Eco-Friendly pH Indicator Based on Natural Anthocyanins from Lycium ruthenicum

An eco-friendly and visual pH indicator was developed based on cotton fabrics dyed with natural Lycium ruthenicum extract(LRE),whose color changed from red to purple,blue and green at pH of 2-10.Three methods for dyeing cotton fabrics with LRE were attempted,namely pre-mordanting,simultaneous mordanting,and post-mordanting methods with different dyeing temperatures,dyeing times and dyebath pH values.The cotton fabrics exhibited the highest K/S value when they were dyed under a dyebath of pH 6 at 20℃for 90 min in the case of the simultaneous mordanting method.Meanwhile,the dyed cotton fabrics also showed reversible pH-dependent color changes.The developed flexible pH indicator based on renewable natural materials is suitable for multiple applications in environmental monitoring and smart textiles.

Rapid Estimation of Enantioselectivity in Lipase-catalyzed Resolution of Glycidyl Butyrate Using pH Indicator

A simple method for rapid estimation of the enantioselectivity of lipase in resolution of chiral esters is described. The enantioselectivity of lipase can be estimated rapidly through comparing the difference of hydrolysis rates for the racemic ester and its slow reacting enantiomer under the same condition because the difference mainly depends on the enantioselective ratio（E values）. The higher the enantioselectivity of enzyme, the larger the difference of hydrolysis rate. The bromothymol blue（BTB） can be used as pH indicator for microplate reader to monitor the formation of acid in lipase-catalyzed hydrolysis of esters. This method has been successfully used to rapidly estimate the enantioselectivity of several lipases in the resolution of glycidyl butyrate.

A Visual pH Indicator through Purple Cabbage Dye for Freshness Test of Venison

A visual pH indicator through purple cabbage dye is selected to test the freshness of venison.Chitosan and cassava starch of an equal weight were used to prepare the film-forming matrix of the indicator.The crystallization of natural purple cabbage dyes with a weight ratio of 5%,10%,20%and 40%were added to the matrix,respectively.The pH color test showed that the natural purple cabbage lyophilized powder with a weight ratio of 40%was the best for the pH indicator,which was used to test the freshness of venison stored at 4℃.The total bacterial count,volatile basic nitrogen(TVB-N)and thiobarbituric acid(TBA)of venison were tested through an experiment.When stored at under 4℃,a significant color change of the indicator from pink to blue-green was shown when the total amount of volatile basic nitrogen(TVB-N)(22.78 mg/100 g)exceeded the critical value(20 mg/100 g).The test result showed that the indicator was very sensitive to pH value and it would help customers identify the freshness of venison.

A biopolymer-based pH indicator film for visually monitoring beef and fish spoilage

Food safety is a worldwide public concern that has recently gained increased attention due to the emerging outbreaks of foodborne diseases.Therefore,there is a pressing need to make simple,cost-effective,and environmentally friendly methods for detecting food spoilage and to mitigate the impact of possible outbreaks.The aim of this study is to develop a biodegradable indicator film which was made by combining cellulose-nanofiber/chitosan dyed with methyl red synthesis(CCM)as a pH indicator film and followed by a single layer coating of polylactic acid(PLA)on its surface,named PLA/CCM film.The microstructural properties of PLA/CCM films were studied using scanning electron microscopy(SEM)and results showed that PLA effectively adhered to the surface of CCM film.The microbial response to PLA/CCM film was determined via a bacterial plating method.It was found that the contact of film with the microbes caused a substantial color change in the film.The coating of PLA upon the CCM film decreased the percentage of the water vapor transmission rate(WVTR).The color of the film vividly altered from slightly red to yellow in response to a pH change in the range of 4-8.The PLA/CCM film was applied to monitor the spoilage of beef and fish at room temperature(23℃)and revealed the onset of food spoilage by displaying the color change from red to yellow after 1 day.The total viable counts(TVC)of microorganisms and pH of the tested beef sample were determined,and the results revealed that both TVC and pH increased concurrently after beef spoilage.

Smart Colorimetric Corn Starch Films Combined with Anthocyanin-Loaded Glutenin-Carboxymethyl Chitosan Nanocomplexes for Freshness Monitoring of Chilled Pork

In this study,intelligent,pH-responsive colorimetric films were prepared by encapsulating anthocyanins in nanocomplexes prepared from glutenin and carboxymethyl chitosan.These nanocomplexes were added to a corn starch matrix and used in the freshness monitoring of chilled pork.The effects of anthocyanin-loaded nanocomplexes on the physical,structural,and functional characteristics of the films were investigated.The addition of anthocyanin-loaded nanocomplexes increased the tensile strength,elongation at break,hydrophobicity,and light transmittance of the films while decreasing their water vapor permeability.This is because new hydrogen bonds are formed between the film components,resulting in a more homogeneous and dense structure.The colorimetric film has a significant color response to pH changes.These films were used in experiments on the freshness of chilled pork,in which the pH changes with changing freshness states.The results show that the colorimetric film can monitor changes in the freshness of chilled pork in real time,where orange,pink,and green represent the fresh,secondary fresh,and putrefied states of pork,respectively.Therefore,the intelligent colorimetric film developed in this study has good application potential in the food industry.

Enhancement of Toxic Gas Detecting Ability of Film Type Colorimetric Sensor

In this study, we tried to develop the in situ coating methods of hydrophilic polymer solution containing water soluble dye on nonwoven sheet for the colorimetric film sensor. And color change of coated dye according to contact various gas samples (as strong acid and base, chloroform, ammonia and HF) of this dye-coated nonwoven film was examined for the application of chemically toxic materials detecting tools in the actual site of working place without aid of any kinds of detecting devices. By the addition of electron transfer agent (quinone derivatives), quick color change behaviors were observed within 10 seconds under the contact of various toxic gases in general condition(room temperature, 50% humidity).