Separation of di- and tripeptides with solvent extraction and an emulsion liquid membrane

The extraction equilibria of various di- and tripeptides with di-2-ethylhexylphosphoric acid (D2EHPA) were studied at low pH values. The complex extracted to organic phase consisted of one molecule of peptide and two molecules of D2EHPA dimer. The extraction constants of the peptides correlated well with the distribution coefficients of peptides between 1-octanol and water, which is a measure of hydrophobicity. The permeation rates of peptides through an emulsion liquid membrane were examined by using D2EHPA as a carrier, Span 80 as an emulsifier and kerosene as a diluent. The rates varied considerably with peptide type, depending upon the hydrophobicity.     

Prebiotic synthesis of sequential peptides on the Hadean beach by a molecular engine working with nitrogen oxides as energy sources

Addressing the still open question of the prebiotic origin of sequential macromolecules (peptides, nucleic acids) on the primitive Earth, we describe a molecular engine (the primary pump), which works at ambient temperature and continuously generates, elongates and complexifies sequential peptides. This new scenario is based on a cyclic reaction sequence, whose keystep is the activation of amino acids into their N‐carboxyanhydrides (NCA) through nitrosation by NOx. This process could have taken place on tidal beaches; it requires a buffered ocean, emerged land and a nitrosating atmosphere. With the help of geochemical studies and computer simulations of atmosphere photochemistry, we show that the primitive Earth during the Hadean may have satisfied all these requirements. © 2001 Society of Chemical Industry.     

大豆多肽复合酶解工艺条件研究

以大豆分离蛋白为原料,经蛋白酶酶解、分离、提纯可以制得大豆多肽。试验采用复合酶解法结合正交试验分析,确定大豆蛋白复合酶解的最佳工艺条件为:三酶复合蛋白酶(由中性蛋白酶、木瓜蛋白酶和菠萝蛋白酶以1∶2∶Z的比例复合而成)、底物浓度4%、pH7.0、酶解时间9h、大豆蛋白酶水解度(DH)84.40%。     

Milk biologically active components as nutraceuticals: review

Milk contains components that provide critical nutritive elements, immunological protection, and biologically active substances to both neonates and adults. Milk proteins are currently the main source of a range of biologically active peptides. Concentrates of these peptides are potential health-enhancing nutraceuticals for food and pharmaceutical applications. Several bioactive peptides may be used as nutraceuticals, for example, in the treatment of diarrhea, hypertension, thrombosis, dental diseases, as well as mineral malabsorption, and immunodeficiency. Minor whey proteins, such as lactoferrin, lactoperoxidase, lysozyme, and immunoglobulins, are considered antimicrobial proteins. Milk also contains some natural bioactive substances. These include oligosaccharides, fucosylated oligosaccharides, hormones, growth factors, mucin, gangliosides, and endogenous peptides, which are present in milk at secretion. Most of the claimed physiological properties of milk bioactive components have been carried out in vitro or in animal model systems, and these hypothesized properties remain to be proven in humans. Whether these milk bioactive components will replace drugs entirely in the immediate future is still unclear, but the increasing appreciation of "drug foods" or nutraceuticals plays a complementary rather than a substitutional role to the synthetic pharmacological drugs.     

Purification and characterisation of antioxidative peptides from unfractionated rice bran protein hydrolysates

Crude rice bran protein (CRBP) was prepared by alkaline extraction and then treated with 0.6 m HCl to remove phytic acid. The phytate‐free rice bran protein (PFRBP) was hydrolysed with proteases M, N, S, P and pepsin under optimal conditions. Hydrolysates obtained from various hydrolysis periods were subjected to analysis for their degree of hydrolysis (DH) and functional properties. The hydrolysates were fractionated by reversed‐phase column chromatography on Kaseigel ODS resin (120–140 μm) using a stepwise gradient of aqueous ethanol, and their activities were measured. The 40% ethanol fraction of protease P 4 h‐hydrolysate was separated by successive reversed‐phase high‐performance liquid chromatography and the amino acid sequences of isolated antioxidative peptides were determined by a protein sequencer and matrix‐assisted laser desorption ionisation‐time of flight mass spectrometry. Crude rice bran protein had higher antioxidative activity than PFRBP, due to the presence of phytic acid. Phytate contents of rice bran, CRBP and PFRBP were 2.5%, 1.42% and 0%, respectively. The activity of PFRBP increased upon protease digestion. Protease M hydrolysates showed the highest DH, but the lowest antioxidative activity. Hydrolysates with DH below 10% had higher antioxidative activity than those above 20%. This result indicates that the antioxidative activity of the hydrolysates is inherent to their characteristics amino acid sequences of peptides depending on the protease specificities.     

