CHARACTERIZATION OF LINEAR AND NONLINEAR DEFORMATION BEHAVIOR OF A WEAK STANDARD GEL MADE FROM HIGH-METHOXYL CITRUS PECTIN

A physical characterization of the deformation behavior up to the gel fracture is given for a weak pectin-saccharose-water standard gel from high-methoxyl citrus pectin. The results refer to citrus pectin from different commercial sources and also to high-methoxyl apple pectin.     

GELPOINT MEASUREMENTS ON HIGH-METHOXYL PECTIN GELS BY DIFFERENT TECHNIQUES

SLow steady shear deformation and small amplitude oscillation measurements have been used to characterize the onset of gelation in high-methoxyl pectin gels. A simplified technique with a shear modulus threshold criterion is proposed for routine evaluation of the gelpoint with a normalized parameter. Limiting conditions of the three methods are discussed.     

ON THE DIFFERING RATES OF FRUCTOSE AND GLUCOSE UTILISATION IN SACCHAROMYCES CEREVISIAE

Fructose is utilised slower than glucose when the two sugars are fermented separately. This phenomenon occurs in a growth promoting medium as well as in brewers wort when using the brewing yeast Saccharomyces cerevisiae. The use of a fructose adjunct in wort at concentrations of 2% w/v and above, may result in residual concentrations of fructose to remain at the end of fermentation and consequently taint the beer with a sweet off-flavour. Glucose and fructose have no effect on maltose utilisation. Thus they do not exert catabolite repression on the maltose membrane transport system in the particular brewing strain of S. cerevisiae under investigation, when fermented in brewers wort.     

EFFECTS OF OIL DROPLET AND AGAR CONCENTRATION ON GEL STRENGTH AND MICROSTRUCTURE OF O/W EMULSION GEL

The effects of oil droplet size and agar concentration on gel strength and microstructure of emulsion gels were investigated by compression test and cryoscanning electron microscope (Cryo-SEM). At all agar concentrations, the compressive stress values of emulsion gels were lower than those of the oil-free gels. Compressive stress and energy were significantly affected by oil droplet size and agar concentration, but compressive strain was not. SEM observation revealed that the overall volume of void spaces decreased and strand compactness increased with increasing agar concentration. Gels containing oil droplets had some void spaces between the gel network and the oil droplets. The strands of emulsion gels did not cover the oil globules completely, a phenomenon which was also observed for the gel with high agar concentration.     

INFLUENCE OF SUCROSE, GLUCOSE AND LACTOSE ON LOSS OF WATER FROM SOLUTIONS

SUMMARY— Moisture losses from solution of 40, 50, and 60% lactose, sucrose, glucose, and combinations of these sugars were determined at 80°F and 27 in. vacuum. Differences in rate of water loss of 20–50% were observed depending on type of sugar and concentration. Rate of water loss from solution was in ascending order of sucrose, lactose, glucose, and pure water. In mixtures, the rate increased with increased proportion of lactose or glucose, and decreased with increased proportion of sucrose. In all cases, after lactose crystallization occurred, the water loss first increased and then decreased.     

硅胶、脯氨酰内肽酶处理对啤酒非生物稳定性的影响

采用SDS-PAGE电泳,对分别经硅胶吸附和脯氨酰内肽酶水解的啤酒后酵液进行蛋白分布研究;通过测定浊度和泡持性研究二者对啤酒非生物稳定性的影响.结果表明经硅胶吸附和脯氨酰内肽酶水解后的蛋白分子量均集中在8ku～14.4ku和35ku～45ku;经处理后的样品浊度明显下降,而泡持性没有显著变化.其中用脯氨酰内肽酶处理时浊度下降更明显.且对啤酒的泡持性影响更小.因此,在啤酒后酵液中添加脯氨酰内肽酶,能够有效的除去啤酒冷混浊蛋白.提高啤酒的非生物稳定性.     

INFLUENCE OF PARBOILING ON RICE STARCH STRUCTURE AND COOKED-RICE TEXTURE

Four varieties of rice having very high (29.4%) to low (17.6%) amylose-equivalent (AE) were parboiled by steaming at atmospheric (PB-O) and at 3 kg/cm2 (PB-3) gauge pressure. The cooked rice texture of the raw, PB-0 and PB-3 rice was determined by Viscoelastographe. Gel permeation chromatography of rice flour starch on Sepharose CL-2B, in general, indicated thermal breakdown of starch. The extent of starch breakdown and the firmness values of cooked PB-0 and PB-3 rices were reasonably well correlated suggesting that starch breakdown during parboiling may have some role to play in varying the texture of rice by parboiling. The chain profile of rice starch remained unaltered after parboiling.     

DEVELOPMENT OF POLYGALACTURONASE ACTIVITY AND SOLUBILIZATION OF PECTIN IN PEACHES DURING RIPENING

SUMMARY –Polygalacturonase activity, water-soluble pectin, total pectin, molecular weight distribution of water-soluble pectin, and fruit firmness were determined during ripening of freestone peaches. Polygalacturonase activity was not present in unripe peaches, but it developed during both tree and postharvest ripening. The development of activity paralleled the formation of water-soluble pectin characteristic of freestone peaches. Fruit firmness began to decrease before polygalac-turonase was detected, but the peaches softened rapidly after the appearance of the enzyme. Application of gel filtration revealed that the molecular weights of peach pectin range from about 100,000 to several million and decrease progressively during ripening. The results indicate a role for polygalacturonase in pectin solubilization during ripening of peaches.     

PITCHING RATES RELATED TO GLUCOSE AND FRUCTOSE UTILIZATION IN Saccharomyces cerevisiae

Pitching rates, in the range 1.5 g/litre to 24 g/litre of yeast in high gravity sucrose adjunct laboratory-scale wort fermentations, are directly proportional to the natural logarithm of glucose utilization throughout fermentation, whereas this relationship only holds for fructose utilization during the intermediate phases. The natural logarithmic rate of fructose utilization in the latter stages of fermentation remains constant irrespective of the pitching rate used. Adjustment of the pitching rate allows residual fructose concentrations at the end of fermentation to be regulated such that they remain below the fructose taste threshold in beer. The difference in utilization rates produced by the preferential utilization of glucose over fructose appears to remain constant irrespective of the pitching rate used. This differential may be ascribed to the competitive inhibition of fructose transport by glucose for their common hexose constitutive facilitated diffusion membrane transport system in S. cerevisiae.     

INFLUENCE OF SALTS AND pH ON THE FIRMNESS OF COOKED SNAP BEANS IN RELATION TO THE PROPERTIES OF PECTIN

Solute conditions inside cooked bean pods were adjusted by soaking the pods in different solutions. Interactions of Ca⁺⁺ and Na⁺ showed increasing firmness as Ca⁺⁺ concentration was raised and decreasing firmness as Na⁺ was raised. Chelating agents removed Ca⁺⁺ and decreased firmness. Higher pH gave lower firmness except in the presence of excess Ca⁺⁺. The presence of Na⁺ decreased the effect of pH on firmness. Urea decreased firmness when pods had been previously treated with a chelator. The effects of treatments on firmness were related to the behavior of pectin solutions and gels.