Physico‐functional and antioxidant properties of purple‐flesh sweet potato flours as affected by extrusion and drum‐drying treatments

Effects of extrusion and drum‐drying treatments on physico‐functional and antioxidant properties of flours prepared from purple‐flesh sweet potato were evaluated. Extrusion variables were feed moisture contents (MC; 10%, 13%, 16%) and screw speeds (SS; 250, 325, 400 r.p.m.), whereas drum‐drying was done at 120, 130 or 140 °C. Effects of MC were generally greater than SS on flour properties. Extruded flours showed higher water absorption and water solubility indices compared with control nonextruded flours. Regardless of SS, total phenolic content and antioxidant activities (DPPH and ABTS) of flours processed at 10% MC were significantly higher than those at 13% and 16%. Both extruded and drum‐dried flours exhibited no peak viscosity, indicating complete gelatinisation of starch. Maximum phenolic content and antioxidant activities of drum‐dried flours were obtained at 140 °C. Although drum‐dried flours had higher antioxidant capacity than extruded flours, both flours could potentially be used as food ingredients.     

Viscoelastic properties and pasting characteristics of fermented maize: influence of the addition of malted cereals

Investigations were conducted on the viscoelastic properties and pasting characteristics of fermented maize with malted cereals and their suitability for infant feeding. A 3 × 3 × 2 factorial experimental design with malting time, cereal malt concentration and cereal type was used. Maize, millet, and sorghum malts were added to fermented maize to reducing its bulk density. Samples were analysed for their viscoelastic properties and pasting characteristics using Brabender Viscoamylograph. Sorghum malt in comparison to millet and maize malts was not effective in terms of lowering the hot and cold paste viscosities of the fermented maize. Maize and millet malts liquefied the dough considerably during both the hot and cold paste viscosities. The effect of 4‐day malted millet was most pronounced whilst the highest activity of maize malt was observed with the 3‐day malted flours. The addition of maize and millet malts to fermented maize were most effective in lowering the viscoelastic properties of the resulting porridges.     

Evaluation of functional,antinutritional, pasting and microstructural properties of Millet flours

In the present study finger and pearl millet grains were milled and sieved to obtain flour. The flours were evaluated for chemical composition, nutritional, antinutritional, pasting and micro structural properties. Significant difference (p < 0.05) in nutrient and antinutrient contents was found among the millet flours. Protein, ash and fiber content of millet flours vary from 7.3 to 8.0 g/100 g, 2.73 to 5.16 g/100 g and 3.03 to 3.05 g/100 g. Results obtained for antinutrient factors in finger and pearl millet flours were (3.5 mg/g) and (2.2 mg/g) for tannic acid and (6.1 mg/g) and (9.2 mg/g) for phytic acid respectively. Mineral availability of pearl and finger millet flour (mg/100 g) was (109.2–139.2), (0.73–4.2), (1.18–8.7.0), (15.03–17.36) and (67.53–30.03) for calcium, zinc, iron, sodium and potassium respectively. Finger millet flour showed higher peak viscosity, breakdown, final and set back value compared to pearl millet flour. Findings from the scanning electron microscopy analysis showed microstructural differences in both millet flours. FTIR analysis showed that both finger and pearl millet flours possessed O–H and C–H compounds.     

Rheological and textural properties of lafun,a stiff dough,from improved cassava varieties

We studied the textural and rheological (viscoelastic) properties of fresh lafun dough, a fermented cassava product, and their changes during storage at 45 °C for 5 and 24 h, in order to determine after-cooking storability. Lafun flours were produced from three types of cassava varieties: seven improved white-fleshed varieties, seven improved provitamin A carotenoids (pVAC) varieties and two local white-fleshed varieties; and processed into lafun doughs. Pasting properties of the flours were assessed. Flours from local varieties had pasting profiles with highest viscosities, while pVAC flours had the lowest. The three types of cassava varieties varied significantly in most of their pasting properties. Four promising improved varieties were identified, based on high peak viscosity (55.8–61.5 P) and stiffer texture than local varieties during storage. Undesirable varieties were also found, which softened during storage instead of hardening. Optimum texture of lafun dough was obtained after 5 h of storage.     

