Investigations into the nutritional and sensory potential of taewa (Māori potatoes) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy, Nutritional Science, at Massey University, Palmerston North, New Zealand
The term Taewa refers to a collection of at least 18 different potato cultivars belonging to the Solanum tuberosum family, which have been cultivated by the Maori peoples of New Zealand for at least 200 years.
Due in part to its economic importance worldwide, the chemical and nutritional composition of today’s mainstream potato varieties, and the mechanisms by which composition impacts on their culinary and gastronomic properties, have been extensively researched. However few investigators have studied the nutritional, sensory or potential health properties of Taewa, or which Taewa varieties may be the most preferred for eating. Previous Taewa nutritional research has concentrated on anthocyanin, phenolic or flavonoid content and antioxidant potential, glycoalkaloid content and starch characteristics. The variation in culinary quality and different tuber pigmentation of Taewa suggest that the composition, nutritional and sensory properties of Taewa are diverse and are therefore worthy of investigation.
The first goal of the PhD focused on identifying nutritionally beneficial or commercially viable properties of Maori potatoes. This was carried out by quantifying the macronutrient, selected micronutrient, phenolic and glycoalkaloid components and assessing antioxidant activity (using ORAC and FRAP analysis) of four Taewa varieties (Huakaroro, Karuparera, Moemoe, Tutaekuri) and comparing them against Nadine, a potato variety commonly available in New Zealand. Analysis was carried out on tuber flesh, tuber skin and whole tuber components over two consecutive harvests. In addition, the effects of 6 months storage at 4oC in 80-90% humidity and par-boiling on the nutrient content were also explored.
The second goal of this research was to ascertain the most popular, commonly eaten and commonly grown Taewa varieties; preferred Taewa cooking and eating practices; the availability of Taewa cultivars across New Zealand and to collate information regarding marketable traits or factors that might affect Taewa consumption. In order to achieve this, group discussions were held with 25 adult participants between 18 to 75 years of age from the Manawatu region. Four key themes emerged from these discussions and were used to develop 20 questions for a larger scale survey from a wider crossection of Taewa consumers.
The third goal of the research aimed to assess two characteristics of nutritional or health value (increased resistant starch in potato boiled then cooled at 4oC for 24 h) and antioxidant capacity (by measuring the total phenolic content, DPPH and FRAP potential) in four common Taewa varieties (Huakaroro, Karuparera, Moemoe, Tutaekuri) using a popular Taewa cooking practice (boiling whole with the skin on) to develop a Taewa product with improved health benefits. Consumer acceptance was then measured by assessing the sensory ratings of 56 adult volunteer subjects.
Results of the nutrient analysis consistently showed all four Taewa had promising nutritional value with regards to a greater nutrient content, greater accumulation of resistant starch, greater total phenolic content and antioxidant capacity compared to Nadine. The nutrients in Taewa likely to be of most biologically significant nutritional value in comparison to Nadine and other more common NZ potato cultivars included the soluble and insoluble fibre content, the minerals potassium, magnesium and iron and the vitamins thiamine, pyridoxine and niacin. All four Taewa (particularly Tutaekuri) also showed excellent potential with regards to accumulating resistant starch and exhibiting antioxidant potential compared to Nadine.
Commonly eaten Taewa varieties included Tutaekuri, Pawhero, Peruperu, Moemoe, Karuparera and Huakaroro. These Taewa varieties were also grown and eaten by residents in a greater number of regions across New Zealand than other Taewa varieties. Cooking and eating preferences included boiling them whole, unpeeled and cooked on their own; eating them hot or warm, with the skin on and seasoned with butter, salt and pepper. If destined to be pre-cooked or served cold, it was suggested that Taewa varieties should be waxy so as to hold together better, be purple or buttery-yellow to add interest with regards to visual appeal, be an appropriate size for the intended dish and have a sweet, nutty, buttery or delicate taste.
New Zealanders should be encouraged to both eat and grow Taewa due to their value as a popular inexpensive food of high nutritional quality, their promise as a means through which to develop functional food products with added health benefits and their cultural significance to all New Zealanders as a unique heritage food. Government agencies, those involved in the Potato Industry, research institutions and funding agencies should be encouraged to work with Maori growers, to ensure the increased production and nationwide availability of Taewa and support the development of Taewa-based functional and snack food products in way that will be beneficial to all.