Application of ultrasound and its real-time monitoring of the acoustic field during processing of tofu: Parameter optimization,protein modification,and potential mechanism

Tofu is nutritious, easy to make, and popular among consumers. At present, traditional tofu production has gradually become perfect, but there are still shortcomings, such as long soaking time, serious waste of water resources, and the inability to realize orders for production at any time. Moreover, tofu production standards have not yet been clearly defined, with large differences in quality between them, which is not conducive to industrialized and large-scale production. Ultrasound has become a promising green processing technology with advantages, such as high extraction rate, short processing time, and ease of operation. This review focused on the challenges associated with traditional tofu production during soaking, grinding, and boiling soybeans. Moreover, the advantages of ultrasonic processing over traditional processing like increasing nutrient content, improving gel properties, and inhibiting the activity of microorganisms were explained. Furthermore, the quantification of acoustic fields by real-time monitoring technology was introduced to construct the theoretical correlation between ultrasonic treatments and tofu processing. It was concluded that ultrasonic treatment improved the functional properties of soybean protein, such as solubility, emulsifying properties, foamability, rheological properties, gel strength, and thermal stability. Therefore, the application of ultrasonic technology to traditional tofu processing to optimize industrial parameters is promising.     

南豆腐加工过程中品质及蛋白质结构的变化

以大豆为原材料,采用传统豆腐制作工艺,探讨加工工艺对南豆腐品质的影响,并利用傅里叶变换红外光谱和十二烷基硫酸钠-聚丙烯酰胺凝胶电泳研究加工过程中大豆蛋白结构的变化。以豆腐得率、保水性、质构特性和色差为评价指标,当凝固剂质量分数1.2%、蹲脑时间20 min和压型力度3.0 g/cm2时,制得的豆腐得率和保水性均较高,硬度和咀嚼性较好,色泽偏白,符合南豆腐“嫩”的特征。未经处理的大豆蛋白二级结构中以β-折叠（46.36%）为主,其次为β-转角（18.48%）和无规卷曲（15.45%）,浸泡、打浆会导致β-折叠含量下降、β-转角含量增加,蛋白质构象由收缩的紧密结构逐渐转变为展开状态;而点脑、蹲脑以及加压操作后,大豆蛋白的β-折叠含量不断回升,无序结构减少,蛋白结构较为稳定。豆腐加工操作对大豆蛋白的亚基影响较小,只有豆腐脑与南豆腐蛋白的电泳条带灰度变浅,而成型后的南豆腐含有一定量的7S亚基以及11S亚基,说明在加工过程中蛋白质的保持率较好。     

不同加工条件对全豆豆腐凝胶强度的影响

针对全豆豆腐加工中豆腐凝胶强度低的问题,研究了全豆豆腐煮浆工艺和凝固工艺中酶添加量、凝固温度、凝固时间和NaCl添加量对全豆豆腐凝胶强度的影响。得出全豆豆浆加热至90℃,保温10min的加热条件下,全豆豆腐凝胶强度最佳。通过单因素和正交实验,得到最佳的凝固条件为:酶添加量1.2U/mL豆浆、凝固温度50℃、凝固时间2h和NaCl添加量0.125%,制得的全豆豆腐品质优良,几乎包含大豆全部营养,比传统豆腐营养更丰富。      

豆浆加工工艺对全子叶豆腐品质影响的研究

为研究豆浆加工工艺对全子叶豆腐(Whole Cotyledon Tofu,WCT)品质的影响,以传统工艺作对照,选用去皮大豆为原料,比较研究两种豆浆加工工艺即湿法工艺(泡豆打浆)和干法工艺(制粉调浆)对制备WCT的组成成分、出品率、表观形态、色泽、质构特性的影响。结果表明:干法工艺和湿法工艺生产出的WCT的基本成分没有显著差异(p<0.05);与传统工艺相比,湿法工艺和干法工艺分别提高产量41.23%和46.67%,但后者比前者效率更高;干法工艺获得的WCT比湿法工艺外观更为顺滑细腻;两种工艺生产的WCT色泽无明显差异;干法工艺获得的WCT硬度、弹性、内聚性和咀嚼性均高于湿法工艺,且整体质构特性接近传统工艺豆腐。由此表明干法工艺比湿法工艺更适合生产品质优良的WCT,并能有效提高出品率。      

