Characterization of Volatile Compounds by HS-GC-IMS and Chemical Composition Analysis of Colored Highland Barley Roasted at Different Temperatures

Colored highland barley (CHB) is featured with its potential health-promoting benefits. CHB is frequently processed through roasting, which changes its volatile smells, color, and composition. The objective of this work was to establish the volatile fingerprints of CHB that had been roasted at different temperatures using E-nose and headspace-gas-chromatography-ion-mobility spectroscopy (HS-GC-IMS). The findings showed that roasting increased the relative contents of pyrazines, aldehydes, and ketones while decreasing the relative contents of alcohols, esters, and sulfides. Pyrazines were identified as the markers for volatile substances of the roasted CHB (RCHB). The outcomes of the principal component analysis (PCA) and hierarchical clustering analysis (HCA) demonstrated that the volatiles could easily distinguish between raw CHB and RCHB instead of differentiating between CHB roasted at different temperatures. Additionally, after roasting, the color characteristics and CHB constituents underwent changes, and the effect of roasting temperature on these changes differed depending on the cultivar. Protein, free amino acids, and flavonoids appeared to primarily participate in the variations of volatile substances, and the free fluorescence intermediary compounds might involve changes in color parameters and aromas. These findings improved our knowledge of the volatiles in CHB that were roasted under various conditions.

Effects of Seed Roasting Temperature on Sesame Oil Fatty Acid Composition, Lignan, Sterol and Tocopherol Contents, Oxidative Stability and Antioxidant Potential for Food Applications

Roasting is a key step for preparing sesame oil that leads to important changes in its organoleptic properties and quality. In this study, white sesame seeds were roasted for 20 min in an electric oven at different temperatures (120, 150, 180, 210, 250 and 300 °C). The oils extracted from unroasted and roasted seeds were compared for their chemical composition: fatty acids (including trans isomers), phytosterols, lignans (sesamin and sesamolin), tocopherols and total phenolic compounds, as well as their oxidative stability and antiradical capacity. There were no obvious differences in the oil densities, refractive indexes or iodine values, but the saponification values were affected by temperature. Relevant primary and secondary lipid oxidation were observed at T > 250 °C, resulting in a higher p-anisidine value and K232 as well as K268 values. Roasting improved oil yield (from 33.5 to 62.6%), increased its induction period (from 5.5 to 10.5 h) and enhanced the total phenolic content (from 152 to 194 mg/100 g) and antiradical activity of the extracted oil. Depending on roasting temperature, a gradual decline was recorded in total amounts of phytosterols (up to 17.4%), γ-tocopherol (up to 10.6%), sesamolin (maximum of 27.5%) and sesamin (maximum of 12.5%). All the investigated oils presented a low quantity in triglyceride polymers, clearly below the maximum tolerated quantity according to the European regulation. The optimal roasting temperature for obtaining high nutritional grade oil within the permissible values was 210 °C. The unsaponifiable components (including lignans and sterols) extracted from roasted seeds have been shown to be natural additives to fresh meatball products to extend shelf life. The results of this study may help to boost the nutritional content of plant-based diets by allowing for the use of roasted sesame seed oil and its components.

Effects of Temperature on the Composition and Xanthine Oxidase Inhibitory Activities of Caffeic Acid Roasting Products

The high-temperature treatment of caffeic acid by a model reaction for the processing of foods by roasting enhanced its xanthine oxidase (XO) inhibitory activity. The thermal reaction products included various oligomeric compounds, whose structures were determined as being produced via the intermediate 4-vinylcatechol. Measurements of their XO inhibitory activities were also carried out. Among the identified oligomers, the coupling products of caffeic acid and vinylcatechol, which were mainly produced at 140-170 °C, presented stronger XO inhibitory activities than the other types of oligomers produced. Further reacted compounds, which were mainly formed at 200 °C by the addition or elimination of catechol unit in the oligomers, displayed weaker activities. These results indicated that thermal enhancement of the XO inhibitory activity of caffeic acid can be explained by the differences in the XO inhibitory activities of the various constituents of the thermal reaction products. Caffeic acid and its derivatives are polyphenols found widely distributed in foods. Moreover, XO inhibition is closely related to the prevention of the life-style-related disease gout. The results suggest that a simple roasting process (170 °C) can lend useful human-health-related functionalities to caffeic acid containing foods such as coffee.