Preparation Of Areca Nut Coating Material Based On Cowhide Gelatin-polysaccharide And Improvement Of Water Blocking Property

The epidermis of areca nut is dull and rough,and the pig skin gelatin coating method is usually applied to the surface to improve the apparent gloss and maintain the moisture.However,the pig skin gelatin film is easy to fall off during processing and storage,resulting in the deterioration of apparent gloss quality.In addition,pig skin gelatin is still involved in issues of religious disputes.Therefore,it is urgent to find an areca nut coating agent with non-pig skin source,high gloss,good adhesion stability and water blocking property.In this study,the influence of environmental factors on the properties of areca nut in pig skin gelatin coating during storage and the effect of gelatin properties on the characteristics of areca nut coating were investigated,and the concentration and gel strength of cowhide gelatin suitable for areca nut coating were determined.The regulation effect of polysaccharide compounding and cowhide gelatin-polysaccharide synergy on the properties of areca nut coatings was further illustrated.On this basis,the improvement effect of sucrose esters on the water-resistance of coatings was explored.Taking the glossiness,film thickness,mechanical properties,water resistance,viscosity and solidification temperature of the coating solution as indicators,the influence of the gelatin type on the properties of the coating areca nut was firstly clarified.It was found that compared with fish skin gelatin and pig skin gelatin,the cowhide gelatin coating film has higher gloss.The effects of concentration and gel strength of cowhide gelatin on the optical,mechanical and water blocking properties of the coating were investigated,and the reasons for the differences in the properties of the coating were analyzed by means of infrared spectrometer and X-ray diffraction.The results showed that the cowhide gelatin film-forming solution with a concentration of 10%-15%not only increased the gloss of the areca nut epidermis by 7-14 times,but also endowed the film with good tensile strength（～46 MPa）,elongation at break（～19%）and water vapor permeability coefficient(～0.948 g mm m^-2 h^-1k Pa^-1).Although the improvement of gelatin gel strength helped increase the gloss of the coated areca nut,it had no significant effect on the mechanical and water blocking property of film.The differences in the content of intermolecular hydrogen bonds and triple-helical structures in the films were important internal factors for the different properties of gelatin after film formation.The rheological analysis revealed that the viscosity and solidification temperature of the coating solution with a concentration of 10%-15%were more suitable for improving the uniformity of the coating film.In order to find a polysaccharide coating material that can replace gelatin,the effect of polysaccharide coating on the apparent properties of betel nut was investigated,and it was found that sodium alginate（SA）,xanthan gum（XG）and gum Arabic（AG）had higher gloss.For enhancing the gloss of areca nut polysaccharide-based coating agent,the effect of the ratio of SA to XG on the properties of the coating film was mainly investigated.The result indicated that the areca nut coated by SA-XG in a ratio of 50:50 presented the higher gloss（2.69 GU）,and the wetting of the coating solution on the surface of the areca nut was improved with a diffusion coefficient of-33.957 m N/m.Light transmittance,fourier transform infrared spectrometer and scanning electron microscopy showed that SA and XG had good compatibility.The SA-XG composite films were collocated more closely and had a denser microstructure due to intermolecular hydrogen bonding interactions.In addition,the SA-XG combination improved the mechanical property and water vapor permeability coefficient of the film,and reduced the water loss rate of the coated areca nut in low humidity（RH30%）environment.In order to further improve the water blocking property of the system,the effect of the combination of cowhide gelatin and polysaccharide on the properties of coated areca nut was studied.It was found that the combination of sodium alginate,xanthan gum or gum Arabic and cowhide gelatin were all helpful to improve the water blocking property of the film.The results indicated that the gelatin and gum Arabic composite coating showed the highest gloss（9.71GU）in areca nut,and the film transmittance at 600 nm reached 90%,showing good compatibility,tensile strength（～54 MPa）,elongation at break（～22%）and water vapor permeability coefficient(～0.85 g mm m^-2 h^-1 k Pa^-1),which was associated with an increased proportion of triple helical structures in the composite membrane.The rheological analysis further proved that the combination of the two had no effect on the viscosity and solidification temperature of the solution.In addition,after accelerated storage in low humidity（RH30%）and high humidity（RH80%）environments for 7 days,the combination of the two could reduce the moisture change rate of coated areca nut by 13.2%in low humidity environment and 0.5%in high humidity environment.Based on the cowhide gelatin-gum Arabic composite system,the regulation effect of sucrose ester addition on the water blocking property of the composite film was studied.The results showed that the introduction of sucrose ester in the composite coating could further improve the water resistance of the system,and the suitable type of sucrose ester was determined to be S₁₁ and the concentration was 1%.Although the addition of S₁₁ reduced the gloss of areca nut to 7.81 GU,the elongation at break of the film increased to about 24%and the water vapor permeability coefficient decreased to 0.69 g·mm·m^-2·h^-1·k Pa^-1.After accelerated storage for 7 days in low humidity（RH30%）and high humidity（RH80%）environments,the presence of S₁₁ further reduced the water loss rate of the coated areca nut by 12.0%in low humidity and increased by 0.1%in high humidity,so as to maintain the water content of areca nut.