Effects of acid leaching on halloysite

A characteristic iron-containing halloysite sample from Turkey was subjected to acid leaching using organic and inorganic acids for removing iron impurities. The aim of this study was to compare the raw hydrated and dehydrated halloysites with the leached products. Hydrochloric acid and oxalic acid were chosen as leaching agents for the removal of iron impurities at 80 °C for 2.5 h. The physicochemical properties of the acid-treated halloysite were analyzed by XRF, XRD, FTIR, TGA, DTA, SEM, and TEM. The XRF results showed that the acid treatment caused the dissolution of minor amounts of Al3+ ions from the clay layer. The XRD results indicated that the crystalline structure was unchanged after the leaching. However, it was observed that the hydrated (1 nm) halloysite readily lost its interlayer water and was transformed to the dehydrated (0.7 nm) form. In addition, no visible effects of the acid treatment on the tubular structure of halloysite were detected in the SEM and TEM images. Typical pores of varying dimensions were observed in all of the samples regardless of their form or treatment. Furthermore, the TG-DTA and FTIR analysis results were similar for both the raw and the acid-treated samples

Microstructural changes in hazelnuts during roasting

The microstructure of raw and roasted hazelnuts was investigated with light microscopy (LM). Tissue sections were fixed chemically using a mixture of formaldehyde, glutaraldehyde and buffer. Polyester was used as a resin. Thin sections were prepared by using a grinding method. Thermal changes in the microstructure developed gradually with increasing air temperature, air velocity and roasting time. Roasting led to some degree of cell wall separation and intercellular spaces, partial disruption of cytoplasmic network, swollen and aggregated protein bodies. These changes were observed in the microstructure of extremely liked quality of hazelnuts (roasted at 165 degreesC, 1 m/s. 25 min.). Due to the increase in the volume of intercellular spaces, crispness and crunchiness of roasted hazelnuts were increased

Determination of optimum hazelnut roasting conditions

The objective of this study was to test the hypothesis that the roasting conditions used for hazelnuts, such as the air temperature, air velocity and roasting time (independent variables), could be optimized by using Response Surface Methodology. Effects of independent variables on sensory and physical characteristics were determined. A consumer test was used to determine the acceptable samples. Very dark and very light roasted samples, corresponding to 165 degreesC, 3 m/s, 25 min and 125 degreesC, 1 m/s, 15 min process conditions, respectively, were unacceptable. Superimposed contour plots were used to determine the values of independent variables and these showed the process conditions where all product characteristics were acceptable to consumers. At low velocity (0.3 m/s), acceptable products were produced at about 165-179 degreesC for 20-25 min. When air velocity increased, air temperature shifted to lower temperatures. Samples roasted at 145 degreesC, 2 m/s, 28 min, 165 degreesC, 1 m/s, 25 min and 145 degreesC, 3.7 m/s, 20 min produced the most acceptable products. The sample roasted at 165 degreesC, 1 m/s, 25 min required the least air velocity and was the most economical in terms of energy consumed among the samples rated most acceptable by consumers