Effects of processing and cooking on the levels of pesticide residues in soybean samples

The effects of processing and cooking on the levels of pesticide residues in soybean samples were investigated for 14 pesticides in pre-harvest samples. On soaking, the transfer ratios (%, total pesticide residue amount in product/that in soybean) of soaked soybean were greater than 60% for most of the pesticides investigated. The transfer ratio of soymilk ranged from 37% to 92%, and that of tofu ranged from 7% to 63%. The processing factor (Pf, the concentration (mg/kg) of pesticide in product/that in soybean) of tofu ranged from 0.026 to 0.28. These values varied among pesticides. There was a high correlation between the log P(ow) and the transfer ratio of tofu. The test described here should be useful to obtain the transfer ratios of pesticide residues in processing and/or cooking steps.     

Effects of the β‐glycosidase reaction on bio‐conversion of isoflavones and quality during tofu processing

BACKGROUND: Isoflavones are the most common group of phytoestrogens which are present in significantly large amounts in soybean and soy products such as tofu. Isoflavones occur naturally in glycoside forms having lower bioavailability than their aglycone forms. β‐Glycosidase acts as a bio‐catalyst for the conversion of isoflavone glycosides to isoflavone aglycones, raising the bioavailability of isoflavones; therefore, it can be used to improve the quality of tofu. We need to establish process conditions for the optimal outcome of the enzyme reaction in tofu. RESULTS: By using the β‐glycosidase (0.02% w/v) reaction at 55 °C for 30 min, a maximum 84.5% conversion of isoflavone glycoside to isoflavone aglycone was obtained. The enzyme reaction caused no significant effects on the sensory acceptability of soft tofu. The hardness of enzyme‐treated hard tofu increased with the coagulant amount whereas prolonged heating resulted in decrease of hardness. Incorporation of enzyme reaction before the coagulation process during soft tofu processing provided a sufficient bio‐conversion of isoflavones at optimal conditions. CONCLUSION: β‐Glycosidase can be effectively used for the bioconversion of isoflavones in soft tofu manufacturing process at optimal reaction conditions before the onset of coagulation process. Copyright © 2010 Society of Chemical Industry     

Effect of processing,fermentation, and aging treatment to content and profile of phenolic compounds in soybean seed,soy curd and soy paste

This study reports the effect of processing, fermentation, and aging treatment on the content and profile of 43 phenolic compounds in soybean seeds, soy curd (tofu), and soy paste (ChungGukJang, CGJ). Mean content of phenolic compounds was ranked as soybean seed = CGJ aged for 3 days (CGJ-3D) = CGJ aged for 6 days (CGJ-6D) > tofu (P < 0.0001). Low percent recovery (47.1%) of phenolic compounds in tofu was due to heating (boiling), leaching in water, filtering, coagulation, and whey exclusion during tofu making. Aging period did not affect the mean contents of 43 phenolic compounds in the CGJ, whereas it affected the phenolic acids contents in the CGJ (P < 0.01). Benzoic, ferulic, chlorogenic, gentisic, protocatechuic, or β-Resorculic acid was major phenolic compounds in soybean seeds, tofu, CGJ-3D, or CGJ-6D. Especially, the CGJ-3D contained large amounts of isoflavone aglucons and phenolic acids compared to soybean seeds or tofu.     

