Food or edible material: processes – compositions – and products – Processes – Treatment with aqueous material – e.g. – hydration – etc.
Reexamination Certificate
2002-08-30
2003-10-28
Yeung, George C. (Department: 1761)
Food or edible material: processes, compositions, and products
Processes
Treatment with aqueous material, e.g., hydration, etc.
C426S463000, C426S464000, C426S622000, C426S626000
Reexamination Certificate
active
06638554
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to a method of low-temperature and near neutral-pH precooking for the production of corn flour and, more particularly, to one that achieves continuous partial hydrolysis of the corn insoluble fiber and avoids excessive pregelatinization with a xylanase as a processing aid during the manufacture of an instant corn flour for the elaboration of arepa and tortilla and derivatives.
2. Description of Related Art
The production of high-quality masa flour can be produced by conventional techniques only if the food-grade dent corn has the following characteristics: uniformity in kernel size and hardness, low number of stress-cracks and kernel damage and ease of pericarp removal during the lime-water cooking process. The mature kernel has four separable components, on a dry weight basis: tip cap (0.8-1.1%), pericarp or bran (5.1-5.7%), endosperm (81.1-83.5%), and germ (10.2-11.9%). In dry or wet-milling processes the bran includes the pericarp, tip cap, aleurone layer and adhering pieces of starchy endosperm as well. Nixtamalized corn flour (NCF) is produced by the steps of alkaline cooking of corn, washing, milling the nixtamal and drying to give corn masa flour. This flour is sieved and blended for different product applications and it is usually supplemented with additives before packaging for commercial table or packaged-tortilla and snack production. Although the pericarp or bran is partially removed during the alkaline-cooking and washing process stages, there is still fiber left from the corn kernel (Montemayor and Rubio, 1983, U.S. Pat. No. 4,513,018). Whole Nixtamalized corn flour or masa flour can contain from 7-9% of total dietary fiber or bran with 6-8% mainly consisting of insoluble fiber on a dry basis (Sustain, 1997).
The cell walls or non-starch polysaccharides (NSP) are the major corn dietary fiber components and are composed of hemicellulose (heteroxylan or pentosan and &bgr;-glucan: 4.4-6.2%), cellulose (2.5-3.3%) and some lignin (0.2%). According to Watson (1987: Tables IV and VII), the corn pericarp makes up 5-6% of the kernel dry weight. This pericarp also contains 90% insoluble fiber (67% hemicellulose and 23% cellulose) and only 0.6% soluble-fiber (soluble-arabinoxylan and &bgr;-glucan). It is estimated that dietary fiber in both pericarp or bran (4.9%) and endosperm (2.6%) make up 80% of the total dietary fiber. The corn insoluble fiber is mainly found in the pericarp and endosperm (aleurone and starchy) which make up 68% of the total dietary fiber (9.5% in a dry-weight basis).
Unlike corn endosperm, in which soluble fiber amounts to 12% of the total fiber (4.1%), in whole wheat, soluble fiber represents 22% of total fiber (about 20% of the flour water-uptake is bound to the soluble pentosan fraction). Arabinoxylan is a complex polymer (20,000-170,000 Daltons) with a linear backbone of (1,4)-&bgr;-xylopiranosyl units to which substituents are attached through O2 and O3 atoms of the xylosil residues (mainly, &agr;-L-arabinofuranosyl). This polymer is apparently linked to the cellulose skeleton in the corn cell wall by ester linkage cross-bonding through ferulic and diferulic acid (Watson, 1987). However, heteroxylan insolubility in corn bran might be due to protein-polysaccharide linkages and a highly branched structure (23% of the xylan backbone does not bear side-chains) as opposed to wheat bran (Saulnier et al., 1995).
During alkali-cooking and/or steeping, there are chemical and physical changes such as nutrient losses along with partial pericarp or bran removal, degradation of the endosperm periphery with starch gelatinization/swelling and protein denaturation in the precooked corn kernel. The most important nutritional modifications are: an increase in the calcium level with improvement in the Ca to P ratio, a decrease in insoluble dietary fiber and zein-protein, a reduction in thiamin and riboflavin, an improvement of the leucine to isoleucine ratio reducing the requirement for niacin, and leaching the aflatoxins into the wastewater (Sustain, 1997).
