Kinetics of hydroxymethylfurfural,lactulose and furosine formation in milk with different fat content

In the context of the general applicability of hydroxymethylfurfural (HMF), lactulose and furosine as time-temperature integrators (TTIs) for thermal processing of milk, the influence of milk fat content was studied. Formation kinetics were analysed for milk with fat content of 4.0 +/- <0.1%. In previous experiments, it was observed that, under isothermal and non-isothermal heating conditions, formation of the three chemical compounds could be described by pseudo-zero order kinetics. Since the kinetic model was known, the experimental design could be simplified. Data were analysed by a non-linear regression procedure and results were evaluated by construction of joint confidence regions and temperature time tolerance (TTT-) diagrams. Formation kinetics of HMF and lactulose was not affected by milk fat content. Regarding furosine, significant differences were observed between kinetic parameters in whole, semi-skimmed and skimmed milk. The observed differences however were negligible in the context of process impact evaluation.     

Effect of dipotassium phosphate and heat on milk protein beverage viscosity and color

Our objective was to determine the effect of addition of dipotassium phosphate (DKP) at 3 different thermal treatments on color, viscosity, and sensory properties of 7.5% milk protein-based beverages during 15 d of storage at 4°C. Micellar casein concentrate (MCC) and milk protein concentrate (MPC) containing about 7.5% protein were produced from pasteurized skim milk using a 3×, 3-stage ceramic microfiltration process and a 3×, 3-stage polymeric ultrafiltration membrane process, respectively. The MCC and MPC were each split into 6 batches, based on thermal process and addition of DKP. The 6 batches were no postfiltration heat treatment with added DKP (0.15%), no postfiltration heat without added DKP (0%), postfiltration high-temperature, short time (HTST) with DKP, postfiltration HTST without DKP, postfiltration direct steam injection with DKP, and postfiltration direct steam injection without DKP. The 6 MCC milk-based beverages and the 6 MPC milk-based beverages were stored at 4°C. Viscosity, color, and sensory properties were determined over 15 d of refrigerated storage. MCC- and MPC-based beverages at 7.5% protein with and without 0.15% added dipotassium phosphate were successfully run through an HTST and direct steam injection thermal process. The 7.5% protein MCC-based beverage contained a higher calcium and phosphorus content (2,425 and 1,583 mg/L, respectively) than the 7.5% protein MPC-based beverages (2,141 and 1,338 mg/L, respectively). Pasteurization (HTST) had very little effect on beverage particle size distribution, whereas direct steam injection thermal processing produced protein aggregates with medians in the range of 10 and 175 μm for MPC beverages. A population of casein micelles at about 0.15 μm was found in both MCC- and MPC-based beverages. Larger particles in the 175-μm range were not detected in the MCC beverages. In general, the apparent viscosity (AV) of MCC beverages was higher than MPC beverages. Added DKP increased the AV of both MCC- and MPC-based beverages, while increasing heat treatment decreased AV. The AV of beverages with DKP increased during 15 d of 4°C of storage for both MCC and MPC, whereas there was very little change in AV during storage without DKP and a similar effect was observed for sensory viscosity scores. The L value of beverages was higher with higher heat treatment, but DKP addition decreased L value and sensory opacity greatly. Sulfur-eggy flavors were detected in MPC beverages, but not MCC-based beverages.     

热处理对牛乳蛋白还原性的影响

借鉴AOAC的蛋白-还原物质（PRS）测定法,对不同受热处理的牛乳以及酪蛋白、乳清的还原性进行了检测研究。通过比较、分析不同热处理牛乳PRS,得到了区分巴氏乳与其它热处理牛乳PRS,同时得出乳清蛋白与酪蛋白之间的热反应性是影响牛乳蛋白还原性的主要原因,为进一步研究乳清蛋白的热变性以及乳清蛋白与酪蛋白之间的热反应奠定了基础。     

加热对牛乳蛋白过敏原的影响

对牛乳中主要过敏原β-乳球蛋白、α-乳白蛋白和酪蛋白进行了介绍,分析了在加热过程中牛乳过敏原的物理变化和化学改性,详细论述了加热对牛乳过敏原抗原性的影响及作用机理.     

