Fruit, pectin from

Arabinogalactans (AGs) are widely spread throughout the plant kingdom. Many edible and inedible plants are rich sources of these polysaccharides. AGs occur in two structurally different forms described as type I and type II, associated with the pectin cell-wall component by physical bonds and some of them are covalently linked to the complex pectin molecule as neutral side chains. Commercial pectins always contain AG 10-15%). AG of type I has a linear (1 4)-y0-o-Galp backbone, bearing 20-40% of of-L-Ara/ residues (1 5)-linked in short chains, in general at position 3. It is commonly found in pectins from citrus, apple and potato [6]. Recently, this AG type has been isolated from the skin of Opuntia ficus indica pear fruits [372]. 

Figure 3 Size fractionation of EDTA-soluble polyuronides from Rutgers and transgenic fruit juice processed by cold- and hot-break methods. Pectin from processed juice was extracted as ethanol-insoluble solids and size fractionated on a Sepharose CL4B column. Under the same chromatographic conditions, elution of the branched dextrans with average molecular mass 2000, 500, 252, 151, 40 and 17.7 kD-peaked in fraction number 46, 50, 54, 62, 67 and 72, respectively. Modified from Thakur et al. [23].

Pectins from different tissue zones, namely epidermis, the outer parenchyma, the parenchyma of the Ccirpels zone, the carpels and the core line, were isolated firom alcohol-insoluble solids (AIS. In both zones of parenchyma, the cell-wall material represented about 80% of the total cell-wall material from the whole fruit. The pectins from the outer parenchyma accounted for 70% of the total. However, there was no change in galacturonic acid concentration. The enzymatic solubilisation of tissues or AIS was higher in the parenchyma zones than in the others. Nevertheless, the depolymerisation of the soluble pectins from parenchyma zones with an endopolygacturonase required the action of pectin methylesterase. The depoiymerisation of pectins from the other zones, however, did not. 

In apple processing, enzymatic treatment of the crushed fruit leads to a lower degree of degradation of the peel and the core than the rest of the fruit. Figure 1 shows the separate tissue zones in diagrammatic form. Their anatomic origins are different the epidermis and outer parenchyma zones are tissues derived from the fusion of the calyx, corolla and stamens of the flower the inner zones correspond to tissue derived from ovaries and carpels. The characterisation of the cell-wall material, especially pectins, from the different zones of the fruit may provide additional information on the possibility of finding uses for the discarded fractions. 

The best established use of pectin is in making jam. While some fruit have sufficient pectin and acidity to make a well set jam others, e.g. strawberries, benefit from the addition of pectin from another fruit. 

Tamarind seed polysaccharide, the gum fraction obtained from tamarind kernel polysaccharide, forms gels over a wide pH range in the presence of high sugar concentrations (>65 wt%), and it can therefore substitute for fruit pectins (65). 

Interest in pectin from a nutritional standpoint has increased with new evidence of its influence on several physiological processes. Long acknowledged as an effective antidote to diarrhea, pectin has now been found to be of possible benefit in control of cholesterol levels and in management of diabetes. As one of the richest potential sources of pectin, citrus fruits could enjoy enhanced nutritional status from these findings. 

Pectin is obtained from unripe apples or citrus fruit. In both cases the residues left after pressing to extract juice are used for pectin production. In the fruit, pectin is responsible for the firm structure. Apples, for example, have a firm texture despite a water content of more than 85%. Pectin is sold almost exclusively in powder form. 

Of the D-aldohexoses, only D-glucose and D-galactose are common in nature. D-Glucose is by far the most abundant of all D-aldoses. D-Glucose comes from the hydrolysis of starch and cellulose, and D-galactose comes from the hydrolysis of fruit pectins. 

Component of pectins from the skin of the fruit of Passiflora edulis (passion fruit) Component of the gum exudates of Sterculia setigera Component of algal polysaccharides such as agar... 

The USP 28 describes pectin as a purified carbohydrate product obtained from the dilute acid extract of the inner portion of the rind of citrus fruits or from apple pomace. It consists chiefly of partially methoxylated polygalacturonic acids. 

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