Changes in the chemical compositions and biological properties of kombucha beverages made from black teas and pineapple peels and cores.

Several raw materials have been used as partial supplements or entire replacements for the main ingredients of kombucha to improve the biological properties of the resulting kombucha beverage. This study used pineapple peels and cores (PPC), byproducts of pineapple processing, as alternative raw materials instead of sugar for kombucha production. Kombuchas were produced from fusions of black tea and PPC at different ratios, and their chemical profiles and biological properties, including antioxidant and antimicrobial activities, were determined and compared with the control kombucha without PPC supplementation. The results showed that PPC contained high amounts of beneficial substances, including sugars, polyphenols, organic acids, vitamins, and minerals. An analysis of the microbial community in a kombucha SCOBY (Symbiotic Cultures of Bacteria and Yeasts) using next-generation sequencing revealed that Acetobacter and Komagataeibacter were the most predominant acetic acid bacteria. Furthermore, Dekkera and Bacillus were also the prominent yeast and bacteria in the kombucha SCOBY. A comparative analysis was performed for kombucha products fermented using black tea and a fusion of black tea and PPC, and the results revealed that the kombucha made from the black tea and PPC infusion exhibited a higher total phenolic content and antioxidant activity than the control kombucha. The antimicrobial properties of the kombucha products made from black tea and the PPC infusion were also greater than those of the control. Several volatile compounds that contributed to the flavor, aroma, and beneficial health properties, such as esters, carboxylic acids, phenols, alcohols, aldehydes, and ketones, were detected in kombucha products made from a fusion of black tea and PPC. This study shows that PPC exhibits high potential as a supplement to the raw material infusion used with black tea for functional kombucha production.

Gene organization and molecular modeling of copper amine oxidase from Aspergillus niger: re-evaluation of the cofactor structure.

Amine oxidase AO-I from Aspergillus niger AKU 3302 has been reported to contain topa quinone (TPQ) as a cofactor; however, analysis of the p-nitrophenylhydrazine-derivatized enzyme and purified active site peptides showed the presence of a carboxylate ester linkage of TPQ to a glutamate. The catalytic functionality of such a cross-linked cofactor has recently been shown unlikely by spectroscopic and voltammetric studies on synthesized model compounds. We have obtained resonance Raman spectra of native and substrate-reduced AO-I demonstrating that the catalytically active cofactor is unmodified TPQ. The primary structure of the enzyme (GenBank acc. no. U31869) has been reviewed and updated by repeated isolation and sequencing of AO-I cDNA. This allowed rectification of several errors that account for previously reported low homology to other amine oxidases in the regions around copper binding histididyl residues. The results were confirmed by cloning the ao-1 structural gene (GenBank acc. no. AF362473). Analysis of the gene 5'-upstream region of the gene revealed potential binding sites for an analog of NIT2, the nitrogen metabolism regulatory protein found in Neurospora crassa and other fungi. The molecular structure of AO-I was modeled by a comparative method using published crystal structures of amine oxidases as templates.

Polyphenol-induced inhibition of the response of na(+)/glucose cotransporter expressed in Xenopus oocytes.

To study the effects of polyphenols on the Na(+)/glucose cotransporter (SGLT1) response, SGLT1 was expressed in Xenopus oocytes by injecting cRNA synthesized from the cloned cDNA of the small intestine cotransporter of rats, and the electrical response elicited by glucose or galactose was measured by a voltage clamping method. Most phenol derivatives had no effect on the response. However, the polyphenols (+)-catechin, (-)-epicatechin gallate (ECg), and (-)-epigallocatechin gallate (EGCg), which are components of green tea, caused an inhibition of the response, which was almost independent of glucose concentration. The inhibition constants were estimated to be 2.3 mM for (+)-catechin and 0.45 mM for both ECg and EGCg, assuming the noncompetitive inhibition mechanism. Saponin prepared from tea seeds also inhibited the response significantly. Tannic acid and aqueous extracts of teas induced nonspecific electrical responses in both cRNA-injected and noninjected oocytes at lower concentrations than those that caused an inhibition of the SGLT1 response when their dose-dependent effects were examined. These results are possibly helpful in the development of a dietary supplement for diabetic patients.