Physicochemical Properties and Starch Digestibility of Autoclaved-Cooled Water Yam (Dioscorea alata L.) Flour

Water yam (Dioscorea alata L.) is suitable for resistant starch high flour because of its high amylose content. The purple, yellow, and white water yams were treated by autoclaving and cooling with one, two, and three cycles to obtain resistant starch. Water yam tubers were cooked in an autoclave for 15 min, and then cooled prior to drying. Autoclaving–cooling of water yams decreased protein, fat, dietary fiber, water soluble polysaccharide, dioscorin, and diosgenin but increased amylose and sugar. The treatments significantly raised resistant starch and reduced in vitro starch digestibility that depended on water yam types, and affected starch granule morphology.     

Process Optimization by Response Surface Methodology and Characteristics Investigation of Corn Extrudate Fortified with Yam (Dioscorea alata L.)

Response surface methodology was used to investigate the optimum operation conditions of a single screw extruder and to analyze the effects of extrusion processing variables, including yam flour contents (10–30 %), moisture content (10–18 %), and screw speed (250–350 rpm) on characteristics of the corn–yam extrudates. Quadratic polynomial equations were also obtained by multiple regression analysis. The predicted models were adequate based on the lack-of-fit test and coefficient of determination obtained. By superimposing individual contour plots of the different responses, regions meeting the optimum conditions were also derived. The moisture content had critical effect on all responses variables. All the characteristic of the corn–yam extrudates evaluated were significantly affected by three process variables. Feed moisture content was the most significant variable with on most of characteristics. Increasing moisture content caused increase in bulk density, water absorption index and hardness, but decrease in radial expansion ratio. However, graphical optimization studies resulted in 21–23 %, 12–13 %, and 305–320 rpm of yam flour level, moisture content, and screw speed, respectively. The results suggested that corn extrudates fortified with yam produced by using the single-screw extruder are suitable for snack food development.     

Effect of Storage on the Pasting Characteristics of Yam Tubers

Yam is a popular root and tuber crop which is important as a dietary staple and potential export crop. Storage of yam tubers is an age long practice in yam growing communities of West Africa, while pasting characteristic is an important indicator of potential utilization of yam tubers. The study was carried out to investigate effect of storage of the tubers on their pasting characteristics. Six varieties each of D. alata and D. rotundata were used for the study. At harvest, the tubers were divided into two groups. The first group was stored in a conventional open-air yam barn for four months, while tubers in the second group were not stored. Pasting characteristics of both fresh and stored tubers were determined by Rapid Visco Analyser (RVA). The result showed that the effect of storage on the yam tubers were species dependent. In D. alata there was an increase in peak viscosity (231.36 to 257.56 RVU), breakdown (71.68 to 122.47 RVU), setback (42.58 to 65.99 RVU), while there was a decrease in most of the parameters except break-down and setback viscosities in D. rotundata. Generally, a decrease in peak viscosity, holding strength, final viscosity and peak time of the yam tubers during storage was observed, while the breakdown and setback viscosities of the tubers increased significantly (p < 0.05) on storage. The industrial implication of this is that starches of stored tubers may have high retrogradation tendencies but more resistance to shear-thinning and have more paste stability during processing.     

Water absorption as an evaluation method of cooking quality for yam (Dioscorea alata) and cassava (Manihot esculenta crantz)

Water absorption as a new method of cooking quality (hard cooking or mealy cooking) of yam and cassava cultivars determination was studied by cooking eight (08) cultivars. 30 g of each were boiled in 500 ml of water during 20 minutes and dried at 70 °C for 15 hours and 103 °C for 3 hours in a vacuum oven. Results showed that cassava and yam have different cooking quality. Dry matter content does not influence the cooking quality of yam and cassava. Mealy cooking quality of yam absorbs less water (6.6%) during cooking but looses more soluble dry matter (9.5%) during the same process. Hard cooking quality of yam absorbs much water (23.5%), but looses less soluble dry matter (3.9%). The soluble dry matter is the main parameter to determine the quality of D. alata. It stands at 9.5% ± 2.9 for mealy cooking quality and 3.9 ± 0.73 for hard cooking quality cultivars of D. alata. Water absorbed by mealy cooking cassava (27.6%) is significantly (p < 0.05) higher compared to water absorbed of hard cooking cassava (12.4%). Water absorbed during cooking is the main parameter in determining the quality of cassava cultivars. Water absorbed stands at 27.6% ± 8.8 for mealy cooked quality and 12.4% ± 1.9, for hard cooked quality of cassava cultivars. A close relation between water absorption and cooking quality was revealed to contribute to a better selection procedure for cultivars in the frame of food security.     

