[4] G. A. Gilbert: A Survey of the Action of Air on Aqueous Solutions [13] F.L. Bates, D. French, and R. E. Rundle: Amylose and Amylopectin of Starch. Stärke 10 (1958), 95Ð99. Content of Starches Determined by Their Iodine Complex Forma- [5] W. Everett and J. F. Foster: The Conformation of Amylose in So- tion. J. Am. Chem. Soc. 65 (1943), 142Ð148. lution. J. Am. Chem. Soc. 81 (1959), 3464Ð3469. [14] A. Hebeish, I. Abd El Thalouth, and M. El Hashouti: Gelatinization [6] P.J. Killion and J. F. Foster: Isolation of High Molecular Weight of Rice Starch in Aqueous Urea Solutions. Starch/Stärke 38 (1981), Amylose by Dimethylsulphoxide Dispersion. J. Polymer Sci. 46 84Ð90. (1960), 65Ð73. [15] D. Goodison and R. S. Higginbotham: 13 Ð The Fractionation of [7] W. Banks and C. T. Greenwood: The Fractionation of Laboratory- Starch Part VI Ð the Fractionation of Amyloses. J. Textile Inst. 42 Isolated Cereal Starches using Dimethylsulphoxide. Stärke 19 (1951), T249ÐT273. (1967), 394Ð398. [16] N. W.H. Cheetham and L. Tao: Amylose Conformational Transi- [8] W. Banks, C. T. Greenwood, and J. Thomson: The Properties of tions in Binary DMSO/Water Mixtures. Starch/Stärke 49 (1997), Amylose as Related to the Fractionation and Subfractionation of 407Ð419. Starch. Makromol. Chem. 31 (1959), 197Ð213. [17] A. Hayashi, K. Kinoshita, and Y. Miyake: The Conformation of [9] H. Yun, G. Rema, and K. Quail: Wheat Starch Fractionation, in: Amylose in Solution. I. Polymer J. 13 (1981), 537Ð541. Cereals 1997, Proceedings of the 47th Australian Cereal Chemistry Conference. Eds. A. W Tarr, A. S. Ross and C. W. Wrigley. Royal Australian Chemical Institute, Melbourne 1997, pp. 365Ð368. [10] J.-L. Jane and J.-F. Chen: Effect of Amylose Molecular Size and Amylopectin Branch Chain Length on Paste Properties of Starch. Cereal Chem. 69 (1992), 60Ð65. [11] S. J. McGrane, H. J. Cornell, and C. J. Rix: A Simple and Rapid Address of authors: Prof. Hugh J. Cornell, Scott J. McGrane, and Colorimetric Method for the Determination of Amylose in Starch Colin J. Rix, Department of Applied Chemistry, RMIT University, GPO Products. Starch/Stärke 50 (1998), 158Ð163. Box 2476V, Melbourne, Victoria, 3001, Australia. [12] C. E. Jarvis and J. R. L. Walker: Simultaneous, Rapid, Spectropho- tometric Determination of Total Starch, Amylose and Amylopectin. (Received: September 10, 1999). J. Sci. Food Agric. 63 (1993), 53Ð57. (Accepted: November 8, 1999).

Effects of Steep Time and SO2 Concentration on Steepwater Profiles and Milling Yields Using a Continuous Countercurrent Steep System Ping Yang, Jianhua Qiu, Kent D. Rausch, Phil Buriak, Mike E. Tumbleson, and Steven R. Eckhoff, Urbana (U.S.A.)

Effects of SO2 concentration and steep time on maize steep profiles and Steeping, from the perspective of maize, can be viewed as a three-stage wet milling results were studied using a continuous countercurrent process including a lactic acid dominated stage, a SO2 absorption stage steep system. Maize was steeped at 50 ± 2 ¡C at different SO2 con- and a SO2 diffusion stage. From the perspective of steepwater, increas- centrations (target value at 1,000, 2,000 and 3,000 ppm) for different ing SO2 concentration increases the total dry solids increase rate and lengths of time (18, 24, 30 and 36 h). Steepwater profiles, including pH, SO2 decrease rate. Starch yield can be significantly increased by in- SO2 concentration, total acidity and steepwater solids content versus creasing either steep time or SO2 concentration. tank number for each combination of SO2 level and steep time were generated. Three steeped maize samples for each condition were milled and average product yields were reported.

