The utilisation of potato flour in pasta production: the effect of starch-protein interactions on the physical chemical properties, and in vitro digestion behaviour, of potato enriched pasta : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University

Abstract

Potato (Solanum tuberosum L.) is consumed throughout the world and regarded as a carbohydrate rich staple food, ranking behind rice, wheat, and maize as the fourth most important global crop. The potato is not only used as a vegetable, but also as the source of raw materials for processing into starch derivatives production. Potato flour can be preserved for a long time, due to its low moisture content, and it can maintain the nutrition and flavour of fresh potato. Potato flour is rich in the necessary nutrients for the human body and can be substituted for wheat flour in the preparation of new types of food to meet the requirement of people for nutritional staple foods. Potato is classified as a high glycaemic index (GI) food, and gluten free. The addition of potato flour affects the functional nutrition and digestion characteristics of flour products. Therefore, in order to provide a theoretical basis and technical support for the application of potato flour in pasta, this dissertation studied the effects of potato flour on the functional nutrition and digestion characteristics on pasta and the interaction between starch and protein. In this study, two different types of potato (Agria and Nadine), in combination with wheat flour (Semolina), were used as the main raw materials for the production of pasta and gels. The research investigated the effect of different treatment methods on the physicochemical, pasting and digestion properties of potato flour. Potato was used as raw potato flour, potato flour which from cooked potatoes, and cooked and frozen potato flour derived from cooking potatoes and then subjecting the potatoes to blast freezing before being made into flour. In total, six different kinds of potato flour were made, three different processing parameters for both the Agria and Nadine potatoes. These were mixed with wheat flour at different proportions to make a range of potato and wheat flour blends. The textural and pasting characteristics of the blends were determined. Pasta was made using the potato and wheat flour blends. The texture of the potato flour pasta was found to be weaker than the control pasta samples. In order to improve these textural characteristics, soy protein was added to the pasta mixes at different proportions. The viscosity and digestion properties and the quality of pasta were determined. The proximate analysis, pasting, and digestibility properties of raw, cooked, and cooked-frozen potato flour were determined. The cooked and cooked-frozen process significantly (P < 0.05) decreased the content of total starch, amylose content, and resistant starch (RS), while influenced water solubility index (WSI), water absorption index (WAI) and swelling capacity (SWC). It also increased (P < 0.05) the dietary fibre markedly. The pasting properties of potato flour were studied by a Rapid Visco Analyser (RVA), the viscosity of the cooked potato flour was found to be higher than those of raw, and the cooked-frozen potato flour, but showed the lowest pasting temperature. In vitro digestion of the RVA samples was conducted to measure the predictive glycaemic response in potato flour. The process of forming a gel via the RVA significantly increased the rate of starch digestion, and the total area under the curve (AUC). The AUC was calculated as the amount of reducing sugar released from a 120 min in vitro glycaemic digestion process (mg reducing sugar/ mg sample) × min] and was used to compare the predictive glycaemic response of potato flour pasta and gels. The functional and pasting characteristics of wheat flour and their blends with three different treatment of potato flour at 10 to 50% were investigated in this study. The effect of the characteristics of the mixtures were studied in terms of change to the protein, total starch, amylose, dietary fibre, resistant starch, solubility, swelling capacity, water absorption, and pasting properties. The results showed that the moisture, protein and amylose content decreased with the increasing proportion of potato flour used, and that the total starch, dietary fibre and resistant starch showed a gradual increase with the level of potato flour added. Compared with wheat flour, potato flour had a higher pasting characteristic and lower solubility. The addition of potato flour increased the WSI, WAI, and SWC of the blends, the peak viscosity, final viscosity and setback increased with an increase in the potato flour from 10%-50%. In conclusion, the effect of substitution of durum wheat semolina with two local cultivars of potato (Agria and Nadine) flour on viscosity, digestion properties and the quality of pasta was investigated. Compared with durum wheat semolina pasta, the cooking loss was significantly increased by adding potato flour but there was a decrease in WAI. Supplementation of potato flour also influenced the texture properties of potato-wheat pasta, the addition of potato flour increased the firmness and as the amount added increased and then decreased, the potato flour pasta made with 30% had a stable structure. In addition, all enriched pasta with potato flour showed a significant increase in reducing sugar released during an in vitro digestion and standardised AUC values compared to control pasta. Fortification improved the pasting and nutraceutical of pasta products and promoted the processing of potato staple food.