Effects of Cultivar and Drying Method on Color,Pasting and Sensory Attributes of Instant Yam (<Emphasis Type="BoldItalic">Dioscorea rotundata</Emphasis>) Flours

Effect of cultivar (Efuru and Abuja) and drying method (cabinet and foam mat) on color, pasting, and sensory properties of instant pounded yam flours was investigated. Color (L*, a*, b*) values of fresh and dried flour samples were measured, and deltachroma (∆C), color difference (∆E), and hue angle were calculated. Pasting properties of flour and sensory attributes of fresh and reconstituted flour were determined. Foam density of yam pastes decreased from 0.97 g/cm³ to between 0.362–0.538 and 0.308–507 g/cm³ for cultivars Abuja and Efuru, respectively. Foam-mat dried flour showed higher L*, ΔC, ΔE, and hue angle but lower a* and b* values. Peak viscosities of cabinet and foam-mat dried Abuja and Efuru were 217, 304, 377.42, and 316.50 RVU, respectively. Sensory attributes of reconstituted foam-mat dried Abuja and fresh pounded yam were not significantly different (p > 0.05). However, fresh pounded yam (8.5–8.9) and reconstituted foam-mat dried flour (7.4–8.5) samples were significantly different (p > 0.05) from the cabinet-dried (6.9–7.9) and commercial samples (7.2–7.8).     

山药淀粉的特性及应用研究

详细介绍了山药淀粉的制备与组成,并对其物理化学特性和加工特性,包括淀粉的颗粒形态、溶解度和膨胀度、凝胶特性等进行了较全面的综述.     

Volatile components of cooked tubers of the water yam (Dioscorea alata)

Volatile constituents were isolated from yams, during cooking, by concurrent steam distillation-solvent extraction. The essence which resulted was analysed by linked gasliquid chromatography-mass spectrometry (g.l.c.-m.s.) employing capillary columns and by gas-liquid chromatography coupled with sensory evaluation of the column effluent (nasal appraisal). In addition to hydrogen sulphide and a number of high-boiling fatty acids, 29 compounds, comprising seven hydrocarbons, eight alcohols, eight aldehydes, four ketones, a furan and a disulphide, were identified for the first time in yam. A further five components were tentatively identified by g.l.c.-m.s. and by thinlayer chromatography of derivatives. 4-Phenylbutan-2-one was the major constituent of the acid-free essence.     

Effects of blanching, drying and extraction processes on the antioxidant activity of yam (Dioscorea alata)

The effects of blanching, drying and extraction processes on the antioxidant activities of one kind of Taiwanese yam peel, Darsan (Dioscorea alata), were investigated. The antioxidant measurements included total phenolic content, reducing power and α ,α‐diphenyl‐β‐pricryl‐hydrazyl (DPPH) radical‐scavenging activity. The 50% ethanolic, hot water and water extracts from the peel all had much higher antioxidant activities than those extracts from the flesh. Among three extraction methods, 50% ethanolic extraction resulted in the highest antioxidant activities in the peel, while hot water extraction was more appropriate for the flesh. Blanching by immersing the peel in 85 °C water for 30 s caused significant reductions in the antioxidant activities of all the extracts from the peel. Generally speaking, freeze‐dried peel maintained higher antioxidant activities than hot air‐dried peel.     

