Physicochemical and sensory properties of milk supplemented with lactase microcapsules coated with enteric coating materials

In this paper, we report the physicochemical and sensory properties of milk supplemented with a powder of microencapsulated lactase. The core material was lactase (β-galactosidase), the primary coating material was medium-chain triglyceride (MCT), and the secondary (enteric) coating material was either hydroxypropyl methylcellulose phthalate (HPMCP) or shellac, comparing both against market milk as a control. The physicochemical properties of both types of microcapsules were analyzed, including the particle size, zeta potential, and in vitro release behavior. To survey the stability of the microcapsules in milk during storage, we studied the residual lactose content and pH. Furthermore, to determine the properties of milk supplemented with the microcapsules, changes in color and sensory properties were evaluated during storage. The particle sizes (volume-weighted mean; D[4,3]) of the microcapsules coated with HPMCP or shellac were 2,836 and 7,834 nm, respectively, and the zeta potential of the capsules coated with shellac was higher than the zeta potential of those coated with HPMCP. The pH levels of milk supplemented with the lactase microcapsules were similar to those of the control (unsupplemented market milk); however, for milk supplemented with HPMCP-coated microcapsules, the pH was slightly lower. The core material, lactase, was released from the microcapsules during 12-d storage, and 18.82 and 35.09% of lactose was hydrolyzed in the samples for HPMCP- and shellac-coated microcapsules, respectively. The sensory characteristics of milk containing microcapsules coated with HPMCP did not show significant differences from the control, in terms of sweetness or off-taste, until 8 d of storage. However, shellac-coated microcapsules showed significant difference in sweetness and off-taste at d 8 and 6 of storage, respectively. The color of milk containing HPMCP-coated microcapsules did not show a significant difference during storage. However, that containing shellac-coated microcapsules was somewhat higher in color values than others. In particular, it showed significance from 0 to 4 d storage in L* and C* values. In conclusion, a powder of lactase microcapsules coated with HPMCP can be suitable as a supplement for milk.     

Organoleptic and physical properties of yogurt made from lactose hydrolysed milk

Low-lactose yogurt has been manufactured by using two commercial lactase enzymes: Lactozym and Maxilact. For each lactase enzyme two different enzyme treatments were examined: hydrolysing before fermentation and hydrolysing during fermentation.
When evaluated by the triangle test it was not possible to detect any significant difference in organoleptic properties, including sweetness, between the control yogurt and the yogurt samples made from hydrolysed milk. The addition of fruit and sugar made it possible to detect a difference in sweetness when triangle tested.
When lactase was added to evaporated milk (approx. 10% S N F) together with the starter culture, the results showed that addition of an amount equal to 500 - 700 LAU/litre resulted in a yogurt with about 2% lactose. A technology based on these results seems applicable to industrial manufacture.     

山羊乳-FOS/GOS库德毕赤酵母DS8-1微胶囊的制备及体外评价

前期从新疆传统乳制品酸驼乳中筛选得到一株具有潜在益生特性的库德毕赤酵母DS8-1（Pichia kudriavzevii DS8-1）,为增加菌株对体外环境的抗性,以海藻酸钠为壁材使用锐孔法制备酵母菌微胶囊。将干燥的藻酸盐（SA）微胶囊外包山羊乳或在微胶囊壁材中添加低聚果糖（fructooligosaccharides,FOS）/低聚半乳糖（galactooligosaccharides,GOS）分别制备3 种酵母菌微胶囊：SAM微胶囊、SAMF微胶囊和SAMG微胶囊。对微胶囊进行傅里叶红外光谱和扫描电子显微镜表征、模拟胃液的耐受性、消化液的释放特性和贮藏稳定性实验,研究冻干微胶囊对菌株活性的影响。结果表明：使用羊乳包衣的3 种冻干微胶囊（SAM微胶囊、SAMF微胶囊和SAMG微胶囊）的菌株活力为7.16～7.67（lg（CFU/g））。与SA微胶囊相比,SAMF微胶囊在连续的模拟消化液处理后能够延缓酵母菌的释放,提高菌株存活率,以及对α-淀粉酶和α-葡萄糖苷酶具有较高的抑制活性。SAMG微胶囊在－20、4、25 ℃贮藏30 d后菌株活力在7（lg（CFU/g））以上。结论：在海藻酸钠中添加FOS/GOS且使用羊乳包衣可用于包埋库德毕赤酵母,制备的酵母菌微胶囊具有提高菌株活性的作用,在功能性食品输送体系中具有一定的应用前景。     

