Rérat Alain, Calmes Régine, Vaissade Pierre, Finot Paul-André
CRJ-INRA, Jouy-en-Josas, France.
Eur J Nutr. 2002 Feb;41(1):1-11. doi: 10.1007/s003940200000.
During the processing of foods, the Maillard reaction may occur contributing to altering the nutritional value of proteins. In dairy products the formation of lactuloselysine reduces the availability of lysine but the effects on the other nutrients are not very well known.
Determination of the consequences of a high level of lactuloselysine in milk on the bioavailability of skim milk nutrients and the kinetics of their appearance in the portal blood and of their urinary and faecal excretions and extrapolation to lower heat treatments and to man, using the pig model.
Sub-adult pigs were fitted, under anaesthesia, with permanent catheters in the portal vein, carotid artery and urethra, and with an electromagnetic flow probe around the portal vein. Each animal was successively fed with two experimental meals containing an equal amount of dried skim milk (SM), either lyophilised or heat treated to obtain an intense Maillard reaction, (M-SM) resulting in a 50% lysine blockage. Portal and arterial concentrations and flux of individual amino acids (AA), glucose, galactose and fructoselysine were measured for a period of 12h after the meals. Lysine, fructoselysine and AA excreted in the urine and faeces within 72h were also determined.
In M-SM containing 50% blocked lysine, no other AA was chemically modified. Fructoselysine appeared in the portal blood very late compared to amino acids resulting from a very slow release and corresponded to 8.2 and 18.6% of the ingested amount after 12 and 72h, respectively. Significant changes of the appearance in the portal blood were observed only for lysine (-60%), alanine (-17%) and cystine (+37%). A small decrease in the digestibility of most AA during the same period was observed, which was significant after 48h for lysine, phenylalanine, cystine, aspartic acid, glycine and total AA (-6%).
It was confirmed that lactuloselysine was not bioavailable. The loss in protein nutritive value was mainly due and proportional to the deterioration of lysine and, to a lesser extent, to the decrease in the digestibility of some essential AA. Taking into account the very high level of lactuloselysine in the M-SM sample studied, it may be concluded that in common foods such as milk, infant formulas, biscuits, bread, pasta, containing lower levels of blocked lysine, the nutritional loss is primarily due to the loss of lysine and to a less extent to the decrease in the digestibility of other essential AA.
在食品加工过程中，美拉德反应可能发生，从而改变蛋白质的营养价值。在乳制品中，乳果糖赖氨酸的形成会降低赖氨酸的利用率，但对其他营养素的影响尚不太清楚。
利用猪模型，确定牛奶中高水平的乳果糖赖氨酸对脱脂牛奶营养素生物利用率的影响，以及它们在门静脉血中出现的动力学、尿液和粪便排泄情况，并外推至较低热处理程度及人体情况。
对未成年猪在麻醉状态下，在门静脉、颈动脉和尿道插入永久性导管，并在门静脉周围安装电磁流量探头。每只动物先后喂食两种实验餐，餐中含有等量的冻干脱脂牛奶（SM），一种是冻干的，另一种经过热处理以引发强烈的美拉德反应（M-SM），导致50%的赖氨酸被阻断。餐后12小时内测量门静脉和动脉中各氨基酸（AA）、葡萄糖、半乳糖和果糖赖氨酸的浓度及通量。还测定了72小时内尿液和粪便中排泄的赖氨酸、果糖赖氨酸和氨基酸。
在含有50%被阻断赖氨酸的M-SM中，没有其他氨基酸发生化学修饰。与氨基酸相比，果糖赖氨酸在门静脉血中出现得非常晚，释放非常缓慢，在12小时和72小时后分别相当于摄入总量的8.2%和18.6%。仅观察到门静脉血中赖氨酸（-60%）、丙氨酸（-17%）和胱氨酸（+37%）的出现有显著变化。同期大多数氨基酸的消化率略有下降，48小时后赖氨酸、苯丙氨酸、胱氨酸、天冬氨酸、甘氨酸和总氨基酸（-6%）的下降具有显著性。
证实乳果糖赖氨酸无法被生物利用。蛋白质营养价值的损失主要且成比例地归因于赖氨酸的降解，在较小程度上归因于一些必需氨基酸消化率的降低。考虑到所研究的M-SM样品中乳果糖赖氨酸的水平非常高，可以得出结论，在牛奶、婴儿配方奶粉、饼干、面包、面食等常见食品中，赖氨酸阻断水平较低，营养损失主要是由于赖氨酸的损失，在较小程度上是由于其他必需氨基酸消化率的降低。
