The Properties and Tortilla Making of Corn Flour from Enzymatic Wet-Milling.

Corn flour was prepared by wet-milling with the treatment of neutral protease and the gelatinization, thermal and rheological properties were analyzed. Tortilla was prepared with enzyme treated corn flour (ECF) and additives (xanthan gum and cassava starch) and the properties were analyzed. Compared with dry-milling corn flour (DCF) and wet-milling corn flour (WCF), the ECF had less average particle size (16.74 µm), higher peak viscosity and higher final viscosity of 2997 cP and 3300 cP, respectively. The thermal properties showed that ECF had higher ∆H and lower To, Tp and Tc. The G' of ECF gel (6%, w/w) was higher than that of DCF gel and WCF gel. Dynamic viscoelastic measurement indicated that the tortillas made of ECF had lower G' and G″ over the frequency range (0.1-100 rad/s) after adding xanthan gum and cassava starch. The gel structure of tortillas made of ECF was homogeneous in distribution of pores. The gelatinization, thermal and rheological properties of corn flour were improved by addition of neutral protease. The addition of xanthan gum and cassava starch helped to make the tortilla with porous structure and good sensory quality.

Effects of Heat-Moisture Treatment on the Digestibility and Physicochemical Properties of Waxy and Normal Potato Starches.

Heat-moisture treatment (HMT) is a safe, environmentally friendly starch modification method that reduces the digestibility of starch and changes its physicochemical properties while maintaining its granular state. Normal potato starch (NPS) and waxy potato starch (WPS) were subjected to HMT at different temperatures. Due to erosion by high-temperature water vapor, both starches developed indentations and cracks after HMT. Changes were not evident in the amylose content since the interaction between the starch molecules affected the complexation of amylose and iodine. HMT increased pasting temperature of NPS from 64.37 °C to 91.25 °C and WPS from 68.06 °C to 74.44 °C. The peak viscosity of NPS decreased from 504 BU to 105 BU and WPS decreased from 384 BU to 334 BU. The crystallinity of NPS decreased from 33.0% to 24.6% and WPS decreased from 35.4% to 29.5%. While the enthalpy values of the NPS declined from 15.74 (J/g) to 6.75 (J/g) and WPS declined from 14.68 (J/g) to 8.31 (J/g) at 120 °C. The solubility and swelling power of NPS decreased while that of WPS increased at 95 °C. Due to the lack of amylose in WPS, at the same HMT processing temperature, the reduction in peak viscosity of treated WPS compared to that of native starch was smaller than that of NPS. The resistant starch (RS) content of NPS after HMT at 120 °C was 73.0%. The slowly digestible starch (SDS) content of WPS after HMT at 110 °C was 37.6%.

Effect of Amylose and Crystallinity Pattern on the Gelatinization Behavior of Cross-Linked Starches.

Starches from normal maize (NM), normal potato (NP), waxy maize (WM), and waxy potato (WP) were cross-linked with seven different concentrations (0.01, 0.05, 0.1, 0.5, 1, 5, 10%) of sodium trimetaphosphate and sodium tripolyphosphate. The use of low-amylose WM and WP as well as A-crystalline maize and B-crystalline potato starches can determine the influence of the amylose content and crystallinity pattern on the cross-linking of starches. The results showed that the viscosity of the cross-linked starch (CLs) first increased and then deceased, and finally no viscosity was detected; WM showed no viscosity at 5% and NP at 1%. In addition, the viscosity of NM first increased and then became undetectable at 0.5%. Strikingly, the WP developed viscosity even at a 10% reagent level (RL), and it developed the highest viscosity of all samples at 1%. The starch-iodine method was a facile and high-performance method for the characterization of the cross-linking degree (CL%), having been applied to normal starches, because the increase in the CL% resulted in a decrease of iodine-complexed amylose and blue intensity. In this study, the starch-iodine method was extended to waxy starches, which stained brown with iodine, and the brown intensity decreased with the increase of the CL%. Moreover, the CL% and RL showed a linear-log relationship.

