IO Pasta and Whole Grain Foods Pasta Cooking quality of pasta Pasta is the collective term used to describe Particle size of the semolina is an important products such as macaroni, spaghetti, vermicelli, characteristic: it is recommended that at least 90% noodles etc. which are traditionally made from of the particles should fall between 150 pm and the semolina milled from hard durum wheat (T. 340 pm in size. Particles larger than 340 pm durum) (cf. p. 154 for milling of semo). The impede the activity of enzymes in the dough highest quality pasta products are made from (Milatovic, 1985). Good quality of the pasta durum wheat alone, but other hard wheat, e.g. may be defined as the ability of the proteins to CWRS or HRS, can be substituted, but only at form an insoluble network capable of entrapping the expense of quality. The Plate wheat Taganrog swollen and gelatinized starch granules (Feillet, used for puffing (cf. p. 87) is not liked for pasta 1984), and is thus related to the composition of as it tends to yield a brownish-coloured product. the protein. A strong correlation (+0.796) has Durum wheat grown in Britain has been success- been found between pasta cooking quality and fully used for pasta, although parcels with high acid-insoluble residue protein (Sgrulletta and De alpha-amylase activity are unsuitable. U.K.- Stefanis, 1989); a highly significant correlation grown durum wheat will probably be blended in was also found between good cooking quality and small quantities into a grist in which imported the total sulphydryl plus disulphide (SH + SS) durum wheat will predominate. content of glutenins extracted by sodium tetra- Historically, pasta products are believed to decanoate solution (Kobrehel and Alary, 1989; have been introduced into Italy from China in Alary and Kobrehel, 1987), and also with certain the 13th century, but were first produced low mol. wt glutenin subunits, particularly the in Europe in the 15th century, in Germany band 45 of the electrophoretic pattern. On the (Pomeranz, 1987). other hand, poor cooking quality was associated with the 42 band, and it is suggested that this association could be a useful indicator for Degree of cooking the breeding of durum wheat for pasta-cooking Pasta products, as sold, could be described as qualities (du Cros and Hare, 1985; Autran et al., ‘uncooked’, ‘partially cooked’, or ‘fully cooked’ 1989). (pre-cooked), depending on the degree to which In uncooked pasta, the protein is largely the protein is denatured and the starch gelatinized. undenatured, and most of the starch is ungelatin- Traditionally, pasta products are prepared in ked. The processing conditions of dough moisture an uncooked state, because dry, uncooked pasta content and extrusion temperature were carefully can be stored at room temperatures for long controlled to prevent protein denaturation and periods while maintaining its highly glutinous starch gelatinization. properties. 233 234 TECHNOLOGY OF CEREALS Traditional (kneadinglsheeting) process Drying of pasta In the traditional manufacturing process in use Finally, in the traditional process, the extruded at the beginning of the 20th century, a dough is product is dried to about 12.5% m.c. In Italy, first made by mixing semolina and water to give drying might be done outdoors, but elsewhere a moisture content of about 30% in the dough. special equipment is used in which the temperature A moisture content of 30% is needed to ensure and relative humidity of the air can be carefully that the viscosity of the dough is low enough to controlled. The rate of drying must be correct: avoid the use of excessive pressure within the drying at too low a rate could lead to the extruder. The dough is then kneaded, brought development of moulds, discoloration and souring, to a temperature of about 49"C, and is then whilst drying too rapidly could cause cracking extruded through a hydraulic press to form a thin ('checking' in the U.S.A.) and curling. Until sheet which can then be cut into strips and the recently, drying temperatures were about 50"C, strips carefully dried. A temperature not above and the drying process took 14-24 h. 49°C is necessary to prevent cooking the product A three-stage drying process, comprising pre- and avoid denaturing the protein. A modification drying, sweating, and drying, has been described of this process, in which the dough was extruded (Antognelli, 1980). In the pre-drying stage, air through special dies to make shaped products - at 55"-90"C circulates round the product and rods, strips, tubes, etc. - was first introduced dries it to 17-18% m.c. in about 1 h. Moisture about 50 years ago (Pomeranz, 1987). migrates from the centre to the periphery, where it evaporates, resulting in a marked moisture gradient in the product. In the sweating period that follows, the pasta is rested to allow moisture Extrusion process equilibration between the inner core of the pasta In the extrusion process, the moisture content and the surface to occur. In the drying stage, of the dough would be about 28% and the diminishing periods of hot-air circulation alternate extrusion temperature, i.e. the temperature of the with periods of sweating. Temperatures in the extrusion barrel, would be around 54"C, low drying stage are 45"-70"C, and the total drying enough to avoid cooking the product. The extru- time is 6-28 h. sion barrel would be provided with a jacket in In the late 1970s, the processing of macaroni which water could be circulated to maintain the was improved by drying at temperatures above required temperature. 