Effect of sugar addition on glass transition temperatures of cassava starch with low to intermediate moisture contents.

This work studies how sucrose (S) addition modifies the thermal properties of cassava starch (CS). Neat CS and CS-S blends with 4, 6 and 8% sugar contents (CS-S-4%, CS-S-6% and CS-S-8%) were prepared and analyzed by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA), in a wide range of moisture levels (2-20%). In equilibrated samples with moisture contents lower than 10%, twoendothermic steps were observed during first DSC heating scans and two corresponding relaxation maxima in tan δ were detected by DMTA. The first transition, detected at around 45-55°C by both DSC and DMTA, is frequently found in starchy foods, while the second observed at higher temperatures is associated to the glass transition temperature of the blends. At higher moisture contents, only one thermal transition was observed. Samples analyzed immediately after cooling from the melt (i.e., after erasing their thermal history), exhibited a single glass transition temperature, regardless of their moisture content. Addition of sugar promotes water plasticization of CS only at high moisture contents. In the low moisture content range, anti-plasticization was observed for both neat and sugar-added CS samples. Addition of sugar decreases the moisture content needed to achieve the maximum value of the glass transition temperature before plasticization starts. The results of this work may be valuable for the study of texture establishment in low moisture content extruded food products.

Maduración de queso de cabra con cepa autóctona de Leuconostoc mesenteroides aislada de queso artesanal / Ripening of Goat Cheese With a Native Strain of Leuconostoc mesenteroides Isolated from Artisan Cheese

Se elaboró queso de cabra madurado empleando una cepa liofilizada de Leuconostoc mesenteroides como cultivo iniciador, aislada a partir de la flora natural de quesos de cabra, elaborados artesanalmente con leche cruda de cabra del municipio Torres, estado Lara, Venezuela. El proceso de maduración fue de 4 sem, a 14°C y 70% de humedad relativa. Durante el tiempo de maduración, se evaluaron semanalmente los cambios en pH, sólidos totales y parámetros de textura; mientras que el contenido de proteínas, se determinó al inicio y al final del estudio. Al finalizar la maduración, se realizó un estudio con consumidores para evaluar la aceptabilidad de los quesos obtenidos en comparación con un queso control inoculado con una cepa comercial. El contenido de sólidos totales disminuyó entre 23 y 31% a lo largo del estudio (p<0,05), el pH en 6%, mientras que el contenido proteico no registró cambios al final de la maduración. La dureza y gomosidad en los quesos se incrementaron entre 1,64 y 2N; y 0,72 y 0,83N, respectivamente, con la maduración; correlacionándose positivamente con la variación en sólidos totales (R²>0,90) para ambos quesos mientras que la adhesividad y cohesividad no registraron cambios importantes. En la evaluación sensorial, el queso elaborado con L. mesenteroides obtuvo una aceptabilidad promedio del 70%, al compararlo con un queso de cabra obtenido a partir de una cepa comercial de Lactococcus lactis.

A ripened goat cheese was developed using a lyophilized strain of Leuconostoc mesenteroides as starter culture. This strain was isolated from the natural flora of artisan goat cheese made with raw milk in the municipality of Torres, the State of Lara, Venezuela. The maturation process lasted 4 weeks, at 14°C and 70% relative humidity. During the ripening period, changes in pH, total solids, and texture parameters where registered every week, while protein content was determined at baseline and at the end of the study. After maturation was completed, its acceptability was assessed through a consumer test against a control cheese inoculated with a commercial strain. The total solids content fell between 23 and 31% throughout the study (p<0.05), the pH at 6%, while the protein content was unchanged at the end of ripening. The hardness and gumminess in cheese increased between 1,64 and 2N; and 0,72 and 0,83N, respectively, with maturation; their were positively correlated with the variation in total solids (R²>0,90) for both cheeses while adhesiveness and cohesiveness showed no major changes. In the sensory evaluation, the cheese made from L. mesenteroides obtained an average acceptability of 70%, when compared with a goat cheese obtained from a commercial strain of Lactococcus lactis.

Glass transitions and physical aging of cassava starch - corn oil blends.

Glass transition temperatures and physical aging of amorphous cassava starch and their blends with corn oil were assessed by differential scanning calorimetry (DSC). Two enthalpic relaxation endotherms, well separated in temperature values, were exhibited by neat amorphous cassava starch with 10.6% moisture content, evidencing two amorphous regions within the starch with different degrees of mobility. The phase segregation of these two amorphous regions was favored by added corn oil at low moisture contents during storage. The presence of amylose-lipid complexes in this matrix, may also affect the molecular dynamics of these two amorphous regions at low moisture contents. Increasing moisture content, leads to a homogeneous amorphous phase, with an aging process characterized by a single enthalpic relaxation peak. In all cases, after deleting the thermal history of the samples only one glass transition temperature was detected (during DSC second heating runs) indicating that a single homogeneous amorphous phase was attained after erasing the effects of physical aging. Trends of the enthalpic relaxation parameters were also different at the two moisture contents considered in this work.

Anti-plasticization of cassava starch by complexing fatty acids.

The effect of adding 1-8% amylose complexing fatty acids (CFA), such as linoleic and oleic acids, on the glass transition temperature (Tg) of cassava starch (CS) with moisture content varying from 5 to 35% (dry basis) was studied. The main relaxation temperature (Tα), associated with the glass transition temperature of the samples (Tg), was determined by dynamic-mechanical-thermal analysis. The plasticizing behavior of water in the blends was evidenced by a decrease of Tα values with moisture content. The effect of CFA on CS was found to be a function of moisture content. At low moisture (<11%) it caused an anti-plasticization effect, while at higher moisture contents it produced plasticization. The anti-plasticizing effect of CFA on CS was attributed to amylose-lipid complex formation.