中老年低乳糖低脂营养牛奶的研制

针对中老年人的生理特点及营养需求,合理补充钙铁锌硒及维生素等,适当调整脂肪含量,并通过添加乳糖酶将乳糖部分水解,缓解＂乳糖不耐受症＂,采用合理的杀菌方式,全面保持牛奶的营养成分.     

低乳糖学生营养奶的研制

本文主要研究了低乳糖学生营养奶的配方组成及其生产工艺条件等,同时探讨了铁锌钙添加剂及其稳定剂等对产品稳定性能的影响。实验研究结果表明,该产品具有营养丰富全面、口味香甜纯正以及稳定性良好和无褐变等特点。     

Lactose oxidase: Enzymatic control of Pseudomonas to delay age gelation in UHT milk

Shelf-stable milk is consumed worldwide, and this market is expected to continue growing. One quality challenge for UHT milk is age gelation during shelf life, which is in part caused by bacterial heat-stable proteases (HSP) synthesized during the raw milk storage period before heat processing. Some Pseudomonas spp. are HSP producers, and their ability to grow well at refrigeration temperature make them important spoilage organisms for UHT processors to control. Previous studies have shown that lactose oxidase (LO), a natural and commercially available enzyme that produces hydrogen peroxide and lactobionic acid from lactose, can control bacterial growth in raw milk. In this research, we investigated the ability of LO to control HSP producer outgrowth, and thus delay age gelation in UHT milk. Six strains of Pseudomonas spp. were selected based on their ability to synthesize HSP and used as a cocktail to inoculate both raw and sterile (UHT) milk at a level of 1 × 10⁵ cfu/mL. Groups were treated with and without LO, stored for 4 d at 6°C, and monitored for cell count and pH. Additionally, a sample from each was tested for HSP activity via particle size analysis (average effective diameter at 90° angle and 658 nm wavelength) and visual inspection on each day of the storage period. The HSP activity results were contrasted using Tukey's HSD test, which showed that in UHT milk, a LO treatment (0.12 g/L) effectively prevented gelation as compared with the control. In raw milk, however, a concentration of 0.24 g/L of LO was needed to obtain a similar effect. This test was scaled up to 19-L pilot plant batches of raw milk where they were challenged with Pseudomonas cocktail, treated with LO for 3 d, and then UHT processed. Resulting UHT milk bottles were monitored for gelation. Significant differences in particle size between the LO-treated samples and the control were observed as early as 1 mo after processing, and gelation was not detected in the LO-treated samples through 6 mo of storage. These results demonstrated that LO can be used to delay age gelation in UHT milk induced by HSP-producing Pseudomonas spp., representing an opportunity to improve quality and reduce postproduction losses in the shelf-stable milk market sector.     

Lactose oxidase: A novel activator of the lactoperoxidase system in milk for improved shelf life

The lactoperoxidase system (LS), an antimicrobial system naturally present in milk that is activated by H₂O₂, has been used to inhibit microbial outgrowth in raw milk in areas where refrigeration is not viable. This study evaluated lactose oxidase (LO) as a novel activator of the LS. Lactose oxidase oxidizes lactose and produces H₂O₂ needed for the activation of the LS. The antimicrobial effect of different concentrations of LO with and without components of the LS, thiocyanate (TCN) and lactoperoxidase (LP), was evaluated in model systems and then applied in pasteurized milk and raw milk. In general, an increase in LO caused greater reductions of Pseudomonas fragi in the model systems and treatments were more effective at 6°C than at 21°C. At 6°C, the LO solution at 0.12 and 1.2 g/L showed significantly higher microbial reduction than the control when both added alone and combined with LS components. At 21°C, treatments with 1.2 g/L of LO solution achieved a reduction of >2.93 log cfu/mL in 24 h, but at lower levels there was not a significant reduction from the control. Higher concentrations of TCN led to a greater P. fragi reduction at both temperatures when LO was added alone but not when combined with LP. In pasteurized milk, the LO solution at 0.12 g/L caused a reduction of approximately 1.4 log of P. fragi within 24 h when added alone and a reduction of approximately 2.7 log when combined with LP and TCN. Bacterial counts remained at significantly lower levels than the control during storage, and the TCN-supplemented milk exhibited an approximately 6-log difference from the control by d 7. In raw milk, the total bacterial growth curve showed a longer lag phase when the LS was activated by LO (11.3 ± 1.4 h) compared with the control (4.0 ± 1.0 h), but it was not different from the recommended method (9.4 ± 1.0 h). However, the total bacterial count after 24 h for the sample treated with LO and TCN (5.3 log cfu/mL) was significantly lower compared with the control (7.2 log cfu/mL) and the recommended method (6.1 log cfu/mL). Results from this study suggest that LO is an alternative source of H₂O₂ that enhances the microbial inhibition achieved by the LS. Lactose oxidase could be used to develop enzyme-based preservation technologies for applications where cold chain access is limited. This enzymatic approach to improving the shelf life of dairy products also represents a novel option for clean label spoilage control.     