Natural plant enzyme inhibitors. Purification and properties of an amylase inhibitor from yam (Dioscorea alata)

A high-molecular-weight α-amylase inhibitor has been isolated from mature tubers of Dioscorea alata by extraction with 0.02M acetate buffer (pH 5.0), negative absorption on CM-cellulose and ultracentrifuging. The inhibitor was fairly heat stable and was active against human salivary, human pancreatic and pig pancreatic amylases. The inhibitor had no action on Bacillus subtilis and Aspergillus oryzae amylases. Trypsin and α-chymotrypsin inactivated the inhibitor. Pre-incubation of the inhibitor with starch or concanavalin A resulted in complete abolition of its activity. Chemical modification of the amino groups with trinitrobenzene sulphonic acid led to loss of activity. The inhibitor was found to be a glycoprotein with 64% carbohydrate. The monosaccharide units present were glucose, mannose and galactose in a molar ratio of 5.5:3.8:1.     

Manufacturing of Ogi from Malted (Germinated) Corn (Zea mays):Evaluation of Chemical, Pasting and Sensory Properties

The properties of Ogi derived from malted corn using wet and dry milling processes were studied. Residual protein content of malted Ogi was slightly higher than those of Ogi. Malted dry milled Ogi retained a higher protein level. Malted Ogis gave lower amylograph maximum viscosities than nonmalted Ogis. Other pasting characteristics (starch stability, index of gelatinization and ease of cooking) were not adversely affected by malting in wet milled Ogis. Dry milled malted Ogi had lower stability and index of gelatinization values. Color, texture and flavor of malted and nonmalted Ogi porridges differed (P < 0.05). Ogi porridge and paste derived from malted grains using wet milling were acceptable (P < 0.05).     

地理标志产品绍兴黄酒与非地理标志黄酒感官评价分析的研究

根据5位黄酒国家级评酒委员对地理标志产品绍兴黄酒与非地理标志黄酒的感官品评,对其醇和度、甜度、鲜爽度、酸度、协调性进行量化评分,采用P-value假设数据统计法进行比较分析.结果表明,绍兴地理标志黄酒产品在醇和度、鲜爽度和协调性3个方面得分均高于非绍兴地理标志黄酒产品,醇和度、鲜爽度和协调性的口感指标可以作为绍兴地理标志黄酒区别于非地理标志黄酒的特征性感官鉴定指标,为黄酒鉴别进一步研究打下基础.     

水肥耦合对小麦产量及淀粉特性的影响

利用干旱棚,以洛阳1971～1999年20年的降雨量为依据,以每月占年平均降雨量的加权值进行分配,模拟不同水肥条件下对小麦产量及淀粉特性的影响.结果表明:不同降雨年型不同施肥组合有以下规律:N、P水平相同的情况下,水分高的处理产量高;在欠水年和丰水年,P肥相同的情况下,N肥高的产量低;在平水年,不同施肥水平呈现出不同变化,氮肥N105＞N0＞N210,氮肥相同水平下P84 ＞P168 ＞P0.水分是产量的主导因素.小麦产量的提高可通过协调成产3因素来实现.淀粉的峰值黏度、终结黏度、稀懈值及反弹值受水肥影响较大,而糊化温度和低谷黏度受水肥影响较小,在平水年以N105P84处理的淀粉糊化特性各参数值较高,在一定程度上改善了面条品质,而在丰水年氮肥较高的各参数的值较低.     

A Study of the Kinetics of Retrogradation in a Starch-based Dough made from Dehydrated Yam (Dioscorea rotundata L. Poir)

Changes in the physical characteristics of reconstituted, dehydrated yam (Dioscorea rotundata) flour, during storage at different temperatures, were followed by rheological tests and X-ray studies. The rate of change of these characteristics was found to be temperature dependent, decreasing with increase in storage temperature. X-ray patterns obtained were typical of those expected with tuber starches. When quantified the X-ray results agreed well with the rheological data obtained. The rates of change observed were many times faster than those reported for wheat doughs, a phenomenon not yet satisfactorily explained.     