大豆活性肽抗氧化力与其分子量关系的研究

大豆活性肽具有抗氧化性,其抗氧化力大小与大豆活性肽的分子量有关。采用凝胶柱层析分离法对碱性蛋白酶所制备的大豆活性肽(水解度为19.5%)进行分离纯化,得到六个组分,然后比较六个大豆活性肽组分(浓度均为1mg/mL)的抗氧化力大小,结果表明,组分4的抗氧化效果最好。用电喷雾质谱(ESI-MS)测定抗氧化大豆肽组分4的分子量,根据质谱图采用电喷雾质谱软件分析得出,抗氧化大豆肽组分4的平均分子量500,氨基酸数目为4个。     

双酶复合法制备大豆多肽工艺的研究

确定了双酶复合法提取制备大豆多肽的工艺条件.大豆蛋白经双酶复合酶解、活性炭脱色、超滤、真空浓缩和离心喷雾干燥等工艺,提取得到大豆多肽.通过试验确定,最佳复合酶解条件:中性蛋白酶与菠萝蛋白酶比例为3:1、pH 7.0、底物浓度4.0%、酶解时间9 h;最佳脱色处理条件:粉末活性炭用量2.0%、温度50℃、pH 3.0、吸附时间3 h;超滤分离条件:NF-1纳滤膜、截留分子量2000 D、超滤压力1.0 mPa.     

Inhibition of verocytotoxigenic Escherichia coli by antimicrobial peptides caseicin A and B and the factors affecting their antimicrobial activities

The antimic robial activities of caseicin A and B antimicrobial peptides (AMPs) were assessed against a selection of verocytotoxigenic Escherichia coli (VTEC) strains (n = 11), other bacterial pathogenic and spoilage bacteria (n = 7), using a model broth system. The ability of the AMPs to retain their antimicrobial activities against a strain of E. coli O157:H7 380-94 under various test conditions (pH, temperature, water activity, sodium chloride concentrations, inoculum size and the presence of competitive microflora) was assessed and the minimum inhibitory concentrations (MIC) and number of surviving E. coli O157:H7 calculated. The mean number of VTEC surviving after exposure to 2 mg/ml caseicin A and B was reduced by 4.96 and 4.19 log₁₀ cfu/ml compared to the respective controls. The susceptibility of E. coli O157:H7 to the caseicin AMPs decreased as temperature, pH, water activity and inoculum size were reduced. The presence of sodium chloride (0.5-2.5%) did not affect the activity of caseicin A (p > 0.05), however it did inhibit the activity of caseicin B. The presence of a competitive microflora cocktail did not significantly (p > 0.05) affect the activities of the AMPs for the majority of the concentrations tested. Using a quantitative PCR assay, the levels of verotoxins (vt1 and vt2) expressed by E. coli O157:H7 following exposure to a sub-inhibitory concentration (0.5 mg/ml) of caseicin A showed that the verotoxin levels did not differ from the levels produced by the control cultures. The antimicrobial activity of caseicin A against E. coli O157:H7 was also tested in a model rumen system, however concentrations of ≥ 2 mg/ml did not significantly (p > 0.05) reduce E. coli O157:H7 numbers in the model system over a 24 h period. The application of caseicin AMPs in food and/or animal production may be valuable in combination with other antimicrobials although further research is required.     

Stability of antioxidant peptides from duck meat after post‐mortem ageing

The stability of antioxidant peptides from aged duck meat during processing and simulated gastrointestinal digestion was investigated. The antioxidant peptides preserved a high stability in the presence of diverse NaCl or upon various time heating. The antioxidant activities were strengthened by the addition of 4–8% glucose or by heating at 100 °C, whereas they were lost under alkaline conditions. During in vitro digestion, the antioxidant activities increased with pepsin treatment but then decreased following trypsin digestion. Pepsin hydrolysed peptides into short fragments and results in the increased exposure of internal hydrophobic amino acids. With further treatment by trypsin, peptides can be hydrolysed completely and more free amino acids were released, leading to the decline in surface hydrophobicity. These variations might be responsible for the change in antioxidant activity during in vitro digestion. The antioxidant peptides from aged duck with high stability can be used as functional food ingredients to improve human health.     

酶解乳蛋白制取乳源肽的研究

用酸性蛋白酶、中性蛋白酶和碱性蛋白酶对牛乳蛋白进行水解，研究了水解工艺，并通过正交试验对工艺进行了优化。结果为：酸性蛋白酶水解牛乳蛋白的最佳工艺条件是：水解温度50℃，时间120min，pH值3．0，加酶量8．0％；中性蛋白酶水解温度50℃，时间90min，pH值7．0，加酶量1．60％；碱性蛋白酶水解温度60℃，时间105min，pH值9．0，加酶量8．0％。中性蛋白酶水解物苦昧最小，最适宜作食品。