| Cherry tomato(Lycopersicum esculentum Mill)rich in lycopene,which is characterized by gorgeous color and high-level nutrition.Like preserved fruits,dried cherry tomatoes have a high sugar content,which is not consistent with consumers' demand.In the meantime,there is a lack of studies about the preservation of semi-dried cherry tomato,as well as microorganism growth in semi-dried cherry tomato during storage.Therefore,this project aimed at investigating and optimizing the osmotic dehydration process of cherry tomato prior to drying.After that,the effects of hot-air drying,microwave drying and vacumm drying on the quality of cherry tomato were studied,respectively.Furthermore,the influence of antioxidant addition(Ascorbic acid and Tea Polyphenols)during osmotic dehydration on the quality of dried cherry tomoato was explored.In addition,the quality stability of dried cherry tomoato at various water activities,as well as those treated by cold plasma sterilization was assesed during storage.All these studies can providance for scaling up the production of semi-dried cherry tomato with low sugar content.The main results are shown as follows:1.Among all the pre-treatments before osmotic dehydration,incluing blanching combined with lineation,acupuncture,lineation and sonication,the combination of blanching and lineation was regarded as the best pre-treatment prior to osmotic dehydration,which can increase the water loss and lower the solid gain during osmotic dehydration.Besides,blenching can protect the color of cherry tomato.According to the results about single-factor study and respnse surface design,the best conditions for osmotic dehydration of cherry tomato were 0.080 MPa for vacumm degree,50 ° Brix for sugar content,53.37? for temperature and 4.88 h for osmotic dehydration duration.Under these conditions,the predcted values of water loss and solid gain after osmotic dehydration were 25.56%and 3.61%.2.The effects of various drying methods,including hot-air drying(50??60?,70?and 80?),microwave drying(200 W?250 W?300 W and 350 W)and vacuum drying(0.06?0.07?0.08 and 0.09 MPa),on the lycopene content,composition and sensory quality of cherry tomato were studied,respectively.The cherry tomatoes treated by vacuum osmotic dehydration were used as experimental materials.Microwave drying spent less time to reduce the water content to 20± 1%compared to hot-air drying and vacuum drying,and the energy consumption during microwave drying was also lower than that during hot-air drying and vacuum drying.However,the contents of soluable sugar and lycopene in dried cherry tomato after microwave drying were lower than that in cherry tomato after hot-air drying and vacuum drying(P<0.05).The contents of soluable sugar and lycopene in samples treated by hot-air drying were similar to that in samples treated by vacuum drying(P>0.05),whereas the drying rate of vacuum drying was lower than that of hot-air drying.In summary,the best methodology for cherry tomato drying was hot-air drying at 60?.Under this condition,the loss of nutrients and energy consumption were relatively low,and the color of dried cherry tomato was satisfactory.3.Both AA(0;0.25,0.5,0.75 and 1.00%)and TP(0,0.25,0.5,0.75 and 1.00%)with different concentrations were added in osmotic solution.After osmotic dehydration and hot-air drying,the quality of semi-dried cherry tomato was assessed.Generally,the addition of AA and TP could alleviate the loss of lycopene and phenolics during drying.Meanwhile,the antioxidant activity of semi-dried cherry tomato enhanced with the increase of antioxidant addition.TP was more efficient than AA to improve the antioxidant activity of cherry tomato after drying(P<0.05).Furthermore,the addition of AA and TP resulted in the decrease of lightness of cherry tomato.The redness of dried cherry tomato after the addition of TP was significantly higher than that of sample with the addition of AA and control sample(P<0.05).When the concentrations of TP added were 0.75%and 1%,the nutrients in cherry tomato were preserved well,while the colour and antioxidant ability of the dried products also reached the highest values.Considering the cost for drying,TP addition at 1%was regarded as the optimal treatment.4.Semi-dried cherry tomatoes with different water activities(0.746,0.812 and 0.868)were first vacuum packaged,and then stored at 4,20 and 35?,respectively.The evolution of semi-dried cherry tomato quality during storage for 60 d was studied.Studied the influence of different water activity(0.746,0.812 and 0.868)of cherry tomato semi-dried products after vacuum packaging in 4?,20 ? and 35? respectively under the conditions of storage 60 d on quality changes.The results showed that the greater water activity,the smaller lycopene content loss and the greater total phenol content loss.Along with the increase of storage time,contents of both lycopene content and total phenol content were decreased gradually.Their decreasing rates increased with temperature.On the whole,the higher the storage temperature,the greater the decrease trend.Furthermore,the value of a*of semi-dried tomato with different water activities all decreased during storage.The sensory score of semi-dried cherry tomato with aw at 0.812 was significantly higher than that of samples aw at 0.868 and 0.746.In addition,the total number of colonies and mold in semi-dried cherry tomato with low water activity increased slowly during storage,indicating that low water activity and low temperature can benefit the preservation of semi-dried cherry tomato.The values of a*of semi-dried cherry tomato with different water activities all decreased during storage.The sensory value of sample with a*at 0.812 was significantly higher than that of samples with with a*at 0.746 and 0.868.In addition,the total number of colonies and mold in semi-dried cherry tomato with low water activity increased slowly during storage,indicating that low water activity and temperature can benefit the preservation of semi-dried tomato.5.Semi-dried cherry tomatoes with aw at 0.868 was first sent to modified atmosphere packaging,and then treated by atmospheric pressure plasma sterilization for 0,30,60,90 and 120 s,respectively.After that,samples were stored at 35? for 60 d.It was found that plasma sterilization resulted in the decrease of lycopene and total phenol contents.The duration of plasma sterilization was negatively correlated with lycopene content,whereas it did not affect total pehnolic content significantly.In the later stage of storage,the contents of lycopene and total phenol in samples treated by plasma sterilization decreased slowly.Furthermore,plasma sterilization duration did not affect the L*of semi-dried cherry tomato during storage.Sensory scores and a*of control sample and sample treated by plasma sterilization for 0s-30 s decreased significantly after 45-60 d storage.In addition,the total number of colonies and mold in semi-dried cherry tomatoes treated by plasma sterilization for longer time increased slowly during storage.In conclusion,semi-dried cherry tomatoes treated by plasma sterilization has a significant effect,but it will cause damage to lycopene. |
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