Trypsin hydrolysis of whey protein concentrates: Characterization using multivariate data analysis

Hydrolysis of whey protein concentrates (WPCs) was performed using trypsin under different combinations of temperatures and pH values in a total of three experiments, namely experiment A at 37 °C and pH 8, experiment B at 37 °C and pH 9, and experiment C at 50 °C and pH 8. Monitorization of the degradation of native whey proteins and the peptide formation throughout hydrolysis was performed by reverse phase HPLC/UV. Seven main peptides were separated according to their polarity and numbered from T1 to T7. In general a difference was observed between rate of hydrolysis of α-lactalbumin and β-lactoglobulin; in the former case hydrolysis was complete by 15 min in experiments B and C and by 120 min in experiment A, whereas in the later case the rate of hydrolysis was much slower.     

乳糖异构化制备乳果糖的研究

本文介绍了一种生产食品和医药添加剂乳果糖的可行性方法。采用牛乳超滤液作为乳糖来源，蛋壳作为催化剂。这是利用工业废物的一种可供选择的方法。研究了催化剂填料，乳糖浓度以及pH值对乳糖异构化的影响。温度在98℃，采用6mg／ml的催化剂填料，反应60min就可以获得乳果糖的最佳产品。乳果糖的量为1．18g／100ml，通过这种反应条件可以生产出低水平的二级产品（表乳糖，半乳糖以及有机酸）。确定了从65％-92％的乳果糖糖浆中脱除有色副产品的方法。     

Hydrolysis of lactose in whey permeate for subsequent fermentation to ethanol

Fermentation of lactose in whey permeate directly into ethanol has had only limited commercial success, as the yields and alcohol tolerances of the organisms capable of directly fermenting lactose are low. This study proposes an alternative strategy: treat the permeate with acid to liberate monomeric sugars that are readily fermented into ethanol. We identified optimum hydrolysis conditions that yield mostly monomeric sugars and limit formation of fermentation inhibitors such as hydroxymethyl furfural by caramelization reactions. Both lactose solutions and commercial whey permeates were hydrolyzed using inorganic acids and carbonic acid. In all cases, more glucose was consumed by secondary reactions than galactose. Galactose was recovered in approximately stoichiometric proportions. Whey permeate has substantial buffering capacity-even at high partial pressures (>5500 kPa[g]), carbon dioxide had little effect on the pH in whey permeate solutions. The elevated temperatures required for hydrolysis with CO2-generated inhibitory compounds through caramelization reactions. For these reasons, carbon dioxide was not a feasible acidulant. With mineral acids reversion reactions dominated, resulting in a stable amount of glucose released. However, the Maillard browning reactions also appeared to be involved. By applying Hammet's acidity function, kinetic data from all experiments were described by a single line. With concentrated inorganic acids, low reaction temperatures allowed lactose hydrolysis with minimal by-product formation and generated a hexose-rich solution amenable to fermentation.     

酵母乳糖酶对牛乳乳糖水解作用的研究

采用乳酸克鲁维酵母的乳糖酶(β-乳糖苷酶)对乳糖溶液、喷雾干燥脱脂奶以及全脂奶进行了试验,以确定将乳糖转化成单糖的最适条件。当牛奶中酶浓度为3u/ml时,于40℃反应2小时或4℃反应24小时,约60％的乳糖得以水解。随着乳糖浓度的增高,水解程度也有所提高。当酶浓度为10U/ml时,于40℃反应2小时,90％乳糖得以水解。用自制的乳酸克鲁维酵母的乳糖酶和加拿大lactaid Inc.生产的乳糖酶制剂lactaid水解乳糖无大的差异。     

以酶法改性乳清蛋白为基质的脂肪替代品在冰淇淋中的应用

以酶法水解的乳清蛋白WPC-80为基质制备脂肪替代品,替代中脂冰淇淋中25%的脂肪。随着乳清蛋白水解度的增加,冰淇淋浆料粘度和膨胀率略有下降,抗融化率提高,制得低脂冰淇淋的各项感官指标均优于对照组。当乳清蛋白的水解度为4%时,制得的脂肪替代品添加到冰淇淋中,各项感官指标最佳。     

乳清中乳糖的酶法水解

本文研究了Aapergillur niger CWL2NU-3乳糖酶在乳清中的应用,探讨了温度、pH、金属离子、底物浓度、酶浓度及水解时间等因素对乳清中乳糖的酶法水解速度的影响,在此基础上确定了主要影响因素,通过正交试验,获得乳清中乳糖水解的最佳工艺条件(65℃、pH4.5、乳糖15%、[E]/[L]=0.03、水解时间2.5h),在此条件下乳糖水解率为91.0%。     