1 Introduction which chemical and biochemical reactions are involved. Studies have shown that lactic acid is produced by fermenta- The importance of steeping in maize wet milling has been tion during countercurrent steeping and the production of well addressed by many researchers [1Ð6]. During the early lactic acid benefits the wet milling process [2], [6], [10Ð17]. years of the wet milling industry, maize was steeped using a Variables affecting countercurrent steeping are: steep batch method that resulted in lack of uniformity in kernel time, steep temperature, type and activity of bacteria, type softness and a loss of large quantities of soluble materials and grade of maize, initial concentration of SO2, composi- [7]. In continuous countercurrent steeping, invented at the tion of process water, steepwater draw rate and number of beginning of the 20th century [7Ð9] and used by industry tanks. Studies conducted to understand and to improve the ever since, dry maize contacts low levels of SO2 and high steeping process [2], [11Ð21], were all Ð except the study levels of lactic acid first and as the corn moves through the conducted by Steinke and Johnson [19] Ð done using the steep cycle, it is exposed to increasing levels of SO2. With batch steeping method. It is difficult to perform meaningful the moving of steepwater, maize eventually contacts high experiments in an actual wet milling plant due to uncontrol- levels of SO2 and low levels of lactic acid right before lable changes in some variables including grain condition milling. Countercurrent steeping is a complicated process in and mill house water composition [16].

Starch/Stärke 51 (1999) Nr. 10, S. 341Ð348 © WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999 0038-9056/99/1010-0341$17.50+.50/0 341 The objectives of this study were (1) to study the effect of followed by Duncan’s multiple range test using the Statisti- steep time and initial SO2 level on steepwater profiles in- cal Analysis System [30]. cluding pH, total solids content, SO2 concentration and total acidity and (2) to study the effect of steep time and SO2 con- centration on maize wet milling yields. 3 Results and Discussion

