Effects Of High Hydrostastic Pressure Treatment On The Properties Of Konjac Glucomannan/Soybean Isolate Protein/Capsaicin Composite Film

For decades,the research of edible films has received attention.The current research direction of edible films tends to develop biologically active functions or provide packaging systems with additional functional characteristics.Therefore,in this study,konjac glucomannan（KGM）and soy protein isolate（SPI）were used as film-forming substrates,and capsaicin（CAP）was added to prepare KGM/SPI/CAP composite film.In this paper,single factor test and response surface optimization test are used to first explore the best formula of the composite film.The film solution prepared by the best formula is subjected to HHP treatment with different pressures and different pressure holding times.Further explore the effects of HHP treatment on the mechanical properties,water contact angle,moisture absorption,moisture barrier,oxygen barrier,light transmittance and CAP content of the composite film,and analyze the KGM/SPI/CAP composite spicy film with a variety of structural characterization methods.The structure and thermal stability of the KGM/SPI/CAP film and the storage stability of the composite film were explored.The study prefer to make an edible film with spicy flavor due to Yunnan,Guizhou and Sichuan and the spicy film provides reference for further promoting the in-depth development and utilization of capsaicin in food and other fields.The main research contents and results are as follows:（1）On the basis of the preliminary experiment of preparing the composite film,the single factor experiment explored the influence of the total mass fraction of KGM/SPI,the mass ratio of KGM/SPI and the CAP concentration on the tensile strength（TS）and elongation at break（E）of the KGM/SPI/CAP composite film.The results showed that surface water contact angle of the film was basically greater than 80°and the moisture absorption rate of the composite film was less than 50.0%,indicating that the surface of the composite film has better hydrophobicity and moisture resistance.Based on the single factor experiment,it is determined that TS and E of the composite film are used as the response values to optimize the response surface and considering comprehensively to obtain the best formula for film production:The total mass fraction of KGM/SPI is 1.1%,the mass ratio of KGM/SPI is 12:8,and the CAP concentration is0.030%.（2）After the KGM/SPI/CAP composite film was treated with a HHP of 0～500 MPa,the properties of the composite film have changed significantly.The pressure mainly improves the properties of the composite film at low pressure and destroyed it at high pressure.The results showed that the mechanical properties and surface hydrophobicity of the composite film gradually enhance with the increase of pressure at low pressure（0～300 MPa）.The TS,E and water contact angle reached the best value at 300 MPa which were 51.7 MPa,4.6%and 120.0°,respectively.The moisture absorption rate,moisture permeability coefficient and oxygen permeability coefficient of the film gradually decreased,namely,the moisture resistance and oxygen resistance were enhanced.At 300 MPa,the moisture absorption rate,moisture permeability coefficient and the oxygen permeability coefficient respectively were 27.9%,1.1×10^-12g·cm/cm²·s·Pa and 2.4×10^-14 cm³·cm/（cm²·s·cm Hg）.At the same time,the composite film possessed the maximum transparency in the visible light region at 300 MPa,which is greater than 75.0%.HHP pressure（300 MPa）indicate that the CAP was distributed in the KGM/SPI system and the absorption peak of the hydroxyl group around 3300cm^-1moved to the lower wave number,indicating that the hydrogen bonding force was strengthened after HHP treatment.The crystallinity of the composite film increased by18.6%andΔH increased by 41.5%.At this time,the surface and cross-section images of the composite film showed that a uniform,dense and flat film structure.Combining the results of multiple indicators,the properties of the composite film were better when the HHP pressure reached 300 MPa.（3）HHP treatment for appropriate time（5～10 min）can improve the properties of the composite film,but overlong HHP treatment is not conducive.When treated for5～10 min,the mechanical properties and surface hydrophobicity of the composite film gradually increased with the increase of the HHP treatment time.The mechanical properties reached the optimum value and the hydrophobicity of the film surface increased by 76.9%compared with the control group at 10 min treatment.The moisture absorption rate,moisture permeability coefficient,and oxygen permeability coefficient gradually decreased,namely,the moisture resisitance and oxygen resisitance were enhanced.The moisture absorption rate significantly decreased by 31.0%compared with the control group.Simultaneously,the moisture permeability and oxygen permeability decreased by 38.2%and 67.1%respectively,indicating that the barrier properties of the composite film reached the best under the 10 min treatment.The transparency of the composite film is bigger than 70.0%in the visible light region at10～15 min resulted the greater light transmittance.An appropriate time can strengthen the molecular hydrogen bonding between the film substrate according to FTIR.With the extension of the pressure holding time,the thermal stability and crystallinity of the film showed a trend of first increasing and then decreasing.The thermal stability is better under 10 min treatment.At this time,the composite film was smooth with no small particles,and the cross-section was compact with no faults.Thus,combining the results of multiple indicators,the properties of the composite film were better when the pressure holding time reached 10 min.（4）The KGM/SPI/CAP composite film treated with HHP would not cause the loss of the total CAP content.Appropriate HHP treatment conditions could reduce the free content of CAP on the surface of the composite film and promote the close combination of CAP with the KGM/SPI membrane matrix.The free content of CAP on the surface of the composite film showed a trend of first decreasing and then increasing with the increase of pressure.In the 300 MPa group,it was reduced by 5.5%compared with the control group,and the effect was the best.After different pressure holding time treatments,the reduction of the free content of CAP was 3.5～6.2%compared with the control group and the 10～15 min treatment time was the best.In summary,HHP treated the KGM/SPI/CAP spicy composite film,stretching and opening the curled molecular chains of KGM and SPI and promoting the orderly arrangement of molecules which exposed more CAP binding sites.The bond of CAP in KGM/SPI system was closer,which improved the stability of CAP in composite film.（5）The storage experiment results of the composite film showed that the mechanical properties,surface hydrophobicity,moisture absorption rate,moisture permeability,oxygen permeability and other properties of the HHP group better than the control group.The water contact angle of the HHP group did not change significantly and the values were bigger than 100.0°.The moisture absorption rate of the HHP treatment group increased slightly and reached 30.7%after 90 d,which was still far lower than the control group.The free CAP content of the composite film of the control group was increased after storaged for 15 d and the content increased significantly at 120 which reached to 16.2%.However,the free CAP content on the film surface of the KGM/SPI/CAP composite film treated with HHP did not appear significant changes after storage for 60 d and the CAP free content was still less than 6.0%at 120 d,which was much lower than the control group.The results showed that HHP was beneficial to consolidate and stabilize the ability of the polysaccharide-protein system to bind small molecules and CAP molecules bound with each other more tightly after HHP treatment.