卡拉胶

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卡拉胶（Carrageenans 或 carrageenins；/ˌkærəˈɡiːnənz/ karr-ə-gee-nənz，CAS 9000-07-1），又称鹿角菜胶、角叉菜胶、爱尔兰苔菜胶，是一組从海洋可食用红藻（包括角叉菜属、麒麟菜属、杉藻属及沙菜属等）中提取的綫性硫化多糖的统称。這些多糖體廣泛應用於食品产业，, for their gelling, thickening, and stabilizing properties. Their main application is in dairy and meat products, due to their strong binding to food proteins. There are three main varieties of carrageenan, which differ in their degree of sulfation. Kappa-carrageenan has one sulfate group per disaccharide, iota-carrageenan has two, and lambda-carrageenan has three.

卡拉胶的名字来源于爱尔兰苔菜（Chondrus crispus，也称角叉菜）在愛爾蘭語的称呼carraigín，而這種植物作為食品添加劑使用早於15世紀已經開始。卡拉膠是素食主義 及維根主義支持者對明膠使用的另類選擇，因為在甜品中經常使用的明膠是動物製品。

当用于食品时，在包装的卡拉胶以欧洲联盟的E編碼E407（藻酸盐）表示。

性质

Carrageenans are large, highly flexible molecules that form curling 螺旋 structures. This gives them the ability to form a variety of different 凝胶s at room temperature. They are widely used in the food and other industries as thickening and 稳定剂.

All carrageenans are high-molecular-weight polysaccharides made up of repeating galactose units and 3,6 anhydrogalactose (3,6-AG), both sulfated and nonsulfated. The units are joined by alternating α-1,3 and β-1,4 糖苷键.

类型

不同類型角叉菜膠的結構

商業應用的卡拉胶以下列三个类型為主：

• 阿欧塔型（ι，Iota） - 柔软、富有弹性的凝胶，从麒麟菜属植物Eucheuma denticulatum或Eucheuma spinosum中提取。
• Kappa forms strong, rigid gels in the presence of potassium ions, and reacts with dairy proteins. It is sourced mainly from Kappaphycus alvarezii.
• Lambda does not gel, and is used to thicken dairy products.

The primary differences that influence the properties of kappa, iota, and lambda carrageenan are the number and position of the ester sulfate groups on the repeating 半乳糖 units. Higher levels of ester sulfate lower the solubility temperature of the carrageenan and produce lower strength gels, or contribute to gel inhibition (lambda carrageenan).

Many red algal species produce different types of carrageenans 世代交替. For instance, the genus Gigartina produces mainly kappa carrageenans during its 配子體 stage, and lambda carrageenans during its 孢子体 stage.

All are soluble in hot water, but in cold water, only the lambda form (and the sodium salts of the other two) are soluble.

When used in food products, carrageenan has the 欧洲联盟 additive E编码s E407 or E407a when present as "processed eucheuma seaweed". Technically carrageenan is considered a dietary fibre.

In parts of Scotland and Ireland, where it is known by a variety of local and native names, Chondrus crispus is boiled in milk and strained, before sugar and other flavourings such as vanilla, cinnamon, brandy, or whisky are added. The end-product is a kind of jelly similar to 意式奶凍, 太白粉, or blancmange.

生产

Eucheuma denticulatum being farmed for iota-carrageenan in an off-bottom cultivation in Tanzania

Although carrageenans were introduced on an industrial scale in the 1930s, they were first used in 中华人民共和国 around 600 B.C. (where Gigartina was used) and in 爱尔兰岛 around 400 A.D. Carrageen gelatin can be prepared by boiling 5 ounces (142 gm) of rinsed Irish moss in 8 quarts (7.57 litres) of water for 10 minutes, stirring the mixture as it boils. Two quarts (1.9 litres) of cold water are rapidly added to the hot brew, and after the mixture has cooled, it is strained through a cloth. It is then cooled for 24 hours, during which time it becomes gelatinous.

