绿茶提取物对乳清蛋白发泡特性、流变特性和热力学特性的影响

本文选用三种不同的绿茶提取物(CGT、NGT和UGT,分别来自中国、日本和肯尼亚),探讨绿茶提取物对乳清蛋白的发泡特性、流变特性和热力学特性的影响。研究结果表明:绿茶提取物可以显著提高乳清蛋白的发泡能力、发泡稳定性及胶体强度;绿茶提取物不影响乳清蛋白变性温度,但可以使其热焓值显著下降。研究结果暗示乳清蛋白与绿茶提取物中的一些主要组分发生了协同相互作用。     

Pumping-induced ebullition: a unified and simplified method for measuring multiple dissolved gases

The incorporation of multiple dissolved gas measurements in biogeochemical studies remains a difficult and expensive challenge. Incompatibilities in collection, handling, and storage procedures generally force the application of multiple sampling procedures for multiple gases. This paper introduces the concept and application of pumping-induced ebullition (PIE), a unified approach for routine measurement of multiple dissolved gases in natural waters and establishes a new platform for development of in situ real-time dissolved gas monitoring tools. Ebullition (spontaneous formation of bubbles) is induced by pumping a water sample through a narrow-diametertube (a "restrictor") to decrease hydrostatic pressure (PH) below total dissolved gas pressure (PT). Buoyancy is used to trap bubbles within a collection tower where gas accumulates rapidly (1 mL/min) to support multiple chemical analyses. Providing for field collection of an essentially unlimited and unified volume of gas sample, PIE afforded accurate and precise measurements of major (N2, 02, Ar), trace (CO2, N20, CH4) and ultratrace (CFC11, CFC12, CFC113, SF6) dissolved gases in Wisconsin groundwater, revealing interrelationships between denitrification, apparent recharge age-dates, and historical land use. Compared to conventional approaches, PIE eliminates multiple gas-specific sampling methods, reduces data computations, simplifies laboratory instrumentation, and avoids aqueous production and consumption of biogenic gases during sample storage. A lake depth profile for CO2 demonstrates PIE's flexibility as an in situ real-time platform for dissolved gas measurements. The apparent departures of some gases (SF6, H2, N2O, CO2) from solubility equilibrium behavior warrant further confirmation and theoretical investigation.     

Aquatic toxicity of nine aircraft deicer and anti-icer formulations and relative toxicity of additive package ingredients alkylphenol ethoxylates and 4,5-methyl-1H-henzotriazoles

Characterization of the effects of aircraft deicer and anti-icer fluid (ADAF) runoff on aquatic organisms in receiving streams is a complex issue because the identities of numerous toxic additives are proprietary and not publicly available. Most potentially toxic and endocrine disrupting effects caused by ADAF are due to the numerous additive package ingredients which vary among manufacturers and types of ADAF formulation. Toxicity investigations of nine ADAF formulations indicate that endpoint concentrations for formulations of different manufacturers are widely variable. Type IV ADAF (anti-icers) are more toxic than Type I (deicers) for the four organisms tested (Vibrio fischeri, Pimephales promelas, Ceriodaphnia dubia, and Selenastrum capricornutum). Acute toxicity endpoint concentrations ranged from 347 to 7700 mg/L as ADAF for Type IV and from 1550 to 45,100 mg/L for Type I formulations. Chronic endpoint concentrations ranged from 70 to 1300 mg/L for Type IV and from 37 to 18,400 mg/L for Type I formulations. Alkylphenol ethoxylates and tolyltriazoles are two known classes of additives. Nonylphenol, nonylphenol ethoxylates, octylphenol, octylphenol ethoxylates, and 4,5-methyl-1H-benzotriazoles were quantified in the nine ADAF formulations, and toxicity tests were conducted with nonylphenol ethoxylates and 4,5-methyl-1H-benzotriazoles. Toxicity units computed for glycol and these additives, with respect to toxicity of the ADAF formulations, indicate that a portion of ADAF toxicity can be explained by the known additives and glycols, but much of the toxicity is due to unidentified additives.     

The Stability of Theaflavins During HPLC Analysis of a Decaffeinated Aqueous Tea Extract

It has been shown that the theaflavins and thearubigin hump of decaffeinated aqueous extracts of black tea remain virtually stable for up to 850 min, thus permitting their automated overnight analysis. Within-run coefficients of variation for the total chromatogram area and peak area for each of the major theaflavins, following repeated (up to 10 times) injections of a single extract, did not exceed 2·5 and 6·0%, respectively. The corresponding values obtained by pooling data obtained on three separate occasions were 3·0 and 7·3%, respectively. Trend-line analysis indicated that there was a tendency for each of the areas studied to decline by factors in the range 0·11–0·53% of the original value per injection. This factor was not statistically significant for theaflavin-3,3′-digallate but reached 5% significance for theaflavin and total chromatogram area and 1% for both theaflavin monogallates. The magnitude of these changes is too small to warrant an avoidance of automated sample handling in routine screening or quality assurance programmes where the increased throughput allowed is advantageous. It was also noted that the use of citric acid to acidify the chromatographic solvents was not superior to acetic acid. © 1997 SCI.     

