Influence of Thermal Aging on Microstructural Development of Mullite Containing Alkalis

The influence of annealing treatments at temperatures of 900°C up to 1630°C on the microstructure of a 3Al₂O₃2SiO₂ mullite that contains a small amount of alkali (<3 wt%) has been studied. Annealing treatments of a base mullite material at the sintering temperature (1630°C) and at two temperatures lower (900°C) and higher (1200°C) than the lowest invariant points of the SiO₂-Al₂O₃-Na₂O system have been performed. Microstructures have been characterized by using scanning and transmission electron microscopy. Special attention has been given to grain-boundary characteristics-particularly the amount, composition, and distribution of the remaining glasses. Aging of this material at high temperature leads to a redistribution of the microstructure toward an equilibrium that involves the dissolution of the mullite grains, formation of a liquid phase, and liquid-phase grain growth. As the aging temperature increases, liquid-phase grain growth progressively overcomes the effect of the dissolution of mullite and a bimodal microstructure with an increasing number of large, tabular grains develops.     

Oxidation of BN/Nicalon Fiber Interfaces in Ceramic-Matrix Composites and Its Effect on Fiber Strength

Microstructural changes at the interface were analyzed in two Nicalon-fiber ceramic-matrix composites with a dual BN/SiC coating on the fibers after thermal exposure at different temperatures (in the range 800°-1400°C) and in different environments (air and argon). The outer SiC coating acted as a barrier to oxygen, which penetrated into the composite via pipeline diffusion along the BN/fiber interfaces. Oxygen penetration led to the formation of an SiO₂ layer by oxidation of the fiber surfaces. The in situ fiber strength at different temperatures, as determined from the radius of the mirror region on the fiber fracture surface, indicated that this SiO₂ layer severely degraded the fiber strength. Oxidation was highly dependent on the nature of the BN/fiber interface. The presence of a thin carbon-rich interlayer, which burned out rapidly at high temperature, favored the entry of oxygen and accelerated oxidation of the fibers.     

Apparent chemical composition of nine commercial or semi-commercial whey protein concentrates, isolates and fractions

Summary Analytical results are given for whey powders prepared on a commercial or semi-commercial scale by three companies. Altogether, five preparations enriched in β-lactoglobulin, four whey protein isolates and a fraction enriched in α-lactalbumin were analyzed for protein composition, including %β-lactoglobulin, α-lactalbumin, bovine serum albumin, casein (glyco) macropeptide and the main triglycerides. Protein composition was determined by high pressure gel permeation and reversed phase liquid chromatography and by capillary zone electrophoresis. The extent of modification of the native β-lactoglobulin structure was also measured through the degree of lactosylation and the fraction of accessible free sulphydryl groups. One significant finding was that the calculated recovery of protein following quantitation of the chromatogram or electropherogram was seldom above 90% and occasionally below 60% of that loaded onto the column or capillary, raising doubts as to the reliability of the analytical results. Extrapolation by linear regression to 100% recovery allowed estimates to be made of the true β-lactoglobulin composition of the samples. The nine samples could be placed into three distinct groups with estimated true β-lactoglobulin weight % of 70.9 ± 1.1, 62.0 ± 3.4 and 39.5 ± 4.9. Physico-chemical properties of the group of samples are reported elsewhere (Holt et al ., 1999).     

Changes in chemical composition and nutritional quality of fried sardine (Clupea pilchardus) produced by frozen storage and microwave reheating

Modifications in proximate composition, fatty acids, amino acids and –SH groups content, as well as changes in solubility and nutritional quality of protein, were studied in fillets of sardine (Clupea pilchardus) that had been successively pan-fried, frozen stored and reheated by two different means, namely conventional oven and microwave oven. Upon pan-frying in olive oil the sardine absorbed C18: 1(n-9) and C18: 2(n-6) and lost saturated (SFA) and polyunsaturated fatty acids (PUFA); this loss continued upon reheating, and as a consequence the percentage of MUFA increased compared to the just-fried sardine. A loss of water was observed during all processes. Upon frying there was a decrease of cyst(e)ine. Upon reheating by both microwave and conventional oven, methionine decreased; however, cyst(e)ine only decreased with the use of a conventional oven. A loss of –SH groups was recorded during frying and this phenomenon continued upon reheating. Biological value (BV) together with net protein utilisation (NPU) decreased upon both frying and reheating. © 1997 SCI.     

