Study On The Effect Of Processing On The Bioavailability Of Polyphenol In The Casein-polyphenol System And Their Interactions

Functional dairy beverages containing polyphenols have attracted the attention of consumers due to their health benefits,while bioavailability is the premise for polyphenols to exert their health functions in the human body.The bioavailability of polyphenols is generally poor,which is not only related to the structure of polyphenols but affected by other components in the food matrix and food processing factors.At present,the effects of food processing on the antioxidant activity,the bioavailability of polyphenols,and protein-polyphenol interaction were rarely involved.In this study,casein(CN)and three kinds of polyphenols commonly found in foods including cyanidin-3-O-glucoside(C3G),chlorogenic acid(CA),and phlorizin(Phl)were chosen as the research objects.Two common processing conditions(enzymatic hydrolysis and thermal treatment)were used to study the effects of processing factors on the antioxidant activity of protein-polyphenol complexes and the bioavailability of polyphenols.The changes in protein-polyphenol interaction mode under different processing conditions were also investigated.It is expected to provide a theoretical basis and guidance for improving the health function of dairy beverages containing polyphenols.The major research contents and the results are as follows:Firstly,CN was hydrolyzed by alcalase to obtain casein hydrolysates(CNHs)with different molecular weight distributions.The changes in antioxidant activity were evaluated by ABTS free radical scavenging ability and ferric ion reducing antioxidant power(FRAP),and it was found that enzymatic hydrolysis could enhance the antioxidant activity of CN.After hydrolysis and compared with CN-C3 G,the FRAP and ABTS free radical scavenging ability of CNHs-C3 G complexes increased by 3.13%–8.59% and 6.60%–9.18%,respectively.The complexation of CN/CNHs and C3 G caused an antagonistic effect in ABTS free radical scavenging ability;the complexation of CN and C3 G had no obvious effect on FRAP(p>0.05),while the complexation of CNHs and C3 G caused a synergistic effect in FRAP.Then,under different thermal treatments(65?/30 min,100?/15 min and 121?/15 min)and protein/polyphenol molar ratios(10:1,1:1 and 1:10),the antioxidant activity of ?-CN-CA and ?-CN-Phl complexes and the in vivo bioavailability of CA and Phl were studied.The results showed that after thermal treatments,the ABTS free radical scavenging ability of ?-CN-CA and?-CN-Phl complexes increased by 4.36%–19.98% and 5.53%–38.36%,the FRAP of ?-CN-CA complexes decreased by 8.11%–45.67%,and the FRAP of ?-CN-Phl did not change significantly(p>0.05).The complexation of ?-CN with CA and Phl under thermal treatments caused a synergistic effect in FRAP,while an antagonistic effect in ABTS scavenging ability.The thermal stability of CA was poor and CA would undergo isomerization under thermal treatments at high temperature.?-CN could protect CA to a certain extent,while the thermal stability of Phl was relatively good and thermal treatments would not affect it.The pharmacokinetic results of ?-CN-CA and ?-CN-Phl complexes in rats under thermal treatments showed that thermal treatments had different effects on the bioavailability of CA and Phl.Under the treatment of 65?,100?,and 121?,the bioavailability of CA decreased by 17.36%,47.70%,and 55.84%.The bioavailability of Phl did not change significantly under the treatments of 65? and 100?(p>0.05),while decreased by 58.71% under the treatment of121?.Lastly,fluorescence spectroscopy,circular dichroism,infrared spectroscopy,matrixassisted laser desorption ionization time-of-flight mass spectrometry(MALDI-TOF-MS),gel electrophoresis(SDS-PAGE),particle size distribution,and amino acid analysis were used to study the interaction between CN/CNHs with C3 G and ?-CN with CA/Phl under different processing conditions.The results showed that the interaction mode between CN and C3 G shifted from hydrogen bond or van der Waals force to hydrophobic interaction after hydrolysis,and the binding affinity reduced by 68.79%(CNH-1),83.33%(CNH-2),and 64.89%(CNH-3),respectively.The secondary structure of CN tended to be more open and disordered after hydrolysis,and the interaction between C3G-CN/CNHs had little effect on the secondary structure of the protein.Both hydrolysis and complexation with C3 G could enlarge the particle size of protein particles.For ?-CN-CA and ?-CN-Phl complexes,CA and Phl mainly interacted with ?-CN via hydrophobic interaction,hydrogen bond or van der Waals forces at 25?,and thermal treatments would not alter the type of interaction,while affecting the binding affinity.Under the treatment of 65? and 100?,the binding affinity of ?-CN with CA/Phl did not change significantly(p>0.05),while under the treatment of 121?,the binding affinity reduced by 84.30% and 62.86%,respectively.Neither thermal treatments nor the interaction would have an obvious effect on the secondary structure of ?-CN.MALDI-TOF-MS,SDS-PAGE,and amino acid analysis showed that there might be no covalent bond between ?-CN and CA/Phl under the conditions set by this study.The casein-polyphenol interactions under different processing conditions caused antagonistic/synergistic effects on the antioxidant activity of the complexes to different extents,and the binding affinity of the interaction was significantly correlated with the changes in the bioavailability of polyphenols after processing.