| Intelligent food freshness indicator films have received increasing attention because consumers are concerned about the quality and safety of food products.Due to unique pH-dependent color changing ability of plant-derived betacyanins,the immobilization of betacyanins in biodegradable film matrix can produce intelligent food freshness indicator films.In this study,five different plant-derived betacyanins and three polysaccharides were selected to prepare pH indicator films.The effects of betacyanins sources and matrix types on the structure,physical properties and function of the films were evaluated.In addition,double-layer film technology was used to improve the stability of the films containing betacyanins.The prepared pH indicator films were tested for their ability in monitoring shrimp freshness.The main results of this study are summarized as follows:(1)pH indicator films were prepared by immobilizing betacyanins from five different plants(red pitaya,prickly pear,red beetroot,globe amaranth and red amaranth)in starch/polyvinyl alcohol based matrix.The structural,physical and functional properties of the films containing betacyanins from different plant sources were compared.Results showed betacyanins from red pitaya.prickly pear and red beetroot were betanin-type betacyanins.Betacyanins from globe amaranth and red amaranth leaf were gomphrenin-type and amaranthin-type betacyanins,respectively.The films containing betacyanins from red pitaya and prickly pear presented more uniform cross-sections and had the highest water vapor barrier and mechanical strength.However,the film containing betacyanins from globe amaranth presented higher UV-Vis barrier property and antioxidant activity.The films containing betacyanins were sensitive to pH 8-12 buffer solutions and volatile ammonia.Among different films.the film containing betacyanins from red pitaya was most suitable for monitoring shrimp freshness.(2)pH indicator films were prepared by immobilizing betacyanins from red pitaya in different polysaccharides(chitosan,?-carrageenan and locust bean gum)and polyvinyl alcohol based matrix.The structural,physical and functional properties of different polysaccharide/polyvinyl alcohol films containing betacyanins from red pitaya were compared.Results showed chitosan/polyvinyl alcohol-betacyanins film,?-carrageenan/polyvinyl alcohol-betacyanins film and locust bean gum/polyvinyl alcohol-betacyanins film had homogeneous,layered and nodular cross-sections,respectively.Chitosan/polyvinyl alcohol matrix established hydrogen bonds and electrostatic interactions with betacyanins and induced the degradation of betacyanins.However,?-carrageenan/polyvinyl alcohol and locust bean gum/polyvinyl alcohol matrices mainly established hydrogen bonds with betacyanins,which were benefit to maintain the stability of betacaynins.The color,light transmittance,water vapor permeability,tensile strength,elongation at break,pH-sensitivity and ammonia-sensitivity of the films were greatly affected by the type of polysaccharide/polyvinyl alcohol matrix.Locust bean gum/polyvinyl alcohol film containing betacyanins showed the highest color stability and effectively indicated the freshness of shrimp.(3)In order to improve the stability of betacyanins,double-layer film was prepared by immobilizing red pitaya betacyanins and titanium dioxide nanoparticles in locust bean gum/polyvinyl alcohol and agar/polyvinyl alcohol film matrices,respectively.Reutls showed the double-layer film had strong UV-Vis light barrier ability and antioxidant activity.When the double-layer film was exposed to alkaline solutions and ammonia atmosphere,it changed from initial red-violet to brown/yellow.The double-layer film showed good color stability during storage at 4? for 48 days.The double-layer film was effective in monitoring shrimp freshness and the color change of the film showed a positive correlation with the total volatile basic nitrogen level of shrimp. |
PDF Full Text Request