The known cooking methods (batch or continuous) have been proposed as the critical variables (Sahai et al., 2001) which determine soluble-solid loss (1% to 1.6% COD) in limewater residue for anaerobic biodegradation (Alvarez and Ramirez, 1995). Dry solid matter (1.5%-2.5%) includes an average of 50-60% dietary fiber, 15-20% ash, 15% starch, 5-10% protein and 5% fat. Bryant et al., (1997) showed an optimum change in starch behavior at a lime level similar to the corn masa industry where starch gelatinization indicators (enzyme digestion, water retention capacity, starch solubility and DSC-peak temperature=69° to 75° C.) are increased with lime addition of 0 to 0.4%, peaking at 0.2%. They also found a peak-viscosity temperature reduction upon the addition of lime up to 0.5%, indicating faster granule swelling that requires less thermal energy. Corn pericarp nixtamalization (Martinez et al., 2001) has a first-order stage associated with a fast dissolution of hot-water soluble fractions as starch and pectin, and alkali-soluble fat. A second stage is due to a slow alkaline-hydrolysis of the hemicellulose-cellulose-lignin structure with a higher hemicellulose loss proportional to alkaline-pH concentrations.
Arabinoxylan degrading enzymes include xylanases (1,4-&bgr;-D-xylan xylanohydrolase, EC 3.2.1.8) and &bgr;-xylosidases (1,4-&bgr;-D-xylan xylohydrolase, EC 3.2.1.37). The former endozyme randomly hydrolyze the insoluble and soluble xylan backbone (EC 3.2.1.8) whereas the latter exozyme hydrolyze xylose from the non-reducing end of the xylose-polymer (EC 3.2.1.37). Xylose is not usually the major product and it is typically produced after xylobiose and xylotriose (smallest oligomer). Virtually all xylanases are endo-acting as determined by chromatography or their kinetic properties (substrate and product formation), molecular weight and pH (basic or acidic) or its DNA sequence (crystal structure). They can be structurally classified into two major families or isoenzymes (F or 10 and G or 11) of glycosyl hydrolases (Jeffries, 1996). F11 xylanases are larger, with some cellulase activity and produce low DP oligosaccharides (less specific); F11 are more specific for xylan and with lower molecular weight (i.e.,
B. Circulans
and
T. harzianum
).
In addition, the Enzyme Technical Association (ETA, 1999; FDA, 1998) classified as carbohydrases the following hemicellulases (trivial name): a) endoenzymes (EC 3.2.1.32=1,3-&bgr;-xylanohydrolase, 78=mannanohydrolase and 99=arabinohydrolase) and b) exoenzymes only attack branches on the xylose-polymer (pentosan), producing xylo-oligomers (EC 3.2.1.55=&agr;-L-arabinofuranosidase, glucuronic-acid glycosilase and ferulic-acid esterase).
Currently recognized endoenzymes (xylanases) and exoenzymes produced from
A. niger
(EC 3.2.1.8 and 37,55),
A. oryzae
(EC 3.2.1.8 or 32),
B.subtilis
(EC 3.2.1.99), and
Trichoderma longibrachiatum
(formerly reseei: EC 3.2.1.8) are Generally Recognized As Safe (GRAS; 21 CFR 182, 184 and 186) and require no further approval from the U.S. Food and Drug Administration or Recognized As Safe (RAS in Europe: Mathewson, 1998). However, direct and indirect food additives (i.e., packaging materials) are regulated in 21 CFR 172 and 174-178 as well. Secondary direct additives, a sub-class of direct additives, are primarily Processing Aids which are used to accomplish a technical effect during food processing but are not intended to serve a technical or as a functional additive in the finished food. They are also regulated in 21 CFR 173 (Partial List of Enzyme Preparations that are used in foods). Finally, all GRAS Substances produced through recombinant-DNA which were widely consumed prior to 1958, and which have been modified and commercially introduced after 1958 must comply with regulatory requirements proposed in 21 CFR 170.3 (GRAS Notice).
The benefits of using a commercial xylanase (endoenzyme) in cereal flours instead of a non-speci
Contreras Roberto
Rubio Felipe
Rubio Manuel J.
Roberto Gonzalez Barrera
Yeung George C.
Young & Thompson
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