Effect Of Pretreatment On Drying Quality Of Yellow Peach Slices And Its Drying Model Research

Yellow peach has delicate flesh,sweet and sour taste,rich aroma and rich nutrition,and is deeply loved by consumers.In recent years,with the expansion of yellow peach planting area,the output is increasing day by day,and the national annual output is about 5.5-6.5 million tons.However,yellow peaches are produced in hot summer,and fresh sales are limited,so they urgently need to be processed and digested.In addition,mechanically damaged and irregularly shaped yellow peaches also need to be processed.Yellow peach slices are a kind of dried fruit and vegetable products obtained through simple sun drying or hot air drying,and have a certain consumer market in rural areas.However,hot air-dried yellow peach slices often have high hardness,dark gray color and unfull shape,which lack market competitiveness.Therefore,it is necessary to properly pretreat yellow peach slices before drying to improve their sensory quality.In this paper,fresh yellow peaches were used as raw materials to study the effects of different pretreatments on the drying quality of yellow peach slices,and its drying model,in order to explore a suitable hot air drying process for yellow peach slices.The main contents of this study are as follows:(1)Using fresh yellow peaches as raw materials,four pretreatments including ultrasonic-assisted ethanol treatment(US ethanol),blanching treatment and freezethaw treatment were used to compare the effects of four pretreatments on the quality of hot air-dried yellow peach slices.The results showed that compared with the control,the quality of hot-air-dried yellow peach slices after four pretreatments was significantly improved.Compared with blanching treatment and freeze-thaw treatment,the yellow peach slices treated with ethanol ultrasonic treatment for 5 minutes and 10 minutes have more beautiful appearance color(P<0.05),and the hardness and brittleness are significantly lower(P<0.05),and the puffing degree is significant higher(P<0.05),with better taste.In addition,after ethanol ultrasonic treatment for 10 minutes,the dried yellow peach slices retained more important nutrients such as Vc,reducing sugar,titratable acid and total flavonoid content,which was more beneficial to human health.The hygroscopic rate of ethanol ultrasonic 5 min,ethanol ultrasonic 10 min and freeze-thaw treatment of yellow peach slices were all higher,and the storage in vacuum packaging would have a longer shelf life.Both principal component analysis and sensory evaluation methods have confirmed that the quality of peach slices is the best,which is a more suitable processing technology for yellow peach slices.The SEM image characterizes its structure,showing that after ultrasonic treatment with ethanol for 10 minutes,there are more pores and a looser tissue structure,so the quality is better.(2)Using fresh yellow peaches as raw materials,the effects of hot air drying temperature,wind speed and thickness of yellow peach slices on the hot air drying characteristics of yellow peaches were studied,the effective diffusion coefficient and activation energy during the drying process were calculated,and four drying kinetic models were selected for fitting analysis.The results showed that the higher the hot air temperature,the faster the drying rate and the shorter the drying time;the thinner the yellow peach slices,the faster the drying rate and the shorter the drying time;the wind speed had little effect on the drying rate.The whole drying process from hot air drying of fresh yellow peach slices to the end point is mainly a speed-decreasing stage,and the drying rate of yellow peach hot air drying increases with the increase of temperature and wind speed,and decreases with the increase of thickness of yellow peach slices.The Two-term model can fit the hot-air drying process of yellow peach slices well,and the experimental values are in good agreement with the predicted values,and the fitting effect is good.Calculated according to Fick’s second law,the effective diffusion coefficient Deff of hot air drying of yellow peach slices is between 2.7795×10-107.6448×10-9 m2/s,and the activation energy Ea is 21.95 kJ/mol.(3)Taking yellow peach slices pretreated by ethanol ultrasonic pretreatment under hot air drying as the research object,the sensory quality,Vc content,and microbial indicators of yellow peach slices in different packages were compared with the storage time.The results showed that with the prolongation of storage time,the sensory quality and Vc content of yellow peach slices in vacuum packaging,nitrogen-filled packaging and hygroscopic agent packaging showed a downward trend with the prolongation of storage time,and the total number of bacterial colonies and growth trend.Compared with nitrogen-filled packaging and hygroscopic agent packaging,vacuum packaging isolates moisture in the air,can effectively inhibit the growth and reproduction of bacteria,and the total number of bacterial colonies grows slower.In addition,the E.coli count index for all samples was negative.Using the first-order kinetic reaction model combined with the Arrhenius equation,a prediction model for the shelf life of yellow peach slices with different packaging methods was established.The relative error between the predicted value and the actual value of the model was within±5%,indicating that the model was reliable.