Quality evaluation of tannia corm (xanthosoma sagittifolium (L.) schoot) and its suitability for product development

Abstract

Tuber crops are known as poor man’s crop as it provides cheap food of high calorific value and quality starch. Tannia is an edible root crop belonging to the family Araceae grown in the tropics and sub tropics. Tannia corms are mainly used as planting material and excess corms are left unharvested. Its acridity, poor storage quality, browning reactions and bulkiness limits the use of tannia corms. Through appropriate processing techniques, these problems can be minimised. The present study entitled ‘Quality evaluation of tannia corm (Xanthosoma sagittifolium (L.) Schott) and its suitability for product development’ was conducted to evaluate the nutritional, antinutritional and organoleptic qualities of tannia corm. The study also evaluated the quality aspects of flour, starch powder and an instant soup mix developed using tannia corm. Constituents like moisture, starch, total sugars, carbohydrates, protein, fibre, total ash, acidity, calcium, iron, phosphorus, sodium, potassium, polyphenols, oxalates, in vitro digestibility of starch, in vitro availability of calcium, iron and zinc of the raw tannia corm were analysed. The starch and carbohydrate content of the corm was 30 % and 72 % respectively and the protein content was 8.48 mg/100g. The content of calcium, iron, phosphorus in 100 g of tannia corms were as 8.2mg, 0.42mg, and 40 mg respectively. Organoleptic qualities of cooked rhizomes obtained a mean score of above 7.00 for all parameters. The oxalate content of raw tannia corm was found to be 1.03 g/100g. Various pretreatments were given to tannia corm for reducing the oxalate content and to reduce browning reactions. Organoleptic qualities of pretreated tannia corm flours were evaluated and found that treatment with one per cent potassium metabisulphite (T3) was effective in preventing browning reactions. For all organoleptic quality parameters, the treatment T3 obtained mean score of above 7 and the oxalate content reduced to 0.20 mg/100g Pretreatments like precooking tannia corms for 5 minutes and boiling in water at 900C for 60 minutes was also found to be good in organoleptic qualities. Porridge prepared by T1 (boiling in water at 900 C for 60 minutes) and T2 (pressure 64 cooking for 5 minutes) were obtained mean scores of 6.55 and 7.04 respectively for overall acceptability. But the pretreatments like T4 (), T5, T6, T7, and T8 resulted in products with poor organoleptic qualities. As pretreatments like T4 (Soaking in 2 % citric acid for 30 minutes), T5 (Soaking in 2 % tartaric acid for 30 minutes), T6 (Soaking in 2 % baking soda in cold water for 30 minutes), T7 (Soaking in 2 % ascorbic acid for 30 minutes), T8 (Soaking in 2 % citric acid + 2 % ascorbic acid for 30 minutes) resulted in products with poor sensory qualities, these treatments were found to be not effective in preventing browning reaction hence, tannia corn flour with pretreatment T1, T2 and T3 only were selected for further studies. The nutritional constituents of the selected pretreated tannia corm flours were estimated. The constituents like moisture, starch, total sugars, carbohydrates, protein, fibre, total ash, acidity, calcium, iron, phosphorus, sodium, potassium, polyphenols, in vitro digestibility of starch, in vitro availability of calcium, iron, zinc and oxalate content of the samples were also analysed. From the various pretreatments tried for the selection of flour, the most acceptable treatment was selected for developing instant soup mix. Starch powder was prepared from tannia corm. The shelf life qualities of selected tannia corm flour and starch powder were estimated initially and at monthly intervals. The bulk density of corm flour and starch was found to be 0.63 g per cc and 0.54 per cc respectively. A decrease in water absorption index in corm flour and starch powder were observed after three months of storage. Bacterial count in corm flour was found to be 0.4 ×105 cfu g-1 initially which increased to 2.2×105 cfu g-1 by the end of storage period. The fungal growth was not detected initially in flour but at the end of third month of storage, a fungal count of 1.2×103 cfu g-1 was observed. The fungal growth in tannia corm starch powder was found to be 0.6 ×103 cfu g-1 initially which increased to 1.4 ×103 cfu g-1 at the end of storage. Yeast growth was not detected in corm flour and starch powder initially but a yeast content of 1.2 ×103 cfu g-1 was found at the end of the storage period in the starch powder. There was no considerable change in sensory qualities in both flour and starch powder after three months of storage. 65 An instant soup mix was standardised using different proportions of selected tannia corm flour and corn flour. Treatment with 30 per cent tannia corm flour and 70 per cent corn flour (T8) had the maximum mean score for overall acceptability (7.9). The selected instant soup mix were packed in metallised polyethylene covers (200 gauge) and kept for storage studies for three months. The instant soup mix was found to be shelf stable up to three months of storage. Tannia corms contain good amount of starch, carbohydrate, protein and mineral constituents like sodium, phosphorus, calcium and potassium. Oxalate content and browning reactions were reduced by various pretreatments. The present study found that good quality flour and starch powder could be prepared from tannia corms. Tannia corm flour and starch powder were of good sensory qualities and can be used to prepare acceptable products like instant soup mix. The tannia corm flour and starch powder could be effectively utilised for the development of instant mixes and is very much suited for various food applications.