60"C, using shorter processing times, and It is claimed that the kneadingkheeting process sterilizing the product during drying. has the advantage of producing a springy, elastic A rapid drying process using microwave energy texture in the product, leading to good eating has been described (Katskee, 1978). A pre-drying quality, while advantages claimed for the extru- stage uses hot air at 71"-82°C to reduce the m.c. sion process are that it produces a pasta with a of the pasta to 17.5% in 30 min. In the microwave firmer texture in a larger variety of shapes, that stage that follows, the product is fully dried to it is more efficient and less time-consuming, and the target m.c. in 10-20 min. The microwave that the extruded dough has a lower moisture system operates at about 30 kW, an air temperature content requiring a shorter drying time to complete of 82°C and 15-20% r.h. The final, or cooling and the preparation of the pasta. However, pasta equalization stage, operated at 70-80% r.h., made by the extrusion process lacks the laminated brings the total drying time up to 1.5 h. Advan- structure and desirable eating qualities of pasta tages claimed for the microwave drying process, made by the kneadingkheeting process, and the besides the considerable saving of time, include colour of the pasta is less appealing (U.S. Pat. space-saving, improved product quality - cooking No. 4,675,199). quality, colour enhancement, and microbiological PASTA AND WHOLE GRAIN FOODS 235 - modification of the temperature of the doughing water, the temperature in the cooking zone, and the extrusion temperature (Milatovic , 1985; Euro. Pat. Appl. Nos 0,267,368 and Recent processing changes 0,288,136); Within the last 20 years or so, numerous - Partially Pre-cooking the dough by Pre- processing changes have been introduced to the conditioning (Euro. Pat. Appl. No. 0,267,368); pasta-manufacturing industry which are directed - soaking partially-cooked pasta in acidified towards achieving various objectives, including water (U.S. Pat. No. 4,828,852); the following: - use of higher drying temperatures (Manser, 1986; Abecassiset al., 1989a; Euro. Pat. Appl. - improvement in pasta quality, e.g. by reducing Nos 0,309,413, 0,322,053 and 0,352,876); cooking loss, avoidance Of cracking, imprOV- - back-mixing the dough, combined with high ing the colour of the product, elimination of drying temperature (Brit. Pat. Spec. No. dark specks, destruction of micro-organisms, 2,151,898; U.S. Pat. No. 4,540,592); improving the appearance and firmness of - venting the product between the cooking and the product (Milatovic, 1985; Manser, 1986; the forming zones (Euro. Pat. Appl. No. Abecassis et al., 1989a; Euro. Pat. Appl. 0,267,368); No. 092679368; U.S. Pat. Nos 4,539,214 and - pre-drying and drying as two separate stages 4,876,104); (Milatovic, 1985); - improvement in nutritional quality, e.g. by - use of superheated steam for simultaneously better retention of vitamins and other nutrients cooking anddrying (U.S. Pat.No. 4,539,214); (Manser, 1986; Euro. Pat. APPl. No. 0,322, - high-temperature after-treatment to make pre- 153); cooked pasta (Abecassis et al., 1989a,b; - improvement in shelf-life of the product (U. S. Mestres et al., 1990; U.S. Pat. No. 4,830,866); Pat. Nos 4,828,852 and 4,876,104); - pasteurization (U.S. Pat. No. 4,876,104); - reduction in drying time, with consequent - extrusion into N~/c~~ or into vacuum to saving in energy expenditure (Abecassis, improve storability (Euro. Pat. Appl. No. 1989b); 0,146,510; U.S. Pat. No. 4,540,590); - faster-cooking Products, e.g. a rapidly - use of extrusion cooking instead of ordinary rehydratable pasta, or a microwave-cookable extrusion (U.S. Pat. No. 4,540,592); Product (Euro. Pat. APPl. Nos 0,267,368, - use of additives, e.g. emulsifiers, in the 0,272,502 and 0,352,876; U.S. Pat. Nos 4, dough (Euro. Pat. Appl. Nos 0,352,876 and 539,214 and 4,540,592); 0,288,136). - a ready-to-eat pasta, or an instant pre-cooked pasta (U.S. Pat. Nos 4,540,592 and 4,828,852). Use of non-wheat materials Another objective has been the diversification In some countries, e.g. France and Italy, the of the starting material, i.e. the replacement of material used for making pasta must be durum some (or all) of the durum semolina with other semolina, but other countries allow the use of cereal materials or even with