3.1 Steepwater profiles 2 Materials And Methods Sulfur dioxide concentration and solids content in steep- water increased rapidly and lactic acid level gradually in- 2.1 Maize sample creased during steeping. Steepwater pH increased rapidly at Maize hybrid Pioneer 3394, harvested in 1997 and the beginning and then stabilized (Figs. 1Ð4). The lowest cleaned using a 4.8 mm (12/64 ) round hole screen, was used SO2 concentration and the highest solids and lactic acid lev- for this study. The initial moisture content of the maize els were reached in tank 11 under all steep conditions. Com- (13.3%) was determined by the 103 ¡C, 72 h convection pared to tank 11, tank 12 (with dry maize) had a lower solids oven method [22]. The maize sample contained 72.3% content and a lower concentration of lactic acid but a higher starch, 8.3% protein, 1.9% fiber and 3.2% fat, analyzed us- SO2 level. The reason for a lower level of solids in tank 12 ing near-infrared transmittance (GrainSpec, Foss Electric, was that when dry maize was put into the steep tank, it ab- Brampton, Ontario, Canada) by the Identity Preserved Grain sorbed a large amount of water with solubles and lactic acid Laboratory, Champaign, IL. Transmittance readings of 250 g before it released any solubles. Due to the preferential ab- were taken over a wavelength range of 800Ð1100 mm. sorption of water, tank 12 had a higher SO2 level. Since the level of solubles in tank 12 was lower than that in tank 11, 2.2 Steepwater profiles fewer solubles were available for fermentation and resulted Maize samples (1,000 ± 0.3 g in each tank) were steeped in a lower level of lactic acid in tank 12. Changing the initial in a laboratory scale continuous countercurrent system at 50 SO2 concentration in fresh steepwater affected the solids ± 2 ¡C. The system was started with light steepwater that was content and the lactic acid concentration as well as the pH of obtained from a local wet milling plant [23]. Twelve tanks the steepwater. The degree of this effect depended on the were used to steep maize at any given time and the other four steep time (Figs. 1Ð4). were used as a buffer so that the system could be left unat- Steeping can be viewed as a three-stage process with dif- tended for a certain period of time [23]. The steepwater recy- ferent reactions and different mechanisms dominating each cle rate was set at 5.0 mL/s and the draw rate of the light stage. The first stage (approximately the last four tanks, i. e., steepwater was 600 mL/kg. The SO2 concentration and steep tanks 9Ð12) is the lactic acid dominated stage. In this stage, time were independent variables and total solids content, to- maize comes in contact with high levels of lactic acid and tal acidity and pH of steepwater and the milling results were solids while the concentration of SO2 and pH are low. The dependent variables. The initial target SO2 concentration in high level of lactic acid at this stage slightly reduces steep- fresh steepwater was 1,000, 2,000 and 3,000 ppm while water pH and creates holes or pits in the corneous endosperm steep times were 18, 24, 30 and 36 h. cell walls, which allowed steepwater to move throughout the The countercurrent steep system was initially run for kernel during the steeping process [31]. eight days to allow the steep variables to stabilize [24]. After Although the mechanism of lactic acid activity during the system reached its steady state, approximately 30 mL of steeping is not fully understood, a recent study has shown steepwater sample from each tank was taken out to deter- that lactic acid increases starch yield by 2.9 to 12.0% de- mine steep variables (SO2 concentration, solids content and pending on the maize hybrid [15]. The second stage (approx- lactic acid concentration in steepwater and steepwater pH). imately the middle four tanks, i. e., tanks 5Ð8) is the SO2 dif- The steepwater samples were taken out each time right be- fusion stage where maize began to contact an increasing lev- fore the system was transferred into the next set of twelve el of SO2 and a decreasing level of lactic acid. Solids content tanks. Sulfur dioxide concentration was determined by titra- in this stage is lower than in the lactic acid dominated stage. tion with iodine solution [25]. Solids content in steepwater The holes and pits in the corneous endosperm cell walls cre- was determined using a two-stage convection oven method ated in the previous stage theoretically allow SO2 and water [26]. Lactic acid concentration was estimated using a titri- to move into the maize kernels more rapidly and begin to re- metric method [27] and steepwater pH was measured using a act with the protein matrix. Earp et al. [31] reported that the digital pH meter (Corning, model 120). degradation of the protein matrix occurred around 18 h of steeping. The final stage (approximately the first four tanks) 2.3 Milling of steeped maize is the SO2 dominated stage. In this stage, maize contacts an Three 1-kg (initial weight) samples of steeped maize were increased level of SO2 which diffuses into the kernels de- milled using the procedure described by Eckhoff et al. [28], grading the protein. The reason for high SO2 levels in this the average product yields and standard deviations were re- stage is to insure that sufficient SO2 exists in the steepwater × ported. Protein content (N 6.25) in the starch isolated from during the SO2 diffusion stage. In this stage, lactic acid and maize steeped for 18 h, in which the separations are the most solids content were low. The pH at this stage was in the range difficult, was determined by Silliker Laboratories Group, of 4.5 to 4.8 except in the first tank and in the fresh steepwa- Inc., Cedar Rapids, IA by Kjeldahl nitrogen content, Method ter (Figs. 1Ð4). B-48 [29]. 3.2 Milling yields of steeped maize 2.4 Statistical analysis Maize steeped for 24 h and longer was easier to fraction- The differences in the product yields were compared be- ate based on yield data and imperial laboratory experiment. tween maize samples steeped in different concentrations When maize was steeped for only 18 h with low level of of SO2 for different periods of time by one way ANOVA SO2, fewer solubles were released (Fig. 1b), which is in

342 Starch/Stärke 51 (1999) Nr. 10, S. 341Ð348 Fig. 1. Effect of initial SO2 concentra- tion on maize steepwater profiles when steeping maize at 50 ¡C for 18 h. Tank 1 contained the oldest maize and tank 12 contained the newest maize. a) 693 ppm SO2; b) 1,998 ppm SO2; c) 2,423 ppm SO2 ( = SO2, = Solids content, + = Lactic acid, = pH).

agreement with Lopes Filho [32] and Singh and Eckhoff (Tab. 1). Steeping 18 h with increased SO2 concentration [33]. The lower amount of solubles decreased fermentation, from approximately 1,000 ppm to 3,000 ppm increased the resulting in a lower level of lactic acid and a higher pH com- density of first grind slurry from 6.3 ± 0.3 to 7.2 ± 0.5. As a pared to other steep times (compare Fig. 1 with Figs. 2Ð4). result, the germ separation was significantly improved. In- At 18 h of steeping with less than 3,000 ppm SO2, there was creasing SO2 concentration also significantly increased not enough starch released after the first grind due to the fact starch yield (Tab. 1). that starch granules were still held tightly by the protein ma- When increasing steep time from 18 to 24 h, solids con- trix [34]. As a result, the density of the first grind slurry was tent in steepwater increased especially for 2,000 and 3,000 low and germ was difficult to float and separate. When steep- ppm (target value) SO2. This made more solubles available ing maize for only 18 h with low level of SO2, poor separa- for lactic acid fermentation and resulted in an increased lev- tion among the maize components was indicated by a lower el of lactic acid concentration and decreased pH of steepwa- starch and germ yields and higher fiber and gluten yields ter (compare Fig. 2 to Fig. 1). As a result, starch yield and