截至2011年 (2011-Missing required parameter 1=month!), global sales of carrageenan were estimated at $640 million. The largest producer of industrial carrageenan was the 菲律宾, where cultivated seaweed produces about 80% of the world supply, while China is the main exporter to global markets in the US and Europe. The most commonly used sources are E. cottonii (Kappaphycus alvarezii, K. striatum) and E. spinosum (Eucheuma denticulatum), which together provide about three-quarters of the world production. These grow from the sea surface to a depth of about 2 metres. The seaweed is normally grown on nylon lines strung between bamboo floats, and it is harvested after three months or so, when each plant weighs approximately 1 kg.

The E. cottonii variety has been reclassified as Kappaphycus cottonii by Maxwell Doty (1988), thereby introducing the genus Kappaphycus, on the basis of the phycocolloids produced (namely kappa carrageenan).

After harvest, the seaweed is dried, baled, and sent to the carrageenan manufacturer. There the seaweed is ground, sifted to remove impurities such as 沙, and washed thoroughly. After treatment with hot 碱 solution (e.g., 5–8% 氢氧化钾), the 纤维素 is removed from the carrageenan by centrifugation and 过滤. The resulting carrageenan solution is then concentrated by 蒸发. It is dried and ground to specification.

There are three types of industrial processing:

Semi-refined

This is only performed using E. cottonii or E. spinosum. The raw weed is first sorted and crude contaminants are removed by hand. The weed is then washed to remove salt and sand, and then cooked in hot alkali to increase the gel strength. The cooked weed is washed, dried, and milled. E. spinosum undergoes a much milder cooking cycle, as it dissolves quite readily. The product is called semi-refined carrageenan, Philippines natural grade, or, in the U.S., it simply falls under the common carrageenan specification.

                           cleaned and washed seaweed 
                                   ↓
                                extraction
                                   ↓
                             coarse filtration   → seaweed residue
                                   ↓ 
                              fine filtration    → used filter aids
                                   ↓
            ↓-------------- concentration --------------↓
   preparation with KCl                        preparation with alcohol
            ↓                                           ↓
       gel pressing                                alcohol recovery 
            ↓                                           ↓
         drying                                      drying
            ↓                                           ↓ 
         milling                                     milling 
            ↓                                           ↓ 
         blending                                    blending
            ↓                                           ↓
    gel refined carrageenan                     refined carrageenan

Refined

The essential difference in the refining process is that the carrageenan is first dissolved and filtered to remove cell wall debris. The carrageenan is then precipitated from the clear solution either by isopropanol or by potassium chloride.

Mixed processing

A hybrid technology in which seaweed is treated heterogeneously as in the semirefined process exists, but alcohol or high salt levels are used to inhibit dissolution. This process is often used on South American seaweeds and gives some of the cost benefits of semirefined processing, while allowing a wider range of seaweeds to be processed, however, the naturally low cellulose levels in some South American seaweeds allow them to be heterogeneously processed and still be sold under the EU refined specification.

Grades

参见：Food grading

There are two basic grades of carrageenan: refined carrageenan (RC) and semi-refined carrageenan (SRC). In the United States both grades are labeled as carrageenan. In the European Union, refined carrageenan is designated by the E编码 E-407, and semi-refined carrageenan as E-407a. Refined carrageenan has a 2% maximum for acid insoluble material and is produced through an alcohol precipitation process or potassium chloride gel press process. Semi-refined carrageenan contains a much higher level of cellulosic content and is produced in a less complex process. Indonesia, the Philippines, and Chile are three main sources of raw material and extracted carrageenan.