non-cereal materials soft wheat flour, maize flour, or various other (Molina et al., 1975; Mestres et al., 1990). diluents. Countries which are non-wheat pro- These objectives have been addressed, and ducers, e.g. many African countries, are interested in most cases attained, by modification of the in pasta made from non-wheat materials, e.g. traditional process in various ways, such as: maize, sorghum. Preparation of such pasta is - modification of the moisture content of difficult because of the lack of gluten which is formed when wheat is the starting material, and which contributes to dough development during quality - and lower installation and operating costs. the product before drying (Abecassis et al., 1989a,b); 236 TECHNOLOGY OF CEREALS mixing and extrusion, and thus prevents disag- system is restricted to preparation of pasta from gregation of the pasta during cooking in boiling semolina or flour having more than 32% wet water (Feillet, 1984; Abecassis et al., 1989a). It gluten content. This system produces the most has been suggested that the lack of gluten can be rapid hydration of gluten and gelatinization of overcome by blending pregelatinized starch or the starch, but of course cannot be employed if corn flour before adding water and mixing, or by ascorbic acid is included, because the latter gelatinizing some of the starch during mixing or decomposes at these temperatures and has no extruding (Molina et al., 1975). A compromise is beneficial effect. to use a blend of semolina and maize flour, from which good quality pasta can be obtained, provided Glyceryl monostearate as additive the maize flour has fine granularity (less than 200 pm) and a low lipid content (not higher than The use of glyceryl monostearate as a flour 2% on d.b.). By submitting the dried pasta to modifier is proposed in order to permit the thermal treatment at 90°C for 90-180 min, a extrusion of the dough at a lower m.c., viz. 28%, blend of 70 maize flour: 30 durum wheat semolina than is customary in making uncooked pasta. The was found to be satisfactory (Mestres et al., 1990). temperature of the dough at extrusion is above 54"C, but not so high as to cause gelatiniza- tion of the starch. Other flow modifying agents L-Ascorbic acid as additive suggested are whey solids and sulphydryl reducing The use of L-ascorbic acid as an additive for substances such as L-cysteine, glutathione, sodium improving the quality of pasta has been suggested bisulphite or calcium sulphite at levels of 0.025- (Milatovic, 1985). Ascorbic acid, which is oxidized 0.1% by wt (Euro. Pat. Appl. No. 0,288,136). to dehydroascorbic acid, a strong reducing agent, inhibits the destruction of naturally occurring Prevention of starch leaching from uncooked pasta pigments, leading to improvement in the colour of the product by inhibiting lipoxygenase activity. Addition of 300 mglkg of L-ascorbic acid to the High temperature (above 74°C) drying of pasta doughing water improved the colour of the pasta causes denaturation of the protein, thereby en- made from all soft wheat flour or from 50 soft trapping the starch and rendering the pasta stable wheat flour: 50 semolina, and also reduced the to starch leaching in the presence of cold water. loss of solid matter and protein from the cooked If dried at the lower, traditional, temperature, product. the protein is not denatured and, as a result, starch leaches out, making a gummy, mushy product, unless the pasta is immediately con- Doughing water temperature tacted with extremely hot water, to set the protein The temperature of the doughing water is matrix. An uncooked pasta which can withstand important. Water at 36"-45"C is normally used for exposure to cold water without leaching of starch cold dough making, 45"-65"C for a warm system may be made by the addition of low-temperature using high temperature drying, and 75"-85"C coagulatable materials such as albumin, whole for very warm processing. If egg is an addi- egg, whey protein concentrates, but preferably tive, the doughing water temperature should egg white, added at a level of 0.5-3.0% by wt. not exceed 50"C, since albumen coagulates at Sulphydryl reducing agents, e.g. cysteine, gluta- 49°C. Similarly, when ascorbic acid is added, thione, which reduce disulphide (-SS-) bonds to the water temperature should not exceed 55"C, sulphydryl groups (-SH), thereby facilitating the otherwise degradation of the additive will be irreversible denaturation of the gluten, can be accelerated. In the warm system, the gluten added at levels of 0.02-0.04% by wt: their addi- hydrates rapidly, reducing the length of the tion is essential at drying temperatures below dough preparation time. Use of the very warm 74°C. A modern drying process would use two PASTA AND WHOLE GRAIN FOODS 237 (below 24% m.c. crackingmay occur, while above 30% m.c. the dough becomes too soft and elastic). The sheeted dough is cut into pieces which are partially dried in 1040 sec by, e.g. infrared heating lamps and hot air at 204°C. The product is then steamed and pasteurized to kill micro- organisms, cooled to O"-lO"C and packed in sterile trays with injection of C02/N2 (25:75 to 80:20). Such packaged products should be storable at 4"-10"C for at least 120 days (U.S. Pat. No. 4,876,104). stages: drying at 71"-104°C for 24 h, followed by further drying at 32"-71"C for 0-120 min, but with the use of a high velocity air current (150 ft3/ rnin), the drying times could be shortened to 15- 30 min for the first step plus 30-120 min for the second. Pasta made in this way can be rehydrated by soaking in cold water, and then cooked in about 2 min by conventional boiling or by micro- wave energy (Euro. Pat. Appl. No. 0,352,876). 