Storage and loss moduli for various stiff porridges

Stiff porridges were prepared from composite flours of maize, sorghum, Bulrush millet and cassava. Cylindrical samples of stiff porridges of 1 cm in diameter and 1 cm long were made and vibrated on a rheolograph at a constant frequency of 3 Hz. The corresponding storage and loss moduli for each composite sample were recorded, and the loss factors were computed. Bulrush millet stiff porridge had the highest storage and loss moduli compared to other porridges. Cassava had the highest loss factor, suggesting that more energy would be spent in chewing the stiff porridge in the mouth. Addition of cassava flour into composite flours resulted in the reduction of both storage and loss moduli in all cases, levelling off at about 30% cassava.     

STUDIES ON COMPARATIVE MALTING CHARACTERISTICS OF SOME TROPICAL CEREALS AND MILLETS

Malts prepared from some of the tropical cereals and millets were evaluated for their suitability in weaning food formulations. Pearl millet and finger millet malts exhibited high α-amylase activity within 2–3 days of germination, while maize, sorghum, wheat and triticale malts showed high enzyme activity after 4–5 days of germination. Malting drastically lowered the paste viscosity of cereal flours especially millet. Finger millet malt had desirable flavour and taste besides high amylase activity. Wheat and triticale malts also had acceptable flavour. Rice malt was bitter and pearl millet malt developed rancid odour and bitterness within a week after preparation.     

Production of high energy density fermented uji using a commercial alpha-amylase or by single-screw extrusion

The effects of alpha-amylase and extrusion on the viscosity and energy density of uji, a spontaneously fermented thin porridge from different combinations of maize, finger millet, sorghum and cassava, were investigated. Fermentation alone was not able to reduce the viscosity of uji, but addition of 0.1-2.1 ml/100 ml alpha-amylase to the fermented slurry or extrusion of the fermented and dried flour at 150-180°C and a screw speed of 200 rpm reduced the viscosity of 20 g/100 ml uji from 6000-7000 to 1000-2000 cP, measured at 40°C and a shear rate of 50 s⁻¹. The amount of flour required to make uji could thus be increased by a factor of 2.0-2.5 and consequently it was possible to produce uji with acceptable energy densities (0.6-0.8 kcal/g) for child feeding.     

Physicochemical and pasting properties of maize flour as a function of the interactive effect of natural-fermentation and roasting

The effect of natural-fermentation and roasting on maize physicochemical and functional properties were evaluated. Natural fermented maize seeds were soaked for variable times (0, 24 and 48 h) and directly decorticated or roasted before milling into flour. Generally during the 24 to 48 h natural fermentation, total sugars (80.3–92.0 g/100 g) and proteins contents (4.0–7.6 g/100 g) decreased while they significantly increased with soaking. Soluble sugars content of the unroasted maize significantly decreased with fermentation while that of roasted maize significantly increased. Reverse observations were made on soluble proteins. The antinutrients (phytates and total polyphenols) contents of the grains as well as the functional properties of their flours were observed to have been significantly changed following fermentation and roasting. In particular the least gelation concentration (6 to 18 g/100 mL), an important reverse index of gelating power significantly increased with fermentation and roasting. As consequence the viscosity of the fermented maize flours were systematically significantly lower than that of the unfermented flour. Generally while the effects of duration of fermentation and roasting on the viscosity were not consistent, the 48 h natural fermented and roasted flour was observed to particularly produce flours of much lower viscosity. This highlighted the positive effect of combining fermentation and roasting to improve the quality of weaning flour made from maize.     

Functional Property Changes in Partially Defatted Peanut Flour Caused by Fungal Fermentation and Heat Treatment

Changes in functional properties of flour made from partially defatted peanut fermented with Rhizopus microsponrus var. oligospoms and treated with steam were investigated. An ester-like aroma was detected in fresh fermented peanut and soy sauce or meat-like flavors were detected in dried fermented peanut. Nitrogen solubility (pH 4.0–6.0), emulsion capacity and viscosity. water adsorption, and water and oil retention of flours were slightly increased as a result of fermentation. Steam treatment of nonfermented and fermented peanut flours for up to 45 min enhanced some functional properties.     

