Gallic Acid Epoxy Modifies Gelatin And Characterizes Properties

Animals such as livestock,poultry,and fish are the main sources of meat,and the demand for them is constantly increasing.In the production process,connective tissues such as skin,bones,and scales are major by-products.These by-products can be processed to obtain gelatin,which can be used in food,medicine,materials,and other fields.Gelatin also has many active groups such as amino,hydroxyl and carboxyl groups on its molecular chain,which can be modified by chemical reactions.This study aimed to explore modified gelatin with different properties,expand the application field of gelatin,and increase its added value.Using a chemical modification method,we reacted a polyphenolic epoxy with the primary amine groups in gelatin to obtain crosslinking modified gelatin.After analyzing the properties of the modified gelatin,we found that the hydration properties and thermal stability were improved.The main research contents and results are as follows.(1)The synthesis of gallic acid epoxy(GAE): Gallic acid(GA),a food-derived compound,was used as the raw material to synthesize GAE via two-step reactions of allylation and epoxidation.The conditions for the epoxidation reaction were optimized by a single-factor experiment to investigate the effects of the dosage of m-chloroperoxybenzoic acid(m-CPBA),4,4’-Thiobis(6-tert-butyl-M-cresol)(t.b.c),epoxidation temperature,and reaction time on the epoxy value of the GAE.Based on the factors and levels determined by the single-factor experiment,an orthogonal experiment was performed to determine the optimal synthesis conditions: 8 mmol of m-CPBA and 0.3mmol of t.b.c were used for 1 mmol of allylated gallic acid(AGA),and the epoxidation reaction was carried out at 40 ℃ for 48 hours,the epoxy value of GAE was 0.796mmol/100 g.Finally,FT-IR and NMR were used to characterize the chemical structural changes from GA to GAE,and the successful synthesis of GAE was confirmed.(2)The modification of gelatin by GAE: The crude product of GAE obtained under optimal synthesis conditions was purified by silica gel column chromatography and used as a bio-crosslinking agent for chemically crosslinking gelatin.A single-factor experiment was conducted to investigate the effects of the molar ratio of epoxy groups of GAE to primary amine groups of gelatin,p H,reaction temperature,and reaction time on the cross-linking degree of GAE modified gelatin(GAEG)during the chemical modification process.Based on the factors and levels determined by the single-factor experiment,an orthogonal experiment was performed to determine the optimal modification conditions: molar ratio of epoxy groups of GAE to primary amine groups of gelatin was 4:1,p H was 10,reaction temperature was 45 ℃,reaction time was 10 hours,the cross-linking degree of GAEG was 72.68%.(3)Characterization of GAEG: GAEG samples with different molar ratios of epoxy groups to primary amine groups were prepared under the optimal modification conditions,and glycerol was added as a plasticizer to prepare modified gelatin film samples.The chemical structure,hydration properties,thermal stability,and mechanical properties of the films were tested.The results of the above tests showed that the epoxy groups of GAE can react with the primary amine groups of gelatin to form C-N bond and covalent crosslink.The swelling ratio of GAEG in water was increased by about 5 times.With the cross-linking degree increased from 41.13% to72.68%,the swelling ratio decreased from 7831% to 6448%.While the gelatin dissolved completely in water within 24 h,the GAEG remained intact for 7 days,and the disintegration rate decreased significantly with the increase of cross-linking degree.The water contact angle decreased from 88.01° to 59.87° after the modification,indicating increased hydrophilicity.The denaturation temperature increased from55.0℃ to 61.7℃,and the thermal decomposition temperature increased from 240℃ to274℃,with a relative decrease in thermal weight loss.The modification treatment led to a slight decrease in mechanical properties.This study demonstrated that GAE improved the hydration properties and thermal stability of gelatin,contributed to the application of gelatin as water retaining agent and stabilizer in food industry.