| Arrowhead(Sagittaria sagittifolia L.),a perennial aquatic herb,its underground bulb is also called Cigu,which is a unique aquatic vegetable in China.Arrowhead native starch(ANS)is one of the main nutrients of arrowhead,accounting for about 50% of its dry weight.Moreover,the content of amylose in ANS is relatively high,which is a high-quality resource of resistant starch(RS).It is widely known that RS has a large number of excellent physiological functions such as reducing postprandial blood glucose and improving intestinal microenvironment,however,the information about arrowhead resistant starch(ARS)is extremely limited.Based on this,this paper aimed to evaluate the effect of subcritical water(SW),ultrasound-assisted subcritical water(USW),autoclaving(AM)and ultrasound-assisted autoclaving(UAM)on ARS preparation.Furthermore,the differences of structural properties,physicochemical characteristics and functional characteristics among four tested samples structure were investigated and compared,and the influences and mechanisms of different preparation methods on the structure and functional characteristics of ARS were also revealed.We hope this research may provide feasible preparation technology for the research of high-performance ARS,and lay a theoretical foundation for the development and utilization of arrowhead resource.The main content and research results are as follows:1.Preparation technology of ARSBased on single factor and orthogonal test,the optimal processing parameters of preparing ARS with subcritical water was obtained: starch concentration was 30%,treatment temperature was 150 ℃,treatment time was 50 min,and regeneration time was 36 h.Meanwhile,subcritical water,ultrasound assisted subcritical water,autoclaving and ultrasound assisted autoclaving were also employed to prepare ARS.Four samples obtained were respectively labeled as SW-ARS,USW-ARS,AM-ARS and UAM-ARS,and the RS content of these samples were 5.48,4.39,5.43 and 6.06(g/100g),respectively.In terms of RS content,ultrasonic assisted autoclaving is the best,subcritical water and autoclaving have the same effect on RS formation(p<0.05);After enzymatic purification,the final RS content of four samples were 56.01,53.48,54.21 and 54.38(g/100g),respectively.2.Structural characteristics of ARSThe structural characteristics of ANS and ARS were analyzed by scanning electron microscope,polarizing microscope,particle size analyzer,Fourier-transform infrared spectrometer,X-ray diffraction,solid-state nuclear magnetic resonance and differential scanning calorimeter.The results showed that the particle size distribution of ARS was larger than that of ANS,and the particle size of the sample pretreated by ultrasound was significantly larger than that of the sample not pretreated by ultrasound(p<0.05).Furthermore,ARS had no birefringence.Compared with ANS,the morphological structure of starch granules was completely destroyed,and a certain amount of starch granules were embedded in UAM-ARS.The molecular order degree of SW-ARS,USW-ARS,AM-ARS and UAM-ARS were respectively 0.860,0.804,0.782 and 0.916,and the corresponding double helix content were 1.151,1.177,1.061 and 1.240,respectively.Meanwhile,SW-ARS,USW-ARS,AM-ARS and UAM-ARS exhibited a B-type crystallinity pattern with different degree of crystallinity(37.54%,50.33%,45.83%,43.53% and 55.04%,respectively).The molecular weight distribution of SW-ARS and USW-ARS was narrower than that of AM-ARS and UAM-ARS.Besides,UAM-ARS had the strongest iodine absorption capacity.All samples displayed high gelation enthalpy,suggesting that ANS and ARS could be used as biodegradable films and environmentally friendly heat-resistant materials.3.Functional characteristics of ARSThe functional properties of ANS and ARS were evaluated by solubility,swelling capacity,transmittance,water and oil holding capacity,rheological and fermentation characteristics.The results showed that the solubility of ANS was higher than that of ARS,and the swelling capacity was lower than that of ARS.ARS had higher transmittance than ANS(p<0.05),indicating that ARS could be used in the food production and processing,such as beverage and jelly.Compared with ANS,the water holding capacity(WHC)and oil holding capacity(OHC)of ARS were higher(p<0.05),among which the WHC of each sample of ARS had no significant difference(The WHC of SW-ARS,USW-ARS,AM-ARS and UAM-ARS was 10.67,10.67,10.12 and 11.20%,respectively)(p>0.05),however,the OHC had significant difference(The WHC of SW-ARS,USW-ARS,AM-ARS and UAM-ARS was 3.97,4.48,4.84 and 5.02%,respectively)(p<0.05).Meanwhile,the digestibility of ANS was higher than that of ARS(p<0.05).The in vitro digestibility of ANS was 61.47%,while that of ARS showed in vitro anti digestibility(SW-ARS,USW-ARS,AM-ARS and UAM-ARS were 13.31%,13.32%,12.63% and 15.07%,respectively,in which UAM-ARS had the highest digestibility,p<0.05).Furthermore,the shear thinning phenomenon existed in ANS and ARS.And the apparent viscosity of ARS was lower than that of ANS,and there was no significant difference in the apparent viscosity of SW-ARS,USW-ARS,AM-ARS and UAM-ARS.The storage modulus(G′)and loss modulus(G′′)of all samples was increased with the increase of angular frequency(ω),and G′ was greater than G′′.Moreover,there was a cross phenomenon between G′and G′′of ARS after ultrasonic pretreatment,indicating that the gelation of ARS could be enhanced by ultrasound.The ability of ANS to reduce the pH of fermentation broth was higher than that of ARS,among which USW-ARS,AM-ARS and UAM-ARS had the same ability.ANS did not produce acetic acid under the fermentation of mice feces,and USW-ARS had the strongest ability to produce acetic acid.Both ANS and ARS could be fermented to produce formic acid,and USW-ARS had the strongest formic acid production ability.Therefore,as far as the acid production by fermentation was concerned,the ARS prepared by ultrasonic assisted subcritical water was the best. |
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