Marcela P. Tolaba

Effects of drying conditions on head rice yield and browning index of parboiled rice

Abstract Long-grain paddy of intermediate amylose content was parboiled by steaming to obtain samples of gelatinized rice. The drying was performed in two stages with an intermediate tempering time between drying steps. The variables of the drying process were air temperature, tempering time and initial moisture level for tempering treatment. The quality of parboiled rice was measured as head rice yield and browning index (BI). The values of head yield were confined in a narrow segment, 68–74%, it was observed that temperature has a negative influence on head yield while tempering time affects it positively. The BI was mainly affected by air temperature. Tolerable light yellow parboiled rice was obtained using air temperature of 70°C or below. Based on response surface methodology (RSM) it was obtained a second order polynomial model which describes satisfactorily the effects of drying conditions on head parboiled rice yield and BI.

Amaranth Milling Strategies and Fraction Characterization by FT-IR

Amaranth nutritional value has been widely recognized, but the required conditions for its processing cannot be adapted to traditional technologies. For the proposal of alternative strategies, the changes of several components should be understood. Enriched starch and lipid–protein fractions of amaranth flour upon different milling treatments were obtained and characterized by attenuated total reflectance–Fourier transform-infrared spectroscopy. Starch- and lipid–protein-enriched amaranth fractions were obtained by abrasive milling; amaranth starch was isolated by wet-milling procedure, and flour samples were obtained from planetary ball milling. Changes on starch, protein, and lipids relative contents, on starch crystallinity and on lipids and protein stability after milling and 6-month storage, were evaluated. The Fourier transform-infrared (FT-IR) spectroscopy peaks of the main grain components were identified in the middle-infrared range. By calculating the ratios between height intensities of selected specific peaks, several characteristics of the samples could be explained: increased protein content and lipid proportion of the enriched fraction; decrease of the starch crystallinity degree by abrasive milling and especially by ball milling due to starch amorphization during these processes; and lipids modification in milled and in 6-month aged samples. FT-IR analysis can be considered a rapid, nondestructive, solvent-free, sensitive, and useful tool to investigate starch, lipid, and protein modifications provoked by processing and storage as well as to determine, based on intensity ratio, the relative proportion of grain components within amaranth milling fractions. The abrasive milling associated to planetary ball milling to obtain modified different fractions is presented as an interesting strategy for the processing of amaranth grain.

Comportamiento reológico de la fracción proteíca del grano de amaranto extraída mediante molienda húmedo-ácida

Interest in the grain amaranth has increased in recent years due to its great potential as a functional food. The investigation showed the effect of soaking conditions in an acid atmosphere (temperature and concentration of SO2 ) on thermo-viscoelastic behavior of the protean fraction (FP) of the amaranth grain. It used a 32 factorial design, involving two factors: temperature (40-60°C) and concentration of SO2 (0,01-0,1% w/v). By the same way, it used a dynamic oscillatory rheometry, with heating and cooling cycles (25-90°C), tempered at 90°C, and followed by a frequency sweep (0,1 to 10 Hz) at a constant temperature. The viscoelastic module (MV) and the thermal properties were affected by both factors, with significant interaction effects. Mechanical FP spectra were previously denatured by sweeping from 0,1 to 10 Hz at 25°C, and constant (0,5%) deformation. The results revealed the formation of gels whose character depends on the soaking conditions. The different conditions of maceration caused different degrees of denaturation of the protein components, which influenced the rheological behavior