Stability And Application Of Active And Intelligent Packaging Films Based On Anthocyanins From Lycium Ruthenicum Murr.

Nowadays,the development of active and intelligent packaging films based on plant-derived anthocyanins with antioxidant activity,antimicrobial activity and pH-sensitivity has received increasing attention in food engineering field.Anthocyanin-rich packaging films can be not only used to extend the shelf life of food but also used to monitor the freshness of food.However,the utilization of anthocyanin-rich packaging films in food industry is limited by the low stability of anthocyanins.Therefore,it is essential to study the stability of anthocyanin-rich packaging films and adopt some technologies to improve the stability of the films.In this study,active and intelligent packaging films were developed based on cassava starch,polyvinyl alcohol and Lycium ruthenicum anthocyanins.The functionality and stability of the films under different storage conditions were evaluated.Meanwhile,nano-encapsulation technique was used to enhance the stability of L.ruthenicum anthocyanins in the films.Finally,the developed films were applied to package and indicate the freshness of refrigerated largemouth bass(Micropterus salmoides)fillets.Our results contribute to broadening the application of anthocyanin-rich films in food industry.The main research results of this study are summarized as follows:(1)The structural,physical and functional properties of active and intelligent packaging films based on cassava starch and L.ruthenicum anthocyanins were evaluated.Results showed L.ruthenicum anthocyanins were composed of pelargonidin-3-O-acetylglucoside(10.50%),petunidin-3-O-(p-coumaroyl)rutinoside-5-O-glucoside(1.70%),petunidin-3-O-(6-acetylglucoside)(3.64%),dimmermalvidin-3-O-glucoside-petunidin-3-O-glucoside(80.11%),peonidin-3-O-rutinoside(2.30%)and cyanidin-3-O-(6-acetylglucoside)-5-O-glucoside(1.75%).Fourier transform infrared and X-ray diffraction analyses revealed hydrogen bond interactions formed between starch and L.ruthenicum anthocyanins in the films.The incorporation of L.ruthenicum anthocyanins significantly enhanced the water vapor and ultraviolet-visible light barrier ability,tensile strength,antioxidant ability and pH-sensitivity of starch films.Meanwhile,the barrier,antioxidant and pH-sensitive properties of cassava starch/L.ruthenicum anthocyanins films were positively correlated with the content of anthocyanins(2)Polyvinyl alcohol was added into cassava starch/L.ruthenicum anthocyanins film to enhance the properties of films.The stability of starch/polyvinyl alcohol//.ruthenicum anthocyanins film at different storage temperatures(4,20 and 35℃),light(with or without light)and storage time(1,2,3 and 5 months)was investigated.Results showed storage time and temperature were key factors affecting the stability of the films.With the increase of storage time and temperature,the cross-section of the films gradually became uniform and the crystallinity of the films gradually increased.The initial purple color of the films gradually faded and turned green or yellow at the fifth month.Anthocyanins in the films gradually degraded during film storage.The mechanical properties of the films gradually enhanced,however,the antioxidant activity and pH-sensitivity of the films decreased during film storage.Notably,the films stored at 4℃ preserved acceptable antioxidant activity and pH-sensitivity for three months.(3)Anthocyanins-loaded nanocomplexes were added into cassava starch/polyvinyl alcohol film.The structural,physicochemical and functional properties of the film were evaluated.Results showed anthocyanins-loaded nanocomplexes had average particle size of 242.1 nm,zeta potential of+28.13 mV,and polydispersity index of 0.186.Anthocyanins-loaded nanocomplexes had an encapsulation efficiency of 68.4%and a core-shell structure.Starch/polyvinyl alcohol/L.ruthenicum anthocyanins nanocomplexes film had denser micro-structures,stronger intermolecular interactions,and higher water vapor blocking,mechanical properties and stability than starch/polyvinyl alcohol/L.ruthenicum anthocyanins film.However,starch/polyvinyl alcohol/L.ruthenicum anthocyanins film presented higher light blocking and antioxidant properties than starch/polyvinyl alcohol/L.ruthenicum anthocyanins nanocomplexes film.Therefore,starch/polyvinyl alcohol/L.ruthenicum anthocyanins nanocomplexes film was more suitable to be used as active and intelligent packaging material.(4)Starch/polyvinyl alcohol/L.ruthenicum anthocyanins nanocomplexes film and starch/polyvinyl alcohol/L.ruthenicum anthocyanins film were further applied to package and indicate the freshness of refrigerated largemouth bass(Micropterus salmoides)fillets.Results showed that both films could effectively inhibit the increase of pH value,lipid peroxidation degree,total volatile basic nitrogen content and total colony count of largemouth bass fillets during cold storage.Moreover,both films could effectively relieve the decrease of weight,color values(L and a values),hardness and elasticity,and sensory characters of largemouth bass fillets.The largemouth bass fillets wrapped in thses two films deteriorated after 8 days at 4℃ storage.Meanehile,thses two films presented remarkable color changes when largemouth bass fillets spoiled.