1. Field of the Invention
The present invention relates to methods for making pectin and pectocellulosic products which are used, for example, in gelling foods, cosmetics, drugs, protective colloids, emulsifying agents, and dehydrating agents.
2. Discussion of the Related Art
a. Background
Pectin is a naturally occurring polymerized sugar-acid derivative belonging to a family of compounds referred to as pectic substances. A pectocellulosic product is essentially an impure pectin. Pectic substances are high molecular weight hydrocolloidal compounds related to carbohydrates, and consist chiefly of partially methoxylated galacturonic acids joined in long chains.
Pectin is primarily a component of fruit and plant cell walls and, together with other components such as cellulose and hemicelluloses, pectin constitutes both the structural tissue and the "cement" which gives rigidity to fruit and plant cells. It is present in all fruit and plant tissue in variable amounts, such as in apples and citrus fruits, some roots such as beets and carrots, tubers such as potatoes, sunflower heads, and elsewhere. Levels of pectic substances range from about 0.1 to 4% by weight of the plant's whole fruit. Apples and citrus fruits are the major commercial sources of pectin raw material. Dried apple pomace and citrus peels (wet or dried) are abundantly available as by-products of juice processing.
Pectin has long been used in the home for gelling jams employing, for example, apple core or quinces as the pectin source. Today, the fruit and confectionery industry uses pectin for its gelling properties in acid and sugar media. It is also used in cosmetics, drugs, protective colloids, emulsifying agents, and dehydrating agents. Other properties of pectin, such as its thickening properties and its gelling action in less acidic medium and in the presence of calcium, also contribute to the role of pectin in the manufacture of food and pharmaceutical products.
Polygalacturonic acids composed of anhydrogalacturonic acid units make up the basic skeleton of all pectic substances. Upon analysis, the pectic substances can be defined as weight percent anhydrogalacturonic acid ("AGA") or as galacturonic acid ("GA"). AGA depends on the degree of methylation/esterification. When expressed as weight percent GA, a polymer is calculated as if it were depolymerized to the individual acid residue. When calculated on the basis of GA, the molecular weight is 2-5% greater than its corresponding AGA content, depending upon the number of acids in the polymer that are methylated, known as the degree of methylation ("DM"). The following table explains the relationship between DM, AGA, and GA.
TABLE 1 ______________________________________ RELATIONSHIP OF MOLECULAR WEIGHT (MW) EXPRESSED AS AGA TO MW EXPRESSED AS GA MW of MW as AGA .div. MW as GA Pectin DM 100 AGA Units (= 194.14 .times. 100) ______________________________________ 90 18,878 0.9724 85 18,808 0.9688 80 18,738 0.9652 75 18,668 0.9616 70 18,598 0.9580 65 18,528 0.9544 60 18,458 0.9508 ______________________________________
Manufactured pectin is not 100% AGA. Nonpectic solids ("NPS"), such as neutral sugars within the polymer chain or polysaccharides associated with the polymer, are present and known as "ballast materials." Metallic ions are also associated with some of the carboxylic acids. Finally, moisture or water is also present. These all will dilute the weight percent of AGA or GA. The combined solids can be considered as total solids ("TS"). A typical pectin composition contains the following:
TABLE 2 ______________________________________ Component Wt. % As-Is Wt. % Dry Basis ______________________________________ ##STR1## 74.5 14.5 3.0 8.0 92.0 80.98 15.76 3.26 -- 100.0 ______________________________________
If the above pectin were 80 DM, its GA content would be reported as 83.9%. This is calculated using the factor from Table 1: 80.98/0.9652=83.9. The Food Chemical Codex specifies that a pectin must contain not less than 65% AGA.
Most commercially available pectins are purified to about 70% to 80% by weight GA and have a varying DM. High methoxyl pectins, having a DM above about 50%, require sugar for gelation. They typically form gels at pH values below about 3.5 and in the presence of sugar levels above about 60%. High methoxyl pectins, which are frequently referred to as "slow" or "rapid" setting with respect to their ability to gel high concentrations of sugar, are generally used for gelling preserves and confectionery foods.
Low methoxyl pectins, having a DM between about 20% and 50%, are used for low sugar products as they do not require the presence of sugar for gelation. They form gels at wider pH ranges, but require the presence of divalent cations (i.e., metallic ions, mostly calcium) for gelation.
