摘要:

ABSTRACTHardcore in sweet potatoes is caused by chilling followed by non‐chilling temperatures and appears as hard tissue after cooking. Changes in pectic substances and the involvement of tissue softening by beta‐elimination of pectic substances were studied in relation to hardcore development. Pectic substances from cell wall, middle lamella extracts of hardcore tissue resisted degradation by betaelimination. This resistance was associated with reduced esterification and increased levels of bound cations. The mechanism of hardcore formation appears to involve activation of demethoxylation during chilling and rapid demethoxylation of pectic substances when subsequently exposed to nonchilling temperature. Demethoxylated pectic substances and pectate salts may then restrict degradation by beta‐elimination and concomitant softening during co

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1982.tb00292.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

ABSTRACTMature oranges were analyzed for citrate synthase, acyl coenzyme A reductase, acyl coenzyme A and palmitaldehyde. Peeled oranges contained 9640 units citrate synthase and 150 units of acyl coenzyme A reductase per kg. The level of fatty acyl coenzyme A (3 pM) was suggested as a potential effector of citrate synthase. Palmitaldehyde(0.04 pM) was suggested as a product of the acyl coenzyme A reductase reaction with palmityl coenzyme A.

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1982.tb00293.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

ABSTRACTA preliminary investigation of the membrane lipid ofHalobacterium halobiumas a food additive. F. J. Post and N. F. Collins, Biology Department, Utah State University, Logan, Utah 84322.A study was made of the suitability of the diether phytanyl phosphatidyl glycerol phosphate lipid component of the cell membrane ofHalobacterium halobiumNRC 34003 as a potential food additive. The lipid was shown to be a possible emulsifier with a hydrophile‐lipophile balance (HLB) of7–8 producing a water in oil emulsion. Its use as a possible noncaloric fat substitute is also discussed. The lipid had a melting point at‐120to ‐150C and was nontoxic at an 0.8 g kg‐1, one‐dose exposure to mice either by feeding or by intraperitoneal injection. Some methods for increasing the yield of lipid a

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1982.tb00294.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

ABSTRACTXylan from Larchwood was utilized as a carbon source by three species ofBacteroidesfrom the human colon:Bacteroides ovatus, Bacteroides eggerthiiandBacteroides fragilissubsp. a. Xylan‐degrading enzymes of all three species were cell‐associated rather than extracellular, i.e. xylanase activity was detected in sonically disrupted bacteria but not in the extracellular fluid. The state of hydration of the xylan was an important factor in determining the extent to which the xylan was hydrolyzed by the bacterial enzymes. When xylan which had been partially hydrated by autoclaving was subjected to centrifugation at 17,000 xg for 20 min at 40C, a portion of the xylan was pelleted. This portion, which was presumably less well hydrated than the xylan which remained in solution, was not digested at all by the bacterial enzymes. By contrast, xylan which remained soluble after centrifugation (soluble xylan) was degraded by bacterial xylanases. Xylose was the main product of digestion, although traces of arabinose, glucose and higher oligomers of xylose were also detected. Even after exhaustive hydrolysis, less than 60% of the soluble xylan was hydrolyzed. Removal of most of the arabinose branches did not increase the extent of hydrolysis. Moreover, the carbohydrate composition of the portion of the soluble xylan which resisted hydrolysis was the same as the composition of the xylan which was hydrolyzed. Thus it is likely that hydrolysis was limited by aggregate formation rather than by structural features such as arabinose branc

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1982.tb00295.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

ABSTRACTThe susceptibility of isolated cell walls to solubilization by polygalacturonase and the effect of pectinesterase on the solubilization were examined. The two polygalacturonases in ripe tomatoes were purified to remove pectinesterase. Both polygalacturonases solubilized uronic acid from pectinesterase‐free tomato cell walls most rapidly at about pH 3.5, well below p H 4.5, the pH optimum for their hydrolysis of pectic acid. At p H 3.5, very low levels of pectinesterase increased cell wall solubilization by the polygalacturonases seueralfold, whereas high concentrations of pectinesterase completely inhibited solubilization. A t pH 5, pectinesterase also increased cell wall solubilization, but higher concentrations were required than at pH 3.5 and high levels were not inhibitory. The materials solubilized at pH 3.5 were galacturonan with a molecular weight of about 110,000 and two fractions of much higher molecular weights consisting primarily of neutral sugars. Galactose accounted for about two‐thirds of the monosaccharides in the neutral polysacchari

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1982.tb00296.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY