C. Benedito de Barber

INFLUENCE OF HYDROCOLLOIDS ON DOUGH RHEOLOGY AND BREAD QUALITY

Abstract The effect of different hydrocolloids (sodium alginate, κ-carrageenan, xanthan gum and hydroxypropylmethylcellulose) on the rheological properties of the wheat flour dough and the final quality of breads was investigated. A complete study of the rheological behaviour of the dough containing hydrocolloids was performed by using the following instruments: farinograph, extensograph, alveograph and rheofermentometer. The baking response was also determined by using an oven rise recorder. Xanthan and alginate had the most pronounced effect on dough properties yielding strengthened doughs. A great improvement in dough stability during fermentation was achieved by adding hydrocolloids. Regarding their effect on bread properties, the hydrocolloids increased the specific volume, with the exception of alginate, as well as both moisture retention and water activity. In addition, textural studies revealed that addition of κ-carrageenan or hydroxypropylmethylcellulose reduced the firmness of bread crumb. In conclusion, k-carrageenan and hydroxypropylmethylcellulose could be used as improvers in the bread-making performance.

Pasting properties of different wheat flour-hydrocolloid systems

Abstract The effect of several hydrocolloids on the pasting properties and gelling behaviour of wheat flour was investigated. The influence of the selected hydrocolloids (guar gum, pectin, alginate, κ-carrageenan, xanthan and hydroxypropylmethylcellulose (HPMC)) on wheat flour was tested by using two different techniques: amylograph and differential scanning calorimetry (DSC). In order to have a general overview of their effect, hydrocolloids were chosen from different sources implying a broad diversity of chemical structures. Differences among hydrocolloid-wheat flour suspensions were more evident from amylographic analysis than from DSC examination. The hydrocolloid addition largely modified the amylograph parameters of wheat flour—even at the low levels tested [0.5 and 1% (w/w), flour basis], and the extent of their effect depended upon the chemical structure of the added hydrocolloid. The greatest effect on pasting temperature was observed when 1% alginate was added, which produced a decrease of ca 3°C. This reduction is really important since it implies an earlier beginning of starch gelatinization and, in turn, an increase in the availability of starch as enzyme substrate during baking period. Xanthan and pectin increased the cooking stability while κ-carrageenan and alginate did not modify it. Setback was augmented by guar gum and HPMC but alginate, xanthan and κ-carrageenan showed the opposite effect. The bump area related to the formation of amylose–lipid complex, was favoured by κ-carrageenan, alginate and pectin, and slightly affected by xanthan and HPMC. In summary, each tested hydrocolloid affected in a different way the pasting properties of wheat flour. The results obtained are important for the appropriate use of these hydrocolloids as ingredients in the bread making process.

Rice Bran: Chemistry and Technology

Rough rice, or paddy, consists of a white starchy endosperm kernel surrounded by a tightly adhering bran coat, an adhering germ with the total enclosed within a loose outer hull or husk. All rice is milled before consumption, producing hull, bran, germ, and white rice. Although a small amount of rice is consumed as brown rice, which still contains the bran and germ, white rice is the principal food staple of over 2.5 billion people worldwide.

Headspace flavour compounds produced by yeasts and lactobacilli during fermentation of preferments and bread doughs.

Production of volatile flavour compounds during fermentation with pure cultures of Saccharomyces cerevisiae and Candida guilliermondii, Lactobacillus brevis and Lactobacillus plantarum have been investigated, using wheat doughs and several preferements as substrates. For yeast, preferments consisted of 10% (w/v) glucose, maltose and sucrose solutions, whereas for lactobacilli they consisted of supplemented and unsupplemented (3% and 10% (w/v)) glucose solutions, and a 10% (w/v) wheat flour slurry. Seven volatile compounds (acetaldehyde, acetone, ethyl acetate, ethanol, hexanal+isobutyl alcohol, and propanol) were detected when using yeasts. All these compounds, except propanol, appeared for all the substrates assayed, with ethanol as the predominant component. Generally, S. cerevisiae produced higher amounts of the different components than C. guilliermondii. Both yeasts produced larger amounts of volatile flavour compounds during fermentation in glucose and sucrose solutions than in maltose or wheat dough. In general the yeasts examined produced more flavour components than the lactobacilli. For the lactobacilli the highest number of volatile flavour compounds were observed for substrates containing flour.

Effect of processing conditions on acidification properties of wheat sour doughs.

The pH, total titratable acidity (TTA) and lactic and acetic acids production have been investigated for wheat sour doughs with and without yeast addition, inoculated with two strains of Lactobacillus plantarum (B33, B39). To study the effect of flour extraction rate (0.54, 11.11 and 1.68% ash content), dough yield (DY) (160, 200 and 240 of sour dough/100 g flour), and fermentation temperature (25, 30 and 35 degrees C) a response surface regression, factor analysis and K-means clustering analysis were used. Results from factor analysis point out that the extraction rate of fluor governs TTA and acetic acid content; this factor accounts for the 53% of variability of the data. Dough yield is highly correlated with lactic acid content, explaining 27% of the total variance. Finally, temperature explains the remaining 16% of variation, but it is not related to any analytical variable. From K-means clustering analysis, flour extraction rate of 1.68% ash content leads to the highest TTA and acetic acid values, whereas DY of 240 g sour dough/100 g flour gives the greatest lactic acid content, and DY of 160 leads to the lowest levels of TTA and organic acids.

Chemical and Biological Data of Rice Proteins for Nutrition and Feeding

Husks, bran, brokens and milled rice, the four major products from rice milling, differ in the quantity and the quality of the protein they contain. The protein content and the protein quality of these milling fractions is critically reviewed in the ligth of available data on: total protein (P), true protein (TP), non-protein nitrogen (NPN), individual amino acids (AA), essential amino acids (EAA), available amino acids (AAA), limiting amino acid (LAA), amino acid score, protein efficiency ratio (PER), net protein ratio (NPR), net protein utilization (NPU), biological value (BV), true digestibility (TD), and other indices.

Low molecular weight peptides of bread dough and bread. Dynamics during fermentation and baking

Abstract Dynamics in low molecular weight peptides (LMWP) during wheat bread dough fermentation and baking have been investigated by comparing the amino acid composition and the partial N-terminal amino acid sequence of the LMWP fraction of purified acetic acid extracts from unfermented, 2.5 hour-, and 24 hour-fermented straight doughs, and bread. Nutritional requirements on LMWP of yeast and lactic acid bacteria starting the fermentation are only evidenced when aspartic acid and asparagine levels are reduced. Specific endo and exoproteolytic activities releasing basic and hydrophobic nitrogen chains along breadmaking process, as well as level of hydrophylic residues in unfermented doughs affect browning and bread flavor.