Starch/Stärke 51 (1999) Nr. 10, S. 341Ð348 343 Fig. 2. Effect of initial SO2 concen- tration on maize steepwater profi- les when steeping maize at 50 ¡C for 24 h. Tank 1 contained the ol- dest maize and tank 12 contained newest maize. a) 687 ppm SO2; b) 2,177 ppm SO2; c) 2,583 ppm SO2 ( = SO2, = Solids content, + = Lactic acid, = pH).

germ yield increased significantly for any given level of SO2 30 h steeping as that for 24 h steeping (compare Fig. 3b to comparing to steeping for only 18 h (Tab. 1). The separation Fig. 2b). This result indicated that there was a maximum lev- between starch and fiber and starch and gluten were also im- el of solids released into steepwater. Correspondingly, the in- proved, particularly when steeping in 2,000 and 3,000 ppm crease in lactic acid concentration with the increase in SO2 SO2 (target value) solution (Tab. 1). This results were in was not as great for 30 h steeping as that for 24 h steeping. agreement with Cox et al. [34]. As a result, increasing the level of SO2 did not significantly When increasing steep time to 30 h, the solids level in increase starch yield (Tab. 1). steepwater was further increased, particularly for 1,000 ppm A lower starch yield and a higher fiber yield was obtained (target value) SO2. The increase in solids content in steepwa- when steeping maize in 1,000 ppm SO2 (target value) for ter when increasing SO2 concentration was not as great for 36 h than steeping maize in the same level of SO2 for 30 h

344 Starch/Stärke 51 (1999) Nr. 10, S. 341Ð348 Fig. 3. Effect of initial SO2 con- centration on maize steepwater profiles when steeping maize at 50 ¡C for 30 h. Tank 1 contained the oldest maize and tank 12 contained newest maize. a) 1,163 ppm SO2; b) 1,900 ppm SO2; c) 2,681 ppm SO2 ( = SO2, = Solids content, + = Lactic acid, = pH).

(Tab. 1) due to the low SO2 content in steepwater (comparing a 50% increase in steep time (from 24 to 36 h) increased the Fig. 4a to Fig. 3a). The total recoveries for 36 h steeping at starch yield by 3.6%. Starch yield can be improved either by 1,000 and 2,000 ppm SO2 (target value) were 1 to 2% lower increasing steep time or by increasing SO2. It is not econom- than those for 30 h at the same SO2 levels due to unknown ically beneficial to increase both steep time and SO2 concen- losses. At 36 h, increasing SO2 to 3,000 ppm (target value) tration. significantly increased starch yield and decreased gluten The separation of maize components was most difficult yield compared to the steep times of 18, 24 and 30 h (Tab. 1). when steeping maize for only 18 h. The protein content in At 3,000 ppm SO2 (target value), a 20% increase in steep starch isolated from maize steeped for 18 h was 0.4% for all time (from 30 to 36 h) increased the starch yield by 2.8% and three levels of SO2.

Starch/Stärke 51 (1999) Nr. 10, S. 341Ð348 345 Fig. 4. Effect of initial SO2 concentration on maize steep- water profiles when steeping maize at 50 ¡C for 36 h. Tank 1 contained the oldest maize and tank 12 contained the newest maize. a) 1,152 ppm SO2; b) 2,183 ppm SO2; c) 2,981 ppm SO2 ( = SO2, = Solids content, + = Lactic acid, = pH).

4 Conclusions Increasing steep time or SO2 level in steepwater de- creased steepwater pH and increased solids content in steep- From the perspective of maize, steeping can be viewed as water. Increasing the steep time from 18 to 24 h or longer a three-stage process: lactic acid dominated stage, SO2 ab- significantly improved the separation between maize com- sorption stage and SO2 diffusion stage. Steepwater condi- ponents, indicated by a higher starch yield and a lower gluten tions including pH, steepwater solids content and lactic acid and fiber yield except at 1,000 ppm (target value). However, and SO2 concentration are different from stage to stage. the increase in starch yield with a 20% increase in steep time

346 Starch/Stärke 51 (1999) Nr. 10, S. 341Ð348 Tab. 1. Wet milling yield of countercurrent steeped maize using different steep times and SO2 concentrations.