DIRECT ENZYMATIC CONVERSION OF LACTOSE TO ACID: GLUCOSE OXIDASE AND HEXOSE OXIDASE

The conversion of lactose directly to an acid by glucose oxidase and hexose oxidase as a method of milk acidification was studied. Under the appropriate conditions, both enzymes demonstrated the capability to catalyze the conversion of sugar in milk to an acid, producing coagulation. A uniform distribution of oxygen under quiescent conditions was essential for the reaction and could be accomplished with the addition of hydrogen peroxide in the presence of catalase. Commercial samples of glucose oxidase caused a gradual decrease in pH of skim milk containing added glucose or lactase, (beta-galactosidase). Hexose oxidase, which can react with galactose and lactose as well as glucose, produced acid at a very slow rate in skim milk alone. When lactase was incorporated into the milk, the rate of reaction increased significantly.     

不同乳糖酶酶学特性比较及在无乳糖原料奶生产中的应用

以3 种乳糖酶为研究对象,研究其酶学特性,并应用于无乳糖原料奶的生产。采用聚丙烯酰胺凝胶电泳法分析乳糖酶的成分及分子质量;邻硝基苯酚β-D-半乳糖苷法测定乳糖酶活力;用电子鼻检测原料奶储存过程中气味的变化。结果表明：酶A的等电点为4.0和5.0,酶B为5.0,酶C为3.0;酶A在40 ℃和pH 6.5时酶活最高,酶B在35 ℃和pH 6.5时酶活最大,酶C在45 ℃和pH 5.0时活力最高。电子鼻检测结果表明,在4～10 ℃储存12 h,原料奶气味无显著性差异。在4～6 ℃条件下,添加6 000 U/g乳糖酶A在5～6 h内可将原料奶中乳糖水解至0.5%以下;添加6 000 U/g乳糖酶B在8～9 h将原料奶中乳糖水解至0.5%以下。因此,乳糖酶A和酶B为中性乳糖酶,乳糖酶C为酸性乳糖酶;生产无乳糖原料奶采用中性乳糖酶A较好。     

Evaluation of enzymes produced from yeast

Pichia pinus was found to be capable of growing on mango wastes, producing pectinase (pectin lyase, EC-4.2.2.10) and lactase (beta-galactosidase, EC-3.2.1.23) enzymes. The two enzymes were successively purified by precipitation with ammonium sulfate followed by chromatography on Sephadex G-120. The purification procedure provided 1,846 and 929 fold purification with 20.6 and 24% yield recovery of pectinase and lactase, respectively. the km value of pectinase was 0.33% for pectin at pH 4.5 and that for lactase was 0.166% for lactose at pH 7.0. The purified enzymes, pectinase and lactase are stable up to 50 degrees C for 60 and 45 min, respectively, with 20 and 35% loss of their activity. Gel filtration on Sephadex G-200 indicated that the molecular weights of the purified pectinase was 90 x 10(3) Dalton and of lactase 115 x 10(3) Dalton. On the basis of the evaluation tests done, the enzymes were considered to have a potential technological interest as treating mango pastes (residues left after mango juice preparation) with the two prepared enzymes resulted in an increase of the colour intensity, total carbohydrate content and juice yield. Treating milk with the purified lactase also showed an increase in the total carbohydrate and reducing sugar produced.     

Effects of medium-chain fatty acids and tributyrin supplementation in milk replacers on growth performance,blood metabolites,and hormone concentrations in Holstein dairy calves

