Preparation Of Peroxide-Responsive Bamboo Nanocellulose Hydrogels And Its Application In Vegetable Oil Detection

Edible vegetable oils are an important part of our daily diet,providing the energy and essential fatty acids needed for normal human development.However,oxidation of lipids can reduce the content of nutrients,produce bad flavor and even threaten human health.Traditional methods for evaluating the freshness of lipids have the disadvantages of long testing time,tedious operation,high cost and the need for professional technicians,while the colorimetric method can present the freshness of food to consumers with visual color changes,with the advantages of simple operation,fast and low cost.At present,the colorimetric method is mainly used to evaluate of perishable foods such as meat and seafood,and less research has been reported on the colorimetric testing of edible oil.Bamboo has a high growth rate and many processing by-products,and the redevelopment of waste has certain environmental and economic significance.In this study,a peroxide-responsive hydrogel based on bamboo nanocellulose（CNF）was developed with bamboo flakes as raw material,and eight commonly used edible vegetable oils,including camellia oil,canola oil,peanut oil,olive oil,corn oil,linseed oil,soybean oil and palm oil,were used as the research objects for rapid detection of edible oil freshness by colorimetric method.The main research contents are as follows:（1）Preparation and characterization of CNFs:Bamboo flakes was used as raw material,and lignin and hemicellulose components were removed by alkali and bleaching treatment to obtain cellulose.Further,the CNFs were prepared using 2,2,6,6-tetramethylpiperidine-nitrogen-oxy radical（TEMPO）oxidation method,and the structure,microscopic morphology,oxidation degree and gelation phenomena of the prepared CNFs were investigated.The results showed that the CNFs exhibited a cellulose type I structure with an average width of 7.48 nm and an average length of 436.17 nm,and the TEMPO oxidation resulted in a negatively charged nanocellulose surface with an oxidation degree of 12.96%and a surface charge density of0.8×10^^-3 mmol/kg.The high aspect ratio and strong intermolecular hydrogen bonding of the nanocellulose caused the CNFs to intertwine and gel.The gel viscosity was influenced by the concentration and cation valence state.（2）Preparation of peroxide-responsive hydrogels:nanocellulose and acrylamide were used to construct double-network hydrogels,the hydrogels were used as peroxide-responsive hydrogels substrates,and ferrous sulfate,sulfosalicylic acid and ascorbic acid were used as peroxide-sensitive indicators.The ratios of initiator,crosslink accelerator,functional monomer and peroxide-sensitive indicator were optimized for the double-network hydrogels,respectively.The optimal conditions were:the molar ratio of ascorbic acid to ferrous ions was 1:15;the molar ratio of sulfosalicylic acid to ferrous ions was 1:2;the addition of crosslinking accelerator TEMED was 0.7μL/m L;the addition of initiator KPS was 0.5 mg/m L;and the addition of functional monomer AM was 1.0 mg/m L.The responsiveness of the peroxide-responsive hydrogels prepared under the optimal conditions to hydrogen peroxide was investigated.The responsiveness of the peroxide-responsive hydrogels to hydrogen peroxide was evaluated by UV and digital image analysis.The results showed that the absorbance change value（ΔA）was segmentally linearly correlated with the hydrogen peroxide concentration:R² was 0.9769 for0-0.5 mmol/kg,and 0.5-11 mmol/kg.The value of color change（ΔR）was exponentially related to the peroxide concentration:R² was 0.9445 for 0-11 mmol/kg.（3）Peroxide-responsive hydrogel for the freshness of vegetable oils:The freshness of polyunsaturated vegetable oils（camellia oil,canola oil,peanut oil,olive oil）,monounsaturated vegetable oils（corn oil,linseed oil,soybean oil）and saturated vegetable oils（palm oil）were evaluated by colorimetric determination using peroxide-responsive hydrogels,respectively.The results showed that peroxide-responsive hydrogel could be used to identify the degree of vegetable oil rancidity and determine the edibility of vegetable oil according to the national standard limit value of 9.82 mmol/kg.In the UV analysis method,ΔA satisfied the linear function model with the peroxide values of all oil samples,and the correlation coefficient was greater than 0.95;in the digital image method,ΔR satisfied the exponential function model with the peroxide values of monounsaturated and polyunsaturated vegetable oils,and the correlation coefficient was greater than 0.92,whileΔR satisfied the linear function model with the peroxide values of saturated vegetable oils,and the correlation coefficient was greater than 0.90;based on the results of the image method,a colorimetric card for peroxide values applicable to monounsaturated and polyunsaturated vegetable oils was established,and its accuracy was verified by using blended oil,rice oil and sunflower oil,etc.The results showed that the correct discrimination rate of the method was 91.67%.A joint smartphone detection device was designed to achieve simultaneous detection of multiple apertures with faster response and the advantage of simple operation,and its potential in practical applications was verified by colorimetric analysis.