Lactose uptake rate measurements by C-labelled lactose reveals promotional activity of porous cellulose in whey fermentation by kefir yeast

Lactose uptake rate by kefir yeast, immobilized on tubular cellulose and gluten pellets during fermentation of lactose and whey, was monitored using ¹⁴C-labelled lactose. Results illustrated that, in all cases, lactose uptake rate was strongly correlated with fermentation rate and the fermentation’s kinetic parameters were improved by kefir yeast entrapped in tubular cellulose. As a result, twofold faster fermentations were achieved in comparison with kefir yeast immobilized on gluten. This is probably due to cluster and hydrogen bonds formation between cellulose and inhibitors, such as Ca⁺⁺ and generated lactic acid, by which they leave the liquid medium. The findings, regarding the promotional effect of cellulose, seem promising for application in industrial whey fermentations.     

Lactose hydrolysis and lactase activity in fermented mixtures containing mare's,cow's,sheep's and goat's milk

The degree of lactose hydrolysis and exogenous lactase activity of fermented mare's milk (MM) mixed with cow's (CM), sheep's (SM) and goat's milk (GM) was investigated. Moreover, the overall sensory desirableness of the novel products was also evaluated. A mixture MM + CM, or MM + GM, or MM + SM at a 1:1 ratio, significantly reduced the amount of contained lactose (P < 0.05). Fermented MM + SM mixture may be considered the product with the greatest potential consumer desirability. This particular product is preferable for patients with secondary lactose intolerance. Its additional advantage is connected with the predicted course of fermentation assessed on the basis of changes in pH, the count of mesophilic LAB and yeast as well as their survival rates during storage.     

Effect of whey protein enzymatic hydrolysis on the rheological properties of acid-induced gels

A protein dispersion blend of β-lactoglobulin and α-lactalbumin was heat-denatured at pH 7.5, hydrolyzed by α-chymotrypsin and then acidified with glucono-δ-lactone to form gels at room temperature. Heat treatment induced the formation of whey protein polymers with high concentration of reactive thiol groups (37 μmol/g). The reactive thiol group concentration was reduced by half after 40 min enzymatic hydrolysis. It was further reduced after enzyme thermal deactivation. During acidification, the first sign of aggregation for hydrolyzed polymers occurred earlier than for non hydrolyzed polymers. Increasing the hydrolysis duration up to 30 min resulted in more turbid gels characterized by an open microstructure. Elastic and viscous moduli were both reduced, while the relaxation coefficient and the stress decay rate constants were increased by increasing the hydrolysis duration. After one week storage at 5 °C, the hardness of gels made from hydrolyzed polymers increased by more than 50%. The effect of polymer hydrolysis on acid-induced gelation is discussed in relation to the availability and reactivity of thiol groups during gel formation and storage.     

Lactose crystallisation in concentrated whey: the influence of vat type

This work aimed to describe the rate of lactose crystallisation in concentrated whey carried out using two different crystallisers, utilising central or lateral stirring. The lactose crystallisation rate differed between treatments, showing high values with use of the central stirrer. Under the experimental conditions, after 4 h of crystallisation, in neither of the vats was 70% lactose crystallisation achieved. With the standardised conditions applied in this study, with soluble solids, time, and stirring and rate cooling being constant, it was possible to verify the influence of the vat type on the rate of lactose crystallisation.     

Lactose/beta-lactoglobulin interaction during storage of model whey powders

The objective of this study was to evaluate the presence or absence of interaction between lactose and beta-lactoglobulin during storage of model whey powders at different water activities (a(w)). Model whey powders were prepared by colyophilization of lactose with increasing quantities of beta-lactoglobulin. These colyophilized beta-lactoglobulin:lactose powders, assigned as BL powders, were stored from 0.11 to 0.95 a(w). The water sorption behavior of BL powders was studied gravimetrically, and the state of lactose was investigated using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Before storage, BL powders were amorphous. After storage, a loss of water was observed on moisture sorption isotherms of BL powders. It was related to the formation of lactose crystals, detected by DSC and SEM analysis, and to the structural collapse of the powders. Water loss due to lactose crystallization was shifted to higher a(w) with increasing beta-lactoglobulin content in BL powders. Moreover, kinetics of moisture sorption demonstrated that beta-lactoglobulin was also responsible for a slower crystallization process in BL powders. Then, the water sorption behavior of BL powders was very different from the behavior of the 2 compounds mixed after separate lyophilization. All these results pointed out interaction between lactose and beta-lactoglobulin, which appeared during lyophilization and still occurred during storage. This lactose/beta-lactoglobulin interaction stabilized model whey powders against lactose crystallization.     

