【作者】 李鹏；

【导师】 钱海峰；

【作者基本信息】 江南大学 ， 食品科学与工程， 2020， 硕士

【摘要】 黑豆因具有多种营养物质和植物活性成分,被广泛开发成多种产品,但由于其种皮较厚、质地坚硬,蒸煮过程不易熟化。因此在蒸煮前对黑豆进行适当预处理,对黑豆大米共煮同熟至关重要。本文以黑豆为研究对象利用低场核磁共振分析技术（LF-NMR）对浸泡过程中黑豆内部水分分布以及氢质子弛豫时间进行分析;采用不同方式浸泡黑豆研究其对浸泡的影响,并通过Fick扩散模型和Peleg模型研究其对黑豆吸水特性的影响;利用响应面优化黑豆预熟化工艺,检测预熟化前后营养成分以及内部结构改变。研究内容如下:首先通过LF-NMR研究黑豆浸泡水分分布及质子迁移变化。黑豆吸水速率因温度不同而有较大差距,但最终饱和含水率相似。在研究质子流动性过程中,发现种子内部主要存在3种质子团T21、T22和T23,延长浸泡时间和提高浸泡温度均可使弛豫曲线向右偏移,浸泡温度越高质子流动性越强。研究3种质子团所占比例,发现M₂₁、M₂₃均随着浸泡时间的延长而降低,M₂₂从约1%提高到90%,表明浸泡增加的水分主要为自由水。不同浸泡温度弛豫时间对比发现高温可以使得氢质子弛豫时间在较短时间内达到稳定状态,这与水分含量增长趋势一致。核磁共振成像（MRI）分析结果表明水分沿着细胞壁无序的渗透到种子内部。随后通过Fick扩散模型和Peleg模型对比了普通浸泡和超声处理对黑豆吸水特性的影响。两种模型均可较好的拟合两种处理方式中黑豆水分含量的变化,相关系数R²大于0.9873,其中Fick扩散模型中水的扩散系数随着温度的升高而升高,两种浸泡方式在70℃条件下水的扩散系数分别达到最大值17.72和14.22。同时根据有效扩散系数与绝对温度的关系,通过Arrhenius方程计算发现超声处理使黑豆浸泡活化能从36.40 kJ/mol降至32.22 kJ/mol。以黑豆水分含量为对象,研究两种处理方式对Peleg速率参数K₁值的影响,结果发现K₁值随温度变化呈线性减小。采用扫描电镜（SEM）对浸泡后的黑豆种皮进行检测,发现超声处理后种皮表面孔洞和破裂之处加深,增加水分渗透途径,减少浸泡时间。最后基于响应面分析法优化预熟化黑豆处理工艺,并通过差示扫描量热仪（DSC）、傅里叶变换红外光谱（FT-IR）、SEM研究预熟化前后黑豆内部结构以及营养成分变化情况。响应面优化最佳条件为:浸泡温度50℃、浸泡2 h、蒸煮60 min。在该条件下黑豆糊化度为76.98%、感官评分为86.31,且与大米共煮达到同熟效果。FT-IR分析发现,黑豆经预熟化后蛋白二级结构发生改变,α-螺旋结构增多、β-转角结构增多,β-折叠结构减少,说明预熟化过程中有序结构发生转变;并对黑豆粉进行SEM观察,发现预熟化后,因加热聚集导致颗粒成团、体积变大,微孔增多;采用DSC测试发现预熟化后黑豆未检测出吸热峰,表明其蛋白发生变性。更多还原

【Abstract】 Black beans were widely developed into a variety of products due to their high contents of nutrients and plant active ingredients.However,black beans contain the thick seed coat and hard texture,which causes great inconvenience to the cooking process.Therefore,proper pretreatment of black beans before cooking is essential when cooked with rice together.In this paper,the distribution of water and the relaxation time of hydrogen protons in black beans were analyzed by low-field nuclear magnetic resonance technique（LF-NMR）during soaking;Different treatments were used to study the effect of soaking on the black beans,and Fick diffusion model and Peleg model were used to study the effect of black beans on water absorption;Response surface methodology was applied respectively to optimize the technology of black beans precooking,and to detect the changes of nutrients and internal structure before and after precooking.The main research contents are as follows:Firstly,the LF-NMR was used to study the water distribution and proton mobility of black beans during soaking.The different soaking temperature caused the black beans to absorb the water at different rates,but the final saturated moisture contents were similar.During the study of proton mobility,it was found that there were three kinds of protons T₂₁,T₂₂ and T₂₃ in black beans.Prolonging the soaking time and increasing the soaking temperature could make the relaxation time curve shift to the right,and the proton mobility increased with the increase of soaking temperature.When studying the proportion of the three types of proton clusters,it was found that M₂₁ and M₂₃ both decreased with the increase of the soaking time,while M₂₂increased from about 1%to 90%,indicating that the increased content of water for soaking was mainly free water.Comparing the relaxation time of different temperatures,it was found that high temperature could make the hydrogen proton relaxation time reach a stable state in a short time,which was consistent with the increasing trend of moisture content.The results of magnetic resonance imaging（MRI）showed that water infiltrated into the seed along the cell wall disorderly.Subsequently,the effects of ordinary soaking and ultrasonic treatment on the water absorption characteristics of black beans were compared by Fick diffusion model and Peleg model.Both Fick diffusion model and Peleg model could well fit the moisture content of black beans with the two treatments,and the correlation coefficient R² was greater than 0.9873.The diffusion coefficient of water in Fick diffusion model increased along with the temperature,and the diffusion coefficient of water in the two soaking methods reached the maximum value of17.72 and 14.22 at 70℃.At the same time,according to the relationship between the effective diffusion coefficient and the absolute temperature,it was found that the activation energy of black beans decreased from 36.40 kJ/mol to 32.22 kJ/mol by ultrasonic treatment.Taking the water content as the study object,the effects of the two treatments on the K₁ value of Peleg rate parameter were studied.It was found that the K₁ value decreased linearly with the change of temperature.Scanning electron microscopy（SEM）was used to examine the seed coat of black beans after soaking.It was found that the holes and cracks on the surface of the seed coat were deepened after the ultrasonic treatment,which increased the channels for the water penetration and reduced the soaking time.Finally,response surface analysis（RSM）was used to optimize the processing technology of precooked black beans,and the changes of internal structure and nutrients of black beans before and after cooking were studied by differential scanning calorimetry（DSC）,SEM and fourier transform infrared spectroscopy（FT-IR）.The response surface results showed that soaking at 50℃for 2 h and cooking for 60 minutes could make the black beans gelatinization degree reach 76.98%and the sensory score reached 86.31,which could achieve to be cooked with rice together.FT-IR analysis found that the secondary structure of black bean proteins changed after pre-treating,α-helix structure andβ-turn structure increased,andβ-sheet structure decreased,which indicated that more ordered structures changed during pre-treating;SEM observations of black bean powder revealed that the particles after pre-treating aggregated and agglomerated after heated,in the same time the volume became larger,and the pores bacame larger.DSC results showed that the black bean protein was denatured and the endothermic peak disappeared after pre-treating.更多还原