Concentrations1

Yields at different steep times and SO2 levels [%] 2 3 Product SO2 level Industrial 18 24 30 36 SWS4 1 3.3g5 3.3 ± 0.1c 5.0 ± 0.2c 4.2de 2 7.5 3.3g 4.7c 5.0 ± 0.4c 4.2 ± 0.1de 3 3.9f 5.5 ± 0.1b 5.9 ± 0.1a 5.0 ± 0.1c Germ 1 6.3 ± 0.1cd 6.8 ± 0.9bcd 7.3ab 6.4 ± 0.7bcd 2 7.5 6.0 ± 0.8d 7.3 ± 0.1ab 7.1 ± 0.1abc 6.8 ±0.5bc 3 6.4 ± 0.3bcd 7.8 ± 0.3a 6.7 ± 0.2bcd 6.6 ± 0.2bcd Fiber 1 13.1 ± 0.1abc 13.9 ± 1.6ab 10.7 ± 0.2de 14.3 ± 1.7a 2 11.5 13.0 ± 0.5abc 10.2 ± 0.6e 11.7 ± 0.5cde 10.3 ± 0.2e 3 12.3 ± 0.3bcd 10.9 ± 0de 12.1 ± 0.4cd 10.4 ± 0.5e Starch 1 63.4 ± 0.5f 65.2 ± 0.7e 68.0 ± 0.2b 66.1 ± 0.4de 2 67.5 63.5 ± 0.3f 67.3 ± 0.7bc 67.7 ± 0.3b 67.1 ± 0.8bcd 3 66.3 ± 0.7cd 67.5 ± 0.1b 68.0 ± 0.3b 69.9 ± 0.2a Gluten 1 11.2 ± 0.4ab 8.8 ± 0.4d 8.6 ± 0.4de 7.7 ± 0.3f 2 5.8 11.8 ± 0.7a 9.9 ± 0.3c 8.1 ± 0.1ef 8.8 ± 0.7d 3 10.7 ± 0.3bc 10.1 ± 0.6c 8.7 ± 0.1d 7.7 ± 0.3f Total 1 97.4 ± 0.1 98.1 ± 0.2 99.6 ± 0.7 98.7 ± 0.3 2 99.8 97.6 ± 0.5 99.4 ± 0.5 99.7 ± 0.2 97.2 ± 0.2 3 99.6 ± 0.1 101.8 ± 0.4 101.5 ± 0.5 99.5 ± 0.6 1 The data was on dry basis and expressed as the average of three replicates ± one standard deviation. 2 For 18 h, actual SO2 level 1, 2 and 3 was 693, 1,998 and 2,423 ppm, respectively. For 24 h, actual SO2 level 1, 2 and 3 was 687, 2,177 and 2,583 ppm, respectively. For 30 h, actual SO2 level 1, 2 and 3 was 1,163, 1,900 and 2,681 ppm, respectively. For 36 h, actual SO2 level 1, 2 and 3 was 432, 1,413 and 1,779 ppm, respectively. 3 Anderson and Watson [35]. 4 SWS = Steepwater seolids. 5 Yields in a row followed by the same letter are not significantly different at a 95% confidence level. is only 2.8% and a 50% increase in steep time only resulted [11] M. Roushdi, Y. Ghali, and A. Hassanean: Formation of lactic acid in 3.6% increase in starch yield. The economic factors of in- during corn steeping. Egypt. J. Food Sci. 7 (1979), No. 1-2:17-25. creasing steep time to improve starch yield have to be taken [12] M. Roushdi, A. A. Fahmy, M. Mostafa, and K. Ei-Sheikh: Role of into account. Increasing SO2 level can increase the starch lactic acid in corn steeping and its relation with starch isolation. yield except when steeping for 30 h. Starch/Stärke 33 (1981), 426Ð428. [13] R. Ruan, J. B. Litchfield, and S. R. Eckhoff: Simultaneous and non- destructive measurement of transient moisture profiles and struc- tural changes in corn kernels during steeping using microscopic Bibliography nuclear magnetic resonance imaging. Cereal Chem. 69 (1992), 600Ð606. [1] P. H. Blanchard: Wet millings in: Technology of Corn Wet Milling [14] D. L. Shandera, A. M. Parkhurst, and D. S. Jackson: Interactions and Associated Processes. Elsevier Science Publishers, Amster- of sulfur dioxide, lactic acid, and temperature during simulated corn dam, The Netherlands 1992. pp 69Ð125. wet milling. Cereal Chem. 72 (1995), 371Ð378. [2] M. J. Cox, M. M. MacMasters, and G. E. Hilbert: Effect of the sul- [15] V. Singh, A. E. Haken, Y. X. Niu, S. H. Zou, and S. R. Eckhoff: Hy- furous acid steep in corn wet milling. Cereal Chem. 21 (1944), brid-dependent effect of lactic acid on yields. Cereal 447Ð465. Chem. 74 (1997), 249Ð253. [3] J. B. May: Wet milling process and products. In: Corn: Chemistry and Technology. Eds. S. A. Watson and P. E. Ramstad. Am. Assoc. [16] S. A. Watson, C. B. Williams, and R. D. Wakely: Laboratory steeping Cereal Chem.: St. Paul, MN. 1987. pp 377Ð397. procedures used in a wet milling research program. Cereal Chem. [4] J. S. Wall: Disulfide bonds: determination, location and influence 28 (1951), 105Ð119. on molecular properties of proteins. J. Agr. Food Chem. 19 (1971), [17] S. A. Watson, Y. Hirata, and C. B. Williams: A study of the lactic 619Ð625. acid fermentation in commercial corn steeping. Cereal Chem. 32 [5] J. S. Wall: Corn and sorghum grain proteins. in: Advances in Ce- (1955), 382Ð394. real Sciences and Technology, Vol. II. Ed. Y. Pomeranz. Am. As- [18] S. A. Watson and E. H. Sanders: Steeping studies with corn endo- soc. Cereal Chem.: St. Paul, MN. 1978. pp 135Ð167. sperm sections. Cereal Chem. 38 (1961), 22Ð33. [6] S. A. Watson: Corn and sorghum starches: production. Chapter XII [19] J. D. Steinke and L. A. Johnson: Steeping maize in the presence of in: Starch: Chemistry and Technology, 2nd ed. Eds. R. L. Whistler, multiple enzymes. I. Static batchwise steeping. Cereal Chem. 68 J. N. BeMiller, and E. F. Paschall. Academic Press, Inc., Orlando, (1991), 7Ð12. FL. 1984. [7] A. W. Lenders: Steeping Apparatus. U. S. Pat. 925,583 (1908). [20] J. D. Steinke, L. A. Johnson, and C. Wang: Steeping maize in the [8] F. L. Jefferies: Steeping Apparatus. U. S. Pat. 1,007,783 (1911). presence of multiple enzymes. II. Continuous countercurrent [9] A. W. Lenders: Process of steeping grain. U. S. Pat. 948,514 (1910). steeping. Cereal Chem. 68 (1991), 12Ð17. [10] S. R. Eckhoff and C. C. Tso: Wet milling of corn using gaseous SO2 [21] F. Meuser, J. Wittig, and H. Huster: Effects of high pressure disin- addition before steeping and the effect of lactic acid on steeping. tegration of steeped maize on the release of starch granules Cereal Chem. 68 (1991), 248Ð251. from the protein matrix. Starch/Stärke 41 (1989), 225Ð232.

