Preparation Of PH Intelligent Indicator Film Based On Passion Fruit Peel By High Pressure Homogenization And Its Application

Passion fruit peel as a food processing by-product,the peel accounts for about 50%～55%of the fresh fruit,its outer peel is rich in anthocyanins,and the inner peel is rich in pectin and fiber,which is a good raw material for the preparation of p H intelligent indicator film.High-pressure homogenization technology is used to treat the film-forming solution of passion fruit peel,which can reduce the particle size and microstructure of the material through intense shear force and high-speed collision,and then improve its various properties.Sorbitol is chemically stable and is often used as a plasticizer in the preparation of films to improve the brittleness,flexibility and ductility of films.Therefore,in this study,we firstly extracted anthocyanins from the outer peel of passion fruit and optimized the extraction process;secondly,we combined high-pressure homogenization technology and added sorbitol to prepare indicator films and optimized the optimal process parameters;finally,we applied the films to monitor the freshness of fish meat in real time.The main research contents and results are as follows:（1）The pericarp of passion fruit was used as the source of anthocyanins,and ultrasonic assisted extraction of anthocyanins from pericarp was performed with ethanol as solvent.The effects of solid-liquid ratio,ultrasonic time and ultrasonic temperature on the extraction yield of anthocyanins from pericarp were analyzed,and the optimal extraction parameters were determined by single factor and orthogonal experiments.The results showed that the optimal extraction parameters were as follows:solid-liquid ratio of 1:15,ultrasonic time of60 min,ultrasonic temperature of 40℃.The extraction rate of anthocyanins was 0.489 mg/g.The color change and UV spectrum of anthocyanin solution under different p H conditions were investigated.The results showed that the color change of anthocyanin solution under different p H conditions was significant,so it can be used as a p H indicator.（2）The film-forming solution of passion fruit peel was modified with sorbitol as plasticizer and combined with high pressure homogenization technique.The effects of homogenization pressure,homogenization times and sorbitol mass fraction on the microstructure and rheological properties of the film-forming solution and on the performance of p H-intelligent indicator film based on passion fruit peel in terms of 1 min ammonia response value(△E_（NH3）),tensile strength（TS）,elongation at break（EAB）,light transmission（T）and water solubility（WS）were investigated.Combined with the principal component analysis and the comprehensive evaluation method of affiliation,the comprehensive score of the indicated films was used as the index for evaluation,and the preparation process was optimized by orthogonal tests.When the high-pressure homogenization pressure was 40 MPa,the number of homogenization was 10 times,and the mass fraction of sorbitol was 0.6%,the comprehensive performance of the indicator film obtained was better,and the△E_（NH3）of the corresponding film was 35.23,TS was 20.07MPa,EAB was 16.11%,T was 46.18%,and WS was 54.32%at this time.（3）The indicator films prepared with the above-mentioned optimal process parameters were selected for the monitoring of fish freshness.Firstly,the color change and color difference values of the indicator film for monitoring fish freshness under storage conditions at room temperature of 25°C for 30 h were measured,as well as the volatile salt nitrogen（TVB-N）,total bacterial colony（TVC）and p H values of the fish for 30 h.The results showed that the TVB-N value exceeded the threshold value of the national standard（20 mg/100 g）at 20 h,while the TVC value exceeded the threshold value of the national standard.The results showed that the TVB-N value of fish exceeded the national standard threshold（20 mg/100 g）at 20 h while the TVC value exceeded the threshold（7 lg CFU/g）at 15 h.In addition,the color change and color difference of the indicator film at 15 h showed that the TVB-N value exceeded the national standard threshold（20 mg/100 g）.In addition,the color of the indicator film reached the inflection point at 15 h.TheΔE value was as high as 16.03.The time when the color of the indicator film reached the inflection point was approximately the same as the time when the total number of colonies in fish meat reached the threshold value,and the color difference value of the film correlated well with the freshness index of fish meat,indicating the potential application of the indicator film in monitoring the freshness of fish meat and other food products.