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Isolation and chemical analysis of pectin from tomato waste

The industrial processing of tomato results in the accumulation of large amounts of by-products composed of peel, seed and small amount of pulp. This material is disposed of as a solid waste or used as animal feed, but the abundance of bioactive compounds in by-product fractions suggests the possibility of utilizing it as a cheap source of different biopolymers. One of them is pectin. Although pectin occurs in the plant tissues, the number of sources that may be used for the commercial manufacture of pectin is limited (citrus fruits and apples). The alternative sources for pectin extraction were described by several authors, but to date, no research has been done on the extraction of pectin from dried tomato peels. This work reports methodology of pectin isolation from two types of tomato peels obtained as waste from canning factory. Pectin was extracted under reflux at 90°C, using ammonium oxalate/oxalic acid as extracting agent. The extraction was carried out during 24 h in the first step, and then again with a fresh volume of extracting agent during 12 h in the second step. The isolated pectins were evaluated in terms of methoxyl (MeO) and anhydrouronic acid (AUA) contents and degree of esterification (DE). Total pectin substance estimated as calcium pectate was determined gravimetrically. The structure of pectin was evaluated using FTIR spectroscopy. The results indicate that extraction parameters such as peel to extractant ratio, number of extractions and extraction time have a different effect on the yield and quality of pectin. Amongst them, number of extractions as well as time of extraction has shown the strongest effect on all measured parameters. The highest pectin yield but the lowest pectin quality was obtained at extraction time of 12 h which points out that higher pectin yields are not necessarily connected with higher pectin quality. The highest pectin yield (15.0 and 14.9 %), MeO content (5.8 and 4.0 %), AUA content (40.0 and 27.4 %) and DE (81.5 and 82.7 %) were obtained after 24 h of extraction of two different batches of dried tomato peels, respectively. The results of FTIR analyses revealed that there are no differences in structure between extracted pectins. This preliminary investigation point out that utilization of dried tomato peel for pectin production will not only solve the problems of waste disposal but also meet the requirements of pectin in the market to some extent.

Pectin characterization; Pectin extraction; Tomato waste

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