摘要:

ABSTRACTThe effect of haptenic carbohydrates, N‐acetyl‐galactosamine and galactose, on soybean agglutinin (SBA) thermal denaturation was measured by differential scanning calorimetry (DSC) and batch heating in an oil bath. Thermodynamic parameters were determined by scanning from 30 to 11OC, at 1C/min. Lectin activity was measured by a hemagglutination test after heating at 80, 85, 90 and 95C for 5, 10, 15 and 20 min. Soybean lectin denaturation was an irreversible process with ΔH±= 120 kcal/mol that was significantly reduced by carbohydrates, and it was a carbohydrate concentration dependent phenomenon. In addition, haptenic carbohydrates induced an increase of the Tmaxand Ttrof SBA denaturation when compared with soybean lectin solution alone. The loss of lectin activity was faster in absence of haptenic carbohydrates than those obtained from solutions with the specific sugars. It was concluded that haptenic sugars protected the SBA against denatur

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1993.tb00475.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTNative wheat, oat, potato and lentil starches were annealed at various starch/water ratios at 50C for time intervals ranging from 0.5 to 72 h. Annealing did not change granule size and shape. Oat starch granules were less compactly packed after annealing. X‐ray diffraction patterns remained unchanged and X‐ray intensities changed only marginally in all starches. The swelling factor (SF), amylose leaching (AML) and the gelatinization temperature range (GTR) decreased on annealing. The extent of decrease in SF and AML followed the order: lentil>wheat>potato>oat, while the corresponding order for GTR was: wheat>lentil>oat>potato. The gelatinization transition temperatures (GTT) and enthalpy (ΔH) increased on annealing. However, the increases in GTT and ΔH did not begin concurrently during the time course of annealing. Increases in ΔH were slower and were evident only after 1, 2, 6 and 48 h, respectively, in lentil, potato, oat and wheat starches. The extent and rate of increase in GTT and ΔH followed the order: potato>lentil>wheat>oat. The magnitude of changes in GTT and ΔH increased with increase in annealing moisture content. The susceptibility of oat starch to enzyme and acid hydrolysis increased on annealing. However, decreases occurred in the other starches (lentil>wheat>potato). Thermal and shear stability of starch granules increased on annealing (potato>lentil>wheat>oat). The results showed that the above changes in physicochemical properties were due to increased interaction between starch components during a

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1993.tb00476.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTRed pears had higher PPO activity, total phenolics and chlorogenic acid concentration than Bosc pears. PPO activity and phenolics both decreased in fruits held at room temperature. pH and temperature optima for Bosc and Red pears PPOs were 5.0 and 5.5, and 20 and 23C, respectively. 4‐Methylcatechol, catechol and dopamine were good substrates for PPO from both pear cultivars; however, no activity was observed with any of the mono‐hydroxy substrates studied. Higher Kmand lower Vmaxvalues were observed for Bosc pear PPO. Heating at 75C for 30 min completely inactivated the enzyme from both cultivars. Heating at 55 and 65C for the same duration resulted in partial inactivation (45–60%) of this enzyme. Ascorbic acid, L‐cysteine, sodium metabisulfite and thiourea effectively inhibited browning due to pe

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1993.tb00477.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTThree isozymes of pectin methylesterase (EC 3.1.1.11) have been purified to homogeneity from tomato (var. S. marzano). The isozymes were separated by affinity chromatography on Heparin‐Sepharose column. They exhibited a molecular mass of 31 kDa when analyzed in sodium dodecyl sulfate gel electrophoresis and of 35 kDa in gel‐filtration chromatography in native conditions. The isoelectric points of all three isozymes were found to be higher than 9.3. The Kmscalculated for the three isozymes were different toward citrus pectin used as substrate; one had a Kmof 9.7 mM (by expressing the pectin concentration as mmoles/L of methoxy groups) and the other two had similar Kmsof 3.0 and 2.6 mM, respectively. The isozyme having the higher Kmfor substrate was inhibited by citrus pectin (which had a degree of methylation of 70%) at concentrations higher than 5 mM, but no inhibition was found using a pectin with a degree of methylation of 30% at concentrations up to 13 mM (i.e. 9 mg/ml) with a Kmof 14.7 mM. Furthermore, this isozyme showed a more broad range of activity in a pH range 5–10 with respect to that exhibited by the other two isozymes. All three isozymes were found to be glycosylated, although to different ex

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1993.tb00478.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Book reviewed in this article:FOOD TAINTS AND OFF‐FLAVOURS, Edited by M.J. Saxb

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1993.tb00479.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY