Handbook of Cereal Science and Technology, Revised and Expanded
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gluten quality involves the addition of low levels of gluten, ied typically are compared to results obtained by some about 2%, to a standard test flour, which often is of a type of baking test. McDermott [85] compared baking "weak" type, and observing the effects on bread quality. (Chorleywood bake test) and other properties of 30 com-Water absorption is adjusted as appropriate for the gluten mercial glutens, mostly of European origin (Table 8), and levels added [23]. A stressed gluten-enriched baking test found that under his test conditions six samples were of was identified [31], which assumes that gluten is added to relatively poor quality; correlation between baking perfor-enable production of specialty breads using substantial mance and other measured properties was not high. levels of non-gluten-containing ingredients such as rye Weegels and Hamer [130] studied a group of 32 European flour, dietary fiber, bran and germ, or raisins [49]. Czucha-commercial glutens. These workers devised a test involv-j owska and Pomeranz [31] described a simple, repro-ing protein content, denaturation index (based on a series ducible method for baking undiluted gluten, highly corre-of sodium dodecyl sulfate sedimentation measurements), lated with the gluten-enrichment baking test. and extensigraph resistance; a model utilizing these tests A prime reason for performing end-use tests of func-was able to predict 59% of the baking quality variation of tionality, of course, is to monitor variations in the quality the glutens. Bushuk and Wadhawan [20] examined 27 of commercial wheat glutens that can occur. Differences commercial gluten samples, although only 8 were subject-among commercial gluten are usually attributable to varia-ed to extensive end-use testing; the highest correlation co-tions in the starting material, wheat or flour, and/or efficients were between loaf volume and acetic acid-solu-changes caused by production processing conditions. Dur-ble protein (r = 0.88) and between loaf volume and ing processing, the drying of gluten is critical, as noted fluorescence of acetic acid extract (r = 0.98). above, and investigators have shown that less than opti-mum heat treatment can lower the baking quality of gluten (b) Nonbaking Tests. Considerable efforts have been [14,49,98,111,130]. However, McDermott [85] reported expended in developing nonbaking tests to evaluate the no definite relationship between manufacturing variables quality or vitality of wheat gluten for baking purposes. The and gluten quality in a group of 30 commercial glutens. baking test is often cited as being labor intensive, relative-Dreese et al. [38] studied commercial and hand-washed ly expensive, requiring skilled workers, and not effectively lyophilized gluten and found that differences were more differentiating gluten quality [86]. The farinograph has attributable to washing procedures than to drying proce-been used to evaluate gluten for many years. The usual ap-dures. proach has been to test the gluten as a gluten-flour mixture Results obtained by other methods that have been stud-(e.g., Refs. 5, 18, 36, and 49), while an alternative method TABLE 8 Properties of 30 Commercial Glutens Baking performance Property Average Range Poor Average Good Increase in loaf volume, %a 10 7.7-12.2 8.3 10.2 11.8 Protein, %b 77.4 66.4-84.3 76.2 77.4 81.1 Moisture, % 7.55.3-10.2 8.877.7 Particle size, % <160 p.m 88.8 55.8-98 80.5 91 90.3 Color 68.3 56.5-75 65.2 68.9 69.5 Lipid, % 5.84.2-7.65.86.15.1 Ash, % 0.69 0.44-0.94 0.71 0.74 0.6 Chloride, %` 0.08 0.01-0.28 0.10.08 0.08 Water absorption, mug protein 2.37 1.84-2.93 2.26 2.45 2.29 SDS sedimentation volume, ml/g protein 99 55-159 70 107 127 Lactic acid sedimentation, % reduction in turbidity 18 2-68 49 11 7 Hydration time, min 0.90.2-10 2.72.40.6 Extensibility, units/min 3.80.7-9.33.23.93.9 Viscosity, cP 117 73-222 159 109 101 '2% gluten protein. Dry matter basis. `As NaCl. Source: Ref. 85.
