Béla S. Buslig

FRACTIONATION AND PRETREATMENT OF ORANGE PEEL BY DILUTE ACID HYDROLYSIS

Abstract Solubilization and depolymerization of carbohydrates by treatment of orange peel with dilute (0·06 and 0·5%) sulfuric acid at 100, 120 and 140°C has been investigated. The acid treatments solubilized a large portion of total carbohydrates in orange peel. However, only soluble sugars and sugars derived from hydrolysis of hemicelluloses were efficiently released by the treatment with hot dilute sulfuric acid. Cellulose and segments of pectin containing galacturonic acid units were very resistant to acid-catalyzed hydrolysis. The treatment with dilute sulfuric acid had a positive effect on the rate of subsequent enzymatic hydrolysis of orange peel by a mixture of cellulolytic and pectinolytic enzymes.

Flavonoids in the Living System

Flavonoids and related phenols are ubiquitous in land plants (Mabry and Ulubelen, 1980), and as a common element of plants they have taken their place in importance in far ranging arrays of biological systems, being integral to the function of most living systems. The study of these compounds has attracted the attention of generations of chemists. In fact, as one of the first flavonoids described, hesperidin, the primary flavanone glycoside in citrus, was first reported by Lebreton nearly 170 years ago (Lebreton, 1828). Although there has been a long history of the use of medicinal plants rich in flavonoids, our recent interest in the biological properties of the flavonoids began with the findings of Szent-Gyorgyi who found that citrus flavonoids were important to proper capillary function (Rusznyak and Szent-Gyorgyi, 1936). Although the vitamin status that was briefly attributed to flavonoids was discontinued in 1950, subsequent research has clearly shown an ever increasing list of biological systems over which flavonoids exert significant control. The pace of this research has rapidly accelerated, and recently, a much clearer understanding has emerged of the significance of these compounds, not only in plants, but also in animal systems, and ultimately pertaining to human health. This volume is based primarily on an American Chemical Society symposium held in Orlando, FL in August, 1996. Some of the material was added later to highlight new findings regarding the biological properties of flavonoids. It is not intended to be a comprehensive treatment of flavonoid research, nevertheless it is hoped that it shows new perspectives and encourages new research into this broad subject area at the cellular and molecular levels.

Production of ethanol from enzymatically hydrolyzed orange peel by the yeast Saccharomyces cerevisiae

We extended our previous investigations of enzymatic hydrolysis of polysaccharides in orange peel by commercial cellulase and pectinase enzymes to higher, more practical concentrations of orange peel solids. High yields of saccharification could be maintained even at substrate concentrations as high as 22–23%, but the rates of solubilization and saccharification decreased 2-3-fold. We also tested the fermentability of these hydrolysates by the yeastSaccharomyces cerevisiae, which revealed the presence of inhibitory compounds. These compounds could be removed by the filtration of hydrolyzed peel. Successful fermentations of filtered hydrolysates were achieved after pH adjustment with calcium carbonate.

Fermentation of galacturonic acid and other sugars in orange peel hydrolysates by the ethanologenic strain of Escherichia coli

SummaryEnzymatic hydrolysates of orange peel contain relatively high levels of galacturonic acid and arabinose which are not fermentable to ethanol by yeasts. We observed complete utilization of both sugars during fermentation of peel hydrolysates by the ethanologenic construct of E. coli KO11. The bacterium exhibits a novel pattern of galacturonic acid fermentation producing equimolar amounts of acetate and ethanol accompanied by carbon dioxide.

Fermentation of galacturonic acid and pectin-rich materials to ethanol by genetically modified strains of Erwinia

Evaluation of the four ethanologenic constructs of bacteria in the genus Erwinia indicates that two strains E. chrysanthemi EC16 and E. carotovora SR38 show promise for development of direct hydrolysis and fermentation of pectin-rich substrates to mixtures of ethanol and acetate. Both strains fermented glucose to ethanol in nearly theoretical yields, but produced mainly acetate and ethanol by fermentation of D-galacturonic acid. Both strains depolymerized citrus pectin, polygalacturonic acid and polysaccharides in citrus peel and converted resulting sugars to carbon dioxide, acetate, ethanol and lesser amounts of formate and succinate.