'Cooking value ' of pasta 'Cooking value' is a measure of the texture or consistency of the pasta after cooking. The cooked pasta should offer some resistance to chewing but should not stick to the teeth. To retain these qualities and to avoid loss of nutrients, current procedures limit drying temperature to not above 60"C, but such drying takes a long time - 16- 24 h. Higher drying temperatures, while still avoiding nutrient loss and adversely affecting cooking value, can be used in a step-wise process, e.g. by isothermal application of heat at temper- atures between 40" and 94°C while maintaining the vapour pressure within the pasta (A,) below 0.86. In one such drying schedule, the product passes through eight areas in which the tempera- tures are (successively) 40", 50", 60", 70", SO", 84", 94" and 70"C, taking about 3 h to complete the drying. The product, with 13% m.c., is then cooled to 25°C (Euro. Pat. Appl. No. 0,322,053). Micro-organism control Control of micro-organisms in stored pasta products is essential. The use of high temperature (above 60°C) drying to improve pasta product sterility has been described (Milatovic, 1985). Another process is described in which dough is made from flour (durum wheat semolina, or whole soft wheat flour plus corn flour, rice flour or potato flour) about 75 parts, with about 25 parts of whole egg, but with no water. Additives such as wheat gluten, soya protein isolate, algin- ates and surfactants may be added. The dough is sheeted through a series of rollers to a thickness of 0.03 in, while keeping the m.c. about 24% Quick-cooking pasta A process described for making a quick-cooking pasta starts by making a dough from flour or semolina of which at least 90% is derived from durum wheat, with the addition of 0.5-5.0% by wt of an edible emulsifier, such as glyceryl or sorbitan monostearate, lecithin or polysorbates. Water, at 79"C, is added to bring the m.c. to 22-32%. The ingredients are mixed at 76"-88"C, extruded through a co-rotating twin-screw extruder at 60"-88"C. The extruder comprises three zones: a cooking zone, a venting zone, and a forming zone. When passing through the venting zone, the material may be subjected to a degree of vacuum (2.5-5 psi) to draw off excess moisture. The product can be cooked by microwave energy (Euro. Pat. Appl. No. 0,272,502). Another process for making rapidly rehydrat- able pasta simultaneously cooks and dries the extruded dough (made from semolindflour and water) by the use of superheated steam at a temperature of 102"-140"C for 7-20 min. The product is in an unexpanded condition and can be packaged without further cutting or shaping (U.S. Pat. No. 4,539,214). A process to eliminate darkened specks in a quick-cooking pasta pre-cooks a mixture of pasta flour and water in a pre-conditioner before it passes through an extruder with three zones: cooking, venting, extruding. The temperature of the mixture is kept below 101°C in the cooking zone to prevent the formation of darkened specks symptomatic of burning during cooking (Euro. Pat. Appl. No. 0,267,368). 238 TECHNOLOGY OF CEREALS Pre-cooked pasta A method of preparing instant, pre-cooked pasta is disclosed in U.S. Pat. No. 4,540,592. The pasta dough is completely gelatinized in a co-rotating, twin-screw extrusion cooker, incorp- orating at least one high-shear back-mixing cook- ing zone, and using high temperature and pressure so that the final product rehydrates to a cooked pasta instantly in hot water. Shelf-stable, pre-cooked pasta preparation of a pre-cooked product which is shelf-stable for long periods is described (U. S. Pat. No. 4,828,852). The starting material can be durum semolina or flour, soft wheat flour, corn flour, pregelatinized corn flour, rice flour, waxy rice flour, pre-cooked rice flour, potato flour, pre- cooked potato flour, lentil flour, pea flour, soya flour, kidney or pinto beans, Mung bean flour, corn starch, wheat starch, potato starch, pea starch etc. A dough of 2628% m.c. is extruded to make pasta of 1.0-2.0 mm thickness. The pasta is then boiled in acidified water (using acetic, malic, fumaric, tartaric, phosphoric or adipic, but preferably lactic or citric acid) and then soaked those containing egg, additional gluten