Bitterness compounds in coffee brew measured by analytical instruments and taste sensing system.

We investigated the bitter compounds in coffee brews using multivariate analysis of the data obtained from analytical instrument and electronic taste sensor experiments. Coffee brews were prepared from coffee beans roasted to four different degrees. Each brew was fractionated into four fractions by liquid-liquid extraction. The relative amounts of 30 compounds in each fraction were analyzed by analytical instruments, and the bitterness response value of each fraction was analyzed by a taste sensor. Candidate bitter compounds in the coffee brews were identified with reference to their variable importance in projection and by coefficient of projection to latent structure regression (PLS-R) analysis. PLS-R analysis suggested that nicotinic acid, l-lactic acid, and nicotinamide contributed to the bitterness of the coffee brews. In fact, the coffee brews with added nicotinic acid, l-lactic acid, and nicotinamide had an increased bitterness response value compared to those without.

Decrease in the acrylamide content in canned coffee by heat treatment with the addition of cysteine.

Acrylamide (AA) is classified as a Group 2A carcinogen according to the International Agency for Research on Cancer. Although coffee contains a small amount of AA, it is a popular beverage worldwide. Approximately 10 billion canned coffees are consumed each year in Japan. In this study, we investigated how to decrease AA contained in canned coffee by modifying the heat treatment used for sterilization during the manufacturing process. The AA content of both types of canned coffee (black and milk) was decreased by approximately 95% by heat treatment with adding cysteine at 121 °C for 6 min. The content was also decreased by heat treatment with dithiothreitol, although that with cystine had no effect. Therefore, it is shown that thiol groups in cysteine and dithiothreitol might play an important role in decreasing the AA content.

Degradation kinetics of chlorogenic acid at various pH values and effects of ascorbic acid and epigallocatechin gallate on its stability under alkaline conditions.

5-Caffeoylquinic acid (5-CQA) is generally referred to as chlorogenic acid and exhibits various biological activities such as antioxidant activity and porcine pancreas α-amylase inhibitory activities. 5-CQA may be useful as an antioxidant for food and to prevent diabetes and obesity. The degradation of 5-CQA and caffeic acid (CA) in an aqueous solution at 37 °C and pH 5.0-9.0 was studied. The degradation of 5-CQA and CA, demonstrating time and pH dependence (i.e., the rate constant, k, was higher at higher pH), was satisfactorily described by the Weibull equation. The stability of 5-CQA at pH 7.4 and 9.0 was improved by adding (-)-epigallocatechin gallate (EGCG) and ascorbic acid (AA). Moreover, the degradation of 5-CQA in the presence of EGCG or AA could be described by the Weibull equation. The k value in the presence of EGCG or AA was dependent on their concentration.

Inhibitory activity of chlorogenic acids in decaffeinated green coffee beans against porcine pancreas lipase and effect of a decaffeinated green coffee bean extract on an emulsion of olive oil.

A decaffeinated green coffee bean extract (DGCBE) inhibited porcine pancreas lipase (PPL) activity with an IC50 value of 1.98 mg/mL. Six different chlorogenic acids in DGCBE contributed to this PPL inhibition, accounting for 91.8% of the inhibitory activity. DGCBE increased the droplet size and decreased the specific surface area of an olive oil emulsion.

High antioxidant activity of coffee silverskin extracts obtained by the treatment of coffee silverskin with subcritical water.

Coffee silverskin (CS) is a thin tegument of the outer layer of green coffee beans and a major by-product of the roasting process to produce roasted coffee beans. CS extracts obtained by the treatment of CS with subcritical water at 25-270°C were investigated for their antioxidant activity using hydrophilic oxygen radical absorption capacity (H-ORAC) and DPPH radical scavenging capacity assays. The antioxidant activity increased with increasing the extraction temperature and the highest activity was observed with the extracts obtained at 270°C. The H-ORAC and DPPH values of the extracts were 2629±193 and 379±36µmol TE/g of CS extract, respectively. High correlation (R=0.999) was observed between H-ORAC and DPPH values for the CS extracts. High correlation of the antioxidant activity was also observed with protein and phenolic contents in the extracts. The CS extracts could be useful as a good source of antioxidative materials.

Inhibitory effect of a hot water extract of coffee "silverskin" on hyaluronidase.

Coffee "silverskin" (CS) is a by-product of the roasting procedure for coffee beans. A CS extract (CS-ext) was found to have a high inhibitory effect against hyaluronidase. It seems that the higher-molecular-weight substances in CS-ext contributed most to the hyaluronidase inhibition, while acidic polysaccharides mainly composed of uronic acid played a major role in this hyaluronidase inhibition by CS-ext.

Kinetic analysis and mechanism on the inhibition of chlorogenic acid and its components against porcine pancreas alpha-amylase isozymes I and II.

Chlorogenic acid (5-caffeoylquinic acid, 5-CQA) is a kind of polyphenol and is richly included in green coffee beans. The inhibitory effects of 5-CQA and its components, caffeic acid (CA) and quinic acid (QA), on the two porcine pancreas alpha-amylase (PPA) isozymes, PPA-I and PPA-II, were investigated using p-nitrophenyl-alpha-D-maltoside as substrate at pH 6.9 and 30 degrees C. The inhibition potencies of the respective inhibitors against both PPA isozymes were almost the same and in the order of 5-CQA > CA >> QA. Their IC(50) values were 0.07-0.08 mM, 0.37-0.40 mM, and 25.3-26.5 mM, respectively. The inhibition mechanisms of 5-CQA and CA were investigated by kinetic analyses, and the inhibitor constants K(i) and K(i)' (for the free enzyme and enzyme-substrate complex, respectively) were determined. It was indicated that 5-CQA and CA showed mixed-type inhibition with K(i) > K(i)' against both PPA-I and PPA-II. The binding of PPA-I or PPA-II with 5-CQA or CA was all exothermic and enthalpy-driven. QA is a poor inhibitor, and its inhibitory mode was unique and hardly analyzed by a simple Michaelis-Menten-type interaction between the enzyme and inhibitor. However, it was shown that the inhibitory activity of CA was enhanced 5 times by ester-bond formation with QA in the form of 5-CQA. These results provide us with significant hints for the development of alpha-amylase inhibitors useful for the prevention of diabetes and obesity.