Low temperature post-harvest storage of New Zealand Taewa (Maori potato): Effects on starch physico-chemical and functional characteristics

Fresh tubers from four traditional Taewa (Maori potato) cultivars (Karuparera, Tutaekuri, Huakaroro and Moemoe) and one modern potato cultivar (Nadine) of New Zealand, were stored at 4 °C and 80–90% relative humidity for six months after harvest. Starch was isolated from tubers after every three month period, and its physico-chemical and functional properties measured. Considerable changes in these properties occurred during storage. The extent of changes varied significantly from cultivar to cultivar. Starch swelling power, solubility and light transmittance decreased during tuber storage while a slight increase was observed in starch amylose content. The starch granule size distribution shifted to smaller granule size during tuber storage. Scanning electron micrographs showed degradation/erosion and pitting on the surfaces of many of the starch granules isolated from stored tubers. Transition temperatures and enthalpies of gelatinization of the starches increased somewhat during tuber storage, suggesting that changes in the stability of starch crystalline structures had occurred. Pasting, viscoelastic and texture profile analysis (TPA) characteristics of starch gels were found to have been influenced by tuber storage time for all the cultivars, but to the greatest extent for Nadine and Huakaroro. Gels made from starches from the stored tubers had a reduced tendency towards retrogradation as evidenced by the decrease in syneresis (%) during gel storage at 4 °C.