This study aimed to evaluate the effects of triglycerides containing medium-chain fatty acids (MCT) and tributyrin (TB) supplementation in a milk replacer (MR) on growth performance, plasma metabolites, and hormone concentrations in dairy calves. Sixty-three Holstein heifer calves (body weight at 8 d of age, 41.1 ± 2.91 kg; mean ± SD) were randomly assigned to 1 of 4 experimental MR (28% crude protein and 18% fat): (1) containing 3.2% C8:0 and 2.8% C10:0 (in fat basis) without TB supplementation (CONT; n = 15), (2) containing 6.7% C8:0 and 6.4% C10:0 without TB supplementation (MCT; n = 16), (3) containing 3.2% C8:0 and 2.8% C10:0 with 0.6% (dry matter basis) TB supplementation (CONT+TB; n = 16), (4) containing 6.7% C8:0 and 6.4% C10:0 with 0.6% TB supplementation (MCT+TB; n = 16). The MR were offered at 600 g/d (powder basis) from 8 to 14 d, up to 1,300 g/d from 15 to 21 d, 1,400 g/d from 22 to 49 d, down to 700 g/d from 50 to 56 d, 600 g/d from 57 to 63 d, and weaned at 64 d of age. All calves were fed calf starter, chopped hay, and water ad libitum. The data were analyzed using a 2-way ANOVA via the fit model procedure of JMP Pro 16 (SAS Institute Inc.). Medium-chain fatty acid supplementation did not affect the total dry matter intake. However, calves that were fed MCT had greater feed efficiency (gain/feed) before weaning (0.74 ± 0.098 vs. 0.71 ± 0.010 kg/kg) compared with non-MCT calves. The MCT calves also had a lower incidence of diarrhea compared with non-MCT calves during 23 to 49 d of age and the weaning period (50 to 63 d of age; 9.2% vs. 18.5% and 10.5% vs. 17.2%, respectively). Calves fed with TB had a greater total dry matter intake during postweaning (3,465 vs. 3,232 g/d). Calves fed TB also had greater body weight during the weaning (90.7 ± 0.97 vs. 87.9 ± 1.01 kg) and postweaning period (116.5 ± 1.47 vs. 112.1 ± 1.50 kg) compared with that of non-TB calves. The plasma metabolites and hormone concentrations were not affected by MCT or TB. These results suggest that MCT and TB supplementation in the MR may improve the growth performance and gut health of dairy calves.     

生物技术在乳糖不耐受防治中的应用

原发性乳糖酶缺乏和乳糖不耐受（吸收不良）是全球性的健康问题。从基因工程技术生产乳糖酶、利用生物反应器生产低乳糖奶、基因治疗等3个方面介绍了生物技术在乳糖不耐受（吸收不良）防治中的应用，并提出口服经改造的益生菌制剂，从根本上解决乳糖酶缺乏的新思路。     

壳聚糖固定化绿豆乳糖酶的特性及应用的初步研究

以壳聚糖凝胶颗粒为载体,采用共价键偶联法固定绿豆乳糖酶,研究壳聚糖固定化绿豆乳糖酶的酶学性质并对其进行水解牛乳中乳糖的初步应用研究。结果表明：固定化酶的热稳定性在4～55℃范围内;最适温度60℃;最适pH3.5;固定化酶的表观米氏常数Km 为0.04%,溶液酶米氏常数Km 为0.33%,是溶液酶米氏常数Km 的0.12 倍;固定化酶的操作半衰期为30d,较溶液酶长。用固定化酶制备填充床式反应器水解牛奶中乳糖,水解率可达60% 以上。     

纳米Ag@SiO2改性聚偏二氯乙烯涂膜材料及提高清洁鸡蛋贮藏保鲜效果

通过添加不同质量分数的纳米Ag@SiO2改性聚偏二氯乙烯（polyvinylidene chloride,PVDC）涂膜材料,以期提高PVDC涂膜材料对清洁鸡蛋的涂膜保鲜效果,延长鸡蛋货架期。结果表明：纳米Ag@SiO2可以明显提高PVDC成膜材料对致病菌的杀菌作用,并且能够稳定地填充于PVDC涂膜材料的分子空隙中,提高PVDC成膜致密度,显著降低PVDC涂膜液的黏度并提高其成膜阻水性（P＜0.05）;纳米Ag@SiO2质量分数为0.21%时对PVDC材料有较好的改性效果,并且可以明显减小清洁鸡蛋在贮藏过程中的质量损失并抑制微生物的生长,保持鸡蛋的新鲜度。综上所述,纳米Ag@SiO2改性PVDC涂膜材料是一种良好的清洁鸡蛋涂膜保鲜包装新材料,可延长清洁鸡蛋保质期至7周。     

Antimicrobial effect of the lactoperoxidase system in milk activated by immobilized enzymes

Immobilized lactase and glucose oxidase were used to produce H₂O₂ to activate the lactoperoxidase system in milk. The enzymes were immobilized on nylon pellets. With a ratio of 35 g of catalyst/L of milk, a concentration of 0.75 mM was produced in 3 min. Raw milk treatment with the catalyst reduced coliforms by 79%; Staphylococcus aureus reduction was 68%, psychrotrophs 91%, and fungi 100%. Results were similar when milk was treated by addition of H₂O₂. Thiocyanate was not limiting because addition of NaSCN did not increase the effectiveness of the lactoperoxidase system.

The stability of the catalyst was poor when successive treatments were applied to milk, having lost one half of the activity every eight determinations. Activation of the lactoperoxidase system by immobilized enzymes could be of interest if stability could be ensured.     

