如何控制成品饲料氧化

发布时间:2016-12-11 10:24:13   来源:猪OK网   阅读:2347次

  Finished feeds are always prone to oxidation, especially if rich in lipids or stored for a prolonged period of time under unfavorable conditions.

  成品饲料易被氧化,尤其是高脂饲料或在不利条件下长时间贮存的饲料。

  Oxidation of lipids in feeds is a natural phenomenon; it happens whether we take measures to prevent it or not. In reality, what we try to achieve is delaying the process so that when the feed reaches the animal, the oxidation of lipids is minimal. This avoids the drop in feed intake observed when animals are offered rancid feeds. Therefore, measures to control oxidation should be undertaken long before the feed is manufactured, starting from selecting the right raw materials and appropriate antioxidant additives.

  饲料脂肪氧化是一种自然现象,无论我们是否采取措施都会发生。事实上,我们所要做的就是延缓这个过程,以使动物采食的饲料中脂肪氧化程度最小。这可避免动物因采食酸败的饲料引起的采食量下降。因此,应从挑选合适的原料和适宜的抗氧化添加剂开始,远在饲料制好之前就采取防氧化措施。

  How rancidity develops饲料酸败是如何形成的

  Oxidation of lipids, also called oxidative rancidity, is a natural reaction between unsaturated fatty acids and free oxygen. Such fatty acids exist in all fats and oils, but certain vegetable oils such as soybean and corn oil are especially rich in them. For example, the ratio between saturated and unsaturated fatty acids in coconut oil is over 11, whereas in corn oil it is only 0.15, indicating the richness of corn oil is unsaturated and thus vulnerable to oxidation.

  脂质氧化,也称氧化酸败,是不饱和脂肪酸与氧自由基之间的自然反应。不饱和脂肪酸存在于所有油脂中,但某些植物油如大豆油、玉米油含量尤为丰富。例如,椰子油饱和脂肪酸与不饱和脂肪酸的比例大于11,而玉米油只有0.15,说明玉米油富含不饱和脂肪酸,易于氧化。

  Lipid oxidation is enhanced by exposure to air (open bags), light, high temperatures and certain inorganic minerals such as iron and copper. The reaction is autocatalytic and, once started, oxidized fatty acids continue to form, and peroxides, the end product of oxidation, accumulate.

  在光照、高温、暴露在空气中(开袋)以及有铁、铜等金属离子存在的条件下,脂肪氧化反应会被加速。这个反应是自动的,且一旦反应开始,被氧化的脂肪酸不断形成,氧化终产物过氧化物不断积聚。

  Saturated to unsaturated fatty acids ratio in selected lipid sources

  所选脂肪源饱和与不饱和脂肪酸比例

  Lipids

  脂肪Saturated

  饱和脂肪酸Unsaturated

  不饱和脂肪酸S:U ratio

  饱和脂肪酸:不饱和脂肪酸

  Tallow 牛油49.845.81.09

  Lard猪油39.256.30.70

  Soybean oil 大豆油14.481.20.18

  Corn oil 玉米油12.782.90.15

  Coconut oil椰子油86.57.611.4

  数据来源: McWilliams,1999

  Why oxidized feed is undesirable被氧化的饲料有何坏处?

  Oxidized fatty acids, also referred to as free radicals, react not only with other fatty acids but also with amino acids, rendering them unavailable to the animal. Methionine and tryptophan are particularly susceptible to oxidation by free radicals. Methionine and tryptophan are limiting amino acids in diets, and they are often added in the form of crystalline amino acids to supplement natural ingredients. In a controlled study, lipid oxidation caused during flaking reduced bioavailability of methionine and tryptophan in wheat, rye, barley and oats by as much as 26 percent.

  脂肪酸氧化后,新自由基产生,可继续与其他脂肪酸和氨基酸反应,使它们不能被动物所利用。蛋氨酸和色氨酸对自由基的氧化作用尤为敏感。蛋氨酸和色氨酸是日粮中的限制性氨基酸,通常以晶体氨基酸的形式补充到饲料中。研究表明,脂肪氧化可引起小麦、黑麦、大麦、燕麦中的蛋氨酸和色氨酸生物利用率下降26%。

  Other side-effects of rancidity include the creation of objectionable flavors such as “fishy” or “beany” flavor in oils rich in linoleic and linolenic fatty acids (e.g.,soybean, rapeseed and fish oils). This process, called reversion, can take place even under anaerobic conditions, and currently there is no way to prevent it.

  饲料酸败还可引起富含亚麻油酸和亚麻脂肪酸的油脂(如大豆油、菜籽油、鱼油)产生难闻的腥臭味或豆腥味。该过程甚至可以在厌氧条件下发生,且目前尚无任何方法阻止其发生。

  It is evident that in nutrient-dense diets enhanced with fats, lipid oxidation can easily become problematic. A drop in feed intake is observed when animals are offered rancid feeds, resulting in reduced weight gain.Increased rancidity in choice white grease (lard), added at 6 percent of the diet, linearly depressed growth rates and feed intake in weaned pigs that were fed complex starter diets. From the same study, it was demonstrated that dietary concentrations of peroxides should not exceed 240 mEq to prevent depression of growth performance.

