Controlling acridity in Tannia (Xantosoma sagittifolium (L.) Schott cv white and purple) tubers using various processing treatments

The inherent acridity of two varieties of Tannia tubers, white and purple, were studied and controlled using physical (washing, soaking, blanching, and pressure cooking), chemical (application of 3% salt and 1% lime solution) and microbiological treatments (natural fermentation). The oxalate concentration which is an indicator of acridity was measured in the fresh as well as in the processed tubers. Results showed that oxalate concentration of raw unpeeled tubers ranges from 74.53-107.69 mg/100 g for white and purple tubers, respectively. Oxalate level reduction was remarkably high in purple than white tannia variety for the raw (fresh) tubers. Washing, soaking and heat treatment significantly lowered and eventually controlled the oxalate of the tubers resulting in acceptable product models; 'French fries' for the fresh tubers and 'pandesal' for the processed tubers. Salt, lime and natural fermentation also controlled the acridity of the tubers however, sensory evaluation of the product models showed low scores in terms of color, odor, flavor, and general acceptability hence were not acceptable. The two product models, 'French fries' and 'pandesal', were evaluated as neither liked nor disliked in the salted, limed, and fermented samples while the physically treated 'French fries' and 'pandesal' were highly acceptable. Photo microscopy of the starch particles of the flour of both Tannia varieties were found finer for the fresh samples but upon soaking and heat treatment, the starch particles swelled and increased in size particularly the heated samples. Proximate composition of the flour samples showed that the moisture content ranges from 6.63-7.30%; ash, 1.55-3.77%; fat was negligible, crude fiber, 1.49-2.38%; crude protein, 2.71-4.00%; and NFE, 83.47-86.47%. Oxalate level reduction was remarkably high in the purple fresh tuber and flour than in white tannia variety. Among the processing treatments, liming and fermentation gave lowest oxalate concentration (4.50 mg/100 g) than the control, blanched and autoclaved samples (9-16.50 mg/100 g). The blanched and autoclaved fries and 'pandesal' were more acceptable than limed and fermented. Thus, physical treatments of the Tannia tuber are recommended since blanching and autoclaving not only controlled acridity in Tannia tubers but also results in acceptable and good quality food products. Furthermore, white variety is recommended for making fries while both varieties is ideal for 'pandesal' especially the white control and purple autoclaved flours.