TABLE 3 Major Commercial Fermentation Conditions for Cereal Foods Fermentation conditions Bread Beer Whiskey Soy sauce Miso Main starters Baker's yeast Brewer's yeast Distillery yeast Molds Molds (Saccharomyces (Saccharomyces (Saccharomyces (Aspergillus spp.) (Aspergillus spp.) cerevisiae) cerevisiae) cerevisiae) Saccharomyces rouxii Lactic acid bacteria Lactobacillus delbrueckii Cereals Milled wheat Barley (malted) Corn Soybeans (defatted) Rice Milled rye Sorghum Rye (malted or not) Wheat Barley Minor: Minor: Barley (malted) Minor: Soybeans Barley (malted) Corn Wheat Barley flour Wheat (malted) Rice Wheat Other ingredients Water Water Water Water Salt Salt Hops Salt Hot pepper Sugar Adjuncts Fat (corn syrup, sugar Emulsifiers or starch) Dough strengtheners Preservatives Enzymes Fermentation 1-6h2-10 days 2-3 days (Koji: 3 days at 30°C) (Koji: 2 days at 30°C) conditions 20-42°C 3-24°C 32-35°C 3-12 months 2 days to 1 year Aging: Aging: 15-30°C 30-50°C 3 days-1 month 2-3 years or more 0-13°C 21-30°C baker's yeast is probably the most common of these microorganisms that may be a problem are bacteria (usual-starters; it is commercially produced in liquid, paste (com-ly spore-forming or lactic acid bacteria, especially in some pressed), or dry form. Recently, commercial lactic acid yeast fermentations), wild yeasts, and molds. bacteria starters have been introduced for cereal fermenta-Several spore-forming bacteria (e.g., Bacillus spp.) may tions, but this application is less frequent than their regular produce amylases and degrade hydrated starchy materials. use in dairy or meat fermentations. A close control of the In bread, heat-tolerant spores of Bacillus subtilis (formerly performance of commercial starters is important, since it Bacillus mesentericus) survive the baking process; after a has a major effect on the final products. few days in bread, they produce a spoilage called ropiness, characterized by yellow spots on crumb, putrid pineapple aroma, and stringiness when breaking a piece of bread. The spores of these species, when contaminating flour, may Considering the diversity of the microbial flora that may cause a major problem in bakeries since they are highly re-be present in cereals to be fermented, undesirable microor-sistant in the environment and difficult to eliminate. How-ganisms are likely to be part of this flora and may produce ever, these bacterial infections have become rare in recent problems in the main fermentation process with subse-years, presumably due to improved sanitation. In beer, un-quent adverse effects on the final product. Nowadays these desirable microbial contamination is exhibited by viscosity, problems are lessened by good sanitary practices. Sources appearance, as well as aroma and flavor problems. of these organisms may be the cereals themselves, soil, as Microbial pathogens are usually not a problem for fer-well as any particular ingredient, surface contamination, mented cereals because of the inhibition brought about by and unsanitary handling. acids and ethanol generated by fermenting organisms. A Table 4 summarizes microbial problems likely to occur large proportion of fermented cereals are also eaten shortly during major cereal fermentations. In general, undesirable after complete cooking. However, the biggest problem
minutes retention depending on the oil processed. Then, Synthetic silica hydrogels: Described in the immediately the oil is heated to 70°C, (158°F) to assist "breaking" the preceding section. emulsion and the mixture is passed through a primary (first) centrifuge. The general dosage of acid-activated bleaching earths is 0.3-0.6%, depending on the quality of the oil and bleach-In contrast, the short-mix process, developed in Europe, ing earth. Bleaching earths provide catalytic sites for de-is conducted at 90°C (84°F), uses a more highly concen-composition of oxidation products. Peroxide values (mea-trated caustic, and a mixing time and primary centrifuging sure of aldehydes) and p-anisidine values (precursors for time of less than 1 minute [135]. Less heat damage to the oxidative degradation) first rise and then decrease during oil and higher refining yield are claimed by advocates of