【作者】 王金美；

【导师】 曾凡坤；

【作者基本信息】 西南大学 ， 农产品加工及贮藏工程， 2010， 硕士

【摘要】 大头菜是我国传统腌制品,风味独特,深受人们喜爱。传统大头菜加工需要经过晾晒,多道加盐脱水腌制,一方面产品含盐量高,需要在腌制后熟以后进一步脱盐,另外生产时间长,不利于现代化生产。而一次性保温生产可以明显缩短加工周期,减少工艺步骤。大头菜的研究主要是集中在传统腌制的大头菜脱盐工艺上,关于风味物质的研究较少。研究大头菜的风味物质不但可以推测其风味的组成,防止不良气味的生成,还为工艺的优化和风味的调配提供理论依据。本实验以大头菜为主要原料,主要研究了新工艺大头菜预处理工艺以及不同加工工艺产品理化指标的变化；利用正交试验对新工艺大头菜的最佳工艺参数进行优化；采用同时蒸馏萃取-气相色谱-质谱联用仪对不同加工工艺的大头菜及其原料的挥发性风味物质进行了分析。主要试验结论如下：1.大头菜新工艺流程为：大头菜→清洗→切丝→预腌→机械脱水→冷却→加盐→装袋→抽真空密封→避光后熟→成品。↓25℃保温→成品大头菜新工艺脱水工艺采用0.5%的盐预腌脱水,能够保证大头菜营养成分损失少,通过热风脱水降低大头菜带菌量,实现大头菜生产机械化,卫生化。2.大头菜新工艺最佳工艺参数是：大头菜含水量控制在73%-76%,用盐量6%,真空度0.091MPa。新工艺大头菜理化特性变化如下：(1)蛋白质变化：随腌制时间延长大头菜蛋白质含量持续下降。蛋白质的分解率随着盐分的增加而减小。5%用盐量的大头菜蛋白质从6.084%降到4.47%,而11%含盐量的大头菜蛋白质从6.087%降到5.22%。(2)氨基酸态氮变化：大头菜后熟过程中氨基酸态氮一直呈现上升趋势,与蛋白质含量成负相关。(3)乳酸含量的变化：大头菜腌制过程中,乳酸的含量一直呈现上升趋势。在低盐腌制的菜丝中乳酸产生速度快,产量高。(4)还原糖的变化：大头菜后熟过程中还原糖含量整体呈现下降的趋势。7%加盐量腌制的大头菜在腌制60d后还原糖出现了上升,而9%加盐量腌制的大头菜在腌制的90d后还原糖出现了上升。(5)维生素C变化：在大头菜后熟过程中,维生素C的含量一直下降。但是低盐分的大头菜中Vc含量较高,高盐分Vc损失比较大。(6)大头菜亚硝酸盐呈峰值变化,峰出现的时间随着食盐浓度加大而延迟,可能是低盐分的大头菜乳酸含量高,分解亚硝酸盐。(7)色泽变化：在腌制过程中,大头菜颜色逐渐加深,而盐分低的大头菜颜色加深速度最快。(8)硬度变化：大头菜原料经过脱水后,硬度下降。在后熟过程中,大头菜硬度开始呈上升趋势,在腌制一个月左右开始下降,并且最后保持在一个比较稳定的硬度水平。3.新工艺大头菜营养成分：与传统大头菜相比,新工艺大头菜营养价值提高。新工艺大头菜蛋白质含量增高23%,还原糖增高7.8%,维生素C含量增高115.8%。乳酸和亚硝酸盐的含量分别降低272.5%和33.5%。4.新工艺大头菜市场接受程度与传统大头菜无显著差异,有足够的市场接受程度。5.实验建立了新工艺大头菜及其原料中挥发性风味物质的分析方法。采取同时蒸馏萃取法(SDE),准确称取100 g样品于2L圆底烧瓶中,加入1L的蒸馏水,萃取瓶加入40mL无水乙醚,圆底烧瓶内保持微沸,萃取瓶在40℃水浴锅中加热,回流2h,无水乙醚提取液在0℃经过无水硫酸钠干燥静止12h后过滤,滤液用旋转蒸发仪在冰浴条件下浓缩至1 mL,待气质联用上柱分析。气相色谱条件：石英毛细管柱Rtx-wax (30mx0.32mmx0.25μm),程序升温,柱温40℃,保持1min,以5℃/min升至120℃,再以20℃/min升至160℃,最后以5℃/min升至22℃,保持3min,载气为高纯He,柱流量1.02mL/min,进样口温度250℃,分流比20：1,接口温度250℃。质谱条件：EI电子源,扫描范围35-450m/z。图库：NIST05。在此条件下能够较好的完成对大头菜及其原料中挥发性风味物质的分离和分析。6.通过SDE-GC/MS分析,共从大头菜原料、新工艺大头菜、传统大头菜、脱盐大头菜四个样品中分别检验出90种挥发性香气物质,其中酯类化合物22种,醇类化合物16种,醛类化合物14种,酸类化合物8种,酮类化合物5种,甲基硫化物6种,腈类化合物3种,烃类化合物9种,其他杂环类化合物7种。确定了大头菜及其原料中的主体风味物质,包括：大头菜原料主体风味物质有异硫氰酸苯乙酯、环己醇、异硫氰酸烯丙酯、苯乙腈；新工艺大头菜中的主要风味物质有异硫氰酸苯乙酯、异硫氰酸烯丙酯、环己醇、邻苯二甲酸二丁酯、亚麻酸乙酯、二甲基三硫、亚油酸乙酯、亚油酸甲酯、巴豆腈、棕榈酸甲酯；传统大头菜主体香气成分为十五酸、环己醇、异硫氰酸苯乙酯、异硫氰酸烯丙酯、二甲基三硫；脱盐处理后的大头菜主要香气为十五酸、(E)-9-硬脂酸、亚油酸、亚油酸甲酯、麝香酮等。新工艺大头菜、传统大头菜、脱盐大头菜中分别检测出68,56,28种挥发性香气物质。从检测出的香气物质的种类来说,新工艺大头菜品质高于传统大头菜和脱盐大头菜。由离子流图可以看出,脱盐使大头菜香气成分损失。结合对大头菜的感官评价,脱盐后的大头菜酯香气不足,酸味重,没有传统大头菜和新工艺的大头菜的风味好。更多还原

【Abstract】 Kohlrabi is one kind of traditional curing food with unique flavor, which is very popular in China. Traditional processing of kohlrabi need sun drying, and several times salt dehydration. Further desalination process is needed because of high slat content after ripening, moreover, the long production cycle made it not appropriate for modern production. While one-time heat production can sharply shorten the processing cycle and reduce process steps. Research about Kohlrabi is mainly concentrated on the desalination process of traditional pickled turnip, however, less research on the volatile compounds. The study on the volatile compounds of kohlrabi not only can speculate the composition of its flavor and prevent the formation of bad odors, but also provide theoretical basis for the optimization of the process and for the mix of flavor.The pre-treatment process of