Characterization of Colocasia esculenta L. Schott var. esculenta grown in Tonga for food applications : a thesis presented in partial fulfilment of the requirements for the degree of Master in Food Technology at Massey University, Palmerston North, New Zealand

Abstract

This study characterized two Colocasia esculenta L. Schott var. esculenta cultivars, Holoitounga and Lau’ila, focusing on their corms and ungelatinized flours, and evaluated their potential to partially substitute wheat flour in crackers, shortbread biscuits and bread. Fresh corms were analzyed for physicochemical, microstructure, and cooking characteristics, while derived flours were assessed for nutritional composition, microstructure, water and oil absorption properties, pasting behaviour, thermal properties, foaming and emulsion properties and rheological behaviour, including protein fortification with egg white, casein and pea protein. Holoitounga exhibited higher dry matter (38.43 %), amylose content (12.75%), dietary fiber (4.54 g/100g), crude fat (1.76 g/100g) and carbohydrates (89.29 g/100g), with loosely packed starch granules and shorter cooking time (12-14 minutes), whereas Lau’ila had higher starch (68.40 %) and protein contents (3.49 g/100g), higher amylopectin content (90.55 %), and denser microstructure, contributing to longer cooking time (14-16 minutes) and greater cohesiveness. Holoitounga flour showed finer particle size with an average diameter of 74.08 µm, higher bulk density (0.59 g/mL), water absorption index (4.70 g/g), water absorption capacity (94.61 g/100g), oil absorption capacities (92.51 g/100g) gelatinization temperature (78.92 oC) and pasting viscosity (4952.33 cP). Lau’ila, in contrast, displayed higher swelling power (5.64 g/g), water solubility (0.30 g/g) and foaming capacity (7.69 %). Protein fortification significantly improved the rheological properties of both flours, particularly the egg white and casein protein, making them more comparable to wheat flour dough. In bakery applications, low to moderate substitution levels (≤ 50%) maintained acceptable physical, textural, and nutritional attributes with shortbreads and crackers tolerating higher levels (50% - 100%) better than bread. Holoitounga samples consistently outperformed those from Lau’ila in puffiness, colour, and texture, likely due to their higher amylose content. Nutritionally, substitution reduced energy and protein content but increased carbohydrates and sugars, indicating the need for protein enrichment at higher substitution levels. These findings highlight the potential of Tongan taro flours, particularly Holoitounga, in supporting import substitution strategies, while future research should explore storage stability, sensory acceptance, and further protein fortification to enhance their application in gluten-reduced and gluten-free bakery products.