| Lotus root starch(LS)is a primary powdered product made from processed lotus root,which is widely used in food industry as stabilizer,thickener and gelling agent.However,its application in the food industry is restricted due to the poor stability under heat and shear conditions,sensitive to p H changes,low retrogradation resistance.Therefore,many scholars focus on the modification of starch to improve the application value of LS in food industry.The use of polysaccharides to improve the physicochemical properties and processing quality of starch food has been widely investigated due to safety and convenience.The interaction between polysaccharide and starch can significantly improve the gel,texture and rheological properties of starch,and inhibit the digestion of starch.The addition of polysaccharides can improve the functional properties of native starch;however,the thickening effect and stability of simple mixing system should be further improved.Ultrasound technology,as an effective physical modification method could affect the pasting viscosity,gel properties and digestion characteristics of starch.Currently,the influence of ultrasound on raw starch granule structure and starch paste properties has been widely reported.The research of modification of starch/polysaccharides composite system by ultrasound treatment is limited;moreover,the mechanism of action of ultrasound modified starch/polysaccharide composite system is unclear.In this study,lotus starch(LS)was complexed with bamboo shoot polysaccharide(BSP).The LS/BSP composite system was further treated with ultrasound to improve the physicochemical properties,in vitro digestive characteristics and structure of LS.The influence of different amounts of BSP on pasting,rheology,retrogradation and digestion characteristics of LS were clarified,and the influence of different ultrasound treatments power and time on the physicochemical,digestion properties and structure of LS/BSP composite system were further investigated.The mechanism of regulating physicochemical and digestive properties of LS/BSP by ultrasound treatment was elucidate at molecular level.Specific research and related conclusions are as follows:(1)The addition of BSP inhibited the gelatinization of LS,and decreased the peak viscosity,through viscosity and final viscosity.The content of leaking soluble starch initially increased and then decreased with increasing content of BSP.At the final viscosity stage,the content of leaking soluble starch increased by 8.2% when 3%BSP was added,and decreased by 15% when 15%BSP was added.The addition of BSP decreased the apparent viscosity and viscoelasticity of LS,and further decreased with increasing content of BSP.The hardness and cohesiveness of LS gel increased with the addition of3% BSP,whereas,the hardness and cohesiveness of LS gel decreased when the content of BSP were 6～15%.3-6% BSP promoted the uniform distribution of water molecules in the starch paste,whereas,the addition of 12% and 15% BSP resulted in uneven water distribution and large holes on the gel surface.The retrogradation of LS increased with the BSP addition increased from 3% to 9%.The addition of 12% and 15% BSP inhibited the short and long term retrogradation of LS.After adding 12%BSP,the content of RDS decreased by 11.6%,the content of RS significantly increased by 75%,and the digestibility of starch decreased.(2)The effects of different ultrasound treatment power and time on physicochemical and digestive properties of LS/BSP composite system were systematically investigated.After ultrasound treatment,the pasting viscosity and leakage of soluble starch of LS/BSP increased.When the ultrasound power was 180 W and 360 W,the viscosity of starch paste gradually increased.After treatment at 360 W for 30 min,the leakage of soluble starch increased by 6.4% compared with that of native starch.When the ultrasound power was greater than 360 W,the pasting viscosity of starch gradually decreased,and lower than that of LS/BSP composite system under 720 W ultrasound treatment.The pasting viscosity of LS increased and then decreased with the increase of ultrasound time.The pasting viscosity reached the maximum under 30 min ultrasound treatment.After ultrasound treatment,the apparent viscosity,stress and viscoelasticity of LS/BSP increased,the pseudoplasticity and thixotropy enhanced.The apparent viscosity,stress and viscoelasticity decreased,pseudoplasticity and thixotropy weakened when the ultrasound power was 540 W and 720 W,and the treatment time was 40 min.After retrograded for14 d,the hardness of 180 W and 360 W samples increased from 100.79 g to 107.46 g and 115.71 g,respectively,while the hardness of 540 W and 720 W samples decreased to 90.06 g and 84.76 g,respectively.The hardness increased by 2.9～14.8%after 10～30 min ultrasound treatment,and decreased by 6.8% after 40 min ultrasound treatment.The content of RDS decreased by 17.7% and SDS content increased by 51.1%after treatment at 360 W for 30 min.After treating under 540 W for 30 min,the content of RS increased by 32.5%.The hydrolysis gradually increased with the increase of ultrasound power to 540 W(from 97.82% to 93.13%)after 180 min in vitro digestion.After 720 W ultrasound treatment,the digestibility of starch increased(96.83%).With the increase of ultrasound treatment time,the digestibility of LS/BSP gradually decreased,and the lowest digestibility was 94.15% at 30 min of ultrasound treatment.(3)The effects of different ultrasound treatment power and time on the structure of LS/BSP composite system was investigated by modern analytical techniques.After ultrasound treatment,cracks and holes appeared on the surface of LS granules,and BSP changed from massive to flake.With the increase of ultrasound power,the cracks and holes on the surface of LS granules become large,and the starch granules was significantly damaged,BSP becomes small flake structure.The structure of LS with the addition of BSP and ultrasound treatment became loose,the thickness of semicrystalline increased.Adding BSP decreased the diffraction peak intensity,gelatinization enthalpy and short-range order degree of LS.After ultrasound treatment,the relative crystallinity,gelatinization enthalpy and short-range order degree of LS/BSP increased,but decreased with the increase of ultrasound power and time.After the addition of BSP,the size of the flake starch paste significantly increased,and the gel surface became smooth and dense.After ultrasound treatment,the particle size of starch paste slightly decreased compared with that of LS/BSP group.After 180 W ultrasound treatment,the LS/BSP paste still had a flake structure and became dense.After 360 W ultrasound treatment,the LS/BSP paste showed a massive structure.After ultrasound treatment of 540 W and 720 W,the surface of some starch paste was loose.With the increase of ultrasound time,the surface of starch paste became dense;however,the surface of LS/BSP massive structure appeared holes and cracks after 40 min ultrasound treatment. |
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