Physicochemical and pasting properties of maize as affected by storage temperature

Maize grains are used as raw material in various food products. In countries where the production is seasonal, the grains must be stored throughout the year in order to provide sufficient maize supply for the food industries and consumers. During storage, the environmental temperature is considered as one of the most critical variables that affects grain quality. This study aimed to evaluate the effects of various storage temperatures (5, 15, 25 and 35 °C) on the proximate composition, pH, fat acidity, percentage of grains infected by molds, grain color, protein solubility and pasting properties of maize stored for 12 months. Grains stored at 35 °C during the 12 months period showed the greatest decrease in grain yellowness, pH, protein solubility and breakdown viscosity. An increase in disulfide bonds within the protein structure and interaction between starch and non-starch components seems to be responsible for the changes in protein solubility and pasting properties determined in maize during the storage period. Fat acidity and the percentage of grains infected by visible molds were concluded to be very dependent of moisture content. The result of this study demonstrated that the minimum temperature of 5 °C was able to maintain the quality of maize stored for up 12 months.     

Physicochemical and functional properties of Caryota urens flour as compared to wheat flour

Starch digestibility, thermal, pasting and gelling properties of Caryota urens (CU) flour were investigated using wheat flour as reference. Amylose content of CU and wheat flour was 32.1% and 28.3%, respectively. CU flour had very low content of protein and lipid but had a high content of total starch (98.2%) and resistant starch (RS) [42.5%]. Gelatinisation temperature (78.5 °C) of CU flour was higher than wheat flour. Pasting behaviour of CU flour was similar to that of high swelling tuber and root and waxy starches. CU flour retrograded to a greater extent than wheat flour. Very specific gelling behaviour was noticed for CU flour where it produced significantly harder gel with high paste clarity, fracture ability, adhesiveness, gumminess and chewiness. Expected glycaemic index (eGI) of CU and wheat flour was 92.4 and 100.4, respectively. CU flour had high eGI despite high content of resistant starch.     

蜡质玉米粉的糊化特性研究

为了解蜡质玉米粉及其不同制粉方法对糊化特性的影响,测定了干磨、湿磨、挤压制蜡质玉米粉以及蜡质玉米淀粉、糯米粉的溶胀度和RVA参数。结果表明:蜡质玉米粉糊化进程中溶胀度高,水合能力强,具有较高的糊化参数。不同品种蜡质玉米粉的破损值、谷值、峰值和终黏度的变异程度较大,蜡质玉米粉的峰值与谷值、终粘度和回生值、谷值与回生值、谷值与终粘度、终粘度与回生值均呈极显著正相关。湿法制粉糊化进程中水合能力强,主要RVA参数显著高于干法制粉和挤压制粉,具备很强的成糊能力和黏滞性,干法制粉成糊后稳定较好,抗老化性较强,挤压制粉的糊化进程不明显。     

亲水胶体对面粉糊化特性和面条品质的影响

采用RVA快速黏度法、质构测定等方法研究瓜尔豆胶、魔芋胶、CMC和黄原胶4种亲水胶体对面粉糊化特性和面条品质的影响.结果表明,4种亲水胶体对面粉的糊化温度影响不显著;添加瓜尔豆胶、CMC和黄原胶面粉的峰值黏度、谷值黏度和最终黏度呈递增的趋势,添加魔芋胶的面粉的糊化性质变化不明显;添加魔芋胶和瓜尔豆胶面条的拉伸性能、切割性能呈递增的趋势;添加CMC和黄原胶面条的拉伸性能和切割性能先升高后降低;综合考虑各方面因素,4种亲水胶体均可用于面条的加工,适宜添加量为0.5%～1.0%.     

Effect of rice storage on pasting properties of rice flour

The pasting properties of rice flour following storage of the grain for up to 16 months were investigated. Storage produced changes in the RVA pasting curves of the flour as a varietal, time and temperature dependent phenomenon. The data confirm that viscograms from samples stored at 4 and 37 °C provide a valid comparison of the effects of ageing on pasting behaviour. The most significant change in the pasting curve was the decrease in BD over time and the gradual disappearance of a clearly defined peak in aged samples. Chemical (β-mercaptoethanol) and enzyme treatments (hemicellulase, cellulase and protease) of flour obtained from aged rice produced various changes in the RVA viscograms. The most notable effect was produced by protease treatment which increased PV and decreased FV of flours from aged (higher temperature storage) rice samples. Aged samples treated in this way showed a peak and trough as normally seen in fresh rice. Thus, protein appears as a key component in the ageing process.     

