Relation between high temperature mastication and Mooney viscosity relaxation in natural rubber

International audienceMastication of natural rubber (NR) is undertaken as a preliminary step towards the preparation of NR-based vulcanizates, a process during which the elastomer is broken down to a homogeneous matrix of lower viscosity. Several tests and indicators are in use for characterizing the behavior of elastomers but these have mostly been adopted for the nonmasticated product. This study uses coefficients generated from modeled Mooney relaxation data, as indicators of elasticity, to examine the effect of high-temperature mastication on the processability of the masticated rubber. Some derived coefficients such as the terminal relaxation time (s) from Maxwell's triexponential model, the elastic component (a) from Wu-Abbott model [Y ¼ 1 þ a* ln(t) bt/(c þ t)], and the constant (b) from the Power law model (Y ¼ at b), adequately characterized the effect of mastication on NR. Although the NR grades studied were quite different with respect to their initial molar mass distributions, they followed a similar response to the mechanical models before and after mastication, indicating therefore that mastication decomposes to a similar extent, the various components (long isoprene chains, densely crosslinked solvent-insoluble gel, etc.) that account for the viscoelastic behavior of the raw elastomer

Chemical and Orgarnoleptic Quality of Figs from Selected Sweet bananas (Musa Spp)

The chemical composition and organoleptic quality of four Cameroonian industrial banana varieties at two ripening stages and figs made from them, were evaluated. The results showed that sucrose content and Lovibond colour index increased significantly with ripening in both fresh fruits and figs and appeared to be the main factors that influenced the appreciation of the quality of the figs. Of the four varieties evaluated for appearance, bitterness, texture, odour and taste, figs from Gros Michel were the most appreciated with respect to all the parameters put together The Journal of Food Technology in Africa Volume 5 Number 2 (April - June 2000), pp. 70-7

AGRICULTURE AND BIOLOGY JOURNAL OF NORTH AMERICA Potentials of some cement by-products for liming of an acid soil in the humid zone of South-Western Cameroon

ABSTRACT Aluminium (Al) toxicity is the major limiting factor of plant growth in acid soils. A pot trial was carried out to evaluate the effects of lime (CaCO 3 ) from three liming materials on soil Al toxicity and the yield of maize (Zea mays L.). Two cement by-products (Agri-56 and Filler) and a conventional liming material (Limbux) were used. The acid neutralizing values for Limbux, Agri-56 and Filler were 126, 88 and 34% CaCO 3 equivalent, respectively. Five rates of lime equivalent: 0, 2, 4, 8 and 16 tons CaCO 3 ha -1 and the three liming materials were applied in combinations as treatments. Agri-56 was as efficient as Limbux in neutralizing Al toxicity. Aluminium saturation decreased from 83% to 31, 37and 69% for Limbux, Agri-56 and Filler, respectively when 2 tons CaCO 3 ha -1 was applied. Limbux and Agri-56 increased the soil pH from 4.3 to 7.1 and 6.5, respectively at equivalent rate of 16 tons CaCO 3 ha -1 . There was a 53.5 and 67.2% increase in maize yield for Limbux and Agri-56, respectively when 2 tons CaCO 3 ha -1 was applied. Because of its availability and easy to use, Agri-56 is therefore recommended as the liming material on the acid soils of South-western Cameroon

Preparation and characterization of non-vulcanized natural rubber-based cocoa pod husk composites

Several ingredients are often introduced into rubber matrices during the production of natural rubber (NR) based articles, essentially to modify and improve upon the properties of the final products as well as to reduce their costs. In this study, composites of natural rubber and cocoa pod husk were prepared by solution casting and tested for their rheological and thermal properties in order to ascertain the suitability of the latter as a substitute for standard fillers in the NR industry. An increase in the level of substitution significantly reduced the rheological properties of the composites in the linear viscoelastic region but had no significant effects on their thermal stability, glass transition temperature and on the α-relaxation of the NR composites except at the highest level of substitution (25%). However, α-relaxation and rheological shift factors were always temperature-dependent and had a direct influence on their electrical conductivity with no permanent chemical bonds formed or broken during preparation of the composites. Hence, untreated cocoa pod husk could serve as non-reinforcing filler for raw natural rubber.The authors are grateful to the Material Physics Centre-Donostia and the Women for Africa Foundation-Madrid for the financial support.Peer reviewe

Temperature/duration couples variation of cocoa beans roasting on the quantity and quality properties of extracted cocoa butter

Roasting is an important process that could influence the quantity of butter extracted. Central Composite Design (CCD) approach was used to study the influence of the couple temperature/duration of roasting on the quantity of extracted butter. The roasting conditions used were temperatures in the range of 110–197 °C and time ranging from 10 to 57 min. A total of 13 couple was tested. The result highlight that roasting conditions significantly affected the quantity of obtained butter. The best couple temperature – duration were 125 °C/57 min and 140 °C/40 min with an extraction yield of about 25%. However, obtained cocoa butter presented a wide diversity with respect to texture, colour and odour characteristic. Physicochemical properties of extracted butter were not function to the roasting conditions. Iodine and saponification indices were within the norms. However, the humidity rates of the studied cocoa butter were largely above the standard rates. Findings of this research are useful to food industries, and the impact of cocoa roasting on the extracted butter properties could help developed new products. Keywords: Cocoa beans, Roasting conditions, Cocoa butter, Physicochemical properties, Sensorial propertie

Effect of fortification with baobab (Adansonia digitata L.) pulp flour on sensorial acceptability and nutrient composition of rice cookies

In order to fight malnutrition, functional cookies fortified with baobab pulp flour at partial substitution rates of 10, 20 and 30% were evaluated for consumer acceptability and nutritional quality. Consumer acceptability was evaluated in terms of taste, aroma, color and texture (hedonic characteristics) while nutritional quality was evaluated in terms of macro- and micro-nutrient compositions. Results showed that composite flours exhibited good functional properties. Twenty percent fortification cookies produced the most acceptable cookies which were rich in calories (490.24 kcal per 100 g), total fibre (8.65%), and total fat (27.52% DM). According to the National Agency of Sanitary Security recommendations concerning the contribution of each macromolecule to the total energy, crude protein intake was lower, polysaccharide intake was within the recommended value, while total fat intake was largely beyond that value. Mineral profile showed that cookies enriched with 20% of baobab pulp flour were rich in iron (15.6 mg/100 g), calcium (30 mg/100 g), magnesium (20 mg/100 g), potassium (930 mg/100 g), and vitamin C (60 mg/100 g). Thus, incorporation of baobab pulp flour at 20% improved sensory and nutritional qualities of rice cookies. Baobab fortified cookies can therefore be an alternative non costly and accessible snack to alleviate malnutrition in general and micronutrient deficiencies in particular. Keywords: Rice cookies, Baobab pulp flour, Nutritional properties, Sensorial qualit