Volatile compounds in whole meal bread crust: The effects of yeast level and fermentation temperature.
The influence of fermentation temperatures (8°C, 16°C, and 32°C) and yeast levels (2%, 4%, and 6% of the flour) on the formation of volatile compounds in the crust of whole meal wheat bread was investigated. The fermentation times were regulated to optimum bread height for each treatment. The volatile compounds were extracted by dynamic headspace extraction and analyzed by gas chromatography-mass spectrometry. The results were evaluated using multivariate data analysis and ANOVA. In all crust samples 28 volatile compounds out of 58 compounds were identified and the other 30 compounds were tentatively identified. Higher fermentation temperatures promoted the formation of Maillard reaction products 3-methyl-1-butanol, pyrazine, 2-ethylpyrazine, 2-ethyl-3-methylpyrazine, 2-vinylpyrazine, 3-hydroxy-2-butanone, 3-(methylsulfanyl)-propanal, and 5-methyl-2-furancarboxaldehyde whereas at lower temperature (8°C) the formation of 2- and 3-methylbutanal was favored. Higher levels of yeast promoted the formation of 3-methyl-1-butanol, 2-methyl-1-propanol and 3-(methylsulfanyl)-propanal, whereas hexanal was promoted in the crust fermented with lower yeast level.
How Maillard Reaction Influences Sensorial Properties (Color, Flavor and Texture) of Food Products?
ABSTRACT Maillard reaction products are largely responsible for the development of color, taste and especially aroma of thermally treated food. For this reason, our review focused on gathering literature from the last 10 years about the influence of the Maillard reaction products formation on food acceptance in aspects of color, texture and flavor. Maillard reaction products have a characteristic odor note and can significantly positively or negatively influence the sensory acceptance of a product. For example, pyrazines and thiols were found in most cases as the most potential odor compounds formed in MR. Another important aspect of high sensorial acceptability is food color. Color development of thermally treated products is mainly attributed to the formation of brown polymers called melanoidins. It was also noted that the increasing concentration of “probably carcinogenic and mutagenic” acrylamide is related to the darker color of a product. Not much attention is focused on the connection between Maillard reaction products formation and textural properties. Therefore, textural properties have been mostly investigated in meat products. Changes in the texture of meat products were estimated as the difference in linkage formations between proteins and polysaccharides.
Experimental study on bond behavior between high-strength grout and deformed steel bars
Abstract Engineers use high-strength grout to connect precast concrete members for its low shrinkage and good fluidity. This paper designed 87 central pull-out specimens using the control variable method to investigate the influence of factors on the rebar-grout bond property such as compressive strength, steel grade, bar diameter, transverse stirrups, and bond length. The test result showed that improving grout compressive strength (85.8 MPa–122.7 MPa) cannot improve the bond strength, which was different from the previous conclusions of concrete pull-out tests. Simplified formulas were presented for calculating the characteristic values of bond strength, residual strength, peak slip, and relative slip of load-holding platform based on parameter analysis. Then, a constitutive model was proposed to predict the full-range bond stress-slip curve of high-strength grout and steel bar specimens from bearing to failure. Finally, FEA models were established to evaluate the applicability and accuracy of the constitutive model.