應用

食物及其他家居用途

• 甜品s, carrageen, 冰淇淋, cream, milkshakes, yogurts, salad dressings, sweetened 煉奶s
• 醬汁s: to increase viscosity
• 啤酒: clarifier to remove haze-causing proteins
• 肉醬 (歐洲)s and processed 肉类食物s (e.g., ham): substitute for fat, increase water retention, increase volume, or improve slicing
• 牙膏: stabilizer to prevent constituents separating
• Fruit Gushers: ingredient in the encapsulated gel
• Fire fighting foam: thickener to cause foam to become sticky
• 洗髮精及化粧乳膏：增稠劑
• 空氣清新凝膠
• Marbling: the ancient art of paper and fabric marbling uses a carrageenan mixture on which to float paints or inks; the paper or fabric is then laid on it, absorbing the colours
• Shoe polish: to increase 黏度
• 生物技术: to immobilize cells and enzymes
• Pharmaceuticals: used as an inactive 賦形劑 in pills and tablets
• 豆浆 and other 植物奶s: to thicken
• Diet sodas: to enhance texture and suspend flavours
• 寵物食品
• 人体润滑剂s
• Vegetarian hot dogs

Regulatory status

In the U.S., carrageenan is allowed under FDA regulations as a direct food additive and is considered 公认安全 when used in the amount necessary as an emulsifier, stabilizer, or thickener in foods, except those standardized foods that do not provide for such use. FDA also reviewed carrageenan safety for infant formula. The European Food Safety Authority concluded "there is no evidence of any adverse effects in humans from exposure to food-grade carrageenan, or that exposure to degraded carrageenan from use of food-grade carrageenan is occurring", Furthermore, the Joint FAO/WHO expert committee on food additives stated in a July 2014 review of carrageenan "that the use of carrageenan in infant formula or formula for special medical purposes at concentrations up to 1000 mg/L is not of concern".

Although the National Organic Program (NOP) had added carrageenan to its National List of additives allowed to be included in organic foods in 2003, and reviewed and reauthorized it in 2008, noting it as "critical to organic production and handling operations", on November 18, 2016 the NOP's National Organic Standards Board (NOSB) voted to recommend carrageenan be removed from the National List of additives allowed in organic food production.

On April 4, 2018 the Agricultural Marketing Service (AMS) (美国农业部) published a document to announce the renewal of carrageenan on the National List, allowing its continued use in food products. The document states, “The NOSB recommended removing carrageenan because they determined that alternative materials, such as gellan gum, guar gum, or xanthan gum, are available for use in organic products” continuing, “AMS found sufficient evidence in public comments to the NOSB that carrageenan continues to be necessary for handling agricultural products because of the unavailability of wholly natural substitutes (§ 6517(c)(1)(ii)). Carrageenan has specific uses in an array of agricultural products, and public comments reported that potential substitutes do not adequately replicate the functions of carrageenan across the broad scope of use. Therefore, carrageenan continues to meet the OFPA criteria for inclusion on the National List.” The rule went into effect May 29, 2018.

In the most recent review by an independent panel, the Joint Expert Committee of the 联合国粮食及农业组织 of the 联合国 and 世界卫生组织 on Food Additives released a technical report in 2015 on the use of carrageenan in 配方奶粉 and found that the additive was ‘not of concern’ in infant formula as food for special medical purposes at concentrations up to 1000 千克s per 公升. The use of carrageenan in infant formula, organic or otherwise, is prohibited in the EU for precautionary reasons, but is permitted in other food items.

In the UK, the Food Standards Agency issued a product recall for sweets containing carrageenan, stating that carrageenan “is not permitted as an ingredient in jelly confectionery products as it presents a choking hazard”.

Toxicity research

Degraded carrageenan (poligeenan) has been found to cause inflammation of the gut, altering microbiota, and was found to be a triggering factor of inflammatory bowel diseases such as ulcerative colitis and Crohn Disease.

Food-grade carrageenan has been confused with poligeenan, although they are completely different products, creating a controversy over the food-additive's safety. Food-grade carrageenan's safety has been proven through various studies.

延伸閱讀

• McHugh, Dennis J. FAO Fisheries Technical Paper 288 - Production and Utilization of Products from Commercial Seaweeds, Chapter 3 - Production, Properties and Uses of Carrageenan, 联合国粮食及农业组织, Rome, 1987
• Guiry, Michael D.R. Carrageenans, The Seaweed Site: information on marine algae.

参见

• 琼脂
• 琼胶
• 洋菜
• 果胶

外部連結

• 开放目录项目中的“Food Additives: Gums and Hydrocolloids”