Precipitation of proteins from potato juice with bentonite

The recovery of proteins from potato juice by treatment with bentonite has been investigated. All proteins can be precipitated from potato juice by acidification and addition of bentonite. The acid-coagulatable protein fraction is adsorbed less by bentonite than the acid-soluble protein fraction. Maximum adsorption of the acid-soluble fraction occurs at pH 5.0. The working conditions recommended for obtaining a protein-free potato juice are acidification to pH 4.5 and addition of bentonite to obtain a weight ratio of soluble protein: bentonite of 0.9. At the natural pH of potato juice (pH 5.8-6.0), adsorption of potato proteins on bentonite is irreversible. About 62% of the adsorbed protein can be recovered by alkali treatment at pH 13.     

Concentration of selenium by precipitating proteins from potato juice

The selenium concentration of potato tubers (cv. Mira) obtained from Shuan He, Enshi, Hubei, China is 0.16 mg kg^?1 by fresh weight (0.64 mg kg^?1 dry weight), but it is as high as 20–40 mg kg^?1 on dry basis in various concentrates of potato protein. The experimental results indicated a linear relationship between the amount of the protein precipitated and that of selenium coprecipitated from potato juice. Selenium concentrations in ultrafiltration, ferric chloride and citric phosphate buffer concentrates are 5.12, 5.92 and 8.08 times higher than those in potato powder when their protein contents are concentrated 6.10, 6.65 and 7.08 times, respectively. These results are important relating to the production of valuable dietary supplements, e.g. pills, capsules or foods with Se‐level being accurately controlled applicable to selenium‐deficient areas. Recovery of selenium by precipitating proteins from potato juice is a time‐ and energy‐saving method may be applied to the establishment of a large‐scale processing plant.     

Recovering proteins from potato juice by complexation with natural polyelectrolytes

Potato proteins (PP) in the lab‐made potato juice consists of patatins (38.1%), protease inhibitors (56.7%) and other high molecular weight proteins (5.1%) as characterised by Tricine‐SDS‐PAGE and MALDI‐TOF/TOF‐MS. To recover PP from potato juice, the complex behaviours of PP with several natural polyelectrolytes as a function of pH and protein to polyelectrolyte ratio (R_{PP/Polysaccharide}) were studied by turbidimetric titration. Results indicated that the turbidity curves of PP‐polysaccharides displayed a shift to higher pH for chitosan and lower pH for anionic polysaccharides with the decreasing of R_{PP/Polysaccharide}. Chitosan could be used to selectively recover patatin with the purity of 88.6%, and the highest protein yield (51.9%) was achieved at pH 6.0 and R_PP/chitosan of 1:2. Carrageenan, one typical anionic polysaccharide, could recover all the PP in potato juice at pH 3.5 and R_{PP/carrageenan} of 2.5:1 with no special protein selectivity.     

马铃薯淀粉废水中蛋白质和游离氨基酸的回收研究

利用天然聚电解质复合法回收马铃薯淀粉废水(PFJ)中蛋白质,并用离子交换色谱法分离纯化游离氨基酸。选用阴离子多糖卡拉胶(CG),研究了复凝聚过程中的相行为和不同p H、蛋白/卡拉胶比例对蛋白质回收效果的影响,并选用001×8型苯乙烯强阳离子交换树脂回收游离氨基酸。确定了最佳蛋白质回收条件,在p H3.5,蛋白/卡拉胶=2.5∶1(w/w)下,蛋白质回收率达到100%。游离氨基酸回收率达88.4%,氨基酸干基含量达89.5%。本研究得到的实验条件使得马铃薯淀粉废水中含氮物质得到充分回收,为其处理提供一定的指导作用。      

The solubility of potato proteins from industrial potato fruit juice as influenced by pH and various additives

The effects of pH and various additives on the precipitation and (re)solubility at pH 7 of potato proteins from industrial potato fruit juice (PFJ) were studied. The use of various strong and weak acids did not result in differences in protein precipitation, which on average occurred to a maximum of 60% of total protein at pH 3. Weak acids did, however, result in precipitates with a higher resolubility at pH 7 compared with strong acids. At pH 5, addition of FeCl₃ or ZnCl₂ increased both precipitation and resolubility compared with the situation without additives. The largest increases in both precipitation and resolubility were achieved using organic solvents at pH 5 as an additive, resulting in a maximum precipitation and maximum resolubility at pH 7 of 91 and 83% of total protein respectively. The results described in this study lead to the hypothesis that precipitation and resolubilisation of potato proteins from PFJ are not determined by their isoelectric pH but by their interactions with low‐molecular‐weight components. © 2001 Society of Chemical Industry     