or other additives) to conform to the following standard: protein 11.5% (min.), m.c. 12.5% (max.) when packed, ash 0.60-0.85°/~. Degree of acidity and colour are also specified. ~~~~~~~~ c~~~~~~~ is a type of pasta product made in Algeria from a durum semolina and water paste which is dried and ground. The product is size- graded, and is similar in size to that of very coarse semolina. Thus prepared, the couscous has exce11ent keeping qualities- Pasta composition semolina in the U.K. is shown in Table 10.1. pasta ConsumPtion The per capila consumpt~on of pasta products in 1989 was (in kg) 21 in ~~~l~, 6 in F~~~~~, G~~~~~, portugal, switzerland, 5 in G~~~~~~ FR, 4 in Sweden, 3.5 in ~~~~~i~ and the u.K., 3 in spain, 2 in Finland and Ireland, 1.5 in ~~l~i~~, The composition of pasta made from durum in Water acidified to pH 3.84.3 to 6l-68% m.C. The partially cooked pasta is drained and then Denmark and The Netherlands, and 0.2 in N~~~~ (European Food Marketing Directory, 1991). coated with an acidified cream at pH 4.14.4. The acidification gives a better shelf life, and thickens the cream to improve coating. The Rice substitutes product is then flush-packaged with an inert gas, or is vacuum packaged. Finally, the containers are sealed and heated to 9Oo-100"C for 20-40 min to complete the cooking of the pasta. U. K. Code of Practice A Code of Practice for dry pasta products in the U.K. requires all pasta products (other than Bulgur Bulgur consists of parboiled whole or crushed partially debranned wheat grains, and is used as a substitute for rice, e.g. in pilaf, an eastern European dish consisting of wheat, meat, oil and herbs cooked together. The ancient method of producing bulgur, which is referred to as Arisah TABLE 10.1 Nutrients in Pasta* (per lOOg) Carbohydrates, g 75 Thiamin, mg 0.09 Calcium, mg 10 Protein, g 12 Riboflavin, mg 0.1 Iron, mg 1.2 Lipoprotein, g 1.8 Niacin, mg 2.0 Phosphorus, mg 144 Calories 380 * Source: Home Economics 1972, Dec.: 24. PASTA AND WHOLE GRAIN FOODS 239 in the Old Testament, consists of boiling whole grain lightly milled, and the product sieved to wheat in open vessels until it becomes tender. separate large from small bulgur (Certel et al., The cooked wheat is spread in thin layers for 1989). drying in the sun. The outer bran layers are During the soaking and cooking stages, a removed by sprinkling with water and rubbing proportion of the vitamins and other nutrients by hand. This is followed by cracking the grains present in the outer layers of the grain are by stone or in a crude mill. mobilized, and move to the inner part of the A product resembling the wheat portion of the grain, in a similar way to that described for pilaf dish was developed in the U.S.A. in 1945 parboiled rice (q.v.). Thus, removal of the outer as an outlet for part of the U.S. wheat surplus. layers of the grain, after soaking, cooking and In one method of manufacture of bulgur, described drying, does not much reduce the nutritive value by Schafer (1962), cleaned white or red soft of the bulgur. wheat, preferably decorticated, is cooked by a Bulgur is sent from the U.S.A. to peoples in multistage process in which the moisture content the Far East, as part of the programme of is gradually increased by spraying with water and American aid to famine areas. In 1971,227,000 t raising the temperature. Eventually, when the of bulgur were produced in the U.S.A., of which m.c. has reached 40%, the wheat is heated at 5% was used domestically, the remainder being 94°C and then steamed for 1.5 min at 206.85 used in the Foods for Peace Program. The staple kN/m2 (30 lb/in2) pressure so that the cooked food of people in these areas had always been product is gummy and starchy. The starch is boiled rice; the process of breadmaking was partially gelatinized. The m.c. is then reduced to unknown; wheat and wheat flour were therefore about 10% by drying with air at 66"C, and the unacceptable foods. Bulgur provided a cheap dried cooked wheat is pearled or cracked. One food that was acceptable because it could be brand of the whole grain product is called Redi- cooked in the same way as rice and superficially wheat in the U.S.A.; the crushed is Cracked- resembled it. The level of bulgur exports from Bulgur (Nouri, 1988). the U.S.A. for the food aid programme is now Other processes for making bulgur are reviewed about 250,000 t per year (Certel et aE., 1989). by Shetty and Amla (1972). Bulgur can be stored for 6-8 months under In a continuous system used in the U.S.A. for a wide range of temperature and humidity condi- the production of bulgur, the wheat is soaked in tions, and its hard and brittle nature discourages a succession of three tanks in which the m.c. is attack by insects and mites. raised progressively to 25-30% during 3.54 h Nutritive value in the first tank, to 3540% m.c. during 2.5 h in the second and to 45% m.c. during 2-2.5 h in the third, giving a total soaking time of 8 h. The The nutritive value