Starch/Stärke 51 (1999) Nr. 10, S. 341Ð348 347 [22] American Association of Cereal Chemists: Approved Methods of [31] C. F. Earp, C. M. McDonough, and L. W. Rooney: Changes in the the AACC, 8th ed. Method 44Ð15A. The Association: St. Paul, MN. microstructure of the during the wet milling steeping 1983. process. Final Research Project Progress Report to the Corn Refi- [23] P. Yang, L. E. Pruiett, R. J. Shunk, and S. R. Eckhoff: A laboratory- ners Association. 1985. scale continuous countercurrent steep system for corn wet milling, [32] J. F. Lopes Filho: Intermittent milling and dynamic steeping pro- Part I. Assembly of the system. Trans. ASAE. 41 (1998), 721Ð726. cess for corn starch recovery. Ph.D. Thesis. University of Illinois, [24] P. Yang and S. R. Eckhoff: A laboratory-scale continuous counter- Urbana, 1995. current steep system for corn wet milling, Part II. Evaluation of the [33] V. Singh and S. R. Eckhoff: Effect of soak time, soak temperature system. Trans. ASAE. 42 (1999), 443Ð448. and lactic acid on germ recovery parameters. Cereal Chem. 73 [25] S. R. Eckhoff: Measurement of sulfur dioxide in light steepwater. (1996), 716Ð720. Wet Milling Notes, Note No. 1. University of Illinois, Urbana, IL. [34] M. J. Cox, M. M. MacMasters, and G. E. Hilbert: Effect of the sul- 1989. furous acid steep in corn wet milling. Cereal Chem. 21 (1944), [26] American Association of Cereal Chemists: Approved Methods of 447Ð464. the AACC, 8th ed. Method 44Ð18. The Association: St. Paul, MN. [35] R. A. Anderson and S. A. Watson: The corn industry, in: CRC Hand- 1983. book of Processing and Utilization in Agriculture, Vol 2, Part 1. Bo- [27] Corn Refiners Association: Standard Analytical Methods of the ca Raton, FL.: CRC Press. 1982. pp. 31Ð61. Member Companies of the Corn Refiners Association, 6th ed. Me- thod J-4. The Association: Washington, D. C. 1991. [28] S. R. Eckhoff, K. D. Rausch, E. J. Fox, C. C. Tso, X. Wu, Z. Pan, and P. Buriak: A laboratory wet milling procedure to increase re- Address of the authors: Ping Yang, Post-doctoral Research Associ- producibility and accuracy of product yields. Cereal Chem. 70 ate, Jianhua Qiu, Former Research Technician, Kent D. Rausch, Assis- (1993), 723Ð727. tant Professor, Phil Buriak, Professor, Mike E. Tumbleson, Professor, and [29] Corn Refiners Association: Standard Analytical Methods of the th Steven R. Eckhoff, Professor, University of Illinois at Urbana-Cham- Member Companies of the Corn Refiners Association, 6 ed. Me- paign, Urbana, IL 61801, U.S.A. thod B-48. The Association: Washington, D. C. 1984. [30] SAS Institute, Inc.: SAS User’s Guide: Procedures, Statistics. The (Received July 2, 1999). Institute: Cary, NC. 1994. (Accepted November 15, 1999).