Fractionation and characterization of yeast proteins

Fractional profile of proteins from baker's, brewer's, and alcoholic yeasts was studied, applying a consecutive treatment of commercial biomasses, with solutions with a gradient of ionic strength and pH. It was found that a large part (35-50%) of total proteins from investigated biomasses is extracted by means of 0.01 M KCl, pH 7.0, which together with proteins extracted by means of 0.65 M KCl, pH 9.5, makes the part of the easily extractable proteins (50-64% of the total protein amount). The remaining part of proteins is extracted by means of alkaline solutions only. The amino-acid composition of the isolated fractions indicated that they are suitable for usage as food product ingredients.     

甘薯汁饮料的研制

探讨了甘薯汁饮料的生产工艺 ,确定了最佳工艺流程与生产条件。     

Comparison of composition, enzyme activity and selected functional properties of potato proteins isolated from potato juice with two different expanded bed resins

Protein concentrates prepared by expanded bed adsorption (EBA) chromatography from industrial potato juice (PJ) were analysed for chemical composition, color, enzyme activities, thermal properties and selected functional properties (solubility and emulsifying stability). Two EBA multi-modal resins, MIMO I-45 and MIMO 1300 (UpFront Chromatography), were employed under various pH conditions resulting in four potato protein concentrates, A-D. Concentrate B contained an electrophoretically pure protease inhibitor fraction (20-21 kDa), whereas concentrate A, C and D contained both patatin (41 kDa) and protease inhibitors. The potato protein concentrates were explored for the presence of transitions from native to denatured states using differential scanning calorimetry (DSC). Concentrate C had lower heat of transition (ΔH) and T-onset than the other concentrates. The concentrate containing protease inhibitors exhibited the highest denaturation temperature and enthalpy. All concentrates differed significantly (P < 0.05) in color brightness, with concentrate B and D emerging as the brightest. The solubility of the concentrates was evaluated at pH 6 and pH 4.5. All concentrates had lower solubility at pH 4.5 than at pH 6 (70-80%). The stability of emulsions (1% protein, 20% oil, 0.08% xanthan gum) against creaming was analysed with a new method based on the Single electrode Capacitance Probe (SeCaP) technology. Small differences among concentrates were observed by the new SeCaP method.     

Fractionation of proteins in reconstituted skim-milk

Properties of the dried milk were improved when calcium chloride was added to the raw milk prior to the drying process. Solubility, wettability, undenatured whey protein and protein retention indices of the dried milk were increased and the reconstitutability was improved. The elution profile of the protein fractions on a Sephadex G-100 column differed according to the forward preheating of the raw milk and the addition of calcium chloride.     

Fractionation and characterization of tartary buckwheat flour proteins

Protein fractions (albumin, globulin, prolamin and glutelin) were extracted from defatted tartary buckwheat flour. Albumin was the predominant protein fraction (43.8%) followed by glutelin (14.6%), prolamin (10.5%), and globulin (7.82%). Albumin was relatively rich in histidine, threonine, valine, phenylalanine, isoleucine, leucine and lysine. Globulin had high levels of methionine and lysine. Prolamin was high in histidine, threonine, valine, isoleucine, and leucine. Glutelin was rich in histidine, threonine, valine, isoleucine, and leucine. SDS–PAGE analysis, under non-reductive and reductive conditions, showed that disulfide bonds existed in the four fractions. Non-reduced albumin showed major bands at 64, 57, 41, and 38 kDa, and globulin at 57, 28, 23, 19 and 15 kDa. Reduced albumin and globulin shared two common bands at 41 and 38 kDa. Reduced prolamin showed major bands at 29, 26, 17 and 15 kDa. In vitro pepsin digestibility of the four fractions (from high to low) was: albumin > globulin > prolamin and glutelin.     

