A new household ultrasonic cleaning method for pyrethroids in cabbage

Chengwei Yu,Xu Huang,Yawei Fan,Zeyuan Deng

State Key Laboratory of Food Science and Technology,Nanchang University,Nanchang 330047,China

ABSTRACT Pyrethroid is widely used in developing countries and is a potential threat to human health.So putting forward an effective pyrethroid cleaning method is of vital importance.Clearance of fenpropathrin,cypermethrin and deltamethrin in cabbage by using ultrasonic treatment accompanied with different baking soda concentrations were investigated in this study.The results of response surface methodology showed that the maximum clearance rate was 70.61%for fenpropathrin under the optimal power,treated time, treated temperature and baking soda concentration, which were 260.02 W, 10 min, 20.15°C and 0.014 g/mL,respectively.Similarly,the maximum removal efficiency was 73.72%for cypermethrin under 240 W,13.84 min,19.53°C and 0.014 g/mL,and 92.15%for deltamethrin under 238.99 W,12.42 min,25°C and 0.013 g/mL.The clearance rate of pyrethroid by this method was significant higher(P ＜0.05)than traditional cleaning methods(bathing and running water washing).The contents of the compositions such as vitamin C, total soluble sugar, protein and dietary fiber, texture and sensory evaluation of cabbage were not found obvious changes after the ultrasonic treatment combined with baking soda (P ＞0.05).Results showed that ultrasonic treatment combined with baking soda was an effective way to eliminate the fenpropathrin,cypermethrin and deltamethrin in cabbage without influencing cabbage quality.

Keywords:Pyrethroid Cabbage Ultrasonic treatment Baking soda Quality

1.Introduction

Pyrethroids are synthetic analogues of pyrethrins which are natural chemicals extracted from the chrysanthemum flowers [1].Pyrethroids have been extensively used in agriculture,forestry, horticulture, industry, and home applications, and its annual demands were expected to be approximately 3800 tons in 2016, increased by 8.4% than last year in China [2,3].Nowadays, synthetic pyrethroid (PYR) insecticides have increasingly replaced organophosphorus pesticides and organochlorine pesticides because of their relative safety for humans and higher insecticidal potency to pesticides [4].But pyrethroid residues are considered to be one of the most important sources of pollution in agricultural production and may be a potential threat to public health [5,6].Pesticides poisoning is an important cause of morbidity and mortality in developing countries [1].According to Chinese government report, the chemical poisoning took 23.76% of the total food poisoning, and chemical poisoning took 52.78%of the total people died of food poisoning.The acute symptoms of pyrethroid poisoning in humans include nausea,vomiting,respiratory depression, mental change, acute kidney injury, etc.Furthermore, pyrethroids have been frequently detected in vegetables at high concentration in some areas of China and other developing countries [2,7].So putting forward a new effective washing method for pyrethroids in our daily life is of great importance.

Ultrasonic treatment, which is generally considered to be safe,non-toxic, and environmentally friendly, has been widely used in food processing [8], such as thawing, freezing, crystallization,extraction, cleaning, realizing microbial inactivation and elimination, etc [9-14].The cavitation caused by ultrasonic is the main reason for cleaning.Water bubbles caused by cavitation can be bigger and then explode so as to result in the shock waves which impact the food surface and remove the contaminants [13,14].Many studies have reported that ultrasonic treatment can be used for the decontamination process of some fruits and vegetables,including strawberry,lettuce,carrot,spinach leaves,etc[13,15-20].Moreover, ultrasonic treatment has been proved to be a useful approach to remove the organophosphorus pesticide residue in apple juice including malathion,chlorpyrifos,diazinon[21,22].So it is reasonable to speculate that ultrasonic treatment also have the ability of cleaning pyrethroids, and ultrasonic combined with other physical or chemical conditions,such as pH,amplitude,pressure, manothermosonication and etc [23-26], can lead to a better result.Yang [27] found that the baking soda could remove the pesticides in apples effectively because pyrethroids were unstable in alkaline solution [28].So the combination of ultrasonic and baking soda may hold better pyrethroid cleaning effect.In China,there have been many patents of small ultrasonic cleaner for household use, and household ultrasonic cleaners, which usually called“dish-washing machine”or“vegetable washer”by Chinese in daily life,are developing rapidly in families,canteens and restaurants in China.Hence, this new pyrethroid cleaning method would be an easy and common-used method in our daily life if its better effect than traditional cleaning methods was proved.

