Discovery of Polyhydroxyalkyl Pyrazine Generation upon Coffee Roasting by In-Bean Labeling Experiments

Flavor enhancement pathways and mechanisms of cold-pressed walnut oil based on defatted cold-pressed walnut meal hydrolysates

The present study aimed to investigate the effect and underlying mechanism of Maillard reaction products (MRPs) derived from defatted cold-pressed walnut meal hydrolysates (DCWMH) on the aroma enhancement of cold-pressed walnut oil (CWO). Nineteen key aroma-active compounds were identified in CWO, hot-pressed walnut oil (HWO), and flavored walnut oil (FWO) using gas chromatography-olfactory-mass spectrometry (GC-O-MS) and odor activity values (OAVs). Principal component analysis (PCA) based on quantitative descriptive analysis (QDA) showed that the "roasted flavor" was positively correlated with FWO. Correlation analysis of free amino acids identified aspartic acid (Asp) as a key aroma precursor. Additionally, a novel pathway for furfural formation via Schiff base intermediates was proposed from the free radical cleavage process of the Maillard reaction in the [13C5]Xylose-Asp model system. Overall, this study provides valuable insights into the control of flavor quality during walnut oil production and supports the potential for the comprehensive utilization of walnut by-products.

Insight into the mechanism of roasting-induced characteristic aroma formation in Wuyi rock tea using an "in-leaf" model with isotopic labeling

Wuyi Rock Tea (WRT) undergoes complex chemical transformations during roasting that significantly influence its aroma. This study explores the mechanisms involved in the formation of key aroma compounds, specifically alkylpyrazines and furans. Using HS-SPME-GC-O-MS and aroma dilution analysis, we identified 15 odor-active compounds, including three alkylpyrazines (2,6-diethyl-pyrazine, 2-ethyl-3,5-dimethyl-pyrazine, and 2-methyl-3,5-diethyl-pyrazine) and two furans (furfural and 5-methyl-2-furancarboxaldehyde), with odor-active values exceeding 1. An "in-leaf" labeling approach utilizing isotopically labeled alanine ([15N]-Ala) and glucose ([U13C6]-Glc) was employed to explore the contributions of tea leaf matrix and soluble compounds. Results indicated that the incorporation of two nitrogen atoms from alanine was the predominant pathway for alkylpyrazine formation, while five or six carbon atoms from glucose were primarily responsible for furan formation. Additionally, the insoluble tea leaf matrix contributed 13 % to 32 % of alkylpyrazines and 12 % to 25 % of furans. These findings enhance our understanding of the Maillard reaction's role in WRT's flavor development.

Analysis of roasted peanuts based on GC-MS combined with GC-IMS

The present study used gas chromatography-mass spectrometry (GC-MS) and gas chromatography-ion mobility spectrometry (GC-IMS) to separate and identify the characteristic volatile flavor substances in 30 roasted peanut samples. GC-MS identified 59 volatile compounds, and GC-IMS detected 61 volatile flavor substances. The 30 peanut varieties were then divided into four groups on the basis of their volatile flavor substances using principal component analysis (PCA), and a fingerprint profile of the varieties' volatile characteristics was established from information peaks identified in the spectra. Descriptive sensory analysis (DSA) was performed to distinguish differences in flavor attributes between roasted peanut varieties. Partial least squares regression (PLSR) was performed with the volatile flavor content of roasted peanuts as the independent variable and the flavor attribute score as the dependent variable. These findings provide a basis for predicting the appeal of roasted peanuts based on their composition and demonstrate a potential avenue for improving food flavor quality.

Chemical Analysis, Toxicity Study, and Free-Radical Scavenging and Iron-Binding Assays Involving Coffee (Coffea arabica) Extracts

We aimed to analyze the chemical compositions in Arabica coffee bean extracts, assess the relevant antioxidant and iron-chelating activities in coffee extracts and instant coffee, and evaluate the toxicity in roasted coffee. Coffee beans were extracted using boiling, drip-filtered and espresso brewing methods. Certain phenolics were investigated including trigonelline, caffeic acid and their derivatives, gallic acid, epicatechin, chlorogenic acid (CGA) and their derivatives, p-coumaroylquinic acid, p-coumaroyl glucoside, the rutin and syringic acid that exist in green and roasted coffee extracts, along with dimethoxycinnamic acid, caffeoylarbutin and cymaroside that may be present in green coffee bean extracts. Different phytochemicals were also detected in all of the coffee extracts. Roasted coffee extracts and instant coffees exhibited free-radical scavenging properties in a dose-dependent manner, for which drip coffee was observed to be the most effective (p < 0.05). All coffee extracts, instant coffee varieties and CGA could effectively bind ferric ion in a concentration-dependent manner resulting in an iron-bound complex. Roasted coffee extracts were neither toxic to normal mononuclear cells nor breast cancer cells. The findings indicate that phenolics, particularly CGA, could effectively contribute to the iron-chelating and free-radical scavenging properties observed in coffee brews. Thus, coffee may possess high pharmacological value and could be utilized as a health beverage.