Influence of enzyme active and inactive soy flours on cassava and corn starch properties

The aim of this work was to study the influence of enzyme active and inactive soy flours on the properties of cassava and corn starches. Four starch/soy flour composites were evaluated: cassava/active soy flour (Cas/AS), cassava/inactive soy flour (Cas/IS), corn/active soy flour (Corn/AS) and corn/inactive soy flour (Corn/IS). Starch gelatinization occurred at 58.67°C for Cas and at 64.19°C for corn; gelatinization occurred at higher temperatures when soy flours were present, while ΔH diminished. The presence of AS reduced 80% the retrogradation enthalpy of Cas and 40% that of corn. Cas presented lower pasting temperature than corn starch (67.8 and 76.8°C, respectively) and higher peak viscosity (427.9 and 232.8 BU, respectively). The pasting properties of both starches were drastically reduced by soy flours, and this effect was more noticeable in Cas; AS had higher effect than IS. X‐ray diffraction pattern of retrograded samples showed that both starches recrystallisation (mainly that of Cas) was reduced when AS was added. Tan δ values decreased with AS addition to corn, but they increased when added to Cas. The images obtained using confocal laser scanning microscopy (CLSM) showed that IS was distributed as large aggregates, whereas AS distribution was more homogeneous, especially when incorporated to Cas. These results show that cassava starch interacts specifically with active soy flour (AS, mainly in native state). The delaying effect of AS on cassava starch retrogradation was clearly shown. This finding could be useful in obtaining gluten‐free breads of high quality and low retrogradation rate.     

Changes in characteristics of sweet potato flour prepared by different drying techniques

The changes occurring in the characteristics of sweet potato flour as a result of processing were investigated. Pasting behaviour of drum dried and hot air-dried sweet potato flour was determined using Rapid Visco-Analyser. The pasting characteristics decreased due to gelatinization of starch during processing. The degradation of starch by amylases during hot air drying further lowered the water binding capacity/viscosity and total amylose and increased the digestibility compared to those of drum dried and native flour. Swelling power and solubility of the flours increased as a result of processing which subsequently increased with increase in temperature. Scanning electron micrographs of starch granules showed tendency of clustering, especially in drum dried samples. X-ray diffraction patterns showed alteration from Ca-type to V-type with a marked reduction in crystallinity index as a result of processing. The ¹³C NMR spectra of processed starches showed reduced peak intensities and line widths due to depolymerizing effects, and also pointing to their change in crystallinity.     

Pasting,thermal, gel texture,resistant starch and colour properties of unripe banana flour from 10 desert banana varieties cultivated in South Africa

Unripe banana flour is a potential commercial ingredient in various food products for increased resistant starch and reduced gluten contents. In the present study, the pasting (rapid visco-analysis), gel texture (penetration test), thermal (differential scanning calorimetry), colour (tri-stimulus colour indices) and the resistant starch properties of unripe banana flour produced from different dessert banana varieties (n?=?10) cultivated in South Africa, were analysed and juxtaposed to wheat and maize flour. The functional properties varied significantly (p?≤?0.05) between banana varieties, and from wheat and maize flours, to various extents. Selected functional property ranges of unripe banana, wheat and maize flours, respectively included; flour colour index (63.16–76.42, 77.34 and 80.96), paste viscosity (405.5–556.6, 124.7 and 115.6 RVU), gelatinization temperature (64.67–71.21, 71.11 and 69.95?°C), gel firmness (7.24–11.44?×?10^??2 N, 3.49?×?10^??2 N and 6.56?×?10^??2 N) and resistant starch content (19.9–47.4, 2.8 and 2.2% w/w). Multivariate analysis (principle component analysis) showed that the unripe banana flours from different varieties were distinguished from each other based on the pasting temperature. The unripe banana flours were distinguished from both wheat and maize flour based on breakdown and peak paste viscosities. The breakdown viscosity was the most positively related measure to the resistant starch content with a linear regression R-squared value of 0.898, indicating a significant role played by granule structure in resistance to enzymatic hydrolysis. The present research demonstrates that selection of appropriate dessert banana variety is important when replacing staple flours (wheat and maize) with unripe dessert banana flour as a functional ingredient.     

Processing Factors Affecting the Yield and Physicochemical Properties of Starch from Cassava Chips and Flour

Three processing factors, namely, raw materials type (RMT) (i.e. chips and flour) and raw material drying mode (RDM) (i.e. sun‐ and oven‐drying at 55 °C) were related to the yield and some physicochemical properties of starch in a 2³ factorial experiment. The quality characteristics investigated were: moisture content, pH, crude fiber content, peak viscosity and pasting temperature. Starch yields from oven‐dried chips and flour were significantly higher (at 5%) than from sun‐dried materials. The optimal yield of 55.9 g (per 70 g of dried product or 79.9%) was obtained from oven‐dried starch extracted from oven‐dried flour. The peak viscosities (PV) of starches extracted from flour and chips were similar while the observed pasting temperatures of flour‐extracted starches were not significantly different from those derived from chips.     

