Weiss W P
Department of Animal Sciences, Ohio Agricultural Research and Development Center, Ohio State University, Wooster 44691, USA.
J Dairy Sci. 2001 Oct;84(10):2302-7. doi: 10.3168/jds.S0022-0302(01)74677-2.
The addition of exogenous ascorbic acid to milk reduces the development of oxidized flavor. This experiment was conducted to determine whether feeding ascorbic acid to cows influenced vitamin C concentrations in milk. Thirty-two midlactation Holstein cows were fed a basal diet of 56% forage, 36.6% concentrate, and 7.4% roasted whole soybeans (dry basis) that was top-dressed with a premix that provided 0, 3, 16.5, or 30 g/d of L-ascorbic acid (provided by ascorbyl-2-polyphosphate) for 28 d. Supplementation had no effect on milk yield or composition or dry matter intake. Treatment linearly increased plasma concentrations of ascorbic acid (19.8, 22.3, 21.9, and 25.7 mumol/L, respectively) but had no effect on plasma dehydro-L-ascorbic acid (DHAA). Concentrations of ascorbic acid (103.7 mumol/L) and DHAA (9.5 mumol/L) in milk were not affected by treatment. Secretion of ascorbic acid into milk appeared to follow Michaelis-Menton kinetics, with a Vmax of 3.92 mmol/d and a Km of 3.59 mumol/L. Milk flavor as evaluated by a panel was normal for all samples after 1 d of storage. After 7 d of storage, the average flavor score was 2.5 (moderate oxidized flavor), but no differences among treatments were observed. Supplemental dietary vitamin C did not increase vitamin C concentration in milk, probably because the maximum potential secretion of the vitamin was occurring in unsupplemented cows.
向牛奶中添加外源性抗坏血酸可减少氧化风味的产生。本试验旨在确定给奶牛饲喂抗坏血酸是否会影响牛奶中的维生素C浓度。选用32头处于泌乳中期的荷斯坦奶牛，给它们饲喂由56%粗饲料、36.6%精饲料和7.4%烤全大豆（干基）组成的基础日粮，并在其上添加预混料，预混料分别提供0、3、16.5或30 g/d的L-抗坏血酸（由抗坏血酸-2-多聚磷酸提供），持续28天。补充抗坏血酸对牛奶产量、组成或干物质采食量没有影响。处理使血浆中抗坏血酸浓度呈线性增加（分别为19.8、22.3、21.9和25.7 μmol/L），但对血浆脱氢-L-抗坏血酸（DHAA）没有影响。牛奶中抗坏血酸（103.7 μmol/L）和DHAA（9.5 μmol/L）的浓度不受处理影响。抗坏血酸向牛奶中的分泌似乎遵循米氏动力学，Vmax为3.92 mmol/d，Km为3.59 μmol/L。储存1天后，所有样品经品评小组评定的牛奶风味均正常。储存7天后，平均风味评分为2.5（中度氧化风味），但各处理间未观察到差异。日粮中补充维生素C并未增加牛奶中的维生素C浓度，可能是因为未补充维生素C的奶牛已达到该维生素的最大潜在分泌量。