Identification of lactose ureide, a urea derivative of lactose, in milk and milk products

With the widespread consumption of milk, the complete characterization of the constituents of milk and milk products is important in terms of functionality and safety. In this study, a novel nonreducing carbohydrate was separated from powdered skim milk and was identified using electron spray ionization-mass spectrometry (m/z 385.1[M + H⁺]), ¹H, ¹³C, ¹H¹H-correlation spectroscopy, and heteronuclear single quantum-nuclear magnetic resonance spectra. The carbohydrate was identified as a lactose derivative of urea, N-carbamoyl-o-β-d-galactopyranosyl-(1–4)-d-glucopyranosylamine (lactose ureide, LU). For the HPLC analysis of LU in milk and milk products, benzoylated LU, hepta-o-benzoyl lactose ureide (melting point 137–139 °C; m/z 1,113 [M + H⁺]; wavelength of maximum absorption, λ_max, 229 nm; molar extinction coefficient, ε, 8.1037 × 10⁷), was used as a standard. The crude nonreducing carbohydrate fraction from raw milk, thermally processed milk, and milk products such as powdered milks were directly benzoylated and subjected to HPLC analysis using an octadecylsilyl column to determine the quantity of LU. The content of LU in 10% solutions of powdered skim milk and powdered infant formula (5.0 ± 1.1 and 4.9 ± 1.5 mg/L, respectively) were almost 3-fold higher than that of UHT milk (1.6 ± 0.5 mg/L) and higher than that of low-temperature, long-time-processed (pasteurized at 65 °C for 30 min) milk (1.2 ± 0.3 mg/L) and the fresh raw milk sample (0.3 ± 0.1 mg/L). A time-course of the LU content in raw milk during heating at 110 °C revealed that LU increased with time. From these results, it is likely that LU is formed by the Maillard-type reaction between the lactose and urea in milk and milk products. Because the concentration of LU in milk increased with the degree of processing heat treatment, it could serve as an indicator of the thermal deterioration of milk. Although it is known that the human intestine is unable to digest LU, the gastrointestinal bacteria in human subjects are able to digest and utilize urea nitrogen in formation of essential amino acids that are available to the host human. These findings suggest that LU in milk might have a functional role in human health.     

Purification and identification of lactoperoxidase in milk basic proteins as an inhibitor of osteoclastogenesis

A milk protein fraction with alkaline isoelectric points (milk basic protein, MBP) inhibits both bone resorption and osteoclastogenesis for in vitro models. We previously identified bovine angiogenin as a component of MBP that inhibits bone resorption. However, purified angiogenin had no effect on osteoclastogenesis, suggesting that MBP contains unidentified component(s) that inhibit osteoclast formation. In this study, we purified lactoperoxidase (LPO) as the predominant inhibitor of osteoclastogenesis in MBP. The LPO treatment downregulated levels of reactive oxygen species in osteoclasts. Signaling by receptor activator of NF-kappa-B ligand/receptor activator of NF-kappa-B (RANKL/RANK) was downregulated in LPO-treated cells, and, in particular, the ubiquitination of tumor necrosis factor receptor associate factor 6 (TRAF6) and activation of downstream signaling cascades (JNK, p38, ERK, and NFκB) were suppressed. Ultimately, LPO treatment led to decreased expression of c-Fos and NFAT2. These results suggest that MBP contains at least 2 components that independently suppress bone resorption through a unique mechanism: angiogenin inhibits bone resorption and LPO inhibits RANKL-induced osteoclast differentiation. These data explain many of the positive aspects of milk consumption on bone health.     