In-vitro multienzyme digestibility of protein of some plant source flours blended with bovine plasma protein concentrate

The in-vitro multienzyme protein digestibilities of the flours of maize, cassava, pigeon pea (Cajanus cajan), African yambean (Sphenostylis stenocarpa) and bambara groundnut (Vigna subterranea), blended with bovine plasma protein concentrate were investigated. The multienzyme system consists of trypsin, chymotrypsin and peptidase. It was found that the addition of bovine plasma protein concentrate improved the protein digestibility of the flours compared with flours without the additive. The digestibilities were increased by between 3% in bambara groundnut blended flour to about 10% in cassava blended flour. When the flours were wet-heat treated, the digestibilities further increased in all samples with increments between 7·5 % in bambara groundnut and 16·6% in cassava flour. Bovine plasma protein concentrate may be a good source of protein for the fortification of protein-deficient foods, particularly maize and cassava flours.     

Whey Protein Concentrate Fortified Baked Goods from Cassava-Based Composite Flours: Nutritional and Functional Properties

Composite flours are extensively used in the bakery industry to develop designer food products, having specific nutritional or functional properties. Though rich in carbohydrate, cassava flour has not been properly exploited for making bakery products, mainly because of its low protein content contributing to poor dough characteristics. Induced malting using amylolytic enzymes and pregelatinization through hydrothermal cooking were tried to modify the textural and functional attributes of cassava flour, which was then blended with various cereal and legume additives as well as rice bran and used for making two baked products such as muffins and biscuits. Whey protein concentrate (WPC) was added to fortify protein in all the formulations. Pseudo-malted cassava flour-based muffins and biscuits had lower starch content (36–44% and 36.5–41.2%, respectively) than similar products from unmalted cassava flour (39–46% and 43.75%, respectively). The crude protein content of the muffins and biscuits from WPC fortified composite mixes ranged from 7.96% to 14.36% and 9.63% to 11.00%, respectively, which was significantly higher than the native cassava flour (1.30%). Besides, the total dietary fiber could be enhanced to the extent of 1.54–3.10% in muffins and 1.70–2.61% in biscuits, through fortification with cereal and/or legume flours or bran sources, which is also considerable when compared to only 0.435% in native cassava flour. In vitro starch digestibility was the lowest for cassava (unmalted)-/rice bran-based muffins (25.02 units) and cassava (unmalted)-/finger millet flour-based biscuits (36.08 units), indicating the potential of these combinations for making therapeutic baked products for obese and diabetic people. Spread ratio and spread factor were the least (9.27 and 60.99, respectively) for the biscuits made with unmalted cassava/finger millet mixes, while use of Termamyl pseudo-malted cassava/finger millet raised the spread ratio to 11.11 and spread factor to 73.09.     

Effect of Acid‐Methanol Treatment on the Physicochemical and Structural Characteristics of Cassava and Maize Starches

Physicochemical, structural and morphological characteristics of maize and cassava starches treated with 0.36% concentrated HCl in anhydrous methanol at 54ºC for 1–8 h were analyzed and compared. Average yield of modified starch was about 97% for both starches. The solubility of the acid‐methanol treated starches increased with temperature and after 3 h of treatment reached 93% for maize starch and 97% for cassava starch at 95ºC. After 8 h of treatment, the average size of the cassava starch granules decreased from 14.9 to 11.1 µm. The action of acid‐methanol on the maize starch was more subtle, reducing the granule average size from 11.8 to 11.3 µm. Scanning electron micrographs showed that the granule surfaces were rough and exfoliated after treatment suggesting exocorrosion that was more evident for cassava starch. From GPC, it was noted that amylose and amylopectin were partially degraded during treatment. Starch crystallinity gradually increased with duration of treatment. The amylose content decreased from 21.4 to 18.8% and from 26.3 to 23.0% and the intrinsic viscosity was reduced from 2.36 to 0.21 and from 1.85 to 0.04 for cassava and maize starches, respectively. The gelatinization temperatures increased whereas pasting viscosities decreased with reaction time, especially for cassava starch. These results suggested that the attack of acid‐methanol, which was more effective on cassava starch granules, occurred preferentially in the amorphous areas located in the granule periphery and composed of amylose and amylopectin.     

