Genetic variation in color of sweetpotato flour related to its use in wheat-based composite flour products

Sweetpotato flours vary widely in color depending on genotype, and when used in wheat-based composite flours, they will impart characteristic colors which may be favorable or unfavorable for particular food products. Sweetpotato flour (SPF) was prepared from 44 genotypes and analyzed for proximate composition and biochemical properties. The Hunter Color L*, a*, b* values of the dry SPF and their modified Pekar slicks (PS) with water and with alkali were measured. Polyphenol oxidase activity, α-amylase activity, and total sugar were significantly correlated to L* values of dry SPF and of their PS tests with water and with alkali. The yellow pigment level was significantly correlated to the yellowness (b*) of the dry flour and of the PS test with water, but less correlated to b* of the PS test with alkaline. The results indicated a complex biochemical basis to SPF color, and no single biochemical factor examined was adequate to predict the color of a food product made from SPF. However, the PS color parameters were highly correlated with the color of dough sheets for white-salted and yellow-alkaline noodles made from wheast and sweetpotato composite flour (75:25). Thus, the simple modified PS test could be used in screening of genotypes for color stability and suitability for a specific end-use. SPF genotypes conferred a wide range of colors on composite flour dough preparations. Some colors, particularly the range of greens and bright orange, may be useful in specialty product development.link_to_subscribed_fulltex

pH dependent amylase activity and pasting properties of sweet potato flour and wheat- Sweet potato composite flours

Differences in pasting profiles (measured with a Rapid Visco-Analyser, RVA) of sweet potato flour (SPF) of 4 different genotypes were due mainly to differences in diastatic activity. Furthermore, at 25% (w/w) substitution of SPF with wheat flour, the pasting of the composite flour was greatly altered compared to 100% wheat flour. Addition of 25% (w/w) CL-946-25 flour, an SPF with high amylase activity, decreased the peak viscosity (PV) by 60%, but addition of 25% CL-1489-89, an SPF with minimal amylase activity, lowered the peak viscosity by only 24%. This sensitivity of wheat starch to sweet potato amylases is a major constraint to its use in composite flours. Composite flours pasted over a pH range of 3 to 11 showed marked differences in the pasting parameters. At pH 4 and at pH 10-11, there were no significant differences in the pasting profiles of the SPF composite flours as compared to all-wheat flour, due to amylase inhibition under extreme pH conditions. Composite flours with added mercuric chloride (20 ppm) (an amylase inhibitor which did not alter the pH of the flour slurry) showed no significant differences in pasting profiles compared to composite flours to which various acidulants were added. Thus food additives such as ascorbic acid, HCl and lactic acid can be used in some cases to reduce the effect of amylases. Where end-product quality would be adversely affected by low pH, screening for sweet potato varieties with minimal amylase activity would be appropriate and can be done using the RVA. Screening for this purpose should be done at around pH 6 where the sweet potato amylase activity is at the optimum.link_to_subscribed_fulltex

Bihon-type noodles from heat-moisture-treated sweet potato starch

Sweet potato starch (SPS) has limited uses in the Philippines, but modification of its properties may make it more suitable for use in traditional products that normally use other types of starch. Heat-moisture treatment was applied to native SPS (HMTSPS), which was used as a substrate and composite with maize starch (MS) to produce bihon-type starch noodles. Preliminary quality scoring showed that acceptability scores of raw starch noodles, plain boiled, and sautéed noodles made from 100% HMTSPS and 50% HMTSPS:50% MS were not significantly different from the commercial bihon. However, consumer testing is recommended to further validate acceptability of the sweet potato for bihon.link_to_subscribed_fulltex