Evaluation of the effects of canning variables on the mineral composition of canned cowpeas (Vigna unguiculata l. Walp) using multi-response analysis.

This study aims to investigate the effects of canning variables (cooking time, storage time, volume of vinegar, salt and sugar) on the mineral composition of canned cowpea (Vigna unguiculata (L.) Walp) and which conditions provide optimised preservation of the mineral content of the grains. Different formulations of canned cowpeas were produced following two levels factorial experimental design using five variables. A set of 11 different formulations were evaluated using the desirability function with essential minerals (Ca, Cu, Fe, Mn, Mg, P and Zn) as the response. The optimal multi-response conditions for higher mineral retention were: 360 days of storage at 30 ± 5 °C (ST2), 30 ml of vinegar, 9.0 g of NaCl, 18 min of cooking time, and 9.0 g, 19.5 g or 30 g of sugar (the effect of the sugar content at the evaluated range was not significant at 95% confidence level).

Evaluation of the nutritional quality of cereal bars made with pulse flours using desirability functions.

The development of nutritious, low-cost snacks has become increasingly important due to consumer demand for healthier diets. In this study, sensory and physical-chemical parameters and mineral compositions (P, Ca, Na, K, Mg, Fe, Zn, Al, Cu, Mn, Ni and Ba) of cereal bars were evaluated. The bars were made with flours of Lablab purpureus L. Sweet (mangalo), Vigna unguiculata L. Walp (cowpea) or Cajanus cajan L. Huth (pigeon pea) and the desirability function was used to attain the best formulation for maximising the content of protein, fibre, ashes and essential elements. Sensory analysis revealed satisfactory acceptability. Acidity did not change significantly (p > 0.05), and water activity values ​​did not exceed 0.557 over 90 days, indicating stability. Principal component analysis revealed no significant differences when comparing the mineral content between the bars. The desirability function indicated that the cowpea-based bar had a higher nutritional quality, with a protein content of 4.91 ± 0.25 g 100 g-1, P content of 187.7 ± 3.6 mg 100 g-1, Mg content of 87.37 ± 1.19 mg 100 g-1 and Mn content of 2020 ± 130 µg 100 g-1, than the other bars. The overall sensory evaluation also yielded a high score for the cowpea-based bar (overall quality equal to 6.23 ± 1.10). Therefore, pulse flours could be potential nutritional ingredients for making snacks, and in particular, cereal bars containing them could be a viable product alternative for small rural cooperatives.

A sensitive flow analysis system for the fluorimetric determination of low levels of formaldehyde in alcoholic beverages.

A sensitive FIA method was developed for the selective determination of formaldehyde in alcoholic beverages. This method is based on the reaction of Fluoral-P (4-amine-3-pentene-2-one) with formaldehyde, leading to the formation of 3,5-diacetyl-1,4-dihydrolutidine (DDL), which fluoresces at lambda(ex)=410nm and lambda(em)=510nm. The analytical parameters were optimized by the response surface method using the Box-Behnken design. The proposed flow injection system allowed for the determination of up to 3.33x10(-5)molL(-1) of formaldehyde with R.S.D.<2.5% and a detection limit of 3.1ngmL(-1). The method was successfully applied to determine formaldehyde in alcoholic beverages, without requiring any sample pretreatment, and the results agreed with the reference at a 95% confidence level by paired t-test. In the optimized condition, the FIA system proved able to analyze up to 60 samples/h.

Spectrophotometric determination of sulphate in automotive fuel ethanol by sequential injection analysis using dimethylsulphonazo(III) reaction.

A sensitive SIA method was developed for sulphate determination in automotive fuel ethanol. This method was based on the reaction of sulphate with barium-dimethylsulphonazo(III) leading to a decrease on the magnitude of analytical signal monitored at 665 nm. Alcohol fuel samples were previously burned up to avoid matrix effects for sulphate determinations. Binary sampling and stop-flow strategies were used to increase the sensitivity of the method. The optimization of analytical parameter was performed by response surface method using Box-Behnker and central composite designs. The proposed sequential flow procedure permits to determine up to 10.0mg SO(4)(2-)l(-1) with R.S.D. <2.5% and limit of detection of 0.27 mg l(-1). The method has been successfully applied for sulphate determination in automotive fuel alcohol and the results agreed with the reference volumetric method. In the optimized condition the SIA system carried out 27 samples per hour.