Therefore, three common used pyrethroids including fenpropathrin, cypermethrin and deltamethrin were selected in this study, and cabbage, one of the most popular vegetables in China,was used as the experiment sample.The pyrethroid clearance rates by ultrasonic treatment were determined and compared with traditional cleaning methods(water bath and running water washing).The aim of our study was to provide an easy household method to eliminate most of the pesticides residues in cabbage and have little influence on the quality of cabbage.

2.Materials and methods

2.1.Reagents and materials

Fenpropathrin (No.GSB 05-2306-2008), cypermethrin (No.GSB 05-2308-2008) and deltamethrin (No.GSB 05-2310-2008)standard solutions (100 μg/mL) were purchased from Agro-Environmental Protection Institute,Ministry of Agriculture,China.Florisil PR (6 mL/1000 mg) was purchased from Shimadzu Corp.Hexane, acetonitrile and acetone were HPLC grade and were obtained from Aladdin.NaCl(AR)was purchased from Sinopharm Chemical Reagent Co., Ltd.SiO2(AR) was provided by Tianjin Hengxing Chemical Reagent Co.,Ltd.Fenpropathrin,cypermethrin and deltamethrin emulsion were obtained from Chemical Market,Nanchang,China.

Fresh cabbage sample was purchased from local Rainbow Department Store,Nanchang,China.

2.2.Response surface design

The response surface design was divided into two parts.For the first part, the cabbage samples were treated by ultrasound in different frequency(28,40,68 kHz),power(180-300 W),temperature(10-35°C)and time(5-25 min),respectively.For the second part,the samples were treated by different baking soda concentration(0.1%-3.0%)and time(5-20 min),respectively.

Response surface methodology(RSM)was adopted to estimate the main effects of ultrasound frequency,power,temperature,time and baking soda concentration on pyrethroids pesticide clearance rates in cabbage.The selected conditions of ultrasound frequency,power, temperature, time and baking soda concentration were attained from single-factor experiment.The RSM was applied to the experimental data by using a commercial statistical package,Design-Expert version 8.01(Statease Inc.,Minneapolis,USA).

2.3.Analysis of pyrethroid contents by gas chromatographic(GC)

The cabbage samples were chopped and then grinded by a ceramic grinder with SiO2to make them fully pulverized.Then 5 g sample which mixed with 10 mL acetonitrile was added into a 50 mL centrifuge tube and treated by a ultrasonic cleaner(KUDOS,Shanghai) at 25°C for 25 min.After that, the mixture was quickly filtrated and the residue was extracted twice with 10 mL acetonitrile.The filtrate was all transferred into stoppered cylinder which contained with 4-5 g NaCl and vortexed for 1 min.The filtrate was allowed to stand still for 30 min to layer completely.

Ten milliliter supernatant was carefully transferred into a 50 mL glass centrifuge tube and evaporated to dryness by nitrogen,then it was re-dissolved by 2 mL hexane.The extract was purified by solid phase extraction(SPE)(Florisil PR,6 mL/1000 mg),which was activated with 5 mL of hexane/acetone(9:1,V/V)and 5 mL hexane previously.The glass centrifuge tube was washed three times with 15 mL hexane/acetone solvent system (9:1, V/V) and then eluted the Florisil PR.The eluent was dried by nitrogen in water bath at 50°C and re-dissolved by 2 mL hexane.After being filtered through 0.22 μm filter,the final solution was analyzed by GC.

The analysis of fenpropathrin, cypermethrin and deltamethrin was performed on the Agilent 6890 series GC equipped with ECD detector.Separation was in a column-HP-5(30 m×0.32 mm×0.25 μm, made in USA).Both carrier gas and makeup gas were nitrogen.One microliter sample solution was injected into the GC.The oven temperature was set at 150°C for 1 min, and heated to 250°C for 5 min at a constant rate of 10°C/min and held for 5 min,then rised up to 270°C for 5 min at a constant rate of 3°C/min.The injection and detector temperature were set at 280 and 300°C,respectively.