of bulgur is similar to that grain is then cooked with steam at a pressure of the wheat from which it is made. Fat, ash and of 1.5-3 bar for 70-90 sec and then dried to crude fibre levels are slightly lower, but protein 10-11% m.c. The outer layers are removed, the level is unchanged. Retention of thiamin and TABLE 10.2 Nutrients in Bulgur* (per 100 g) Carbohydrates, 75.7 Thiamin, mg 0.28 Phosphorus, mg 430 Protein, g 11.2 Riboflavin, mg 0.14 Potassium, mg 229 Fat, g 1.5 Niacin, mg 5.5 Magnesium, mg 160 Energy, kcal 354 Vitamin B6, mg 0.32 Calcium, mg 22.6 Pantothenic acid, mg 0.83 Iron, mg 7.8 Folacin, mg 0.038 Zinc, mg 4.4 Iodine, mg 14 * Source: Protein Grain Products International, Washington, D.C. 240 TECHNOLOGY OF CEREALS niacin is about 98% of the original, that of in addition the nutritive value of the milled rice riboflavin about 73%. Iron and calcium contents is increased by this treatment, because the water are slightly increased, while phosphorus content dissolves vitamins and minerals present in the is decreased by the parboiling process. The hulls and bran coats and carries them into nutrient composition of bulgur is shown in Table the endosperm. Thus, valuable nutrients which 10.2. would otherwise be lost with the hulls and bran Bulgur of acceptable quality has also been in the milling of raw rice are retained by the prepared from triticale (Singh and Dodda, 1979) endosperm. It has been shown that rice oil and from maize (Certel et al., 1989). migrates outwards during parboiling: therefore in The consumption of bulgur in Turkey is esti- parboiled rice the oil content of the milled kernel mated at 20-30 kg/head/annum. Turkey is said is lower, and bran content higher, than in raw to export about 100,000 t of bulgur per annum rice. (Certel et al., 1989). By gelatinizing the starch in the outer layers of the grain, parboiling seals the aleurone layer and scutellum so that these fractions of the grain are retained in milling to a greater degree in milled WURLD Wheat Peeled bulgur wheat is a light-coloured, low- parboiled than in milled raw rice (Hinton, 1948). fibre bulgur, made to resemble rice by removal Parboiling toughens the grain and reduces the of the bran in a lye-peeling operation. The wheat amount of breakage in milling. Moreover, par- grain is treated with sodium hydroxide, and the boiled rice is less liable to insect damage than is loosened bran removed by vigorous washing with milled raw rice, and has an improved storage life. water. The grain is then treated with warm dilute Con version acetic acid to restore the surface whiteness, and dried. This treatment leaves the aleurone layer intact. Peeled bulgur made from a red wheat is Conversion of rice is the modern commercial known as WURLD wheat, a U.S. Department development of parboiling. In the H. R. Conver- of Agriculture Western Utilization Research sion Process, wet paddy is held for about 10 min Laboratry Develpment (Shepherd et al., 1965). in a large vessel which is evacuated to about 635 mm (25 in) of mercury. The paddy is then steeped for 2-3 h in water at 75-85°C introduced under a pressure of 552-690 kN/m2 (80-100 lb/in2). The Ricena Ricena is a rice substitute, originating in steeping water is drained off and the paddy is Australia, made from wheat by a relatively in- heated under pressure for a short time with live expensive patented process which gives a yield of steam in a steam-jacketed vessel. The steam is about 65% (Brit. Pat. No. 1,199,181). The wheat blown off, and the pressure in the vessel reduced is washed, cleaned, steamed under pressure and to 711-737 mm (28-29 in) of vacuum. The dried. The product sells at the price of low-grade product is then vacuum dried to about 15% m.c. rice, although the protein, iron and vitamin B1 in the steam-jacketed vessel, or it can be air- contents of ricena exceed those of milled rice. dried at temperatures not exceeding 63°C. After cooling, the converted paddy is tempered in bins for 8 h or more to permit equilibration of moisture, and is then milled. In the Malek process, paddy is soaked in water at 38°C for 4-6 h, steamed at 103.4 kN/m2 (15 lb/in2) pressure for 15 min, dried and milled. The product is called Malekized rice. Redistribution of thiamin (vitamin B1) in rice parboiled by the Malek process was investigated Parboiled rice The parboiling (viz. part-boiling) of rice is an ancient tradition in India and Pakistan, and consists of stepping the rough rice (paddy) in hot water, steaming it, and then drying it down to a suitable moisture content for milling. The original purpose of parboiling was to loosen the hulls, but PASTA AND WHOLE GRAIN FOODS 241 by Hinton (1948). By microdissection of raw and this problem. If the steep water is maintained at Malekized rice grains, followed by microanalysis a temperature of 65"C, the steeping time can be of the fractions, Hinton showed that the thiamin limited to 4 h, and odour development is avoided. content of the endosperm