Process Variables, Gelatinized Starch and Moisture Effects on Physical Properties of Mungbean Noodles F.C.F. GALVEZ, A.V.A. RESURRECCION and G.O. WARE ABSTRACT The effects of amounts of gelatinized starch and moisture in the final slurry or dough, cooking time, holding time, and holding temperature on physical properties of mungbean noodles were studied. Cooking loss, cutting stress, work to cut, and transparency of noodles were measured.Moisture content of the final slurry or dough, cooking time, and holding temperature were the most important factors that affected physical properties of mungbean noodles. Processing should be done at moisture contents not exceeding .55%, cooking times not longer than 40 set, and holding temperaturesnot lower than 3°C using 5% of total starch as gelatinized starch and holding time of 36 hr. Key Words: mungbean,noodles, physical properties,gelatinizedstarch, cook time INTRODUCTION THE PROCESS for manufacture of mungbean noodles (glass noodles) involves mixing dry and gelatinized starch to form a slurry or dough, extruding it directly into boiling water to cook, cooling the formed noodles in cold tap water, holding at refrigerated or freezing temperature, warming in cold tap water, and drying (Francisco, 1963; Lii and Chang, 1981; Singh et al., 1989). The publishedprocesses vary on the amount of gelatinized starch used (O-5% of total starch), amount of moisture in the final slurry or dough before cooking (54-90%), the cooking time for extruded noodles (20 set or longer), hold- ing temperatures (- 18 to SOC), and the length of holding time (12-24 hr). These ranges may account for wide variations in quality of mungbean noodles. The use of starches from sweet potato and corn (Sin-I, 1974), red beans (Lii and Chang, 1981), cassava (Sin-I, 1974; Ka- wabata et al., 1984), and pigeonpeas (Singh et al., 1989) in the manufacture of glass noodles have been investigated and compared with thoseprepared from mungbeans. However, there are no published studies on the effects of relative amounts of gelatinized starch and moisture and of process variables on quality characteristics. The purpose of our study was to determine the effects of the amount of gelatinized starch, moisture content of the slurry or dough, cooking time, holding temperature, and holding time on physical properties of mungbean noodles. Specific objec- tives were to (1) identify important variables, (2) develop pre- dictive models, (3) establish ranges of variablesfor optimization, and (4) determine the direction of response variables. MATERIALS & METHODS Experimental design A fractional factorial designwas adopted which allows investigators to model interactions among factors using an efficient number of com- binations rather than the full set (Box et al., 1978). Due to logistic Authors Galvez and Resurrection are with the Center for Food Safety & Quality Enhancement, Dept. of Food Science & Tech- nology, Univ. of Georgia, Georgia Agricultural Experiment Sta- tion, Griffin, GA 30223-1557. Author Ware is the with Georgia Agricultural Experiment Station, 209 Conner Hall, Univ. of Geor- gia, Athens, GA 30602. 378-JOURNAL OF FOOD SCIENCE-Volume 59, No. 2, 1994 and time constraints, it was necessary to conduct experiments in in- complete blocks. The design used was generated by a computer soft- ware program, E4, developedby Evolutionary Software, Inc. (1991). Five factors (two ingredient andthree process) at three levels each were studied which included amount of gelatinized starch (x1), mois- ture content of the final dough (x2), cooking time (xX), holding tem- perature (x,,), and holding time (x5). The experimentalranges of factors (Table 1) were established either from preliminary experiments or from published values. The design had 50 treatmentsin 10 incomplete blocks with 5 treatments/block (Table 2). Preparation and processing Mungbeans (Vigna radiata (L.) Wilczec) obtained from Adams- Briscoe Seed Co. (Jackson, GA) were stored at 7°C until used. Starch was extracted from mungbean seedsas described earlier (Galvez and Resurrection, 1993). Noodles were prepared by the method of Lii and Chang (1981). The required portion of starch was gelatinized in water by heating the mixture in boiling water for 5 min with contin- uous stirring until a translucent slurry was obtained. This was mixed with the remaining dry starch and water to form a dough or slurry in a Hobart mixer Model M-SO (Hobart Corp., Troy, Ohio) (total of 3 min at Speed 1 and 1 min at Speed 2 using the flat beater). The moisture content of the mixture was adjusted to the assigned level. The sIurry or dough was extruded directly into boiling water. An apparatusdesigned and fabricated for extrusion of the products was utilized using high-pressureN2 gas (Galvez, 1992). The noodles were cooked and immediately cooled in tap water, drained and held at the required temperature for the period of time. These were equilibrated in cold tap water for 2 hr and dried in a forced-air oven at 40°C for about 6 hr until dry. Productswere stored in plastic bags at ambient temperature until needed for tests. Physical measurements Test materials. Noodles (50g) were soaked in 750 mL cold tap water for 5 min, drained, and cooked in 1.5L boiling water for 5 min, as determined in preliminary tests for doneness.The cooked noodles were immediately cooled in cold tap water for 1 min and drained. Physical measurements of instrumental texture (maximum cutting stress and work to cut), solid loss during cooking and transparency were determined on both processed samples and commercial controls. Instrumental texture measurement. The maximum cutting stress and work to cut were measured by a cutting test using the In&on Universal Testing Instrument model 1122 (Instron Inc., Canton, MA) that was fitted with a 2-kg load cell and a fabricated stainless steel flat blade (width = 38 mm, height = 78 mm, thickness = 0.46 mm). The full scale was 50 g and the crosshead and chart speeds were both set at 100 mm/min. The tests were done on single noodle strands placed on a sample holder (Galvez, 1992). This test was conducted in triplicate. Table 1 -Factors and levels studied to determine effects of starch, mois- ture and process variables on physical properties of mungbean noodles Levels Factors Symbols 1 2 3 Amount of gelatinized Xl 4.0 4.5 5.0 starch (% total starch) Moisture content of X2 50 55 60 final dough (%) Cooking time (set) X3 20 40 60 Holding temp (“C) X4 -18 -5 a Holding time (hr) X5 18 27 36