Synthesis Of Starch Aldehyde-catechin Conjugate And Its Application In Active Packaging

Catechin is a polyphenolic substance with strong antioxidant and antibacterial activities.However,its instability in light,heat,oxygen and alkaline environments limits its application in the food industry.Therefore,molecular modification is necessary to enhance the stability of catechins.In this study,starch aldehyde-catechin conjugates were synthesized by covalently connecting catechin and starch aldehyde via acid-catalyzed condensation for the first time.The structure characteristics,stability and antioxidant activity of starch aldehyde-catechin conjugates were mainly studied.Starch aldehyde-catechin conjugates were further prepared into food active packaging film and coating preservative,which were used for edible oil and pork preservation.The results provide a basis for the application of starch aldehyde-catechin conjugates in food industry.The main research results of this study are summarized as follows:（1）Firstly,cassava starch aldehyde was functionalized with catechin through acid catalyzed condensation reaction.The structural characterization,stability and antioxidant activity of starch aldehyde-catechin conjugates were investigated,Folin-ciocalteu test showed that the conjugate ratios of starch aldehyde-catechin conjugates were 233.29,270.17 and 341.31 mg/g,respectively.Thin layer chromatography revealed the conjugates did not contain free catechin.UV-vis spectra of the conjugates exhibited a characteristic absorption peak of catechin B-ring at 280 nm.Fourier-transform infr ared and proton nuclear magnetic resonance spectroscopy demonstrated the conjugation occurred between the H-6/H-8 of catechin A-ring and the aldehyde groups of starch aldehyde.X-ray diffraction pattern indicated that the conjugates had an amorphous structure.Scanning electron microscopy showed the conjugates were fragmentary slices with rough surfaces.Notably,the conjugates were more stable than catechin in phosphate buffered saline（pH 7.4）.In addition,the conjugates could not be digested by simulated saliva,gastric juices and small intestinal fluids.The reducing power and free radical scavenging activity of starch aldehyde were remarkably elevated by conjugating with catechin.Meanwhile,the conjugates were non-cytotoxic to RAW264.7 mouse macrophage cells and possessed higher resistant starch contents than starch.（2）Starch aldehyde-catechin conjugates were added into quaternary ammonium chitosan（QAC）/polyvinyl alcohol（PVA）blend to prepare active packaging films.The structural,physical and antioxidant properties of films were determined.Results showed starch aldehyde-catechin conjugates formed hydrogen bonding with QAC/PVA film matrices and changed the uniformity of films.After starch aldehyde-catechin conjugates were added into films,the water vapor permeability,tensile strength and elongation at break of films were increased by 2.51%-16.03%,11.73%-20.15%and 0.78%-12.15%,respectively;whereas the oxygen permeability of films was reduced by 6.67%-53.33%.Starch aldehyde-catechin conjugates increased the 2,2-diphenyl-1-picrylhydrazyl and 2,2’-azino-bis-（3-ethylbenzothiazoline-6-sulfonic acid）radical scavenging efficiencies of films by 852.3%-995.5%and 599.5%-669.3%,respectively.The film was made into oil bags for peanut oil packaging.As compared with oil packaged in QAC/PVA film,oil packaged in QAC/PVA films containing starch aldehyde-catechin conjugates showed significantly lower peroxide values and thiobarbituric acid reactive substance levels.Results suggested QAC/PVA films containing starch aldehyde-catechin conjugates had a good potential in peanut oil packaging.（3）Finally,starch aldehyde-catechin conjugate and chitosan were mixed to prepare the coating preservative and used for the preservation of chilled pork loin.The weight loss,color,pH value,microbial spoilage,lipid oxidation,protein oxidation,texture and sensory attributes of pork loin during cold storage（4±1℃,14 days）were analyzed.Results showed chitosan and starch aldehyde-catechin conjugate had synergistic antioxidant and antimicrobial actions.On day 14,as compared with uncoated and chitosan coated pork lions,chitosan/starch aldehyde-catechin conjugate coated pork lions showed lower weight loss（7.16%）,pH value（5.99）,total viable count（7.11 1g CFU/g）,total volatile base nitrogen content（13.02 mg/100 g）,lipid oxidation level（0.47 mg/kg）,protein oxidation level（46.57μmol/g protein）and shear force（27.40 N）.Meanwhile,chitosan/starch aldehyde-catechin conjugate composite coating effectively maintained the color,micro-structure and sensory attributes of pork lions throughout chilled storage period.The shelf life of pork lions was extended from 8 days（uncoated samples）to 14 days by chitosan/starch aldehyde-catechin conjugate composite coating.Therefore,chitosan/starch aldehyde-catechin conjugate composite coating had a good potential in fresh pork storage.