Fermentation of sugars in orange peel hydrolysates to ethanol by recombinant Escherichia coli KO11

The conversion of monosaccharides in organe peel hydrolysates to ethanol by recombinantEscherichia coli KO11 has been investigated in pH-controlled batch fermentations at 32 and 37°C. pH values and concentration of peel hydrolysate were varied to determine approximate optimal conditions and limitations of these fermentations. Very high yields of ethanol were achieved by this microorganism at reasonable ethanol concentrations (28–48 g/L). The pH range between 5.8 and 6.2 appears to be optimal. The microorganism can convert all major monosaccharides in organe peel hydrolysates to ethanol and to smaller amounts of acetic and lactic acids. Acetic acid is coproduced in equimolar amounts with ethanol by catabolism of salts of galacturonic acid.

Discriminant and principal component analyses to classify commercial orange juices based on relative amounts of volatile juice constituents

Pasteurised orange juices and two types of commercial orange juice from frozen concentrate were differentiated based on the combined levels of 15-25 volatile constituents monitored in each of 44 juice samples. Multivariate analysis programs were used to calculate discriminant and principal component analyses and to display the results graphically. Since this group of samples was part of a nutritional database study, other parameters were included in an effort to improve discrimination of the types of juice samples monitored. Addition of °Brix and acid values improved the separation by principal component analysis of the three types of juice studied. Discriminant analysis provided better separation of juice types than did principal component analysis.

The metabolism of linalool in Citrus plants

Abstract Citrus fruit and leaf explants were fed linalool-3- 14 C. Volatile oils were recovered by steam distillation and fractionated by gas—liquid and thin-layer chromatography. α-Terpineol and other terpenoid alcohols were the predominant metabolites in leaves. Fruit also produced α-terpineol, but significant label could also be found in (+)-limonene and other hydrocarbons.

Fermentation of orange peel hydrolysates by ethanologenic Escherichia coli : Effects of nutritional supplements

Orange peel, an abundant byproduct of the citrus processing industry, is converted to a mixture of glucose, galacturonic acid, fructose, arabinose, galactose, and xylose by hydrolysis with mixed pectinase and cellulase enzymes. All these sugars can be fermented to ethanol or ethanol and acetic acid by the recombinant bacteriumEscherichia coli KO11. The fermentation efficiency is improved by the addition of yeast extract, tryptone, mixed amino acids, corn steep liquor, or, by proteolytic digestion of endogenous proteins. Batch fermentations of supplemented peel hydrolysate containing 111 g/L of initial total sugars produced 35–38 g/L of ethanol in 48–72 h and a 75–85% yield.Orange peel, an abundant byproduct of the citrus processing industry, is converted to a mixture of glucose, galacturonic acid, fructose, arabinose, galactose, and xylose by hydrolysis with mixed pectinase and cellulase enzymes. All these sugars can be fermented to ethanol or ethanol and acetic acid by the recombinant bacterium Escherichia coli KO11. The fermentation efficiency is improved by the addition of yeast extract, tryptone, mixed amino acids, corn steep liquor, or by proteolytic digestion of endogenous proteins. Batch fermentations of supplemented peel hydrolysate containing 111 g/L of initial total sugars produced 35-38 g/L of ethanol in 48-72 h and a 75-85% yield.

New furanocoumarins detected from grapefruit juice retentate

Grapefruit (Citrus paradisi Macf.) furanocoumarins and related compounds have been shown to interact with the enterocyte cytochrome P450, CYP3A4, and as a result they affect the bioavailibility of certain drugs. Only a few grapefruit furanocoumarins have been identified so far. In this study, grapefruit juice retentate, rich in furanocoumarins, was extracted and then separated by flash chromatography for the examination of new compounds. Finally, nine new furanocoumarins were detected in different fractions according to their UV spectra and mass spectrometric properties by LC-MS (liquid chromatography mass spectrometry) and tentatively designated as FC 338, FC 420, FC 524, FC 530, FC 540, FC 546, FC 552, FC 570 and FC 614.