热处理对鲜牛乳和复原孔蛋白多态性的影响

利用三种模拟生产加热处理,来研究鲜牛乳和复原乳蛋白多态性变化.通过调控pH和加热温度,发现鲜牛乳和复原乳中α-乳白蛋白、β-乳球蛋白、非沉淀酪蛋白和蛋白胶束的粒径大小均变化差异显著.     

Effect of homogenization and heat treatment on the behavior of protein and fat globules during gastric digestion of milk

The effects of homogenization and heat treatment on the formation and the breakdown of clots during gastric digestion of whole milk were investigated using a human gastric simulator. Homogenization and heat treatment led to formation of coagula with fragmented and crumbled structures compared with the coagulum formed from raw whole milk, but a larger fraction of the protein and more fat globules were incorporated into the coagula induced by action of the milk-clotting enzyme pepsin. The fat globules in the whole milk appeared to be embedded in the clots as they formed. After formation of the clot, the greater numbers of pores in the structures of the clots formed with homogenized milk and heated whole milk led to greater rates of protein hydrolysis by pepsin, which resulted in faster release of fat globules from the clots into the digesta. Coalescence of fat globules occurred both in the digesta and within the protein clots no matter whether they were in homogenized or heated milk samples. The formation of clots with different structures and hence the changes in the rates of protein hydrolysis and the release of milk fat into the digesta in the stomach provide important information for understanding the gastric emptying of milk and the potential to use this knowledge to manipulate the bioavailability of fat and other fat-soluble nutrients in dairy products.     

热加工中牛乳热损伤监控技术研究进展

本文分析了牛乳在热加工过程中的化学变化,介绍了几种牛乳热损伤监控标识物(如热敏性酶类,蛋白质变性产物,美拉德反应产物和乳糖异构化产物)的特点,并详细论述了已有的牛乳热损伤监控技术:对变性β-乳球蛋白含量的监控,对糠氨酸和乳果糖含量综合水平的监控,对羟甲基糠醛含量的监控,以及以变性蛋白质(以色氨酸的荧光强度计,FTry)和美拉德反应荧光产物(FAMP)的聚集量为基础,评估牛乳热加工损伤程度的FAST方法。     

Effect of ACTH and oxytocin treatment on lactoferrin and citrate in cows' milk

Six dairy cows were treated before milkings with either oxytocin (Pitocin, 20 i.u.) or ACTH (Synacthen, 150 i.u.), principally to determine their effect on the ratio of citrate: lactoferrin concentrations in the milk. With ACTH treatment, after 3 d milk yield and citrate concentration decreased significantly, lactoferrin and bovine serum albumin (BSA) concentrations increased significantly. Somatic cell counts (SCC) increased temporarily in the milk of three of the cows which previously had greater than 100 000 cells/ml. Lactoferrin yield remained fairly constant but citrate yield was significantly reduced. The citrate: lactoferrin molar ratio decreased from 1373 to 606. With oxytocin treatment, after 4 d milk yield first increased and then significantly decreased, citrate concentration decreased significantly while there were no significant changes in lactoferrin or BSA concentration or in the yield of any other milk constituents. The citrate: lactoferrin molar ratio decreased from 1621 to 1301. There were no significant changes in SCC either during treatment or 4 d after treatment but there was a significant rise at 16 d after treatment. It was concluded that in lactating cows both hormones affected citrate and lactoferrin concentrations in the direction that would improve the antibacterial properties of milk, but that this was accompanied by adverse effects on milk secretion. The extent of the change was not sufficient to be likely to produce inhibition of coliform bacteria.     

Effect of heat treatment on milk protein functionality at emulsion interfaces. A review

Heat treatment affects the molecular structure of milk proteins at the interfaces of oil-in-water emulsions and in aqueous media. Experimental evidence of the impact of thermal processing on milk protein structure is presented and the contribution of whey proteins and caseins at film formation during emulsification is discussed. Recent advances in understanding the effect of heat treatment in milk protein functionality at emulsion interfaces are reviewed with particular emphasis on the emulsifying ability of whey proteins with or without the presence of the casein fraction. The major findings regarding the destabilizing mechanisms of oil-in-water emulsions brought about by heat-induced denaturation of milk proteins are presented. This paper aims to combine recent knowledge on how thermal processing of milk proteins affects their molecular configurations in bulk and particularly at interfaces, which in turn appear to be important with respect to the physico-chemical properties of milk protein-stabilized emulsions.     