发酵型土豆汁饮料的工艺研究

以土豆为原料,利用酵母菌、乳酸菌混合后发酵制成土豆汁饮料.经试验表明,最佳工艺条件为:接种菌配比1:1.5、接种量0.75%、发酵温度35℃、发酵时间48h.添加8%蔗糖、0.2%的混合稳定剂(0.1%黄原胶、0.1%CMC-Na)可制得酸甜可口的土豆汁饮料.     

Fractionation of a whey growth factor for Streptococcus agalactiae into two active components containing proteins

Previously three factors (F-1, F-2, F-3) that stimulated in vitro growth of Streptococcus agalactiae were separated from wheys of milk and colostrum by chromatographic procedures. Now F-1 was separated further into two active components, F-1a and F-1b, when rechromatographed on an anion exchange resin with distilled water as eluent. The stimulatory activity was associated with two protein peaks whereas a third protein peak that was eluted in those fractions containing lactose was not stimulatory. Most of the stimulatory activity (76 to 80%) and protein (90 to 93%) were retained by a filter with retention of greater than 1,000 MW. Two stimulatory factors were confirmed by separation of F-1 fractions by step-gradient elution on a column of octadecylsilica; one protein peak was found for each of the three solvents. Samples with protein eluted with .1 N formic acid and formic acid: methanol (1:1) had stimulatory activity, whereas the sample with protein eluted with 100% methanol was inactive. Results were similar when F-1 fractions were applied to Sep-Pak (muBondapack C18) cartridges and eluted with water, 50% methanol, and 100% methanol. Proteins in the Sep-Pak eluates with stimulatory activity (water and 50% methanol) were heterogeneous and different when separated by high-voltage paper electrophoresis. Proteose-peptone preparations with added lactose were chromatographed on columns of anion exchange resin, with distilled water as eluent, and produced two peaks of protein with elution volumes comparable to peaks 1 and 3. Lactose appeared to be a major factor in eluting the second protein peak.(ABSTRACT TRUNCATED AT 250 WORDS)     

马铃薯淀粉废水中蛋白质回收方法的研究进展

介绍了马铃薯蛋白质的基本性质,马铃薯淀粉生产废水中蛋白质回收的意义。综述了目前马铃薯淀粉废水中蛋白质回收的物理和化学方法,分析了各种方法的优缺点,并对未来的研究方向进行了展望。     

Characterization of potato starch fractions and their interaction with hydrocolloids

Commercial potato starch was separated through sedimentation into three fractions of the size < 25, 25–70 and >70 µm estimated with the laser particle meter method and <21.6, 21.7–30.6 and >30.7 µm according to the Sartorius balance method. Amylose and amylopectin content in particular fractions did not depend on the granule size. Number average and weight average molecular weight slightly decreased and phosphorus content increased with the size of granules in the fractions. Starch fractions and, for comparison, non‐fractionated starch were gelatinized in aqueous solutions of arabic, carob, karaya and xanthan gums and carrageenan. Except for the arabic gum, all tested hydrocolloids decreased onset temperature of gelation, T₀, of all starch fractions. Carob and xanthan gums and carrageenan the most remarkably decreased that parameter for large fraction, whereas other gums most considerably decreased T₀ of starch of the medium fraction. Effect of gums upon such parameters of the characteristics of gelation as η_max, η_min and η_25°C depended irregularly on the size of starch granules. In gels from gums and small granules, the role of G′ and G″ module differed from that in gels from the other starch fractions.     

Ultrastructure of denaturated potato proteins

The structure of potato protein precipitates formed by heat treatment or acidification of potato juice was investigated by transmission electron microscopy. Precipitates formed by heat denaturation (3 min at 100°C) consist of electron-dense particles of diameter < 300 nm, aggregated into three-dimensional open networks. Precipitates, formed by acidification to pH 3.0 and holding the acidified juice at room temperature, consist of network-like aggregates of electron-dense particles embedded in thin films which hinder the formation of a dense sediment. This structure explains the high sediment volumes which are typical of this kind of precipitate. By warming the acidified potato juice to 40°C, rapid flocculation and sedimentation of the suspended insoluble protein are observed within a few minutes and a dense sediment is finally obtained. This sediment consists mainly of the network-like aggregates of electron-dense particles and material of low electron density formed by the collapse of the films. Protein films have also been observed in precipitates of heat-denatured bovine serum albumin (BSA). High-methoxyl pectin promotes the formation of protein films on heat denaturation of potato proteins or BSA.     