2.4.Analysis of vitamin C content in cabbage

Preparation of standard solution of ascorbic acid (0.1 mg/mL):50.0 mg ascorbic acid standard was weighted and mixed with 5%metaphosphoric acid-10% acetic acid to a final volume of 500 mL[29].Standard solutions of ascorbic acid (0.005, 0.01, 0.02, 0.03,0.04 and 0.05 mg/mL)were prepared by proper dilution.

Sample preparation:fresh cabbage was cleaned up by distilled water, and dried with blotting paper.The edible part of cabbage(20 g) was placed into ceramic grinder and mixed with 10 mL 5%metaphosphoric acid-10% acetic acid in order to prevent vitamin C oxidation.The mixture was fully ground and transferred into 250 mL flask.After being centrifuged at 4200 r/min for 5 min,10 mL supernatant liquid was carefully weighed into 10 mL volumetric flask and then was volume to 100 mL with the mixed acid solution above.

The final solution was detected at 243 nm by UV-2450 ultraviolet and visible spectrophotometer(Shimadzu).

2.5.Analysis of total soluble sugar in cabbage

Total soluble sugar in cabbage was analyzed by traditional anthrone spectrophotometric analysis.Standard glucose solution(0.1 mg/mL with three drops of toluene); anthrone reagent: 2 g anthrone was dissolved in 1000 mL of 80% sulfuric acid; standard solutions of glucose(0,0.01,0.02,0.03,0.04 and 0.05 mg/mL)were prepared with 0.1 mg/mL stock solution of glucose by proper dilution in 10 mL colorimetric tubes and placed in ice-water bath for 5 min before adding 4.0 mL anthrone reagent.After that,the tubes were heated by boiling water for 10 min and cooled down with running water for 10 min at room temperature.The sample was analyzed at wave length of 620 nm by 722 G spectrophotometer(Inesa Analylical Instrument Co.,Ltd).

Fig.1.The optimized conditions selection of test speed(mm/s)(a)and compression ratio(%)(b)on the texture analysis of cabbage.

Sample preparation and detection: fresh cabbage was cleaned by distilled water,dried with blotting paper,the edible part of cabbage (1 g) sample was carefully weighed into a ceramic grinder.Distilled water was added to the sample and fully grinded, and the mixture was transferred into a flask and volumed to 30 mL.Whereafter, 20 mL 6 mol/mL hydrochloric acid was added into a conical flask, then the solution was hydrolyzed in boiling water for 30 min.Finally, the solution was neutralized to neutral and diluted to 100 mL with distilled water,then it was centrifuged for 5 min at 4200 r/min, 10 mL supernatant liquid was weighed into a 100 mL volumetric flask and then was volume to 100 mL by distilled water.The final solution was total sugar hydrolysate.The total sugar hydrolysate was measured to detect the reducing sugar content by 722 G spectrophotometer(Inesa Analylical Instrument Co.,Ltd).

2.6.Instrumental texture profile analysis(TPA)of cabbage

The texture profiles of cabbage including hardness, cohesiveness and resilience were measured by texture analyzer(TA/XT plus,Stable Micro Systems,UK)through P/5 cylindrical probe.The cabbage samples were cut into slices (30 mm×30 mm).The effects of different speed(3-7 mm/s)or different compression(30%-80%)on hardness,cohesiveness and resilience of cabbages were investigated at a certain compression ratio or text speed.

The effect of speed on cabbage texture was shown in Fig.1a.Both cohesiveness and resilience values increased with the increase of test speed from 3 mm/s to 5 mm/s.However, there was no significant enhancement with the increase of test speed from 5 mm/s to 7 mm/s.Therefore, 5 mm/s was selected as the optimum test speed.According to Fig.1b,cohesiveness and resilience values were also influenced by compression ratio.The resilience value increased sharply from 0.9 mm to 2.5 mm when compression ratio increasing from 30% to 50%, and then decreased from 50% to 80%.While,the cohesiveness value increased from 30%to 50%,then no apparent changes occurred till 80%.So 50%was selected as the optimum compression ratio.

