Lesson 6

Reading Material Mineral

In general，minerals are the constituents which remain as ash after the combustion of plant and animal tissues. Human body uses minerals to activate the enzymes，hormones，and other molecules that participate in the function and maintenance of life processes. Mineral elements are present in relatively low concentrations in foods. Nevertheless，they play key functional roles in both living systems and foods. Minerals are absolutely essential，as they cannot be synthesized by the body.

Chemical properties of minerals

Many different chemical forms of mineral elements are present in foods. These forms are commonly referred to as species and include compounds，complexes，and free ions. Given the diversity of chemical properties among the mineral elements，the number and diversity of nonmineral compounds in foods that can bind mineral elements，and the chemical changes that occur in foods during processing and storage，it is not surprising that the number of different mineral species in foods is large indeed. Moreover，since foods are so complex and many mineral species are unstable，it is very difficult to isolate and characterize mineral species in foods. Thus，our understanding of the exact chemical forms of minerals in foods remains limited. Fortunately，principles and concepts from the vast literature in inorganic，organic，and biochemistry can be very useful in guiding predictions about the behavior of mineral elements in foods.

Function and classfication

Minerals have several functions in the body. Body building minerals serve as structural constituents in the hard tissues of the body，such as the bones and teeth. Thus，the minerals are needed in comparatively large amounts to help normal growth and development of bones and teeth. Minerals are also the components of soft tissues（muscle，nervous tissue）. They form a part of compounds essential for body functions（haemoglobin，thyroxine，insulin etc.）

Some minerals help to maintain acid-base balance and while others regulate water balance in the body. Some minerals are important in transmission of nerve impulses，while others are necessary for muscle contraction and relaxation. Some metals are integral part of enzymes，while others function as cofactors of some enzymes.

The number of different minerals necessary to maintain good health is still unknown . While dietary deficiencies of only a few minerals such as iron or iodine can be linked to disease directly，some authorities claim that as many as 60 elements are necessary for optimum longevity and quality of life in humans. What has become more widely recognized is that a number of minerals are required by the body，and deficiencies in these minerals may not produce obvious symptoms but can still result in poor health or a shortened life expectancy. Even some minerals once considered solely “toxic” have now been identified as important in supporting longevity and quality of life. Selenium was long viewed as a toxic compound，but several international studies have demonstrated that dietary selenium markedly reduces the incidences and death of cancer. Some forms of chromium are also considered toxic，but trivalent chromium is a mineral associated with fat metabolism and has been linked to the regulation of blood glucose levels in the body.

There are two groups of minerals，major minerals and trace minerals. Major minerals（also known as macrominerals or macroelements）are needed in the diet in amounts of 100mg or more each day. They include calcium，magnesium，sodium，potassium and phosphorus. Macrominerals are present in virtually all cells of the body，maintaining general homeostasis，and are required for normal functioning. Acute imbalances of these minerals can be potentially fatal，although nutrition is rarely the cause of these cases. Trace minerals（also known as microminerals）are micronutrients that are chemical elements. They include iron，chromium，copper，iodine，manganese，selenium，zinc，and molybdenum. They are dietary minerals needed by the human body in very small quantities（generally less than 100 mg/day）.

There are several other minerals that may be essential for humans，but research has not established their importance，including tin，nickel，silicon and vanadium. There are also minerals found in the body that are regarded as contaminants including lead，mercury，arsenic，aluminum，silver，cadmium，barium，strontium and others.

Solubility of Minerals in Aqueous Systems

All biological systems contain water，and most nutrients are delivered to and metabolized by organisms in an aqueous environment. Thus the availabilities and reactivities of minerals depend，in large part，on solubility in water. This excludes the elemental form of nearly all elements from physiological activity in living systems since these forms，such as elemental iron，are insoluble in water and therefore are unavailable for incorporation into organisms or biological molecules.

The solubilities of mineral complexes and chelates may be very different from that of inorganic salts. For example，if ferric chloride is dissolved in water，the iron will soon precipitate as ferric hydroxide. On the other hand，ferric iron chelated with citrate is quite soluble. Conversely，calcium as calcium chloride is quite soluble，while calcium chelated with oxalate ion is insoluble.

Minerals in Food Processing

Generally，there are metal ions，derived from food itself or acquired during food processing and storage，which interfere with the quality and visual appearance of food. They can cause discoloration of fruit and vegetable products and many metal-catalyzed reactions are responsible for losses of some essential nutrients，for example，ascorbic acid oxidation. Also，they are responsible for taste defects or off-flavors，for example，as a consequence of fat oxidation. Therefore，the removal of many interfering metal ions by chelating agents or by other means is of importance in food processing.