基于气相色谱-质谱联用技术分析酸浆豆腐加工过程中风味物质的变化

目的以酸浆豆腐为研究对象,结合气相色谱-质谱联用法(gas chromatography-mass spectrometry,GC-MS)优化酸浆豆腐不同加工阶段中挥发性风味物质的捕获方法,对酸浆豆腐的加工阶段进行分类。方法采用顶空-固相微萃取法(head space-solid phase microextraction,HS-SPME)结合GC-MS对风味物质进行检测,优化风味物质捕获方法,内标法进行定量,结合聚类分析对加工阶段进行分类。结果不同批次酸浆豆腐中风味物质变化具有较高的稳定性,酸浆豆腐加工过程中共鉴定出90种挥发性风味物质,制浆、煮浆、点浆、蹲脑10 min、蹲脑20 min和压制工序分别鉴定出27、25、32、39、45和22种挥发性风味物质,主要为醛类、酮类、醇类等风味物质。对加工过程中风味物质进行聚类分析发现:适当延长煮浆与蹲脑时间,可促进更多良好风味物质的形成。结论该方法操作简单,适合酸浆豆腐中风味物质的测定且稳定性好,在后续实验中可进一步对加工工艺进行调控。     

Changes of soybean quality during storage as related to soymilk and tofu making

ABSTRACT:  Soybeans are stored and transported under various humidity and temperature conditions. Soymilk and tofu are two of the most important foods made from whole soybeans. The objective of this study was to investigate the influence of storage conditions on soybean quality as related to soymilk and tofu-making properties. Soybeans of 3 different genotypes (Proto, IA2032, and Vinton 81) were stored in varying conditions: temperature ranging from 4 to 50 °C, relative humidity from 55% to 80%, initial moisture content from 6% to14%, and storage time up to 15 mo depending upon storage conditions. The effects of different storage conditions on soybean color, solids and protein extractability, soymilk pH, tofu yield, tofu solids and protein contents, tofu color, and texture were investigated. While no significant changes occurred for the soybeans stored at 4 °C, the soybeans stored at high temperatures (30 to 50 °C) exhibited significant quality loss ( P < 0.05). The degradation of soybean lightness (Hunter L ), color difference (Δ E ), and solid extractability exhibited a linear relationship with time. Soak weight decreased at high temperature and relative humidity, but increased at mild storage conditions. Several combinations of storage conditions at temperatures exceeding 30 °C produced a drastic loss in tofu yield. Storage also affected the tofu making process by reducing optimum mixing time to produce the highest tofu yield. Varietal difference in soybean storability was observed. The results provided useful information for the soybean processing industry to store soybeans using the optimal storage conditions and to estimate soybean quality after storage.     

加工工艺对北方豆腐品质特性的影响

分别以生浆法、熟浆法、热水套法3种工艺制备北方豆腐,以出品率、保水性为指标,获得最佳制浆方式后,研究磨浆料液比、凝固温度、Mg Cl2溶液添加量、凝固时间对北方豆腐品质特性的影响以及出品率、保水性与质构特性的相关性。结果表明:熟浆法制成北方豆腐的出品率、保水性明显高于生浆法和热水套法;豆腐工艺的最佳优化条件为磨浆料液比1∶7(g/m L)、凝固温度80℃、0.6 mol/L?Mg Cl2溶液添加量18 m L/L、凝固时间20 min,制作的北方豆腐出品率和保水性均最高;根据相关性分析得出:不同加工条件下,硬度、内聚性及回复性与北方豆腐出品率、保水性均呈负相关,咀嚼性、胶着性及弹性与北方豆腐出品率、保水性均呈正相关。     

Effect of processing on nutritive values of milk protein

Milk is an essential source of nutritionally excellent quality protein in human, particularly in vegan diet. Before consumption, milk is invariably processed depending upon final product requirement. This processing may alter the nutritive value of protein in a significant manner. The processing operations like thermal treatment, chemical treatment, biochemical processing, physical treatments, nonconventional treatments, etc. may exert positive or negative influence on nutritional quality of milk proteins. On one side, processing enhances the nutritive and therapeutic values of protein while on other side intermediate or end products generated during protein reactions may cause toxicity and/or antigenicity upon consumption at elevated level. The review discusses the changes occurring in nutritive quality of milk proteins under the influence of various processing operations.     