this new technology and the changes of physical and chemical indicators of different products with different process were investigated in this paper, with Kohlrabi as raw materials. Orthogonal experiments were used to optimize the process parameters of this new technology. Besides, SDE-GC/MS was used to analysis the volatile flavor compounds of different Kohlrabi and raw materials. The main conclusions were as follows:1. new process of kohlrabi:kohlrabi→Cleaning→shred→pre-salt cured→mechanical dehydration→cooling→add salt→vacuum-sealed bags→ripening in dark→finished product j insulation at 25℃0.5% pre-salt cured was used in the Kohlrabi dehydration, which can decrease the loss of nutritional content. While hot air dehydration can reduce the germ-carrying of kohlrabi and realize the mechanization of this product.2. optimal parameters for the new process:water content of Kohlrabi 73%-76%, with 6% salt and vacuum 0.091 MPaChanges in physical and chemical characteristics of kohlrabi produced with new technology: (1) changes of protein content: protein has been decreased with the curing time. Degradation rate of protein decrease with the increase of salinity. The protein content of kohlrabi cured with 5% salt droped from 6.084% to 4.47%, and protein content of kohlrabi cured with 11% salt droped from 6.087% to 5.22%. (2) Changes of amino acid nitrogen content: the amino acid nitrogen content of kohlrabi taken on an rising trend in the ripening process, a negative correlation with protein content. (3) Changes of lactic acid content: in the ripening process, lactic acid of kohlrabi also taken on an rising trend. While the produce of lactic acid in low-salt pickled Caisi was faster with high yield. (4)Changes in reducing sugar content: overall in ripening process reducing sugar of kohlrabi taken on deline trend. Reducing sugar of kohlrabi cured with 5% salt reduced when marinated 60 days, while this happened when marinated 90 days in kohlrabi cured with 9% salt. (5) Changes in vitamin C content: vitamin C content has been declining in ripening process. The content of Vc in low salt Kohlrabi is high, relatively large loss in Kohlrabi of high-salt. (6) Changes in nitrite content: the nitrite content of Kohlrabi has a peak and the peak time was delayed with the increase of salt concentration, possibly because of the decomposition effect of high content of lactic acid in low-salt kohlrabi. (7) Color change:in curing process, the color of Kohlrabi gradually deepened, particular faster in low salt kohlrabi. (8) Hardness Change:the hardness of raw Kohlrabi materials decreased after dehydration. In the ripening process, kohlrabi hardness rised in the first month, then declined, and finally maintain at a stable hardness level.3.nutrition of kohlrabi produce with new process:compared with traditional kohlrabi, the nutritional value of this product increased. In products of new process, protein content increased 23%, reducing sugar increased 7.8%, vitamin C content increased 115.8%. While lactic acid and nitrite contents were decreased 