Study On The Peeling Technology Of Three Canned Fruits

Peeling is one of the pretreatment process of canned fruits and vegetables,which is crucial for maximizing the efficiency of the processing equipment and facilitating uniform thermal processing of the product.Manually peeling,steam/hot water peeing,mechanical peeling,lye peeling and enzymatic peeling are the most commercialized peeling methods in vegetables and fruist industry.However,they all have some limitations.In this study,peaches,cherry tomatoes and citrus were used as raw materials to determine the peeling performance,product quality and microstructure of different peeling methods.The main research results were presented as follows:1.The effects of peeling temperature,alkali concentration,peeling time and ultrasound intensity on peeling performance were investigated to optimize the lye peeling condition and the lye combined with power ultrasound peeling condition.Peaches treated by 2%sodium hydroxide concentration for 120 s at 90 ? demonstrated low peeling loss(9.05%),bright color(L*=87.29,a*=-2.07,b*-=34.98),suitable hardness(11.96 N)and high nutrient preservation rate(SS=7.1%;TA=0.46%).Peaches treated by 2%sodium hydroxide concentration combined with power ultrasound treatment at 40 kHz and 270 W/L for 90 s at 90 ? demonstrated low peeling loss(9.36%),bright color(L*=87.50,a*=-1.87,b*=34.82),suitable hardness(10.78 N)and high nutrient preservation rate((SS=7.2%;TA=0.46%).After power ultrasound assisted peeling,the thickness of the cell wall became inhomogeneous,the cell membrane separated from the cell wall and the cell membrane ruptured.And the mitochondria and other structures were unidentifiable.Compared to the lye peeling in industry,lye combined with power ultrasound peeling reduced the alkali concentration,and shorten the peeling time,which indicated power ultrasound is a potential environmental-friendly peeling method.2.The effects of peeling temperature,alkali concentration,peeling time and ultrasound intensity on peeling performance were investigated to optimize the lye peeling condition and the hot water combined with power ultrasound peeling condition.Cherry tomatoes treated by 2%sodium hydroxide concentration for 45 s at 95 ? demonstrated low peeling difficulty,low peeling loss(9.52%),bright color(L*= 34.85,a*= 27.24,b*= 18.36),suitable hardness(1.63 N),high lycopene content(29.29 mg/kg),similar pH(4.23)and titration acid(0.69%).Cherry tomatoes treated by hot water at 95 ? combined with power ultrasound treatment at 40 kHz and 270 W/L for 60 s demonstrated low peeling difficulty,low peeling loss(8.18%),bright color(L*=36.94,a*=-28.95,b*=19.00),suitable hardness(1.59 N),high lycopene content(33.48 mg/kg),similar pH(4.18)and titration acid(0.70%).The peel of hot water combined with power ultrasound peeling were silimar to that of hot water peeling,but the visibility of cell contour was significantly reduced.Compared to the lye peeling in industry,hot water combined with power ultrasound peeling eliminated the usage of lye,reduced the peeling loss of quality,which indicated power ultrasound is a potential environmental-friendly peeling method.3.The effects of blanching temperature and time on the peeling performance were investigated to optimize the blanching condition.Citrus blanched at 85 ? for 70 s led to the piercing force(8.68 N)reduced,the tensile strength(0.18 MPa)enhanced,internal porosity increased(29.31%),the aroma and taste improved and the coverage of albedo lawyer decreased significantly,as a result,the peeling performance enhanced.Therefore,blanching can enhance performance by influencing mechanical property and microscopic structure of the citrus peel.