Enrichment And Purification Of Alkylresorcinols (ARs) From Wheat Bran And The Digestibility Of Starch-ARs Complex In Vitro

Alkyl resorcinol(ARs)is a kind of phenolic lipids in grain bran and a biochemical marker of whole grain food and its intake;At the same time,it has the functions of bacteriostasis,anti-tumor,inhibiting the activity of glucose and lipid metabolism enzymes,and has high value in food utilization.However,there are some bottlenecks in the separation,extraction and food application of ARS from wheat bran.Firstly,ARs in wheat bran was mainly concentrated in the middle layer,and the content in the exocarp and aleurone layer was very low;The lipids rich in aleurone layer are easy to be co extracted with ars,which affects the separation and extraction efficiency and purity of ARs.In addition,ARs has a certain bitter taste and smell,and its direct addition will affect the color and flavor of food.It needs to be added after compounding with starch and other components to play its function and reduce the impact on food flavor.In this paper,the primary enrichment of ARs components in wheat bran was realized by dry stripping,crushing,screening and classification,so as to provide highquality raw materials for the extraction of ARs;Then,the effect and conditions of extracting ARs from wheat bran by subcritical propane ethanol were explored,and ARs was purified by silica gel column chromatography and low temperature sedimentation,which laid a foundation for large-scale and efficient separation and purification of ARs;Finally,the starch ARs complex was prepared by hydrothermal method to characterize and explore the effect mechanism of ARs on starch digestion in vitro,so as to provide a theoretical basis for the food utilization of ARs.The main conclusions of this paper are as follows:(1)After impact crushing and screening,the particles of the structural layer in the60 mesh sieve were larger and relatively complete,and the exocarp,middle layer and aleurone layer had not been dissociated;The exocarp was enriched in 60-80 mesh powder;Under 150 mesh sieve,most of them were cell wall fragments,aleurone layer contents and starch;In the stripped wheat bran powder with different particle sizes,the content of ARs first decreases and then increases with the particle size.Among them,the content of ARs in the 200 mesh sieve is higher and the fat content is lower,so it is a better raw material for ARs extraction.Compared with traditional oscillating extraction,the extraction rate of ultrasonic assisted extraction decreased slightly(p >0.05),but the content of ARs in the crude extract was higher than that of oscillating extraction,and the extraction time was greatly shortened.The extraction rates of ARs with different organic solvents from high to low were as follows: methanol > ethanol >ethyl acetate > acetone > cyclohexane > hexane > petroleum ether.The content of coextracted compounds in acetone extract was the lowest.When the ratio of solvent to material is greater than 10,the ratio of material to liquid has little effect on ARs extraction.(2)The extraction of ARs from wheat bran by subcritical propane ethanol increased with the increase of ethanol content in the extraction solution,but the extraction of ARs from wheat bran by subcritical propane ethanol was low due to the limitation of solvent polarity range.When the amount of ethanol was 7%,the extraction of wheat bran oil could reach 94%,but the extraction of ARs was only 11.54%.Silica gel column chromatography can effectively separate oil and ARs from the crude extract of wheat bran.After separation,the concentration of ARs in the separation solution can be increased from 28.82 mg/g to 194.70 mg/g.Low temperature freezing can effectively increase the concentration of ARs in the crude extract of ARs and change the composition of ARs homologues.Compared with single temperature,the purification effect of ARs crude extract by multi temperature stage(4℃ and-80℃)freeze crystallization was the best.The freeze crystallization products are mainly saturated homologues,and the content of unsaturated homologues is very low(< 1%),which can realize the effective enrichment of saturated ARs homologues;When the freezing time was longer than 6 h,the freezing time had no significant effect on the yield of ARs.When refrigerated at-80℃,the selectivity of methanol to ARs was significantly better than that of ethanol,acetone and ethyl acetate,and the content of ARs in methanol frozen crystals could reach 246.11 mg/g;Combined with silica gel column chromatography,the sedimentation effect of low-temperature freezing was better,and the ARs content in the crystal can reach 285.60 mg/g.(3)Starch can form V-shaped crystal with ARs at 90℃,and the composite effect with ARs frozen supernatant was the best.Effects of ARs on starch digestive enzymes(α-amylase and starch glucosidase)had inhibition,but the inhibition rate was low(<50%).The binding of starch ARs was the main reason why ARs inhibited starch digestion.The resistant starch(RS)increment of starch-ARs(3%,dry basis)complex prepared by heating first and adding ARs at 90℃ was up to 35.6%.Among the starchARs complexes prepared at different temperatures,the highest increase of resistant starch was 22.69% in the complex of starch and ARs frozen supernatant prepared at90℃;The proportion of resistant starch in starch-ARs(frozen crystallization)complex increased by about 12.69%,which was higher than that of starch-ARs(frozen supernatant)complex;The proportion of resistant starch increased first and then decreased with the increase of ARs addition.When the addition amount was 3%,the anti digestion effect of starch-ARs complex was the best,and the RS content increased from 4.40% to 39.95%;With the addition of 3%,the way of gelatinizing first and then adding lipids was more conducive to the formation of starch-ARs complex.