272.5% and 33.5%, respectively.4. The market acceptance of new technology and traditional turnip kohlrabi have no significant difference, there is sufficient market acceptance.5. The analysis method of volatile flavor compounds in raw materials and finished product were established in this paper. The methods was:take simultaneous distillation and extraction (SDE) method.100 g sample were accurately weighed and then put into a 2 L round bottom flask, added 1 L of distilled water, then extracted by adding 40 mL of anhydrous ether into the extraction bottle, maintain a slight boiling stage in the round bottom flask, while extraction bottles heated in 40℃water bath pot, circumfluence for 2 hours, anhydrous ether extracts was dryed through anhydrous sodium sulfate at 0℃for 12 hours and then filtered, the filtrate was concentrated to 1 mL with a rotary evaporator under the conditions of ice bath. GC conditions: Quartz capillary column Rtx-wax (30 m X 0.32 mm X 0.25μm), temperature-programmed, Column temperature 40℃, keep 1 min, rose to 120℃with 5℃/min rate, then rose to 160℃with 20℃/min speed, finally, rose to 220℃with 5℃/min rate, keep 3min, carrier gas was high-purity He, column flow 1.02 mL/min, inlet temperature 250℃, split ratio 20:1, interface temperature 250℃. MS conditions:EI electron source, scan range 35-450 m/z. Gallery: NIST05. Under these conditions, it can better complete the separation and analysis of volatile flavor compounds in turnip and raw materials.6.90 kinds of volatile aroma substances were detected from raw materials, kohlrabi of new technology and the traditional turnip by SDE-GC/MS, including 22 esters,16 alcohols,14 aldehydes,8 acids,5 ketones,6-methyl sulfide,3 nitriles,9 hydrocarbon compounds and seven other heterocyclic compounds.The main flavor components in Kohlrabi and materials are:phenethyl isothiocyanate, cyclohexanol, allyl isothiocyanate, phenyl acetonitrile; the major flavor compounds of Kohlrabi of new technology are phenethyl isothiocyanate, allyl isothiocyanate, cyclohexanone, dibutyl phthalate, ethyl linolenate, dimethyl trisulfide, methyl linoleate, ethyl linoleate, croton nitrile and methyl palmitate; the main flavor of traditional turnip is 15 acid, cyclohexanol, phenethyl isothiocyanate, allyl isothiocyanate, dimethyl trisulfide; the main flavor component of desalination kohlrabi are pentadecylic acid, (E)-9-stearic acid, linoleic acid, linoleic acid methyl ester, musk ketone, etc.68、56、28 kind of volatile aroma components were detect in Kohlrabi of new technology, the traditional turnip and desalination kohlrabi, respectively. From the detected volatile aroma components species, the Kohlrabi of new technology has better quality than traditional turnip and desalting kohlrabi. As can be seen from the ion current, desalination resulted in the loss of aroma components of kohlrabi. Combined with the result of the sensory evaluation of kohlrabi, desalination kohlrabi has less ester aroma but with heavy sour taste, thus has less flavor than traditional kohlrabi and new process kohlrabi.更多还原