2.7.Analysis of cabbage composition

Moisture content was determined by keeping cabbage at 105°C until the sample became constant weight.Protein content was analyzed by using Kjeldah method.Ash content was analyzed by using muffle furnace to heat the cabbage at 550°C for 5 h.Dietary fiber content was analyzed by using α-amylase, protease and glucosidase to eliminate protein and starch of cabbage and then the treated sample was kept at 105°C until it became constant weight.

2.8.Sensory evaluation of cabbage

Ultrasonic combined with baking soda treated cabbage and untreated cabbage were cut into the same size pieces and boiled in the boiling water for 2 min.Twenty participants were invited to evaluate the taste of treated and untreated cabbage,including color(good:8 ≤score ≤10,medium:4 ≤score ＜8,bad:0 ≤score ＜4),smell(good:8 ≤score ≤10,medium:4 ≤score ＜8,bad:0 ≤score＜4),moisture(juicy:8 ≤score ≤10,medium:4 ≤score ＜8,dry:0≤score ＜4),hardness(hard:8 ≤score ≤10,medium:4 ≤score ＜8,soft:0 ≤score ＜4),fibrous(very fibrous:8 ≤score ≤10,medium:4 ≤score ＜8,not fibrous:0 ≤score ＜4),viscosity(good:8 ≤score≤10, medium: 4 ≤score ＜8, bad: 0 ≤score ＜4) and sweetness(sweet: 8 ≤score≤10, medium: 4 ≤score ＜8, bitter: 0 ≤score ＜4).The sensory evaluation results were collected and analyzed to evaluate the sensory quality of treated and untreated cabbages.

2.9.Statistical analysis

All experiments were performed in triplicate, and data were expressed as mean value±standard deviation.All statistical analyses were performed by using SPSS 20.0.One-way ANOVA analysis with Duncan test was used to compare the differences between mean values.A level of probability at P ＜0.05 was set as statistically significant.

3.Results and discussion

3.1.Ultrasonic condition selection

The influence of ultrasound treatment on foods’ physical and chemical properties was strongly associated with the amplitude of ultrasonic waves, power, exposure time, food composition and treatment temperature[26,30].Ultrasonic treatment is effective for cleaning chemical contaminations and pathogenic microorganism[14,31-35].

As shown in Fig.2.1a, the ultrasonic frequency varied from 28 kHz to 68 kHz significantly affected the clearance rates of fenpropathrin, cypermethrin and deltamethrin residues in cabbage.For these three pyrethroids, the highest clearance rate was found at 28 kHz,while the lowest was observed at 40 kHz.Lower frequencies produced larger bubbles, and higher energy liberation than those higher frequencies [30], which might be a good explanation to our experiment result.The implosion of cavitating bubbles caused shock waves, water jets, and microstreaming.High-speed water jets were formed when a bubble implodcts near a solid surface, impinging on the surface of the solid and helping to remove contaminants [13,14].It was also reported that low frequencies between 20 kHz and 45 kHz had a better decontamination effect on lettuce,spinach,shredded carrot,truffles,cherry tomatoes,and strawberries[13].The optimum of ultrasonic frequency was 28 kHz.

Fig.2.The ultrasonic condition selection on the clearance rates of fenpropathrin, cypermethrin and deltamethrin in cabbage.a, b and c showed the statistical difference(P ＜0.05).

According to Fig.2.1b, when the ultrasonic power increased from 180 W to 300 W,the trend of three pyrethroids clearance rates was firstly increased and then decreased.In general,power represents the strength of a treatment.Theoretically, higher ultrasonic wave powers produce higher pressure to the samples and more contaminations can be removed, but when the ultrasonic power was too high, the bubbles caused by cavitation might be hard to generate, which resulted in the decreases of pyrethroid clearance rate[36].The best ultrasonic power in this research was 240 W.