低乳糖益生菌乳粉制备研究

本实验以全脂牛奶为原料,探究低乳糖高益生菌乳粉的制备工艺,考察水解温度、pH、时间和乳糖酶添加量对水解率的影响.同时通过海藻酸钠-大豆分离蛋白复配壁材微胶囊包埋益生菌,各自制备完成后分别真空冷冻干燥低乳糖牛乳和益生菌微胶囊,干燥结束将低乳糖乳粉与益生菌微胶囊粉按质量比7:1的比例混合制得低乳糖益生菌乳粉.结果表明,牛乳...     

应用重组乳糖酶LacLM生产无乳糖奶的研究

为明确由第三军医大学基础部微生物学教研室研发的重组乳糖酶LacLM的工业价值和应用方式,采用葡萄糖氧化法(GOD/POD)测定了该酶水解乳糖的酶学特性,以及对牛奶中所含乳糖的水解率。实验测得该酶对乳糖的Km和Vmax值分别是13.9±1.05mM和14.1±0.31μmol glucose/(min·mg)protein。该酶水解乳糖的最适温度和pH分别为37℃和7。在10℃下每升牛奶加入40mg酶可以在12h内完全水解牛奶中的乳糖;在25℃下每升牛奶加入5mg酶可以在18h内完全水解牛奶中的乳糖;在37℃下添加2.5mg酶就能在10h内完全水解牛奶中的乳糖。试验结果表明,重组乳糖酶LacLM可以直接加入牛奶中,在低温或常温下去除牛奶中的乳糖,适合用于无乳糖奶的工业化生产。     

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。     

Optimizing microencapsulation of peanut sprout extract by response surface methodology

This study was carried out to optimize conditions for peanut sprout extract microencapsulation by response surface methodology (RSM). The coating materials of microencapsulation were medium-chain triacylglycerol (MCT) for primary emulsion, and whey protein concentrates (WPC), maltodextrin (MD) and gum Arabic (AG) for secondary emulsion. The yield of microencapsulation of peanut sprout extract was investigated with respect to four variables (ratio of core and coating materials, concentration of primary emulsifier, ratio of W/O emulsion and secondary coating materials and concentration of secondary emulsifier) in RSM. The optimal conditions for microencapsulation of peanut sprout extract were 1:2 as the ratio of core material to coating material, 1.25% (w/v) of primary emulsifier concentration, 1:1.23 as W/O emulsion to secondary coating material, 1.21% (w/v) as secondary emulsifier concentration and 30% (w/w) as WPC concentration for spray drying. In conclusion, the microencapsulation of peanut sprout extract under the optimized conditions by RSM ensures the smaller size (3–7 μm) of microcapsules with the highest yield reaching to 98.74%.     

Influence of high-oryzanol rice bran oil on the oxidative stability of whole milk powder

The effect of high oryzanol rice bran oil (RBO) on the oxidative stability of low-heat and high-heat whole milk powder (WMP) was investigated. Milk (3.6% fat) was fortified with RBO at 0.1 and 0.2% (wt/wt) and was concentrated and dried. Control WMP was made without RBO addition. Thiobarbituric acid reactive substances (TBARS) were used to monitor oxidation during storage at 45 degrees C for 40 d. The oxidation of low-heat WMP was significantly reduced by addition of 0.1% RBO, but there was no significant effect on the oxidation of high-heat WMP. An increase of RBO to 0.2% did not significantly improve the oxidative stability when compared with 0.1% RBO. The TBARS in RBO-fortified, low-heat WMP increased with storage time up to 30 d but decreased with further storage to 40 d. The TBARS in all high-heat WMP and low-heat control WMP increased up to 20 d storage and then decreased with further storage. The most likely reason for this increase was due to the reaction of TBARS with milk proteins. Addition of RBO reduced the L (lightness) value and increased the b (yellowness) value but had no effect on the a (redness) value. When compared with the control milk powder, consumers could not detect any effect on the flavor of the reconstituted 0.1% RBO WMP but could detect a flavor difference in the 0.2% RBO WMP.     