Effects of protein hydrolysis on pasting properties of wheat flour

Protein hydrolysis is used widely in the food industry for the purpose of improvement of food or industrial quality, and the processing exists concurrently or subsequently with starch pasting. The effects of protein hydrolysis using papain, pepsin, trypsin, and dithiothreitol (DTT) on flour pasting properties were here investigated at five set concentrations. There were notable decreases in the peak, the trough viscosity, and the integral area of the viscosity curve as the concentrations of papain, trypsin, and DTT increased. DDT and pepsin concentration did not have any effect on final viscosity. Both breakdown and setback showed significant downtrends as the concentration of papain increased but no change as DDT concentration varied. Low concentrations of papain and pepsin prolonged peak time slightly, but higher concentrations shortened it significantly. For trypsin and DTT, low concentrations increased peak time notably, but high concentrations decreased it significantly. Pasting time and temperature increased in the presence of papain, pepsin, and trypsin, more so at higher concentrations. These results supply a basis for the utilization of hydrolyzed protein in the food industry and for the further studies on the interactions between protein and starch during processing.     

Storage stability and pasting properties of hydrothermally treated pearl millet flour

Hydrothermal treatment (30 ± 2% moisture and steaming at 1.05 kg m^?2 for 0, 10, 15, 20 and 25 min) was given to whole and pearled pearl millet grains. Flour obtained after each treatment was evaluated for physical, functional and pasting properties. Flour obtained from steamed before pearling (SBP, 20 min) and steamed after pearling (SAP, 15 min) grains exhibited no lipase activity and acceptable physical, functional and pasting properties. Significant (P ≤ 0.05) reduction (28.65%) was observed in total phenol content after pearling. Tannins content of control flour was 120.3 ± 2.15 mg, and a reduction of 25.2% and 16.5% was observed after 20 and 15 min of steaming in SBP and SAP samples, respectively. Significant (P ≤ 0.05) increase in bulk density, functional properties and decrease in pasting properties of treated flour samples was observed with increase in duration of steaming. Selected flour samples (SBP, 20 min and SAP, 15 min) were found acceptable for 50 days when stored in polyethylene pouches (75 μ) at ambient conditions (15–35 °C).     

大米蛋白对大米粉糊化性质的影响

以DOM为20%的晚籼米为材料,通过利用差示扫描量热分析仪(DSC)、快速粘度测定仪(RVA)和环境扫描电镜(SEM)和测定润胀性和溶解性等方法,对添加不同梯度大米蛋白后的米粉样品的润胀性和溶解性、DSC热谱、RVA图谱和形态进行比较分析。结果表明,添加一定梯度的大米蛋白后,米粉样品的润胀性和溶解性、峰值粘度、低谷粘度、崩解值和终值粘度逐渐降低,糊化温度、回生值、峰值时间和热焓值(ΔHr)增加,大米蛋白与淀粉呈现出网状结构,表明大米蛋白能与淀粉发生相互作用,形成网状结构,实验结果说明,大米蛋白对大米淀粉的糊化和膨胀过程起着抑制作用。      

木聚糖酶对面粉糊化特性和面包品质的影响

探讨不同添加量的木聚糖酶对面粉的糊化特性、面包焙烤品质以及面包贮存品质的影响.结果表明:添加木聚糖酶对面粉的糊化温度、衰减值、回生值影响不大,但可降低面粉的峰值黏度、最低黏度和最终黏度,木聚糖酶能有效地改善面包焙烤品质,显著增加面包比容,有效改善面包的硬度和弹性,明显的降低了面包的老化程度.当木聚糖酶添加量为10 mL/kg面粉时,面包焙烤品质及贮存效果最佳.     

生物酶对玉米面粉糊化性质的影响

采用蛋白酶、脱支酶、乳酸菌胞外酶处理玉米面粉,用RVA测其糊化曲线,筛选出对糊化性质有所改善的生物酶及其用量,并分析其改良机理。结果表明:蛋白酶可明显改善原面粉的糊化性质,其回生值和破损值都减小;脱支酶的作用效果不明显;乳酸菌胞外酶在一定浓度下也可以改善面粉的糊化性质。     

大米蛋白对大米粉糊化性质的影响

以DOM为20％的晚籼米为材料,通过利用差示扫描量热分析仪(DSC)、快速粘度测定仪(RVA)和环境扫描电镜(SEM)和测定润胀性和溶解性等方法,对添加不同梯度大米蛋白后的米粉样品的润胀性和溶解性、DSC热谱、RVA图谱和形态进行比较分析 结果表明,添加一定梯度的大米蛋白后,米粉样品的润胀性和溶解性、峰值粘度、低谷粘度、崩解值和终值粘度逐渐降低,糊化温度、回生值、峰值时间和热焓值(△Hr)增加,大米蛋白与淀粉呈现出网状结构,表明大米蛋白能与淀粉发生相互作用,形成网状结构,实验结果说明,大米蛋白对大米淀粉的糊化和膨胀过程起着抑制作用.     