adjoining the scutellum The soaking conditions must be chosen care- increased from 0.4 to 5.2 iu/g, while that of the fully so as to hydrate the grain sufficiently for it scutellum decreased from 44 to 9 iu/g,and that to be gelatinized on subsequent heating, but so of the pericarp/aleurone from 10 to 3 iu/g. as to avoid splitting the hull - which leads to The thiamin content of the whole endosperm excessive hydration and leaching of nutrients. increased from 0.25 to 0.5 iu/g. The redistribu- Rate of hydration increases with temperature of tion of thiamin was due to the inward passage the steeping water, but above about 75°C the of water through the thiamin-containing layers rate of hydration increases so rapidly that splitting rendered permeable by heat to the vitamin. of the hull occurs. Thus, the solution is to limit In a process called double-steaming, raw paddy the moisture level in the grain to 30-32% either is presteamed for 15-20 min and then steeped in by soaking at 70°C or lower, or by starting the water for 12-24 h. The water is drained off, and soaking at 75°C and allowing the material to the product is steamed again and then dried. cool naturally during soaking. This method Parboiling may induce discoloration of the gives the fastest hydration without complications grains or development of deteriorative flavour (Bhattacharya, 1985). changes. A suggested remedy for reducing flavour A process devized by F. H. Schule GmbH does changes is steeping in sodium chromate solution not involve steaming. Rough rice is soaked for (0.05%). It has been shown that the additional 2-3 h in water at a medium temperature while chromium present in the milled rice is not absorbed the hydrostatic pressure is raised to 4-6 kg/cm* when the rice is consumed, and thus poses no by admitting compressed air. The pressure is health hazard (Pillaiyar, 1990). A remedy suggested released, and the rice is cooked in water at about for bleaching is steeping in sodium metabisulphite 90°C. The rice is then pre-dried in a vibratory solution (0.32%), but this treatment lowers the drier and subsequently dried by three passes availability of thiamin. through columnar driers with successively decreas- If steeping time exceeds about 8 h, the steep ing air temperature (Bhattacharya, 1985). water tends to develop an off odour which is A high-temperature, short-time process for picked up by the rice. The odour is due to the parboiling rice has been described (Pillaiyar, activity of anaerobic bacteria in the steep water. 1990). Paddy steeped to about 24% m.c. is simul- Various methods have been suggested to avoid taneously parboiled and dried in a sand-roaster TABLE 10.3 Nutrient Composition of Rice* (gl1OOg) Product Moisture Protein Fat Crude fibre Carbohydrate Ash Calories Brown rice 12 7.5 1.9 0.9 76.5 1.2 360 White rice 12 6.7 0.4 0.3 80.1 0.5 363 Parboiled rice 10 7.4 0.3 0.2 81.1 0.7 369 (mg/lOOg) Product Ca P Fe Na K Thiamin Riboflavin Niacin Tocopherol Brown rice 32 221 1.6 9 214 0.34 0.05 4.7 29 White rice Unenriched 24 94 0.8 5 92 0.07 0.03 1.6 - Enriched 24 94 2.9 5 92 0.44 - 3.5 - Enriched 60 200 2.9 9 150 0.44 - 3.5 * Source: U.S. Dept. Agric., Agricultural Research Service, Agricultural Handbook 8 (1963). Parboiled rice 242 TECHNOLOGY OF CEREALS in which the paddy is mixed with hot sand and remains in contact with the sand for about 40 set, after which the sand and the rice are separated by sieving. During this process the rice loses about 10% of moisture. For a comprehensive survey of other processes, see Bhattacharya (1985). AUTRAN, J. C., AIT-MOUH, 0. and FEILLET, P. (1989) Thermal modification of gluten as related to end-use properties. In: Wheat is Unique, pp. 563-593, POMERANZ, Y. (Ed.). Amer. Assoc of Cereal Chemists Inc. St. Paul MN. U.S.A. BHATTACHARYA, K. R. (1985) Parboiling of rice. In: Rice: Chemistry and Technology, Ch. 8, pp. 289-348, 2nd edn. JULIANO, B. 0. (Ed.). Amer. Assoc. of Cereal Chemists Inc. St. Paul MN. U.S.A. BRITISH PATENT SPECIFICATION NOS 2,151,898 (back-mixing of dough); 1,199,181 (ricena). CERTEL, V. M., MAHNKE, S. and GERSTENKORN, P. (1989) Bulgur-nichte eine turkishe Getreide spezialitat. Muhle Mischfuttertechnik, 126(6 July): 414-416. DE CARO, L., RINDI, G. and CASELLA, C. (1949) Contents in thiamine, folic acid, and biotin in an Italian converted rice. Abst. Commun. 1st Int. Cong. Biocha. 31. Du CROS, D. L. and HARE, R. A. (1985) Inheritance of gliadin proteins associated with quality in durum wheat. Crop Sci. 25: 674-677. European Food Marketing Directory, 2nd edn (1991) Euro- monitor plc., London. EUROPEAN PATENT APPLICATIONS Nos 0,1463 10 (extrusion into N2/C02); 0,267,368 (quick-cooking pasta); 0,272, 502 (quick-cooking pasta); 0,288,136 (shaped pasta products); 0,322,053 (drying Pasta); 0,352,876 (shelf- stable, microwave-cookable pasta). FEILLET, P. (1984) Present knowledge on biochemical basis of pasta cooking quality. Consequence for wheat breeders. Sci. Aliment. 