Vocabulary

calcium 钙

hormone 激素

chelate 螯合

inorganic 无机的

cofactor 辅因子

iodine 碘

copper 铜

iron 铁

chromium 铬

magnesium 镁

discoloration 变色

manganese 锰

homeostasis 动态平衡

mineral 矿物质

molybdenum 钼

silicon 硅

potassium 钾

sodium 钠

phosphorus 磷

symptoms 症状

selenium 硒

zinc 锌

参考译文 矿物质

矿物质通常指动植物组织经过燃烧后剩余的灰分。人体能利用矿物质激活参与维持机体生理功能的酶、激素和其他分子。食物中的矿物质浓度也相对较低，尽管如此，它们在生命系统和食品中都起着重要作用。由于人体自身不能合成矿物质，因此它们是人体必不可少的元素。

矿物质化学性质

矿物质元素以不同的形式存在于食品中，包括化合物、复合物和游离离子的形式。鉴于矿物质元素的化学性质多样，以及食品中能够结合矿物质元素的非矿物质化合物的数量和种类都多，并且食品在加工和储存过程中也会发生化学变化，因此，食品中拥有如此多矿物质形态就不足为奇了。此外，由于食品成分复杂，许多矿物质形态也不稳定，因此很难分离和鉴定食品中的矿物质。因此，我们对食品中矿物质的准确化学形态的了解仍然有限。幸运的是，无机、有机和生物化学的大量文献中的原理和概念对于指导和预测食品中矿物质元素的形态非常有用。

功能和分类

矿物质对机体有多种功能，它们是构成机体结构组织的成分，如骨骼和牙齿，因此，机体需要大量的矿物质来帮助骨骼和牙齿的正常生长发育。矿物质也是软组织的组成成分（如肌肉、神经组织），它们是维持机体功能必需化合物的组成成分（如血红蛋白、甲状腺素、胰岛素等）。

有些矿物质有助于维持机体酸碱平衡，其他一些矿物质则可调节机体内的水分平衡。有些矿物质对神经兴奋的传导有重要作用，而另一些矿物质则是肌肉收缩和放松所必需的物质。还有些金属元素是酶的组成成分，有的还可以作为酶的辅助因子。

维持身体健康所必需的矿物质数量还是未知的。虽然膳食中只有少数矿物质如铁或碘的缺乏直接与一些疾病相关，但权威人士认为，人类要想长寿和拥有好质量的生活则需要多达60种的矿物质元素。众所周知，人体需要多种矿物质，这些矿物质的缺乏可能不会产生明显的症状，但仍然会导致健康状况不佳或者预期寿命缩短。即使一些曾被认为是“有毒”的矿物质，现在已经确定它们对长寿和生活质量的影响非常重要。硒就被长期视为一种有毒物质，但一些国际研究表明，膳食中的硒显著降低了癌症的发生率和死亡率。某些形式的铬也被认为是有毒的，但三价铬与脂肪的代谢有关，并且与体内血糖水平的调节有关。

矿物质可分为主要矿物质和微量矿物质。主要矿物质也称为大量矿物质或常量元素，每日膳食中大量矿物质需要量为100mg以上。它们包括钙、镁、钠、钾、磷。大量矿物质几乎存在于身体所有细胞中，用来维持体内动态平衡和正常功能。这些矿物质的急性失衡可能是致命的，虽然营养上它们不是导致这些病例的原因。微量矿物质（也称微量元素）是化学元素中的微量营养物质，包括铁、铬、铜、碘、锰、硒、锌和钼。它们是人们膳食中必需的矿物质，需求量非常少（通常小于100mg /d）。

还有其他几种可能对人类至关重要但研究尚未确定其重要性的矿物质，包括锡、镍、硅和钒。人体中还存在些被认为污染物的矿物质，如铅、汞、砷、铝、银、镉、钡、锶等。

矿物质在水中的溶解度

所有生物系统都含有水分，生物体中的大多数营养物质都是在水环境中进行传递和代谢的。因此，矿物质的可利用性和反应活性在很大程度上取决于其在水中的溶解度。但这不包括生物系统中有生理活性的矿物质元素的基本形态，因为这些形态如元素铁不溶于水，它不能融入生物体或生物分子。

矿物质的复合物和螯合物的溶解度可能与无机盐非常不同。例如，如果氯化铁溶解在水中，铁很快会以氢氧化铁形式沉淀，而另一方面，三价铁与柠檬酸螯合后则易溶于水。相反，钙作为氯化钙时易溶于水，而与草酸根离子螯合的钙则不溶。

矿物质与食品加工

通常，食物自身含有的或加工和储存过程中获得的金属离子会影响食品的质量和外观。它们可能引起水果和蔬菜产品的变色，并且许多金属催化的反应会导致必需营养物质的损失，如抗坏血酸氧化。此外，它们也会导致味觉缺陷或异味，如脂肪氧化后。因此，食品加工中利用螯合剂或其他方法去除许多干扰的金属离子具有重要意义。

Exercise

1.Answer questions

（1）What are the functions of minerals?

（2）Which are the major minerals and which are the trace minerals?

2.Translation

（1）In general，minerals are the constituents which remain as ash after the combustion of plant and animal tissues. Human body uses minerals to activate the enzymes，hormones，and other molecules that participate in the function and maintenance of life processes.

（2）Minerals have several functions in the body. Body building minerals serve as structural constituents in the hard tissues of the body. Some minerals help to maintain acid-base balance and while others regulate water balance in the body. Some minerals are important in transmission of nerve impulses，while others are necessary for muscle contraction and relaxation. Some metals are integral part of enzymes，while others function as cofactors of some enzymes.