马铃薯淀粉汁水中Patatin的纯化及结构研究

马铃薯淀粉汁水经分离与纯化后得到马铃薯糖蛋白Patatin。通过对Patatin纯度、结构的测定与分析表明:Patatin纯度在90%以上,分子量为40.6 k Da。Patatin是糖和蛋白质的复合物。单糖组成为:鼠李糖、甘露糖、葡萄糖和半乳糖。Patatin中含有α-糖苷键,糖苷类型为吡喃型;糖链和肽链之间由O-型糖肽键连接。Patatin的热变性温度为75℃。      

马铃薯淀粉加工汁水蛋白的臭氧鼓泡分离及营养评价

采用臭氧鼓泡分离马铃薯淀汁水蛋白质,以蛋白质回收率为指标,在单因素筛选基础上,通过正交实验,进行工艺参数优化。结果表明,臭氧浓度对回收率影响最大,温度对回收率影响最小。臭氧鼓泡分离蛋白质的最佳工艺参数为臭氧浓度为5.00g/h,温度10℃、pH8.0、通气时间90min,此条件下蛋白质回收率为93.21%;加入0.20%羧甲基纤维素钠溶液,干物质回收率从原有的40.65%提高到57.60%;臭氧处理回收的蛋白质,非必需氨基酸含量48.82%,必需氨基酸占41.73%,与全鸡蛋蛋白贴近度为0.867,仍具有较好的营养价值。     

加工过程中紫薯汁化学成分变化分析

为探讨加工过程对紫薯汁品质的影响,对紫薯汁加工中护色、烫漂、酶解、灭菌过程中游离氨基酸、游离糖、花青素、可溶性蛋白含量变化进行了测定。结果表明:护色和烫漂可导致游离氨基酸、游离糖、花青素损失,但是酶解过程会使紫薯汁中的游离氨基酸、游离糖、花青素增加。杀菌过程中,无论是巴氏杀菌还是高压蒸汽灭菌均可造成花青素、游离糖、游离氨基酸含量降低,但高压蒸汽灭菌造成的损失高于巴氏杀菌。水溶性蛋白在加工过程中整体呈下降趋势,尤其是热烫处理后降低为护色后的20%。     

不同品种甘薯汁抗氧化活性的研究

研究了9个品种甘薯汁的酚类物质及其抗氧化活性,旨在为甘薯汁的开发利用提供参考依据。分别采用Folin-酚法、亚硝酸钠法、pH示差法测定了甘薯汁的总酚、总黄酮、总花色苷含量。结果表明,甘薯汁中含有丰富的酚类物质,不同品种甘薯汁的总酚、总黄酮和总花色苷含量存在差异。通过4个体外抗氧化体系（FRAP法、DPPH自由基法、ABTS+自由基法、OH自由基法）评价了甘薯汁的抗氧化能力。结果显示,不同品种甘薯汁所呈现的抗氧化能力不同,酚类物质含量较高的甘薯汁其抗氧化能力较强。从抗氧化能力方面考虑,杭引薯1号、杭引薯3号、浙紫薯1、13号这4个抗氧化能力较强的品种较适合用于果汁加工以及功能性饮品的开发。      

甘薯浓缩汁加工过程中营养成分变化的研究

以Vc、甘薯多糖、胡萝卜素以及膳食纤维含量为指标,研究了甘薯浓缩汁在加工过程中的营养成分变化。结果表明,Vc在破碎过程中受到高温水(85～95℃,破碎过程)和剪切力的影响而氧化水解,几乎全部损失;β-胡萝卜素在浓缩和巴氏杀菌的高温处理过程中损失,高达98.6%;可溶性膳食纤维(SDF)受到果胶酶作用使果胶水解,在多级过滤、超滤和膜过滤后,部分不溶性膳食纤维(IDF)被截留,造成浓缩汁中总膳食纤维(TDF)含量减少88.6%;淀粉酶在水解淀粉后生成了大量的麦芽糖和葡萄糖,使甘薯汁中多糖含量增加283.15%。