Production of low-dosage lactose milk using lactase immobilised in hydrogel

A hydrogel based on chitosan was employed for the immobilisation of lactase with the aim of hydrolysing lactose and producing low-dosage lactose milk. The degree of swelling of the hydrogel was affected by the type of aqueous solution, pH and temperature. The lactase immobilisation capacities at pH 4.0 and pH 7.0 were 257.12 ± 3.18 and 157.87 ± 1.96 mg enzyme per g dried hydrogel, respectively, after 1440 min at room temperature. The activity of immobilised lactase ranged from 97.91 to 56.04 and 97.91 to 71.80% from the first to the tenth cycle of hydrolysis of standard lactose and lactose contained in UHT milk, respectively. Immobilised lactase in hydrogel could be applied for the production of low-dosage lactose milk for at least ten successive hydrolysis cycles. Moreover, hydrogels containing immobilised lactase could also be useful for the enzyme release in individuals with lactose intolerance.     

Enhancement of lactase activity in milk by reactive sulfhydryl groups induced by heat treatment

The effects of heat treatments of milk and whey prior to lactose hydrolysis with Kluyveromyces lactis beta-galactosidase were studied. It was observed that heat treatment of milk significantly increases lactase activity, with a maximum activity increase found when milk was heated at 55 degrees C. In whey from 55 up to 75 degrees C, beta-galactosidase activity decreased slightly. Nevertheless, heating whey at 85 degrees C for 30 min raised the rate of hydrolysis significantly. Electrophoretic patterns and UV spectra proved that the activity change correlated with milk protein denaturation, particularly that of beta-lactoglobulin. Heating whey permeate did not increase the enzyme activity as heating whole whey; but heating whey prior to ultrafiltration also resulted in enzyme activation. Measurement of free sulfhydryl (SH) groups in both whey and heated whey permeate showed that the liberation of free SH is highly correlated to the change of the activity. Furthermore, this activation can be reversed by oxidizing the reactive sulfhydryl groups, proving that the observed effect may be related to the release of free SH to the medium, rather than to the denaturation of a thermolabile protein inhibitor.     

一种新型乳糖酶在制备低乳糖牛奶中的应用研究

目的通过检测一种新型乳糖酶在不同条件下对牛乳中乳糖的水解率,研究其在制备低乳糖牛奶的最适条件。方法产乳糖酶基因工程菌株发酵并提取乳糖酶,分别在10,25和37℃条件下按不同比例添加该新型乳糖酶液,使用HPLC检测其乳糖水解率。结果该酶在10℃（0．9％）水解率可达83％以上,25℃（0．9％）水解率93％以上,37℃（0.3％）水解率94％以上。结论该酶在低温下具有良好的乳糖水解率,在工业上具有广阔的应用前景。     

Form of calf diet and the rumen. II: Impact on volatile fatty acid absorption

Diet is known to affect rumen growth and development. Calves fed an all-liquid diet have smaller and less developed rumens and a decreased ability to absorb volatile fatty acids (VFA) compared to calves fed both liquid and dry feed. However, it is unknown how rumens respond when challenged with a defined concentration of VFA. The objective of this study was to assess the effects of 2 different feeding programs on VFA absorption in preweaned calves. Neonatal Holstein bull calves were individually housed and randomly assigned to 1 of 2 diets. The diets were milk replacer only (MRO; n = 5) or milk replacer with starter (MRS; n = 6). Diets were isoenergetic (3.87 ± 0.06 Mcal of metabolizable energy per day) and isonitrogenous (0.17 ± 0.003 kg/d of apparent digestible protein). Milk replacer was 22% crude protein, 21.5% fat (dry matter basis). The textured calf starter was 21.5% crude protein (dry matter basis). Feed and ad libitum water intakes were recorded daily. Calves were exposed to a defined concentration of VFA buffer (acetate 143 mM, propionate 100 mM, butyrate 40.5 mM) 6 h before euthanasia on d 43 ± 1. Rumen fluid samples were obtained every 15 to 30 min for 6 h to measure the rate of VFA absorption. Rumen tissues were obtained from the ventral sac region and processed for morphological and immunohistochemical analyses of the VFA transporters monocarboxylate transporter 1 (MCT1) and 4 (MCT4). Body growth did not differ between diets, but empty reticulorumens were heavier in MRS than MRO calves (0.67 vs. 0.39 ± 0.04 kg) and MRS calves had larger papillae areas (0.76 vs. 15 ± 0.08 mm²). We observed no differences between diets in terms of the abundance of MCT1 and MCT4 per unit area. These results indicate that the extrapolated increase in total abundance of MCT1 or MCT4 in MRS calves was not due to increased transporter density per unit area. Modeled VFA absorption metrics (flux, mmol/h, or 6 h absorbed VFA in mmol) were not different across diets. These results demonstrate that the form of calfhood diet, whether solely MR or MR and starter, does not alter VFA absorption capacity when the rumen is exposed to a defined concentration of VFA at 6 wk of age.