Setting, pectin

The colours, flavours and remaining acid are added. Once this acid has been added the product can set. A slow set pectin is used otherwise the product could pre-set with disastrous consequences. 

The starting pectin was a commercial apple pectin (Rapid-set pectin, from Unipectine, Redon, France). It was purified by precipitation with cupric ions. A pectin sample with a high degree of esteri-... 

Jelly pH. Another factor which Influences the Internal gel strength Is the jelly pH. In the laboratory, Olllver (53) found pH differences between 2.82 and 3.12 could cause a variation In jelly grade of about 30%. The Interactions between jelly pH and gel strength Is shown In Figure 1. Acids are used to control the pH within the gelling range. The optlmlum pH Is about 3.1 and 3.4 for slow set HM pectins and rapid set pectins, respectively (47). 

The differences that were observed in breaking strength or Internal strength between the four pectin samples, all of which had a 150 SAG and a degree of methoxylatlon (DM) of 65, can be attributed to differences in molecular weigiht. Most investigations so far have worked on slow set pectins, which on the U. S. market is by far the most widely used pectin type. 

The curves of Figure 4 show how quickly jelly firmness is lost as the pH goes above 3.3 to 3.4. The four rapid-setting pectins were from four different manu-... 

Grape juice jellies, 1 week old Four brands of rapid-set pectin... 

Most slow-setting pectins give optimum performance between pH 2.8 and 3.2, while rapid-setting pectins show their best behavior in the region of pH 3.0 to 3.4. Many times an addition of acid to lower the pH only 0.1 unit may be sufficient to prevent complete failure of a jelly batch. 

Pectin also contains araban and galactan. Il is present in fruits, root vegetables and other plant products, and confers on jams their typical gelling property. Pectin is manufactured as a white powder, soluble in water, and used to assist the setting of jams and jellies, and for numerous other purposes. Low melhoxyl pectins, with under 7% methoxyl, give firmer gels than pectins proper. 

Other Food Uses. Jellies, jams, and preserves use malic acid to balance flavor and adjust pH for pectin set. Canned fmits and vegetables employ malic acid in combination with ascorbic acid to produce a synergistic effect that aids in the reduction of browning. Wine and cider producers use malic acid in malolactic fermentation to provide bouquet and for pH adjustment. 

Other Food. Tartaric acid is also used ia the manufacture of gelatin (qv) desserts and ia fmit jellies, especially ia pectin jellies for candies where a low pH is necessary for proper setting. It is used as a starch modifier ia starch jelly candies so that the product flows freely while being cast. It is used ia hard candy because its melting poiat permits it to fuse iato the "glass" and does not contribute to moisture. 

The pectin solutions were mixed at 70°C with hot CaCl2 or CuCl2 solutions for 3 minutes and then poured into sealed tubes. After standing at least 48 hours at the setting temperature, the tubes were tilted and phase diagrams were determined by visual inspection. 

Fig. 5. Effect of PGl digestion on the ethylene synthesis-inducing activity of CDTA-soluble tomato pectin (a), Na2C03-soluble tomato pectin (b) and polygalacturonic acid (c). Controls were treated with solutions of heat-inactivated PGl. Treatment doses were 10 /tg of uronic acid equivalents. The line legends shown in panel a apply to all panels. Bars indicate SEs for the means of measurements of sets of 8 discs/teatment. fr wt, Fresh weight.

The gelation processes are not solely temperature dependent but also time dependent. The determination of the setting temperature is therefore dependent on the temperature profile being used. Results can only be compared, when the pectin preparations are pretreated and measured with exactly the same parameters. 

In the present investigation we set before ourselves the task to check the influence of chlorids of different alkali and alkali-earth metals on the rate of the hydrolysis, ammonolysis and depolymerization of apple pectin in aqueous solution of ammonia. 

By comparing the level of the binding isotherms (figure 3) for both metals and pectins, it became possible to set up an affinity order of pectins, whatever their origin, for the five metal ions Cu2+ Pb + Zn2+ Ni2+ > Ca2+. This scale, already found by pH-measurements, confirmed that Cu2+ and Pb2+ were more strongly bound than the other thi cations with no difference between pectins. 

The resuhs may be summarized as follows Na seemed to inhibit the gelhng ability of each pectin tested. Ca always substantially increased the setting tenperature in relation to other ions, but its influence on the strength of the gels greatly changed with the nature of the pectin. 

Commercial Rapid Set citrus pectin (864 mg galacturonic acid per g, degree of methylation 73) was from SBI (Beaupte, France). 

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