Characterizing endogenous and exogenous peroxidase activity for bleaching of fluid whey and retentate

The lactoperoxidase (LP) system may be used to achieve the desired bleaching of fluid whey with the addition of low concentrations (<50 mg/kg) of hydrogen peroxide. The addition of an exogenous peroxidase (EP) to whey may also be used to aid in whey bleaching when the LP system is not fully active. The objectives of this study were to monitor LP activity in previously refrigerated or frozen milk, fluid whey, and whey retentate (10% solids) and to evaluate peroxidase activity in fluid whey and whey retentate (10% solids), with and without additional EP (2, 1, or 0.5 dairy bleaching units), over a range of pH (5.5–6.5) and temperatures (4–60°C). Subsequent experiments were conducted to determine the relationship between enzyme activity and bleaching efficacy. Raw and pasteurized milk, fat-separated pasteurized whey, and whey retentate (10% solids) were evaluated for LP activity following storage at 4 or −20°C, using an established colorimetric method. A response surface model was applied to evaluate both endogenous and EP activity at various temperatures and pH in freshly manufactured whey and retentate. Refrigerated or frozen storage at the parameters evaluated did not affect LP activity in milk, whey, or retentate. In fluid whey, with and without added EP, as pH decreased (to 5.5) and temperature increased (to 60°C), peroxidase activity increased. Retentate with EP exhibited behavior similar to that of fluid whey: as pH decreased and temperature increased, activity increased. However, in retentate without EP, as pH increased and temperature increased, activity increased. Enzyme activity was negatively correlated to bleaching time (time for >80% norbixin destruction) in fluid whey but a linear relationship was not evident in retentate. When fluid whey is bleached enzymatically, if pH is decreased and temperature is increased, the rate of reaction increases (e.g., bleaching occurs in less time). When bleaching in retentate, a higher pH (pH 6.5 vs. pH 5.5) is desired for optimal bleaching by the LP system. Due to processing restraints, this may not be possible for all dairy producers to achieve and, thus, addition of EP could be beneficial to improve bleaching efficacy.     

乳糖利用酵母菌的筛选及其特性初步研究

从水果表皮和生牛奶中筛选出可利用乳糖的酵母菌,并对其利用特征进行初步研究。结果共得到10株可利用乳糖的酵母菌,初步的降解试验表明,菌株B1、B2、H1和H2对牛奶中乳糖的利用效果最明显。对该4株酵母菌的生长曲线、最佳处理时间和接种量进行分析,结果表明,4株菌在20 h～26 h生长量达到最大,26小时后均可将牛奶中的乳糖含量从5%左右降至2.5%左右,与国家标准低乳糖牛奶的含量相当;菌株B1的最佳接种量为6%,B2、H1和H2的最佳接种量均为8%。对4株酵母菌处理后的纯牛奶的气味进行初步的感官评定,发现各菌株处理后的牛奶均有不同程度的香味。采用形态观察法结合18S rRNA基因序列比对的方法对该4株酵母菌进行鉴定,其中B1、B2分别为梅奇酵母菌属(Metschnikowia sp.)和威克汉姆酵母菌属(Wickerhamomyces sp.),H1和H2均为毕赤酵母菌属(Meyerozyma sp.)。     

低乳糖奶粉的研制

研究了低乳糖奶粉的制作,通过乳糖酶的添加量、乳糖酶的水解温度、水解时间及水解时的pH对乳糖水解率、牛乳中微生物的影响,确定了低乳糖奶粉的水解条件;并对工艺条件进行了讨论。     

Sensory evaluations and stability determinations of goat milk containing galactooligosaccharides

The objectives of this study were to evaluate the feasibility of producing goat milk containing galactooligosaccharides (GOS) by β‐galactosidase and to determine the sensory attribute and stability of goat milk containing GOS. The results indicated that the maximum GOS obtained were approximately 13.9% of total sugars at pH 4.5 and temperature 40 °C. The sensory attribute of the obtained GOS was determined using a 5‐point hedonic scale in terms of taste, flavour, appearance and overall acceptability. There were significant increases in taste and overall acceptability of goat milk containing higher GOS concentration when compared to regular goat milk (control). Also, goat milk containing GOS presented a good stability over the acidic conditions. GOS in goat milk were also stable after the high heat treatment and shelf life conditions.     