bleaching. Bleaching processes used include atmospheric the long mix process. batch, vacuum batch, and continuous vacuum. Vacuum 4. Silica Absorption bleaching has the advantage of excluding air, partially by In traditional refining, oil from the primary centrifuge is vaporization of water in the earth, and is recommended. A washed with warm soft water to remove residual soap and typical vacuum bleaching process is 20-30 minimum at passed through a (secondary) centrifuge. The washed oil 100-110°C (212-230°F) and 50 mmHg absolute [135]. then is dried under vacuum. However, disposal of wash The reactions catalyzed during bleaching continue into water is increasingly becoming a problem, and the indus-the filter bed and are known as the "press bleaching ef-try is shifting to a modified caustic "waterless" refining fect." The reactive components of oil remain in the bleach-process. Soaps poison the adsorption sites of clays in later ing bed. Care should be taken to "blow" the filter press as bleaching operations and are removed by silica hydrogels. free of oil as possible and to wet the filter cake (which can The oil may be degummed with use of chelating acids, be very dusty) to prevent spontaneous combustion [137]. caustic neutralized, passed through a primary centrifuge, At this point, the product is RB ("refined, bleached") and may be partially vacuum-dried. Synthetic silica hy-oil. If the intended product is an oil, it can be sent to the de-drogels, effective in removing 7-25 times more phos-odorizer and become RBD. If solids are desired, the solids-phatides and soaps than clay on a solids basis, and for re-temperature profile of the oil may be modified by hydro-moving phosphorus and the major metal ions, is added genation, interesterification, or chill fractionation, alone or and mixed with the oil. By absorbing these contaminants in combination. first, the bleaching clay is spared for adsorbing chloro-6. Hydrogenation phyll and the oxidation-degradation products of oil Hydrogenation is the process of adding hydrogen to satu-[136-138]. rate carbon-to-carbon double bonds. It is used to raise try-5. Bleaching glyceride melting points and to increase stability as by jective of bleaching is to remove various contami-converting linolenic acid to linoleic in soybean oil [141]. A The ob lighter, "brush" hydrogenation is used for the latter pur-nants, pigments, metals, and oxidation products before the pose. oil is sent to the deodorizer. Removal of sulfur is especial-Most of the catalysts that assist hydrogenation are nick-ly important before hydrogenation of canola and rapeseed el-based, but a variety is available for special applications. oils. Flavor of the oil also is improved. As mentioned in the "Selectivity" refers to ability of the catalyst and process to preceding section, silica hydrogels will adsorb many of sequentially saturate fatty acids on the triglycerides in the these contaminants and spare the bleaching earth. Howev-order of most unsaturated to the fully saturated. For row er, earths are still used for these purposes in installations crop oils, perfect selectivity would be: that have not adopted hydrated silicas. Types of bleaching materials available include [136,139,140]: C18:3 C18:2 C18:1 Linolenic acid Linoleic acid Oleic acid Neutral earths: Basically hydrated aluminum silicates, sometimes called "natural clays" or "earths," and C18:0 fuller's earth, which vary in ability to absorb pigments. Stearic acid Acid-activated earths: Bentonites or montmorillonites, Although typical hydrogenation is not selective, it can be treated with hydrochloric or sulfuric acid to improve favored to a limited degree by selection of catalyst and by their absorption of pigments and other undesirable temperature and pressure of the process. Efficient hydro-components, are most commonly used. genation requires the cleanest possible feed stock (without Activated carbon: Expensive, more difficult to use, but of soaps, phosphatides, sulfur compounds, carbon monoxide, special interest for adsorbing polyaromatic hydrocar-nitrogen compounds, or oxygen-containing compounds) bons from coconut and fish oils. and the purest, driest hydrogen gas possible [140].