Enzymatic Recycling of Starch-Containing Desizing Liquors Klaus Opwis, Dierk Knittel, Annemarie Kele, and Eckhard Schollmeyer, Krefeld (Germany)

Starch-containing desizing liquors from the pretreatment of cotton fab- processes a loss of enzyme activity occurs, due to the presence of ionic rics can be transformed into bleaching liquors by a two-stage enzymat- surfactants. This loss of activity can be counteracted by addition of cy- ic treatment. The bleaching ability of these liquors is comparable to that clodextrins. Trials have been done to immobilize glucose oxidase on of conventional bleaching liquors. The process results in saving of eco- the cheap carrier material cotton, so it can be used more often than on- logically harmful chemicals and process water. In enzymatic textile ly one time as regenerable enzyme.

1 Introduction internal circulation leads to an improvement of efficiency, combined with a decrease of emissions and a careful use of 75% of the sizing agents used worldwide are starch and its resources [7, 8]. derivatives. They are far more important than synthetic and In this context simple and reasonable strategies for reduc- more expensive sizing agents such as poly(vinyl alcohols) ing the high COD-waste water load caused by starch are de- (PVA) or polyacrylates (PAC). The desizing liquors resulting sirable. These processes should allow a specific utilization from starch removal are usually disposed of with the waste and recirculation of starch-containing desizing liquors, that water. 50Ð80% of the Chemical Oxygen Demand (COD) in contain partly degraded oligosaccharides and cannot be re- effluents of textile finishing industries is caused by sizing used directly. agents, which contribute considerably to water pollution Compared with conventional procedures, enzymatic [1Ð6]. In future starch will continue to be the dominant siz- methods are advantageous in terms of ecology and economy. ing agent for cotton products (CO) Ð especially because of its Enzymes can be used in catalytic amounts and often under low costs. physiological conditions, i.e., at ambient temperatures, Technologies for development of economically and eco- resulting in a low energy demand. The excellent substrate logically well-tolerated textile finishing are gaining increas- selectivity of enzymes allows more gentle conditions, so the ing public interest. These technologies allow a recirculation loss of quality of the treated goods is much smaller than in of raw materials, process water or auxiliary substances. This conventional finishing [9].

348 Starch/Stärke 51 (1999) Nr. 10, S. 348Ð353 © WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999 0038-9056/99/1010-0348$17.50+.50/0