Physicochemical and functional properties of whole legume flour

The physicochemical, functional and pasting properties of whole flours from pinto bean, lima bean, red kidney bean, black bean, navy bean, small red bean, black eye bean, mung bean, lentil and chickpea were investigated. Significant differences in physicochemical characteristics and functional properties were observed (P < 0.05). Bulk densities, water absorption indices, water solubility indices, oil absorption capacities, emulsion activities, and emulsion stabilities ranged from 0.543 g/mL to 0.816 g/mL, 4.09 g/g to 6.13 g/g, 19.44 g/100 g to 29.14 g/100 g, 0.93 g/g to 1.38 g/g, 61.14%–92.20%, and 84.15%–96.90%, respectively. Phaseolus legume flour exhibited higher water absorption capacity, oil absorption capacity, emulsion activity, and emulsion stability compared with other kinds of legume flour. Pasting properties were significantly different (P < 0.05). Pasting temperatures and the peak, final, and setback viscosities of the flours ranged from 73.2 °C to 83.0 °C, 96.2 RVU to 216.8 RVU, 118.5 RVU to 243.8 RVU, and 28.3 RVU to 103.2 RVU, respectively.     

The effect of roasting on the nutritional and antioxidant properties of yellow and white maize varieties

Maize varieties (yellow and white) were roasted for 17 min; and allowed to cool, and later milled into powder. The nutritional evaluation (proximate composition, mineral and antinutrient content determination) and antioxidant properties investigation (reducing power, free radicals scavenging ability and Fe²⁺ chelating ability) of the product was subsequently carried out. The result of the study revealed that roasting caused a significant increase (P < 0.05) in the crude fat, carbohydrate, Ca, Na, Mg and Zn content. Conversely, a significant decrease (P < 0.05) was observed in crude protein, crude fibre, Fe and K content. A significant decrease in the phytate content was also observed. However, the reduced phytate content did not have sparing effect on Zn bioavailability. Roasting significantly (P < 0.05) reduced the extractible phenol and flavonoid content of the maize varieties. The antioxidant properties (1,1‐diphenyl‐2‐picrylhydracyl free radical scavenging ability and Fe²⁺ chelating ability) followed the phenolic content pattern. However, roasting caused a significant increase in the ferric reducing antioxidant power of the maize varieties. Thus, roasting reduced the protein content of maize but also increased the energy value and antioxidant capacity as exemplified by high reducing power.     

Physicochemical properties of rice flour as affected by alkaline soaking and washing treatments

Effects of alkaline [NaOH, saturated Ca(OH)₂ and/or limewater] soaking and subsequent washing (with water vs. without washing) treatments on physicochemical properties of rice flour were investigated. Alkaline soaking treatment generally caused a loss of granule angularity but some birefringence was observed for unwashed alkali-soaked flour granules. After soaking, protein content of the flours significantly (P < 0.05) decreased but swelling power significantly (P < 0.05) increased compared to the control (soaked in water). The washed flours had lower protein content than unwashed flours (3.77–6.87% vs. 5.26–7.87%). The NaOH-soaking treatment yielded higher swelling power and solubility, respectively, for unwashed and washed flours. Alkaline soaking increased breakdown but decreased pasting temperature, trough viscosity, final viscosity and setback of the paste compared to the control. Compared to the control, hardness of soaked flour paste was lower due to lower final viscosity and setback. Overall, physicochemical properties of rice flour could be modified by alkali-soaking and washing treatments.     

Proximate compositions, pasting and rheological properties of mumu– a roasted maize meal

Genetically improved maize variety (TZRS‐W) grains were used to produce mumu– a roasted maize meal. The grains were divided into six treatment groups namely: non‐soaked, non‐cooked (NSNC); non‐soaked, cooked (NSC); soaked, non‐cooked (SNC); soaked, cooked (SC); germinated non‐cooked (GNC); and germinated, cooked (GC). Each group was roasted in the oven at 150 °C for 1 h to produce mumu. No significant differences (P ≤ 0.05) were found in the protein, fat, ash, fibre and carbohydrate contents of the different products. Soaking and germination without cooking resulted in lower breakdown viscosities of the products. The peak viscosity (20.17 Rapid Visco Unit (RVU)) and final viscosity (28 RVU) of the GNC samples were significantly higher (P ≤ 0.05) than the corresponding values (5.17–7.25 RVU) of the NSNC, NSC, SNC, SC and GC products. No significant differences (P ≤ 0.05) were found in the pasting temperatures (63.40–64.85 °C) between all the six groups. Germination for 24 h without cooking may yield poor quality products with low nutrient density.     

Physicochemical, pasting and thermal properties of tuber starches as modified by guar gum and locust bean gum

This study was carried out in order to compare the functional characteristics of isolated starch from five tuber crops, yam, taro, sweet potato, yam bean and potato, as well as effect of guar gum (GG) and locust bean gum (LBG) on pasting and thermal properties of tuber starches. The results showed that total amylose content of five tested starches ranged from 17.85% to 30.36%. The results of pasting behaviour showed that potato starches exhibited the highest peak viscosity and yam starch presented a stable curve with little breakdown viscosity. Addition of GG and LBG resulted in a significant increase in peak, final viscosity, breakdown and setback viscosity for all tuber starches ( P  < 0.05), but a slight decrease in pasting temperature. The gelatinisation enthalpy (Δ H ) for starches with GG and LBG was slightly lower than those of the starches alone in yam and sweet potato, but not in taro and yam bean.