Development Of Intelligent Films Base On Pitaya Peel And Its Application In Pork Packaging

With food packaging playing an increasingly important role in food quality and safety,intelligent packaging film has become a hot research topic as a new packaging technology that can provide feedback on food quality by monitoring and indicating environmental changes inside the package.Pitaya peel accounts for about a third of the whole fruit,which usually be discarded in fresh consumption and processing.Components such as fiber,polyphenols and natural pigments are also wasted.They were usually extracted from pitaya peel and to be used in functional food processing,but most of the extraction processes were complicated with low utilization rate.In recent years,environment-friendly packaging materials have been widely explored.The preparation of edible films and functional packages with fruit and vegetable processing by-products is not only conducive to utilize resource and protect environmen,but also meet the multi-demands of novel food packaging.In this study,pitaya peel was used as a film-forming substrate to prepare indicator film and to construct real-time intelligent packaging,as well as to simulate its film-forming system to optimize the performance of indicator films and use them to monitor the freshness of pork.This study aimed to develop a new intelligent packaging and to expand the high-value utilization of pitaya peel.The main results were as following:(1)The compositions of pitaya peel,as well as the compostion,color response to p H and temperature stability of betacyanins extracted from pitaya peel were analyzed,to evaluate the potential of using pitaya peel to prepare indicator films directly.The results showed that there were 92.36%water,1.44%pectin,1.24%crude fiber and 5.82 mg/100g betacyanins in pitaya peel(all calculated by wet weight).The purified extractive contained 9.52 mg/g of betacyanins,and 6 of betacyanins were mainly phyllocactin(46.49%)and betanin(34.35%)as the top two monomers.Betacyanins was stable in p H 3.0～7.0 and showed purplish red.With the increase of p H,it gradually changed to purple(p H 8.0～11.0)and yellow(p H 12.0),indicated that betacyanins in pitaya peel can be used as a natural indicator of p H.The sensitivity of betacyanins response to tyramine was improved by adjusting the initial p H of betacyanins solution to 7.0 and 8.0.In addition,betacyanins solution was relatively stable at4~oC.The above results indicated that pitaya peel and contained betacyanins can be used to prepare films with the potential of responding to p H change.(2)Pitaya peel was used to prepare intelligent indicator film,and the effects of peel pulp concentration(60%～100%),glycerol concentration(0%～4%)and p H of film-forming solution on the structure,physical and mechanical properties,and response sensitivity to ammonia of indicator films were investigated.Meanwhile,a preliminary evaluation of films to monitor the freshness of pork during storage at 4~oC was conducted.The results showed that the indicator film PPC80-GC2-p H4.3,prepared with 80%peel pulp,2%glycerol and p H 4.3had the strongest intermolecular interactions and the most ordered and dense structure,and exhibited good mechanical properties.The indicator films PPC80-GC2-p H7.0 were prepared by adjusting the p H of its film-forming solution to 7.0,which significantly improved their sensitivity to ammonia without weakening its physical and mechanical properties,and the color remained stable in storage at 4~oC for 20 d(ΔE<5).Its detection limits for ammonia,dimethylamine and trimethylamine were 95.28μM,79.47μM and 92.64μM,respectively.The results also showed that the color of the indicator film PPC80-GC2-p H7.0 changed from an initial purplish red to bright red color at 4 d(sub-fresh)and light pink color at 6 d(spoiled)during monitor the freshness of pork.TheΔE values were greater than 5 and revealed significant difference(p<0.05),indicating that it could distinguish the freshness and spoilage of pork.(3)The film-forming substrate with pecyin,carboxymethylcellulose and betacyanins extract to simulate pitaya peel,and to improve the hydrophobicity,mechanical properties and sensitivity to ammonia of the indicator film.The results showed that the indicator film PEGE1-CMC-BE0.5 prepared from 0.8%pectin,0.4%gelatin,1.0%carboxymethylcellulose and 0.5%betacyanins extract had the maximum tensile strength while minimum water vapor permeability,and a water contact angle of 92.47°.By adjustment of the content of betacyanins extract to 0.3%,the obtained indicator film PEGE1-CMC-BE0.3 had the maximum tensile strength while minimum water vapor permeability,and the highest sensitivity toammonia.The indicator film PEGE1-CMC-BE0.3-p H7.0 prepared by adjusting the p H of its film-forming solution to 7.0 showed a significant increase in tensile strength and elongation at break,while the sensitivity to ammonia was improved furtherly.In monitoring the freshness of pork during storage at 4°C,the color of the indicator film PEGE1-CMC-BE0.3-p H7.0 gradually and obviously changed to yellow,theΔE values were above 5 at 4 d and 6 d and significantly differen(p<0.05),indicating that it could distinguish the grades of fresh,sub-fresh and spoiled pork.