Antioxidant and antimicrobial packaging films developed based on the peel powder of different citrus fruits:A comparative study

Citrus is the largest fruit crop planted worldwide.However,the global citrus fruit processing byproducts have not been fully utilized up to now.Citrus peels contain valuable biopolymers and bioactive substances,which are suitable to develop food packaging films.In this study,active packaging films were prepared by directly utilizing citrus peels in their powder form.The films produced from the peel powder of four different citrus fruits(orange,lemon,pomelo and mandarin)were compared for their structural and functional properties.Results showed the four kinds of citrus peel powder contained 16.36%-23.80%pectin,5.68%-8.23%protein,3.17%-7.65%lipid,2.88%-6.27%crude fiber and 11.45-15.47 mg GAE/g polyphenols.Four kinds of citrus peel powder based films exhibited rough surface and transverse with yellow or flesh color.These films had 0.124-0.157 mm of thickness,18.16%-25.25%of moisture content,51.98-121.64°of water contact angel,1.34-1.92×10^(-1)0 g m^(-1)s^(-1)Pa^(-1)of water vapor permeability,0.36-0.69 cm^(3)mm m^(-2)day^(-1)atm^(-1)of oxygen permeability,8.26-9.14 MPa of tensile strength and 8.05%-17.18%of elongation at break.These films also showed strong antioxidant and antimicrobial activity,which retarded corn oil oxidation.Among the films,mandarin peel powder based film was most effective in retarding oil oxidation due to the excellent light and oxygen barrier capacity and antioxidant activity of the film.Results suggested mandarin peel powder based film was suitable for the active packaging of corn oil.

Modulating the functionality of black wolfberry anthocyanins-based freshness indicators by adjusting the pH value of film-forming solution

In this study,freshness indicators were prepared through solvent casting method by anchoring black wolfberry anthocyanins into cassava starch/polyvinyl alcohol matrix and adjusting the pH value of film-forming solution.The aim of this study was to explore the impact of the pH value(3.0,4.0,5.0,6.0 and 7.0)of film-forming solution on the functionality of anthocyanins-based freshness indicators.The indicators were characterized by scanning electron microscopy,Fourier transform infrared spectroscopy,micrometer,UV-vis spectrophotometer,water vapor permeability tester,water contact analyzer,gas permeability tester,texture analyzer,thermogra-vimetric analyzer,differential scanning calorimeter and colorimeter.Meanwhile,the pH-responsive and ammonia-responsive properties of the indicators were determined.The indicators were finally used to indicate the freshness of shrimps.Results showed pH adjustment greatly changed the cross-sectional morphology and intermolecular hydrogen bonding strength of the indicators.The indicator prepared at pH 3.0 had the highest visible light/oxygen barrier ability and antioxidant activity,while the indicator prepared at pH 4.0 exhibited the highest water vapor barrier ability.The indicators prepared at pH 3.0,4.0 and 5.0 showed remarkable color changes when exposed to buffer solutions and ammonia gas.The indicator prepared at pH 3.0 could effectively indicate the freshness of chilled shrimp through color changes.This study reveals that the functionality of anthocyanins-based freshness indicators can be modulated by adjusting the pH value of film-forming solution.

Preparation of cost-effective and hydrophobic freshness indicating labels based on passion fruit peel powder and stearic acid

Freshness indicating labels embedded with pH-sensitive anthocyanins are one type of smart packaging tech-nology.However,the application of freshness indicating labels is mainly restricted by the high cost and hy-drophilicity of the labels.In order to reduce the manufacturing cost,passion fruit(Passiflora edulis)peel powder rich in dietary fibers and anthocyanins was used to prepare freshness indicating labels in this study.Moreover,the prepared labels were further soaked in 0.01,0.05 and 0.1 mol/L of stearic acid ethanol solution to increase the hydrophobicity of the labels.Structural characterization results showed the surface of the labels was covered by self-assembled stearic acid crystals.Stearic acid treatment significantly decreased the moisture content(16.90%→10.92%),hydrophilicity(water contact angle of 40.36°→103.01°),water vapor permeability(18.68×10^(-11) g m^(-1) s^(-1) Pa^(-1)→8.10×10^(-11) g m^(-1) s^(-1) Pa^(-1))and water uptake ability of the labels,which effectively prevented the leak of anthocyanins from the labels.In addition,stearic acid treatment greatly elevated the inner compactness of the films,resulting in improved tensile strength(3.12 MPa→6.18 MPa)and thermal stability.Moreover,stearic acid treatment well maintained the pH-dependent color changeable ability of the labels.The labels changed from reddish brown to olive and brown in the application of shrimp freshness indicating.When the labels were buried in natural soil at 20℃ for 10 days,82.74%-98.83%of the labels could be degraded.Therefore,this study provides a new and facile way to prepare freshness indicating labels.