Physico‐chemical characteristics of non‐irradiated and γ‐irradiated yams cultivars (Dioscorea rotundata,Dioscorea alata) and sweet potato (Ipomoea batatas (L) Lam)

Physico‐chemical (pasting) properties of non‐irradiated (fresh) and γ‐irradiated yam cultivars and sweet potato were determined using Rapid Visco Analyser (RVA). Generally, pasting characteristics of the commodities decreased significantly with increased γ‐irradiation dose. Non‐irradiated sweet potato showed significantly higher peak (45.79), trough (35.25), breakdown (10.54), final (75.21) and setback (39.96) viscosities (in RVU) than γ‐irradiated samples. Also, peak time (6.97 min) and pasting temperature (50.18 RVU) significantly reduced with increased γ‐irradiation dose of tubers. The pasting properties of non‐irradiated and γ‐irradiated sweet potato showed similar but clearer trend compared with yam flours. Also, non‐irradiated and γ‐irradiated Dioscorea rotundata and Dioscorea alata showed significantly higher values of each of the pasting characteristics than values noted in sweet potato. Aside from the TDr 03/00196, peak time did not vary significantly with γ‐irradiation dose.     

Cassava (Manihot esculenta Crantz) and Yam (Dioscorea spp.) Crops and Their Derived Foodstuffs: Safety,Security and Nutritional Value

Cassava (Manihot esculenta Crantz) and yam (Dioscorea spp.) are tropical crops consumed by ca. 2 billion people and represent the main source of carbohydrate and energy for the approximately 700 million people living in the tropical and sub-tropical areas. They are a guarantee of food security for developing countries. The production of these crops and the transformation into food-derived commodities is increasing, it represents a profitable business and farmers generate substantial income from their market. However, there are some important concerns related to the food safety and food security. The high post-harvest losses, mainly for yam, the contamination by endogenous toxic compounds, mainly for cassava, and the contamination by external agents (such as micotoxins, pesticides, and heavy metal) represent a depletion of economic value and income. The loss in the raw crops or the impossibility to market the derived foodstuffs, due to incompliance with food regulations, can seriously limit all yam tubers and the cassava roots processors, from farmers to household, from small-medium to large enterprises. One of the greatest challenges to overcome those concerns is the transformation of traditional or indigenous processing methods into modern industrial operations, from the crop storage to the adequate package of each derived foodstuff.     

Physical,Chemical and Sensory Properties of Baked Products from Blends of Wheat and African Yam Bean (Sphenostylis stenocarpa) Water-Extractable Proteins

Blends of wheat flour (WF) and African yam bean water-extractable proteins (AYBWEP) were processed into bread and cookies in the following ratios: 100: 0; 95: 5; 90: 10; 85: 15; 80: 20. The proximate composition, physical, chemical properties and sensory properties of bread and cookies samples from the blends were determined. Breads and cookies produced from the resultant blends were significantly higher (p < 0.05) in protein (16.39% – 18.36%) than the control (11.80% – 12.58%). Carbohydrate content decreased from 60.74% with addition of AYBWEP to 52.81% following 20% substitution. The pH of bread samples prepared from whole wheat flour and blends of wheat flour and AYBWEP were significantly different (p < 0.05) while bulk density and specific volume were not significantly different (p > 0.05). The pH of bread samples and cookies decreased with increase in the proportion of the AYBWEP blend from 5% to 20%. The highest specific volume (3.70 ml/g) was observed in bread samples prepared from the control 100: 0 blends while the 80:20 blends had the lowest specific volume (3.10 ml/g). There was no significant difference (p > 0.05) in the bulk density and thickness of the cookies. The cookies prepared using 80: 20 blends had the higher diameter (22.53 cm) and spread factor (54.03 cm) compared to the control. Generally, acceptability of the bread and cookies decreased with higher ratios of AYBWEP inclusion. The sensory acceptability scores showed the best AYBWEP substitution level for making bread and cookies was 5% and 10% of the AYBWEP respectively. The results are discussed in the context of the growing importance of promoting the processing and utilization of lesser known local crops in baked products.enrichment.