Seasonal Changes in the Composition and Properties of a High Dietary Fibre Powder from Grapefruit Peel

Seasonal changes in composition and properties of a high dietary fibre product from grapefruit peel were studied. Total dietary fibre decreased in January as compared to September (586–686 g kg^-1). Main constituents from soluble fibre were: uronic acids (172–233 g kg^-1), arabinose (13–41 g kg^-1), galactose (4–11 g kg^-1), glucose (5–10 g kg^-1) and xylose (2–3 g kg^-1). Insoluble dietary fibre (385–392 g kg^-1) did not significantly change during the season. Its main constituents were: Klason lignin (29–37 g kg^-1), uronic acids (33–70 g kg^-1) and neutral sugars: glucose (149–196 g kg^-1), mannose (45–50 g kg^-1), xylose (25–38 g kg^-1), galactose (20–22 g kg^-1) and arabinose (16–45 g kg^-1). Total neutral sugars from dietary fibre decreased over the harvest period (315–383 g kg^-1) and an inverse trend was observed in total free-sugars from samples (49–85 g kg^-1). Both, water holding capacity (7·0–9·3 g water g^-1 dry sample) and glucose retardation index (7·0–25·3%) decreased from early stages in fruit development until late in the harvest season. Seasonal changes in grapefruit peel should be taken into account, in order to standardise the quality of rich fibre products. © 1997 SCI     

Influence of freezing process on free sugars content of papaya and banana fruits

Changes in individual sugar content (fructose, glucose and sucrose) during freezing and frozen storage have been evaluated by HPLC on papaya (Carica papaya grupo Solo var Sunrise), fruits proceedings from female and hermaphrodite flowers, and banana (Musa cavendishii var enana). Effects of thermal treatments, such as blanching and microwaving, prior to freezing banana fruit were examined. Both an increase in total sugar levels of papaya samples during freezing and a decrease in sucrose, by invertase, were found followed by an increase in fructose and glucose. A slight decrease in total sugars of banana samples during freezing and storage has been observed, with no significant differences between the pretreatments applied. © 1998 SCI.     

Carotenoid Pigments and Colour of Hermaphrodite and Female Papaya Fruits ( Carica papaya L) cv Sunrise During Post-Harvest Ripening

The predominant carotenoids in extracts of female and hermaphrodite Papaya fruits (Carica papaya L) Solo cv Sunrise were determined by high-performance liquid chromatography on a C₁₈ reversed-phase column using a diode-array detector. Three classes of carotenoids were separated and identified from the papaya extract without saponification; these were xanthophylls, hydrocarbon carotenoids and carotenol fatty acid esters. The xanthophylls were identified as trans-zeaxanthin, cryptoflavin and β-cryptoxanthin; other xanthophyls were detected in very small quantities. The major hydrocarbon carotenoid was identified as lycopene. Carotenol fatty acid esters were identified as carotenol fatty acid esters of β-cryptoxanthin, cryptoxanthin-5,6-epoxide, lutein, zeaxanthin and violaxanthin. There were no qualitative differences among the carotenoid pattern of female and hermaphrodite papaya fruits. Changes in carotenoid composition during ripening in hermaphrodite and female papaya fruits (cv Sunrise) were investigated in three different stages of ripeness. These changes could be shown in terms of Hunter colour values.     

Sequence analysis of a 14·6 kb DNA fragment of Saccharomyces cerevisiae chromosome VII reveals SEC27, SSM1b,a putative S-adenosylmethionine-dependent enzyme and six new open reading frames

The nucleotide sequence of a fragment from the left arm of Saccharomyces cerevisiae chromosome VII has been determined. Analysis of the 14,607 bp DNA segment reveals nine open reading frames (ORFs) longer than 300 bp. G2827 is the SEC 7 gene, an essential coatomer complex subunit. G2834 encodes SSM1b, a ribosomal protein. The G2838 product shows homology to hypothetical yeast proteins, YIF0 and YE09, of unknown function. The G2830 product shows homology with the cell division protein FtsJ from Escherichia coli, with two hypothetical proteins from yeast, YCF4 and YBR1, and with R74.7, a hypothetical protein from Caenorhabditis elegans. Two of the ORFs are completely internal to longer ones and a third is partially embedded in G2850. The remaining ORFs give no significant homology with proteins in the databases. The sequence has been deposited at the EMBL database under Accession Number X92670.