Calcium, phosphate and citrate in human milk at initiation of lactation.

The onset of copious milk secretion (lactogenesis II) in women occurs between 1 and 3 d after birth, and during this period the composition of breast milk changes. During the first 5 d of lactation we measured the concentrations of total, diffusible and ionized Ca (Catot, Cad, Ca2+), diffusible phosphate (Pid), diffusible citrate (Citd) and lactose in the breast milk. On day 1 after birth the concentrations (mean +/- SEM) were Catot, 5.71 +/- 0.30 mM; Cad, 2.66 +/- 0.19 mM; Ca2+, 2.90 +/- 0.18 mM; Pid, 0.26 +/- 0.16 mM; Citd, 0.25 +/- 0.03 mM and lactose, 76 +/- 11 mM. Between day 1 and day 4 the concentration of Catot increased 1.7-fold to 9.56 +/- 0.39 mM, Cad increased 1.8-fold to 4.75 +/- 0.26 mM, Ca2+ decreased by 20% to 2.33 +/- 0.13 mM, Pid increased 6.6-fold to 1.69 +/- 0.11 mM, Citd increased 20-fold to 5.06 +/- 0.21 mM, and lactose increased 2.3-fold to 173 +/- 4 mM. A high correlation has been found between [Cad] and [Citd] in the milk of both ruminant and non-ruminant species, which show a wide range in concentrations of [Cad] and [Citd], and the data fit a simple physicochemical model of ion equilibria in the aqueous phase of milk. The results of the present study confirm the relationship between [Cad] and [Citd] in human milk, even during lactogenesis II when the composition of the milk is changing very rapidly.     

牛奶加热过程中乳糖变化的研究

乳糖由于其在牛奶中含量的稳定性和所占比重,适合作牛奶热损伤研究分析。本文综述了乳糖在牛奶热处理过程中的变化,除了降解产生有机酸,还存在水解途径、美拉德途径和异构化途径三个可逆过程间的动态平衡,这三个途径常被单独用作牛奶热损伤分析。此外,本文还介绍了高效液相色谱法在热处理牛奶乳糖变化研究中的应用。     

Formation of lysinoalanine during heat treatment of milk

The heat-induced formation of lysinoalanine (LAL) was studied in raw skim milk that had been subjected to heat treatments as is usual in milk technology. Preheat treatment of milk at temperatures below 100 degrees C up to 20 min resulted in neglectable LAL amounts below 10 ppm i.p. (i.p.=in the protein) if at all. Tests with an UHT pilot plant showed that there was no proven formation of LAL with direct UHT-treatment at 110-130 degrees C for 10-25 min. In indirect UHT-treated milk vert small LAL amouints up to 50 ppm i.p. were detected only in those milk samples that were treated at temperatures high than 145 degrees C and holding times longer than 10 s. Autoclave sterilization in the range of 110-129 degrees C/10-25 min induced LAL amounts of 110 to 710 ppm i.p.. LAL formation in autoclave sterilized milk was almost directly dependent on heating temperature and time. Pre-treatment at temperatures below 100 degrees C induced no further LAL formation in any sterilization processes subsequent to preheating. In the pH range 6,50-6,90 LAL amounts in autoclave-sterilized milk increased directly with higher pH values at all temperatures. The varying degree of LAL formation with pH value was substantially more noticeable at higher than at lower temperatures. Increasing of lactose concentration caused only an insignificant decrease in LAL formation in autoclave-sterilized milk.     

Changes in the surface protein of the fat globules during homogenization and heat treatment of concentrated milk

The changes in milk fat globules and fat globule surface proteins of both low-preheated and high-preheated concentrated milks, which were homogenized at low or high pressure, were examined. The average fat globule size decreased with increasing homogenization pressure. The total surface protein (mg m-2) of concentrated milk increased after homogenization, the extent of the increase being dependent on the temperature and the pressure of homogenization, as well as on the preheat treatment. The concentrates obtained from high-preheated milks had higher surface protein concentration than the concentrates obtained from low-preheated milks after homogenization. Concentrated milks heat treated at 79 degrees C either before or after homogenization had greater amounts of fat globule surface protein than concentrated milks heat treated at 50 or 65 degrees C. This was attributed to the association of whey protein with the native MFGM (milk fat globule membrane) proteins and the adsorbed skim milk proteins. Also, at the same homogenization temperature and pressure, the amount of whey protein on the fat globule surface of the concentrated milk that was heated after homogenization was greater than that of the concentrated milk that was heated before homogenization. The amounts of the major native MFGM proteins did not change during homogenization, indicating that the skim milk proteins did not displace the native MFGM proteins but adsorbed on to the newly formed surface.     

