Ability of Selected Lactic Acid Bacteria to Ferment a Pearl Millet–Soybean Slurry to Produce Gruels for Complementary Foods for Young Children

Abstract

The kinetics of heat denaturation and aggregation for beta-lactoglobulin dispersions (5% w/v) were studied at 3 pHs (6, 6.4, and 6.8) and at a heating temperature of 80 degrees C. Protein aggregates were characterized for hydrodynamic diameter, microstructure, and molecular weight by means of dynamic light scattering, transmission electron microscopy, and polyacrylamide gel electrophoresis, respectively. Concentration of native beta-lactoglobulin decreased with holding time and with a decrease in the pH. Apparent rate constants were calculated for beta-lactoglobulin denaturation applying the general kinetic equation solved for a reaction order of 1.5. Values of the apparent reaction rate constant k = 7.5, 6.3 and 5.6 x 10(-3) s(-1) were found for pH 6, 6.4, and 6.8, respectively. Decreasing the pH of the dispersions produced higher aggregate sizes. After a holding time of 900 s, average hydrodynamic diameters for beta-lactoglobulin aggregates at pH 6, 6.4, and 6.8 were 96, 49, and 42 nm, respectively. These results were confirmed by transmission electron microscopy images, where a shift in the size and morphology of aggregates was found, from large and spherical at pH 6 to smaller and linear aggregates at pH 6.8. beta-Lactoglobulin formed disulfide-linked intermediates (dimers, trimers, tetramers) and so on) which then formed high molecular weight aggregates. From the results obtained by DLS, TEM, and SDS-PAGE a mechanism for beta-lactoglobulin aggregation was proposed. This study shows that heat treatment can be used to produce protein aggregates with different sizes and morphologies to be utilized as ingredients in foods.

Influence of Cofermentation by Amylolytic Lactobacillus plantarum and Lactococcus lactis Strains on the Fermentation Process and Rheology of Sorghum Porridge

“…Starch hydrolysis by extrusion cooking, commercial amylases, cereal malts, or ALAB fermentations can reduce the viscosity of porridges (16,28,33). However, methods that are efficient, relatively cheap, and adaptable to traditional processes are preferable.…”

“…A mylolytic lactic acid bacteria (ALAB) produce amylases which facilitate hydrolysis and fermentation of starch to lactic acid in a one-step process (30). ALAB can thus be utilized in commercial production of lactic acid from starchy materials and in reducing the viscosity of starchy complementary foods (13,24,33). These potential applications explain the diversity of ALAB isolated so far, which includes members of the genera Enterococcus, Lactobacillus, Lactococcus, Leuconostoc, Pediococcus, and Streptococcus (13,29,30).…”

“…Energy and nutrient density can be improved by increasing the flour content to a minimum of 200 g kg Ϫ1 or by fortification with legumes (26,31,33). However, large amounts of starch make the porridges too thick and unsuitable for infant feeding (26).Starch hydrolysis by extrusion cooking, commercial amylases, cereal malts, or ALAB fermentations can reduce the viscosity of porridges (16,28,33). However, methods that are efficient, relatively cheap, and adaptable to traditional processes are preferable.…”

“…These porridges have viscosities (1,000 to 3,000 cP) suitable for infant feeding but are low in energy and nutrient density (31). Energy and nutrient density can be improved by increasing the flour content to a minimum of 200 g kg Ϫ1 or by fortification with legumes (26,31,33). However, large amounts of starch make the porridges too thick and unsuitable for infant feeding (26).…”

“…Spoilage and pathogenic microflora in cereals malts can also pose quality and safety risks in case of slow fermentation (3). Fastacidifying and strong ALAB have thus been proposed to be potential substitutes for cereal malts (24,33,34).Large amounts of glucose, maltose, or sucrose repress amylase synthesis by ALAB and can thus prevent or limit the ALAB effect on viscosity (9, 10). Fermentation of starch with mixed cultures could result in fast depletion of fermentable sugars, therefore rapidly initiating amylase synthesis.…”