Effects of extrusion cooking on functional properties of mixtures of full-fat soy and sweet potato.

Full-fat soy and sweet potato were extruded at 0:100, 25:75, 50:50, 75:25 and 100:0 ratios in an Insta-Pro 600 single screw extruder operated at 180, 200, 220 rpm respectively. Functional properties: bulk density, expansion ratio, water absorption and solubility indices and trypsin inhibitor were assayed. Results showed that addition of soybeans to sweet potatoes considerably increased the protein, fat, ash and trypsin inhibitor levels of the raw material mixtures. It also led to decreases in viscosities of raw mixtures, with corresponding increases in pasting temperatures. Addition of soybean significantly (p <0.05) affected expansion ratio, water absorption and solubility indices and trypsin inhibitor but not bulk density. Variation in screw rotation speed (rpm) significantly (p <0.05) affected only water solubility index at increasing speed. Extrudates generally received severe heat treatment, rendering them applicable only in soup bases, flour mixes and breakfast foods.

Effects of extrusion cooking on some functional properties of soy-sweet potato mixtures--a response surface analysis.

Mixtures of defatted soy flour and sweet potatoes were extruded at 0:100, 25:75, 50:50, 75:25 and 100:0 ratios in an Insta-Pro 600 single screw extruder operated at 180, 200, 220 rpm. Oil (3-5%) was added into the mix before extrusion. A 5 x 32 fractional factorial central composite response surface design was adopted for investigating the variables: feed composition, % oil, and screw rotation speed (RPM). Percent oil and screw speed were randomly investigated at three levels, while feed composition was randomly investigated at five levels. Effect of extrusion cooking on functional properties: bulk density, expansion ratio, water absorption and solubility indices and trypsin inhibitor were assessed. Results showed that feed composition and screw speed had strong influences on the process. The effect of adding oil, into defatted soybean significantly (p < 0.05) affected only trypsin inhibitor content. High extrusion temperature (> 130 degrees C), and accompanying high shear, were the result of the non-pasting nature of the extrudate. Therefore the products may have limited uses.

Proximate composition and some functional properties of extrusion cooked soybean and sweet potato blends.

Mixtures of sweet potato flour and soy flour were made in a pilot mixer. They were moisturized with 18, 25, and 30% water and extruded in a single screw extruder at 80 rpm, using a die of 6mm. Extrusion temperature was maintained at 100 +/- 3 degrees C. Effects of adding soy flour into sweet potato flour, as well as variation in feed moisture on the composition and some functional properties of the extrudates were investigated. Increase in sweet potato content increased carbohydrate values. Protein increased with increase in soy flour. Feed moisture did not significantly (p < or = 0.05) affect extrudate composition. Increase in sweet potato content and feed moisture increased expansion ratio. Bulk density decreased with decrease in feed moisture, but increased with increase in soy flour. Starch content increased as sweet potato content increased. Degree of gelatinization increased with sweet potato content. Lower feed moisture enhanced gelatinization. Water absorption index (WAI) increased as sweet potato content increased. Feed moisture had a slight effect on WAI and water solubility index (WSI). Amylose increased with increase in sweet potato content. Increase in soy flour led to an increase in yellowness (b*) of extrudates.

Physicochemical properties of cissus gum powder extracted with the aid of edible starches.

Gum powder was extracted from the stem and root of the cissus (Cissus populnea Guill and perr Ampelidacae) plant using water. Extraction was facilitated by the incorporation of 25-50% edible starches of sweet cassava, sweet potato, and maize. Dry samples were milled and sieved through a 250-microm sieve. Proximate and physicochemical properties of the gum samples were determined using standard methods. Results of the proximate analyses showed that protein and ash contents of the root gum were appreciably higher than those of the stem gum. Values of the crude fiber and ether extract of the root gum were lower than those of the stem gum. Inclusion of edible starches in the extraction process appreciably lowered proximate values. Results of the physicochemical properties showed that cissus gum samples did not form true gel but a "putty-like" mass. Addition of starches at various levels did not alter the characteristic putty-like nature of the gum. The gum samples had a remarkably low oil absorption capacity. Cissus gum samples had appreciably higher emulsion capacity and stability than the samples containing starch. The pH of the cissus gum powder and those of the starch-containing samples lie in the low-acid range (5.69-6.49). Cissus gum samples were highly hygroscopic; however, the addition of starch lowered the hygroscopicity. Incorporation of 25% starch into cissus mucilage enhanced extraction of the gum without adverse alteration of the physicochemical properties.

Color of single-screw extruded blends of soy-sweet potato flour --a response surface analysis.

Blends of defatted soy flour and sweet potato flour were extruded in a single-screw extruder run at varying pre-set rotational speeds. Die diameter of the extruder was also varied. A central composite, rotatable nearly orthogonal response surface design was used in studying the interactive effects of extrusion variables on color of the extrudates. Color of raw and processed samples was determined on a DRLANGE Tricolor LFM3 instrument. Measurements were made in duplicates to obtain the CIELAB L*a*b* values. Results showed that whiteness (L*) decreased with increase in sweet potato in the blends during extrusion. Reduction in whiteness (darkening) evidenced in decreased L* values of samples was only affected by increase in sweet potatoes in the blends. Redness (a*) significantly increased as sweet potatoes content increased, which confirmed the decrease in whiteness. Yellowness (b*) also increased considerably, but as a result of the die diameter.