4: 551-566. HINTON, J. J. C. (1948) Parboiling treatment of rice. Nature, Land. 162: 913-915. HOUSTON, D. F. (1972) Rice: Chemism and Technology. JULIANO, Inc. St. Paul B. 0. MN. (Ed.) U.S.A. Amer. Assoc. of Cereal Chemists KATSKEE, A. L. (1978) Microwave macaroni drying. Macaroni KIK, M. C. (1943) Thiamin in products of commercial rice milling. Cereal Chem. 20: 103. Material Thiamin Riboflavin Niacin KIK, M. C. and VAN LANDINGHAM, F. B. (1943) Riboflavin in products of commercial rice milling and thiamin, Paddy rice 3.540 0.4-0.5 52.3-55.0 riboflavin and niacin content of rice. Cereal Chem. 20: Converted parboiled rice 1.9-3.1 0.3-0.4 31.2-47.8 563-569. Milled, polished, KOBREHEL, K. and ALARY, R. (1989) The role of a low non-parboded rice 0.4-0.8 0.15-0.3 14.0-25.0 molecular weight glutenin fraction in the cooking quality of durum wheat pasta. J. Sci Food Agrk. 47: 487-500. * Sources: Kik (1943); Kik and van Landingham (1943). MANSER, J. (1986) Einfluss von Trocknungs-Hochst- Temperaturen auf die Teigwarenqualitat. Getreide Mehl Brot. 40: 309-315. MESTRES, C., MATENCIO. F. and FAURE, J. (1990) Optimizing process for making pasta from maize in admixture with durum wheat. J. Sci. Food Agn'c. 51: 355-368. MILATOVIC, L. (1985) The use of L-ascorbic acid in improving the quality of pasta. Int. J. Vitam. Nutr. Res. Suppl. 27: MOLINA, R. MAYORGA, I., LACHANCE, P. and BRESSANTI, R. (1975) Production of high protein quality pasta products using semolina-corn-soya-flour mkture. 1. Influence of thermal processing of cOrn flour on pasta quality, cereal Chem. 52: 240-247. NOURI, N. (1988) Bulgur4in Beitrag zur Vollwert-und vege- tarischen Ernahrung. Getreide Mehl Brot. 42: 317-3 19. PILLAIYAR, P. (1990) Rice parboiling research in India. Cereal Foods Wld 35: 225-227. Consumption Parboiled or converted rice is readily consumed in India and Pakistan, while in the U.S.A. it is used as a ready-to-eat cereal, as canned rice, and as a soup ingredient. Elsewhere, however, parboiled rice is not popular. Nutrient value Specimen figures for the chemical composition of brown rice, white (polished) rice and parboiled rice are given in Tab1e 10.3; the vitamin contents of milled (unconverted) and parboiled (converted) rice are shown in Tab1e 'Oa4' The fo1ic acid 'On- tent of rice is increased from 0.04 to 0.08 pg/g by conversion, whilst that of the polishings is reduced from 0.26-0.40 to 0.12 pg/g (De Car0 et al, 1949). TABLE 10.4 J. June: 12. Vitamin Contents of Rice* (pglg) References ABECASSIS, J., FAURE, J. and FEILLET, p. (19894 Improve- ment of cooking quality of maize pasta products by heat treatment. J. Sci. Food Agric. 47(4): 475485. P. (198913) Effect of moisture content of pasta during high temperature drying. Getreide Mehl Brot 43(Feb): 58-62. ALARY, R. and KOBREHEL, K. (1987) The sulphydryl Plus disulphide content in the proteins of durum wheat and its relationship with the cooking quality of pasta. J. Sci. Food Agric. 39: 123-136. ANTOGNELLI, C. (1980) The manufacture and applications of pasta as a food and as a food ingredient: a review J. Food Technol. 15: 125. ABECASSIS, J., CHAURAND, M., METENCIO, F. and FEILLET, 345-36 1. PASTA AND WHOLE GRAIN FOODS 243 POMERANZ, Y. (1987) Modern Cereal Science and Technology, Further Reading Ch. 20: Extrusion products. VCH Publishers Inc., NY. SCHAFER, W. (1962) Bulgur for underdeveloped countries. ANON. (1987) Bulgur wheat production. Am. Milh Process. SGRULLETTA, D. and De STEFANIS, E. (1989) Relationship AUTRAN, J. C. and GALTERIO, G. (1989) Association between between pasta cooking quality and acetic acid insoluble electrophoretic composition of proteins, quality character- protein of semolina. J. Cereal Sci. 9: 217-220. istics and agronomic attributes of durum wheats. 11. SHEPHERD, A. D., FERREL, R. E., BELLARD, N. and PENCE, Protein-quality associations. J. Cereal Sci. 9: 195-215. J. W. (1965) Nutrient composition of bulgur and lye- JULIANO, B. 0. (Ed.) (1985) Rice: Chemistry and Technology, peeled bulgur. Cereal Sci Today 10: 590. 2nd edn. Amer. Assoc. of Cereal Chemists Inc. St. Paul SHETTY, M. S. and AMLA, B. L. (1972) Bulgur wheat. J. MN. U.S.A. Fd. Sci. Technol. 9: 163. LICHODZIEVSKAJA, I. B., BRANDO, E. E., CHIMIZOV, J. I., SINGH, B and DODDA, L. M. (1979) Studies on the prepara- MUCHIN, M. A., TOLSTOGUZOV, V. B., MUSCHIOLIK, G. tion and nutrient composition of bulgur from triticale. J. and WEBERS, V. (1989) Herstellung von Teigwaren aus Food Sci. 44: 449. Backmehl unter Andwendung von Polysaccharid-Zusatn. U.S. PATENT SPECIFICATION NOS 4,539,214 (rapidly rehydrat- Nahrung 33: 191-201. able pasta); 4,540,590 (extrusion into vacuum); 4,540,592 MORGAN, A. I. Jr, BARTA, E. J. and GRAHAM, R. P. (1966) (pre-cooked pasta); 4,675,199 (extrusionkompression WURLD wheat - a product of chemical peeling. North- process); 4,828,852 (shelf-stable, pre-cooked pasta); west Miller 273(6): 40. 4,830,866 (pre-cooked pasta); 4,876,104 (long shelf-life pasta). Milling 139: 688. 92(10): 17-18.