  研究表明,在脂肪含量高、营养丰富的日粮中,脂肪氧化很容易引发不良后果。当喂给动物酸败饲料,其采食量下降,从而导致体增重下降。猪油易氧化酸败,在断奶仔猪日粮中添加6%的猪油,会使其生长速度和采食量直线下降。

  Which antioxidants to use用何种抗氧化剂

  Antioxidants are frequently added to oils to prevent auto-oxidation during storage. Such additives are also added into complete feeds, concentrates and premixes that contain high levels of fats and oils. As mentioned, antioxidants can only delay the process of oxidation by stabilizing reactive fatty acids, but given enough time, fatty acids will eventually react with available oxygen.

  通常在油脂中添加抗氧化剂来防止贮存期间的自动氧化反应,高脂全价饲料、浓缩料和预混料中也常加入抗氧化剂。如前所述,抗氧化剂只能稳定反应性脂肪酸来延缓氧化速度,但只要时间够长,脂肪酸终会和氧气反应。

  Common antioxidants include ethoxyquin, butylated hydroxytoluene, propyl gallate, citric acid, and vitamins C and E. The last three antioxidants are usually too expensive to be used as antioxidants in feed, yet when they are included in relatively high amounts for other reasons they contribute to the antioxidant status of the feed.

  常见的抗氧化剂包括乙氧喹、丁羟甲苯、没食子酸丙酯、柠檬酸以及维生素C、维生素E。后三种通常因价钱昂贵而不用作抗氧化剂,但当它们以其他用途高剂量加入饲料中时,可保持饲料的抗氧化状态。

  Natural antioxidants are extracts from spices and herbs rich in polyphenols. Such commercial products are derived from spices such as clove, cinnamon, oregano, cumin, garlic and coriander or herbs such as sage, thyme, marjoram, tarragon, peppermint, oregano and rosemary. Several pigments such as carotene, beta-carotene, astaxanthin, zeaxanthin, lutein andcanthaxantin also have antioxidant activities.

  天然抗氧化剂是从富含多酚的香料或草药中提取出来的。商品化生产的抗氧化剂一般来自丁香、肉桂、牛至、小茴香、大蒜、香菜等香料或鼠尾草、百里香、墨角兰、龙嵩叶、薄荷、牛至叶、迷迭香等草药。一些色素如胡萝卜素、β胡萝卜素、虾青素、玉米黄素、叶黄素和茜草色素也具有抗氧化活性。

  Quality control质量控制

  All incoming lipid sources must be checked for rancidity. It is best to buy lipids that have been enhanced with antioxidants if storage conditions favor rancidity. Finished feeds should be tested regularly for oxidation. In addition, samples should be collected from feeding points (troughs) to assess the oxidation status of feeds as they reach the animal.

  所有脂肪源必须做酸败检查。若贮存条件易导致酸败,则最好使用添加抗氧化剂的油脂。成品饲料应定期做氧化程度检测,且用于评估饲料氧化程度的检测样品应在饲喂槽中收集,因为这些饲料才是动物最终采食的。

  Peroxide analysis is a valid index of rancidity, but it does not provide all information required to assess the oxidative status of feed and lipids. Other common tests include analyses for anisidine, malonaldehyde and thiobarbituric acid (TBA). A combination of several tests is usually required to provide a complete picture of oxidation state.

  过氧化分析是酸败的有效指标,但仅用该指标不能充分评估饲料和脂肪氧化程度。其他常规检测还有茴香胺、丙二醛(MDA)、硫代巴比土酸(TBA)分析。通常需要综合这些检测项目的结果来充分判断其氧化程度。

  Practical recommendations

  实用性建议

  The usual addition of a single, inexpensive and low-dosage antioxidant usually suffices for most cases. This involves production of feed in cold(er) environments and consumption within a few weeks after production. Prolonged storage, shipment and storage in warm(er) climates, and, of course, high levels of unstable lipids, require a more generous approach. To this end, using two or three different antioxidants that complement each other is advisable. Using the highest recommended dosage is always a first thought, but very high levels are not recommended unless the feed is expected to go rancid very quickly. Moderation in supplementation levels is best.

  多数情况下,低温环境下生产的并在几周内用完的饲料,只需添加一种廉价的低剂量抗氧化剂。若需船运、长时间或高温贮存易被氧化的高脂饲料,则需采取更严格的措施。为此,可选用两种或三种不同的抗氧化剂相互补充。通常人们最先考虑的是使用推荐的抗氧化剂最高剂量,但除非饲料酸败速度特别快,否则不推荐剂量很高,适量补充最好。

 



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