Selection and proper use of a pectin is dependent upon the finished product desired. High DM pectins are quite versatile, as they can be used in a broad range of conditions. For example, an 80 DM pectin can form high sugar jams or gels at pHs of 3.8-4, or it can be used to form jams having low sugar levels of 48-47% at pHs of 2.7-3. R. M. Ehrlich, "Pectin; Selection And Proper Use," 1977 Annual Meeting of the Institute of Food Technologists, Philadelphia, Pa.
A pectin's gelling capacity varies with the source and quality of the source raw material. Capacity to gel is referred to as "grade," defined as the number of sugar solids one unit of pectin will gel to a standard firmness in a specific test procedure. Pectin is standardized to 150 grade with either dextrose monohydrate or sucrose as the diluent.
The IFT SAG method ("Pectin Standardization," Food Technology, vol. XIII, pp. 496-500 (1959)) is the only universally accepted method of grading pectin. The SAG procedure measures gel rigidity, which is the degree to which a gel will sag within two minutes after it has been removed from a calibrated glass jar and inverted on a glass plate.
b. Prior Methods For Making Pectin And Pectocellulosic Products
Commercial pectin is obtained from plant tissues having a low GA content, such as dried citrus peel having an GA content in the range from about 20% to 30%. Prior to the present invention, extraction methods comprised hydrolysis of protopectin in warm acidic medium to release the potentially soluble pectinic acids from the cellulosic matrix. After separation of the cellulosic components, pectin was precipitated from the resulting pectic juices by, for example, using an alcohol. Typically, the resulting fibrous coagulum was alcohol washed, squeezed, vacuum dried, and then ground to obtain a fine power. The separated cellulosic components are a low volume by-product which can be used, for example, as an animal feed bulking agent.
Various methods for producing pectin-containing material were described prior to the present invention. For example, East German Patent Application No. 258743 (Abstract) describes the production of a pectin-like material for use with comminuted meats. The pectin-containing material is produced from vegetables by comminution, followed by acidification, neutralization, and mechanical dehydration.
Other methods for producing pectin-containing materials are described in U.S. Pat. Nos. 4,923,981 and 4,831,127, which relate to the preparation of "parenchymal cell" cellulose from pectin-containing materials, such as sugar beet and citrus pulp. The fruit or plant tissue is first treated with a strong acid or a strong base at high temperatures for short periods of time to release the cellulosic, hemicellulosic, and pectin components from the fruit or plant tissue without substantial degradation. The fruit or plant tissue is then subjected to physical shearing followed by separating the solid and liquid fractions of the treated mixture.
U.S. Pat. No. 4,143,172 teaches a method for producing a pectin-containing substance using comminuted citrus peel as a pectin material, and U.S. Pat. No. 3,982,003 teaches the preparation of a pectin-like material by comminution of citrus pulp comprising treating the pulp with a mild base to reduce the degree of esterification. U.S. Pat. No. 2,452,750 teaches methods for producing pectin comprising soaking comminuted citrus peel in a reagent which is a non-solvent for pectinous substances, and U.S. Pat. No. 2,132,065 describes a method for separating pectin from citrus peel using a high temperature and alkaline solvent. U.S. Pat. No. 2,022,471 refers to a process for making pectous materials using a filter aid, such as diatomaceous earth, and British Patent No. 1,369,198 describes a process for preparing simulated fruit using a pectate sol. Other methods for producing pectin-containing products are described in Application No. WO 91/15517.
Commercial methods for making high DM pectin prior to the present invention required the use of an acid. Such methods comprised a man-made methylation process, which uses acid as a catalyst and methyl alcohol as the methoxyl source, and are described in U.S. Pat. No. 3,133,053 to Bender et al. and Chemical Abstract No. 61 2401 (1964).
Each of the above references are herein incorporated by reference.
Accordingly, prior to the present invention, methods for producing commercial pectin products required extensive processing steps and the presence of an additional ingredient, an acid, resulting in an expensive, inefficient, and time-consuming manufacturing process. It is therefore desirable to provide less costly methods for producing pectin and pectocellulosic compositions from fruit and plant tissues.