低乳糖牛奶的研制

本文主要研究探讨了低乳糖牛奶产品的配方组成及其生产工艺条件等。实验研究结果表明,该产 品具有营养丰富、口味香甜纯正以及稳定性能良好和无褐变等特点,其乳糖的水解率高达70％以上。     

乳中残留LPS保鲜剂的检测及对乳制品性能的影响

研究了生鲜奶中过氧化氢酶系激活剂残留量的检测方法，以及巴氏杀菌或超高温（UHT）处理后该添加剂残留情况．并评价了原奶中添加该添加剂对液态奶产品风味的影响，最后，还考察了酸奶发酵前、后该添加剂的残留情况，并评价了生鲜奶中添加该添加剂对酸奶发酵和酸奶产品风味的影响。结果表明，应用适当的方法可以检测出乳中残留的LPS保鲜剂成分NaSCN（硫氰酸钠），但H2O2（过氧化氢）很快就检不出残留。合理的添加LPS保鲜剂不会影响巴氏杀菌奶、UHT奶和酸奶产品的加工及产品的风味。     

Lactoperoxidase activity in milk is correlated with somatic cell count in dairy cows

Lactoperoxidase (LPO) is a milk protein with antimicrobial function. The present study was undertaken to examine the correlation between LPO activity and somatic cell count (SCC) in milk to use LPO activity as an indicator of mastitis. Composite milk of 36 cows and quarter milk of 3 cows were collected once per week from 0 to 300 d postpartum and twice per day for 1 wk, respectively. For the measurement of LPO activity, milk was mixed with tetramethylbenzidine solution and incubated at 37°C for 30 min, followed by the measurement of optical density. When only milk with low SCC (132 ± 12 × 10³ cells/mL) was used, a significant decrease in LPO activity was detected in primiparous cows from 0 to 4 mo postpartum. Lactoperoxidase activities of primiparous cows in mo 1, 2, and 3 postpartum were significantly higher than those in multiparous cows. When composite milk was divided based on LPO activity, the SCC was significantly higher in the groups with LPO activity >5 and from 3 to 3.9 U/mL in the second- and fourth-parity cows, respectively, compared with the group with LPO activity <2 U/mL. Extremely high SCC were found in the ≥fifth-parity cows, even in low-LPO activity groups. In the case of quarter milk, higher LPO activity was associated with increased SCC in all 3 cows. The percentage of quarter milk samples with high SCC (4,062 ± 415 × 10³ cells/mL) increased with an increase in the LPO activity. The percentage of quarter milk samples with high SCC was 50.0 to 100% in the milk with LPO activity ≥5 U/mL. These results indicate that the correlation of LPO activity to the SCC in bovine milk may point to the potential use of the former as an indicator of SCC.     

低乳糖中老年奶粉的研究

对低乳糖中老年奶粉进行了研究,通过实验得出配方（以总量100g计）：蛋白质为大豆分离蛋白2%,乳清浓缩蛋白4%,全乳蛋白质14%;脂肪的添加量为大豆油3.6%,菜籽油4.4%;以及各种营养素的强化量：VA1500～3000IU,VC60～80mg,VE15～20IU,VD400～500IU,VB1750～1000μg,VB2850～1000μg,烟酸700～1000μg,叶酸250～600μg,乳酸锌3～6mg,硫酸亚铁6～10mg,采用酶活力2000NLU/L的乳糖酶,添加量为0.2%,水解时间为4h,乳糖水解率达到90%以上。     

乳糖酶及其在乳品工业中的应用

概述了乳糖酶的酶源、特性、反应机理及体内代谢过程，重点介绍其在乳品工业中的应用。     

低乳糖牛奶的研制

本文主要研究探讨了低乳糖牛奶产品的配方组成及其生产工艺条件等。实验研究结果表明,该产品具有营养丰富全面、口味香甜纯正、以及性能稳定和无褐变等特点,其乳糖的水解率高达70％以上,可以有效的预防人体乳糖不耐症的发生。     

低乳糖牛奶的研制

主要研究探讨了低乳糖牛奶产品的配方组成及其生产工艺条件等。实验研究结果表明,该产品具有营养丰富全面、口味香甜纯正以及稳定性能良好和无褐变等特点,其乳糖的水解率高达70%以上,可以有效的预防人体乳糖不耐症的发生。     

乳过氧化物酶的分离纯化和酶学性质研究

采用超滤-离子交换色谱分步洗脱法,对牛初乳中的乳过氧化物酶进行了分离和纯化。经SDS-PAGE测定,分离出的乳过氧化物酶显示为单一区带,相对分子质量为75035D。该酶酶活回收率为76.17%,其最适pH为5.0～5.5,最适温度为55℃。在70℃、75℃时LP酶活的热失活曲线呈现一般植物过氧化物酶失活的双相特征。