Comparison of Two Small-Scale Processing Methods for Testing Silken Tofu Quality

In developing a simple, reliable, small-scale method to assess silken tofu quality in our soybean improvement program, we examined two processing methods and two coagulants, glucono-δ-lactone (GDL) or nigari (magnesium chloride) in two experiments. Silken tofu was prepared from a commercial soybean variety (expt 1) or seven soybean varieties (V1–V7) which were grown and harvested together (expt 2). The soybeans were soaked overnight (the soak method, with 55 g soybeans) or ground dry first (the dry method, with 60 g soybeans) before processing. The quality of the silken tofu was evaluated and compared among varieties and coagulant-processing methods and their interactions. Moisture and protein content in soymilk and soybean seeds, soymilk yield and protein and solid recovery in soymilk were determined. Compared with the dry method, the soak method allowed faster soymilk extraction, produced soymilk with lower solid and higher protein content and firmer silken tofu with either GDL or nigari as coagulant. Depending on whether nigari or GDL was used as coagulant, the soak method also produced silken tofu with the highest or the lowest water loss which correlated strongly and negatively with tofu hardness (r?=??0.93***). Differences were detected among varieties for the key quality attributes. Taken together, the soak method with GDL as coagulant would be the preferred combination to use to assess tofu quality.     

薄荷、茉莉花、荷叶臭豆腐发酵工艺的研究

在传统发酵型臭豆腐的基础上添加薄荷、茉莉花、荷叶以改变其营养价值和风味。在确定薄荷、茉莉花和荷叶混合浸提液对豆腐品质影响基础上,选取毛霉菌粉使用量、前发酵时间、腌制用盐量、发酵温度进行单因素和正交试验,优化薄荷、茉莉花、荷叶臭豆腐前发酵工艺,并检测其理化及微生物指标。结果表明,每500 g黄豆需用4 000 g水中加入薄荷1 g、茉莉花5 g、荷叶10 g得到的浸提液制作豆腐,最优前发酵工艺为豆腐坯500 g、毛霉菌粉2 g、前发酵时间3 d、食盐150 g、发酵温度25 ℃。在此优化条件下,臭豆腐感官评分为93分。臭豆腐呈黄褐色,口感酥脆,有荷叶和茉莉花香气及薄荷的清新口感,品质指标符合国家相关标准。     

榛仁内酯豆腐的制作工艺

本研究以榛仁和黄豆为原料、葡萄糖酸-δ-内酯(GDL)为凝固剂,研究榛仁内酯豆腐的制作工艺。以豆腐的硬度、弹性、内聚性和回复性为指标,通过单因素实验对黄豆与榛仁比例、葡萄糖酸内酯用量、点浆温度及点浆p H条件这四个因素进行筛选,结合正交试验、感官评价和质构分析等方法确定最佳制作工艺,并且对榛仁内酯豆腐与其他常见市售豆腐进行了质构等指标的对比。研究实验结果表明,当黄豆与榛仁比例10:3、GDL添加量1.05 g(GDL/100 g原料)、点浆温度85℃、点浆p H 6.5时,榛仁内酯豆腐的硬度为1±0.21/100 g、弹性为(6.3±0.16)mm、内聚性为0.54±0.01、回复性为1.12±0.21;市售豆腐的硬度为1.4±0.12/100 g与榛仁内酯豆腐硬度差异不显著,并且其感官评分值最高。通过优化榛仁内酯豆腐的各项质构条件不仅提高榛仁内酯豆腐的凝固效果还提高了感官评价得分,得到的豆腐品质结构最好。     