Impact of the environmental conditions and substrate pre-treatment on whey protein hydrolysis: A review

Proteins in solution are subject to myriad forces stemming from interactions with each other as well as with the solvent media. The role of the environmental conditions, namely pH, temperature, ionic strength remains under-estimated yet it impacts protein conformations and consequently its interaction with, and susceptibility to, the enzyme. Enzymes, being proteins are also amenable to the environmental conditions because they are either activated or denatured depending on the choice of the conditions. Furthermore, enzyme specificity is restricted to a narrow regime of optimal conditions while opportunities outside the optimum conditions remain untapped. In addition, the composition of protein substrate (whether mixed or single purified) have been underestimated in previous studies. In addition, protein pre-treatment methods like heat denaturation prior to hydrolysis is a complex phenomenon whose progression is influenced by the environmental conditions including the presence or absence of sugars like lactose, ionic strength, purity of the protein, and the molecular structure of the mixed proteins particularly presence of free thiol groups.

In this review, we revisit protein hydrolysis with a focus on the impact of the hydrolysis environment and show that preference of peptide bonds and/or one protein over another during hydrolysis is driven by the environmental conditions. Likewise, heat-denaturing is a process which is dependent on not only the environment but the presence or absence of other proteins.     

渗透性K.lactis细胞内乳糖酶水解牛乳中乳糖的研究

应用填充床细胞反应器,以渗透性K．lactis细胞内乳糖酶连续催化牛乳中乳糖的水解。渗透性K．lactis细胞内乳糖酶的热失活遵循一级反应动力学,40℃时酶的半衰期为9．5h,表观米氏常数为0．39mmol/ml,最大反应速率Vmax为0．188mmol/min。在2．6cm×50cm填充床生物反应器上,渗透性K．lactis细胞内乳糖酶催化牛乳中乳糖水解的适宜体积流速为1．0ml/min,酶反应的适宜温度40℃,反应速率达到动态平衡后生成的葡萄糖的质量浓度为45．2mg/ml,牛乳中乳糖的水解率为91．3%。     

Lactose recovery from Panela cheese whey: Effect of whey acidification on spontaneous and stirring-induced crystallisation

This work aimed to investigate the kinetics, yield, size and composition changes in lactose crystals when Panela cheese whey was acidified (pH 3.80) or slightly alkalinised (pH 6.89) before being subjected to spontaneous or stirring-induced crystallisation. At pH 3.8, the crystallisation was accelerated, and the incorporation of salts and proteins in lactose crystals decreased. Nevertheless, these conditions induced the formation of amorphous lactose. In contrast, at pH 6.89 and under stirring conditions, the amorphous lactose was not formed and gave a high crystallisation yield (∼25 g of lactose per Kg of whey) with ∼80% of lactose recovery.     

渗透性K.1actis细胞内乳糖酶水解牛乳中乳糖的研究

应用填充床细胞反应器，以渗透性K．1actis细胞内乳糖酶连续催化牛乳中乳糖的水解。渗透性K．1actis细胞内乳糖酶的热失活遵循一级反应动力学，40℃时酶的半衰期为9．5h，表观米氏常数为0．39mmol／ml，最大反应速率Vmax为0．188mmol／min。在2．6cm×50cm填充床生物反应器上，渗透性K．1actis细胞内乳糖酶催化牛乳中乳糖水解的适宜体积流速为1．Oml／min，酶反应的适宜温度40℃，反应速率达到动态平衡后生成的葡萄糖的质量浓度为45．2mg／ml，牛乳中乳糖的水解率为91．3％。     