Effects of Hydrothermal and Microwave Dual Treatment and Zein on the Enzymolysis of High Amylose Corn Starch.

Resistant starch (RS) type 2-high-amylose corn starch (HACS) was subjected to simultaneous hydrothermal (25% moisture content, 90 °C for 12 h) and microwave (35% moisture content, 40 W/g microwaving for 4 min) treatment and zein (at a zein to treated starch ratio of 1:5, 50 °C for 1 h) to improve its resistance to enzymolysis. Scanning electron microscopy (SEM) highlighted the aggregation and adhesion of the composite. The average particle size of the composite (27.65 µm) was exceeded that of both the HACS (12.52 µm) and the hydrothermal and microwave treated HACS (hydro-micro-HACS) (12.68 µm). The X-ray diffraction results revealed that the hydro-micro-HACS and composite remained B-type, while their crystallinity significantly decreased to 16.98% and 12.11%, respectively. The viscosity of the hydro-micro-HACS and composite at 50 °C was 25.41% and 35.36% lower than that of HACS. The differential scanning calorimetry (DSC) results demonstrated that the composite displayed a new endothermic peak at 95.79 °C, while the weight loss rate and decomposition temperature were 7.61% and 2.39% lower than HACS, respectively. The RS content in HACS, the hydro-micro-HACS, and composite was 47.12%, 57.28%, and 62.74%, respectively. In conclusion, hydrothermal and microwave treatment combined with zein provide an efficient physical strategy to enhance the RS type 2-HACS.

Recrystallization kinetics of starch microspheres prepared by temperature cycling in aqueous two-phase system.

The recrystallization behavior of starch microspheres (SMs) prepared by temperature cycling in aqueous two-phase system (ATPS) was investigated. The SMs were carried out under the temperature-cycled treatment at 4°C, 30°C or 4/30°C for 2 to 20 days. X-ray diffraction (XRD) results showed that the crystalline structure of SMs were different from that of degraded cassava starch. Compared to degraded cassava starch, the relative crystallinity of SMs under different temperature decreased, and the increase in relative crystallinity with the storage time was observed. All gelatinization temperature parameters (To, Tp and Tc) and enthalpy of gelatinization (ΔH) of SMs decreased compared with degraded cassava starch. However, these values of SMs stored at 30°C were higher than that of SMs stored at 4°C and 4/30°C. The Avrami equation was applied to analysis the recrystallization behaviors of SMs. The stability test showed that the samples stored at 30°C were more stable than that stored at 4 °C and 4/30°C.

Dietary intakes and behaviours in pregnant women of Li ethnicity: a comparison of mountainous and coastal populations in southern China.

The aim of our study was to describe and compare nutritional status and food related behaviours in rural pregnant women of Li ethnicity as they had been divided into mountainous and costal groups by residential area. One hundred and ninety-six randomly selected healthy rural pregnant women of Li ethnicity for the mountainous group (MG), and eighty-two for the coastal group (CG) were recruited. Data were collected via demographic questionnaires, anthropometric measurements, food related behaviour questionnaires, five day dietary diaries and plasma folate tests. The mean (SD) age, years of education, and height of all participants were respectively 25.7 (3.99) years, 7.57 (2.45) years and 155 (5.04) cm, without significant group differences (p>0.05). Significant differences were shown in dietary intakes of protein, fat, carbohydrate, dietary fibre, thiamine, vitamin C, folate, potassium, sodium and magnesium between MG and CG (p<0.05). The prevalence of plasma folate deficiency differed significantly between groups (3.08% in MG vs 37.8% in CG, p<0.001). High prevalence of active or passive smoking (65.1% in MG vs 68.4% in CG), alcohol consumption (13.8% in MG vs 2.6% in CG), and betel quid chewing (19.6% in MG vs 53.9% in CG) were found in all participants. Differences in alcohol consumption and betel quid chewing rates between groups were also significant (p<0.05). In general, coastal Li pregnant women have a poorer plane of nutrition than their mountainous counterparts. Therefore, healthy diet and lifestyle education are urgently required and should be emphasised during routine prenatal care.