The effect of ultrasonic time was shown in Fig.2.1c.As the time increased to 10 min,the clearance rates of three pyrethroids in cabbage increased to their maximum, however, the clearance rates reduced sharply from 10 min to 20 min, additionally, the clearance rates increased slightly from 20 min to 25 min.This might be attributed to the dynamic balance in this reaction system.When the ultrasonic treatment began,the pyrethriod content in cabbage was high and no pyrethroid was in the water, so the pyrethroids were transferred to water by the ultrasonic cavitation and resulted in the increase of clearance rate.But when the pyrethroid content in the water was over a certain limitation, it might return to the cabbage again because of the constant movement caused by ultrasonic treatment,which led to the decrease of clearance rate.Hence,it might be a wise choice if the washing water was kept refreshing for several times during ultrasonic washing.The highest clearance rates of fenpropathrin,cypermethrin and deltamethrin in cabbage were 52.16%,57.74%and 56.35%,respectively.The results showed that 10 min’ultrasound treatment is the best choice.

The clearance rates of three pyrethroids in cabbage were also influenced by temperature, higher temperature could promte the generation of bubbles and enhance the cavitation [30,36,37].The results were shown in Fig.2.1d.The highest clearance rates of three pyrethroids in cabbage were all found at 20°C.From 10°C to 20°C,the clearance rates increased greatly,however,the clearance rates decreased a lot from 20°C to 35°C.Higher temperature benefited the formation of cavitation under certain conditions,which led to more heat-generating bubble movements and collapses [37].But higher temperature might result in the escape of weensy bubbles from the reaction system.It was known that the intensity of ultrasonic cavitation depended on the amount of the weensy bubbles,microstreaming,and water jets in liquid[14].So the ultrasonic degradation effect might decrease more or less because of higher temperature [38].Furthermore, temperature increase was not appropriate for the minimally processing of fruits and vegetables.Higher temperature would cause structural and physiological alterations of vegetable tissue, and increase the loss of texture,nutrition and other factors related to quality [30].Therefore, it is very important to control the temperature.The best temperature choice was 20°C in this research.

In conclusion, the optimized ultrasonic condition was 28 kHz,240 W,10 min,20°C.

3.2.Baking soda concentration and soak time selection

It was indicated that the sodium hypochlorite and ultrasound treatment had a synergistic effect on vegetables decontamination[33].Because pyrethroids are unstable in alkaline solution[28],so we suspected that there was a synergistic effect of baking soda and ultrasonic treatment.Therefore,in this study,ultrasonic treatment combined with baking soda was carried out to improve the removal efficiency of fenpropathrin,cypermethrin and deltamethrin in cabbage.As shown in Fig.3a, the clearance rates increased obviously and attained its maximum when the concentration increased to 1.0%.However,there was a sharp decrease from 1.0%-2.0%,and no apparent changes were found between 2.0% and 3.0%.Thus, 1.0%was selected as the optimum concentration of baking soda.

The selection of soak time was shown in Fig.3b.The clearance rates increased gradually from 5 min to 15 min and got its maximum at 15 min.However, the clearance rates were sharply decreased from 15 min to 20 min.Thus,15 min was selected as the optimum of soak time.

Due to the instability of pyrethroids in alkaline solution[39,40],baking soda was beneficial to pesticide cleaning.Higher baking soda concentration and more soak time could lead to higher pesticide clearance rates within a certain range.However, when the concentration of baking soda was more than 1.0%, it would influence the surface tension of solution a lot and made the bubbles harder to generate so as to decrease the cavitation effect and the clearance rate.Along with time increasing,the clearance rate would decrease because of the dynamic balance mentioned in previous section.So 1.0%and 15 min were selected for further research.

Fig.3.The baking soda condition selection on the clearance rates of fenpropathrin,cypermethrin and deltamethrin in cabbage.

