Proximate Compositions of Three New Zealand Potato Cultivars (Agria, Lotato and Vivaldi) and their Starch Properties

Abstract

Potatoes (Solanum tuberosum L.) play a significant role in contributing to the nutritional needs and energy of the world population and make an essential contribution to satisfying the food needs in developing and developed countries. Starch is the main component of potatoes, which makes up about 15-20 % of their weight. Different starch properties may affect food applications in the food industry. This research investigated the proximate composition of three potato cultivars (Agria, Lotato and Vivaldi) and their starch properties. The starches were isolated and studied for their properties, including the morphology properties (granule distribution size and appearance) and physicochemical properties (amylose content, phosphorus content, swelling power, solubility and light transmittance, thermal properties, pasting properties, textural properties), followed by sensory evaluation in a food format, i.e., noodle. This study determined the proximate compositions by hot-oven dry, Kedah, muffle furnace and Soxhlet. The total starch kit (Megazyme International, Ireland) was used for determining the total starch content of potato. The laser diffraction particle size analyser and scanning electron microscopy were used to determine the morphological properties of potato starch. Amylose and phosphorus content was determined by the iodine-binding method and ICP-MS, respectively. Moreover, Differential Scanning Calorimetry (DSC) and Texture Profile Analysis (TPA) determined the thermal properties and textural properties. Finally, the starch noodles were made from rice and rice-potato blends and evaluated by sensory evaluation by twelve judges (7 females and 5 males). The Lotato potato had a statistical difference compared to the other two potato cultivars on proximate compositions except for carbohydrate and protein contents. Lotato potatoes had lower carbohydrate (Agria: 16.46 %; Lotato: 9.96 %; Vivaldi: 11.74 %) and protein content (Agria: 2.11 %; Lotato: 1.39 %; Vivaldi: 2.22 %) than Agria and Vivaldi potatoes. In the case of properties of potato starch, the yield of starch isolation of Lotato was the highest (29.76 %), which means Lotato was more straightforward to isolate than the other two potato cultivars. In addition, compared with the other two potatoes, the amylose content of the Lotato potato was the highest (about 33.03 %). In contrast, the phosphorus content of the Lotato potato was the lowest (about 0.0508 g/100g). Potato starch's amylose and phosphorus contents might affect starch properties, including swelling power, granule size, peak viscosity and light transmittance, further affecting potato starch applications in the food industry. Potato starch's higher phosphorus content is one factor for higher swelling power due to the phosphate groups and potato starch's swelling factor was higher than other sources of starch (sweet potato and quinoa) because of the larger granule size. In addition, because of the repulsion among adjacent starch molecules, the light transmittance of potato starch was influenced by the phosphorus content of potato starch. Moreover, the peak viscosity also influenced phosphorus and amylose content. This study attributed higher peak viscosity to higher phosphorus content and lower amylose content. In the experiment about starch noodles, starch noodles made from the same ratio of potato and rice starches were more popular during the testing because they had higher transparency scores and lower tooth packing scores, two critical factors for consumers to choose the starch noodles and the cooking quality (cooking time and cooking loss) was appropriate compared with other ratios of blends. In conclusion, as a new potato cultivar, the difference in carbohydrate content between the Lotato potato and Agria potato was significant (p < 0.05) and research on starch properties also indicated the difference between these different potato cultivars. Due to different starch properties, such as gelatinization temperature and solubility, starch noodles made from different potato starches showed different sensory properties. For example, Agria potato starch was more suitable for starch noodles than Lotato potato starch because of shorter cooking time (gelatinization temperature) and less cooking loss (solubility). In the future, research on the carbohydrate content of Lotato potato is one direction because it has less carbohydrate content than Agria potato. In addition, food products made from Lotato potato starch are another future direction due to less carbohydrate content. Improving the textural properties of food products made from Lotato potato starch is significant.