The Softening Effect Of Natural Deep Eutectic Solvent On Betel Nut(Areca Catechu) And The Development Of Its Softening Technology

In recent years,with the development of the betel nut industry,the number of people chewing betel nut is gradually expanding,and the incidence of oral diseases related to betel nut chewing is increasing day by day.Studies have found that the high incidence of oral diseases is directly related to the hardness of betel nut.Long-term chewing of betel nut with high hardness is easy to cause premature tooth loss,oral mucosa damage,and even lead to oral cancer.However,the existing betel nut softening methods have some problems such as high energy consumption,serious chemical pollution,and poor softening effect.Therefore,betel nut processing enterprises urgently seek new betel nut softening technology.Research has shown that a deep eutectic solvent（DES）,especially the primary metabolites derived from plants of natural deep eutectic solvents（NDES）can effectively remove the lignin as well as the cellulose and hemicellulose in the plant biomass.This makes the gap in the plant cells bigger and presents a highly porous network structure which ultimately reduces the hardness of the plant.This finding provides a theoretical basis for us to study NDES treatment as a new green softening method of betel nut.In this paper,the natural primary metabolites of plants that are safe and harmless to the human body were selected and combined into a new NDES to explore the influence of NDES on the textural characteristics of betel nut and develop the procedures for betel nut softening with NDES.Scanning electron microscopy（SEM）and Fourier transform infrared spectroscopy（FTIR）were used to analyze the structure of the softened betel nut.The changes of betel nut flavor before and after NDES treatment were studied by an electronic nose,electronic tongue,and gas chromatography-mass spectrometry.In order to provide a theoretical basis for the application of NDES in the actual production of betel nut softening process.The main research contents and conclusions are as follows:1.Screening of NDES and its effect on the texture characteristics of betel nut.The effects of different temperatures on water absorption rate and saturated water absorption of betel nut were studied.The results showed that a moderate temperature increase could accelerate the water absorption rate of betel nut and shorten the time to reach the saturated water absorption rate.The optimal rehydration time of the betel nut was 10 h at60℃.By screening the natural plant metabolites,the results showed that NDES composed of lactic acid as the hydrogen bond donor had a better softening effect than glycerol.The NDES composed of choline chloride or betaine as hydrogen bond receptors had no significant influence on the softening effect.Therefore,betaine and lactic acid were selected as the NDES for this experiment.The effect of NDES on the texture characteristics of the betel nut was investigated by a single factor experiment.The results showed that the significant parameters of NDES softening betel nut were:betaine:lactic acid:water=1:（5～10）:（5～10）,time 80～100 min,temperature 80～100℃,the ratio of 1:5:5.The hardness reduction rate of betel nut treated at 5,90℃for 80 min was 27.1%.At the same time,it was found that high lactic acid content would lead to carbonization of betel nut and increase the hardness value.When the treatment time was 100 min,the masticability of betel nut decreased by 23%,which had a great effect on the taste.The effects of time and temperature on the loss rate of arecoline were measured.It was found that the loss rate of arecoline reached 51.97%when treated at 100℃for 80 min.In summary,betaine and lactic acid composed of NDES is a natural betel nut softener.2.Study on the optimization of NDES betel nut softening conditions and its structure.The effect of NDES on betel nut color was determined by the color difference experiment,which provided the reference for sensory evaluation.The sensory evaluation score was used as the response value to design a response surface test to determine the optimal treatment parameters,and the structural changes before and after NDES treatment were analyzed.The results showed that L*and b*of the outer epidermis and inner epidermis decreased and a*increased with the increase of lactic acid addition amount,treatment time,and treatment temperature,indicating that NDES treatment could reduce the color brightness of the inner and outer epidermis of betel nut,in which the outer epidermis became black and the inner epidermis became red.A response surface experiment was designed using the ratio of lactic acid content,time and temperature as three factors,and sensory evaluation score as the response value.The optimal process parameters were obtained as follows:ratio of lactic acid content 0.50（1:5:5）,treatment time 90 min,and treatment temperature 90℃.It provides theoretical parameters for actual processing and production.By SEM observation of the microstructure of the betel nut,it was found that NDES treatment could effectively remove lignin in the structure of the betel nut,and slightly damage the structure of cellulose and hemicellulose.FTIR results indicated that NDES treatment would damage the key position of the betel nut,and the change of characteristic peaks of ester bond and ether bond at the wavenumber of 1735 cm^-1 and 1230 cm^-1 respectively proved that NDES could remove lignin.The results showed that the NDES softening process was consistent with the existing betel nut softening process.3.Optimization and structural analysis of betel nut softened by NDES.The changes of betel nut flavor before and after NDES treatment were studied by an electronic nose,electronic tongue,and GC-MS.The electronic nose test results showed that the response values of W1C and W5C and W1S were relatively increased after NDES treatment,while the response values of W5C and W1S were relatively decreased,indicating that the aromatic substances increased and alkanes decreased after NDES treatment.Through the electronic tongue,it was found that the taste changed obviously after NDES treatment,and the response value of sour taste increased greatly.The volatile flavor compounds of betel nut（DS）and common betel nut（DB）treated by NDES were identified by GC-MS.36 and40 kinds of volatile compounds were detected from DB and DS,respectively.The analysis results showed that the main volatile compounds of betel nut treated by NDES changed from aldehydes,hydrocarbons,and esters to acids,aldehydes,and hydrocarbons.The addition of lactic acid affects flavor.After NDES treatment,the relative content of furfural increased from 0.51%of DB to 6%of DS,which proved that NDES had a degradation effect on lignin in betel nut.The results of the principal component analysis showed that PC1 and PC2accounted for 98.2%and 1.2%of the original variables,respectively,and together accounted for 99.4%of the original variables,indicating that NDES treatment had a significant effect on the relative content of volatile substances in betel nut.