3.3.Response surface optimization design

Four main factors such as ultrasonic power, time,temperature and baking soda concentration were selected in RSM study according to the optimized results of single factors(240 W,10 min,20°C and 1.0%,respectively).The results were shown in Fig.4.The optimal conditions for the fenpropathrin clearance in cabbage were 260.02 W, 10 min, 20.15°C and 0.014 g/mL, the clearance rate of fenpropathrin reached 70.61%.Those for cypermethrin were 240 W,13.84 min,19.53°C and 0.014 g/mL,the clearance rate was 73.72%.Additionally, those for deltamethrin were 238.99 W, 12.42 min,25°C and 0.013 g/mL, and the deltamethrin clearance rate was 92.15%.

3.4.Comparison the combination of ultrasound and baking soda with traditional pesticide cleaning method

Water bath(20°C)and running water washing(20°C)were supposed to be traditional pesticide cleaning methods in this research.

The effect of running water washing on clearance rate was shown in Fig.5a.The pesticide clearances increased from 10 s to 20 s, then decreased to bottom till 40 s and increased from 40 s to 50 s.The effect of water bath time on clearance rate was shown in Fig.5b.The pesticide clearance rates increased from 5 min to 20 min and got their maximum at 20 min,then decreased from 20 min to 25 min.No obvious differences were found from 25 min to 30 min.

Table 1 The texture analyses of cabbage before and after ultrasonic treatment.

According to section 3.3,the optimal ultrasonic treatment clearance rates of fenpropathrin,cypermethrin and deltamethrin were 70.61%, 73.72% and 92.15%, respectively.By comparing to traditional pesticide cleaning methods (18.56%, 19.23% and 34.92%), it could be easily found that the clearance of ultrasonic treatment was apparently higher than traditional cleaning methods(P ＜0.05),which proved that ultrasonic treatment combined with baking soda was a better way to remove the pesticide in cabbage than traditional cleaning methods.According to the Chinese Standard(GB 2763-2016), the upper limits of fenpropathrin, deltamethrin and cypermethrin are 1.0, 0.5 and 2.0 mg/kg, respectively.Cabbage bought from local market was found to contain 0.7 mg/kg for fenpropathrin, 0.3 mg/kg for deltamethrin and 0.3 mg/kg for cypermethrin.According to the above clearance rates by ultrasonic treatment, the pyrethroids in treated cabbage were far below the upper limits of Chinese Standard(GB 2763-2016).

The traditional pesticide cleaning methods, such as washing vegetable with running water and soaking in cleaning water or baking soda solution, could only remove the pesticide contamination on the surface of fruits and vegetables.But in contrast,ultrasonic cleaning could reach the areas that were not easily accessible by using conventional cleaning methods and clean it effectively[41,42].The implosion of cavitating bubbles caused the shock waves,water jets,and microstreaming,andhigh-speedwater jets impinged to the surface of the samples and removed contaminants [13,14].The bubbles cracks could send the baking soda to the surface which is hard to access by traditional washing methods and further improve the clearance rate of pyrethroids.Furthermore,pyrethroids were relative unstable in the baking soda solution,so the combination of ultrasonic treatment and baking soda could lead to a better effect.

3.5.Instrumental texture profile analysis(TPA)

Texture is a physical characteristic that describes the flow behavior or responses to deformation of a liquid or solid food product.As a key property of food quality,texture including hardness,cohesiveness and resilience mainly depend on the microstructure of the product[43].The comparison of hardness,cohesiveness and resilience values between ultrasonic treated and non-treated samples was shown in Table 1.No apparent changes were observed between treated and non-treated cabbages among hardness,cohesiveness and resilience values (P ＞ 0.05), which proved that ultrasonic treatment had no significant influence on the cabbage texture.

3.6.Cabbage quality analysis

Vitamin C,which can be oxidized easily in the air,is one of the most important vitamins in vegetables.The content of vitamin C can be used as a reference to evaluate the quality of cabbage.As shown in Fig.6A, standard solutions of ascorbic acid (0.005, 0.01,0.02, 0.03, 0.04 and 0.05 mg/mL) were scanned from 230 nm to 280 nm, and the maximum absorbance wave-length was 243 nm.The average absorbance values of vitamin C before and after ultrasonic treatments were shown in Fig.6B.The average amounts of treated sample and untreated sample were 2.77 and 2.84 mg/g respectively, which showed no significant difference (P ＞0.05).So the ultrasound combined with baking soda had no obvious influence on the vitamin C content(Fig.6).