Variation in the lactulose content of UHT milk during the running of a pilot and a commercial indirectly heated plant

The lactulose content of UHT milk was measured during the running of a pilot and a commercial indirectly heated UHT plant. The lactulose content of milk processed in the pilot plant was found to decrease as the pressure drop across the heated sections rose. The lactulose content of the milk from the commercial plant varied little and showed no trend during an entire production shift. There was no evidence that deposit in the plants accelerated the formation of lactulose.     

Effect of heat treatment on the rennet coagulation properties of recombined high total solids milk made from milk protein concentrate powder

The effects of heat treatment on the small and large deformation rheological properties of rennet gels made from recombined high total solids milk made from milk protein concentrate were studied. Heat treatment of recombined milk resulted in a slower rate of increase in the storage modulus (G') of rennet induced gels, a reduction in the gelation time and a decrease in the yield force required to fracture gels. The extent of whey protein denaturation (as a result of heat treatment) was related to the decrease in the G' value of gels as well as the yield force.     

大豆磷脂对牛乳蛋白乳状液热稳定性的影响

研究了大豆磷脂对牛乳蛋白乳状液热稳定性的影响,并对相关作用机理进行了探讨.测定了添加磷脂前后牛乳蛋白乳状液的热凝固时间(HCT)、粒径分布、表面疏水性、Zeta位和游离巯基含量的变化.结果表明:添加大豆磷脂能够提高牛乳蛋白乳状液的热稳定性.其中添加量为2.5 g/L时热稳定性最高,最大HCT为23.49 min.大豆磷脂可能通过与乳蛋白发生疏水相互作用改变蛋白的构象、增加乳状液的负Zeta电位、抑制巯基氧化或降低游离豌基之间的反应几率来提高乳状液的热稳定性.     

Effect of collagen content and heat treatment on protein digestibility and biological value of meat products

The digestibility and biological value of meat mixed with various amounts of collagen were measured after heat treatments.
The M. biceps femoris muscle was used as the source of meat and pigskin as the source of collagen. The latter contained 78.9% collagen and digestibility both heated and raw was 95%.
The NPU of mixtures of meat and pigskin showed a relation with collagen content defined as y = 82.8–0.6 x.
Supplementation of pigskin at a pigskin-meat mixture containing 50% collagen with methionine did not increase NPU.
The amount of collagen in untreated meat products is 15–30% and will be of negligible nutritional significance in a whole diet.     

热处理影响牛乳蛋白凝胶特性的研究进展

热处理是各种乳制品生产过程中不可或缺的工艺手段,热处理过程中乳体系的蛋白质会发生变化,影响制品的凝胶特性.介绍了牛乳酸凝胶的模型和酶凝胶的形成阶段,分析了加热过程中蛋白质可能发生的变化,简要阐述了热处理对凝乳效果的影响,指出热诱乳蛋白聚合物与凝乳的机制密切相关,旨在为乳制品加工中热处理的潜在影响提供理论参考.     

湿热处理对牛奶蛋白复合纤维纱线结构和性能的影响

由于牛奶蛋白复合纤维染整加工中经常伴随着湿热加工,因此,着重研究了湿热处理对牛奶蛋白复合纤维结构和性能的影响.结果表明,湿热处理对牛奶蛋白复合纤维的收缩率、强力、白度及表面形态影响显著,对牛奶蛋白复合纤维结构及结晶形态影响很小.随着湿热处理温度的升高,牛奶蛋白复合纤维织物的顶破强力稳步提高,而白度出现下降;当湿热处理温度大于100℃时,收缩率的增幅明显变大,且手感变硬;特别当湿热处理温度超过130℃时,纤维的表面已经几乎没有平整的地方.因此,牛奶蛋白复合纤维宜采用90、100℃为其最高湿热加工温度.