Fractionation of green tea extracts: correlation of antimutagenic effect with flavanol content

The present study was undertaken to evaluate the role of individual flavanols in the antimutagenic potential of green tea. Aqueous extracts of green tea were fractionated into four fractions, each of which was fully defined with respect to its content of (-)-epigallocatechin gallate, (-)-epicatechin gallate, (-)-epigallocatechin, (-)-epicatechin and gallic acid. The ability of each fraction to antagonize the mutagenicity of four model mutagens, namely N-nitrosopyrrolidine, benzo(a)pyrene, 2-aminoanthracene and Glu-P-1 (2-amino-6-methyldipyrido[1,2-a: 3,2-d]imidazole), was investigated in the Ames test. No correlation could be established between any of the flavanols and antimutagenic potential. Similarly, no correlation was evident between the flavanol content of each fraction and its ability to inhibit CYP1A, as exemplified by the O-dealkylations of methoxy- and ethoxy-resorufin. Furthermore, no relationship could be established between CYP2B activity, as exemplified by the O-depentylation of pentoxyresorufin and the antimutagenic potential of green tea. Using a modified Ames test procedure, the ability of each tea fraction to scavenge the metabolically generated reactive intermediates of the model mutagens was investigated, this being an additional mechanism of the antimutagenic potential of green tea. Generally, fractions with high flavanol content were more effective scavengers. It is concluded that the contribution of flavanols to the antimutagenic activity of green tea is, at best, limited. ©1997 SCI     

Influence of heating on the polyphenolic content and antioxidant activity of grape seed flour

Abstract: The production of grape seed flour (GSF) from a waste product generated during winemaking, is of interest in product development applications due to its potential health benefits. However, before GSF can used in baking as a source of additional antioxidants, research on its heat stability is required. The overall objective of this study was to assess changes in phenolic content and antioxidant activity of GSF during heating. Merlot GSF was heated at 5 temperatures (120 to 240 °C) for 0 to 90 min. At each time/temperature combination, total phenolic content (TPC), total flavanoid content (TFC), Trolox equivalent antioxidant capacity (TEAC), 2,2 diphenyl‐1‐picrylhydrazyl (DPPH) radical scavenging, and ferric ion reducing antioxidant power (FRAP) of the extracts were determined. Specific polyphenolic compounds, including catechin, gallocatechin, epicatechin, and gallic acid were also measured. Results showed that when Merlot GSF was heated to ≥180 °C, significant decreases in the TPC and antioxidant activity, measured using FRAP, DPPH, and TEAC, were observed. Longer heating times also caused a reduction in antioxidant capability. Catechin and epicatechin content decreased with increasing heating temperature while gallocatechin and gallic acid content increased. Both catechin and epicatechin content had strong positive correlations (r > 0.91) with TPC and TFC, as well with FRAP and TEAC, suggesting that the GSF antioxidant activity is related to the presence of these particular compounds. Overall, while a decrease in antioxidant content was observed during heating, this occurred at higher baking temperatures. Thus GSF may be suitable for use as an ingredient in baked goods to bolster antioxidant content. Practical Application: In order for Merlot grape seed flour (GSF) to be used in baking as a source of additional antioxidant compounds, the impact of heating on the polyphenolic compounds in the GSF needed to be examined. Thermal treatment of Merlot GSF caused significant decreases in the TPC, antioxidant power, and specific polyphenolic compounds when heated ≥180 °C. Thus while antioxidant content decreased with higher heating temperatures, this occurred at higher baking temperatures. Thus, GSF may be suitable for use as an ingredient in baked goods to bolster antioxidant content.     

Total phenolic content, consumer acceptance, and instrumental analysis of bread made with grape seed flour

Grape seed flour (GSF) from grape pomace, a waste product generated during winemaking, was explored for use in bread production due to its potential health benefits. This study evaluated the consumer acceptance and physical properties of bread, including total phenolic content (TPC), made with varying levels of GSF. Dough and breads were prepared using different levels of replacement of hard red spring wheat flour (HRS) with GSF (0 to 10 g GSF/100 g HRS) and stored for 0, 2, or 6 wk at -20 °C. Replacement of 10 g GSF/100 g HRS increased the bread TPC from 0.064 mg tannic acid/g dry weight to 4.25 mg tannic acid/g dry weight. Consumer acceptance and instrumental analyses were used to investigate changes in sensory and texture properties due to GSF replacement. Replacement above 5 g GSF/100 g HRS decreased the loaf brightness and volume, with an increase in the bread hardness and porosity. Generally, breads containing ≥ 7.5 g GSF/100 g HRS were characterized by lower consumer acceptance. A reduction in overall and bitterness acceptance was observed in bread at 10 g GSF/100 g HRS, with decreased acceptance of astringency and sweetness at 7.5 and 10 g GSF/100 g HRS. Based on these results, the replacement of 5 g GSF/100 g HRS is recommended for the production of fortified breads with acceptable physical and sensory properties and high TPC activity compared to refined bread. PRACTICAL APPLICATIONS: This study shows that grape seed flour (GSF) can be used to replace hard red spring wheat flour (HRS) in bread production, with moderate impact on the physical and sensory properties of the bread. Replacement of up to 10 g GSF/100 g HRS significantly decreased overall consumer acceptance of the bread, with lower consumer acceptance of sweetness and astringency at 7.5 and 10 g GSF/100 g HRS. Thus, a replacement value of 5 g GSF/100 g HRS is recommended for the production of fortified breads.