Influence of hot-air drying condition on dehydrated potato flour gelatinization quality

Abstract: In early 2015, Ministry of Agriculture put forward the strategy that potato is classified as the fourth staple food and transferred into popular principal food suitable for dietary habit in China. Even though the China's potato production ranks the first in the world, the sustainable development of potato processing and consuming is still extremely restricted due to the following reasons: The percentage of potato deep processing remains low; the processing products of potato are single, and have low nutrition and add value; and the potato products as staple food suitable for our dietary habit are in lack. Potato flour is one of prime products in potato deep-processing, and hot air drying has been widely used in the drying for agricultural products because of its easy operation, low cost and simple requirements for environment, court and equipment. The potato gelatinization characteristics affect the reproducibility of dehydrated products of potato. The more highly gelatinized the potato, the worse the reprocessing property, and the more difficult the application of potato as China's principle cooking food. Therefore, it has an important significance to the research of the effects of the hot air drying conditions on the gelatinization characteristics, the drying technology of dehydrated potato products and China's strategy of potato as staple food. Based on thin-layer drying experiment, the paper researched the influence of different temperature (40, 50, 60, 70, 80, and 90 ℃), different air velocity (0.5, 1.0, 1.5, 2.5 and 3.5 m/s) and different dicing length of fresh-cut potato (2.5, 5, 10 and 15 mm) on potato flour gelatinization quality. Microstructure and gelatinization quality of potato flour were analyzed with the use of scanning electron microscopy (SEM) and differential scanning calorimeter, and the water-absorbing capacity was measured. The results showed that gelatinization enthalpy could represent the degree of potato gelatinization; the lower the gelatinization enthalpy, the lower the degree of gelatinization; the range of initial gelatinization temperature was 62.31-64.96 ℃, and the range of termination temperature was 70.16-74.19 ℃, which was higher than the gelatinization temperature of pure starch product; the starch was not completely gelatinized when drying under the temperature higher than gelatinization temperature; the samples dried under the air velocity of 0.5-2.5 m/s showed no significant difference in gelatinization enthalpy (P>0.05), while the gelatinization enthalpy of the samples dried under the air velocity of 3.5 m/s was significantly smaller than that under other air velocities; the enthalpy of potato flour decreased significantly with the increase in dicing length (P<0.05); ungelatinized samples showed no significant difference in water-absorbing capacity, and water-absorbing capacity was strengthened as the degree of gelatinization got higher; the gelatinization degree of potato dehydrated products was low when the hot air drying was under the temperature of 70 ℃, the air velocity of 1.0 m/s and the cutting length of 10 mm. This research can provide theoretical basis for the production of ungelatinized potato flours with hot air drying method.