Saline-tolerant Rice Cultured At Different Saline Concentrations: An Investigation Of Structural And Physicochemical Properties Of Rice Flour And Starch

In China,there are nearly 100 million hm² of saline field inland.The reasonable development and utilization of saline field can not only effectively alleviate the contradiction between land supply and demand,but also has great strategic significance to ensure national food security.Rice is the most important food crop in China,and rice cultivation has been considered an important biological method to improve saline land.In this study,a total of nine rice samples from three varieties of saline-tolerant rice（T477S/Yuehe Si Miao,Guangxiang24S/RA65 and 2020X2L547,replaced by YSM,GSR and GXL,respectively）cultivated at 0%,0.3%and 0.6%saline concentrations respectively（indicated by@0.0,@0.3 and@0.6）were collected.Rice flours were obtained by rice hulling,milling,crushing and sieving,followed by the extraction of rice starches from rice flours using a combination of alkaline extraction and enzymatic digestion,and finally the structural and physicochemical properties of rice flours and starches were analysed,with a view to provide theoretical basis and data support for the further processing and utilisation of salinity-tolerant rice.The main research results were as follows:The length,width and aspect ratio of saline-tolerant rice decreased with increasing saline concentration.The amylose content of normally cultivated YSM,GSR and GXL rice flour was9.57%,17.80%and 24.01%,respectively.The amylose content of YSM and GXL tended to decrease with increasing saline concentration,for example,the amylose contetnt of YSM@0.3and YSM@0.6 was 9.11%and 8.40%.The protein content of rice flour increased significantly with increasing salinity concentration,with the protein content in GXL rice flour increasing from 6.62%（GXL@0.0）to 10.13%（GXL@0.6）;salinity stress also affected the amino acid composition of the proteins,with a greater effect on leucine,lysine and proline;the combination of alkaline extraction and enzymatic digestion was effective in removing protein and fat from the rice flours.In addition,salinity stress increased the fat and ash content of the rice flour,the fat and ash content of GSR rice flour increased from 0.58%and 0.48%（GSR@0.0）to 1.00%and 0.79%（GSR@0.6）respectively.There were no significant differences in the grain morphology of rice flours and starches at different saline concentrations,but the grain size distribution of starches of the same variety correlated with their amylose content,the higher the amylose content,the larger the starch grain size.X-ray diffraction（XRD）results showed that both saline-tolerant rice flours and starches had a typical A-shaped crystalline structure,and there was a weak V-shaped crystalline structure in saline-tolerant rice flours,due to the increased fat content,which led to the formation of V-shaped complexes between starch and fat;the relative crystallinity of all three salinity-tolerant rice flours decreased and that of starches increased as the salinity cultivation concentration increased.And saline stress altered the supramolecular lamellar structure of saline-tolerant starches,with an overall trend of increasing crystalline layer thickness（lc）and semi-crystalline layer thickness（d）,with the most significant change in GXL starches,where the d value increased from 9.37 nm（GXL@0.0）to 10.13 nm（GXL@0.3）.Saline stress significantly increased the molecular weight of three saline-tolerant rice starches.The proportion of A and B₁ chains of YSM and GSR starches showed an overall increasing trend with increasing saline concentration,while the proportion of B₃ chains showed an overall decreasing trend.The water-holding capacity of rice flours increased with increasing saline concentration,while the oil-holding capacity decreased,but the water-holding capacity and oil-holding capacity of starches did not change significantly.The solubility of the rice flours varied with saline concentration in line with their amylose content,the solubility of YSM and GXL rice flours decreased with increasing saline concentration,while the solubility of GSR rice flours reached its maximum value（12.07%）at saline concentration of 0.3%.The variation of starches swelling power with saline concentration was opposite to the trend of their amylose content.The solubility（max.47.84%）and swelling power（max.28.71）of starches were significantly higher compared to rice flours due to the removal of protein.Differential scanning calorimetry（DSC）results showed no significant change in the enthalpy of pastingΔH for rice flours,but pasting temperature interval（ΔT）increased slightly;compared to rice flours,the pasting temperature of starches decreased and the enthalpies of GXL starches gradually increased with increasing saline concentration.Rapid viscometer（RVA）analysis showed that saline stress significantly increased the pasting temperature of rice flours（3°C～9°C）,and the peak time was also delayed with increasing saline concentration,peak viscosity and breakdown value decreased,the regeneration value of GXL rice flours decreased from 1898.50 m Pa·s to 1099.00m Pa·s,which showed the largest change.The results of the rheological analysis showed that G’and G"of the rice flours increased with increasing angular frequency,and G’was always greater than G",indicating that the elastic characteristics were always greater than the viscous characteristics.Saline stress affected the consistency coefficient K of rice flours,the K of YSM@0.3 rice flour（114.38 Pa·sⁿ）was higher than that of the control sample（98.22 Pa·sⁿ）,indicating that the sticky characteristic of YSM@0.3 rice flour was more pronounced;however,the K values of both GSR and GXL with higher amylose content decreased with increasing saline concentration,indicating that the elastic characteristic was more pronounced.After protein removal,both G’and G"of the starches decreased,with GSR starches showing the most obvious trend of decrease.The in vitro digestion results showed that the slowly digestible starch（SDS）content of YSM and GSR starch increased with increasing saline concentration,with the largest change in SDS content of GSR starch from 38.85%to 46.32%.The fast digestible starch（RDS）content of GXL starch gradually decreased with increasing saline concentration,and the greatest resistant starch（RS）content showed the greatest increase from 9.47%to 23.06%.In summary,saline concentration significantly affected the chemical composition,physicochemical properties of saline-tolerant rice flours,and the molecular structure and digestibility of saline-tolerant rice starches,but there was also variation exhibited between rice varieties.The results of this study are intended to provide data to support the application of saline-tolerant rice in food processing.For example,the high protein content of saline-tolerant rice can provide a richer material for rice protein researches,and its indigestibility can be used in the development of health foods.