Jeehyun Lee

Volatile Aroma Compounds in Various Brewed Green Teas

This study identifies and semi-quantifies aroma volatiles in brewed green tea samples. The objectives of this study were to identify using a gas chromatograph-mass spectrometer (GC-MS) paired with a headspace solid-phase micro-extraction (HS-SPME) the common volatile compounds that may be responsible for aroma/flavor of the brewed liquor of a range of green tea samples from various countries as consumed and to determine if green teas from the same region have similarities in volatile composition when green tea samples are prepared for consumption. Twenty-four green tea samples from eight different countries were brewed as recommended for consumer brewing. The aroma volatiles were extracted by HS-SPME, separated on a gas chromatograph and identified using a mass spectrometer. Thirty-eight compounds were identified and the concentrations were semi-quantified. The concentrations were lower than those reported by other researchers, probably because this research examined headspace volatiles from brewed tea rather than solvent extraction of leaves. No relationship to country of origin was found, which indicates that other factors have a greater influence than country of origin on aroma.

A comparison of the flavor of green teas from around the world

BACKGROUND Green teas can be grouped based on their flavor profiles. The country of origin appears to have a strong influence on the flavor of green tea probably because similar processing methods are widely used within each particular country and flavor is dependent, in part, on processing. The aim of this article is to determine what flavor differences exist among a wide range of green teas (n = 138) produced in various countries. RESULTS In this study we found that roast-processed teas were mostly responsible for brown-related flavors and steam-processed teas were responsible for green-related flavors. The prices of the green teas did not differentiate the flavors of the samples. Often highly priced green teas were grouped with low-priced green teas from the same manufacturer or country of origin according to their flavor attributes. CONCLUSIONS Differences in the tea plant varieties or cultivars likely affects flavors in green tea. However, those were not known for many samples in this research and more study will be needed to determine the effects of specific differences in varieties or cultivars.

Eggs and Poultry Purchase, Storage, and Preparation Practices of Consumers in Selected Asian Countries

The objective of this study was to begin characterizing purchase, storage, handling, and preparation of poultry products and eggs by selected consumers in three Asian countries: India, Korea, and Thailand. Approximately 100 consumers in each location were recruited to participate in this study. The consumers were surveyed about eggs and poultry purchase behavior characteristics, such as temperatures and locations, storage behavior, such as storage locations in the refrigerator or freezer, preparation behavior, such as washing eggs and poultry before cooking, and handling behavior, such as using cutting boards during cooking. The results indicated differences in purchase and storage practices of raw eggs. Most Korean consumers purchased refrigerated eggs and stored the eggs in the refrigerator, while Indian and Thai consumers bought eggs that were stored at room temperature, but would refrigerate the eggs at home. Approximately half of the consumers in each country froze raw meat, poultry, or seafood. Food preparation practices showed potential for cross-contamination during cooking, such as using the same cutting board for different kinds of foods or not washing hands with soap and water. The results presented in this pilot study may lead to development of educational messages and raising consumer awareness of food safety practices in Asian countries.

Sensory and Instrumental Flavor Changes in Green Tea Brewed Multiple Times

Green teas in leaf form are brewed multiple times, a common selling point. However, the flavor changes, both sensory and volatile compounds, of green teas that have been brewed multiple times are unknown. The objectives of this study were to determine how the aroma and flavor of green teas change as they are brewed multiple times, to determine if a relationship exists between green tea flavors and green tea volatile compounds, and to suggest the number of times that green tea leaves can be brewed. The first and second brews of the green tea samples provided similar flavor intensities. The third and fourth brews provided milder flavors and lower bitterness and astringency when measured using descriptive sensory analysis. In the brewed liquor of green tea mostly linalool, nonanal, geraniol, jasmone, and β-ionone volatile compounds were present at low levels (using gas chromatography-mass spectrometry). The geraniol, linalool, and linalool oxide compounds in green tea may contribute to the floral/perfumy flavor. Green teas in leaf form may be brewed up to four times: the first two brews providing stronger flavor, bitterness, and astringency whereas the third and fourth brews will provide milder flavor, bitterness, and astringency.

Quantification of volatile flavor compounds in off-flavor and commercial reduced-fat milk samples

Various chemical compounds contribute to the naturally pleasant flavor of milk. Over time, however, and with unwanted chemical reactions, loss of flavor is inevitable. This study was conducted to identify and quantify volatile flavor compounds associated with off-flavored and commercial reduced-fat milk products. Fresh milk was used for the preparation of altered milk samples having off-flavors such as “light-oxidized” and “high-acid.” Milk lacking freshness (i.e., milk produced two weeks before sampling and maintained at 40F in the dark) also was compared with fresh unaltered milk and two commercial milk samples. For headspace analysis, milk samples were subjected to SPME-GC for volatile compound identification. In addition, the composition and aerobic and coliform microbial counts for all milk samples were analyzed. The milk samples did not differ in the concentrations of volatile flavor constituents. When comparing “light-oxidized” milk samples (200 lx exposure for 1 or 3 hr), 2-butanone and pentanal concentrations tended to increase as light exposure time increased. All milk samples had similar fat and total solids contents. “High-acid” milk had a greater total aerobic microbe count than the other milk samples. Fresh milk had a greater octanal concentration than the offflavored reduced-fat milk samples did. This might indicate that octanal is an important contributor to fresh milk flavor and deserves further study. (