Study On Quality Characteristics Of Common Sweet Potato In The South Of China

Sweet potato which have the characteristics of high output, high nutrition, low input and high yield, showed a huge potential in processing industry. Textural characteristics, food components and physicochemical properties of starch of nine different sweet potatoes, including four unimproved varieties which had not been studied previously and five improved varieties commonly available in China, were studied by means of Scanning electron microscope (SEM), X-ray diffraction (X-RD), Texture analyzer, differential scanning calorimetry (DSC), laser diffract instrument, ultraviolet spectrophotometer, and so on. Physicochemical properties of sweet potato starch mainly includes swelling power, gel texture properties, amylose content, particle size distribution, crystal structure diffraction, thermal characteristics, retrogradation characteristics, digestibility characteristics, water absorption characteristics, and so on. Some processing software (Excel, SPSS, Jade, Note Express, and so on) were applied to find the correlation coefficient and build mathematical models. In addition, the prospect for the properties of texture, nutrient and physicochemical properties of starch starch was put forward in last parts. The main results were as follows:(1) Textural characteristics general nutrient components, polysaccharides and physicochemical characteristics of nine different sweet potato (four unimproved and five improved varieties) varieties grown in south of China showed significant differences. The texture of improved varieties for fresh sweet potato showed greater hardness and compression work than the unimproved varieties; The gel texture curve of sweet potato showed different between improved and unimproved varieties; The sensory characteristics of fresh and cooked sweet potato of the nine varieties were in accordance with the texture properties of fresh sweet potato and gel texture properties respectively. Moisture, total soluble sugar, and starch content (wet basis) of the nine varieties varied from63.7to84.2%,3.8to7.6%,5.5to26.5%, respectively. Protein, lipids, sugar, IDF, SDF, TDF, and ash content (dry basis) varied from1.7to2.8%,1.6to4.5%,65.2to79.8%,6.2to12.0%,5.2to14.0%,13.4to23.9%,2.0to3.6%respectively. Swelling power of sweet potato powder varied between6.8 and9.5%. Electrical conductivity and TDS showed a similar variation rule with gel texture properties. Heating showed a significant influence to the SP (soluble polysaccharide) level compared with room temperature. The significant differences between unimproved and improved varieties could be to describe in textural characteristics, electrical conductivity, protein, DF and TSS.(2) The physicochemical properties (swelling power, gel texture, amylose content, particle size distribution, crystal structure diffraction, thermal characteristics, retrogradation characteristics, digestibility characteristics, water absorption characteristics) of nine sweet potato starches showed significantly difference. The maximal absorption wavelength of9sweet potato were about600nm, and the amylose content varied between26.7%and31.8%; differential curve showed bimodal distribution, average particle size varied between10.41and19.90μm;9kinds of starch are C-a model, the relative crystallinity range30.62%to46.54%, and the mean was37.5%; the results showed that there were differences among9kinds of sweet potato from the gelatinization temperature and△Hgel; sweet potato starch granules was main spherical and irregular polygons, and after the enzymatic hydrolysis, the starch granules mainly exists as a karst cave and rupture, it was roughness and some cracks in the surface of the no-karst srarch granules, which showed that amylose had enzyme function. The swelling power, digestion rate, amylose content and water absorption showed main differences for the improved varieties compared with the unimproved varieties; the establishment of the mathematical model and correlation between different physicochemical indexs, which was important guiding significance for in-depth understanding of the starch processing characteristics.(3) The relationships among the various parameters including textural and nutritional index, were evaluated. Starch content showed a significant positive correlation with sugar (r=0.915, p<0.01) and swelling power (r=0.675, p<0.05), and negatively with CSP and TDF; Ash showed a significant positive correlation with EC, while TDS showed a significant negative correlation with swelling power; IDF and H1negatively correlated with each other (r=0.821, p<0.01), while TSS showed a significant positive correlation with lipids. The relationships among physicochemical indexes of starch were also evaluated. SP(swelling power of starch) showed a significant negative correlation with sugar ADF (Adhesive force)(r=-0.816,p<0.01) and MGS (Mean granule size)(r=-0.831,p<0.01), but positive correlation with S.S.A(r=-0.707,p<0.05), Syn (Syneresis)(r=-0.721, p<0.05) and△Hgel (r=-0.803, p<0.01). In addition, MGS showed a significant negative correlation with Syn,△Hgel, Al (Degassed at20℃for40min) and A2(20℃for15min); EH showed a significant positive correlation with Syn(r=0.879,p<0.01). The regression model between H1, EC, swelling power of powder and nutrient content reached significant level, and regression model between SP, EH,△Hgel, A2and AC, MGS, Syn reached significant level too.