酶法水解乳糖与热处理偶联对牛乳Maillard反应的影响

旨在探讨乳糖水解程度及热处理方法与Maillard反应的关系,鲜牛乳用中性乳糖酶处理获得不同水解程度的低乳糖牛乳,然后对牛乳进行不同的热处理,处理后的样本进行Maillard反应程度评价。采用葡萄糖氧化酶法测定不同水解时间的牛乳中葡萄糖质量浓度和乳糖水解率,用高效液相色谱法和紫外分光光度法分别测定水解后牛乳经不同热处理后的糠氨酸和5-羟甲基糠醛(5-hydroxymethylfurfural,5-HMF)含量及牛乳褐变程度的OD值。结果表明,随着乳糖水解时间的延长,牛乳中的葡萄糖含量呈增加的趋势,葡萄糖质量浓度从0.00 mg/100 m L增加到1 721.33 mg/100 m L,但增加趋势逐渐变缓;乳糖水解率从0%增加到70.33%,水解时间2.0 h后的牛乳水解率达到了50%以上。糠氨酸含量呈上升的趋势(P0.05),水解时间在3.0 h以上并经75℃、30 min热处理的牛乳,糠氨酸含量超过了190 mg/100 g pro;水解时间为0.5 h及以上并经75℃、15 s热处理的牛乳,糠氨酸含量超过了12 mg/100 g pro。生鲜牛乳和水解后经75℃、30 min热处理的牛乳,均未检测到5-HMF,水解后经75℃、15 s热处理的牛乳,随乳糖水解时间的延长,牛乳中5-HMF含量增加显著(P0.05)。牛乳的褐变程度随乳糖水解时间显著增加(P0.05),且乳糖酶水解后75℃、30 min热处理的牛乳的褐变程度明显高于75℃、15 s热处理的牛乳。本研究结果说明,乳糖经过酶水解后的牛乳,长时间热处理会加重乳Maillard反应,影响乳的蛋白质品质。     

Effect of lactose hydrolysis on the milk-fermenting properties of Lactobacillus delbrueckii ssp. bulgaricus 2038 and Streptococcus thermophilus 1131

Yogurt is a well-known nutritious and probiotic food and is traditionally fermented from milk using the symbiotic starter culture of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus. However, yogurt consumption may cause health problems in lactose-intolerant individuals, and the demand for lactose-free yogurt has been increasing. The standard method to prepare lactose-free yogurt is to hydrolyze milk by lactase; however, this process has been reported to influence the fermentation properties of starter strains. This study aimed to investigate the fermentation properties of an industrial starter culture of L. bulgaricus 2038 and S. thermophilus 1131 in lactose-hydrolyzed milk and to examine the metabolic changes induced by glucose utilization. We found that the cell number of L. bulgaricus 2038, exopolysaccharide concentration, and viscosity in the coculture of L. bulgaricus 2038 and S. thermophilus 1131 was significantly increased in lactose-hydrolyzed milk compared with that in unhydrolyzed milk. Although the cell number of S. thermophilus 1131 showed no difference, production of formic acid and reduction of dissolved oxygen were enhanced in lactose-hydrolyzed milk. Further, in lactose-hydrolyzed milk, S. thermophilus 1131 was found to have increased the expression of NADH oxidase, which is responsible for oxygen reduction. These results indicated that glucose utilization promoted S. thermophilus 1131 to rapidly reduce the dissolved oxygen amount and produce a high concentration of formic acid, presumably resulting in the increased cell number of L. bulgaricus 2038 in the coculture. Our study provides basic information on the metabolic changes in starter strains in lactose-hydrolyzed milk, and demonstrates that lactose-free yogurt with increased cell number of L. bulgaricus can be prepared without delay in fermentation and decrease in the cell number of S. thermophilus.     

一种高温乳糖酶的酶学性质及对牛乳中乳糖的水解

对重组大肠杆菌产生的β-半乳糖苷酶学性质的研究表明，该酶最适反应温度为55℃，最适PH值为7．0，在50℃时具有良好的热稳定性，K^ ,Mg^2 ,Mn^2 等对酶有一定的激活作用，而重金属盐如Pb^2 ,Sn^2 ,Zn^2 ,Cu^2 等对酶活有一定抑制作用，对乳糖分解试验研究表明，该酶水解乳糖的能力较强，牛奶中添加2NLU／mL时，55℃保温水解2h可达到55％以上的水解率。     

Bitterness in Bacillus proteinase hydrolysates of whey proteins

Whey protein concentrate (WPC) hydrolysates were generated with three commercially available Bacillus proteinase preparations (pH 7.0, 50 °C, 20% (w/v) WPC). Alcalase 2.4L hydrolysates were more bitter than Prolyve 1000 and Corolase 7089 hydrolysates when the proteinase activities were included at equivalent high and low addition levels. A glutamyl endopeptidase (GE) activity present in Alcalase was not detected in the Prolyve and Corolase preparations. Hydrolysate bitterness significantly increased when GE activity was included during Prolyve hydrolysis of WPC, indicating that inclusion of the GE activity was linked with the higher bitterness in Alcalase hydrolysates. A peptide present at higher levels in Prolyve compared to Alcalase hydrolysates was identified by mass spectrometry as β-lactoglobulin f(43–57). Hydrolysis of this peptide by GE was shown to release fragments with increased average hydrophobicity (Q-value). This may, in part, explain the higher level of bitterness associated with Alcalase compared to Prolyve hydrolysates of WPC.