Kyungsoo Woo

Cross-linking of wheat starch and hydroxypropylated wheat starch in alkaline slurry with sodium trimetaphosphate

Abstract Wheat starch was cross-linked at 40 °C and pH 11.0 by slurrying the starch (30% solids) in a solution of sodium trimetaphosphate (STMP), sodium hydroxide, and sodium sulfate. The extent of cross-linking was determined by an increase in alkaline fluidity or by a decrease in alkaline clarity. Response surface analysis showed that cross-linking increased with increasing levels of STMP (0.5-1.5%, based on starch, bos) and sodium sulfate (0–4.0%, bos) over a reaction period of 120–720 min. A regression equation with first and second order terms showed that STMP and sodium sulfate concentrations and the reaction time accounted for 99% of the variability in alkaline fluidity. Wheat starch (37% slurry) was hydroxypropylated by reaction with propylene oxide (8%, bos) for 24h at 45 °C in alkali (pH 11.5) containing 16.0% sodium sulfate (bos). The hydroxypropylated (4.5wt%) wheat starch (DS 0.12-0.13) was not isolated but was cross-linked with STMP (0.1-0.5%, bos) over a 10–40 min reaction period. A comparison of pasting curves at pH 3.5 showed that some of the cross-links produced by STMP were less stable than those produced by phosphoryl chloride, indicating a low level of pyrophosphate as well as monophosphate cross-links. The less stable cross-links were diminished by changing reaction conditions with STMP.

Hot-water solubilities and water sorptions of resistant starches at 25°C

ABSTRACT Resistant starches (RS) were prepared from wheat starch and lintnerized wheat starch by autoclaving and cooling and by cross-linking. Heat-moisture treatment also was used on one sample to increase RS. The experimental resistant starches made from wheat starch contained 10–73% RS measured as Prosky dietary fiber, whereas two commercial resistant starches, Novelose 240 and 330, produced from high-amylose maize starch, contained 58 and 40%, respectively. At 25°C in excess water, the experimental RS starches, except for the cross-linked wheat starch, gained 3–6 times more water than the commercial RS starches, and at 95°C gained 2–4 times more. Cross-linked RS4 wheat starch and Novelose 240 showed 95°C swelling powers and solubilities of 2 g/g and 1%, and 3 g/g and 2%, respectively. All starches showed similar water vapor sorption and desorption isotherms at 25°C and water activities (aw) < 0.8. At aw 0.84–0.97, the resistant starches made from wheat starch, except the cross-linked wheat starch, sho...

Effect of Processing Variables on Texture of Sweet Potato Starch Noodles Prepared in a Nonfreezing Process

Starch noodles are popular staple foods in many Asian countries. Traditionally, mungbean starch has been used for making starch noodles because it provides favorable texture and appearance of the cooked noodles. However, other starches have been examined to replace mungbean starch for equivalent noodle quality because mungbean starch is expensive (Lii and Chang 1981; Singh et al 1989; Galves et al 1994; Jin et al 1994; Kim and Wiesenborn 1996). Among the starch substitutes, sweet potato starch is successfully consumed on a commercial scale in Korea, China, Vietnam, and Taiwan because it has gelling ability and eating quality similar to that of mungbean starch. The starch noodles are traditionally manufactured by dropping a thin slurry of starch into a hot water bath through small openings, thereby cooking the starch slurry into noodle strands (Kim et al 1999). After cooling, the noodle strands are frozen overnight, followed by a quick thawing in water. Freezing tends to render the chewy and elastic texture after cooking that is favored in most Asian countries. However, excess time and cost are required for freezing in this process. Recently, a similar type of starch noodles (kuzukiri) has been manufactured without freezing in Japan (Kim et al 1999). Starch slurry is cooked on a steel belt that moves into a steam chamber. The gelatinized starch is then quickly chilled and removed from the belt in a sort of elastic sheet. The starch sheet is subsequently aged in a refrigerator and then cut into thin noodle strands which are then dried in an air oven. This nonfreezing process is simple and cost-effective and produces straighter strands than the conventional methods. However, the noodles from this process are often inferior with regard to texture and quality after cooking when compared with conventional noodle products produced by freezing. In the present study, several processing parameters in the nonfreezing process for sweet potato starch noodle production were assessed in terms of effects on noodle texture and eating qualities, and optimal parameters were suggested.

In Vitro Digestion of RS4-Type Resistant Wheat and Potato Starches, and Fermentation of Indigestible Fractions

ABSTRACT RS4-type resistant wheat starch (RWS) and resistant potato starch (RPS) were subjected successively to in vitro digestion with pepsin and pancreatin-bile, and the indigestible residues (82.1% db and 74.1% db, respectively) were recovered and subsequently fermented by in vitro techniques using fresh human fecal microbiota as inoculum. Scanning electron microscopy of the indigestible residues showed surface erosion on the residual granules. Total gas production during the in vitro fermentation increased almost linearly over time with the two resistant starches exhibiting similar gas production rates, as well as a similar rate of production of total short-chain fatty acids (SCFA). The indigestible fractions from both starches produced acetate as the major SCFA and relatively higher levels of butyrate than propionate, but wheat starch tended to produce more butyrate over time than potato starch. Fractional molar ratios of acetate, propionate, and butyrate from the RWS and RPS were 0.586:0.186:0.228 a...