Fig.4.Three-dimensional response surface plot of three pyrethroids clearance rates.The interations of temperature, baking soda concentration and ultrasonic power for fenpropathrin (A), the interaction of temperature, ultrasonic time and power for cypermethrin (B), the interaction of time, power and baking soda concentration for deltamethrin(C).

Fig.5.The traditional washing methods condition selection on the clearance rates of fenpropathrin,cypermethrin and deltamethrin in cabbage.a and b represented water bath and running water treatment,respectively.

Fig.6.The vitamin C analysis of cabbage, A: the standard solutions of vitamin C analyzed at 243 nm by ultraviolet and visible spectrophotometer (a→f: 0.00, 0.01,0.02, 0.03, 0.04 and 0.05 mg/mL); B: The average absorbance value of vitamin C before and after ultrasonic treatments.

Table 2 The composition analyses of cabbage before and after ultrasonic treatment.

The total soluble sugar content in untreated sample was 0.073 mg/mL, compared with 0.070 mg/mL in the treated sample,which showed no significant difference (P ＞0.05).So ultrasonic treatment had no obvious influence on the total soluble sugar content of cabbage.

The composition analyses of treated and untreated cabbage were shown in Table 2.Easily found that the contents of protein,moisture, dietary fiber and ash were not significantly influenced(P ＜0.05)by ultrasonic treatment combined with baking soda.The moisture contents of treated and untreated cabbage were 89.55%and 90.16%,only held about 0.6%difference because of soaking in baking soda solution, which was extremely difficult for people to perceive.

The sensory evaluation results were shown in Table 3.The average scores for untreated cabbage were 8.62 for taste,8.15 for smell,8.60 for moisture, 1.00 for hardness, 1.20 for fibrous, 1.00 for viscosity and 7.82 for sweetness,respectively.As for treated samples,the average scores were 8.72 for taste,8.20 for smell,8.55 for moisture,1.00 for hardness,1.15 for fibrous,1.00 for viscosity and 7.88 for sweetness, respectively.No significant difference was found between treated and untreated samples (P ＞0.05), which proved the taste of cabbage was not influenced by ultrasonic treatment combined with baking soda.

In summary, ultrasonic treatment combined with baking soda was an effective way to eliminate the pyrethroids in cabbage without influencing cabbage quality or taste,and household ultrasonic cleaners are developing rapidly in families, canteens and restaurants in China.This cleaning method is very convenient for household-use and has a good application foreground.In addition, many studies have reported that ultrasonic can be used for microbial reductions in the wash-water decontamination process of some fruits and vegetables, including strawberry, lettuce,carrot,spinach leaves,etc[13,15-20].So ultrasonic treatment combined with baking soda might be an effective pyrethroids cleaning method not only for cabbage but also for other vegetables and fruits.Further researches about different vegetables and fruits need be carried out in order to verify this conjecture.

4.Conclusion

The present study demonstrated that the combination of ultrasound treatment and baking soda is an effective and promising method for the removal of fenpropathrin, cypermethrin and deltamethrin in cabbage.The clearance rates of this new method were obvious higher than our traditional daily cleaning methods.The optimum clearance rates for fenpropathrin,cypermethrin and deltamethrin were 70.61%, 73.72% and 92.15% through response surface methodology.Furthermore, the quality of treated and untreated cabbage such as vitamin C, total soluble sugar, texture analysis, composition and sensory evaluation showed no obvious changes.So ultrasonic combined with baking soda is an effective method for household use without influencing cabbage quality.The further study needs to investigate the degradation pathway of fenpropathrin, cypermethrin and deltamethrin in order to further understand their removal mechanism.Further researches about different vegetables and fruits by ultrasonic cleaning are also needed.

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Declaration of Competing Interest

The authors declare that there is no conflict of interest.

Acknowledgement

The authors are grateful to the financial and technology support of State Key Lab of Food Science and Technology of Nanchang University(SKLF-ZZA-201910).