基于豆清发酵液点浆的 二次浆渣共熟生产豆腐的工艺优化

采用豆清发酵液为豆腐点浆的凝固剂,通过单因素实验研究水豆质量比、煮浆温度、豆清发酵液的添加量和煮浆时间对豆腐品质影响。以豆腐得率和蛋白质含量为指标,通过Box-Behnken实验结合响应面法建立二阶多项非线性回归方程和数据模型优化豆腐工艺,结果表明,最佳加工工艺条件为水豆质量比是6:1 kg/kg,煮浆温度是105.7 ℃,煮浆时间是5.8 min,豆清发酵液添加量26.3%。在最佳工艺条件下得到的豆清发酵液豆腐的得率和蛋白质含量分别最高达255%、11.12%,此时豆腐的水分含量及保水性达到最佳,优于市售同类产品,对于豆清发酵液豆腐的制作提供了借鉴价值。     

油焯豇豆的加工工艺研究

为获得高食用品质的油焯豇豆,给蔬菜浸泡油焯工艺条件的选择提供参考,研究了豇豆浸泡油焯的最佳工艺条件及油焯前后部分理化指标的变化。在以乙酸锌浓度、浸泡温度、浸泡时间为单因素的基础上,通过L9(34)正交实验,确定豇豆浸泡的最佳工艺条件为:乙酸锌浓度0.5%,浸泡温度35℃,浸泡时间15min;豇豆浸泡后油焯温度为190℃,油焯时间为75s。在上述条件下制备的油焯豇豆,VC损失了7.48%,叶绿素损失了31.31%,皂苷减少了13.63%;油焯豇豆色泽翠绿、硬度适中,感官品质较好。      

影响面粉品质及加工精度的主要因素及对策

论述了影响面粉品质及面粉加工精度的主要因素,从小麦品质、制粉工艺、面粉粗细度、磨辊表面技术特性、着水量和润麦时间、面粉添加剂的影响等不同角度进行了分析并提出了解决这些问题的具体措施。     

High hydrostatic pressure effects on immunoreactivity and nutritional quality of soybean products

The aim of this research was to evaluate the protein pattern, immunoreactivity and amino acid composition of soybean seeds and commercial tofu after treating by high hydrostatic pressure (HHP) (300 MPa, 15 min, 40 °C), as well as of sprouts obtained from unpressurised and HHP-treated seeds. HHP did not affect the electrophoretic profile of soybean seeds or tofu protein extracts, but lower intensity of some protein bands were observed in HHP-treated products. A significant (P ? 0.05) reduced antigenicity was observed in the sprouts from HHP-treated seeds compared to the sprouts from untreated seeds, while higher antigenicity of the pressurised seeds compared with the untreated ones was found. HHP decreased the total essential amino acid content as well as two nutritional indexes, the Chemical Score (CS) and the Essential Amino Acid Index (EAAI), but only by 18%. The findings suggest that HHP applied to soybean seeds before germination could constitute a valuable technological approach for the industrial production of nutritive hypoallergenic soybean sprouts.     

Effects of heating on protein quality of soybean flour devoid of Kunitz inhibitor and lectin

The effects of autoclaving on protein quality of soybean flours prepared from a conventional soybean (CSB) and an isoline lacking Kunitz inhibitor and lectin (KFLF) were studied. The heating was efficient in the urease, trypsin inhibitors and lectin inactivation, being 15 min sufficient to reduce more than 90% of these compounds and provide protein solubility over 80%. The results of PER, NPR and weight gain showed that heating equally improved the nutritional quality of both soybean flours, although higher autoclaving time was required for KFLF. No significant improvement was observed on NPU and in vivo digestibility of the diets containing KFLF at any heating time. As these later results were similar to those obtained with diets containing CSB, they show the importance of the heating to improve the nutritional value and show that other components rather than trypsin inhibitors and lectins impair the nutritive value of raw soybean.     

First processing steps and the quality of wild and farmed fish

First processing steps of fish are species-dependent and have common practices for wild and for farmed fish. Fish farming does, however, have certain advantages over traditional fisheries in that the processor can influence postmortem biochemistry and various quality parameters. This review summarizes information about the primary processing of fish based on the influence of catching, slaughtering, bleeding, gutting, washing, and filleting. Recommendations are given for the correct primary processing of fish.