.© 2016 The Authors. Animal Science Journal published by John Wiley & Sons Australia, Ltd on behalf of Japanese Society of Animal Science.
Effects of high pressure treatment on the flavour-related components in meat
[J].This paper describes the effects of high-pressure treatment on the water-soluble components of meat responsible for the flavor of meat. The amounts of peptides and amino acids as estimated by phenol reagent positive materials (PPM) apparently increased with increasing pressure applied to the muscle up to 300 MPa, but the differences between each treatment were not statistically significant. When the muscles were stored at 2°C for 7 days after the pressurization, increases in the amount of PPM were observed both in untreated and pressurized muscles. Apparently the contents of serine, glutamic acid, glutamine, glycine and alanine gradually increased in the extracts from pressurized muscle as the pressure increased up to 200 MPa, and some of them, especially glutamine and alanine, tended to decrease in the muscle pressurized at 300 MPa. When the muscles were stored for 7 days after the pressurization, apparent increases of the contents of aspartic acid, serine, proline, alanine and lysine were observed in the extracts both from untreated and pressurized muscles. However, significant differences were not observed in the contents of each amino acid between each treatment. The content of inosinic acid, which is considered to contribute to the 'umani' taste of the meat, was not reduced by the pressurization. High performance liquid chromatograph (HPLC) of soluble peptides revealed no significant changes in any fraction from the pressurized muscles up to 200 MPa and a significant decrease of the peptide fraction (approx. molecular weight 500) from the muscle pressurized at 300 and 400 MPa. When the muscles were stored after pressurization, significant increases in the peptide fraction of molecular weight 300 and the amino acid fraction, and a decrease of the peptide fraction of molecular weight 3000 were observed in the extracts both from the untreated and pressurized muscles. From the results, it is suggested that high-pressure treatment on the post mortem muscle causes almost the same changes in the components responsible for the flavor of meat as those observed in conditioned muscle.Copyright © 1994. Published by Elsevier Ltd.
Concentration of inosine 5’-monophosphate in meat
[J].
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图1