Changes During Accelerated Storage in Millet–Wheat Composite Flours for Bread

Two millet–wheat composite flours, CF1 and CF2, were formulated based on the rheological and textural properties of dough using response surface methodology. The optimized contents of composite flour CF1 were 61.8% barnyard millet flour, 31.4% wheat flour, and 6.8% gluten, respectively. The optimized components of the composite flour CF2 were barnyard millet flour 9.1%, finger millet flour 10.1%, proso millet flour 10.2%, and wheat flour 70.6%. Millet–wheat composite flours were stored in three different packaging materials, namely, low-density polyethylene (LDPE), high-density polyethylene (HDPE), and metallized polyester (MP), at 90% RH and 40 °C temperature for 90 days. For the packaging of millet–wheat composite flour CF1, MP was found best among the tested packaging materials, where moisture gain in samples was minimum (55%) as compared with materials LDPE (124%) and HDPE (100%). Vitamin loss among the different packaging materials was not significantly different at the 5% level of significance. The shelf lives of the composite flours were estimated based on their critical moisture contents. After 90 days of storage of CF1, the highest retention of starch (91.85%) was recorded in MP packaging followed by HDPE (87.5%) and LDPE (84.8%). However, in CF2, the retention was not significant in all three packaging materials (P?相似文献   

Effects of protein removal on the physicochemical properties of waxy maize flours

The effects of protein removal on the physicochemical properties of waxy maize flours were investigated. Protein removal caused significant reduction in the P and S contents of starches. Starch granules had a smoother surface and low protein content (<6 g/kg) compared with the flours. Both flours and starches had a typical A‐type X‐ray diffraction pattern, with a crystallinity range of 29.8–32.2% and 27.7–30.6%, respectively. Flours had higher swelling power and solubility, and lower light transmittance than starches. The gelatinization enthalpy and onset temperature of starches were higher compared with those of their counterpart flours. The retrogradation of flours was significantly greater compared with that of starches. Protein removal increased the peak viscosity, trough viscosity, final viscosity, and breakdown, whereas it decreased the setback and pasting temperature. Genotypic differences in those maize were related to the physicochemical characteristics of the flours and starches.     

Effect of amylase-rich flour (ARF) treatment on the viscosity of fermented complementary foods

Grains of cowpea and maize and slices of fresh cassava, cocoyam, plantain, and yam were steep-fermented in water, while flours from the same plant materials were fermented by backslopping for 24 to 30 hours. The pH and apparent viscosity of the gruels from the resulting flours were determined. Loss in weight due to fermentation was higher in fresh tubers than in dry grains. The pH of the flours decreased during fermentation. Measurements showed that the apparent viscosity only of gruels from flours produced by backslopping decreased after 24 hours. The apparent viscosity of gruels from steep-fermented flours was higher than that of the unfermented flours and those produced by backslopping. The apparent viscosity reduction of gruels from steep-fermented flours using amylase-rich flour (ARF) from five-day white sorghum malt was better with the prepared gruels than when applied to the flour-in-tap-water suspension before it was used to prepare gruels. Viscosity reduction using ARF was also better with the fermented gruels than with gruels from unfermented flours. The implications of these results for the formulation of complementary flour blends for infant feeding are discussed.     

Thermo‐physical properties of composite bread dough with maize and cassava flours

Composite wheat–cassava and wheat–maize flours were produced in ratio 100:0. 60:40, 50:50, 40:60 and 0:100 respectively. Thermo‐physical properties of bread dough were determined. For wheat –cassava composite bread dough, moisture content ranged between 44.02 ± 2.04 to 51.31 ± 2.99% dry basis (db), density (1035.2 ± 20.4 to 975.6 ± 12.6 kg m^?3), specific heat capacity (2.51 ± 0.61 to 3.01 ± 0.42 kJ kg^?1 K) and thermal conductivity (0.362 ± 0.13 to 0.473 ± 0.12 W mK^?1). While wheat–maize mixture gave 44.14 ± 1.94 to 45.09 ± 1.26%(db) of moisture content, 981.4 ± 16.3–960.4 ± 22.5 kg m^?3 density, 1.77 ± 0.17–2.61 ± 0.63 kJ kg^?1 K specific heat capacity and 0.36 ± 0.07–0.39 ± 0.02 W mK^?1 thermal conductivity. Effects of substitutions was significant on moisture content and thermal conductivity of dough while non significant influence was recorded on density and specific heat capacity at P < 0.05.